The Institute of Paper Chemistry

Appleton, Wisconsin

Doctor's Dissertation

The Alcoholysis of 2,3,4,6,Tetra-OAcetyl-aCD Glucopyranosyl Bromide

Leland R. Schroeder

June, 1965 THE ALCOHOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE

A thesis submitted by

Leland R. Schroeder

A.B. 1960, Ripon College M.S. 1962,.Lawrence College

in.partial fulfillment of the requirements of The Institute of Paper Chemistry for the degree of Doctor of Philosophy from Lawrence University, Appleton, Wisconsin

June, 1965 SUMMARY

iv

Comparison of Specific Rate Constant with Literature Values. 73

Thermodynamic Functions of Activation 76

TABLE OF CONTENTS

Page

SUMMARY- 1

INTRODUCTION 4

Koenigs-Knorr Reaction 4

Glycosyl Halides: Reaction:Mechanism Studies 5

Nucleophilic Substitution Reactions 6

Bimolecular Nucleophilic Substitution (S2) 7

Unimolecular Nucleophilic Substitution (SN1) 7

Solvolysis Reactions 8

.Reactions of Glycosyl Halides: Literature Survey 10

Reactivity and Stability 10

Effect of C1 and C2 Substituent Steric Configuration 11

Effect of the Glycosyl.Moiety - 1

Mechanistic Classification 14

Reactions with Hydroxylic Compounds 17

EXPERIMENTAL PROCEDURES AND RESULTS 18

Theory of Calculation of Rate Constants from.Polarimetry 18

Preparation of Compounds 20

Penta-O-Acetyl-P-D-Glucopyranose 20

2,3,4,6-Tetra-O-Acetyl-a-D-Glucopyranosyl Bromide 20

Alkyl 2,5,4,6-Tetra-O-Acetyl-P-D-Glucopyranosides 21

Alkyl 2,3,4,6-Tetra-O-Acetyl-c-D-Glucopyranosides 23

Purification of Solvents 25

Chloroform 25

Methanol, Ethanol, and n-Butanol 25

n-Propanol and iso-Propanol 25

Cyclohexanol 26

Alcohol Storage and Water Content 26 -2-

Acetylated alkyl D-glucosides were prepared for use as reference compounds

in the product analyses. Acetylated alkyl P-D-glucosides were prepared by a

modified Koenigs-Knorr reaction utilizing mercuric oxide (yellow) and mercuric

bromide. Acetylated alkyl a-D-glucosides were prepared from the P-anomer by

rearrangement with titanium tetrachloride in chloroform.

Gas-chromatographic analyses of solutions of acetylated alkyl P-D-glucosides

in alcoholic hydrogen bromide verified that acid-catalyzed transglycosidation

(anomerization) did not cause the observed a-glucoside formation. Analyses of

the same systems indicated that deacetylation of the reactant and products by

acid-catalyzed transesterification was not important at 15% reaction.

Lithium perchlorate caused a positive salt effect in all the alcoholyses.

The relative effect for the iso-propanolysis was larger than expected on the

basis of dielectric constant. The fraction of a-glucoside formed in the iso-

propanolysis was affected by the salt; the primary-alcoholyses were unaffected.

Lithium bromide increased the reaction rate and the fraction of a-glucoside for

all the alcoholyses. For the iso-propanolysis, both effects were large relative

to the primary-alcoholyses. The lithium bromide data suggested the possibility

of a reactive intermediate in the formation of part of the glucosidic products when bromide ions are added to the alcoholyses.

The enthalpies and entropies of activation were significantly different

for the primary- and secondary-alcoholyses. The primary-alcoholyses had enthalpies of activation ranging from 19 to 21 kcal. per mole; the entropies

ranged from -18 to -16 e.u. The iso-propanolyses exhibited an enthalpy of activation of 12 kcal. per mole and an entropy of -48 e.u. Thermodynamic func- tions of activation were not determined for the cyclohexanolyses.-

.Effect of Deacetylation on the.Experimental Specific Rate Constant 69 -3-

The polarimetric kinetic data indicated that electrophilic catalysis of the alcoholyses by the liberated hydrogen bromide can become important at less than

25% reaction.

Analysis of the data indicated that the methanolyses, ethanolyses, n-propan- olyses, and n-butanolyses of 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide occurred by an SN1 reaction mechanism. The iso-propanolyses and cyclohexanolyses exhibited characteristics of SN2 reaction mechanisms. -4-

INTRODUCTION

KOENIGS-KNORR REACTION

The Koenigs-Knorr reaction, in which an O-acyl-glycosyl halide* reacts with an alcohol or phenol, e.g., Equation (1), has been employed successfully for the preparation of numerous glycosides and oligosaccharides (1-6). Since its earliest application in the preparation of. methyl P-D-glucopyranoside (7) the reaction, as a preparative tool, has been improved considerably by the use of additives.

The generation of a hydrohalic acid in the Koenigs-Knorr reaction facili- tates detrimental reactions such as transesterification and transglycosidation, resulting in deesterified and Cl-racemized glycosidic products. To alleviate this problem an acid acceptor is employed in the reaction system, the most common being silver oxide or silver carbonate. An additional advantage in the use of the silver salts is that they are also thought to act as catalysts for the reaction. Amines and mercuric salts have also been employed as acid accep- tors and/or catalysts for the Koenigs-Knorr reaction (8).

*Unless specified otherwise the discussion of sugars will pertain to the pyranose form; terms such as glycosyl and glycopyranosyl will be used interchangeably. -5-

Employment of acid acceptors in the reaction system causes additional compli-

cations however. Silver oxide has been reported to cause the decomposition of

glycosyl halides under the conditions normally employed in the Koenigs-Knorr

reaction (9). Iodine, generally considered to be a catalyst for the reaction,

suppresses this side reaction but also suppresses glycoside formation. However,

because the iodine suppresses the side reaction more effectively than glycoside

formation, an increased yield of the glycoside is obtained.

Desiccants are employed in the Koenigs-Knorr reaction to combine with traces

of water present initially in the system and also to combine with the water formed

when the hydrohalic acid is neutralized by the acid acceptor, e.g.,.Equation (2).

Ag20 + 2HBr -- 2AgBr + H20 (2)

If the reaction system is not desiccated, the water reacts with the glycosyl

halide to form a reducing sugar rather than the preferred glycoside. Evans and

Reynolds (10) found that use of Drierite (anhydrous calcium sulfate) in a

Koenigs-Knorr reaction producing gentiobiose increased the yield from 25 to 80%.

GLYCOSYL HALIDES: REACTION MECHANISM STUDIES

The earliest mechanistic studies of the reactions of glycosyl halides were made by Frush and Isbell (11-13) utilizing reactions employing Drierite and/or

silver carbonate, as in the preparative Koenigs-Knorr reaction. The studies did not utilize kinetic measurements and consisted of reconciling the isolated products with the postulated mechanism. Mechanistic studies involving rate measurements normally do not employ additives such as Drierite and the silver

salts.

Rate measurements for glycosyl halide reactions are normally made by polar-

imetric, titrimetric, or conductimetric techniques. The heterogeneity resulting -6- from the use of insoluble desiccants and acid acceptors prohibits practical utilization of polarimetry for reaction rate measurements. Titration of the liberated hydrohalic acid is impossible when an acid acceptor is employed. A homogeneous reaction medium amenable to polarimetric and conductimetric kinetic measurements can be achieved by employing a soluble amine as the acid acceptor, but the possibility of a side reaction between the glycosyl halide and the amine exists (4, 14).

In addition to the above considerations it is known that complicated kinetic results can be obtained when silver salts are employed in reactions involving scission of a carbon-halogen bond (19, p. 55). This is probably related to a surface catalytic effect and would therefore be dependent on the available surface area (particle size), the age and previous history of the surface

(activity), etc. The probability of consistently duplicating these character- istics is small.

Due to the preceding complications mechanistic studies of the reaction of glycosyl halides are frequently made without the additives normally employed in the preparative Koenigs-Knorr reaction. The results obtained are sometimes extrapolated, with some uncertainty, to the preparative reaction.

NUCLEOPHILIC SUBSTITUTION REACTIONS

The reactions of glycosyl halides with hydroxylic compounds [Equation (1)] belong to the class of reactions known as nucleophilic substitutions. As such the reactions are normally discussed in terms of Hughes' and Ingold's (15-18) mechanistic spectrum in which the terms SN1 (substitution, nucleophilic, uni- molecular) and SN2 (substitution, nucleophilic, bimolecular) refer to mechanisms at the extremes of the spectrum. A brief discussion of the SN1 and SN2 -7- mechanistic concepts follows. More detailed discussions of the nucleophilic substitution mechanisms, including the spectrum intermediate of SN1 and SN2, are available in several sources (18-21).

BIMOLECULAR NUCLEOPHILIC SUBSTITUTION (SN2)

The SN2 mechanism is described as a one-step reaction in which one nucleo- phile (Lewis base) displaces another from a carbon atom. Bond formation between the attacking nucleophile and the carbon atom is simultaneous with the breaking of the initial bond between the carbon atom and the leaving group. In the transition state the attacking group and leaving group are both partially bonded to the carbon atom. Formation of the transition state is the rate-controlling as well as the product-controlling step for the reaction [Equation (3)].

Y: + R:X Y...R... X --- Y:R + :X (3)

Reactants Transition Products State

The reaction results in a sterically inverted product and is frequently referred to as Walden inversion. For the case in which substitution occurs at an asymmetric carbon atom, the reactant being solely of one enantiomorphic form, the resultant steric inversion for the reaction is readily discernible.

Kinetically, the reaction exhibits first-order dependence on both the attacking nucleophile and the compound experiencing substitution, hence the term bimolecular. The reaction rate is also dependent on the nucleophilicity of the attacking reagent, the rate increasing with increasing nucleophilicity.

UNIMOLECULAR NUCLEOPHILIC SUBSTITUTION (SN1)

The SN1 mechanism is described as a preliminary heterolysis of the carbon- leaving group bond which yields an electron-deficient carbon atom [carbonium ion; -8-

Equation (4)].

+ R:X I ' R + X- (4)

The carbonium ion then reacts with the nucleophilic reagent [Equation (5)].

R + + Y -- R:Y (5)

The preliminary heterolysis is normally, but not always (22), the rate-control- ling step, the combination of the carbonium ion with the nucleophile is usually very rapid relative to the heterolysis.

The reaction will normally exhibit first-order kinetics, the rate of reaction being dependent only on the concentration of the compound forming the carbonium ion.

In addition, the rate of reaction will not be markedly dependent on the nucleo- philicity of the attacking molecule. This does not preclude the possibility of a compound which normally reacts by an SN1 mechanism reacting by an SN2 mechanism with a sufficiently strong nucleophile.

Contrasted to a reaction occurring by an SN2 mechanism, the products in an

SN1 reaction are not necessarily steric inverts. For a carbonium ion formed from an asymmetric carbon atom (the reactant being only one enantiomorphic species), the products can be inverted or racemized. The extent of inversion or racemization normally depends on the degree of association between the carbonium ion and the liberated anion. For the case in which the carbonium ion and the anion exist as an ion pair, the product will normally be a steric invert of the reactant.

Steric factors, other than that associated with the departing anion, can also influence the steric nature of the products.

SOLVOLYSIS REACTIONS

When a nucleophilic substitution reaction is studied under conditions of solvolysis, i.e., the nucleophile is in large excess, the mechanistic classification -9-

of the reaction is complicated by the fact that kinetic order is no longer diag-

nostic. Under these conditions, reactions occurring by either mechanism will

exhibit first-order kinetics. First-order dependence only on the electrophile

concentration will be evident.

The rate equations for the SN1 and SN2 mechanisms are given in Equations (6)

and (7).

SN1: Rate = kl[RY] (6)

SN2 : Rate = k2[RY][X] (7)

The compound experiencing nucleophilic substitution is denoted by RY, the nucleo- phile by X. The rate constants k1 and k2 refer to first- and second-order,

respectively. If the substituting nucleophile, X, is in large excess its con-

centration will remain essentially constant as the reaction proceeds. The rate-

equation for the S.2 mechanism [Equation (7)] then becomes

S2(Solvolysis); Rate = k'[RY] (8)

where k' = k2 [X] constant (9)

= pseudo-first-order rate constant

and for a single reaction the mechanism is kinetically indistinguishable from the

SN1 mechanism [compare Equations (6) and (8)].

For reactions in which the substituting nucleophile, X, is not the solvent but is still in large excess, the existence of the preceding kinetic anomaly can be ascertained by determining whether k' is a linear function of [X] for a series

of reactions in which [X] is varied as predicted by Equation (9). The results must be interpreted judiciously as variation of [X] can cause a dependence which -10-

is due to a change in reaction medium rather than nucleophile concentration.

Another method is to plot the same data according to Equation (10) [derived from

Equation (9)] and verify that the slope is approximately equal to one, indicating

a first-order dependence on the nucleophile concentration.

log k' = log k + log[X] (10).

For studies of nucleophilic substitution reactions in which the nucleophile

is used as the solvent, as is the case for the present study, consideration of

reaction characteristics other than kinetic order must be used to ascertain the mechanism. Reaction characteristics which can be mechanistically diagnostic are:

a) the effect of addition of stronger nucleophiles to the reaction system,

b) the effect of salts on the rate of reaction,

c) the steric configuration of the reaction.products,

d) the variation of reaction rate within a series of similar solvents

(for this case the reactant), and

e) the thermodynamic functions of activation.

Discussions of the mechanistic implications of each of the preceding reaction

characteristics will be presented when applicable to either previous studies or

the present work.

REACTIONS OF GLYCOSYL HALIDES: LITERATURE SURVEY

The nucleophilic substitution reactions of glycosyl halides have been the

subject of numerous investigations, many of which are concerned with reaction mechanisms (11-14, 23-39).

REACTIVITY AND STABILITY

The reactivity of a glycosyl halide is dependent on the halogen atom.

The reactivity of the O-acetylglycosyl halides follow the order: iodides > -11- bromides > chlorides > fluorides. The stability of the pure compounds is the reverse of the reactivity order (4). A compromise between reactivity and stability results in the glycosyl bromides and chlorides being most frequently used in preparations and mechanism studies.

Newth and Phillips (24) concluded that the enhanced reactivity of the halo- gen at C1 was due to its being a part of an a-halogeno-ether system. They found that solvolysis could not be detected when the halogen atom was on C2 or C3.

EFFECT OF C 1 AND C2 SUBSTITUENT STERIC CONFIGURATION

Early studies of the alcoholysis reactions of 0-acyl-glycosyl halides demon- strated the importance of the O-acyl group at C2 . When the C 0-acyl group is cis to the halogen atom (I)* the displacement occurs with inversion at C1 as depicted in Equation (11) (11-135, 34-38).

OR ROH / R

OAc OAc (OBz) (OBz) I OAc = O-ACETYL OBz = O-BENZOYL ROH = ALCOHOL X = HALOGEN (BROMIDE OR CHLORIDE)

When the C2 0-acyl group is trans to the halogen atom (II) the reaction products are dependent on the presence of an acid acceptor in the system.

*Roman numerals in parentheses refer to compounds labeled as such. -12-

With an acid acceptor in the system the formation of a "glycoside of ortho

ester structure" ('III) is possible (11-13, 37) as depicted in Equation (12).

ROH ACID ACCEPTOR

OAc O-C-OR (OBz) I CH 3 (C 6 H 5 ) II III

Demonstration of this type of reaction product is frequently used as proof that the C1 and C2 substituents in an O-acyl-glycosyl halide are trans. When the C2

O-acyl group is trans to the halogen atom and an acid acceptor is not employed

in the reaction system the reaction product appears to be dependent on the O-acyl group. With 1,2-trans O-acetyl-glycosyl halides [IV, Equation (13)] the methan- olysis and hydrolysis reactions have yielded products with inversion of configura- tion at C1 (27, 31). The methanolyses of 1,2-trans O-benzoyl-glycosyl halides

[V,. Equation (14)] yield methyl O-benzoyl-glycosides with retention of configura- tion at C1 (54-38).

MeOH (HOH) / \( NO ACID ACCEPTOR \ (13 O{HSH~c~f \ ----- ~OAMe(OH)

OAc OAc

IV

-16-

a trans configuration for the C O-benzoyl group and C1 bromide atom. These

intermediates (VI and VII) have been utilized in explaining orthoester formation

[Equation (12)] in the presence of an acid acceptor (27, 38). In addition, for the O-benzoyl-glycosyl bromides, intermediate VII has been utilized in explaining the retention of configuration at C1 when no acid acceptor is used (38) [see

Equation (14)]. To the author's knowledge intermediate VI has not been reconciled with inversion of configuration at C1 for the O-acetyl-glycosyl halides when no acid acceptor is used [see Equation-(13)].

Lemieux and Huber (32) have reported that addition of acetate ion did not increase the rate of acetolysis of 3,4, 6 -tri-O-acetyl-P-D-glucopyranosyl chloride and concluded that the reaction mechanism was SN1.

Bimolecular nucleophilic substitutions have also been reported for the glycosyl halides (14, 31, 33). Chapman and Laird (14) found that the mechanism for the reaction of amines with 0-acetyl-glycosyl halides in acetone was depen- dent on the nucleophilicity (basicity) of the amine employed. Thus, with the strongly nucleophilic amines, piperidine, di-n-butylamine, and diethylamine, the

O-acetyl-C-D-glucosyl, -galactosyl, and -xylosyl bromides exhibited bimolecularity

(SN2), whereas the tetra-O-acetyl-mannosyl bromide exhibited a mixed reaction order. With the weaker nucleophiles, monomethylaniline, pyridine, and P-picoline,

TAGB exhibited a mixed reaction order while tetra-O-acetyl-a-D-mannosyl bromide reacted independent of the amine employed (SN1). Also, as noted by Chapman and

Laird (14), the reaction of TAGB with sodium iodide in acetone reported by Newth and Phillips (23) is probably another example of an S.2 reaction'

As stated previously, Capon, et al. (31) have concluded that the solvolysis reactions of the 0-acetyl-glycosyl halides studied, including TAGB, in aqueous acetone solvents were SN1. However, it was also shown that, except for

Both of these mechanisms have been disputed by Phillips, et al. (23, 27).

Newth and Phillips (23) found that added hydroxide ions (more nucleophilic than -17-

2,3,4,6-tetra-O-acetyl-Qi-D-mannopyranosyl bromide, the reactions with lithium thiophenoxide (a very strong nucleophile) in a poorer solvent (n-pentanol- toluene) were SN2. Rhind-Tutt and Vernon (33) made an earlier, analogous study with 2,3,4,6-tetra-0-methyl-a-D-glucopyranosyl and -mannopyranosyl chlorides.

They concluded that the methanolyses of both compounds were SN1 but, for the

reaction with thiophenoxide ion in n-propanol, the glucosyl chloride reacted by an SN2 mechanism; the mannosyl chloride reacted by an SN1 mechanism in both

systems.

REACTIONS WITH HYDROXYLIC COMPOUNDS

The effect of glycosyl characteristics on the reactivity of glycosyl halides

has been subjected to intensive investigation. Mechanistic studies of the re-

actions of hydroxylic nucleophiles with glycosyl halides appear to be limited to

hydrolyses and methanolyses.

The present study was initiated as a preliminary phase in the elucidation

of the role assumed by the alcohol in the formation of glycosides by the alcohol-

ysis of glycosyl halides. -18-

EXPERIMENTAL PROCEDURES AND RESULTS

THEORY OF CALCULATION OF RATE CONSTANTS FROM POLARIMETRY

When a reaction system contains a reactant which is optically active, it is generally possible to relate the change in optical activity of the system to the specific rate constant for the reaction. For alcoholyses of glycosyl halides, the equation

ln(at - a) = -kt + ln(o - a ) (15) where

t = time

at = the optical rotation of the reaction system at time

a = the optical rotation of the reaction system at zero time

a = the limiting optical rotation of the reaction system at long times; "equilibrium rotation"

k = first-order or pseudo-first-order specific rate constant has been used frequently to determine the specific rate constant. A derivation of'Equation (15).is given elsewhere (40). Equation (15) predicts that if ln(c - ) is plotted as a function of t, a straight line with a slope equal tt a co to -k will result.

The validity of Equation (15) is dependent on the accuracy with which a represents the true reaction products at all times during the reaction. If more than one optically active product is formed and the ratio of these products to each other is time-dependent, a does not fulfill this condition. If side reactions, such as transesterification and transglycosidiation, transform the initial products, the experimental value of a is also in conflict with its mathematical concept. -19-

The questionability of c describing the reaction conditions necessary for the calculation of initial reaction rates, and the impracticality of the time necessary to experimentally determine a in slow reactions* led to the derivation of Equation (16). The derivation is presented in Appendix I.

ln(at - M) = -kt + ln(a - M) (16) where

at = the optical rotation of the system at time t

a = the optical rotation at zero time

M = a calculated optical rotation related to the reaction products

Assuming that the system contains only unreacted glycosyl halide and the glycosidic anomers,.M is defined by-Equation (17).

M = £(n[a b] + (l-n)[a a ] )MGH6/1 0 0 0 (17) where

I = polarimeter tube length, dm.

H = the initial concentration of glycosyl halide, mole/l.

MG = the gram-molecular weight of the glycosidic product(s)

n = the fraction of the total glycoside concentration accounted for as P-anomer

[a ]= the specific optical rotation of the a-anomeric glycoside

[ab]= the specific optical rotation of the P-anomeric glycoside

*Calculations from initial specific rate constants for the alcoholyses of 2,3,4,6-tetra-0-acetyl-a-D-glucopyranosyl bromide at 25°C. predict 16 days for 95% completion of the n-butanolysis, 55 days for the iso-propanolysis. -20-

Equation (16) is mathematically analogous to Equation (15). The essential difference is that the questionable, experimental a value is replaced by a function, M, which can be calculated. Determination of the values (n, [ca ] ),

[ab] in Equation (17) necessary to evaluate M constitutes a major portion of the experimental work.

PREPARATION OF COMPOUNDS

PENTA-O-ACETYL-P-D-GLUCOPYRANOSE

Three hundred grams of anhydrous dextrose, 132 g. anhydrous sodium acetate, and 600 ml. of glacial acetic acid were placed in a three-liter round-bottom flask and warmed to approximately 100°C. on a steam bath. Over a period of 2 hours, 1620 ml. of acetic anhydride were added. The reaction mixture was heated on the steam bath for an additional four hours and then allowed to cool. After cooling, the mixture was poured into six liters of vigorously stirred ice water.

After approximately 15 min. additional stirring, the precipitated pentaacetyl glucose was filtered, washed with water, and pressed with a rubber dam. The white solids were then recrystallized from a minimum of 95% ethyl alcohol. The yield of primary crystals was 370 g. (57.0% of theoretical). The product melted at 130-131°C., [a] = +4.53 (chloroform). Literature values are 130-131°C., [r]D +3.8 ° (chloroform).

2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

2,3,4,6-Tetra-O-acetyl-a-D-glucopyranosyl bromide (TAGB) was prepared according to the method of Fischer and Fischer (41, 42) in which penta-O-acetyl-

P-D-glucopyranose was reacted with a saturated solution of hydrogen bromide in glacial acetic acid. After three crystallizations from absolute ether by the addition of small amounts of petroleum ether (35-65°C.), the yield was 44% of

21 ° theoretical. The needle-shaped crystals melted at 88-89°C., [a] = +198

(chloroform). Literature values are 88-89°C., [a]D = +198° (chloroform). -21-

The purity of the above material was such that it could be stored in a desic- cator over sodium hydroxide pellets, at room temperature, for times in excess of one year.

ALKYL 2,3,4,6-TETRA-0-ACETYL-P-D-GLUCOPYRANOSIDES

Drierite (10-20 mesh, 20 g.), mercuric oxide (yellow, 6.5 g.), mercuric bromide (0.5 g.), chloroform (purified, anhydrous, 100 ml.), and the appropriate alcohol (purified, anhydrous, 100 ml.) were placed in a stoppered 250-ml. Erlen- meyer flask and stirred for 15-30 minutes by a magnetic stirrer. 2,3,4,6-Tetra-

O-acetyl-a-D-glucopyranosyl bromide (15.0 g.) was then added and the stirring continued for 7-8 hours. The reaction mixture was then filtered through Celite, concentrated to a solid or a thick sirup in vacuo on a rotary evaporator*, dis- solved in chloroform, filtered through Celite to remove any insoluble mercuric bromide, concentrated to a solid or a thick sirup, dissolved in the appropriate solvent (hot), and refrigerated for crystallization. The compounds were recrystal- lized until the melting point and specific rotation were constant for successive crystallizations. In most cases the properties of once recrystallized material were identical to those for the initial crystallization.

Data on the preparation of the alkyl tetra-O-acetyl-p-D-glucosides are given in Table II.

*Since cyclohexanol is difficult to remove without resorting to high temperatures, the reaction mixtures utilizing cyclohexanol were concentrated until essentially all the chloroform was removed. Absolute ethanol was then added to the cyclo- hexanol solution and the solution refrigerated for crystallization. When filtered, the crystals were washed thoroughly with water and dried in a vacuum oven. For the reaction mixtures utilizing n-butanol, water was added to facilitate removal of the alcohol as its aqueous azeotrope. -22-

0 -23-

ALKYL 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSIDES

Alkyl 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosides were prepared by the method originated by Pacsu (45, 46) in which the P-anomer is treated with titanium tetra- chloride in chloroform. The exact procedure used is that reported by Ferguson

(47) for the preparation of ethyl 2,3,4,6-tetra-O-acetyl-Q-D-glucopyranoside. The yields obtained were considerably lower than those reported in the literature (6,

Vol. II, p. 379).

Data on the preparation of the alkyl tetra-O-acetyl-a-D-glucosides are given in Table III.

Properties of two compounds, ethyl- and cyclohexyl tetra-O-acetyl-a-D- glucoside differ from literature values. Recrystallization and/or crystalliza- tion from different solvents did not change the properties of these compounds.

The sirupy product obtained in the preparation of n-butyl tetra-O-acetyl-a-

D-glucoside could not be crystallized in numerous and varied attempts. Paper- chromatographic analysis of the deacetylated material was identical to that for n-butyl D-glucoside. Separation of anomers was not possible with the paper- chromatographic system used. However, gas-chromatographic analysis of the acetylated material showed the presence of 18.5% of the P-anomer and two other very minor-impurities. The specific rotation reported in Table III for n-butyl tetra-O-acetyl-a-D-glucopyranoside was calculated from the specific rotation of the sirup by correcting for the known amount of P-anomer. The true value is probably slightly greater than that calculated. -24!- -25-

PURIFICATION OF SOLVENTS

CHLOROFORM

Reagent-grade chloroform containing 0.75% ethanol as a preservative was purified by a modification of the procedure reported by Evans and Reynolds (50).

Chloroform was shaken with an equal volume of 12% sulfuric acid for one hour on a mechanical shaker, separated, neutralized with a saturated solution of sodium bicarbonate and washed well with water. It was then dried with calcium chloride, decanted, and distilled from Drierite onto Drierite in a dark-colored, glass storage container.

METHANOL, ETHANOL, AND n-BUTANOL

The title compounds were purified by a modification of the procedure re- ported by Herold and Wolf (51). One liter of reagent-grade alcohol was placed in a two-liter flask with 0.5 g. iodine and 5.0 g. magnesium turnings. The flask was warmed gently until the iodine color disappeared. For methanol, cooling was frequently necessary to prevent the initial reaction from becoming too violent.

The mixture was then refluxed with the exclusion of moisture. Methanol and ethanol were refluxed for two hours, n-butanol for five hours. The reflux mix- ture was then fractionally distilled, with the exclusion of moisture, through a

40-cm. Vigreux column. The first 200 ml. of distillate were normally discarded.

The normal yield was 500 ml. of retained distillate.

The water contents of the purified alcohols are reported in Table IV. n-PROPANOL AND iso-PROPANOL

Reagent-grade iso-propanol and practical grade n-propanol, purified by the procedure for methanol, were subjected to the same procedure a second time.

Reflux time was six hours. -26-

The water contents of the purified alcohols are reported in Table IV.

CYCLOHEXANOL (ChOH)

One liter of cyclohexanol was refluxed with 7 g. of metallic sodium strips for six hours with the exclusion of moisture. The reflux mixture was than frac- tionally distilled, in a dry nitrogen atmosphere and with the exclusion of mois- ture, through a 40-cm. Vigreux column. Water at 32-33°C. was pumped through the reflux and distillation condensers to prevent freezing of the cyclohexanol. The retained distillate was subjected to the procedure a second time.

The water content of the purified cyclohexanol is reported in Table IV.

ALCOHOL STORAGE AND WATER CONTENT

The purified alcohols were stored in light-protected, sealed, glass bottles under a dry nitrogen atmosphere and were dispensed by displacement with dry nitrogen.

The water contents of the alcohols, in storage, are reported in Table IV.

TABLE IV

ALCOHOL WATER CONTENTa

Alcohol H 2 0, % by wt.

Methyl 0.0046

Ethyl 0.0032

n-Propyl 0.0076

n-Butyl 0.0056

iso-Propyl 0.018

Cyclohexyl 0.015

aKarl Fischer method. -27-

SYSTEM FOR ISOTHERMAL POLARIMETRY

Figure 1 is a schematic diagram of the system used for isothermal polari-

metric rate studies and studies of the specific rotation of compounds as a

function of temperature.

A, B, C-MONITORING THERMOMETERS PI, P2-WATER-JACKETED POLARIMETER TUBE

Figure 1. System for Isothermal Polarimetry

The constant temperature water bath depicted was capable of + 0.02CC.

internal temperature control and could deliver 110-120 gallons of water per.

hour to an external circuit against a one-foot head.

Thermometers (A, B, and C) in the water line to and from the jacketed

polarimeter tubes (P1 and P2) indicated the temperature of the water in the

,polarimeter tube jacket. The thermometers monitoring the water flow were

equidistant from the polarimeter tubes. The water lines, thermometer wells,

and polarimeter tubes were lagged with asbestos. The temperature differential -28- between entrance and exit flow was negligible when water at approximately room temperature was pumped through the system. When the water temperature was 35-40°C. the temperature differential was 0.1-0.2°C.

The polarimeter tubes* used were glass with a metal jacket forming the annu- lus for circulating water around the tube. The tube was two dm. long, had re- placeable end caps, and had a side arm to facilitate rapid filling.

TEMPERATURE CORRECTION

The actual temperature of the solution in the polarimeter tube could be less or greater than the temperature of the water circulated around the tube. This was due to the fact that heat transfer between the unjacketed end-caps and the side-arm of the polarimeter tube with aix is significant compared to the heat transfer between the circulating water and the solution in the polarimeter tube.

Experimentally, it was found that Equation (18) described the solution tempera- ture provided that air was circulated around the exterior of the polarimeter tube. Utilization of Equation (18) allowed continuous monitoring of the tem- perature of the solution in the polarimeter tube.

At = 0.026(t a t ) = t - tw (l8) where

t = temperature of the solution in the polarimeter tube, °C.

t = temperature of the water in the polarimeter tube jacket, an - average of entrance and exit water temperatures, °C.

t = air temperature, °C.

*0. C. Rudolf and Sons, Caldwell, New Jersey. -29-

Table V indicates the feasibility of applying the correction calculated

from Equation (18).

TABLE V

TEMPERATURE CORRECTION FOR POLARIMETRY

°C.0 C. At (Exp.)a At (Calc. )b tw °C. -Tt --t - 18.0 18.2 25.7 +0.2 +0.18

24.7 24.7 26.6 o.0 +0.04

33.0 32.9 27.4 -0.1 -0.14

41.2 40.9 29.0 -0.3 -0.31

45.53 44.8 27.0 -0.5 -0.48

Calculated from measurements of the solution temperature. bCalculated from Equation (18).

SPECIFIC ROTATION OF ACETYLATED ALKYL D-GLUCOPYRANOSIDES IN THE AGLYCONIC ALCOHOL

A solution of known concentration of the acetylated alkyl glucoside in the

aglyconic alcohol was prepared at a known reference temperature. The solution was then transferred to a water-jacketed polarimeter tube and the optical rota-

tion (5461 A.) was measured at various temperatures in the range 20-45°C. One hour or longer was allowed for thermal equilibrium (with mixing) in the polar-

imeter tube after the water bath had attained equilibrium. Thermal equilibrium was ascertained by constancy of the observed rotation.

Reversibility of specific rotation change with temperature was ascertained by adjusting the temperature of the solution to that of the first measurement

after all other measurements had been made and rechecking the optical rotation.

Such measurements agreed within 0.01 ° observed rotation. -31-

hours. The solvent normally descended approximately 80% of the sheet length.

Sugar position was determined by use of silver nitrate-sodium hydroxide reagent

(54)*. The RG values, listed in Table VIII, were appreciably dependent on the

chromatography tank used. No separation of anomeric pairs was achieved.

TABLE VI

SPECIFIC ROTATIONS OF ACETYLATED ALKYL D-GLUCOPYRANOSIDES IN THE AGLYCONIC ALCOHOLS

t Alkyl Tetraacetyl- [5 4 6 1 D-Glucoside 25 30 35 40

P-Methyl -23.4 -23.0 -22.7 -22.3 a-Methyl 157 157 157 157

P-Ethyl -30.0 -29.3 -28.7 -28.0 Q-Ethyl 165 164 164 163

P-n-Propyl -33.0 -32.5 -32.0 -31.5 a-n-Propyl 169 168 168 167

P-n-Butyl -33.6 -3 3 .2b -32. 8b -32 5 a-n-Butyl (163)b (163) (163)b 163

P-iso-Propyl -36.0 -34.7 -33.4 -32.1 a-iso-Propyl 174 175 175 175

P-Cyclohexyl -34.2 -33.2 -32.2 -31.2 a-Cyclohexyl ------147

aDetermined.from a mixture of anomers in which the a-anomer was estimated at 18.5% of the total glucoside by gas-chromatographic analysis. Two other unidentified minor impurities were present. The error in assuming the value to be independent of temperature is undoubtedly less than the error in the measurement at 40°C. See footnote' a

*The alkyl a-D-glucoside reacted slower than 3-anomer with the reagent. -32-

TABLE VII

THE SPECIFIC ROTATION OF THE METHYL 2,3,4,6-TETRA-O-ACETYL- D-GLUCOPYRANOSIDES IN METHANOLIC SALT SOLUTIONS

Anomer Temp., oC. 0.10OM Salt Concn., g./25 ml.

25.0 -23.4a 25.0 LiC104 -22.6 0.4978 25.0 LiBr -22.8 0.5036

40.0 -22.3a 40.0 LiBr -22.1 .5385 40.0 NH4 Br -22.7 0.5770 40.0 LiC104 -23.3 0.5516 -22.9 40.0 NaClO4 0.5068

25.0 157a 25.0 LiC1O 4 164 0.3027 25.0 'LiBr 162 0.3055

40.0 157a 40.0 LiBr 162 0.3034 40.0 NH4 Br 160 0.3337 40.0 LiC1O4 159 0.3103 160 40.0 NaC1O4 0.3575 aValues taken from temperature dependence data.

TABLE VIII

ALKYL D-GLUCOPYRANOSIDE R VALUES -(G

Alkyl D-Glucoside R

(D-Glucose, reference) 1.0

Methyl 1.6

Ethyl 2.3

n-Propyl 2.9

n-Butyl 3.3

iso-Propyl 2.7

Cyclohexyl 3.6 -33-

GAS-LIQUID PARTITION CHROMATOGRAPHY OF ACETYLATED ALKYL D-GLUCOPYRANOSIDES

It was possible to analyze the alkyl tetra-O-acetyl-D-glucopyranosides by

gas-liquid partition chromatography. An Aerograph Hy-Fi,. Model A-600-B, gas

chromatograph* equipped with a hydrogen flame ionization detector was used in

all analyses. Two types of columns* were used.

The first type of column (CASE column) was composed of 40 cm. of a 1:1, v/v mixture of 20%, w/w Apiezon M grease on Chromosorb W, 60-80 mesh, and 20%, w/w, butanediol succinate polyester on Chromosorb W, 60-80 mesh, and 77 cm. of methyl silicone rubber gum, SE-30, 0.25%, w/w, on 60-80 mesh, glass beads. The

column was housed in 1/8-inch stainless steel tubing. The column was essentially

the same as that used by Jones and Perry (55) for the separation of methyl gly-

cosides.

The second type of column (CA column) did not contain methyl silicone

rubber gum. It was composed of 30 inches (76 cm.) of a 1:1 v/v mixture of 20%,

w/w, Apiezon M grease on Chromosorb W, 60-80 mesh, and 20% w/w, butanediol suc-

cinate polyester on Chromosorb W, 60-80 mesh.

Dry nitrogen was used as the carrier gas. Hydrogen flow to the detector

flame was normally 30 ml. per min. When possible the temperature of the injector

chamber was 25-30°C. higher than the column temperature. The maximum temperature

used for the injector chamber was 220°C.

QUALITATIVE ANALYSIS

It was possible to effectively separate the anomers of the alkyl tetra-O-

acetyl-D-glucopyranosides on the columns described. Reproductions of

*Wilkens Instrument and Research, Inc., Walnut Creek, California. representative separations of anomeric pairs of alkyl tetra-O-acetyl-D-glucosides are shown in Fig. 2-9. The separations shown were not necessarily performed on a new column and the retention times should not be compared to future work as such.* It was found that the CA column is considerably more effective for this type of separation, particularly for the difficult separation of the anomeric methyl tetra-O-acetyl-D-glucosides. While the relative retention times (Reten- tion Ratio) for the anomeric pairs were approximately the same for the CA and

CASE columns, the CA column, because of longer retention times, permitted manipu- lation of conditions to yield greater absolute separation with similar peak reso- lution. The chromatograms (recorder print-outs) in Fig. 4 and 5 show the separations of the anomeric n-propyl tetra-O-acetyl-D-glucosides on the CASE and CA columns, respectively. The chromatograms in Fig. 6 and 7 show the separ- ation of the anomeric n-butyl tetra-O-acetyl-D-glucosides on the two different columns.

Relative retention times (Retention Ratio) for the separation of anomeric alkyl tetra-O-acetyl-D-glucosides are listed in Table IX.

It was not possible to analyze for 2,3,4, 6 -tetra-O-acetyl-a-D-glucopyranosyl bromide with the gas chromatographic conditions employed.

QUANTITATIVE ANALYSIS

For quantitative analysis of the gas chromatograms, response peak areas were determined by the method of approximating triangles. The method is de- scribed by Pecsok (56).

*It was found that even retention times for new duplicate columns could vary considerably. The relative retention times for anomeric pairs were fairly consistent for duplicate columns, however. -35-

CA COLUMN

10 20 30 40 TIME, MIN.

Figure 2. Separation of Methyl 2,3,4,6 -Tetra-0-acetyl-D-glucopyrano- side Anomers. Column Temp., 185°C.; N2 Flow, 15 p.s.i.g.

oC

CA COLUMN

20 TIME) MIN.

Figure 3. Separation of Ethyl 2,3,4,6 -Tetra-0-acetyl-D-glucopyrano- side Anomers. Column Temp., 195°C.; N2 Flow, 15 p.s.i.g. 'a

CASE COLUMN

0 10 20 30 40 TIME) MIN.

Figure 4. Separation of n-Propyl 2,3,4,- 6 -Tetra-O-acetyl-D-glucopyrano- side Anomers. Column Temp., l81°C.; N2 Flow, 15 p.s.i.g.

CA COLUMN

0 10 20 30 TIME, MIN.

Figure 5. Separation of n-Propyl 2,3,4,6 -Tetra-O-acetyl-D-glucopyrano- side Anomers. Column Temp., 195°C., N2 Flow, 15 p.s.i.g. -37-

TIME, MIN.

Figure 6. Separation of n-Butyl 2,3,4, 6 -Tetra-0-acetyl-D-glucopyrano- side Anomers. Column Temp., 190°C.; N2 Flow, 15 p.s.i.g.

CA COLUMN

TIME, MIN.

Figure 7. Separation of n-Butyl 2,3,4 ,6 -Tetra-0-acetyl-D-glucopyrano- side Anomers. Column Temp., 205°C.; N2 Flow, 15 p.s.i.g. -58-

CA COLUMN

TIME, MIN.

of iso-Propyl 2,5,4,6 -Tetra-O-acetyl-D-glucopyrano- Coiumn Temp., 195°C.; N2 Flow, 15 p.s.i.g.

)LUMN

10 20 30 40 TIME) MIN.

Figure 9. Separation of Cyclohexyl 2,3,4, 6-Tetra-0-acetyl-D-glucopyrano- side Anomers. Column Temp. 215°C.; N2 Flow, 14.5 p.s.i.g. -39-

TABLE IX

GAS CHROMATOGRAPHIC SEPARATION OF ANOMERIC ACETYLATED ALKYL D-GLUCOPYRANOSIDES

Acetylated Anomeric RetentionC Alkyl D-Glucosides Column Conditions Ratio, a/3

Methyl CASE A 0.88 CA D o.84

Ethyl CASE B 0.79 CA D 0.79

n-Propyl CASE B 0.76 CA D 0.76

n-Butyl CASE B 0.73 CA E 0.76

iso-Propyl CASE B 0.78 CA D 0.79

Cyclohexyl CASE C 0.78 CA F 0.80

Column description is in the text. Conditions listed as: column temp., °C.; N flow, p.s.i.g.; injector temp., °C.: A, 175, 15, 200; B, 185, 15, 210; C, 210, 15, 215; D, 195, 15, 215; E, 205, 15, 215; F, 215, 14.5, 215. CValue not necessarily determined on a new column.

The response (peak area) per unit weight of material injected was not neces- sarily constant for an acetylated alkyl D-glucoside for successive determinations.

This could have been due to decomposition. Decomposition and rearrangement of sugar derivatives during vapor-phase chromatographic analysis have been reported

(57). For a single determination, the responses of the a- and P-anomer for the anomeric alkyl tetra-O-acetyl-D-glucosides were experimentally equal. The re- sponses (sq. cm./microgram) for successive analyses of varying ratios of anomeric ethyl tetra-O-acetyl-D-glucosides are listed in Table X. -40-

TABLE X

RESPONSE FACTORS FOR ACETYLATED ETHYL D-GLUCOPYRANOSIDE ANOMERIC MIXTURES

Anomer Response, sq. cm./gg.a Sample Code a

ET-2 0.475 0.475

.ET-3 0.633 0.623

ET-4 0.589 0.385

ET-5 0.599 o.637

ET-6 0.341 0.346

Chromatograph sensitivity at 109 and 52X.

Because the responses per unit weight of the a- and p-anomer of acetylated alkyl D-glucosides were equal, the ratio of anomers for a given separation was equal to the ratio of the corresponding peak areas. Quantitative analysis of the composition of anomeric mixtures of the acetylated alkyl D-glucosides by gas chromatography was quite accurate; this is indicated by the data listed in

Table XI.

TABLE XI

QUANTITATIVE GAS CHROMATOGRAPHIC ANALYSIS OF ANOMERIC MIXTURES

Anomeric Acetylated a-Anomer, c-Anomer, Alkyl D-Glucosides known % GC %

Ethyl 0.0 0.0 5.2 5.0 16.1 16.1 32.1 32.5 47.8 48.2 63.5 62.2 78.9 78.8

n-Propyl 0.0 0.0 12.3 11.4

iso-PropyL. 0.0 0.0 15.9 16.3 -41-

The inconstancy of the response per unit weight for a given acetylated alkyl

D-glucoside for successive determinations necessitated the use of an internal

standard to determine absolute concentrations. The theory in the use of an

internal standard is that addition of a known quantity of an internal standard

to a solution containing an unknown concentration of another compound enables

calculation of the unknown concentration from the ratio of gas chromatographic

responses for the internal standard and the unknown. To make the calculation,

the ratio of the response per unit weight for the internal standard to the

response per unit weight for the unknown must be known and constant.

A demonstration of the utilization of an alkyl tetra-O-acetyl-D-glucoside

as an internal standard in the determination of unknown concentrations of other

alkyl tetra-O-acetyl-D-glucosides is presented in the later section on the effect

of alcoholic hydrobromic acid on acetylated alkyl P-D-glucopyranosides.

PRODUCT ANALYSIS PROCEDURES

The procedure used for conducting the alcoholyses of 2,3,4, 6 -tetra-O-acetyl-

a-D-glucopyranosyl bromide is given in a later section. In most instances the

same reaction solution used for polarimetric kinetic measurements was used for

product analysis. When necessary, the reaction conditions used for kinetic measurements were duplicated for product analyses.

ALCOHOLYSIS AND HYDROLYSIS PRODUCTS

An aliquot (6-8 ml.) of the alcoholysis reaction solution was sealed in a

glass ampul and stored in an oven at 55-60°C. for times in excess of one month.

The reaction products were then deacetylated to permit analysis by paper

chromatography. The contents of the ampul were mixed with 10 ml. of dry methanol -42-

and the resulting solution was titrated to the phenolphthalein end-point with

O.03N sodium methoxide in methanol. An excess (0.5 ml.) of the methanolic sodium

methoxide was added and the solution was heated on a steam bath for one-half hour

to insure deacetylation. The solution was concentrated in vacuo to approximately

one milliliter. Fifty microliters of the solution were analyzed by paper chroma-

tography as described earlier.

Except for traces of glucose in the deacetylated n-propanolysis, iso-propan-

olysis, and cyclohexanolysis reaction products, the analyses (comparison with

known compounds) showed only the alkyl D-glucosides. The formation of this

small amount of glucose, probably 2,3,4, 6-tetra-O-acetyl-D-glucose in the

original reaction mixture, could have resulted from the reaction of 2,3,4,6-

tetra-O-acetyl-a-D-glucosyl bromide (TAGB) with trace amounts of water in the alcohols.

The reactions in the presence of salts were not analyzed by the above procedure.

DETERMINATION OF ANOMERIC GLUCOSIDES

To calculate the specific rate constant from polarimetry it was necessary to know the anomeric composition of the glucosidic products in the alcoholysis of TAGB [see n value, Equation (17)]. It was possible, as shown earlier, to determine the composition of anomeric mixtures of acetylated alkyl D-glucosides by gas chromatography. Direct analysis of the alcoholysis reaction solutions could not be used. It was found that a solution of TAGB in the alcohol would react in the gas chromatograph yielding erroneous values for the anomeric gluco- side composition. It was necessary to develop a procedure for removing the un- reacted TAGB from the glucosidic reaction products prior to analysis of the anomeric ratio. -43-

The procedure consisted of hydrolyzing the unreacted TAGB and simultaneously converting the hydrolysis products to saccharinic acids by treating an aliquot of the reaction solution with a large excess of aqueous sodium hydroxide. The alkali, in addition to destroying the hydrolysis products which could interfere with the gas chromatographic analysis of the glucosidic products, neutralized the hydrobromic acid formed in the system and thereby prevented glucoside hydroly- sis and anomerization. The alkali and saccharinic acids were removed from the system by ion-exchange resins. Because the procedure to remove the unreacted

TAGB resulted in deacetylation of the glucosidic products, the product mixture had to be reacetylated prior to analysis on the gas chromatograph.

Analysis Procedure

An aliquot (20 ml.) of the reaction solution was added to 400 ml. of 0.05N aqueous sodium hydroxide. The solution was heated for two hours on a steam bath, concentrated in vacuo to approximately 50 ml. on a cyclone evaporator, diluted with 10 ml. of.N aqueous sodium hydroxide, and heated for two additional hours on a steam bath. After cooling, the sample was passed consecutively through a 50-ml. column (11 mm. I.D.) of Amberlite IR-120 (H+ ) and a 35-ml. column (11 mm.

I.D.) of Amberlite IR-45 (OH-). The columns were eluted with a minimum of 200 ml. of distilled water. The column effluent was then concentrated in vacuo to a small volume (approximately 20 ml.) on a cyclone evaporator and then evaporated to dryness in vacuo on a rotary evaporator.

Acetylation of the sample was accomplished by heating it on a steam bath for 5 hours, with frequent shaking, with a mixture of 0.7-0.8 g. anhydrous sodium acetate in 15-20 ml. of acetic anhydride. After cooling the acetylation mixture, 25 ml. of chloroform were added. The chloroform solution was washed twice with water and an additional 50 ml. of chloroform were added to it. After -44- drying over anhydrous calcium chloride the solution was filtered into 100 ml. of toluene. Additional chloroform (50 ml.) was used to wash the calcium chloride.

The combined solutions were concentrated in vacuo to a small volume on a cyclone evaporator, transferred, with rinsing, to a small round-bottom flask and concen- trated in vacuo on a rotary evaporator to either a solid or a thick sirup. Addi- tional toluene was added if necessary to achieve the desired results in the last concentration procedure.

The sample was dissolved in 0.3-0.5 ml. chloroform and the resulting solution analyzed by gas chromatography. Representative reproductions of gas chromato- graphic analyses are shown in Fig. 10-13.

Verification of the Analysis Procedure

The analysis procedure was checked by preparing a solution containing a known ratio of a- and P-anomeric alkyl tetraacetyl-D-glucoside in the aglyconic alcohol and adding an aliquot (20 ml.) to 400 ml. of 0.05N aqueous sodium hy- droxide. 2,3,4,6 -Tetra-0-acetyl-a-D-glucopyranosyl bromide (0.2 g. solid) was added to the solution. The solution was then subjected to the preceding procedure.

The accuracy of the analytical procedure can be estimated from the data listed in Table XII. An estimate of the accuracy of the procedure is + 2%, based on the total glucoside.

An extraneous compound, labeled as ALG in the gas chromatograms shown in

Fig. 10-13, was common to all the analyses by the preceding procedure. The compound was not a product of the alcoholyses of TAGB. This was demonstrated by the fact that solid TAGB, subjected to the preceding procedure, yielded the same compound (as identified by gas chromatography). Supporting evidence that the compound was formed by the reaction of TAGB with the aqueous alkali was the -45-

(0w U) z CA COLUMN 0 (I 0v a:w oC ALG

Uj0 I-w 0

0 10 20 30 40 TIME, MIN.

Figure 10. Anomeric Glucoside Analysis: Ethanolysis (0.100M NH 4Br) of TAGB at 40°C. and 157 min. Sample 5 X; Sensitivity,

107-lx; Column Temp., 195°C.; N2 Flow, 15 p.s.i.g.

LO ALG A

CA COLUMN

oC

0 10 20 30 40 TIME, MIN.

Figure 11. Anomeric Glucoside Analysis: n-Propanolysis (0.100M LiC104 ) of TAGB at 40°C. and 3.80 hr. Sample 5 X; Sensitivity, 7 10 -lx; Column Temp., 195°C.; N2 Flow, 15 p.s.i.g. -46-

W

O CASE COLUMN

0

W

0 10 20 30 40 TIME, MIN.

Figure 12. Anomeric Glucoside Analysis: iso-Propanolysis of TAGB at 35°C. and 43 hr. Sample, 2 X; Sensitivity, 107-1x; Column Temp., 185°C.; N2 Flow, 15 p.s.i.g.

ALG W C) z 0 (n O CA COLUMN

L- W oC WU IJ 0

0 10 20 30 40 TIME) MIN.

Figure 13. Anomeric Glucoside Analysis: Cyclohexanolysis of TAGB at 40°C. and 36 hr. Sample 7.5 X; Sensitivity, 10 7 -1x; Column Temp., 215°C.; N2 Flow, 14.5 p.s.i.g. -47- decreasing concentration of the compound (relative to the total glucoside formed)

in aliquots of the reaction solution at longer reaction times. The latter char- acteristic could also be that of a reactive intermediate which subsequently forms the glucosidic products, however.

TABLE XII

VERIFICATION OF ANOMERIC'ANALYSIS PROCEDURE

Anomeric Acetylated c-Anomer, % Alkyl D-Glucoside Known Analysis Procedure

Methyl 0 0

Ethyl 0 0 5 6 24 25 42 42

n-Propyl 0 0 12 12 38 .38

iso-Propyl 0 0 16 16 16 15 44 46

ALG was identified as 1, 6 -anhydro-2,3,4-tri-O-acetyl-3-D-glucose (acetyl- ated levoglucosan) by gas-chromatographic analysis. Paper-chromatographic analysis (butanol- pyridine - water, 6:2:3, system) of the deacetylated analog verified this. Haq and Whelan (5) have reported that the reaction of 2,3,4-tri-

O-acetyl-a-D-glucopyranosyl bromide with aqueous barium hydroxide produced levo- glucosan. A similar reaction for TAGB indicates that deacetylation of the C6

0-acetyl group is rapid in aqueous alkali.

Analysis of Alcoholysis Reactions

The preceding procedure was used to analyze the alcoholyses of TAGB. The results are reported in Tables XIII through XVIII. Analyses at less than 15-20% -48-

TABLE XIII

ANOMERIC GLUCOSIDE ANALYSIS: METHANOLYSIS OF 2,3,4,6- TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

Temp., TAGB, Salt, Time, Reaction , a-Anomer, °C. . M x 10 0.100M min.

25.0 2.53 94 19 0- - 181 33 0

30.0 2.33 57 20 0 120 36 0

35.0 2.04 40 22 0 80 39 0

40.0 2.24 23 21 0 50 40 0

25.0 2.47 LiClO4 91 20 0 192 37 0

25.0 2.47 LiBr 83 20 6 157 35 5

25.0 2.45 LiI 71 21 7 145 37 7

40.0 2.44 LiC1O4 25 25 0 53 45 0

40.0 2.44 NaC1O4 25 25 0 55 46 0 40.0 2.48 LiBr 21 26 5 45 47 6

40.0 2.44 NH4Br 20 25 7 43 46 6 aMinimum value; calculated from the average initial specific rate constant. -49-

TABLE XIV ANOMERIC GLUCOSIDE ANALYSIS: ETHANOLYSIS OF 2,3,4,6- TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

Temp., TAGB,2 Salt, Time, Reaction , a-Anomer, °C. M x 10 0.lOOM hr. % % 25.0 2.43 11. 90 18 2 15.65 23 19.28 28 4 23.22 32 5 27.17 37 5

30.0 2.43 7-'20 19 :5 9.17 24 4 11.20 29 4 13.72 34 4 16. 17 38 6

355.0 2.43 4.00 18 4 5.00 22 4 6.40 28 5 8.00 33 5 9.53 38 6-

40.0 2.43 2.35 18 4 3.33 25 4 4.32 31 4 5.38 37 6 6.43 43 7- 40.0 2.44 *LiC104 2.25 .22 5 3.00 28 5 3.75 33 5 4.53 39 5

40.0 2.39 NH4Br 1.32 23 19 1.75 29 22 2.18 35 23 2.62 40 25

40.0 2.44 LiBr 1.33 23 21 1.83 30 25 2.25 .35 25 2.73 41 29

aMinimum value; calculated from the average initial specific rate constant. -50-

TABLE XV

ANOMERIC GLUCOSIDE ANALYSIS: n-PROPANOLYSIS OF 2,3,4,6- TETRA- -ACETYL-a-D-GLUCOPYRANOSYL BROMIDE a Temp., TAGB,2 Salt, Time, Reaction , a-Anomer, °C. M x 10 0.lOOM hr. %9

25.0 1.70 18.0 14 7 24.0 18 5 50.0 22 5 36.0 26 7 41.9 50 8

25.0 1.72 20.2 16 8 42.3 50 7

25.0 1.71 18.3 14 6 29.3 22 8

30.0 1.74 18.9 25 8 24.0 31 7 29.0 36 7 32.7 40 7

35.0 1.73 7.48 18 8 9.98 23 7 12.5 28 6 14.9 33 6 17.4 37 7

35.0 1.76 9.45 22 6 14.5 32 8

40.0 1.75 6.13 25 6 7.92 32 7 9.53 37 8

40.0 1.73 4.45 .19 6 6.03 25 6 7.45 50 7 8.93 35 7 10.5 39 7

40.0 1.75 LiC10 4 3.80 19 8 5.07 25 6 6.33 30 6 7.62 35 6

40.0 1.76 LiBr 1.88 22 26 2.40 27 28 2.98 32 32 3.58 37 33 .MinimumMinimumvalue; value; calculatedcalculate from the initial specific rate constant. -51-

TABLE XVI

ANOMERIC GLUCOSIDE ANALYSIS: n-BUTANOLYSIS OF 2,3,4,6- TETRA- -ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

a Temp., TAGB, 2 Salt, Time, Reaction , a--Anomer, 0C. M x 10 0. 10M hr. % 25.0 1.61 27.2 19 9 33.2 22 11 39.4 26 10 47.2 50 10

25.0 1.62 20.4 14 11 32.3 22 11 42.4 28 11

30.0 17.0 19 10 22.0 24 11 28.1 50 10 33.1 34 11 46.1 44 12

35.0 1.53 8.45 18 11 11.5 23 11 13.9 27 11 16.9 32 10 20.0 37 11

35.0 1.55 8.92 18 10 12.0 24 12 15.1 29 10 18.0 33 11

40.0 8.00 24 11 10.0 29 9 12.0 33 11 13.7 38 10

40.0 1.53 LiC1O4 5.83 24 11 7.27 29 10 8.72 33 -8

40.0 1.52 LiBr 3.05 50 32 3.87 36 34 4.53 41 34 aMinimum value; calculated from the initial specific rate constant. -52-

TABLE XVII

ANOMERIC GLUCOSIDE ANALYSIS: iso-PROPANOLYSIS OF 2,3,4,6- TETRA- O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

Temp., °C. TAGB, Mx 102 Salt, 0.100M Time, hr. a-Anomer, %

25.0 2.03 65.0 12 95.3 18

25.0 2.05 69.6 11 93.5 16 117.6 21 188.8 27

30.0 2.06 43.0 19 60.9 25 74.2 26 89.9 50 108.0 32

35.0 2.07 26.1 21 35.1 25 43.0 28 61.0 32

40.0 2.09 17.0 22 27.9 29 .34.0 31

40.0 2.14 LiC104 14.2 17 19.3 18 28.6 21

40.0 2.06 LiBr 3.92 53 5.23 54 6.52 56 7.65 56

TABLE XVIII

ANOMERIC GLUCOSIDE ANALYSIS: CYCLOHEXANOLYSIS OF 2,3,4,6-TETRA-0-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

Temp., °C. TAGB, M x 102 Time, hr. a-Anomer, %

35.0 1.42 37.1 12 49.0 14 61.1 17 74.0 20

40.0 21.7 13 28.9 16 36.2 22 43.1 23 -53- reaction were not successful. This was due to low glucoside concentration, high ratios of ALG to glucosides, and solvent peak tailing.

EFFECT OF ALCOHOLIC HYDROGEN BROMIDE ON ACETYLATED ALKYL P-D-GLUCOPYRANOSIDES

The alcoholysis of 2,3,4,6-tetra-O-acetyl-a-D-glucosyl bromide (TAGB) gener- ates hydrobromic acid. As noted previously, the acidic system may cause trans- esterification and transglycosidation.

The experimental program was designed to ascertain the effect of hydrobromic acid on the major alcoholyses reaction products, the acetylated alkyl P-D-gluco- pyranosides. Solutions of the acetylated alkyl P-D-glucoside and hydrobromic acid in the aglyconic alcohol were analyzed periodically by gas chromatography.

Formation of the acetylated alkyl a-D-glucosides could not be detected. The re- action time and conditions were such, that the nonformation of the a-anomeric glucoside established that transglycosidation of the acetylated alkyl E-D- glucosides was not responsible for the formation of the acetylated alkyl a-D- glucosides found in the alcoholyses of TAGB.

The concentration of the alkyl tetra-O-acetyl-p-D-glucosides decreased with time in the acidic alcohol. This was believed to be due to acid-catalyzed trans- esterification.* Distillable esters in the reactions of methyl and ethyl tetra-

O-acetyl-p-D-glucosides with methanolic and ethanolic hydrobromic acid, respectively,

supported this. In the methanolic reaction system, the distillable ester was

identified as methyl acetate by gas chromatography.

*In the transesterification reaction an 0-acetyl group on the sugar molecule would be transferred to an alcoholic solvent molecule. The net effect is deacetylation of the sugar molecule. In this sense the terms deacetylation (of the sugar ace- tate) and transesterification will be used interchangeably. -54-

ACID-CATALYZED TRANSESTERIFICATION

Discussions of the mechanism of acid-catalyzed transesterification are

available in several sources (20, 21, 58-60).

The deacetylation of the acetylated alkyl 3-D-glucosides in alcoholic hydro-

bromic acid would be expected to exhibit pseudo-first-order kinetics. The first

step in the deacetylation is protonation of the ester. Combination of the

protonated intermediate with the alcohol is the rate-controlling reaction. A

detailed kinetic description of similar systems has been reported by Juvet and

Wachi (60).

Assuming that the reverse reaction in.Equation (19) is negligible, the rate

of deacetylation of the glucoside tetraacetate to form a glucoside triacetate

can be expressed as in. Equation (20). Each of the glucoside O-acetyl groups

is considered independently.

[TAG]i + ROH > GTA. + ROAc .+ H (19)

where

[TAG]. = one of four possible protonated glucoside tetraacetates

[ROH] = alcohol

GTA. = a glucoside triacetate

ROAc = alcohol acetate 4

d[TAG]/dt = - k2 iKpi[H+][TAG][ROH] (20) 1w -where

k_ = second-order rate constant

K . = formation constant for [TAG]. -pi [TAG] = glucoside tetraacetate

t = time -55-

If the alcohol and acid concentrations, [ROH] and [H+], respectively, are essen- tially constant, Equation (20) may be expressed as

d[TAG]/dt = -k[TAG] (21) 4 where k = k-iKp[H2 ][ROH] a constant 1 and the reaction will exhibit pseudo-first-order kinetics.

Harfenist and Baltzly (58) reported pseudo-first-order kinetics for hydrogen chloride-catalyzed transesterifications of P-naphthyl esters in various alcohols.

Juvet and Wachi (60), in a study of the transesterification of n-propyl propionate in methanol (hydrogen chloride catalyst), found that the reaction was pseudo-second-order but that the system would exhibit pseudo-first-order kinetics for an alcohol-ester ratio of 8:1. They also reported a direct propor- tionality of the reaction rate with acid concentration.

EXPERIMENTAL PROCEDURE

A solution of the alkyl tetraacetyl-P-D-glucopyranoside was prepared and thermally equilibrated in a water bath maintained at 30.0 + 0.005°C.

Hydrogen bromide gas was bubbled into the appropriate purified alcohol and an aliquot of the solution was diluted with distilled water and titrated to determine the acid strength. In the case of n-butanol the titration with aqueous alkali was facilitated by adding iso-lpropanol to the butanolic hydrogen bromide aliquot and then diluting with water.

The amount of alcoholic hydrogen bromide necessary to prepare 100 ml. of a

O.0100N solution was delivered to a 100-ml. volumetric flask by microburet. The -56-

flask was suspended in the constant temperature bath for one-half hour before diluting to volume with the acetylated glucoside solution.

An aliquot of the reaction mixture was shaken with yellow mercuric oxide to neutralize the hydrogen bromide. The time of initial sampling was taken as zero time. The sample was allowed to stand over the mercuric oxide until time permitted further work. After centrifugation, a known volume of the neu- tralized reaction solution was added to a known volume of a standard solution of an internal standard. For the methyl, ethyl, n-propyl, and iso-propyl tetra- acetyl-p-D-glucosides, n-butyl tetraacetyl-P-D-glucoside was used as an internal standard. For the deacetylation of n-butyl tetraacetyl-P-D-glucoside, ethyl tetraacetyl-p-D-glucoside was used as the internal standard.

The solution was then analyzed by gas chromatography. Peak areas were determined by triangulation (56).

Samples at later times were treated in the same manner.

The concentration of the alkyl tetraacetyl-p-D-glucoside in question was calculated using the equation

Cu = (Au/Ai)(l/f)(Vi/Vu)(Gi/Mu) (22) where

C = the concentration of the acetylated glucoside, mole/l.

A = gas chromatographic response for the acetylated glucoside, sq. cm. --u A. = gas chromatographic response for the internal standard, sq. cm.

f = weight response ratio for the acetylated glucoside relative to the internal standard, Table XIX

V. = volume of internal standard solution employed

V = volume of reaction solution employed -u -57-

G. = concentration of the internal standard solution, g./l.

M = the molecular weight of the acetylated glucoside

TABLE XIX

RELATIVE HYDROGEN FLAME IONIZATION DETECTOR RESPONSE PER UNIT WEIGHT FOR ALKYL 2,3,4,6-TETRA-O-ACETYL-D-GLUCOPYRANOSIDES

Acetylated Alkyl b c D-Glucosidea Relative Responseb '

Methyl 0.85 + 0.01

Ethyl 0.88 + 0.01

n-Propyl 0.94 + 0.01

iso-Propyl 0.91 + 0.01

n-Butyl 1.00

aAll evidence indicates that the response is identical for the a- and P-anomer (e.g., see Table X). Response relative to n-butyl tetra-0-acetyl-p-D-glucoside. CAerograph Hy-Fi Gas Chromatograph,. Model A-600-B; built by Wilkens Instrument and Research,.Inc., Walnut Creek, California.

EXPERIMENTAL RESULTS

The integrated form of Equation (21) is

ln[TAG] = -kt + ln[TAG]° (23) 0 where

t = time

[TAG] =,the concentration of the alkyl tetra-O-acetyl-3-D-glucoside at time t

[TAG]o = the concentration of the alkyl tetra-O-acetyl-p-D-glucoside at zero time

k = pseudo-first-order rate constant -58-

The pseudo-first-order rate constants were therefore determined from the

slope of a plot of ln[TAG] versus t by the method of least squares. The rate

constants are listed in Table XX. The concentration-time data used in the calcu-

lations are listed.in.Appendix III.

TABLE XX

HYDROBROMIC ACID-CATALYZED DEACETYLATION OF ACETYLATED ALKYL P-D-GLUCOSIDES IN THE AGLYCONIC ALCOHOL

Acetylated Alkyl k' x 10 sec. Relative 3-D-Glucoside Alcohol (chlcd. for N HBr) Ratea

Methyl Methyl 300 1.00

Ethyl Ethyl 65 0.22

n-Propyl n-Propyl 47 0.16

n-Butyl n-Butyl 64 0.21

iso-Propyl iso-Propyl 3.9 0.013 aRelative to the methanolic methyl tetra-0-acetyl-p-D-glucoside reaction.

The relative rates of deacetylation of the acetylated alkyl P-D-glucosides in the various alcohols listed in Table XX are very similar to the relative rates of deacetylation of P-naphthyl acetate in alcoholic hydrogen chloride reported by

Herfenist and Baltzly (58). Their results are listed in Table XXI.

TABLE XXI

HYDROCHLORIC ACID-CATALYZED DEACETYLATION OF P-NAPHTHYL ACETATE IN ALCOHOLS (58)

k' x 103, min. - 1 Rel native Alcohiol (calcd. for N HC1) R~atea

Methyr1 378 1..00 Ethyl 91.2 0..24 n-Prc)pyl 87.6 0 .23 iso-I'ropyl 5.43 0.015

Relative to the methanolic reaction. -59-

POLARIMETRIC RATE MEASUREMENTS

PROCEDURE FOR CONDUCTING ALCOHOLYSIS REACTIONS

2,3,4,6-Tetra-O-acetyl-a-D-glucosyl bromide was weighed into a 100-ml.

volumetric flask; the flask was sealed with a skirt-type rubber stopper and placed in the constant temperature bath. The amount of the glucosyl halide

used was 0.55-1.00 g. (0.013-0.025M), depending on the alcoholic reagent to be

used. A flask containing the appropriate alcohol was also placed in the constant

temperature bath. After both flasks and their contents were thermally equili- brated (30-45 min.), the alcoholic solvent was added to glucosyl bromide. A

stopwatch was started when approximately one-half of the necessary alcohol had been added. The flask was swirled to dissolve the glucosyl bromide and addi- tional alcohol added to dilute the reaction to 100 ml. When the glucosyl bromide would not readily dissolve in the alcohol, the reaction was diluted to volume, a magnetic stirring bar inserted, and the solution was stirred mag-

netically to facilitate solution. Part of the solution (ca. 12 ml.) was trans- ferred to a water-jacketed polarimeter tube, the tube was sealed, and optical rotation readings were begun. The flask containing the remainder of the reaction solution was sealed with a skirt-type rubber stopper, suspended in the constant temperature bath and used for product analysis.* The time elapsed between the start of the reaction and the first optical rotation reading was usually two to six minutes.

Optical rotation-time data were taken at periodic intervals. Two stop- watches were started at a known time on the master stopwatch. When the polarimeter

*For reactions at 40°C. the bath temperature was 0.1-0.2°C. higher than the tem- perature of the solution in the polarimeter tube. This was not considered significant enough to alter the product analysis procedure. -60-

field was balanced, a stopwatch was stopped and the optical rotation was noted.

A second measurement was made in a similar manner. The average optical rotation and time of the pair of readings constituted one data point. The time required to make and average a pair of readings was 15 to 30 seconds. Thus, when necessary,

optical rotation-time data at one-minute intervals could be obtained. For slow

reactions, the optical rotation of the system was recorded to the nearest minute at longer time intervals. A data point consisted of the average of two to four

readings.

The zero point of the polarimeter, necessary to calculate the absolute optical

rotation, was checked at periodic intervals.

Reactions in the presence of salts* were conducted in a similar manner using a standard alcoholic salt solution (prepared at the temperature of the reaction) as the solvent.

The temperature of the reaction solution was monitored as described in the section on the system used for isothermal polarimetry. Temperature control was better than + 0.1°C. Room temperature was the limiting variable in temperature control.

CALCULATION OF POLARIMETRIC SPECIFIC RATE CONSTANTS

The optical rotation-time data for the alcoholyses of 2,3,4,6-tetra-O-acetyl- a-D-glucopyranosyl bromide are listed in Appendix IV. The initial specific rate constants were calculated from these data by use of

*All salts employed were reagent grade (99+%) and were dried prior to use. Weighing, transfers, and solution of hygroscopic salts were done in a dry nitrogen atmosphere. Final dilution to volume was made at the reaction tem- perature. -61-

ln(at - M) = -kt + ln(Co - M) (24)* where

at = the optical rotation of the alcoholysis system at time t

a = the optical rotation of the alcoholysis system at zero time o M = a calculated optical rotation related to the reaction products

Product analysis showed that the products of the alcoholyses were the anomeric alkyl tetra-O-acetyl-D-glucosides. M could therefore be calculated from

M = £(n[a] + (l-n)[O a].)MGHo/1000 (25) where

X_ = the polarimeter tube length, dm.

H = the initial concentration of TAGB, mole/liter -o M = the gram-molecular weight of the anomeric glucosides -G n = the fraction of the total glucoside concentration accounted for as the 3-anomer

[a the specific optical rotation of the a-anomeric glucoside a ] = [ab] = the specific optical rotation of the 3-anomeric glucoside

The initial specific rate constant, k, was calculated from the slope (method of least squares) from the initial linear portion of a plot of ln(at - M) versus t.

The reactions could be divided into two categories, those in which n, the ratio of anomeric glucosides, was constant and those in which n was time-depen- dent. The first category included the primary alcoholyses, the primary alcoholyses with added lithium perchlorate, and the methanolyses with added halide salts. The second category included the secondary alcoholyses and the alcoholyses with added halide salts (except for the methanolyses).

*See Appendix I for the derivation of Equation (24). -62-

Sample calculations of the initial specific rate constant for each category are given.

Ethanolysis of 2,3,4,6 -Tetra-0-acetyl-a-D-glucopyranosyl Bromide at 30.0°C.

The ethanolysis of TAGB at 30.0°C. resulted in the formation of ethyl tetra- -

0-acetyl-D-glucosides. The anomeric composition of the glucosidic products was adjudged to be time-independent.

The value of M (-0.36) for the reaction was calculated from Equation (25) using the following data:

£ = 2.0 dm. (applicable to all reactions)

H = 0.0222 mole TAGB/liter

.MG = 376.4 g./mole

n = 0.96, see Table XIV

[aa] = 164, see Table VI

[ab] = -29.3, see Table VI

The graphical determination of the initial specific rate constant from the ln(Qt-M) versus time (t) curve is shown in Fig. 14. iso-Propanolysis of 2,3,4,6-Tetra-0-acetyl-Q-D-glucopyranosyl Bromide at 30.0°C.

The iso-propanolysis of TAGB at 30.0°C. produced iso-propyl tetra-0-acetyl-

D-glucosides for which the anomeric composition was time-dependent. Extrapolation of the anomeric glucoside analysis data in Table XVII indicated that at zero time

(initial reaction) the glucosidic products consisted entirely of the P-anomer .

In practice all the necessary calculations were performed with an IBM 1620 computer. Extrapolation of the % a-anomer-time data to 0% a-anomer at zero time can be verified from calculations of the % a-anomer for earlier times from the linear plot of (% a-anomer/time) vs. time.

-64-

The value of M (-0.56) for the initial reaction was calculated from Equation

(25) using the following data:

I = 2.0 dm.

H = 0.0206 mole TAGB/liter -o MG = 390.4 g./mole

n = 1.00 (extrapolation of the data in Table XVII)

[c ] = 175, see Table VI

[ab] = -34.7, see Table VI

The graphical determination of the initial specific rate constant from the initial linear portion of the ln(O t - M) versus time (t) curve is shown in Fig.

15. The experimental data deviate from linearity rapidly, making the determina- tion of the rate constant more difficult than for the preceding ethanolysis re- action. The increasing rate of reaction and formation of a-anomer is believed to be due to reaction of the TAGB with the hydrogen bromide accumulating in the system. This is treated in detail in the discussion of the results.

EXPERIMENTAL SPECIFIC RATE CONSTANTS

The specific rate constants determined for the alcoholyses of 2,3,4, 6 -tetra-

0-acetyl-a-D-glucopyranosyl bromide are listed in Tables XXII, XXIII, XXIV, XXV, and XXVI. Duplicate determinations of rate constants were made in several in- stances to check reproducibility. The poorest reproducibility was obtained for the iso-propanolysis of TAGB at 25.0°C. (Table XXVI); the difference was approx- imately 11%. Reproducibility for other reactions was within 56. Duplicate determinations of the rate constant for the methanolysis of TAGB at 25.0°C.

(Table XXII), made at a time interval of 13 months, agreed within 1.5%. -65- -66-

TABLE XXII

METHANOLYSIS OF 2,5,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE

TAGB, Salt, Temp., °C. mole/i. 0.lOOM k x 105, sec. -1

25.0 0.0245 3.64 0.0263 3.69

30.0 0.0254 6.52 0.0207 6.42

35.0 0. 0204 10.4

40.0 O.0199 17.1 0.0255 17.8

25.0 0.0247 LiC10O 3.94 0.0213 LiC104 4.11

40.0 0.0244 LiC104LiC1O4 19.1

40.0 0.0244 NaC104 18.8

25.0 0.0245 LiBr 4.51 0. 0247 LiBr 4.62

40.0 0. 0247 LiBr 23.4

40.0 0.0244 NH4Br 23.9

25.0 0.0249 LiI 5.5 0.0245 LiI 5.3 -67-

TABLE XXIII

ETHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-S-D- GLUCOPYRANOSYL BROMIDE

TAGB, Salt, -1 Temp., °C. mole/i. 0.100M k x 106, sec.

25.0 0. 0201 4.73 0.0211 4.65

30.0 0.0222 8.55 0.0204 8.11

35.0 0.0224 13.9 0.0209 14.1

40.0 0.0197 24.6 0. 0241 23.8

40.0 0.0244 LiC10 4 30.2

40.0 0.0244 LiBr 55

40.0 0.0239 NH4Br

TABLE XXIV

n-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE

TAGB, Salt, -1 Temp., °C. mole/i. O.10OM k x 106, sec.

25.0 0.0194 2.34 0.0171 2.38

30.0 0.0163 4.29

35.0 0.0176 7.38

40.0 0.0175 15.6 40.0 0.0175 LiC10 4 15.6

40.0 0.0176 LiBr 36 -68-

TABLE XXV

n-BUTANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE

TAGB, Salt, 6 -1 Temp., °C. mole/. 0.100M k x 10 , sec.

25..0 0.0129 2.14

30..0 0.0151 3.54 -

35. .0 0.0155 6.39

40..0 0.0153 9.56

40..0 0.0153 LiClO4 1 5.0

40..0 0.0152 LiBr 32

TABLE XXVI

iso-PROPANOLYSIS OF 2,3,4,6-TETRA-0-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE

TAGB, Salt, -1 Temp. , °C. mole/i. 0.1OOM kk x 10, sec.

257.0 0.0203 -- 6. 537 0.0245 -- 5. 73

3C).0 0.0206 -- 8. 61

357.0 0.0208 -- 12.3

4C).0 0.0209 -- 19.7

4CD.0 0.0206 LiC104 41

4C).0 0.0214 LiBr 250 -69-

EFFECT OF DEACETYLATION ON THE EXPERIMENTAL SPECIFIC RATE CONSTANT

Deacetylation of the reaction products by liberated hydrohalic acid in the alcoholysis of acetylated glycosyl halides was recognized by earlier workers (7,

23, 37). Deacetylation was also detected in the present study. It was found that long term reaction mixtures were insensitive to gas-chromatographic analysis; if the reaction products had still been acetylated, gas-chromatographic analysis would have been possible.

Deacetylation of the reactant or products can produce error in the experi- mental specific rate constant. Two consequences of deacetylation can be envi- sioned. First, deacetylation yields a different compound which may possess a substantially different specific rotation. Thus, the optical rotation of the system would be subject to change other than that due to the alcoholysis reaction.

Assuming that the C6 O-acetyl group is deacetylated first, the possible magnitude of this difference in specific rotations may be deduced from the data shown in

Table XXVII. The second effect of deacetylation is that a partially acetylated glucosyl bromide of different reactivity is produced. From the study on steric effects on the reactivity of 0-acyl-glycosyl halides by Newth and Phillips (25), it can be inferred that removal of an O-acetyl group, at least on the C6 and C4 positions, would result in a more reactive glucopyranosyl bromide. Similarly,

Wadsworth (30) found that 2,3,6-tri-O-benzoyl-a-D-glucopyranosyl bromide was more reactive than 2,3,4,6-tetra-O-benzoyl-a-D-glucopyranosyl bromide toward methanol dioxane solutions.

The importance of deacetylation in the alcoholyses of TAGB can be ascer- tained semiquantitatively by utilizing the rate constants determined for the deacetylation of the alkyl 2,3,4,6-tetra-O-acetyl-p-D-glucopyranosides by -70-

TABLE XXVII

EFFECT OF THE C O-ACETYL ON THE SPECIFIC ROTATION OF ACETYLATED GLUCOPYRANOSE DERIVATIVES

Compound [a]D (CHC13)a, Reference

Methyl 2,3,4,6-tetra-O- acetyl-p-D-glucoside -17.9 This work

Methyl 2,3,4-tri-O- acetyl-B-D-glucoside -19.1 (61)

2,3,4, 6 -Tetra-O-acetyl- a-D-glucosyl bromide +198 This work

2,3,4-Tri-O-acetyl- a-D-glucosyl bromide +218 (5)

1,2,3,4,6-Penta-O-acetyl- B-D-glucose This work

1,2,3,4-Tetra-O-acetyl- B-D-glucose +12.1 (62)

1,2,5,4,6 -Penta-O-acetyl- a-D-glucose +102 (6.)

1,2,3,4-Tetra-O-acetyl- a-D-glucose +119 (64) aThe magnitude of the difference in an alcoholic solvent will probably be similar to that observed for chloroform. -71- hydrogen bromide in the aglyconic alcohol (see Table XX). To start, the assump- tion is made that the calculated alcoholysis rate constant is correct, i.e., deacetylation effects are not important. In addition, the assumption is also made that, in a given alcohol, TAGB and the acetylated glucosides deacetylate at the same rate. The rate of deacetylation may then be expressed as:

dA/dt = -kD[A][HBr] (26) where

A = the tetra-O-acetyl sugar concentration at time t, mole/liter -1 -1 * kD = pseudo-second-order deacetylation rate constant, liter sec. mole

HBr = hydrobromic acid, mole/liter

The formation of hydrogen bromide, assuming the alcoholysis rate constant is correct, can be expressed as:

d[HBr]/dt = k[H - HBr] (27) where

H = the glycosyl halide concentration at time zero, mole/liter

k = the first-order alcoholysis rate constant, sec.

Equation (27) is integrated, yielding

HBr = H (l - exp(-kt)) (28)

Equation (28) is substituted into Equation (26) and the resulting equation inte- grated, yielding the final expression:

ln(A/A) = kDHo[l - exp(-kt)-kt]/k (29)

*Numerically equivalent to the pseudo-first-order rate constant reported in Table XX. -72-

where A = the tetra-O-acetyl sugar concentration at time zero, mole/liter. -o Using H values representative of those used in the kinetic studies, values of

A/A , the fraction of tetra-0-acetyl sugar molecules remaining, may be calculated

from Equation (29). These values, for 30°C. and 15% reaction (as calculated from

the alcoholysis rate constant), are listed in Table XXVIII. Data used in rate

constant calculations were those at less than 15% reaction (as calculated from

the alcoholysis rate constant) except for the methanolysis reactions for which data for approximately 20-25% reaction were considered. Thus, if the assumptions made in the derivation of Equation (29) are not grossly in error, deacetylation, as calculated in Table XXVIII does not appear to be important. This is consistent with the findings of Capon, et al. (31) for the solvolysis of TAGB in aqueous acetone. It is also consistent with the qualitative observations of Newth and

Phillips (23) that deacetylation was detected only when the reaction was slow and at elevated temperatures.

TABLE XXVIII

EXTENT OF DEACETYLATION IN THE ALCOHOLYSES OF 2,3,4,6- TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL-BROMIDE AT 30.00°. AND 15% REACTIONa k x 1064, x 104,b H x 1C2 -1- Alcohol sec. -1 liter - sec. -I mole- -lm mole/li-mo ter

Methyl 64.7 30 2.3 0.99

Ethyl 8.33 6.5 2.1 0.98 n-Propyl 4.29 4.7 1.6 0.98 n-Butyl 3.54 6.4 1.5 0.97 iso-Propyl 0.86 0.39 2.1 0.99

As calculated from the alcoholysis rate constant, k. Numerically equivalent to the pseudo-first-order rate constants reported in Table XX. -735-

COMPARISON OF SPECIFIC RATE CONSTANTS WITH LITERATURE VALUES

The rate constants determined for the methanolysis of TAGB are lower than those obtained by Newth and Phillips (23, 25). This is demonstrated in Table

XXIX. In addition, Newth and Phillips have shown (23) that their polarimetric rate constant agreed with the titrimetric rate constant. In view of this, a possible explanation for the differences in rate constants for the methanolysis of TAGB is necessary.

TABLE XXIX

METHANOLYS IS OF 2,3,4,6- TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE

k x 105, sec-.- Newth and Phillips Temp., °C. (23, 25) Present Study

21.2 2.83 2.42a

35 12.1 10.4

aExtrapolated from the data in Table XXII.

Newth and Phillips (23) found that the hydrogen bromide liberated in the methanolysis of TAGB catalyzed the reaction. Originally this was believed to be a salt effect but Mattok and-Phillips (26) later concluded that the hydrogen bromide acted as an electrophilic catalyst in a manner similar to mercuric salts.

In their study of the methanolysis of TAGB, Newth and Phillips (23) concluded that the catalysis by hydrogen bromide was negligible in the first 70% of the re- action. Thus, in conjunction with this conclusion, only data for the first 50% of the reaction were used to avoid this catalysis effect. This study has shown

(Fig. 16) that this catalytic effect, as shown by deviation from linearity in the plot of ln(at-M) vs. t, is evident much earlier in the reaction. Consequently,

-75- including data points at longer reaction times yield a higher value for the rate constant. This is demonstrated in Table XXX. If the time interval between data points had been longer, the inclusion of the data points which deviate from linearity would have had a greater effect on the calculated rate constant than that demonstrated in Table XXX.

TABLE XXX

METHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE AT 35.0°C.

Reaction Time, _lb Approximate min. Data Points k x 10', sec. % Reactionc

14.5 .4 10.4 9

.29.6 9 10.3 17

44.6 14 10.4 24

53.4 17 10.8 28

74.5 20 11.0 37

Calculations are from the data used in constructing Fig. 16. Calculated by the method of least squares on all data through the indicated reaction time. - Calculated using k = 10.4 x 10 -5 sec.

The fact that Newth and Phillips (23) found good agreement between their titrimetric and polarimetric rate constants would not necessarily imply the exactness of either. If approximately the same extent of reaction was considered in either case, and the difference in the initial concentrations of TAGB in the two determinations was not too great, the deviation in the rate constant due to catalysis would be approximately the same.

.Mattok and Phillips (26) in their study of the catalysis of the methanolysis of TAGB by hydrogen bromide, determined k (25°C.), in the absence of initial hy- drogen bromide, to be 3.67 x 10- sec. . This compares very favorably with the values 3.64 and 3.69 x 10 - 5 sec. obtained in this study (see Table XXII). -76-

THERMODYNAMIC FUNCTIONS OF ACTIVATION

The temperature dependence (Arrhenius Correlation) of the rate constants for the alcoholyses of TAGB are shown in Fig. 17. The thermodynamic functions of activation are listed in Table XXXI. The thermodynamic functions are calculated for 30.0°C. from the data for two temperature ranges: 25-35°C. and 25-40°C. The values for the two temperature ranges do not agree for all the alcoholysis systems.

When a variation exists, it can be attributed to a deviation of the specific rate

constant from the linear Arrhenius Correlation at 40.0°C. (65, p. 377). The deviations do not show a consistent trend and are believed to be due to experi- mental error.

TABLE XXXI

THERMODYNAMIC FUNCTIONS OF ACTIVATION FOR THE ALCOHOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-c-D-GLUCOPYRANOSYL BROMIDE Thermodynamic Functions (30°C.) Temp. Range, -exp' AH, ASt, AF', 0C. Alcohol kcal. kcal. eu. kcal.

25-40 Methyl 19.2 18.6 -16.3 23.5

Ethyl 20.3 19.7 -16.9 24.8

n-Propyl 21.3 20.7 -14.7 25.2

n-Butyl 19.1 18.5 -22.5 25.3

iso-Propyl 13.3 12.7 -44.1 26.1

25-35 Methyl 19.4 18.8 -15.8 23.6

Ethyl 20.1 19.5 -17.5 24.8

n-Propyl 21.0 20.4 -15.8 25.2

n-Butyl 20.4 19.8 -18.2 25.3

iso-Propyl 12.3 11.7 -47.7 26.2 -77-

1000

O METHANOL 500 O ETHANOL M n-PROPANOL O n-BUTANOL ISO-PROPANOL

100

60

_ 30 x0

3

1.O

0.6

0.31I I II 318 322 326 330 334 338

I/T X 105 °K-'

Figure 17. Arrhenius Correlations: Alcoholyses of 2,3,4,6-Tetra- O-Acetyl-a-D-Glucopyranosyl Bromide -78-

CALCULATION OF THE THERMODYNAMIC FUNCTIONS OF ACTIVATION

The Arrhenius activation energies (E ) were calculated by the method of -exp least squares according to the logarithmic form of the Arrhenius equation [Equa- tion (30a)]:

kr = Aexp(-Eexp/RT) (30) or

in k = n A - E xp/RT (30a) r exp where

k the specific rate constant -r = A = the "frequency factor" (empirical correlation coefficient)

The enthalpy of activation (AH ) was calculated from Equation (31) (66)

aH ~ = E - RT + pAv ¢ (31) exp where

pAv O0 since Av , the volume change in the reaction, is virtually zero for the alcoholysis reactions

T = temperatures °K.

R = gas constant, 1.9865 cal./°K. mole

The entropy of activation (AS=) was calculated from Equation (33) which is derived from the Arrhenius equation [Equation (30)] and the relationship between the specific rate constant and the entropy of activation [Equation (32)]. Equa- tion (32) was derived from the theory of absolute reaction rates (66) which relates the free energy of activation to the specific rate constant.

kr = (ekT/h)exp(-Eexp/RT)exp(AS+/R) (52) r* exp -79- where

e = base for napierian logarithms, 2.7183

k = Boltzmann constant, 1.380 x 10 1 6 erg deg.

h = Planck constant, 6.625 x 10 2 7 erg sec.

AS = R ln(A/T) + R ln(h/ek) (33)

= 1.987 in (A/T) - 49.2.

The free energy of activation was calculated from Equation (34):

AF = AH - TAS (34). -80-

DISCUSSION OF RESULTS*

SOLVENT EFFECTS

The effect of solvent variation on the rate of reaction is frequently em- ployed as an indication of a solvolysis mechanism. For reactions in which ionic charge is created or destroyed during the formation of the transition state, the effect of solvent polarity on the rate of reaction can be very pronounced. Crea- tion of charge is favored by polar solvents, destruction of charge by nonpolar solvents.

For nucleophilic substitution reactions involving two neutral molecules, such as the alcoholysis of 2,3,4,6-tetra-0-acetyl-a-D-glucopyranosyl bromide

(TAGB), charge is created in the transition state,.irrespective of whether the reaction mechanism is SN1 or SN2. Thus, the reaction rate will be greater in more polar solvents. However, for the same reactants, an SN1 mechanism will be favored more by solvent polarity than the SN2 mechanism. This is due to the greater concentration of charge (carbonium ion) in the SN1 transition state.

Analysis of solvent effect data must be made with discretion, owing to the obvious difficulty of not being able to predict the magnitude of a solvent effect for a given compound if it were to react by either mechanism. Thus, solvent effects are normally compared to solvent effects observed for compounds for which the reaction mechanisms are known.

The possibility of a mechanistic change with solvent variation must also be considered.

*A general discussion of nucleophilic substitution reactions is presented in the Introduction. -81-

As shown by Streitweiser (19, p. 46, 64), the magnitude of the solvent effect on the rate of reaction in aqueous alcohol, as shown by m value in the Winstein-

Grunwald equation (67), can be, to some extent, indicative of reaction mechanism; compounds prone to react by an SN2 mechanism exhibit less variation in reaction rate with solvent polarity (smaller m values). However, the Winstein-Grunwald correlation has severe limitations in that different solvent systems yield dif- ferent correlation lines.

The effects of alcohol variation on the rate of alcoholysis of TAGB are compared with analogous effects for other compounds in Table XXXII. t-Butyl chloride is believed to react - by an SN1 mechanism in a large number of solvents and, because of this, is frequently employed as a standard in this capacity in attempted correlations of solvolysis rates (67-69). The relative rate for TAGB in methanol and ethanol compares favorably with the ratio exhibited by t-butyl chloride. 2,3,4,6-Tetra-O-methyl-a-D-glucopyranosyl chloride (TMGC) has been included in Table XXII because of its structural similarity to TAGB. Again the solvent effect on the rate of reaction, as measured by the relative rate in methanol compared to n-propanol, is similar to that for TAGB. The methanolysis of TMGC has been classified as SN1 by Rhind-Tutt and Vernon (3553).

TABLE XXXII

EFFECT OF SOLVENT VARIATION ON REACTION RATE

Compound k OH/ aEtOH OHlPOH aMe Reference

2,3,4,6-Tetra-O-acetyl a-D-glucosyl bromide 7.8 15.5 This work t-Butyl chloride 8.5 (2 5 )b (67)

2,3,4,6-Tetra-O-methyl- a-D-glucosyl chloride -- 17.9 (3355)

2,35,4,6-Tetra-O-methyl- c6-D-mannosyl chloride -- 133 (3355) aRelative rates at 25.0°C. Crude estimate from EtOH and MeOH data. -83-

The ion-pair hypothesis has been used by Rhind-Tutt and Vernon (33) to explain the high degree of stereospecificity obtained in the products of the methanolysis of TMGC and the ease of transition of a-D-glucosyl halides to re- action by the SN2 mechanism with strong nucleophiles.

PRODUCT STEREOCHEMISTRY

The data on the anomeric composition of the glucosidic products for the: primary alcoholyses of TAGB* show that the fraction of a-anomeric glucoside is time-independent in the time interval studied. Similar analyses for the iso- propanolyses of TAGB showed that the fraction of a-glucoside formed was time- dependent (Fig. 18). This was also true for the cyclohexanolyses of TAGB (Fig.

19). This dissimilarity of the primary- and secondary-alcoholyses of TAGB is contrasted in Fig. 20.

The extrapolations performed in Fig. 18 and 19 indicate that, initially, the products of the iso-propanolysis and cyclohexanolysis of TAGB are the acetylated P-anomeric glucosides. Contrasted to this, the primary-alcoholyses, except for the methanolysis of TAGB, extrapolate to a finite fraction of a- anomeric glucoside, indicating that both the a- and P-glucoside are formed in the initial reaction (Fig. 20). The product analysis data indicate that the iso-propanolysis (and cyclohexanolysis, although data for this system is limited) of TAGB is mechanistically different from the primary-alcoholyses.

SALT EFFECTS

The role of a salt in the alcoholysis reaction system, barring reaction, is to facilitate the formation of the transition state by an additional mode of charge stabilization. This effect would tend to be greater in less polar solvents.

*Refer to Tables XIII, XIV, XV, XVI, XVII, and XVIII. -84-

-86- -87-

Perchlorate anions are weak nucleophiles (19-21) and, in small concentration, would not be expected to compete effectively with the alcohol to react with TAGB.

Addition of lithium perchlorate to an alcoholysis of TAGB would therefore cause only a salt effect.

The effects of 0.100M lithium perchlorate on the alcoholyses of TAGB are listed in Table XXXIII as (kC1 - k)/k; kC1 is the rate constant for the re- l4 - - 4 action in the alcoholic salt solution and k is the rate constant for the reaction in the pure alcohol.

TABLE XXXIII

SALT EFFECTS FOR THE ALCOHOLYSES OF 2,3,4,6-TETRA- O-ACETYL-a-D-GLUCOPYRANOSYL BROMDEa

Alcohol (k - k)/k =C104 Methyl 0.1

Ethyl 0.3

n-Propyl 0.2

n-Butyl 0.4

iso-Propyl 1.1

0.100M Lithium perchlorate; 40.0°C.

It is known that the salt effect is more pronounced for SN1 than SN2 re- actions. However, no mechanistic inferences can be made from the salt effect in the various alcohols because of the ramifications inherent in the varying de- grees of dissociation and ion-pair formation of the lithium perchlorate. The data do show that iso-propanol is a much poorer solvent for the reaction than would be predicted on the basis of dielectric constant. Although iso-propanol has a larger dielectric constant (18.5 at 25°C.) than does n-butanol (17.1 at -88-

25°C.), the salt effect is very much larger for iso-propanol. This is another

significant difference from the primary-alcoholyses which the iso-propanolysis

reaction exhibits.

BROMIDE SALT EFFECTS

The addition of a bromide salt to the alcoholyses of TAGB will cause a salt

effect analogous to that observed with lithium perchlorate in the reaction system.

Secondary effects, due to the bromide ion and dependent on the reaction

mechanism, may also be observed. Some reactions occurring by an S mechanism

are susceptible to a mass-law or common-ion retardation of the reaction rate.

This effect is caused by reformation of the reactant by the reaction of carbonium

ions with bromide ions. This decreases the rate of disappearance of R:Br [Equa-

tion (35)].

R:Br R + + Br- (35)

The effect appears to be dependent on the stability of the intermediate carbonium

ion. Thus, the effect is quite large for the hydrolysis of triphenyl methyl

chloride and small for t-butyl bromide (19, p. 52; 20, p. 134).

A second effect is due to the nucleophilicity of the bromide ion* and is possible when the reaction mechanism is SN2 or when the bromide ion can effect an S.2 reaction with the electrophile. Bromide ions are fairly strong nucleo- philes and may compete effectively with the alcohol to react with TAGB. The effect of bromide exchange on the observed reaction rate is dependent on the experimental technique used to determine the rate. Reaction rates determined by

*The Swain nucleophilicity parameter for bromide ion is 3.89, hydroxide ion is 4.20, and water is 0.00 in an aqueous system (20, p. 161). -89- titration of the liberated hydrogen bromide will reflect the reactivity of the resultant P-glucosyl bromide. Polarimetrically determined reaction rates would increase or show no change (except for the general salt effect); this is due to the steric inversion accompanying each bromide exchange.

The effects of 0.100M lithium bromide on the alcoholyses of TAGB are listed in Table XXXIV. An attempt, although not rigorous, has been made to isolate the effect of the bromide ion by correcting for the general salt effect (assumed to be represented by the reaction in 0.100M lithium perchlorate).

TABLE XXXIV

BROMIDE ION:EFFECTS FOR THE ALCOHOLYSES OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDEa

Alcohol (k - k1)/k

Methyl 0.3

Ethyl 1.0

n-Propyl 1.5

n-Butyl 2.0

iso-Propyl 11

a.100M Lithium bromide; 40.o0C.

The bromide ion causes the reaction rate to increase. This effect increases for the primary-alcoholyses of TAGB as the polarity of the alcohol decreases.

The effect on the iso-propanolysis reaction is extremely large, the reaction rate being increased by approximately a factor of eleven.

METHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

The 6% increase in the rate of methanolysis of TAGB on addition of 0.04M lithium bromide reported by Newth and Phillips (23) agrees favorably with the -91- effect (rate retardation by bromide ion) was present but superimposed on a salt effect, appears to be erroneous. The absence of a mass-law effect is consistent with TAGB reacting as an ion-pair, similar to that proposed by Rhind-Tutt and

Vernon (33) for the methanolysis of tetra-O-methyl-a-D-glucopyranosyl chloride.

iso-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a- D-GLUCOPYRANOSYL BROMIDE

SN2 REACTION MECHANISM

The time-dependence of the anomeric composition of the glucosidic products for the iso-propanolysis of TAGB (Fig. 18) can be explained on the basis of an

SN2 reaction mechanism being operative. An SN2 reaction mechanism is also con- sistent with the initial reaction product being the P-anomeric glucoside (steric inversion during reaction) and the large effect of lithium bromide (nucleophil- icity dependence) on the reaction.

The time-dependent fraction of Q-glucoside can be accounted for by the bromide ion, from the hydrogen bromide formed in the reaction, reacting with

TAGB to form 2,3,4, 6 -tetra-O-acetyl-p-D-glucopyranosyl bromide which subsequently forms the a-anomeric glucoside. 2,3,4,6-Tetra-O-acetyl-P-D-glucopyranosyl bromide

(P-TAGB) has been isolated (79) but has not, to the author's knowledge, been studied kinetically. Also, P-TAGB has been reported "in solution (70). By analogy with the methanolysis of 2,3,4,6-tetra-O-acetyl-P-D-glucopyranosyl chloride (27) the alcoholysis of 3-TAGB should result in a high yield of the a-anomeric gluco- side and the rate of reaction should be approximately 103 - 10 times that of

TAGB (27, 31).

The exact mechanism for the formation of the-a-anomeric glucoside from the acetylated E-halide has not been clearly defined. It is known that when the C2 -92-

O-acetyl group is trans to the halogen atom, as is the case for the 2,3,4,6- tetra-O-acetyl-B-D-glucopyranosyl bromide, alcoholysis in the presence of an acid acceptor, such as silver carbonate, results in the formation of an alkyl ortho-acetate (11-13, 27). Mattok and Phillips (27) have proposed a cyclic carbonium ion (VIII) as the intermediate in the methanolysis of 2,3,4,6-tetra-

O-acetyl-p-D-glucopyranosyl chloride. The formation of an alkyl orthoacetate

(IX) from this intermediate, as is the case when an acid acceptor is employed in the system, is easy to visualize. However, the role of this intermediate in the formation of an alkyl 2,3,4,6-tetra-O-acetyl-a-D-glucopyranoside, as is the case when no acid acceptor is used, is difficult to visualize.

O-C-CH 3 O-C-CH 3 O-C-CH3- 0-C-CH 3 OR VIII IX

ENTHALPY AND ENTROPY OF ACTIVATION

The lower energy and entropy of activation exhibited by the iso-propan- olyses of TAGB, as compared with the methanolyses (Table XXXI), are also consistent with an SN2 mechanism. The decrease in activation energy for an

SN2 mechanism is due to the partial bond formation by the nucleophilic reagent and a reduction of the necessary extension of the polarized carbon-halogen bond in the transition state. Brown and Hudson (71) demonstrated, in a study of the

-93-

mechanisms of hydrolysis of substituted benzoyl chlorides, that the activation

energies for the SN2 reactions were lower than for the SN1 reactions.

From Table XXXI it can be seen that the entropy of activation for the iso-

propanolysis of TAGB (ca. -45 e.u.) is considerably more negative than the entro-

pies of activation for the primary-alcoholyses (ca. -17 e.u.). Based on the

discussion of Schaleger and Long (72) on the entropy of activation as a mechan-

istic criterion, a bimolecular solvolytic process (SN2, A-2), in which a molecule

of solvent is considered to be bound in the transition state, should reflect the

loss of translational and rotational freedom of the bound molecule by a decrease

in the entropy of activation when compared to the unimolecular process (SN1, A-l).

Part of the entropy differential between the methanolysis and iso-propanolysis

of TAGB is probably accounted for by the degree of association of the solvent.

By being bound in the transition state, in the same manner, an iso-propanol mole-

cule would experience a greater loss of freedom than a methanol molecule because

the iso-propanol solvent is less associated than methanol.

Nucleophilic and electrophilic solvent properties influence the degree of

association in a solvation cage. Steric factors are also important. A methanolic

solvation cage, other effects being equal, would be expected to accommodate more molecules than an iso-propanolic cage because of steric packing.

The entropy of activation can be indicative of other steric factors as well.

From models of TAGB it would be expected that the movement of the C acetoxymethyl

group would be somewhat restricted by the alcohol molecule bound in the transition

state for an S2 mechanism. A similar restriction by the carbonium ion solvation

cage could be envisioned for the SN1 process, but the position of a molecule in the solvation cage is believed to be transitory and thereby less restrictive. -94-

Whereas a quantitative estimate of the mechanistic entropy differential for

SN1 - SN2 reactions is virtually impossible, qualitative considerations indicate

that the SN2 mechanism should exhibit a lower entropy of activation.

Long, et al. (73) showed that esters hydrolyzing by A-1 and A-2 mechanisms

exhibited a mechanistic entropy differential of 25-30 e.u. Schaleger and Long

(72) are of the opinion that this entropy differential is larger than is normally

exhibited between bimolecular and unimolecular reactions. However, the entropy

differential between the SN1 hydrolysis of. -butyl chloride and the SN2 hydrolysis

of methyl chloride is about 17 e.u. (74).

Based on the preceding discussion, the activation-entropy differential of

25-30 e.u. between the methanolysis and iso-propanolysis of TAGB is indicative

of an SN2 mechanism being operative in the latter reaction.

COMPARISON WITH A THEORETICAL MODEL

The best test of the iso-propanolysis of TAGB occurring by the proposed mechanism is to compare the experimental reaction characteristics with a theo- retical model. It was stated previously that the time-dependence of the anomeric composition of the glucosidic products for the iso-propanolysis of TAGB (Fig. 18) could be accounted for by an S 2 reaction mechanism in which the a-glucoside formation is the net result of a reaction of TAGB with bromide ions. In'defining the theoretical model, the reaction of bromide ion with TAGB to form P-TAGB will be the rate-determining step in the formation of the a-anomeric glucoside. The reaction of P-TAGB with iso-propanol should be relatively fast compared to bromide exchange. By analogy with the study of Mattok and Phillips (29) on the extent of halogen exchange between 2,53,4, 6 -tetra-0-acetyl-B'-D-glucosyl chloride and lithium radio-bromide in acetone, the reaction of 2,3,4,6-tetra-O-acetyl-P-D-glucosyl -95- bromide with bromide ions to form TAGB should be negligible.* Thus, the theoreti- cal model can be envisioned as:

k TAGB + HBr - e-- -TAGB + HBr

kL f TAGB + ROH ---- ROG + HBr

k P-TAGB + ROH --- a-ROG + HBr where k > k -a -e and TAGB = 2,3,4, 6 -tetra-O-acetyl-a-D-glucopyranosyl bromide

P-TAGB = 2,3,4,6-tetra-O-acetyl-P-D-glucopyranosyl bromide

ROH = iso-propanol

a-ROG = iso-propyl 2,3,4,6-tetra-O-acetyl-a-D-glucopyranoside

P-ROG = iso-propyl 2,3,4,6-tetra-O-acetyl-p-D-glucopyranoside

k = second-order rate constant, liter mole sec. -e k = pseudo-first-order rate constant, iso-propanolysis, sec.

k = pseudo-first-order rate constant, iso-propanolysis, sec.l

From the theoretical model the following equation can be derived (Appendix

V):

[a-ROG]/([a-ROG] + [P-ROG]) = Fraction of a-anomer

Fraction of a-anomer = l-F[P-ROG]/[exp(F[i-ROG])-l] (36) where

F k /k

*It is possible that P-TAGB is more susceptible to halogen exchange than the chloride analog since bromine is a better leaving group than chlorine. -96-

By defining an initial concentration of TAGB and a'value of F, Equation (36) can

be used to describe a fraction of a-anomer-per cent reaction curve. A sample

calculation is shown in Appendix V. An analogous curve can be constructed from

the polarimetric data for the iso-propanolyses of TAGB, data from the product

analysis curves in.Fig. 18, and Equation (37). The derivation of Equation (37)

and a sample calculation are shown in Appendix VI.

[TAGB] = (1000 at/% - Hof(ci))/([H]MH - f(ci) ) (37)

where

( i) n '([O] - (1-n')([ ]M ).

at = the optical rotation of the solvolysis system at time, t

£ = the length of the polarimeter tube employed, dm.

H = the initial concentration of TAGB, mole/liter

n' = the fraction of a-anomeric glucoside at time t, determined from Fig. 18

ME = molecular weight of TAGB

M = molecular weight of a-anomeric glucoside

M = molecular weight of 3-anomeric glucoside

[aH] = the specific rotation of TAGB, determined by extrapolating - the solvolysis polarimetric data to zero time

[; ] = the specific rotation of the a-anomeric glucoside for the solvolysis conditions

[c ] = the specific rotation of the 3-anomeric glucoside for the solvolysis conditions

As demonstrated in Fig. 21 and 22, the theoretical model correlates with the experimental data for the iso-propanolysis of TAGB at 30 and 40°C. when

F [Equation (36)] is equal to 150. Calculations from the rate constants for the iso-propanolysis of TAGB with 0.100M lithium perchlorate and lithium bromide predict F to be about 110. However, the product analysis curve for the -97-

z

-99- iso-propanolysis of TAGB with 0.100M lithium perchlorate (Fig. 23) shows that the effectiveness of bromide exchange is decreased in the presence of salts.

The deviation of the experimental data from the theoretical model apparent in Fig. 21 and 22 at larger per cent reactions could be caused by electrophilic catalysis of the reaction by hydrogen bromide (26). Also, a salt effect, due to accumulation of hydrogen bromide in the system, could decrease the effectiveness of the bromide exchange which causes the formation of the a-anomeric glucoside.

SALT EFFECTS

It was shown previously that lithium perchlorate increases the rate of iso- propanolysis of TAGB. The interpretation of the product analysis data for the reaction (Fig. 23), i.e., extrapolation to a finite initial amount of a-anomeric glucoside being formed, indicates that the presence of the salt causes incursion of SN1 reaction characteristics.

ETHANOLYSIS, n-PROPANOLYSIS, AND n-BUTANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

THERMODYNAMIC FUNCTIONS OF ACTIVATION AND PRODUCT STEREOCHEMISTRY

The thermodynamic functions of activation for the primary-alcoholyses of

TAGB, listed in Table XXXI, do not vary significantly and therefore indicate that the reactions are mechanistically similar.

The data for the anomeric composition of the glucosidic products as a

function of time also indicate that the ethanolysis, n-propanolysis, and n- butanolysis of TAGB are similar to the methanolysis reaction. As stated earlier,

the anomeric compositions of the glucosidic products formed in the primary-

alcoholyses of TAGB were adjudged to be time-independent in the time interval

-101- studied (Tables XIII, XIV, XV, and XVI). This is somewhat surprising as the addi- tion of bromide ions (lithium bromide) to the reaction systems caused the fraction,

of a-anomeric glucoside to increase (see Tables XIII, XIV, XV, and XVI; Fig. 24,

25, and 26). The anomeric compositions of the glucosidic products would there- fore be expected to change as a function of time because of the bromide ion (hydro- gen bromide) accumulating in the reaction systems. Because the product analysis did not show a change in the anomeric composition of the glucosides, it must be assumed that either the magnitude of the change is within the error of analysis,

or that hydrogen bromide is not as effective as lithium bromide in causing product

racemization.

Although the anomeric composition of the glucosidic products was time-

independent for each of the primary-alcoholyses of TAGB, the fraction of the a- anomeric glucoside formed was a function of the alcoholic system, being zero for the methanolysis and about 0.11 for the n-butanolysis (Table XXXV).

SN1 REACTION MECHANISM

There is good evidence that the ethanolysis, n-propanolysis, and n-butan-

olysis of TAGB occur by the same reaction mechanism as the methanolysis, SN1.

As stated previously, the stereospecificity of product formation and the absence

of a mass-law effect for the SN1 methanolysis of TAGB are indicative of the re- action occurring at no large separation of the carbonium and bromide ions, probably as an ion-pair. In ethanol, n-propanol, and n-butanol, the tendency for the carbonium ion and the bromide ion to exist as an ion-pair should be even greater. A probable explanation for the fraction of a-glucoside formed increasing as an apparent function of alcohol size is steric hindrance encountered by the attacking alcohol. This would allow additional time for dissociation of the ion- pair and subsequent formation of the a-anomeric glucoside by reaction of the -102- -103-

-105-

alcohol on the side of the sugar ring vacated by the bromide ion. From consider-

ations of molecular models, the C5 acetoxymethyl group, aided by the ring oxygen

atom, should predominate in the steric interaction hindering the attacking alcohol.

Participation of the C3 O-acetyl group would not be expected to be very important.

TABLE XXV

PRODUCT COMPOSITION: PRIMARY-ALCOHOLYSES OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

Alcohol Temp., °C. a-Anomera, %

Methyl 25.0 0 30.0 0 35.0 0 40.0 0

Ethyl 25.0 4 30.0 4 35.0 5 .40.0 5

n-Propyl 25.0 7 30.0 7 35.0 7 40.0 7

n-Butyl 25.0 10 50.0 11 35.0 11 40.0 11

aPer cent of total a- and P-anomer.

The magnitude of this steric interaction is not as great as that of the axial C2 O-acetyl group in 2,3,4,6-tetra-0-acetyl-a-D-mannopyranosyl bromide or

6 as that of the axial C2 O-methyl group in 2,3,4, -tetra-0-methyl-cx-D-mannopyrano- syl chloride which prevent thiophenoxide ion from reacting by an SN2 mechanism with these compounds (31, 33). The substituted a-D-glucosyl halides can react more easily by an SN2 mechanism. This is demonstrated by the iso-propanolysis of TAGB and studies of reactions with thiophenoxide ions (31, 33) and amines (14).

6 However, even the primary steric effect of the C2 O-acetyl group in 2,3,4, -tetra- -106-

0-acetyl-a-D-mannosyl bromide does not completely eliminate an SN2 process.

This is demonstrated by the incursion of some bimolecularity in its reaction with strongly nucleophilic amines in acetone (14).

The preceding discussion on the steric effects of the C2 0-acetyl group

in tetra-O-acetyl-a-D-mannosyl bromide suggests that the C- 0-acetyl group in

TAGB could possibly hinder the formation of the a-anomeric glucoside. However,

in the preferred C1 conformation the glucose C2 0-acetyl group is equatorially disposed as opposed to the axial disposition of the C2 0-acetyl group in the acetylated mannosyl bromide.

Thus, the glucose C2 0-acetyl group is displaced somewhat from the reaction path on the "a-side" of the ring, more so than C2 0-acetyl group for a reaction on the

"P-side" of the ring in the acetylated mannosyl bromide. Secondly, the contributir steric effect of the C 5 acetoxymethyl group in substitutions on the acetylated mannosyl bromide is probably underestimated. As the sugar molecule assumes the half-chair transition state, the C 5 acetoxymethyl group is shifted slightly toward an axial disposition which would favor more participation in the steric effect on the "P-side" of the ring. The C5 acetoxymethyl group would not be expected to -107-

hinder reaction on the "a-side" of the glucosyl bromide. The correctness of this

hypothesis could possibly be shown by the ability or inability of a compound like

2,3,4,6 -tetra-O-methyl-P-D-glucopyranosyl chloride to react by an SN2 process with

thiophenoxide ion in a poor solvent. To the author's knowledge, no study of this

type of reaction system has been made.

SALT EFFECTS

In contrast to the iso-propanolysis of TAGB (Fig. 23), lithium perchlorate

did not affect the fraction of a-glucoside formed in the primary-alcoholyses

(Table XXXVI; Fig. 24, 25, and 26). It might be expected that addition of lith-

ium perchlorate to the reaction systems would, in addition to facilitating ion

formation, facilitate the dissociation of the ion-pair and thereby increase the

fraction of a-glucoside formed. This effect, for 0.100M lithium perchlorate, if present, must be within the experimental error of the analysis.

TABLE XXXVI

EFFECT OF LITHIUM-PERCHLORATE ON'PRODUCT COMPOSITION

% a-Anomer , Alcoholysis Temp., °C. No Salt Salt

Methanol 25.0 0 0 40.0 0 0

Ethanol 40.0 5 5

n-Propanol 40.0 7 7

n-Butanol 40.0 11 10

Per cent of total a- and P-anomer. 0.100M lithium perchlorate. TEMPERATURE EFFECT

Higher temperatures would also be expected to facilitate the ion-pair dis- sociation and, assuming the steric factor remains essentially the same, thereby

increase the formation of the a-glucoside. However, the data in Table XXXV do not show significant changes in the fractions of a-glucoside formed for the primary-alcoholyses of TApB from 25 to 40°C. The temperature effect could be very small. This study has shown that an alcohol will react with TAGB in the injection chamber of a gas chromatograph. The fraction of a-glucoside produced by reaction in this manner is considerably greater than that obtained at 25.to 40CC. Using an injector temperature of 225°C., the fraction of a-anomeric glucoside was greater than 20% for a methanolysis reaction and greater than 40% for an ethan- olysis reaction. However, the results are not necessarily conclusive as the possibility of a vapor-phase reaction exists.

INCURSION OF BIMOLECULARITY

The question of incursion of bimoleculari ty, in the primary-alcoholyses of

TAGB as the polarity of the alcohol decreases was considered. As stated prev- iously, the entropies and energies of activation do not indicate this (Table

XXI). The slight increase in the activation energy for the series methanol, ethanol, and n-propanol appears to be consistent with known ionization reactions

(75, P. 138). The slight decrease in the activation energy for the n-butanolyses compared to the n-propanolyses might be indicative of a degree of bimolecularity.

This cannot be definite because of the uncertainty, of the significance of a small variation in an experimental thermodynamic function of activation. The entropies of activation for the primary-alcoholyses of TAGB show a random scatter around approximately -17 e.u. rather than a variation indicative of a change in reaction mechanism. -109-

The only data which do tend to indicate incursion of bimolecularity are the increasing participations of bromide ions as the alcohol polarity decreased (Table

XXXIV; Fig. 24, 25, and 26). On the basis of the proposed steric interaction for the primary-alcoholyses of TAGB, the increase in bromide participation can be partially accounted for by the lesser steric resistance encountered by the smaller halide ion (relative to the alcohol molecule). This allows the smaller bromide ion to compete more effectively with the larger alcohol molecule for the carbon- ium ion. However, the nucleophilicity of the halide ion is also important in the reaction. Iodide ions, which are slightly larger and more nucleophilic than bromide ions*, increased the rate of reaction and the fraction of a-glucoside formed more than bromide ions in the methanolysis of TAGB at 25°C.

ALCOHOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE IN THE PRESENCE OF BROMIDE SALTS

The addition of lithium bromide to the alcoholysis reaction results in an increase in the rate of reaction and an increase in the fraction of a-glucoside produced. This increased fraction of a-glucoside is time-dependent except for the methanolysis reaction. For the methanolysis of TAGB, O.1OOM lithium bromide increased the fraction of a-anomeric glucoside produced from zero (no lithium bromide) to six per cent, the latter appearing to be time-independent. However, in the other alcoholyses of TAGB bromide salts cause an increased degree of C1 - racemization which is time-dependent (Fig. 23-26).

It is expected that the first step in the reaction sequence producing the observed results is the reaction of TAGB with a bromide ion to yield the D-anomeric bromide (3-TAGB). This is known to happen with bromide ions in acetonitrile (70)

*The difference in ionic radii is not extremely large. The relative polariza- bilities of the electron clouds might result in iodide ions having smaller effective radii in nucleophilic substitutions. If this is true, the argument for the importance of nucleophilicity is weakened but not contradicted. -110- and indirect evidence of this is shown by the formation of 3,4,6-tri-0-acetyl-

1,2-(iso-propyl orthoacetate)-C-D-glucopyranose in the reaction of TAGB with

iso-propanol and lutidine or collidine (8). With an acid acceptor in the system, this type of halide, in which the halogen atom and the C2 O-acetyl group exist in a trans relationship, is known to form 1,2-(alkyl orthoacetate) derivatives

(X) with alcohols (11-13). However, the methanolysis of the chloride analog without an acid acceptor results in methyl 2,3,4,6-tetra-0-acetyl-a-D-glucoside

(27).

O-C-OR

X CH3

No acid acceptors were used in the alcoholyses of TAGB in the present study.

Therefore the reaction of B-TAGB, formed by bromide exchange, should result in glucosidic products. However, the possibility of the time-dependent increase in the fraction of a-glucoside formed being accounted for by an increase in the bromide ion (hydrogen bromide) concentration during the reaction can be eliminated

This is evident from the following reasoning.

With no initial bromide salt in the reaction system, the ethanolysis of

TAGB at 40°C. yielded glucosidic products containing 5% of the a-anomer. With

0.lOOM lithium bromide added to the reaction (0.0244M TAGB), extrapolation of the product analysis data (Fig. 24) indicated that initially (zero time), 15% of -111- the glucosidic product was the a-anomer; at 2.73 hours reaction the amount of a- anomer had increased to 28% of the glucosidic products (see Fig. 24). This time- dependent increase of a-anomer is larger than that caused initially by the lithium bromide. The maximum bromide ion (hydrogen bromide) concentration which could have been produced by the reaction was only one-fourth of the initial lithium bromide concentration. It seems implausible that the smaller concentration of hydrogen bromide could have caused a larger increase in the fraction of a-gluco- side formed than did the lithium bromide.

Hydrogen chloride is less dissociated than lithium chloride in acetone (76).

If an analogous relationship exists for hydrogen bromide and lithium bromide in ethanol, more credence is given to the above conclusion.

Similar reasoning can be extended to the n-propanolysis of TAGB (0.0176M) in the presence of 0.100M lithium bromide (Fig. 25).

The n-butanolysis and iso-propanolysis of TAGB in the presence of lithium bromide do not exhibit as drastic time-dependencies for the fraction of a-gluco- side formed (Fig. 23 and 26) and similar reasoning would not be as conclusive.

In view of the known ability of P-TAGB to form 1,2-(alkyl orthoacetates) in the presence of alcohols (70) the results might feasibly be explained by postu- lating the formation of an 1,2-(alkyl orthoacetate) as a reaction intermediate.

The 1,2-(alkyl orthoacetates) are known to be acid labile and the acid-catalyzed alcoholyses have been reported to yield a variety of products (70, 77, 78).

Pacsu (77) proposed a mechanism for the acid-catalyzed alcoholyses of 1,2-(alkyl orthoacetates) which is similar to the acid hydrolysis (77). The proposed product was a partially acetylated sugar with free hydroxyl groups at Cl and C2 . This mechanism obviously cannot account for the results obtained in the present study. -112-

Kochetkov, et al.. (78) reported that 3,4,6-tri-O-acetyl-l,2-(methyl ortho-

acetate)-a-D-glucopyranose or the ethyl analog yield (less than 50% total) the

cholesteryl orthoacetate and the acetylated P-cholesteryl glucoside when boiled

in nitromethane with cholesterol, mercuric bromide, and p-toluenesulfonic acid.

Increasing the amount of mercuric bromide increased the yield of the acetylated

5-cholesteryl glucoside.

Lemieux (70) has shown that with p-toluenesulfonic acid in methylene

chloride, tri-O-acetyl-L,2-(alkyl orthoacetate)-Q-D-glucopyranoses and the

corresponding alkyl alcohol yield the alkyl 3,4,6 -tri-O-acetyl-a-D-glucopyrano-

sides in 60-70% yield. Deacetylation at C would have passed unnoticed in the present study because of the deacetylation and reacetylation involved in the

analysis of the glucosidic anomers.

The studies of Lemieux (70) and Kochetkov, et al. (78) are surprising in that formation of different anomeric alkyl glucopyranosides were reported but neither investigator(s) mentioned evidence for both anomers being present in their respective systems. Neither author(s) has published formally on the mechanism for the acid-catalyzed alcoholyses of 1,2-(alkyl orthoacetates) at the present date. The possibility of the formation of both anomeric alkyl glucopyranosides appears to exist.

The only requirement necessary to explain the results obtained with lithium bromide in the present study is that the 1,2-(alkyl orthoester) intermediate, if present, yieldsthe a-anomer; for the ethanolysis, n-propanolysis, n-butanol- ysis, and iso-propanolysis the ratio a- to P-anomeric glucoside formed must be greater than the fraction of a-anomer formed initially (Fig. 23-26). -Part of the a-anomeric glucoside can be formed by direct reaction of the alcohol with -113. the P-TAGB as shown by the alcoholysis of other acetylated glycosyl halides in which the halogen and C2 0-acetyl group are trans (13).

For the methanolysis of TAGB with lithium bromide the 1,2-(methyl ortho- acetate), if formed, must react further to form the acetylated methyl glucoside(s) rapidly. However, Mattok and Phillips (27) have reported that the methanolysis of 2,3,4,6-tetra-O-acetyl-P-D-glucopyranosyl chloride yields the acetylated methyl-a-D-glucoside. Thus, by analogy, if P-TAGB is formed in the methanolysis of TAGB with lithium bromide, the resultant product should be the acetylated methyl-a-D-glucoside.

The postulation of 1,2-(alkyl orthoacetate) intermediates is speculative.

However, for the alcoholyses of TAGB with lithium bromide the following facts are consistent with the postulate. First, TAGB will react with bromide ion to form P-TAGB which is potentially capable of forming a 1,2-(alkyl orthoacetate) in alcohol. Second, the alcoholysis systems do generate acid and the 1,2-(alkyl orthoacetates) are known to be acid labile and will yield alkyl glycosides when subjected to an acid-catalyzed alcoholysis. Partial deacetylation which may occur would have been masked in the present study because of the acetylation procedure employed in the product analysis. Third, P-TAGB should be capable of reacting directly with the alcohol to yield the acetylated alkyl a-D-glucoside.

This could be important in explaining the initial fraction of a-glucoside evident

in Fig. 23-26.

One consequence of an intermediate being formed in the alcoholysis of TAGB with lithium bromide is that the rate constants, calculated on the basis of only

the anomeric alkyl glucosides being formed, will be in error. The magnitude of

the error will depend on the concentration and specific rotation of the inter- mediate and is difficult to estimate. However, if a tri-O-acetyl-l,2-(alkyl orthoacetate)-a-D-glucopyranose is the intermediate, the true rate constants

would be greater than those obtained because the extent of reaction per degree

of optical rotation decrease would be greater than that assumed in the calcula-

tion.

This consideration would not apply to the methanolysis reaction as the inter- mediate, if present, appears to react very rapidly as demonstrated by the time-

independence of the fraction of a-glucoside formed.

Deacetylation during the formation of the alkyl c-glucoside from the ortho- ester as reported by Lemieux (70) would also affect the polarimetric rate constant. -115-

CONCLUSIONS

The methanolysis, ethanolysis, n-propanolysis, and n-butanolysis of 2,3,4, 6 - tetra-O-acetyl-a-D-glucopyranosyl bromide (TAGB) occur by an SN1 reaction mechan- ism. The carbonium ion and the alcohol molecule normally react while the carbonium ion is closely associated with the departing bromide ion, probably as an ion-pair.

Due to the shielding of the bromide ion, the reaction occurs on the 5-side of the sugar molecule and yields the acetylated alkyl P-D-glucoside as the main product.

When the alcohol molecule is large enough it encounters steric resistance to re- action on the P-side of the sugar molecule. This allows additional time for separation of the bromide and carbonium ions. The acetylated alkyl a-D-glucoside is subsequently formed by reaction of the alcohol on the side of the sugar mole- cule vacated by the bromide ion. Thus, the fraction of a-glucoside formed is a function of the size of the alcohol molecule. The steric hindrance encountered by the attacking alcohol is believed to be due mainly. to the C5 acetoxymethyl group and the ring oxygen atom in TAGB.

The iso-propanolysis and cyclohexanolysis of TAGB occur by an SN2 reaction mechanism. The product of this reaction is the acetylated alkyl P-D-glucoside.

The acetylated alkyl a-D-glucoside in the products is the result of the reaction of TAGB with liberated bromide ion to form 2,3,4,6-tetra-O-acetyl-P-D-glucosyl bromide (P-TAGB). The P-TAGB subsequently forms the acetylated alkyl a-D-gluco- side. -116-

LITERATURE CITED

1. Evans, W. L., Reynolds, D. D., and Talley,,E. A., Adv. Carbohydrate Chem. 6:27(1951).

2. Haynes,. L. J., and Newth, F. H., Adv. Carbohydrate Chem. 10:207(1955).

3. Conchie, J.,.Levvy,.G. A., and Marsh, C. A., Adv. Carbohydrate Chem. 12:157 (1957).

4. .Pigman, W., ed. The carbohydrates. New York, Academic Press,. Inc., 1957. 902 p.

5. Haq, S., and Whelan, W. J., J.. Chem. Soc. 1956:4543.

6. Whistler, R. L., and Wolfrom,. M.. L., ed. . Methods in carbohydrate chemistry. Vol..I and II. New York, Academic Press, Inc., 1963.

7. Koenigs, W., and Knorr,. E., Ber. 34:957(1901).

8. Helferich, B., Doppstadt, A., and Gottschlich, A.,. Naturwissenschaften 40:441(1953); C.A. 49:3026e.

9. Goldschmid, H. R., and Perlin, A. S.,.Can. J. Chem. 39:2025(1961).

10. Evans, D., and Reynolds, W.,.J. Am. Chem. Soc. 60:2559(1938).

11. Frush, H. L., and Isbell, H. S., J. Res. Natl. Bur. Std. 27:413(1941).

12. Frush, H. L., and Isbell, H. S.,.J. Res. Natl. Bur. Std. 35:111(1945).

13. Frush, H. L., and Isbell, H. S., J. Res. Natl. Bur. Std. 43:161(1949).

14. Chapman, N. B., and.Laird, W. E., Chem. and Ind. 1954:20.

15. Hughes, E. D.,,Ingold, C. K., and Gleave,. J.. L.,. J. Chem. Soc. 1935:236, 244.

16. Hughes,. E. D.,..Ingold, C.. K., and Shapiro, V. G., J. Chem. Soc. 1936:225.

17. Hughes,. E. D., Trans. Faraday Soc. 34:185(1938).

18. Hughes, E. D., Trans. Faraday Soc.. 37:603(1941).

19. Streitwieser, A., Jr. Solvolytic displacement reactions. .New York, .McGraw-Hill Book Co.,. Inc., 1962. 214 p.

20. Hine, J. .Physical organic chemistry. 2nd ed. New York,.McGraw4Hill Book Co., Inc., 1962. 552 p.

21. Gould, E. S.. Mechanism and structure in organic chemistry. New York, Holt, Rinehart, and Winston, Inc., 1959. 790 p.

22. Gelles,. E., Hughes,, E. D., and Ingold, C. K.,. J. Chem. Soc. 1954:2918. -117-

23. Newth, F. H., and Phillips, G. 0., J. Chem. Soc. 1953:2896.

24. Newth, F. H., and Phillips, G. 0., J. Chem. Soc. 1953:2900.

25. Newth, F. H., and Phillips, G. 0.,.J. Chem. Soc. 1953:2904.

26. .Mattok, G. L., and Phillips, G. 0., J. Chem. Soc. 1956:1836.

27. Mattok, G. L., and Phillips, G. 0.,.J. Chem. Soc. 1957:268.

28. Mattok, G. L., and Phillips, G. 0., J. Chem. Soc. 1958:130.

29. Mattok, G..L., and Phillips, G. 0., J..Chem. Soc. 1959:2244.

30. Wadsworth, W. W. Doctoral Dissertation. Appleton, Wis., The Institute of Paper Chemistry, 1961.

31. Capon, B., Collins, P. M.,.Levy, A. A., and Overend, W. G., J. Chem. Soc. 1964:3242.

32. Lemieux, R. V., and Huber, G., Can. J. Chem. 33:128(1955).

33. Rhind-Tutt, A. J., and Vernon, C. A., J. Chem. Soc. 1960:4637.

34. Jeanloz, R., Fletcher,.H. G., Jr., and Hudson, C. S., J. Am. Chem. Soc. 70:4055(1948).

35. Ness, R. K., Fletcher, H. G., Jr., and Hudson, C. S., J. Am. Chem. Soc. 72:2200(1950).

36. Fletcher, H. G., Jr., and Hudson, C. S., J. Am. Chem. Soc. 72:4173(1950).

37. Ness, R. K., Fletcher, H. G., Jr., and Hudson, C. S., J. Am. Chem. Soc. 73:296(1951).

38. Ness, R.. K., Fletcher, H. G., Jr., and Hudson, C. S., J. Am. Chem. Soc. 73:959(1951).

39. Capon, B., Chem. and Ind. 1960:689.

40. Schroeder, L. R. Unpublished work, The Institute of Paper Chemistry.

41. Fischer, E., and Fischer, H., Ber. 43:2534(1910).

42. Bates, F. J. Polarimetry, saccharimetry, and the sugars. p. 500. Washington, D. C., United States Government Printing Office, 1942.

43. Lindberg, B., Acta Chem. Scand. 3:151(1949).

44. Kreider, L. C., and Friesen, E., J. Am. Chem. Soc. 64:1482(1942).

45. Pacsu, E., Ber. 61:1508(1928).

46. Pacsu, E., J. Am. Chem. Soc. 52:2568(1930). -ll8-

47. Ferguson, J. H., J. Am. Chem. Soc. 54:4086(1932).

48. Bourne, E. J., Stacey,.M., Tatlow,.J. C., and Worrall, R., J. Chem.. Soc. 1954:2006.

49. Helferich, B., and Mital, H. C., Chem. Ber. 93:1010(1960).

50. Evans, D., and Reynolds, W., J. Am. Chem. Soc. 58:797, 1661(1936).

51. Herold, W., and Wolf, K. L., A. Physik. Chem. 12B:194(1931).

52. Capon, B., Overend, W. G., and Sobell,. M., J. Chem. Soc. 1961:5172.

53. Noller, C. R., and Rockwell, W. C., J. Am. Chem. Soc. 60:2076(1938).

54. Trevelyan, W. E., Procter, D. P., and Harrison, J. S., Nature 166:444(1950).

55. Jones, H. G., and Perry,.M. B., Can. J. Chem. 40:1339(1962).

56. Pecsok, R.. L., ed. Principles and practice of gas chromatography. p. 142-50. New York, John Wiley and Sons, Inc., 1959.

57. Bishop, C. T., Cooper, F. P., and Murray, R. K., Can. J. Chem. 41:2245 (1963).

58. Harfenist,. M., and Baltzly, R., J. Am. Chem. Soc. 69:362(1947).

59. Farkas,. L., Schacter, 0., and Vromen, B. H., J. Am. Chem. Soc. 71:1991 (1949).

60. Juvet, R. S., Jr., and Wachi, F. M., J. Am. Chem. Soc. 81:6110(1959).

61. Oldham, J. W. H., J. Chem. Soc. 127:2840(1925).

62. Helferich, B., and Klein, W., Ann. 450:219(1926).

63. Hudson, C. S., and Dale, J. K.,.J. Am. Chem. Soc. 37:1264(1915).

64. Lardy, H. A., J. Am. Chem. Soc. 69:518(1947).

65. Wiberg, K. B. Physical organic chemistry. New York, John Wiley and Sons, Inc., 1964. 591 P.

66. Glasstone, S., Laidler, K. J., and Eyring,-H. The theory of rate processes. New York, McGraw-Hill Book Company,. Inc., 1941. 611 p.

67.. Grunwald, E., and Winstein, S., J. Am. Chem. Soc. 70:846(1948).

68. Winstein, S., Grunwald,,E., and Jones, H. W., J.. Am. Chem. Soc. 73:2700 (1951).

69. Swain, C. G.,.Mosely, R. B., and Brown, D. E., J. Am. Chem. Soc. 77:3731 (1955). -119-

70. Lemieux, R. V. In Abstracts of Papers Presented at the 148th Meeting of the American Chemical Society, Chicago, Illinois, Aug. 31-Sept. 3, 1964. p. 16E.

71. Brown,.D. A., and Hudson, R. F., J. Chem. Soc. 1953:3352.

72. Schaleger, L. L., and Long, F. A., Adv. Phys. Org. Chem. 1:1(1963).

73. Long, F. A., Pritchard, J. G., and Stafford,. F. E., J. Am. Chem. Soc. 79:2362(1957).

74. Robertson, R. E., Heppolette, R. L., and Scott, J. M. W., Can. J. Chem. 37:803(1959).

75. Frost, A. A., and Pearson, R. G. Kinetics and mechanism. 2nd ed. New York, John Wiley and Sons, Inc., 1961. 405 p.

76. Golomb, D., J. Chem. Soc. 1959:1327.

77. Pacsu, E., Adv. Carbohydrate Chem. 1:77(1945).

78. Kochetkov, N.. K., Khorlin, A. J., and Bochkov, A. F., Tetrahedron Letters 1964:289.

79. Weygand, F., Zieman, H., and Bestman, H. J., Chem. Ber. 91:2534(1958). -120-

ACKNOWLEDGMENTS

The author gratefully acknowledges the assistance, constructive criticisms, and encouragement of the thesis advisory committee: Drs. J. W. Green,.D..C.

Johnson, and D. G. Williams.

The author is deeply indebted to Dr. Green for handling the "day shift" on long kinetic experiments.

The author is grateful to the Analytical Department for the extensive use of their gas-chromatographic facilities and wishes to thank Dr. Johnson and

Mr. C. V. Piper for their advice and assistance in the gas-chromatographic endeavors.

Above all, the author is indebted to his wife for her inexhaustible encour- agement and her help in preparing the necessary manuscripts during this work.

To others, who have helped in some way, the author expresses his apprecia- tion. -121-

APPENDIX I

DERIVATION OF THE EQUATION RELATING THE SPECIFIC RATE CONSTANT TO THE OPTICAL ROTATION OF THE SYSTEM

In a system of two reactants, one of which is in great excess and the con- centration of which therefore remains essentially constant during the reaction or one whose activation is the rate-controlling process (unimolecular reaction),

it can be demonstrated that the rate equation may be expressed as follows:

-dH/dt = kH (38) where

H = the concentration of the variant or rate-controlling component at time t

k = the specific rate constant

The equation yields, with integration

in H/H = -kt (39) where H = the concentration of H at time t = 0. -o - -

The system in question is

H +A = G + P where

H = a glycosyl halide

A = an alcohol used as the solvent

G = the resultant glycoside

P = the resultant halogen acid

Making the assumption that the optical rotations of the individual compon- ents of the system are independent of each other, the following equation may be -122- written:

at= (40) where

at = the observed optical rotation of the system at time t

a. = the optical rotation due to the i component at time t

If the alcoholysis reaction utilizes an optically inactive alcohol and the possibility of the formation of an anomeric pair of glycosides is considered,

Equation (40) may be written as follows:

where

aH = the optical rotation due to the glycosyl halide

a = the optical rotation due to the a-anomeric glycoside

ab = the optical rotation due to the P-anomeric glycoside

It can also be demonstrated that

i = CiA[mi] (42) where

£ = the solution path length of the plane polarized light, dm.

C. = the concentration of the i component, mole/l.

[m.] = molar rotation of the it h component, defined as (degree)(liter)/ - (dm.)(mole)

If G is defined as the total glycoside concentration, the concentrations of the anomeric glycosides may be related to G by Equations (43) and (44).

Gb = nG (43) and G = (l-n)G (44) -123- where

Gb = the concentration of the P-anomeric glycoside

G = the concentration of the a-anomeric glycoside -a n = the fraction of the total glycoside concentration which is P-anomer

Substitution of Equations (42), (43), and (44) into Equation (41) results

in:

(45) where

[mb ] = the molar rotation of the P-anomeric glycoside

[m ] = the molar rotation of the a-anomeric glycoside -a

Differentiating Equation (42) with respect to time results in:

dai/dt = a[mi]dCi/dt (46).

With respect to the glycosyl halide Equations (42) and (46) are:

H = He[mH] (47) and

daH/dt = £[mH]dH/dt (48).

Substituting Equations (47) and (48) into Equation (38) yields:

-daH/dt = kca (49)

From stoichiometry

G= H - H o (50).

From Equation (39)

H = H exp[-kt] (51) -124- thus

G = H - H exp[-kt] (52).

Let

[m ] = a (53) a

[m3b] = b (54).

Substitution of Equations (52), (53), and (54) into Equation (45) yields:

H = at + aHo(exp[-kt]-l) + (b-a)Hon(exp[-kt]-l) (55)

daH/dt = dot/dt - aH k exp[-kt]-(b-a)H nk exp[-kt]

+ (b-a)Ho(exp[-kt]-l)dn/dt (56).

Substitution of Equations (55) and (56) into Equation (49) results in the differential equation relating at to k:

dadt/dt + kat = aok(l-n) + bH kn

-(b-a)H (exp[-kt]-l)dn/dt (57).

To solve Equation (57) the function relating n to t must be known. Two special cases which can- be solved without excessive difficulty are:

Case I; n = a constant

Case II; n = mt + i (linear relationship)

Case I; n = a constant

For this case Equation (57) reduced to:

dat/dt + kat = aHok(l-n) + bH kn t' t 0 0 (58). -125-

Integration of Equation (58) using the defining limit that c = c when t = 0 t o yields:

ln(ct - M) = -kt + ln(o 0 - M) (59) where M = i[m]H (1-n) + _[mb]Hn.

M can be related to the specific optical rotation of the anomeric products by substituting

[m i ] = [ai ] Mi /1 0 O0 where

[a.] = the specific rotation of anomer i for the reaction system

M. =the gram-molecular weight of i

Case II; n = mt + i (linear relationship)

n = mt + i (60)

dn/dt = m (61)

Substituting Equations (60) and (61) into Equation (57) and integrating the resulting equation using the defining limit that at = a when t = 0 yields

n [t-f(t)]/[o-f(t)]} = -kt (62) where f(t) = i[m ]H_(l-i-mt) + 1[mb]H0(i + mt).

General Case; n = q(t)

It would appear from the preceding that when n is defined as any function of t, q(t), that integration of Equation (57) will yield:

In f[t-f(t)]/[co-f(t)]} = -kt (63) where f(t) = _[ma]H (l-q(t)+e[Imb]H (q(t)). -126-

APPENDIX II

SPECIFIC ROTATIONS OF ACETYLATED ALKYL.D-GLUCOPYRANOSIDES

This appendix contains the data for the specific rotations of the acetylated alkyl' D-glucopyranosides in the aglyconic alcohol as a function of temperature using mercury (5461 A. ) plane-polarized light.

Corrections have, been made for concentration changes due to thermal expansion of the solvent.

TABLE XXXVII

TEMPERATURE DEPENDENCE OF THE SPECIFIC ROTATION (5461 A.) OF THE METHYL 2,3,4,6-TETRA-O-ACETYL-D-GLUCOPYRANO- SIDES iIN METHANOL

Anomrler Temp., °C. [] 54 61 Concn., g.,/100 ml.

P 25.0 -- 2.106t3 40 2 -22.3 -- 35.0 -22.6 30.1 -22.9 25.4 -23.3 20.6 -23.6 25.0 -- 1.759( 40.2 -22.3 -- 29.9 -23.2 20.7 -23.7 --

25.0 -- 0.497( 40.9 158 -- 32.5 157 -- 26.1 157 -- 20.0 157 -- 40.5 158 -- 25.0 -- 0.453 40.8 157 --

Equations

P-Anomer; [a] = -25.1 + 0.0696t

ca-Anomer; [a] = 156 + O.0366t -127-

TABLE XXXVIII

TEMPERATURE DEPENDENCE OF THE SPECIFIC ROTATION (5461 A.) OF THE ETHYL 2,3,4,6-TETRA-O-ACETYL-D- GLUCOPYRANOSIDES IN ETHANOL

Anomer Temp., °C. Concn., g./100 ml. [] 5461 25.0 1.9956 40.2 -27.8 35.0 -28.6 30.1 -29.2 25.4 -29.8 20.6 -30.4 25.0 1.8632 40.2 -28.1 29.9 -29.7 20.7 -30.7

25.0 1.0564 40.0 163 32.7 164 25.9 164 19.0 165 39.9 163 25.0 1.0252 30.2 164

Equations

P-Anomer; [a] = -33.3 + 0.132t

a-Anomer; [a] = 167 - 0.0889t -128-

TABLE XXXIX

TEMPERATURE DEPENDENCE OF THE SPECIFIC ROTATION (5461 A.) OF THE n-PROPYL 2,3,4,6-TETRA-O-ACETYL-D- GLUCOPYRANOSIDES IN n-PROPANOL

Anomer Temp., °C. Concn. g./100 ml. []5461 25.0 1.0114 39.9 -31.6 52.2 -32.4 26.0 -32.7 20.1 -33.5 25.0 0.7948 40.9 -31.3

a6 25.0 0.9868 40.0 168 32.7 168 25.9 169 19.0 170 39.9 168 25.0 1.0220 30.2 168

Equations

P-Anomer; [a] = -35.4 + 0.0974t

a-Anomer; [a] = 171 - 0.0899t -129-

TABLE XL

TEMPERATURE DEPENDENCE OF THE SPECIFIC ROTATION (5461 A.) OF THE n-BUTYL 2,3,4,6-TETRA-O-ACETYL-D- GLUCOPYRANOSIDES IN n-BUTANOL

Anomer Temp., 0C. Concn., g./100 ml.

30.0 1.1048 43.0 -32.1 37.2 -32.8 31.6 -33.1 26.1 -33.4 19.3 -34.0 42.9 -32.1 30.0 1.0228 31.8 -33.3 a ax 40.0 1.0284 39.8 163

Equations

P-Anomer; [a] = -35.6 + 0.0786t

a-Anomer; [a] I 163

Determined from a mixture of anomers in which the P-anomer was estimated at 18.5% of the total acetylated glucosides by GC. GC also showed two additional minor impurities. The value determined is probably less than the true value. -130-

TABLE XLI

TEMPERATURE DEPENDENCE OF THE SPECIFIC ROTATION (5461 A.) OF THE iso-PROPYL 2,3,4,6-TETRA-O-ACETYL-D- GLUCOPYRANOSIDES IN iso-PROPANOL

Anomer Temp., °C. Concn. g./100 ml. a] 54 6 1 25.0 0.4116 40.1 -32.1 39.9 -32.1 32.2 -34.3 26.0 -35.3 20.0 -37.5

25.0 40.9 175 32.5 175 26.1 174 20.0 174 40.5 175 25.0 0.4592 40.8 175

Equations

P-Anomer; [a] = -42.5 + 0.259t

a-Anomer; [a] = 173 + 0.0527t

TABLE XLII

TEMPERATURE DEPENDENCE OF THE SPECIFIC ROTATION (5461 A.) OF THE CYCLOHEXYL 2,3,4,6-TETRA-O-ACETYL-D- GLUCOPYRANOSIDES IN CYCLOHEXANOL

Anomer Temp., °C. Concn. g./100 ml.

30.0 1.0792 43.0 -30.4 37.2 -31.7 31.6 -32.9 26.1 -33.7 30.0 0.9100 31.8 -33.0

40.0 1.7604 39.8 147

Equations

P-Anomer; [a] = -39.2 + 0.201t a-Anomer; Insufficient data. -131-

APPENDIX III

DEACETYLATION OF ACETYLATED ALKYL D-GLUCOPYRANOSIDES IN ALCOHOLIC HYDROGEN BROMIDE

TABLE XLIII

DEACETYLATION OF METHYL 2,3,4,6-TETRA-O-ACETYL-P-D- GLUCOPYRANOSIDE IN METHANOLIC HYDROGEN BROMIDE (0.00964N) AT 30.0°C.

Time, hr. Concn., mole/i. x 102

0.00 4.53 1.60 3.95 3.17 3.42 4.63 2.93 6.17 2.59 7.58 2.11 9.10 1.80 10.50 1.59

k' = 2.9 + 0.2 x 1010-5 sec.sec.-1

For 0.0100N HBr

k' = 3.0 + 0.2 x 10-5 sec. 1 -

TABLE XLIV

DEACETYLATION OF ETHYL 2,3,4,6-TETRA-O-ACETYL-P-D- GLUCOPYRANOSIDE IN ETHANOLIC HYDROGEN BROMIDE (0.0100N) AT 30.0°C.

Time, hr. Concn., mole/i. x 102

0.0 9.83 6.1 8.63 12.1 7.60 18.0 6.43 24.1 5.47 30.1 4.94 36.1 4.20 42.1 3.77 -1 k' = 6.5 + 0.4 x 106 sec. -132-

TABLE XLV

DEACETYLATION OF n-PROPYL 2,3,4,6-TETRA-O-ACETYL-P-D- GLUCOPYRANOSIDE IN n-PROPANOLIC HYDROGEN BROMIDE (0.01ON) AT 30.0°C.

Time, hr. Concn., mole/i. x 102

0.0 9.40 7.0 9.02 14.0 8.04 21.0 7.25 27.9 6.22 35.0 5.53 42.0 4.94 48.9 4.51

k' = ' 4.7= + 0.10. x 1010-6 sec. -1

TABLE XLVI

DEACETYLATION OF n-BUTYL 2,3,4,6-TETRA-O-ACETYL-P-D- GLUCOPYRANOSIDE IN n-BUTANOLIC HYDROGEN BROMIDE (O.O010N) AT 30.0°C.

Time, hr. Concn., mole/i. x 102

0.0 8.43 8.0 6.78 16.1 5.64 24.0 4.65 32.0 13.86 39.9 3.24 47.9 2.70 55.9 2.24 -1 k' = 6.4 + 0.1 x 10 6 sec.

TABLE XLVII

DEACETYLATION OF iso-PROPYL 2,3,4,6-TETRA-O-ACETYL-P-D- GLUCOPYRANOSIDE IN iso-PROPANOLIC HYDROGEN BROMIDE (0.0100N) AT 30.0°C.

Time, hr. Concn., mole/i. x 102

0.0 1.93 20.2 1.91 36.7 1.90 54.1 1.83 72.3 1.81 119.4 1.67 -1 k' = 3.9 + 1.0 x 10 7 sec. -133-

APPENDIX IV

POLARIMETRIC RATE DATA: ALCOHOLYSES OF 2,3,4,6- TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

This appendix contains the polarimetric rate data for the alcoholyses of

2,3,4, 6-tetra-O-acetyl-a-D-glucopyranosyl bromide used to calculate specific rate constants. The observed optical rotation of the reaction system is desig- nated as at. All the reactions were observed in a 2.0-dm. polarimeter tube using mercury green light (5461 A.).

SECTION I

METHANOLYSIS REACTIONS

TABLE XLVIII

METHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0245M7 AT 25. 0°C.

_, min. at t, min. at

4.0 4.67 54.5 4.13 7.7 4.58 60.8 4.07 11.8 4.56 70.8 3.95 14.9 4.54 81.0 3.86 20.8 4.48 90.7 3.75 25.6 4.42 101.2 3.63 28.8 4.39 111.4 3.55 33.9 4.33 120.9 3.44 37.8 4.30 142.8 3.25 41.9 4.27 161.1 3.04 45.8 4.23 190.8 2.76 -134-

TABLE XLIX

METHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0263M7 AT 25. 0C.

t, min. t, min. at

3.5 4.98 66.5 4.29 6.5 4.96 72.5 4.22 12.5 4.89 78.4 4.16 18.5 4.81 84.8 4.09 24.5 4.75 90.3 4.04 30.5 4.68 96.4 3.96 36.5 4.62 102.5 3.91 42.5 4.55 108.4 3.84 48.7 4.49 114.5 3.78 54.4 4.42 120.4 3.70 60.6 4.36

TABLE L

METHANOLYS IS OF 2,3,4,6-TETRA-0-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0254M7 AT 30.0°C.

t, min. at t, min.

2.3 4.82 50.4 3.91 6.4 4.73 55.6 3.84 10.5 4.65 60.4 3.75 15.3 4.54 65.4 3.68 20.4 4.45 70.4 3.58 25.5 4.38 75.4 3.50 30.3 4.29 80.4 3.40 25.3 4.20 85.3 3.32 40.4 4.10 90.4 3.24 45.4 4.01 -135-

TABLE LI

METHANOLYSIS OF 2,3,4,6-TETRA- -ACETYL-aC-D-GLUCOPYRANOSYL BROMIDE (0.0207M7 AT 30.0°C.

t, min. at t, min. 2.87 4.7 3.91 77.5 .2.87 9.5 3.85 86.7 2.74 14.5 3.78 92.7 2.65 20.6 3.69 98.5 2.58 28.7 3.58 108.7 2.45 24.7 3.48 113.9 -2.37 42.8 3.35 119.6 2.30 48.7 3.27 142.1 2.04 55.7 3.18 .155.5 1.88 62.4 3.08 187.6 1.54 66.6 3.02 223.5 1.22 71.9 2.95 247.7 1.03

TABLE LII

METHANOLYSIS OF 2,3,4,6-TETRA- O-ACETYL- - D-GLUCOPYRANOSYL BROMIDE (0.0204M7 AT 35.0°C.

t, min. at t, min. "tat

5.7 3.93 35.4 3.20 8.6 3.84 38.5 3.14 11.6 3.77 41.6 3.07 14.5 35.70 44.6 3.00 17.6 3.63 47.4 2.92 20.6 3.55 50.4 2.86 23.4 3.48 53.4 2.77 26.7 3.41 57.5 2.70 29.6 3.34 61.4 2.62 32.5 3.27 74.5 2.36 -136-

TABLE LIII

METHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0199M7 AT 40.0°C.

min. t, min. t" t, t"

4.5 3.55 26.4 2.75 6.5 3.49 28.4 2.69 8.4 3.42 30.4 2.62 10.4 3.36 32.4 2.54 12.6 3.27 34.3 2.48 14.3 3.21 36.4 2.42 16.4 3.12 38.5 2.35 18.4 35.05 40.4 2.29 20.4 2.97 42.4 2.21 22.4 2.90 44.4 2.14 24.4 2.83

TABLE LIV

METHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0255M7 AT 40.0°C.

t, min. at t, min.

2.4 4.78 18.2 3.97 4.3 4.67 19.2 3.92 6.3 4.56 20.4 3.87 8.3 4.46 22.3 3.77 10.3 4.36 24.3 3.68 11.2 4.30 26.3 3.57 12.3 4.25 28.3 3.49 13.3 4.20 30.4 3.40 14.3 4.15 32.4 3.31 16.2 4.07 34.3 3.22 -137-

TABLE LV

METHANOLYSIS (0.100M LiC10 4 ) OF 2,3,4,6-TETRA-O-ACETYL-a- D-GLUCOPYRANOSYL BROMIDE (0.0247M) AT 25.0°C.

t, min. t, min. a

3.2 41.4 4.23 5.3 4.61 44.4 4.20 8.5 4.59 47.3 4.16 11.5 4.56 54.5 4.10 14.3 4.53 57.4 4.06 17.3 4.50 60.4 4.03 20.4 4.47 63.4 4.00 23.4 4.44 68.6 3.93 26.5 4.41 73.4 3.88 29.5 4.37 78.7 3.83 32.5 4.33 83.8 3.77 35.4 4.30 88.5 3.72 38.5 4.26

TABLE LVI

.METHANOLYSIS (0.100M LiC1O4 ) OF 2,3,4,6-TETRA-O-ACETYL-ca- D-GLUCOPYRANOSYL BROMIDE (0.0213M) AT 25.0°C.

t, min. Ca_ t, min. at

2.4 4.06 42.4 3.63 6.3 4.01 45.3 3.61 9.3 3.98 48.3 3.58 12.3 3.95 51.3 3.55 15. 3 3.92 54.3 3.52 18.4 3.88 57.3 3.50 24.4 3.82 60.3 3.47 27.3 3.78 63.3 3.44 30.5 3.75 66.4 3.41 33.3 3.72 69.4 3.37 36.3 3.69 72.4 3.34 39.3 3.66 75.4 3.30 -138-

TABLE LVII

METHANOLYSIS (0.1lOOM LiC10 4 ) OF 2,3,4,6-TETRA-O-ACETYL-a- D-GLUCOPYRANOSYL BROMIDE (0.0244M)-AT 40.0°C.

t, min. t, min. at

2.6 4.54 12.3 4.30 4.4 4.43 13.3 3.97 5.4 4.37 14.3 3-.91 6.3 4.32 16.3 3.82 7.3 4.29 17.4 3.76 8.4 4.23 19.4 3.65 9.3 4.18 20.4 3.60 10. 4 4.13 22.3 3.51

TABLE LVIII

METHANOLYSIS (0.100M NaC104) OF 2,3,4,6-TETRA-O-ACETYL-a- D-GLUCOPYRANOSYL BROMIDE (0.0244M) AT 40.0°C.

t, min. at t, min. at

2.3 4.59 10.4 4.17 3.3 4.53 11.3 4.13 4.3 4.49 12.3 4.07 5.3 4.43 14.4 3.96 6.3 4.38 16.4 3.88 7.3 4.33 18.4 3.76 8.3 4.28 20.3 3.68 .9.4 4.24 22.3 3.58

TABLE LIX

METHANOLYSIS (0.100M LiBr) OF 2,3,4,6-TETRA-O-ACETYL-c-D- GLUCOPYRANOSYL BROMIDE (0.0247M) AT 25.0°C.

t,.min. t, min. at

6.4 4.61 38.4 4.20 9.3 4.57 41.4 4.16 11.3 4.54 44.4 4.12 13.4 4.51 47.4 4.09 15.4 4.48 50. 5 4.05 17.4 4.46 53.4 4.01 20.4 4.42 56.3 3.98 23.5 4.38 59.4 .3.94 26.4 4.33 62.4 3.91 29.4 4.30 67.5 3.85 32.4 4.27 74.5 3.77 35.5 4.23 79.4 3.71 -139-

TABLE LX

METHANOLYSIS (0.100M LiBr) OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE (0.0245M) AT 25.0°C.

t, min. t, min. at

2.5 4.63 33.4 4.23 4.3 4.61 36.3 4.20 6.3 4.58 39.5 4.15 9.3 4.54 42.5 4.12 12.4 4.50 45.3 4.08 15.5 4.46 48.3 4.04 18.5 4.43 51.5 4.00 21.4 4.39 54.5 3.96 24.5 4.35 57.4 3.94 27.4 4.31 60.5 3.90 30.3 4.28

TABLE LXI

METHANOLYSIS (0.100M LiBr) OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE (0.0247M) AT 40.0°C.

t, min. at t, min. at

3.3 4.50 12.2 3.95 4.3 4.42 13.2 3.89 5.2 4.38 14.2 3.83 6.3 4.30 15.2 5.77 7.2 4.24 16.2 3.71 8.2 4.19 17.2 3.65 9.2 4.12 18.3 3.59 10.2 4.06 20.2 3.49 11.2 4.00

TABLE LXII

METHANOLYSIS (0.100M NH4 Br) OF 2,3,4,6-TETRA-O-ACETYL-a- D-GLUCOPYRANOSYL BROMIDE (0.0244M) AT 40.0oC.

t, min. a% t, min. at

2.3 4.50 9.2 4.04 3.3 4.43 10.3 3.98 4.3 4.37 11.3 3.92 5.3 4.30 12.3 3.86 6.2 4.24 14.3 3.73 7.4 4.17 16.3 3.61 8.3 4.10 18.4 3.40 TABLE LXIII

METHANOLYSIS (0.100M LiI) OF 2,3,4,6-TETRA-O-ACETYL-a- D-GLUCOPYRANOSYL BROMIDE (0.0249M) AT 25.0 ° C.

t, min. t, min.

2.5 4.68 36.3 4.16 4.4 4.64 39.4 4.11 6.4 4.60 42.4 4.07 9.4 4.55 45.4 4.03 12.4 4.51 48.3 3.99 15.4 4.46 51.5 53.95 18.3 4.41 54.5 .3.91 21.5 4.37 57.4 5.87 24.4 4.33 60.4 3.84 27.4 4.28 63.4 3.80 30.5 4.25 66.3 3.76 33.4 4.20 69.3 3.72

TABLE LXIV

METHANOLYSIS (0.100M LiI) OF 2,3,4,6-TETRA-O-ACETYL-a- D-GLUCOPYRANOSYL BROMIDE (0.0245M) AT 25.00°C.

t, min. Ot t, min.

2.4 4.66 36.4 4.16 4.4 4.61 39.4 4.12 6.4 4.59 42.3 -- 5.08 9.5 4.54 45.4 4.04 12.4 4.50 48.4 3.99 15.4 4.46 51.4 3.95 18.4 4.42 54.3 3.91 21.3 4.37 57.4 3.87 24.4 4.32 60.3 3.83 27.5 4.28 63.5 3.78 30.5 4.24 66.4 3.74 33.4 4.20 69.4 3.70 -141-

SECTION II

ETHANOLYSIS REACTIONS

TABLE LXV

ETHANOLYSIS OF 2,3,4,6-TETRA- -ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0201M) AT 25.0°C.

min. t, at t, min. at

4.8 3.84 173.1 3.64 11.1 3.82 203.8 3.61 18.8 3.82 233.5 3.57 27.6 3.81 266.0 3.53 34.5 3.80 294.8 3.51 47.8 3.79 342.9 3.45 58.7 3.78 581.9 3.42 71.8 3.76 432.7 3.56 86.6 3.74 483.0 3.50 104.7 3.72 537.7 3.24 122.6 3.70 821.3 2.93 147.7 3.67

TABLE LXVI

ETHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0211M) AT 25.0°C.

t, min. _, min. a%

4.5 4.06 421.8 3.57 30.4 4.02 450.5 3.53 60.4 3.99 482.4 3.50 90.5 3.96 510. 5 3.47 121.5 3.93 542.4 3.42 150.8 3.90 370.7 3.39 181.7 3.86 602.4 .5.563-323.36 210.7 3.83 631.5 242.5 3.79 660.6 5.29 270.4 3.75 691.4 3.25 302.6 3.72 722.4 3.22 331.6 3.68 781.6 35.14 360.8 3.64 842.5 35.07 391.5 3.61 -142-

TABLE LXVII

ETHANOLYSIS OF 2,3,4,6-TETRA- -ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0222M) AT 30. 0°C.

t, min. at t, min. a1

3.4 4.30 242.4 3. 76 19.4 4.26 261.5 .53.73 39.5 4.22 280.6 3.69 61.5 4.18 301.4 3.65 78.5 4.14 331. 5 3.58 120.3 4.04 361.6 3.52 140.6 4.00 390.5 3.45 160.3 3.94 421.5 .537 181.4 3.91 450. 5 3.31 200.5 3.86 480.4 3.25 220.4 3.83 510.5 .5.18

TABLE LXVIII

ETHANOLYSIS OF 2,3,4,6- TETRA- O-ACETYL-- D-GLUC OPYRANOSYL BROMIDE (0.0204Mo) AT 30.0°0 C.

t, min. ct t, min. "x

5.5 3.96 241.7 3.51 20.9 3.91 263.5 3.48 40.7 3.87 279.8 3.44 61.6 3.84 300.7 3.39 84.6 3.80 321. 5 101.8 3.78 343.6 3.305.30 123.9 3.73 362.5 3.27 141.9 3.69 389.5 3.22 160.8 3.65 430.6 3.14 181.6 3.61 449.5 3.09 200.8 3.58 480.6 3.02 222.7 3.55

TABLE- LXIX

ETHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0224M) AT 35. 00°C.

t, min. "a t, min. at 3.8 4.35 161.4 3.79 20.8 4.28 180.5 3.71 40.4 4.20 200.5 3.65 59.5 4.15 219.4 3.58 81.4 4.08 239.4 3.51 100.4 4.00 259.7 3.44 120.5 3.94 279.7 3.36 141.4 3.85 301.4 3.28 -143-

TABLE LXX

ETHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0209M) AT 35.0°C.

t, min. t, min. % 6.6 3.95 149.8 3.49 15.6 3.91 163.7 3.42 30.5 3.87 181.7 3.38 45.8 3.82 200.6 3.30 60.8 3.78 214.5 3.27 75.5 3.74 233.8 3.19 90.7 3.69 248.7 3.15 105.6 3.63 263.7 3.08 122.7 3.58 290.4 2.98 135.8 3.53 320.6 2.87

TABLE LXXI

ETHANOLYSIS OF 2,3,4,6- TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0197M) AT 40.0°C.

t, min. t, min. at 5.6 3.62 98.5 3-.13 8.6 3.60 107.7 3.08 15.5 3.57 119.5 3.02 25.5 3.52 128.5 2.97 35.5 3.45 144.6 2.88 45.5 3.42 154.7 2.85 55.5 3.35 165.8 2.77 65.6 3.30 179.6 2.70 75.-6 3.25 191.5 2.64 87.5 3.19 207.6 2.54

TABLE LXXII

ETHANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0241M) AT 40.0 ° C.

t, min. a t, min. at 3.4 4.55 100.4 3.91 10.4 4.49 110.4 3-.85 20.3 4.43 120.3 3.78 30.4 4.37 130.5 3.71 40.6 4.31 141.3 3.63 50.3 4.24 150.5 3.57 60.3 4.17 161.5 3.50 70.4 4.11 171.3 3.44 80.4 4.06 180.6 3.38 91.4 3.97 -144-

TABLE LXXIII

ETHANOLYSIS (0.100M LiC1O4 ) OF 2,3,4,6-TETRA-O-ACETYL- a-D-GLUCOPYRANOSYL BROMIDE (0.0244M) AT 40.00C.

t, min. t, min. at 35.3 4.53 68.3 4.01 10.2 4.48 75.4 3.95 17.2 4.41 82.3 3.90 23.2 4.37 91.4 3.83 29.3 4.33 98.3 .3.77 35.3 4.28 105.5 3.72 41.2 4.23 114.3 3.66 49.3 4.16 124.4 3.57 55.2 4.11 131.3 3.53 61.3 4.07

TABLE LXXIV

ETHANOLYSIS (O.10OM LiBr) OF 2,3,4,6-TETRA-O-ACETYL- a-D-GLUCOPYRANOSYL BROMIDE (0.0244M) AT 40.0°C.

t, min. "4 t, min. 4.04 3.5 4.54 37.5 4.04 5.3 4.50 42.3 3.97 10.3 4.43 48.3 3.89 13.2 4.38 53.3 3.81 17.3 4.33 60.3 3.72 22.3 4.27 67.3 3.62 26.3 4.20 72.3 3.56 30.3 4.15 78.3 3.48

TABLE LXXV

ETHANOLYSIS (0.100M NH4 Br) OF 2,3,4,6-TETRA-O-ACETYL- a-D-GLUCOPYRANOSYL BROMIDE (0.0239M) AT 40. 0C.

t, min. t, min. iat 35.3 4.54 64.2 3.63 10.2 4.44 68.3 5.60 16.3 4.35 75.3 3.50 22.3 4.27 87.4 3.34 28.3 4.18 95.3 3.22 34.2 4.07 101.3 3.15 42.3 3.95 110.3 3.06 47.2 3.87 120.4 2.94 52.2 3.80 127.3 2.87 57.3 3.74 -145-

SECTION III

n-PROPANOLYSIS REACTIONS

TABLE LXXVI n-PROPANOLYSIS OF 2,3,4,6-TETRA- -ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0194M) AT 25.0°C.

t, hr. t, hr. at

.11 3.64 7.46 3.43 .21 3.64 8.35 3.40 .47 3.63 10.52 3.34 1.05 3.62 11.49 3.31 1.85 3.61 13.44 3.22 2.94 3.58 15.57 3.16 3.92 3.55 23.12 2.93 4.60 3.49 25.11 2.83 5.58 -- 3.47 47.92 1.83 6.55

TABLE LXXVII n-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0171M) AT 25.0°C.

t_,hr. a t t, hr. at

.11 3.29 12.06 2.95 1.07 3.26 13.08 2.92 2.08 3.23 14.04 2.89 3.07 3.21 15.08 2.85 4.07 3.18 16.34 2.81 5.05 3.15 18.13 2.74 6.05 3.12 19.11 2.72 7.12 3.09 20.16 2.69 8.08 3.07 21.02 2.67 9.43 3.02 29.03 2.41 TABLE LXXVIII

n-PROPANOLYSIS OF 2.,3,4,6-TETRA- -ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0163M) AT 30.0°C.

t, min. . a t, min.. a

4.4 3.15 482.6 2.75 42.5 3.13 519.4 2.72 75.4 :3.10 556.8 2.69 121.5 3.07 599.6 2.66 158.4 3.03 637.4 2.62 197.4 3.00 680.4 2.59 ·237.4 2.97 722.5 2.55 282.4 2.93 762.4 2.51 317.7 2.90 800.-6 - 2.48 361.3 2.86 847.5 2.45 396.4 2.83 887.4 2.41 437.8 2.79

TABLE LXXIX n-PROPANOLYSIS OF 2,3,4,6-TETRA-0-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0176M) AT 35.0°C.

t, min. t, min,

3.5 3.32 223.6 3.01 25.5 3.30 246.4 2.97 47.5 3.26 264.5 .2.93 65.3 3.24 286.3 2.91 87.4 3.21 305.5 2.88 104.4 3.19 327.5 2.85 126.4 3.16 345.4 2.81 144.5 3.31 367.3 2.75 166.5 3.09 385.5 2.72 183.5 3.06 406.5 2.68 206.5 3.03 425.5 2.65 -147-

TABLE LXXX n-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0175M) AT 40.0°C.

t, min. t, min. at

3.5 3.34 135.5 2.98 9.5 3.32 153. 5 2.93 32.5 3.26 166.5 2.90 40.4 3.24 183.5 2.87 52.4 3.20 196.5 2.84 61.5 3.17 213.4 2.81 73.4 3.15 226.3 2.77 82.4 3.12 243.4 2.73 100.4 3.08 258.6 2.68 110.5 3.05 274.3 2.64 122.6 3.02

TABLE LXXXI n-PROPANOLYSIS (0.100M LiC1O4 ) OF 2,3,4,6-TETRA-O-ACETYL- a-D-GLUCOPYRANOSYL BROMIDE (0.0175M) AT 40.0°C.

t, min. t, min. at

3.5 3.31 114.3 2.97 14.5 3.29 133.4 2.92 27.4 3.23 147.4 2.86 40.4 3.19 163.5 2.81 55.4 3.14 175.3 2.76 71.5 3.10 194.4 2.73 85.3 3.05 205.5 2.68 104.3 3.00 224.4 2.62

TABLE LXXXII n-PROPANOLYSIS (0.100M LiBr) OF 2,3,4,6-TETRA-0-ACETYL-a- D-GLUCOPYRANOSYL BROMIDE (0.0176M) AT 40.o0c.

t, min. at t, min. at

3.7 3.32 58.3- 2.96 8.3 3.29 65.4 2.90 13.4 3.26 72.4 2.86 18.4 3.24 79.4 2.81 26.3 3.18 87.4 2.76 33.4 3.13 93.4 2.73 39.4 3.10 100.5 2.69 46.4 3.04 107.3 2.65 53.4 2.99 SECTION IV

n-BUTANOLYSIS REACTIONS

TABLE LXXXIII n-BUTANOLYSIS OF 2.,3,4,6-TETRA- -ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0129M7 AT 25.0°C.

t, hr. t, hr. ceta

.31 2.46 10. 13 2.27 1.06 2.44 li..61 2.25 2.11 2.43 13.58 2.20 4.06 2.38 15.11 2.17 5.56 2.35 16.53 2.14 7.11 2.32 18.03 2.11 8.60 2.30 19.55 2.o8

TABLE LXXXIV n-BUTANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0151M7 AT 30.0°C.

t, min. t, min. at

4.5 3.00 476.4 2.73 33.5 3.00 509.5 2.70 70.5 2.98 551.4 2.68 112.4 2.95 590. 5 2.65 152.3 2.93 631.5 2.63 188.4 2.90 670.5 2.60 231.4 2.88 716.5 2.57 272 4 2.85 752.5 2.55 312.5 2.82 794.5 2.52 351.4 2.79 837.6 2.49 390.4 2.77 881.3 2.47 428.6 2.75 -149-

TABLE LXXXV n-BUTANOLYSIS OF 2,3,4,6-TETRA- -ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0155M7 AT 35.0°C.

t, min. t, min. at t

4.4 2.98 272.4 2.67 35.5 2.94 291.5 2.65 52.4 2.92 313.5 2.63 73.4 2.90 331.5 .2.61 91.5 2.88 353.4 2.59 112.3 2.85 371.6 2.56 131.5 2.83 393.6 2.54 152.5 2.81 411.3 2.52 171.4 2.79 430.4 2.49 192.5 2.76 451.5 2.45 211.6 2.74 471.5 2.42 234.3 2.73 490.4 2.40 251.4 2.70

TABLE LXXXVI n-BUTANOLYSIS (3F 2,3,4,6-TETRA- O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE (0.0153M7 AT 40. 0C.

t, min. t, min. at

3.6 3.01 143.6 2.77 13.5 2.98 157.5 2.74 27.5 2.97 174.4 2.72 36.5 2.95 187.4 2.70 48.5 2.93 204.7 2.67 57.4 2.92 217.4 2.64 69.5 2.90 234.3 2.62 78.5 2.88 247.5 2.59 90.3 2.86 266.5 2.55 104.5 2.83 278.4 2.52 118.4 2.80 306.4 2.46 127.4 2.78 338.5 2.41 -150-

TABLE LXXXVII n-BUTANOLYSIS (O.100M LiCl04) OF 2,3,4,6-TETRA-O-ACETYL- a-D-GLUCOPYRANOSYL BROMIDE (0.0153M)-AT 40.0°C.

a,t t, min. a t, min. 3.6 2.96 140.4 - 2.64 20.3 2.90 152.4 2.62 30.4 2.88 167.3 2.58 48 .3 2.84 183.3 2.55 61.3 2.82 198.3 2.51 77.3 2.78 213.4 2.47 93.3 2.75 228.4 2.45 107.4 2.72 241.4 2.41 122.3 2.68 258.3 2.38

TABLE LXXXVIII

n-BUTANOLYSIS (0.100M LiBr) OF 2,3,4,6-TETRA-O-ACETYL- c-D-GLUCOPYRANOSYL BROMIDE (0.0152M) AT 40.0°C.

t, min. t, min. t 4.5 2.84 57-4, 2.58 8.4 2.81 64.4 2.56 12.4 2.79 74.4 2.51 17.4 2.75 80.4 2.47 23.4 2.73 88.5 2.43 29.5 2.71 96.4 2.41 36.4 2.68 105.5 2.37 2.65 118.5 2.32 50.454.4 2.62 128.4 2.28 -151-

SECTION V

iso-PROPANOLYSIS REACTIONS

TABLE LXXXIX iso-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE (0.0245M) AT 25.0°C.

t, hr. a:x t, hr. at .23 4.65 19.47 4.45 1.41 4.63 26.69 4.36 3.47 4.60 33.85 4.25 4.26 4.59 44.93 4.11 5.87 4.57 50.59 4.03 7.33 4.55 66.83 3.81 9.33 4.54 73.73 3.72 12.15 4.52 81.13 3.60

TABLE XC iso-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE (0.0203M) AT 25.0°C.

_, hr. t, hr. at

.10 3.84 44.92 3.46 2.70 3.81 48.90 3.42 4.20 3.80 52.90 5.38 6.93 3.77 56.88 3.34 8.93 3.75 61.15 3..29 20.30 3.66 64.97 3.25 24.48 3.63 73.83 3.14 29.17 3.58 78.07 3.10 34.28 3.54 -152-

TABLE XCI iso-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-Q-D- GLUCOPYRANOSYL BROMIDE (0.0206M) AT 30.0°C.

t, hr. t t, hr. at

.17 3.93 21.83 3.60 1.90 3.91 23.90 3.57 3.80 3.88 25.83 3.53 5.88 3.85 27.88 3.50 7.73 3.83 29.87 3.46 8.07 3.82 31.78 3.43 9.77 3.80 33.95 3.40 11.92 3.77 35.87 3.36 13.97 3.73 37.93 3.31 15.87 3.68 39.92 3.27 17.95 3.67 42.02 3.23 19.87 3.64

TABLE XCII iso-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE (0.0208M) AT 35.0°C.

_, hr. t, hr. cat

.03 3.95 12.57 3.66 1.02 3.93 13.73 3.63 1.97 3.92 14.88 35.59 2.90 3.90 16.08 3.56 4.02 3.88 17.10 3.52 5.35 3.84 18.78 3.47 6.35 3.81 20.02 3.43 7.58 3.78 21.77 3.37 8.90 3.74 23.60 3.31 10.12 3.72 25.52 3.25 11.38 3.69 27.60 3.17 -153-

TABLE XCIII

iso-PROPANOLYSIS OF 2,3,4,6-TETRA-O-ACETYL-a-D- GLUCOPYRANOSYL BROMIDE (0.0209M) AT 40.0°C.

t, hr. t, hr. at

.08 3.95 5.96 3.73 .36 3.94 6.99 3.68 .73 3.94 8.01 3-63 1.47 3.91 9.08 5.58 1.93 3.89 9.99 3'.54 2.51 3.87 11.07 3.47 3.01 3.85 13.13 3.39 3.53 3.82 15.21 3.25 4.58 3.79 16.87 3.16 5.08 3.76

TABLE XCIV iso-PROPANOLYSIS (0.100M LiC10 4) OF 2,3,4,6-TETRA-0-ACETYL- a-D-GLUCOPYRANOSYL BROMIDE (0.0206M) AT 40.0°C.

t, hr. t, hr. at at .17 3.89 5.83 3.56 .60 3.85 6.80 3.50 .98 3.83 7.83 3.43 1.55 3.80 9.02 3;35 2.10 3.76 10.02 3.30 2.60 3.74 10.98 3.25 3.08 3.70 12.05 3.19 3.88 3.67 13.03 3.14 4.85 3.62 14.15 3.07

TABLE XCV

iso-PROPANOLYSIS (0.100M LiBr) OF 2,3,4,6-TETRA-O-ACETYL- a-D-GLUCOPYRANOSYL BROMIDE (0.0214M) AT 40.0°C.

t, min. a1 t, min. 3.6 4.15 148.5 3-.56 10.5 4.13 165.4 3.51 28.5 4.05 178.5 3.47 46.4 3.98 198.5 3.40 56.4 3.93 211.5 3.35 71.6 3.86 226.3 3.30 86.5 3.79 287.0 3.10 106.4 3.73 346.0 2.94 119.4 3.68 404.0 2.79 134. 5 3.62 466. 0 2.67 APPENDIX V

DERIVATION OF THE THEORETICAL MODEL FOR THE iso-PROPANOLYSIS OF 2,3,4,6- TETRA-O-ACETYL-a-D-GLUCOPYRANOSYL BROMIDE

DERIVATION

The theoretical model discussed in the text is:

k TAGB + HBr --- TAGB + HBr

TAGB + ROH - -* -ROG + HBr

k P-TAGB + ROH -- a- -ROG + HBr where k >> k -Q -e and

TAGB = 2,3,4,6 -tetra-0-acetyl-a-D-glucopyranosyl bromide

P-TAGB = 2,3,4,6-tetra-O-acetyl-P-D-glucopyranosyl bromide

ROH = iso-propanol

a-ROG = iso-propyl 2,3,4,6-tetra-O-acetyl-a-D-glucopyranoside

P-ROG = iso-propyl 2,3,4,6 -tetra-O-acetyl-P-D-glucopyranoside

k = second-order rate constant, liter moles sec. -e k = pseudo-first-order rate constant,-iso-propanolysis, sec. -- k = pseudo-first-order rate constant, iso-propanolysis, sec.

Let [TAGB] = H

[HBr] = X

[a-ROG] = A

[P-ROG] = B. -155-

The rate of formation of the P-glucoside, P-ROG, is

dB/dt = k H (64).

Since the formation of P-TAGB is rate controlling, the rate of formation of the

a-glucoside, a-ROG, is

dA/dt = k HX (65).

Assuming the concentration of P-TAGB is small at all times, from stoichiometry

X=A +B (66).

Equations (64)-(66) can be combined to yield the differential equation relating

the concentration of the a-glucoside to the P-glucoside,

dA/dB - FA = FB (67) where F = k e/k-

Integrating Equation (67) using the defining limit that A = 0 when B = 0,

Equation (68) is obtained

A = [exp(FB) - 1]/F - B (68)

or

A + B = [exp(FB) - 1]/F (68a).

Dividing Equation (68) by Equation (68a) the final equation defining the fraction

of the total glucoside concentration accounted for as a-anomer is obtained.

A/(A + B) = 1 - FB/[exp(FB) - 1] (69). -156-

SAMPLE CALCULATION

Let F = 150

and FB = 0.10

therefore; B =6.67 x 10- 4 mole/liter

A/(A+B) = 0.049, from Equation (69)

A + B =7.02 x 10 4 mole/liter.

If the original concentration of TAGB was 2.06 x 10 M the corresponding extent

of reaction is

(A+B)/[TAGB] = 0.034 or 3.4%

The entire fraction a-anomer-per cent reaction can be calculated by using different values of FB. -157-

APPENDIX VI

CALCULATION OF THE EXTENT OF REACTION FROM POLARIMETRIC RATE DATA

DERIVATION

Making the assumption that the optical rotations of the individual components of the reaction system are independent of each other, the following equation may be written:

't =H '+aa+p (70) where

at = the observed optical rotation of the reaction system at time t

aH = the optical rotation due to TAGB

a = the optical rotation due to the a-glucoside

c = the optical rotation due to the P-glucoside

Equation (71) relates the molar concentration and the specific optical rotation of each component to the observed rotation due to that component.

where

O. = the observed rotation due to component i

£ = the polarimeter tube length, dm.

[a.] = the specific optical rotation of component i

M. = the gram-molecular weight of component i

C. = the concentration of component i, mole/liter.

The concentrations of the glucosidic components can be related to the concen- tration of TAGB by -158-

*A = (H - H)n' (72) 0 and

B = (Ho - H)(l-n') (73) where

A = the concentration of the a-glucoside at time t, mole/liter

B = the concentration of the P-glucoside at time t, mole/liter

H = the concentration of TAGB at time t, mole/liter

H = the initial concentration of TAGB, mole/liter

n' = the fraction of the total glucoside concentration accounted for as a-anomer

Substituting Equation (71) into Equation (70) and utilizing Equations (72) and

(73) to eliminate the concentrations of the anomeric glucosides results in

where

f(c) =(n'([%]% )-(l-n')([qpJ1)

at = the optical rotation of the solvolysis system at time t

2 = the length of the polarimeter tube employed, dm.

H = the initial concentration of TAGB, mole/liter -o n' = the fraction of a-anomeric glucoside at time t

MH = molecular weight of TAGB

M = molecular weight of the a-anomeric glucoside

M = molecular weight of the P-anomeric glucoside

[aH ] = the specific rotation of TAGB, determined by extrapolating the - solvolysis polarimetric data to zero time

[a ] = the specific rotation of the a-anomeric glucoside for the solvolysis conditions

[a ] = the specific rotation of the P-anomeric glucoside for the solvolysis conditions -159-

SAMPLE CALCULATION

For the iso-propanolysis of TAGB at 30.0 ° C.:

hr. (Appendix IV) att_ = 3.53 at 25.8

= 2.0 dm. (all reactions)

H = 2.06 x 10 -2 mole/liter (Appendix IV) -o

n' = 0.125 (Fig. 22)

= 411.2

M = M= 390.4

[a] = 232, calculated from the zero-time observed rotation of the reaction system (extrapola- tion of the data in Appendix IV)

[a = 175 (Table VI)

[aH] = -34.7 (Table VI) la[eaI] I3

Substitution of the above values into Equation (74) yields [TAGB] = 1.86 x 10- mole/liter. Comparing this value to H , the extent of reaction is found to be

9.7%.