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The Pennsylvania State University

The Graduate School

Eberly College of Science

THE UNDERFUNCTIONALIZATION OF ALCOHOLS BY HETEROGENEOUS

CATALYSTS

A Thesis in

Chemistry

Jennifer M. Nguyen

Submitted in Partial Fulfillment

of the Requirements

for the Degree of

Master of Science

August 2009 ii

The thesis of Jennifer M. Nguyen was reviewed and approved* by the following:

Ayusman Sen Professor of Chemistry Thesis Adviser

Martin Bollinger Professor of Chemistry

Scott Phillips Professor of Chemistry

*Signatures are on file in the Graduate School.

iii

Abstract

Finite oil reserves along with worries of global warning suggest that alternative sources of fuel are necessary in the future, especially for the transportation industry. As renewable resources are preferable, we look at biomass as a fuel alternative. In order for biomass to be a viable supplement, it must be deoxygenated in order to fit the physical properties of liquid fuels used in the transportation industry today. Since liquid alkanes are highly valuable for this, we attempted to selectively deoxygenate alcohols in an acid-catalyzed hydrogenation reaction using hydroiodic acid and rhodium trichloride. The goal of this research was to find a system that we can then test on straight chain carbohydrates.

Table of Contents

List of Tables…………………………………………………………………………………. v

List of Tables…………………………………………………………………………………. vi

Chapter 1: Introduction………………………………………………………………………. 1

Chapter 2: Experimental……………………………………………………………………… 10

2.1 General Comments……………………………………………………………….. 10

2.2 Synthesis………………………………………………………………………….. 10

Chapter 3: Results and Discussion…………………………………………………………… 12

3.1 Substrate Analyses………………………………………………………………... 14

3.2 Catalyst Analyses…………………………………………………………………. 16

3.3 Solvent Analyses…………………………………………………………………. 19

3.4 Reactant Analyses………………………………………………………………… 20

3.5 Additional Analyses………………………………………………………………. 21

Chapter 4: Conclusions……………………………………………………………………….. 23

References……………………………………………………………………………………... 24

Appendix: Spectral Data………………………………………………………………………. 25

List of Tables

Introduction

Table 1: Conventional and alternative fuels used in transportation…………………. 4

Results and Discussion

Table 2: Alcohol dehydration-hydrogenation reactions ……………………………. 12

Table 3: Diol dehydration-hydrogenation reactions using hydroiodic acid ………… 13

Table 4: Diol dehydration-hydrogenation reactions using sulfuric acid ……………. 14

Table 5: Conversion of alcohols to their corresponding iodoalkane ………………... 15

Table 6: Conversion of iodohexanes to hexane/hexenes …………………………..... 16

Table 7: Catalyst effects on iodoalkanes……………………………………………. 17

Table 8: Catalyst effects on alcohol………………………………………………… 18

Table 9: Solvent effects on the conversion of alcohols to alkanes …………………. 20

Table 10: Reactant effects on the conversion of alcohols to alkanes ………………. 21

Table 11: Effect of iodide in the conversion of alcohols to alkanes………………… 22

List of Figures

Introduction

Figure 1: The growth of biofuel production in the transportation fuel industry between

2000 to 2007…………………………………………………………………… 2

Figure 2: Alcohol sustainability of biomass in fuel production……………………… 3

Figure 3: The opposing issues of underfunctionalization and overfunctionalization with

crude oil and biomass ………………………………………………………… 5

Figure 4: Three primary routes for liquid fuel production from cellulosic biomass…. 5

Figure 5: Fuel production from syn-gasification …………………………………….. 6

Figure 6: Suggested pathway involving acid hydrolysis for selectively deoxygenating

polyols ………………………………………………………………………… 7

Figure 7: Potential applications for the products resulting from the deoxygenation of

linear polyols.…………………………………………………………………. 8

Chapter 1

Introduction

The current decline in oil prices during the latter half of 2008 contradicts the decrease in

the quantity of petroleum across the world. As a fuel, petroleum, otherwise known as crude,

naturally occurring oil, is the main source of energy for transportation vehicles and also

contributes to the production of fuel for heat. From diesel fuel to jet fuel to gasoline, the

transportation market is almost exclusively tied to the petroleum industry. Gasoline and diesel

primarily fuel land vehicles while aircrafts run on kerosene and ships on heavy fuels.1 However,

the downside of this oil dependency lies in the fact that petroleum is not a renewable resource;

the oil used today has been formed from prehistoric organic materials as a result of high

temperature and pressure. Thus, there will be a time that petroleum fuel reserves will dry out

completely. It has been reported from USA Today as well as from reputable scientists that there are only 40 years of petroleum left in the world. Despite this, the longevity of petroleum remains highly debated, yet all agree that petroleum reserves are not a lasting, renewable commodity. To this end, studies into the use of renewable technologies as an alternative to petroleum are ongoing. Sustainable fuels are being sought to minimize the concerns of finite crude oil, cleaner fuel, greenhouse emissions, the Kyoto protocol, and the dependency on imported oil. Such options include solar, wind, hydro, geothermal, and biomass energy. The latter of the aforementioned renewable energy sources, biomass, has recently garnered much attention in both the scientific and general community.2

As a fuel, biomass is seen in roughly 10% of the world’s energy use today. Perhaps the

most prominent example of biomass lies in the ethanol used in conjunction with gasoline today;

this ethanol is derived from the production of corn, where it is then blended with gasoline for use

in automobiles.3 In addition, fatty acid methyl esters are used in blending for diesel engines.2

However, in the transportation fuel market, biomass-derived fuel such as ethanol only contributes about 3% of gasoline consumption while biodiesel contributes less than 0.3% (Figure

1).3

Figure 1: The growth of biofuel production in the transportation fuel industry between 2000 to

2007.3

Nevertheless, not only is biomass a renewable resource, it offers a variety of advantages over the

current petroleum-driven processes. While petroleum production and consumption result in

environmentally unfriendly products such as greenhouse emissions, the sustainability of biomass

can potentially reduce such problems by reusing carbon dioxide emissions and producing less

hazardous waste.

Figure 2: Potential sustainability of biomass in fuel production.4

Additionally, the functionality of highly oxygenated biomass rests in contrast with the

underfunctionality of crude oil, where conditions to underfunctionalize biomass encourages the

use of innovative deoxygenation pathways.

To understand the utilization of biomass as a supplement to crude oil, the specifications for a good fuel should be first discussed. Currently, transportation fuels have both low and high

boiling mixtures of hydrocarbons. Commonly used low boiling fuels include compressed natural

gas (CNG) and liquid petroleum gas (LPG); hydrogen and dimethyl ether are alternative fuels

with similar volatilities.1 Figure 3 below indicates some of the conventional fuels used

worldwide today and correlates their volatilities to alternative fuel sources.

Table 1: Common conventional and alternative fuels used in transportation.1

(CNG = compressed natural gas, LPG = liquefied petroleum gas, DME = dimethyl ether, ETBE = ethyl tertiary butyl ether, GTL = gas to liquids, FAME = fatty acid methyl esters, FAEE = fatty acid ethyl esters, HTU = hydrothermal upgrading)

One of the major problems with utilizing biomass as a fuel resource, however, is the difficulties in converting the functionality of biomass into a usable fuel resource. The cheapest and most abundant source of biomass is lignocellulose. Unfortunately, this biomass cannot be used without deoxygenating the structure, turning it into a higher density liquid fuel.4 Generally, lignocellulosic biomass consists of “40-45 wt % oxygen”.4 By removing the oxygen, the heating value of the liquid fuel becomes higher, which is desirable in the transportation fuel industry; this occurs as the presence of oxygen lowers the energy density of the fuel, where combustion is always an issue. In theory then, as crude oil, composed of mainly hydrocarbons, consists of low oxygen content and often needs to be overfunctionalized, biomass suffers from the reverse: it needs to be underfunctionalized.

Figure 3: The opposing issues of underfunctionalization and overfunctionalization with crude oil

and biomass.4

In this case of underfunctionalization then, there are three primary methods in which cellulosic biomass can be converted into potential fuel reserves.

Figure 4: Three primary routes for liquid fuel production from cellulosic biomass.4

Syn-gas production from gasification, bio-oil production from pyrolysis or liquefaction, and the hydrolysis of polyols are all possible routes to the production of liquid fuels. Syn-gas production encompasses a variety of different fuels, some of which include hydrogen production by the

water-gas shift reaction of carbon dioxide and water. Methanol synthesis and alkane production

by the Fischer-Tropsch process are also syn-gas methods for the manufacture of fuel sources.

Figure 5: Fuel production from syn-gasification.

Bio-fuel production from pyrolysis or liquefaction occurs when biomass is slowly heated in the

absence of air to form liquid products. Finally, the hydrolysis of polyols is the route that addresses the problem of overfunctionality in biomass; producing monomer units from biomass such as sugar cane through acid hydrolysis and subsequent hydrogenation is favorable to then produce targeted fuel sources. However, lignocellulose and biomass with high degrees of oxygenation and stability prove more difficult in this first-step hydrolysis. Nonetheless, much research has been produced with regard to utilizing acid hydrolysis on biomass, as the subsequent hydrogenation of biomass to monomers is an advantageous method to selectively convert the monomers to fuel.4

One particularly noteworthy benchmark in biomass hydrolysis was Dumesic’s recent

three-step process in converting the sugar fructose into 2,5-dimethyltetrahydrofuran through the intermediate hydroxymethylfurfural, a compound with incredible potential use as a transportation fuel.5 Not only does 2,5-dimethyltetrahydrofuran have a higher energy density

than ethanol, its boiling point is also higher and it remains insoluble in water. In 2002, fructose had been shown to convert to hydroxymethylfurfural via an acid-catalyzed dehydration.6 In

2007, Dumesic suggested as well as demonstrated that this conversion can precede the

transformation of hydroxymethylfurfural to 2,5-dimethyltetrahydrofuran. In addition, the

production of hydroxymethylfurfural from glucose has been shown, though it is much less

selective. The mechanism from hydroxymethylfurfural to 2,5-dimethyltetrahydrofuran is,

however, controversial, yet the interest around the dehydration of alcohol groups in fructose has

spurred much research into the field of biofuels.

With respect to Dumesic’s research then, the idea of selective deoxygenation is a long term goal of many researchers. This idea seeks to take sugars and their corresponding polyols

and convert them into simple alcohols utilizing simple catalyst systems for deoxygenation. The

common strategy, as suggested by Schlaf, states: “An acid-catalyzed dehydration followed by a

metal-catalyzed hydrogenation and/or hydrogenolysis”.7 As secondary carbon-oxygen bonds

tend to be more reactive than its primary counterparts, the hope is that eventually, a one-pot

process will be formulated in which sugar polyols can be selectively hydrogenated (Figure 7).

Figure 6: Suggested pathway involving acid hydrolysis for selectively deoxygenating polyols.

As a basis to selectively hydrogenating sugar polyols, we decided to then to first study

the hydrogenolysis of linear chain alcohols. The conversion of linear polyols to primary diols

offers two unique advantages in biomass conversion. The first advantage lies in the fact that

8 with the utilization of linear and simple polyols, we may be better able to understand the mechanisms that can occur through hydrogenolysis of more complex biomass material. Perhaps by studying simple reactions, mechanistic contributions to the unknown hydroxymethylfurfural to 2,5-dimethyltetrahydrofuran conversion can be discovered. Secondly, underfunctionalizing simple linear polyols also contributes a great deal to the biomass hydrogenolysis as well; for example, the deoxygenation of glycerol, a compound that is easily produced in high quantities, has the potential to produce 1,3-propanediol. 1,3-propanediol is an incredibly attractive deoxygenation target, as 1,3-propanediol is used in the synthesis of polypropyleneterephtalate, or

PPT.7 The deoxygenation of linear polyols would result in many applications, some of which are shown in Figure 8 below.

Figure 8: Potential applications for the products resulting from the deoxygenation of linear

polyols.7

This deoxygenation has been accomplished in several ways with varying results.

Glycerol, often a byproduct of oil refineries, has been selectively deoxygenated to 1,3-

propanediol through homogenous catalysis and hydrogenation based upon palladium and

phosphorous complexes; the yield of these experiments, however, is low.8,9 Biotechnological

pathways involving enzymes of bacteria have also been shown to selectively deoxygenate

glycerol; however, the resultant product is difficult to process and gather. Erythritol, through

dehydrogenation and hydrogenation, can be transformed into 1,4-butanediol as well as THF. 10

Dupont has achieved this selectivity to THF by using Re/Ni catalysts supported on carbon in a

hydrogen environment. 11,12 Additionally, xylose has been converted to low yields of 1,5-

pentanediol using heterogeneous catalyst systems based upon copper complexes. 13

As we considered these previously published experiments, we chose our primary

objectives to first center around the deoxygenation of simple alcohols to alkanes. To do this, we

chose to use acid hydrolysis on an alcohol substrate based around hydroiodic acid and a catalyst,

typically rhodium trichloride; this acid and this catalyst were chosen based on their previous

successes in carbohydrate dehydration from the Sen group. The reactants were then subjected to hydrogenation at high temperatures. From this, we hoped to discover the effects of items such as substrate, catalyst activation, and solvent effects on the acid hydrolysis of the alcohols.

Chapter 2

Experimental

2.1 General Comments

All chemicals and solvents were acquired from commercial sources and used in its original form if not stated otherwise. All characterizations were performed at the Pennsylvania

State University. Initial GC spectra were taken on a Agilent gas chromatograph. GC-MS spectra were taken on a Waters LCT Premier mass spectrometer. 1H spectra were taken on a

Bruker Avance spectrometer referenced to trimethylsilane at 360 MHz.

2.2 Synthesis

Preparation of alkyl iodides from alcohols

In a one-neck, round bottom flask, the alcohol (31.5 mmol) and hydroiodic acid (57% wt,

7 mL) was added. The solution was refluxed in an oil bath at 100 oC or 120oC for 4 hours. After

4 hours, the solution was let cool to room temperature before cooling in ice. The organic layer

was isolated, dried by anhydrous sodium sulfate, and analyzed by gas chromatography and

proton NMR.

Preparation of alkanes from alkyl iodides

In a glass liner, the alkyl iodide (1.0 mmol) was added along with rhodium trichloride, or

a different catalyst (0.05 mmol), and a stir bar. The solvent (1 mL) was added to the glass liner.

The solvent (1 mL) was used to coat the inside of a bomb before the liner was loosely capped

and placed inside. The bomb was filled with 500 psi hydrogen and 500 psi argon gas and placed

in an oil bath at 100°C overnight.

The bomb was taken out of the oil bath and let sit to room temperature, then cooled in an

ice bath while the pressure inside was slowly released. The organic solvent both inside and

11 outside of the liner was isolated and analyzed by gas chromatography. Deuterated water was added to the aqueous layer, and a proton NMR was taken.

Preparation of alkanes from alcohols

In a glass liner, the alcohol (1.0 mmol) was added along with rhodium trichloride or a different catalyst (0.05 mmol), hydroiodic acid (57% wt., 5.0 mmol), and a stir bar. The solvent

(1 mL) was added to the glass liner. The solvent (1 mL) was used to coat the inside of a bomb before the liner was loosely capped and placed inside. The bomb was filled with 500 psi hydrogen and 500 psi argon gas and placed in an oil bath at 100°C overnight.

The bomb was taken out of the oil bath and let sit to room temperature, then cooled in an ice bath while the pressure inside was slowly released. The organic solvent both inside and outside of the liner was isolated and analyzed by gas chromatography. Deuterated water was added to the aqueous layer, and a proton NMR was taken.

Chapter 3

Results and Discussion

A dehydration-hydrogenation reaction utilizing catalytic amounts of hydroiodic acid and rhodium trichloride was attempted on a variety of linear alcohols and diols. Concerning the mono-alcohols shown in Table 2 below, it was seen that iodoalkanes were produced.

Table 2: Alcohol dehydration-hydrogenation reactions

Entry Reactant Acid Product Yield (%)

1 1-hexanol HI 1-iodohexane 33.7

2 2-hexanol HI Hexane/hexenes 12.1

2-iodohexane 87.9

3 3-hexanol HI Hexane/hexenes 9.8

3-iodohexane 90.2

*In all of the experiments, 1 mL of toluene lined the inside of both the bomb and glass liner. The bombs were filled with 500 psi H2 and 500 psi Ar. The bombs were placed in an oil bath overnight (12 hours) at 100°C. *Conversion based on gas chromatography.

Conversely, when the system was run with diols, the majority of the diols underwent acid- catalyzed dehydration and cyclization. When the acid was changed to hydrochloric acid or sulfuric acid, similar results were obtained, with the major difference being the dehydration- cyclization of 1,6-hexanediol when the acid catalyst was sulfuric acid.

Table 3: Diol dehydration-hydrogenation reactions using hydroiodic acid

Entry Reactant Acid Product Yield (%) 1 1,6-hexanediol HI None None

2 1,5-hexanediol HI 2-methyltetrahydropyran 55.7

2-ethyltetrahydrofuran 24.6

3 2,5-hexanediol HI cis-2,5- 53.2 dimethyltetrahydrofuran trans-2,5- 47.5 dimethyltetrahydrofuran 4 1,2-hexanediol HI unreacted N/A

Table 4: Diol dehydration-hydrogenation reactions using sulfuric acid

Entry Reactant Acid Product Yield (%) 1 1,6-hexanediol H2SO4 2-ethyltetrahydrofuran 1.8

2 1,5-hexanediol H2SO4 2-methyltetrahydropyran 52.2

2-ethyltetrahydrofuran 5.1

3 2,5-hexanediol H2SO4 cis-2,5- 37.5 dimethyltetrahydrofuran trans-2,5- 38.6 dimethyltetrahydrofuran 4 1,2-hexanediol H2SO4 unreacted N/A

As neither the mono-alcohols nor the diols produced the desired products from hydrogenation, further experimentation was performed varying the substrate, catalyst, and solvent to examine the products of the hydrogenation reaction.

3.1 Substrate Analyses

To analyze the effects of the substrates on the conversion from alcohols to alkanes, we sought to determine if starting with the iodoalkane was necessary for the conversion, as beginning with an alcohol substrate did not produce the subsequent hydrogenated product in high amounts. A simple procedure where the substrate alcohol is reacted with hydroiodic acid at high temperatures was able to produce the necessary iodoalkanes in high yield.14 Primary as well as secondary iodoalkanes were produced from their alcohol counterparts, and primary diols were

also converted to their correlating iodoalkanes (Table 3). However, 1,2-diols were unable to be converted to iodoalkanes.

Table 5: Conversion of alcohols to their corresponding iodoalkane

Entry Reactant Acid Conditions Oil Bath Yield (%) Temp (°C)

1 1-butanol HI Reflux, 4 h 100 73

2 1-pentanol HI Reflux, 4 h 100 98

3 1-hexanol HI Reflux, 4 h 100 95

4 2-hexanol HI Reflux, 4 h 100 92

5 3-hexanol HI Reflux, 4 h 100 94

6 1,3-propanediol HI Reflux, 4 h 120 50

7 1,4-butanediol HI Reflux, 4 h 120 86

8 1,5-pentanediol HI Reflux, 4 h 120 50

Table 6: Conversion of iodohexanes to hexane/hexenes

Entry Reactant Catalyst Oil Bath Temp Yield (%) (°C)

1 1-iodohexane RhCl3 100 2.3

2 2-iodohexane RhCl3 100 4.5

3 3-iodohexane RhCl3 100 3.3

The resultant iodoalkanes were then utilized to determine if it the iodoalkanes were able to be hydrogenated in the presence of rhodium trichloride and hydrogen gas. 1-iodohexane along with 2-iodohexane and 3-iodohexane were the primary substrates used in these experiments, where the iodohexane and the chosen catalyst, rhodium trichloride, were subjected to high pressure hydrogenation within a bomb. The results indicated that little of the iodohexane was hydrogenated to hexane/hexenes.

3.2 Catalyst Analyses

In the case that the catalyst, rhodium trichloride, was not effective for our hydrogenation efforts, we tested a variety of different catalysts on both the alcohol and iodoalkane substrates.

The hexane and hexenes produced from each experiment were low in yield; however, the utilization of the catalyst rhodium trichloride appeared to give the highest percent recovery.

Additionally, changing the catalyst while attempting to hydrogenate the alcohol directly, not the iodoalkane, also presented similar results.

Table 7: Catalyst effects on iodoalkanes

Entry Reactant Catalyst Products Yield (%)

1 1-iodohexane Pd/C hexane/hexenes 2.4

2 1-iodohexane RhCl3 hexane/hexenes 4.5

3 1-iodohexane Rh/C hexane/hexenes 3.4

4 1-iodohexane RuCl3 hexane/hexenes 3.1

5 1-iodohexane Ru/C hexane/hexenes 4.5

6 3-iodohexane Pd/C hexane/hexenes 2.5

7 3-iodohexane RhCl3 hexane/hexenes 4.7

8 3-iodohexane Rh/C hexane/hexenes 3.0

9 3-iodohexane RuCl3 hexane/hexenes 2.7

10 3-iodohexane Ru/C hexane/hexenes 3.2

Table 8: Catalyst effects on alcohols

Entry Reactant Acid Catalyst Products Yield (%)

1 1-hexanol HI Pd/C hexane/hexenes 2.4

1-iodohexane 97.6

2 1-hexanol HI RhCl3 hexane/hexene 4.5

1-iodohexane 95.5

3 1-hexanol HI Rh/C hexane/hexenes 3.4

1-iodohexane 96.6

4 1-hexanol HI RuCl3 hexane/hexenes 3.1

1-iodohexane 96.9

5 1-hexanol HI Ru/C hexane/hexenes 4.5

1-iodohexane 95.5

6 2-hexanol HI Pd/C hexane/hexenes 2.5

3-iodohexane 97.5

7 2-hexanol HI RhCl3 hexane/hexenes 6.7

3-iodohexane 93.3

8 2-hexanol HI Rh/C hexane/hexenes 3.4

3-iodohexane 93.5

9 2-hexanol HI RuCl3 hexane/hexenes 3.5

3-iodohexane 77.0

10 3-hexanol HI Ru/C hexane/hexenes 7.0

3-iodohexane 70

11 3-hexanol HI Pd/C hexane/hexenes 2.9

3-iodohexane 95.8

12 3-hexanol HI RhCl3 hexane/hexenes 9.8

3-iodohexane 90.2

13 3-hexanol HI Rh/C hexane/hexenes 3.5

3-iodohexane 92.5

14 3-hexanol HI RuCl3 hexane/hexenes 5.0

3-iodohexane 72

15 3-hexanol HI Ru/C hexane/hexenes 7.0

3-iodohexane 70

In the case of varying the catalyst with the alcohols, each alcohol produced the

corresponding iodoalkane in high quantity and hexane/hexenes in small quantity. Rhodium trichloride also gave the highest yield of hexane/hexenes as compared to the other four catalysts tested.

3.3 Solvent Analyses

In order to catch the low boiling hydrogenated organic products produced from the reaction mixture, a 2 mL of a solvent was added to both the glass liner and bomb. Generally, toluene was added due to its higher boiling point than water. However, in the case that there were solvent interactions during the reaction, the solvent was varied from nonpolar to polar and

20 from low boiling to high boiling solvents to determine the solvent effect on the hydrogenation of alcohols.

Table 9: Solvent effects on the conversion of alcohols to alkanes

Entry Reactant Solvent Products Yield (%)

1 2-hexanol Toluene Hexane/hexenes 12.1 2-iodohexane 87.9 2 2-hexanol 1,3-dichlorobenzene Hexanes/hexenes 8.0 2-iodohexane 55.0 3 2-hexanol NMP unreacted N/A

4 2-hexanol HMPA unreacted N/A

*In all of the experiments, 1 mL of solvent lined the inside of both the bomb and glass liner. The bombs were filled with 500 psi H2 and 500 psi Ar. The bombs were placed in an oil bath overnight (12 hours) at 100°C. *Conversion based on gas chromatography.

As shown in Table 8 above, polar solvents such as NMP and HMPA were not successful in producing hydrogenated products while benzene, toluene, and the high boiling solvent 1,3- dichlorobenzene produced small yields of the hydrogenated products.

3.4 Reactant Analyses

In the case that any of the components in the reaction mixture was detrimental to the hydrogenation process, we ran a series of reactions to determine the effects of each element on hydrogenation.

Table 10: Reactant effects on the conversion of alcohols to alkanes

Reactant Acid Catalyst H2 Product Yield (%)

2-hexanol HI None Yes Hexane/hexenes 21.4

3-iodohexane 53.8

a3-hexanol HI None None Hexane/hexenes 5.4

3-iodohexane 94.6

2-hexanol None None Yes unreacted N/A

3-hexanol None RhCl3 Yes unreacted N/A

*In all of the experiments, 1 mL of toluene lined the inside of both the bomb and glass liner. The bombs were filled with 500 psi H2 and 500 psi Ar. In a, the bomb was not filled with H2. The bombs were placed in an oil bath overnight (12 hours) at 100°C. *Conversion based on gas chromatography.

When the reaction was run without the catalyst and without the catalyst and hydrogen gas, a small amount of hexane/hexene isomers were still produced in each case. However, when the reaction was run without the acid and the catalyst, the alcohol remained unreacted. In the presence of just the catalyst and hydrogen gas, the solvent was hydrogenated. All four cases, however, indicated that the presence of hydroiodic acid was necessary for the hydrogenation of the alcohol.

3.5 Additional Analyses

In an attempt to increase the generation of hexanes/hexenes from our system, we performed a few experiments that involved increasing the iodide concentration of the solution to see if the hydrogenation was dependent on the amount of iodide in the system.

Table 11: Effect of iodide in the conversion of alcohols to alkanes

Reactant Acid Catalyst H2 Product Yield (%)

3-hexanol HI RhCl3 500 psi Hexane/hexenes 9.6

3-iodohexane 90.4

*In the experiment, 1 mL of toluene lined the inside of both the bomb and glass liner. The bomb was filled with 500 psi H2 and 500 psi Ar. The bomb was placed in an oil bath overnight (12 hours) at 100°C. *Conversion based on gas chromatography.

With the addition of sodium iodide to the reaction mixture, the yield of hydrogenated products remained low; the sodium iodide appeared to have little to no effect.

Chapter 4

Conclusions

With the results tabulated above, the hydrogenation of alcohols was successful in very small yield. By changing the substrate, catalyst, and solvent conditions, the results did not appear to vary widely, and selective deoxygenation was not perceived. In future work, studies could be done computationally and experimentally on the activity of RhCl3. For instance, is there complexation with this catalyst that may hinder the hydrogenation of the iodoalkane?

Perhaps a stable complex is being formed in our hydrogenation attempts. Additionally, is there even a need for a catalyst? When we tested the necessity of reagents, it appeared that the reaction would only proceed with hydroiodic acid. In this case, either an acid or the presence of iodine is a necessity. Further studies on the presence of iodine, perhaps with iodine salts and no acid, would help to resolve these questions.

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Appendix: Spectral Data

Mass Spectrum: 2-iodohexane

Mass Spectrum: 3-iodohexane

Mass Spectrum: 1,4-diiodobutane

Mass Spectrum: 1,3-diiodopropane

Mass Spectrum: 1,5-diiodopentane

Mass Spectrum: 1-iodohexane

Mass Spectrum: 1,6-diiodohexane