Solvolysis of Benzylamine by Ethanol

Indian Journal of Chemical Technology Vol. 3, July 1996, pp. 207-211

Solvolysis of benzylamine by ethanol

DibakarChandraDeka

DepartmentofChemistry,GauhatiUniversity,Guwahati781 014, India

Received18July1995;accepted31January1996 Thermodynamic feasibilityof solvolysisof benzylamine by ethanol has been examined theoretically. Calculation shows that solvolysisof benzylamine by ethanol to produce benzylethylether should not be possible thermodYllamically,but solvolysisof N-ethylbenzylaminemay be possible at high temperatures. This theoretical prediction has been substantiated by carrying out experiments on solvolysisof benzyla• mine by ethanol under different reaction conditions. Under optimum reaction condition 53 mol % of benzylethylether can be obtained at 507 K under reaction pressure of about 9.4 MPa. Solvolysis of benzylamine by ethanol occurs via intermediate formation of N-ethylbenzylamine.A reaction mechan• ismhas been suggested.

In an earlier paper! the solvolysis of benzylamine Thermodynamic calculation shows that reaction (BA) by methanol to yield benzylmethylether has (1) has no thermodynamic feasibility but reaction been reported. From the experimental results in (2) may be feasible at high temperature (Tables 1 that report, it appears that solvolysis .of BA is and 2). mostly the result of direct action of methanol on The process described in this report can be BA. In contrast, the solvolysis of BA by ethanol used for the manufacture of BEE which has got follows a different route in the sense that the final important applications in organic synthesis and as product· benzylethylether (BEE) appears to be the a flavouring agent2• result of the action of ethanol on N-ethylbenzyla• mine (EBA) not on BA. An analysis of the exper• Thermodynamic Calculation imental results obtained under different sets of Standard free energy change (~G') at 298 K conditions shows that BEE must have come from has been calculated by using the relation solvolysis ofEBA by ethanol (Eq. (2)). . .. (3)

PhCH2NH2 + EtOH -. PhCH20Et + NH3 ••• (1) where ~Ho and ~So are the standard enthalpy PhCH2NHEt + EtOH -. PhCH20Et + EtNH2 change and standard entropy change of the reac• ... (2) tion respectively. The standard heats of formation

0.2044.3495.1535.9483504004505005506.7487.5606000.2248.39710.1510.1970.1910.1867000.2120.1753.03995.06657.599810.13315.19954.6700.0941:1821.4202.0852.5653.2323.813'0.1860.1670.1391.013330.3990.04220.2660.0520.0770.061 0.1970.2441.0001.059 3.4950.1013298 p Table I-Thermodynamics of reaction (1)" KO Kp Ky L\G', kJ Temperature,Pressure, K MPa

Free energy changes and equilibrium constants of the reaction at various temperatures and a pressure of 0.10133 MPa and eq• uilibrium constants at various pressures for a constant temperature of 500 K. Kp = K~I Ky, where K~ is the equilibrium constant at 0.10133 MPa and Kp is the equilibrium constant for different pressures at constant temperature. Ky= YBEE'YNH/YB~'YEIOH Y =flp, where fis the fugacity ofthe gas and Y is the fugacity coefficient of the gas. 208 INDIAN 1. CHEM. TECHNOL., JULY 1996

0.0330.0025506007000.00720.65020.52020.38620.26020.13919.9343504004505000.0040.0010.0120.01820.775 20.8840.000298 Table 2- Thermodynamics of reaction (2)"

Ml,kJK~, Temperature, K

1.3771.4540.0040.0030.0030.0030.0030.0032.2020.0070.005 1.000 p Pressure,2.3232.4172.5122.014f,5790.0057.599810.13315.199520.26630.3991.01333.03995.0665 MPa 0.1013 K "K;. YB~~'Y~\NH/ Y~B\' J"'\OH' Rest is same as in Table 1. K,. =

65.79R5.RI34.01- pressuremol11.676.'\.'\0.740..'\2Tarry45.46DEBA9.402R.'\7.'\117.129\Maximumtrace2690.032.7660.6273.602.7393.52O.9R69.51EBA51.01I7.R93.621O.R96.510.14B.materials1.7R2.74g20.19Irace4.76-BEE ..'\3.'\6.14reaction-% ale.TolueneUnreactedfor Mol per centTable of BA3- EffectconvertedBA of reaction to temperature"BA accounted MPa temperature.4R7525507K 407 Reaction

"Benzylamine 0.1 mol \ Hl.l) mL), ethanol 1.0 mol (58.5 mL), cone. HCI 0.1 mol (8.8 mL), mol ratio of ethanol to SA 10:1, mol ratio of BA to acid I: I, initial N ,-pressure 1.4793 MPa, residence period 2 h, release temp. was room temperature.

and entropies for ethanol and ammonia are avail• been determined by .the method described by able in literature3 but those of BA, BEE, EBA DodgeS. The fugacity coefficients (f/p) of the and ethyl amine being nonavailable, have been cal• reactants and products have been calculated from culated by the group contribution method deve• the relation9 loped by Benson et al..J5 !:iG' values at higher temperatures have been calculated by the rela• ... (7) tionships lnp=O1 (1)(0)lnp + OJ (1)(1)lnp /:i.G'= !:iHo- !:iaT In T - + /:i.bT2 - t /:i.cT3 + IT ... (4) and

!:iHo = !:iHo+ !:iaT + 1!:ibT2 +1~rcT3 ... (5) deviation functions of the Lee-Kesler fugacity pressure ratio and OJ is Pitzer's acentric factor. The virial coefficients a, b, and c for ammonia, The acentric factors of ethanol, ammonia and ethanol and ethylamine are available in literature6 ethyl amine are available in literature6 and those of but those of BA, BEE and EBA have been calcu• BA, EBA and BEE have been calculated10•11• As lated by the group contribution method of Rihani the values of critical temperature and critical and Doraiswami7. Integration constants and I pressure are necessary to find out the fugacity co• ~Ho have been calculated by putting the values of efficients of the compounds at higher pressures ~G' and /:i.W at 298 K inEqs (4) and (5). these values for BA, EBA and BEE have been The' equilibrium constants at atmospheric pres• calculated using the equation of L¥dersen 12. sure and various temperatures have been calculat• ed by the relation Standard"enthalpies of reactions, ~H~(298)' have been calculated from enthalpies of formation of

~G'= - RTln KOp ••• (6) reactants and products by the following relation: The effect of pressure on the equilibrium constant !:iH~(298)= l:!:iH~(298)(products) at the optimum temperature 507 K (Table 3) has -l:!:iH~(2yxlreactants)

I "I I Ii

"I 1'1'1 DEKA: SOLVOLYSIS OF BENZYLAMINE BY ETHANOL 209

Enthalpy of formation, ~ff'f(Z98)' for product and SE 30, Carbowax 20M and Apiezon L (all the reactant molecules are either available in litera• columns prepared by Nucon Engineers, India) in ture or calculated. a Gas-Chromatograph Aimil-Nucon Series 5700 Experimental Procedure supplied by Nucon Engineers, India. FID was A high-pressure rocking autoclave (High Pres• used. The best and the desired complete peak resolution was obtained with SE 30 under tem• sure Equipment Co., USA) of 300 mL capacity at 298 K and atmospheric pressure having an angu• perature programming from 60 to 220°C at a rate lar play of 15° with 30 oscillations/min was used. of 6°C min - I. Identification of BA, benzyl alcohol The autoclave is electrically heated externally and and toluene were easily done by comparing their retention time in GLC with those of authentic controlled by means of a sunvic thermoregulator. Benzylamine (> 99%) (Merck-Schuchardt, Ger• samples using three different columns already many), dehydrated ethanol (Bengal Chemicals and mentioned. As the authentic sample was not avail• Pharmaceuticals Ltd, India), hydrochloric acid ahle EBA, DEBA and BEE were isolated from (11.4 N) (Basic and Synthetic Chemicals (P) Ltd, the product mixture, and then identified hy IH India) were used throughout the investigation NMR, boiling point and refractive index measure• without further treatment. ment and preparing a suitable derivative. Calculated volume of BA and ethanol were in• Results and Discussion troduced into a glass liner and was placed in an ice-bath to lower the temperature and then ice• Effecl of reac/ion lemperalure-For solvolysis of cold and calculated amount of concentrated acid BA hy ethanol large excess of ethanol should he was poured slowly into it. The liner was placed present in the reaction system otherwise N• into the autoclave and it was then purged with ni• ethylation of BA is the major reaction I.'. Effect of trogen to avoid interference of oxygen at high temperature has heen studied with EtOH to BA mol ratio of 10:1. Tahle 3 shows that maximum reaction temperature. The glass liner was used to minimise the corrosion ins.ide the autoclave. After cleavage of BA occurs at 507 K. Below this tem• the reactor was loaded with the reaction mixture, perature EBA is the major product. This implies desired nitrogen pressure was applied and the au• that lower temperature favours the N-ethylation toclave was heated slowly to desired temperature process (reaction (8)) whereas higher temperature in about one hour. The autoclave was maintained favours the solvolytic process (reactions (I) and at the desired temperature for the specified time (2)). period and made rocking all the time. At the end PhCHzNHz + EtOH -+ PhCH2NHEt + H20 ... (8) of the time period, the autoclave was left to be . cooled down to room temperature. The same conclusion can also he drawn from the The liquid product was made strongly alkaline standard enthalpy values for these reactions. Cal• with sodiUlll. hy.9roxide solution' to liberate the culated standard enthalpies [~HOr,2l)xJ of reactions amines and -was extracted with diethylether. The (1), (2) and (8) are -1.51, + 21.43 and - 30.31 ether extract was distilled and the distillate was kJ respectively. These values show that reaction analysed by GLC. The tarry product, if formed, (8) is more exothermic than reaction (I) whereas was left as residue. GLC analysis was done using reaction (2) is endothermic. So reaction (2) should

96.8486.6392.84R5.7177.29 pressure9.40289.402853.459.402849.8723.941.129.402850.XO9.402851.0I9.402834.4054.881.494.751.32molTolueneTarryUnreacted12.690.504.1\116.7497.00reaction72.641.29little0.335.414.587.120.9290.51EBADEBAB.ale.3.0592.06617.R92.766O.R9Maximum18.190.867.65-1.5401.2539.51materialsg-17334.44-BEE- %for Mol per cent ofTable BA 4converted - EffectBA of to residence period"BA accounted MPa period1.51.00.52.02.5h , "Real:lioll lell1perature1b~est0 'is same as in Table 3 Residence 210 INDIAN 1. CHEM. TECHNOL., JULY 1996

be favoured by higher temperature. Above 507 K 507 K and then heating was stopped. It can be toluene becomes the major product due to ther• seen from Table 4 that EBA is the major product mal decomposition of BA and/or its reaction pro• up to a residence period of 0.5 h whereas BEE ducts. Similarly formation of small amount of becomes the major product after 1.5 h. This benzyl alcohol (B.alc.)can be explained by hydro• clearly indicates that solvolysis_of BA by EtOH lytic cleavage of BA and/or its derivatives by occurs in two steps-first step being the forma• H20 added in the form of concentrated hydroch• tion of EBA (reaction (8)) and second step being loric acid. the actual cleavage (reaction (2)). From these find• Effect of residence period- Effects of residence ings it can also be concluded that N-ethylation of period has been studied at 507 K with ethanol to BA (reaction (8)) is kinetically controlled reaction BA mol ratio of 10:1. The autoclave was slowly yielding the kinetically controlled product, EBA heated up to this temperature in about 1 hand (!:!.If'c(298) = + 64.517 kJ mol-I) whereas cleavage then maintained at this temperature for the speci• of EBA (reaction (2)) is thermodynamically con• fied time period (Table 4). In case of zero resid• trolled giving the thermodynamically more stable ence period, the autoclave was brought just to product, BEE (!:!.f--rr.(298) = -102.842 kJ mol-I).

Table 5-Effect of acid concentration"'

Amount Mol ratio Maximum Mol per cent of BA converted to BA Tarry ofHCI ofBA to reaction accounted materials mol acid pressure BEE EBA DEBA B. ale. Toluene Unreacted for g MPa BA mol % 92.840.322.29- 0 9.402853.458.231582.7985.403\.181:012.691.3:18.507185.068.0088.900.27250.802.2323.5322.06618.190.867.65-0.42trace26.141.021.861.080.7410.3342.392:18.43821:1-- 0.0750.050.10

"Residence period 1.5 h, rest is same as in Table 4

Table 6-Effect of mol ratio of ethanol to benzylamine" 90.6897.2596.7086.1811.26-BEE Mol ratio8.644949.3333.84\.138.231538.0336.410.97mol9.058333.4240.409.0583pressureTarry9.4.02810.964.31 Maximum2.69752.79EBADEBAB.alc.TolueneUnreacted2.0662.1051.3051.866-9.615.3110.87materials"53.4518.190.867.6512.6949.0730.411.591.10tracegreaction-%for 92.84 Mol per cent of BA convertedBA to BA accounted MPa of ethanol10:114:112:18:1toBA 6:1

"Cone. HCl 0.1 mol (8.8 mL), mol ratio of BA to acid 1:I,rest is same as in Table 5 .

80.4792.8481.5684.19 MaximumpressuremolTa.rryUnreacted12.503351.0014.294351.8710.590.786.6810.5544.462.4422.6097.6512.69EBADEBA7.0011.552.5812.0660.860.8011.2115.64B.reaction0.847.1416.11materials9.402853.4518.198.0248g-BEE %ale.Toluenefor Mol per centTable of 7BA - Effect convertedBA of nitrogen to pressure"BA accounted MPa pressure4.23532.85731.4793MPa 0.1013 Initial

"Ethanol 1.0 mol (58.5 mL), mol ratio of ethanol to BA 10:1, rest is same as in Table 6

I If ~ I; .II~ '11; 'I ' I I ~I DEKA: SOLVOLYSIS OF BENZYLAMINE BY ETHANOL 211

Maximum cleavage (53.45 mol%) of BA by eth• amount of BEE up to a pressure of about 9.40 anol is accomplished at 1.5 h under reaction pres• MPa. Higher reaction pressure than 9.40 MPa has sure of about 9.40 MPa. Beyond 1.5 h, there is little impact on the reaction. little change in the yield of BEE, but thermal de• composition reduces the yield of EBA leading to Acknowledgement the. formation of more amount of toluene and tar• The author is indebted to Profs D K Nandi and ry materials. S K Palit, Department of Chemistry, Indian Insti• Effect of acid concentration-Effect of acid tute of Technology, Kharagpur for laboratory faci• concentration has been studied from zero to a to• lities. tal 0.1 mol of Hel at 507 K with a residence pe• riod of 1.5 h. It is observed from the Table 5 that References nocIeavage occurs in absence of the acid catalyst. 1 Deka D C, Indian J Chem Technol, 2 (1995) 197. It has already been noted that cleavage must have 2 Sax N I, Lewis Sr R J, Hawley's condensed chemical dic• occurred via formation of EBA; the mechanism, tionary, 11th ed (CBS Publishers & Distributors, Delhi), therefore, may be given as follows: 1987. 3 Stull D R, Westrum Jf E F & Sinke G C, The Chemical PhCH,NHEt..~ H+ - PhCH,~- - N+H,Et- PhCH';- thermodynamics of organic compounds, (Wiley, New - - - - York), 1969. 4 Benson S W. Thermochemical kinetics, 2nd ed (Wiley. y--...... -+ + EtNHz PhCHJ+ H-O-Et-PhCHJ-O-Et New York), 1976, Chap 2. 5 Benson S W, Cruickshank F R, Golden D M, Haugen G - .. - rH R. O'Neal H E. Rodgers A S, Shaw R & Walsh R. Chem - PhCHz - 0- Et + H + Re~'.69 (1969) 279. 6 Reid R C, Prausnitz J M & Sherwood T K, The propert• Effect of mol ratio of ethanol to benzylamine• ies of gases and liquids, 3rd ed (McGraw-HilI, New York), The effect of amount of ethanol has been studied 1977. by gradually increasing the mol ratio of EtOH to 7 Rihani D N & Doraiswami L K, Ind Eng Chem Fundam, BA from 6:1 to 14:1. From Table 6 it can be seen 4(1965)17. 8 Dodge B F, Chemical engineering thermodynamics that maximum yield of cleavage product that is (McGraw-Hili, New York). 1944. BEE has been accomplished with the mol ratio 9 Lee B I & Kesler M G. AIChE J. 21 (1975) 510. 10:1. Above and below this ratio, the formation of 10 Pitzer K S. JAm Chem 501',77 (1955) 3427. BEE is decreased. II Pitzer K S, Lippmann D Z, Curl Jr R F, Huggins C M & Effect' of nitrogen pressure-The influence of Peterson DE. JAm Chem Soc, 77 (1955) 3433. 12 Lydersen A I. Estimation of critical properties of organic external pressure has been studied by increasing compounds, Univ Wisconsin Coli Eng, Exp Stn Rep 3, the pressure with nitrogen gas. The results (Table Madison. Wisconsin. April 1955. 7) show that increased pressure causes an in• 13 Deka DC, Nandi D K & Palit S K. J Chem Technol Bi~ creased amount of solvolysis yielding higher tee/mol, 41 (1988) 95.