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Preparation and purification of wax esters — A different approach
Chemistry and Physics of Lipids, 22 (1978) 83-86 © Elsevier/North-HollandScientific Publishers Ltd.
L E T r E R TO THE EDITOR PREPARATION AND PURIFICATION OF WAX ESTERS - A DIFFERENT APPROACH
A.V. PRABHUDESAI and C.V. VISWANATHAN Department of Biochemistry, Maharashtra Association for the Cultivation of Science, Law College Road, Poona 411 004, India.
Received July 2nd, 1 9 7 7
accepted November 23rd, 1977
I. Introduction
A number of methods for chemical synthesis of wax-esters have been reported [1,2]. We report here a simple alternative method in which a fatty alcohol and a fatty acid dissolved in benzene are reacted in the presence of thionyl chloride, overnight at room temperature. Preparative isolation of gram quantities of waxesters, free of reactants is achieved by bulk adsorption of all the components of the reaction mixture on siLicic acid followed by preferential extraction of the desired product with the mixture of benzene : petroleum ether (1 : 1).
II. Procedure
Fatty alcohols - (hexadecanol and octadecanol); fatty acids, (dodecanoic, tetradecanoic, hexadecanoic and octadecanoic) and thionyl chloride, were purchased locally. Thin layer chromatographic (TLC) grade silicic acid was precipitated in the laboratory and washed free of acidity and chloride ion. (A ) Preparation o f a wax-ester
Octadecyl octadecanoate was prepared by reacting an equimolar mixture of octa decanol and octadecanoic acid (5 mmol each; i.e. 1.35 and 1.42 g, respectively) in 50 ml of dry benzene at 0°C in presence of I ml of thionyl chloride, the latter being added dropwise. The reaction mixture was kept overnight (about 16 hr) at room temperature (30-32°C) and then washed twice in a separating funnel with 50 ml of distilled water. The benzene layer was then dried over anhydrous sodium sulfate.
83
84
A. V. Prabhudesai, C. V. Viswanathan, Preparation and purification o f wax esters
(19) Isolation o f a w a x ester
25 g o f activated TLC grade silicic acid was added to the dried benzene layer which
-~SF
0~ -* Start
1
2
3
4
Fi~. 1. Relative chromato~aphic mobilities of rea~ants and the reaction product by TLC. Adsorbent: Silica gel Solwnt system: Benzene. Spot identification: (1) Reaction mixture; (2) Oetadecanoic acid; (3) Octadeeanol; (4) Octadecyl octadecanoate isolated by the adsorption technique using petxoleum ether benzene (1 : 1). Detection: Sprayed with 50% sulfuric acid and charred.
A. V. Prabhudesai, C. V. Viswanathati,Preparationand purification of wax esters
85
Table 1 Melting points,yields and R F values of synthetic wax esters Ester
Tetrfidecyl octadecanoate Hexadecyldode~noate
Hexadecyl tetradecanoate Hexadecyl hexadecanoate Hexadecyl octadecanoate Octadecyl dodeaenoate Octadecyl tetradecanoate Octadecyl hexadecanoate Octadecyloctadecanoate
Melting point in C
Yields %
Observed
Reported [21
Observed a Reported b [2]
41-41.5 48 52 56-56.5 47-48 51.5 -52 54-55 58.9-59
41.2-41.6 51.7-52 53.6-54 58.5-59 52-52.5 59.6-59.9 61.6-61.9
95 95 95 95 95 95 95 95
83 -
-
Rf Silica gel G/ Benzene -
0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
a Yield expressed on the corresponding fatty acid. b Yield expressed on tetradecanol. contained the wax.ester together with the unreacted fatty acid and fatty alcohol. This was stirred with a glass rod until a dry powder was obtained. The resulting powder was extracted thrice, each time with 75 ml o f a mixture o f petroleum ether (80-100°C) : benzene (1 : 1 by vol.). The pooled extracts were evaporated to dryness and the residue weighed (2.21 g, 85.3%). Its purity in relation to original reaction mixture is shown in fig. 1.
( C) Determination o f conversion efficiency The percent conversion efficiency o f the reaction to wax-ester was calculated on the basis o f fatty acid unconsumed by simple titration against 0.1 N sodium hydroxide solution, using phenolphthalein as an indicator. The m e t h o d r e p o r t e d in the present communication is an extension o f that used in the synthesis o f methyl esters o f amino acids [3] and long-chain fatty acid esters o f cholesterol [4]. The yields obtained in the present method were satisfactory (table 1). The synthetic wax-esters were characterized by determination o f thier melting points, chromatographic mobilities and infrared spectra (typical stretching vibrations o f R - C - O - R ' : - C = O : 1740 cm -1, R - C - O : 1245 cm -1 and - O - R ' : 1175 cm -1)
tl
O [1]. The intensities o f these absorption were strong, medium weak and medium strong respectively. A.V. PARABHUDESAI and C.V. VISWANATHAN
Maharashtra Association for the Cultivation o f Science, Poona 411 004, and Lipid
86
A. V. Prabhudesai, C. V. Viswanathan, Preparation and purification of wax esters
Research Laboratories, 8, 'A ', Indrayani Flats, Prabhat Road, Lane No. 15, Poona 411 004 (India)
Acknowledgement The authors are thankful to the Maharashtra Association for the Cultivation of Science, Poona 411 004, for providing laboratory facilities.
References [1] [2] [3] [4]
F. Phillips and C.V. Viswanathan, Lipids 2 (1967) 437 B.T.R. Iyengar and H. Sehlenk, Lipids 4 (1969) 28 M. Brenner and W. Huber, Helv. Chim. Aeta 36 (1953) 1109 A.V. Prabhudesai, Lipids 12 (1977) 242
L E T r E R TO THE EDITOR PREPARATION AND PURIFICATION OF WAX ESTERS - A DIFFERENT APPROACH
A.V. PRABHUDESAI and C.V. VISWANATHAN Department of Biochemistry, Maharashtra Association for the Cultivation of Science, Law College Road, Poona 411 004, India.
Received July 2nd, 1 9 7 7
accepted November 23rd, 1977
I. Introduction
A number of methods for chemical synthesis of wax-esters have been reported [1,2]. We report here a simple alternative method in which a fatty alcohol and a fatty acid dissolved in benzene are reacted in the presence of thionyl chloride, overnight at room temperature. Preparative isolation of gram quantities of waxesters, free of reactants is achieved by bulk adsorption of all the components of the reaction mixture on siLicic acid followed by preferential extraction of the desired product with the mixture of benzene : petroleum ether (1 : 1).
II. Procedure
Fatty alcohols - (hexadecanol and octadecanol); fatty acids, (dodecanoic, tetradecanoic, hexadecanoic and octadecanoic) and thionyl chloride, were purchased locally. Thin layer chromatographic (TLC) grade silicic acid was precipitated in the laboratory and washed free of acidity and chloride ion. (A ) Preparation o f a wax-ester
Octadecyl octadecanoate was prepared by reacting an equimolar mixture of octa decanol and octadecanoic acid (5 mmol each; i.e. 1.35 and 1.42 g, respectively) in 50 ml of dry benzene at 0°C in presence of I ml of thionyl chloride, the latter being added dropwise. The reaction mixture was kept overnight (about 16 hr) at room temperature (30-32°C) and then washed twice in a separating funnel with 50 ml of distilled water. The benzene layer was then dried over anhydrous sodium sulfate.
83
84
A. V. Prabhudesai, C. V. Viswanathan, Preparation and purification o f wax esters
(19) Isolation o f a w a x ester
25 g o f activated TLC grade silicic acid was added to the dried benzene layer which
-~SF
0~ -* Start
1
2
3
4
Fi~. 1. Relative chromato~aphic mobilities of rea~ants and the reaction product by TLC. Adsorbent: Silica gel Solwnt system: Benzene. Spot identification: (1) Reaction mixture; (2) Oetadecanoic acid; (3) Octadeeanol; (4) Octadecyl octadecanoate isolated by the adsorption technique using petxoleum ether benzene (1 : 1). Detection: Sprayed with 50% sulfuric acid and charred.
A. V. Prabhudesai, C. V. Viswanathati,Preparationand purification of wax esters
85
Table 1 Melting points,yields and R F values of synthetic wax esters Ester
Tetrfidecyl octadecanoate Hexadecyldode~noate
Hexadecyl tetradecanoate Hexadecyl hexadecanoate Hexadecyl octadecanoate Octadecyl dodeaenoate Octadecyl tetradecanoate Octadecyl hexadecanoate Octadecyloctadecanoate
Melting point in C
Yields %
Observed
Reported [21
Observed a Reported b [2]
41-41.5 48 52 56-56.5 47-48 51.5 -52 54-55 58.9-59
41.2-41.6 51.7-52 53.6-54 58.5-59 52-52.5 59.6-59.9 61.6-61.9
95 95 95 95 95 95 95 95
83 -
-
Rf Silica gel G/ Benzene -
0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
a Yield expressed on the corresponding fatty acid. b Yield expressed on tetradecanol. contained the wax.ester together with the unreacted fatty acid and fatty alcohol. This was stirred with a glass rod until a dry powder was obtained. The resulting powder was extracted thrice, each time with 75 ml o f a mixture o f petroleum ether (80-100°C) : benzene (1 : 1 by vol.). The pooled extracts were evaporated to dryness and the residue weighed (2.21 g, 85.3%). Its purity in relation to original reaction mixture is shown in fig. 1.
( C) Determination o f conversion efficiency The percent conversion efficiency o f the reaction to wax-ester was calculated on the basis o f fatty acid unconsumed by simple titration against 0.1 N sodium hydroxide solution, using phenolphthalein as an indicator. The m e t h o d r e p o r t e d in the present communication is an extension o f that used in the synthesis o f methyl esters o f amino acids [3] and long-chain fatty acid esters o f cholesterol [4]. The yields obtained in the present method were satisfactory (table 1). The synthetic wax-esters were characterized by determination o f thier melting points, chromatographic mobilities and infrared spectra (typical stretching vibrations o f R - C - O - R ' : - C = O : 1740 cm -1, R - C - O : 1245 cm -1 and - O - R ' : 1175 cm -1)
tl
O [1]. The intensities o f these absorption were strong, medium weak and medium strong respectively. A.V. PARABHUDESAI and C.V. VISWANATHAN
Maharashtra Association for the Cultivation o f Science, Poona 411 004, and Lipid
86
A. V. Prabhudesai, C. V. Viswanathan, Preparation and purification of wax esters
Research Laboratories, 8, 'A ', Indrayani Flats, Prabhat Road, Lane No. 15, Poona 411 004 (India)
Acknowledgement The authors are thankful to the Maharashtra Association for the Cultivation of Science, Poona 411 004, for providing laboratory facilities.
References [1] [2] [3] [4]
F. Phillips and C.V. Viswanathan, Lipids 2 (1967) 437 B.T.R. Iyengar and H. Sehlenk, Lipids 4 (1969) 28 M. Brenner and W. Huber, Helv. Chim. Aeta 36 (1953) 1109 A.V. Prabhudesai, Lipids 12 (1977) 242