Esterification of Mixed Carboxylic-fatty Anhydrides Using Amberlyst-15 as Heterogeneous Catalyst.
The article deals with the use of mixed anhydrides for the synthesis of fatty esters. Both aliphatic and aromatic acids are involved, indicating different behaviors according to the chain length of the aliphatic acid. We describe a novel and efficient method for the synthesis of fatty esters by the esterification reaction of primary, secondary and tertiary alcohols with mixed carboxylic-palmitic anhydrides using resin Amberlyst-15 as heterogeneous acid catalyst. Influence of various reaction parameters such as molar ratio (anhydride/alcohol), catalyst amount, type of alcohol and type of mixed anhydride were studied to optimize the conditions for maximum yield. Among tested anhydrides we quote mainly the 4-chlorobenzoic palmitic anhydride because it was both reactive and selective for the preparation of palmitic acid ester. This anhydride gave a good yield of palmitic ester.
Synthesis of Sucrose Fatty Acid Esters by Using Mixed Carboxylic-fatty Anhydrides.
Fatty acid sugar esters are non-ionic surfactant active agents with excellent performance and many uses. This work is devoted to the synthesis of sugar esters by the esterification reaction of sugar with mixed carboxylicpalmitic anhydrides using resin Amberlyst-15 as heterogeneous acid catalyst. These anhydrides should be stable and react as acylating agents. Influence of different reaction parameters, such as the molar ratio (sucrose/anhydride), the type of solvent and the reaction time on the yield of the esterification reaction were studied. The esterification reaction of sucrose with mixed palmitic benzoic anhydride leads to a mixture of sucrose esters of palmitic acid with a good percentage of conversion. The mixed anhydride was both reactive and selective for the preparation of fatty acid ester.
New method for analysis of enzymatic reactions: Thermolysin-catalyzed synthesis of aspartame precursor
Aspartame is an artificial sweetener which is 200 times sweeter than sucrose. A precursor of aspartame, N-(benzyloxycarbonyl)-l-aspartyl-l-phenylalanine methyl ester (Z-APM) was synthesized and hydrolyzed with thermolysin in an aqueous monophasic system. Graphical plotting methods and/or nonlinear regression have been used to analyze enzymatic reactions because of the nonlinearity of enzymatic rate equations. There are, however, problems: the former require accurate measurement of the initial reaction rate and the latter gives no analytical information. The authors proposed a method to solve the nonlinear enzymatic rate equations with respect to the concentration of a product with the Taylor expansion, especially for the reversible Theorell-Chance mechanism (Murakami, Y., Hirata, M., and Hirata, A., J. Ferment. Bioeng., 82, 246–252, 1996). This solution, however, is complex for practical use. In this paper, a simpler solution to explain the thermolysin-catalyzed synthesis of Z-APM is obtained. New methods to determine the kinetic parameters, especially for the reversible Theorell-Chance mechanism, based on the approximated solution are proposed. The results calculated using the obtained kinetic parameters can satisfactorily explain the experimental results, which demonstrates the effectiveness of the proposed analysis. We must know the relation between the concentrations of substrates and a product, and accurately evaluate of the result obtained using Taylor expansion when we determine the kinetic parameters using our newly developed methods. The methods to determine the kinetic parameters of the reversible Theorell-Chance mechanism described in this paper is, however, expected to be applied to general enzymatic reactions.