Biocatalytic Synthesis of Diethanolamide Surfactants Under Mild Reaction Conditions
Galilee Uy Semblante1, Modesto Tan Chua2, and Soma Chakraborty*1
1Chemistry Department, School of Science and Engineering, Ateneo de Manila University, Loyola Schools, Loyola Heights, Quezon City, Philippines
2Philippine Institute of Pure and Applied Chemistry, Loyolo Schools, Loyola Heights, Quezon City, Philippines
Synthesis of fatty acid diethanolamide was carried out by the condensation of diethanolamine with lauric acid, decanoic acid and octanoic acid in the presence of Novozym 435. The influence of solvent, time, temperature and agitation on the reaction rate was studied. Formation of lauroyl diethanolamide was complete in 6h in acetonitrile at 50° C whereas in toluene the reaction was not complete in 6h. Increase of reaction temperature from 50° C to 70° C increased the reaction rate. Proper agitation of the reaction mixture enhanced the reaction rate. Reaction in solution appeared to be more efficient than the reaction in solvent free system. The surface active property of the fatty acid amides was studied by determining their critical micelles concentration. The critical micelle concentration of lauroyl diethanolamide, decanoyl diethanolamide and octanoyl diethanolamide were found to be 0.63mM, 1.10mM, 1.45mM respectively in deionized water. Micelles of lauroyl diethanolamide were less than 1µm in size.
Fatty acid amides are the surfactants generally derived from the condensation of fatty acids and amines. They are considered as nonionic surfactants of considerable interest and economical importance. The surface active properties of fatty acid amides makes them an essential ingredient of several formulations such as lubricants, dispersants, detergents, shampoos, antistatic agents, antimicrobial agents, dye corrosion inhibitors, antifoaming agents, and pulping aids (Schmitt 2001; Gunstone 1996; Visek 1990). Fatty acid amides are favored in these applications because of their emollient and lubricating properties, ability to stabilize emulsions, and low reactivity (Johansson 2003). Various approaches for the synthesis of fatty acid amide synthesis have been cited in literature. One route involves the reaction of fatty acid and ammonia under pressure at elevated temperature (Roe et al. 1952). There is also a report of producing fatty acid amide by reacting fatty acid with amino alcohols, catalyzed by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline in ethanol reflux (Baek 2006). Another industrial synthesis procedure involves reaction of excess diethanol amine with long chain monocarboxylic acid ester in the presence of sodium methoxide under a slight vacuum (US patent 1994). Apart from utilization of toxic chemical catalysts, these techniques also suffer from the drawback that the product contains several impurities. As an example, in the process of synthesis of diethanolamide from diethanolamine contaminants in the form of N,N’-bis(2-hydroxyethyl) piperazine formed by self-condensation of diethanolamine at elevated temperatures, other impurities include monoesteramines, diesteramines, monoesteramides and diesteramides (O’Connell 1977). Moreover, these high temperature reactions cannot be considered to be highly energy efficient.
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