An overview is given of newly developed Lewis or Bronsted acid and base catalysts for esterification, transesterification and ester interchange reactions. The most relevant applications of these catalysts and reactions in the domain of renewable resources, in particular, oils and fats, are discussed.

Esterification and transesterification of renewable chemicals

Lipases are a group of enzymes naturally endowed with the property of performing reactions in aqueous as well as organic solvents. The esterification reactions using lipase(s) could be performed in water-restricted organic media as organic solvent(s) not only improve(s) the solubility of substrate and reactant in reaction mixture but also permit(s) the reaction in the reverse direction, and often it is easy to recover the product in organic phase in two-phase equilibrium systems. The use of organic solvent tolerant lipase in organic media has exhibited many advantages: increased activity and stability, regiospecificity and stereoselectivity, higher solubility of substrate, ease of products recovery, and ability to shift the reaction equilibrium toward synthetic direction. Therefore the search for organic solvent tolerant enzymes has been an extensive area of research. A variety of fatty acid esters are now being produced commercially using immobilized lipase in nonaqueous solvents. This review describes the organic tolerance and industrial application of lipases. The main emphasis is to study the nature of organic solvent tolerant lipases. Also, the potential industrial applications that make lipases the biocatalysts of choice for the present and future have been presented.

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Organic solvent tolerant lipases and applications.

Glycerol is the main co-product of the vegetable oils industry (especially biodiesel). With the rapid developement of oleochemistry, the production of glycerol is rapidly increasing and chemists are trying to find new applications of glycerol to encourage a better industrial the developement of vegetable oils. In this review, attention is focused on the selective use of glycerol as a safe of organic building block for organic chemistry. An overview is given of the different heterogeneous catalytic routes developed by chemists for the successful and evironmentally friedly use fo glycerol in sustainable organic chemistry. In particular, the effects of differents catalyst structural parameters are discussed to clearly highlight how catalysis can help organic chemists to overcome the drawbacks stemming from the use of glycerol as a safe organic building block. it is shown that hetorogerieous catalysis offers efficient routes for bypassing the traditional use of higly toxic and expensive epichlorohydrin, 3-chloro-1,2-propanediol, or glycerol, which are usually used as a gyceryl donor in organic chemistry.

Rational Design of Solid Catalysts for the Selective Use of Glycerol as a Natural Organic Building Block

Lipase mediated synthesis of sugar fatty acid esters

http://digital.csic.es/bitstream/10261/17327/1/SUCROSE-ESTERS-digitalCSIC.pdf

Enzymatic acylation of di- and trisaccharides with fatty acids: choosing the appropriate enzyme, support and solvent

Selective production of emulsifiers from glucose and fatty acids has been achieved using an immobilized Candida antarctica lipase. Optimization of process selectivity considers the solubilities of the sugar and its monoesters in acetone at different temperatures, the percentage of this organic solvent in the reaction mixture, and the reaction temperature. The solvent (acetone) is both easily eliminated and accepted by the European Community for use in the manufacture of foods and/or food additives. Different fatty acids with a longer length chain than that of caprylic acid may be employed. For saturated fatty acids longer than lauric acid, continuous precipitation of the monoester as it is formed at 40 degrees C permits nearly complete conversion (98%) of glucose to the monoester within 2-3 days. The procedure does not require total dissolution of the sugar, and precipitation of the monoester permits selective conversion of charges of glucose higher than 100 mg/mL solvent. A scaleup of the process under the optimum conditions gives high yields of 6-O-lauroyl glucose, which may be readily prepared on a gram scale. Copyright 1998 John Wiley & Sons, Inc.

Quantitative enzymatic production of 6-O-acylglucose esters

A simple kinetic model derived from a ping-pong bi-bi mechanism is proposed to describe the lipase-catalyzed esterification of glucose with fatty acids. The mathematical expressions derived from this model have been tested using several sets of data obtained from reactions carried out under different reaction conditions. The predicted values provide very good fits of the experimental data for temperatures from 30 to 60°C, enzyme loadings from 90 to 180 mg, and fatty acid concentrations from 0.33M to 1M. Experiments conducted at different temperatures permit one to estimate an activation energy of ∼12 kcal/mol for the rate-limiting step of the reaction (formation of the acyl-enzyme complex). The model also considers the kinetics of inactivation of the biocatalyst during the reaction. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 73: 104–110, 2001.

Kinetics of the lipase-catalyzed synthesis of glucose esters in acetone.

Quantitative enzymatic production of 1,6-diacyl fructofuranoses

The present paper provides a general overview of the factors involved in both the kinetics and the selectivity of partial acylation reactions of polyols (sugars). Different kinetic strategies for maximum production of intermediate esters of various polyols and monosaccharides are reported and discussed. Physicochemical requirements for obtaining maximum selectivities and complementary strategies for reducing reaction times are discussed. The reactions studied include glycerol, glucose, fructose, mannose, sorbitol and an alkyl glucoside as precursors. The high selectivity towards the monoglyceride in the presence and absence of a solvent has been attributed to a combination of the precipitation of the desired ester, use of glycerol in excess and the relatively low solubility of the fatty acid in the system. Unlike the reaction in the presence of a solvent, the reaction in a solvent-free medium produces the diester first. The monoester only accumulates in the medium as a consequence of disproportionation and glycerolysis reactions of the diester formed earlier. Selective esterification of solid sugars (polyols) which have an intermediate solubility in acetone is favored at low temperatures at which a sufficient amount of polyol dissolves and concurrent precipitation of the desired product can be achieved. By contrast, use of elevated temperatures is more appropriate for selective partial esterification of polyols, which are the most soluble in the solvent employed. Polyols (sugars) which are the less soluble into the liquid reaction phase cannot be easily esterified. Diffusional limitations on the rate of dissolution of the solid precursor can be minimized by increasing the surface area of the solid polyol.

Emulsifiers from solid and liquid polyols : different strategies for obtaining optimum conversions and selectivities

The enzymatic synthesis of several sorbitol diesters whose HLB values are similar to those of monoglycerides (the largest single type of food-grade emulsifiers) has been studied. The procedure is carried out by the simple addition of the polyol to a solution of the fatty acid and is based on continuous precipitation of the diester formed at a low temperature. A solvent of relatively low toxicity (acetone) was used. Pure fatty acids of different chain lengths (lauric and caprylic acids) were employed. The procedure was also tested using the acids obtained from total hydrolysis of olive oil, as an example of industrial feedstocks of fatty acids.



This synthesis strategy gave complete conversion of sorbitol and >95% yields of the corresponding 1,6-diesters. In addition, a strategy to reduce the reaction time is reported. The enzymatic procedure permits minimization of the solvent/sugar ratio because it does not require complete dissolution of the sugar in the organic solvent. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 53–60, 1998.

Jose A. Arcos

Papers

Quantitative enzymatic production of 6-O-acylglucose esters

Kinetics of the lipase-catalyzed synthesis of glucose esters in acetone.

Quantitative enzymatic production of 1,6-diacyl fructofuranoses

Emulsifiers from solid and liquid polyols : different strategies for obtaining optimum conversions and selectivities

Quantitative enzymatic production of 1,6‐diacyl sorbitol esters