Transesterification basic catalysis

For these last reactions, acid catalysis gives a better conversion rate than basic catalysis, which promotes transesterification and the formation of side products. The reaction of epoxidized rapeseed methyl esters with heptanol and PTSA (100°C, 12 h, 1 bar) led to fatty ethers with an oxirane value of 0.0 and a saponification number of 130 methyl heptyloxy-hydroxystearate was the main reaction product. 

An initial esterification reaction occurs between an excess of ethylene glycol with dimethylterephthalate under basic catalysis at 150 °C. Removal of methanol by distillation drives the formation of bishydroxyethyl terephthalate, which can be considered an monomer. A secondary transesterification step performed at 280 °C drives polymer formation via ester exchange, which is pushed toward high molecular weight by removal of ethylene glycol via distillation. 

Acid Catalysis Add catalysis transesterification includes the combination of three reversible reactions (Fig. 22.4). The high conversion of the acid catalyzed transesterification procedure is due to the capacity to transesterify fatty acids and fatty acid salts present in the system. The acids employed are HCl, H SO, BFj, and sulfonic acids [15, 22-24]. Generally, acid catdysis is many times slower than basic catalysis. The rate of the biodiesel production reaction... 

In this communication a study of the catalytic behavior of the immobilized Rhizomucor miehei lipase in the transesterification reaction to biodiesel production has been reported. The main drawbacks associated to the current biodiesel production by basic homogeneous catalysis could be overcome by using immobilized lipases. Immobilization by adsorption and entrapment have been used as methods to prepare the heterogeneous biocatalyst. Zeolites and related materials have been used as inorganic lipase supports. To promote the enzyme adsorption, the surface of the supports have been functionalized by synthesis procedures or by post-treatments. While, the enzyme entrapping procedure has been carried out by sol-gel method in order to obtain the biocatalyst protected by a mesoporous matrix and to reduce its leaching after several catalytic uses. 

Fatty acid esters of sugars are also very important biodegradable and biocompatible surfactants that are prepared either by transesterification of methyl ester with sugar on basic catalysts or by esterification of fatty acids with sugar on acidic catalysts. Liquid acids and bases have been replaced by enzymatic catalysis with lipase, giving a higher yield of monoester [43, 44], but solid catalysts have not been used extensively so far. 

Kantam, M.L. and Sreekanth, R (2001) Transesterification of P-keto esters catalysed hy basic porous material. Catalysis Letters, 77, 241-243. 

An alcoholysis reaction, in which an ester reacts with an alcohol to form a new ester and a new alcohol, is called a transesterification reaction. An example of this alcoholysis reaction is given in Figure 19.5. Transesteiification reactions are slow reactions because alcohols are poor nucleophiles and esters have very basic leaving groups hence, they occur under support of acid catalysis (Bmice, 2004). Similar to esterifications, transesteiification reactions are equihbiium reactions (Hoydonckx, Vos, Chavan, Jacobs, 2004) hence, an excess of alcohol and a direct extraction of products is needed to shift the equilibrium. 

Antunes, W. M., C. de Oliveira Veloso, and C. A. Henriques. 2008. Transesterification of Soybean Oil with Methanol Catalyzed by Basic Solids. Catalysis Today 133-135 548-554. 

In the case of base-catalyzed reactions the substrate comes into contact with either HO or any other highly electron-rich catalyst (e.g., alcoholates, strongly basic amines, metal alkyls). Again, the substrate is activated, typically via the intermediate formation of carbanion species. A technically important example of base catalysis is the transesterification of natural oils to fatty acid methyl esters (FAME, better known as biodiesel ), a process typically catalyzed by methanolate salts. 

The role of basicity in catalysis has been less studied than acidity. However, a demand for a deeper knowledge is now required in the field of catalysis, as basic catalysts begin to play an important role in many reactions (e.g., aldolization, transesterification, Michael and Knoevenagel reactions, etc.). A comprehensive review about basicity and the basic properties of zeoHtes has been given by Barthomeuf [59]. 

The easiest acrylates to produce industrially are the epoxy acrylates their preparation (see Scheme 16.28) starts with an epoxide-functional resin (see Section 16.4.2). In principle any epoxide-functional material can be chosen. In this reaction (meth)acrylic resin is added to the epoxide at elevated temperatures, (around 90-130°C). The (meth)acrylic acid adds to the epoxide in a ring-opening reaction resulting in an ester alcohol group. Basically this reaction is similar to the reactions used in the preparation of epoxy resins (see Section 16.4). The reactions can be either acid- or base-catalyzed base catalysis is the more frequently used, since it limits the number of possible side reactions (for instance, transesterifications). Although these reactions can be carried out in solvent, industrially they are most frequently performed in bulk. Generally these preparations are performed in a batch-type process. 

One of the chemical treatments of triglycerides of different vegetable and algae oils and animal fats produces the biofuel known as biodiesel. This development was based on the knowledge of the catalytic processes as well as on the evolution of instrumental techniques, which permitted the elucidation of the esterification mechanisms and consequently, the study of transesterification. Homogeneous and heterogeneous processes were studied focusing on basic, acid, and enzymatic catalysis [13, 15, 16, 22-36], Usually,... 

Manrfquez-Ramfrez, M., et al, 2013. Advances in the transesterification of triglycerides to biodiesel using MgO—NaOH, MgO—KOH and MgO—Ce02 as solid basic catalysts. Catalysis Today 212, 23—30. Available at http //www.sciencedirect.com/science/article/ pii/S0920586112007833 (accessed 27.04.15.). 

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