Organotin compounds transesterification

Organotin compounds such as monobutyltin oxide, the main substance used, accounting for 70% of consumption, dibutyltin oxide, monooctyltin oxide, and dioctyltin oxide are used in certain esterification and transesterification reactions, at concentrations between 0.001% and 0.5% by weight. They are used in the production of substances such as phthalates, polyesters, alkyd resins, fatty acid esters, and adipates and in trans-esterifications. These substances are in turn used as plasticizers, synthetic lubricants, and coatings. Organo-tins are used as catalysts to reduce the formation of unwanted by-products and also provide the required colour properties (ETICA, 2002). 

In parallel with these developments, organotin compounds have found a variety of applications in industry, agriculture, and medicine, though in recent years these have been circumscribed by environmental considerations. In industry they are used for the stabilization of poly(vinyl chloride), the catalysis of the formation of the polyurethanes, and the cold vulcanisation of silicone polymers, and also as transesterification catalysts. 

Organotin compounds are used in many synthetic procedures as stoichiometric reagents (hydrostannolysis, hydrostannation, allylation, Stille coupling, Sn/Li transmetallation, transesterification, etc), and this presents the problem of removing the organotin residues from the required product. This is particularly important in the preparation of pharmaceuticals as these organotin compounds are to some degree toxic. 

Transesterification of an ester is commonly carried out by heating it with an excess of an alcohol in the presence of a strong acid catalyst such as toluene p-sulfonic acid. On the industrial scale, this presents problems of corrosion and of decomposition and colouration of the excess alcohol. Organotin compounds are alternative catalysts they can be used in small amounts (0.1-0.25%), they present no corrosion problem, and the excess of alcohol is not dehydrated or decolourised, and can be recirculated. 

In the presence of an organotin compound, these jS-hydroxyalkyl carbamates can be nsed as crosslinkers or to prepare polynrethane polyols by a transesterification reaction. ... 

PU was fully formed before initiation of the acrylic. In the present system, polyol concentration decreases as delay time increases. It is well-established (16) that organotin compounds are transesterification catalysts. Thus, it is suggested that, in the presence of the tin catalyst and during irradiation, transesterification between BMA and one or more of the OH groups in the polyols may lead to the formation of PU chains terminated with methacrylate moieties to provide grafting sites for BMA polymerization. 

Organotin catalysts have been tested as well with good results for the transesterification of oils. Unfortunately, these compounds are very soluble in fatty acid esters, complicating their separation and adding to environmental concerns. ... 

Since Pereyre and coworkers reported the catalytic activity of tributyltin alkoxide for transesterification reaction [87], organotin derivatives have been used for various kinds of organic transformations. Distannoxane compounds were found to play an important role in the reaction [88-90] and act as pure Lewis acid [91, 92]. Although the transesterification reactions proceeded by using low-molecular-weight catalyst in homogeneous medium, a serious drawback for the industrial processes is a removal of the toxic tin derivatives. In such cases the use of polymer-supported version... 

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