Fischer-type esterification

In an ongoing project, we have set out to investigate the nature and extent of interactions exhibited by the ionic liquid constituents on various solutes. In particular, the Fischer-type esterification was chosen as a model reaction as its kinetics and thermodynamic equilibrium were assumed to be sensitive towards small changes in... 

Maybe one of the most important questions to be answered relates to the degree of dissociation of Brpnsted acids and bases in ionic liquids. Acids are ubiquitously used as catalysts to initiate reactions such as the Fischer-type esterification or ether formation from alcohols. 

Equilibrium reactions, such as the Fischer-type esterification of an alcohol and a carboxylic acid, are an interesting group of reactions to study in ionic liquids, as both kinetic and thermodynamic aspects of the reaction could be solvent dependent. 

Thiopeptide antibiotics are a class of highly modified macrocyclic sulfur-containing peptides, and nearly all the thiopeptide antibioties identified to date inhibit protein synthesis in bacteria. The Bohlmann-Rahtz pyridine synthesis is a useful methodology in the synthetic approach for thiopeptide antibiotics.For example, one-step Bohlmann-Rahtz assembly of 189 and 190 in the presence of ammonium acetate in acetic acid at reflux afforded the corresponding pyridine-thiazole cores of thiopeptide antibiotics 191 in 63% yield.The TBS protecting group was also replaced by an acetate, probably as a consequence of acid-promoted cleavage and consequent Fischer-type esterification of the liberated alcohol. 

Recent reviews (31-34,36,37,51) provide a comprehensive survey of the types of heterogeneous catalytic reactions investigated at supercritical conditions including alkylation, amination, cracking, disproportionation, esterification, Fischer-Tropsch synthesis, hydrogenation, isomerization, and oxidation. Table 2 summarizes reported investigations under these classes of reaction. Some of these examples are described here to show how to systematically exploit supercritical media in heterogeneous catalysis. 

The mechanism for the acid-catalyzed (sulfuric acid) Fischer esterification reaction below is addition, p.t., p.t., elimination write out the mechanism with all its steps. Remember to choose between the three types of additions, AdE2, AdN2, or AdgS, then choose between the three types of eliminations, El, E2, or ElcB. 

Colophony (rosin, pine rosin, wood rosin) is obtained from various species of pine tree. It has a complex chemical composition, of which about 90% is resin acids and the rest is corresponding esters, aldehydes and alcohols. Two main types of acids occur abietic acid with conjugated double bonds and pimaric acid with non-conjugated double bonds. Colophony is not used alone as a drying resin but is used to modify other resins, such as alkyds. Colophony is an important contact sensitizer, but the esterification of organic acids in colophony with alcohol groups in alkyd resins reduces its allergenicity. Rosin esters can be used in paints and varnishes (Mathias 1984 Fischer and Adams 1990 Sadhra et al. 1994). See the chapter on colophony in this book. 

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