Catalysts amidation/esterification

As a dibasic acid, malic acid forms the usual salts, esters, amides, and acyl chlorides. Monoesters can be prepared easily by refluxing malic acid, an alcohol, and boron trifluoride as a catalyst (9). With polyhydric alcohols and polycarboxyUc aromatic acids, malic acid yields alkyd polyester resins (10) (see Alcohols, polyhydric Alkyd resins). Complete esterification results from the reaction of the diester of maUc acid with an acid chloride, eg, acetyl or stearoyl chloride (11). 

Estane VC products, 201 Ester-amide copolymers, 146, 147 Esterases, 82 Esterification, direct, 63 Ester interchange catalysts, 71 Ester interchange reactions, 31, 62-63,... 

The most widely used homogeneous catalysts are simple acids and bases which catalyse well-known reactions such as ester and amide hydrolysis, and esterification. Such catalysts are inexpensive enough that they can be neutralized, easily separated fi om organic materials, and disposed of. This, of course, is not a good example of green chemistry and contributes to the huge quantity of aqueous salt waste generated by industry. 

Schreiber and co-workers (436) prepared a library calculated to contain 2.18 million polycyclic compounds through the 1,3-dipolar cycloaddition of a number of nitrones with alkenes supported on TentaGel S NH2 resin (Scheme 1.83). (—)-Shikimic acid was converted into the polymer bound epoxycyclohexenol carboxylic acid 376 (or its enantiomer), coupled to the resin via a photolabile linker developed by Geysen and co-workers (437) to allow release of the products from the resin in the presence of live cells by ultraviolet (UV)-irradiation. A range of iodoaromatic nitrones (377) was then reacted with the ot,p-unsaturation of the polymer-bound amide in the presence of an organotin catalyst, using the tandem esterification/ dipolar cycloaddition methodology developed by Tamura et al. (84,85) Simultaneous cyclization by PyBrop-mediated condensation of the acid with the alcohol... 

A-Alkyl-4-boronopyridinium halides such as 31 catalyze the esterification of a-hydroxycarboxylic acids <20050L5047>. When the quaternized iV-alkyl group is attached to a polystyrene resin, the supported iV-alkyl-4-boronopyridinium salt 32 serves as a catalyst in amide formation reactions. These catalysts are thermally stable and easily recovered and recycled <20050L5043>. 

Tin(rv) bis(perfluorooctanesulfonyl)amide is a practical catalyst for transesterification and direct esterification using an equimolar ratio of the reactants in a fluorous biphase system (Equation (103)). The tin amide is completely recovered and reused in the immobilized fluorous phase without loss of its catalytic activity.269... 

Amino acid methyl esters are fairly simple to prepare. The classical method uses a suspension of amino acid hydrochloride in MeOH and gaseous HCl as catalyst b° l di-carboxylic acids yield the dimethyl esters.Hydrolytic and alcoholytic cleavage of side-chain amide groups of glutamine and asparagine as well as peptide bond cleavage prevents the use of this method for the esterification of peptide fragments. 

DMAP is often used as catalyst in amidations and esterifications, especially for sterically hindered substrates. 

Catalytic hydrocarboxylations and related esterifications as well as amidations of alkenes belong to a family of carbonylation reactions which has attracted considerable industrial interest. Minor changes in the catalyst system as well as in reaction conditions can lead to simple carboxylic acids, diacids, polyketones, or unsaturated acids as products (Scheme 1). Most importantly, these methods provide routes to monocarboxylic acids, e.g., ethylene to propanoic acid (see Section 2.1.2.2), or 1-olefins (readily available from the oligomerization of ethylene discussed in Section 2.3.1.3) to higher carboxylic acids. 

If a chemical reaction occurs inside a distillation colmnn, with reactants and products subject to the usual requirements of the distillation process (phase eqniUbria, fractionation, and contacting device hydraulics), it is possible to shift the reaction eqnilibrimn in a favorable direction. A soluble or insoluble catalyst is likely to be involved thns, the operation is often known as catalytic distillation. Reactive distillation has been nsed snccessfnlly for etherification and esterification reactions and, to some extent, for alkylation, nitration, and amidation reactions. In most applications, the reaction has occurred in the liqnid phase, and an example of this application, where methyl acetate is produced from methanol and acetic acid nsing a solnble catalyst, has been described in detail. Flows for a generalized reactive colmnn are shown in Figm-e 12.21. 

Esterification of starch dialdehyde with chlorosulfonic acid in formamide gave a sulfate ester that could be transformed into an amide and methyl ester.532-536 The classical method of sulfonation, namely, by the action of sulfur trioxide in pyridine, is also applicable.537,538 Hemiacetals of starch dialdehyde result upon treatment with suitable alcohols in the presence of an acidic catalyst. In acetic media amides condensed with the carbonyl groups. Acetylation of starch dialdehyde with acetic anhydride is an obvious reaction. Esters with hexanedioic (adipic) acid were also prepared.537 Starch dialdehyde undergoes etherification with monochloroacetic acid in an alkaline medium.538... 

A thorough study indicates that (l-methyl-4-pyridinio)boronic acid iodide is a superior catalyst for amidation under azeotropic conditions, and esterification of 2-hydroxyalkanoic acids. ... 

---