Catalysis by Solid Acids and Bases

Solid acid catalysts are, in principle, applicable to a plethora of acid-promoted processes in organic synthesis [27-29]. These include various electrophilic aromatic substitutions, e.g. nitrations, and Friedel-Crafts alkylations and acylations, and numerous rearrangement reactions such as the Beckmann and Fries rearrangements. 

Another case in point pertains to the manufacture of the bulk chemical, caprolactam, the raw material for Nylon 6. The conventional process (Fig. 1.9) in- 

Hydrolysis of products Phase separation Distillation organic phase Solvent recycle 85-95% yield 

H-beta, catalytic regenerable No solvent No water necessary 

As any organic chemist will tell you, the conversion of an amino acid to the corresponding ester also requires more than one equivalent of a Bronsted acid. This is because an amino acid is a zwitterion and, in order to undergo acid catalysed esterification, the carboxylate anion needs to be protonated with one equivalent of acid. However, it was shown [38] that amino acids undergo esterification in the presence of a catalytic amount of zeolite H-USY, the very same catalyst that is used in naphtha cracking, thus affording a salt-free route to amino acid esters (Fig. 1.11). This is a truly remarkable reaction in that a basic compound (the amino ester) is formed in the presence of an acid catalyst. Esterification of optically active amino acids under these conditions (MeOH, 100 °C) un- 

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Iglcsia. E Barton, D(i Biscardi, JA Gines. MJL Soled, SL, Bifunctional pathw ays in catalysis by solid acids and bases. Catalysis Today. 1997 38, 339-360. 

Catalysis by Solid Acids and Bases By S Malinowski and M Marezewski... 

Because catalysis by solid acids and bases is central to a variety of industrial processes, relationships between solid acid-base behavior and catalytic properties have been explored [68,120]. However, many concepts, either qualitative or empirical, demand closer scrutiny. 

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