And pinacol rearrangement

Acid Form - Pseudoliquid Phase Behavior. Owing to a high affinity for polar molecules, large quantities of molecules such as alcohols and ether are absorbed within the bulk phase of crystalline heteropolyacids. The amounts of pyridine, methanol, and 2-propanol absorbed correspond to 50-100 times that which can be adsorbed on the surface, while nonpolar molecules like ethylene and benzene are adsorbed at the surface only. Catalytic reactions of polar molecules occiu both on the surface and in the bulk, so that the solid heteropolyacid behaves as a highly concentrated solution, called a pseudoliquid phase . The dehydration of alcohols, various conversions of methanol and dimethyl ether to hydrocarbons in gas-solid systems, and the alkylation of phenol and pinacol rearrangements can all occur in the pseudoliquid. The transient response using isotopically labeled 2-propanol provides evidence for the pseudoliquid phase behavior of H3PW12O40. This behavior influences the selectivity, for example, the aUcene/aUcane ratio, in the conversion of dimethyl ether. 

Pocker, Y. Wagner-Meerwein and pinacolic rearrangements in acyclic and cyclic systems, in Molecular Rearrangements (ed. De Mayo, P.), 1, 1-25 (Wiley, New York, 1963). 

A recent review (Collins, 1960) of the pinacol rearrangement covers nearly all of the pertinent isotopic experiments that have been performed. One example of the use of two carbon-14 labels to relate the aldehyde-ketone and pinacol rearrangements will be discussed in detail here. The anomaly of the apparent reversal, in the aldehyde-ketone rearrangement, of the usual order of migratory aptitudes has been mentioned by Wheland (1949) and by Ingold (1953), and relates to the fiict that, for example, 2-methyl-2-phenylpropionaldehyde (67), in concentrated sul-... 

Photogenerated acids can also catalyze various other reactions, e.g. the cross-linking of polymers containing epoxide groups (see Chart 9.4), or Claisen and pinacol rearrangements in polymers as shown in Scheme 9.5. Resist systems operating on the basis of these reactions have been proposed [12, 13]. 

Fig. 8. Adelberg s scheme for aldol condensation of two molecules of pyruvate and pinacol rearrangement in biosynthesis of valine [modified from 1B7). ...

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