Cannizzaro reaction salts

Pentaerythritol, used in the production of alkyds, is produced by a crossed Cannizzaro reaction of the aldol condensation product of formaldehyde and acetaldehyde. The by-product formate salt is a major source of formic acid. 

Formylfuran behaves in a very similar manner to benzaldehyde and undergoes the usual reactions of an aromatic aldehyde, e.g. (i) the Cannizzaro reaction with cone, sodium hydroxide to give furan-2-ylmethanol and the sodium salt of furoic acid, (ii) the Perkin reaction with acetic anhydride and sodium acetate to yield an aldol product that dehydrates to 3-(furan-2-yl)propenoic acid, and (iii) a condensation with potassium cyanide in alcoholic solution to form furoin (under these conditions, benzaldehyde undergoes the benzoin condensation) (Scheme 6.32). 

The Cannizzaro reaction can be avoided if an easily reducible substance is added to the reaction mixture. Thus Del6pine reacted Raney nickel with a mixture of galactose and the sodium salt of either cinnamic or crotonic acid in the presence of alkali. This reaction has also been noted by Tomkuljak (72), who, when hydrogenating D-xylose in water... 

Aldehydes can undergo an intermolecular oxidation—reduction (Cannizzaro reaction) in the presence of base to produce an alcohol and a carboxylic acid salt. Any aldehyde is capable of participating in such a reaction, however, it is more common for those containing no protons on the alpha carbon, for example... 

Product recovety is some combination of rote methods of using processing tools and inspired application of new and conventional separation tools. For example, if aldehydes make distillation infeasible because of polymerization products and/or vacuum distillation costs, then one can consider utilizing the Cannizzaro reaction to make organic acid salts and ketones from the aldehydes before proceeding. Many bench-scale processing techniques such as thin-film evaporation have been scaled up to handle larger quantities of temperature sensitive materials. Assistance in utilization of these techniques can usually be obtained from the equipment vendors. 

Successive elimination of an alkoxy group adjacent to an active hydrogen atom and intramolecular Cannizzaro reactions in alkaline solution, such as are found in saccharinate formation, are demonstrated by the conversion of 2-hydroxy-3-methoxy-3-phenylpropiophenone (X) to a salt of 2,3-diphenyllactic acid (XI). 

There are, however, numerous organic precendents. The Cannizzaro reaction, in which two equivalents of a nonenolizable aldehyde such as bezaldehyde are reacted with hydroxide to form a primary alcohol and the salt of a carboxylic acid, is thought to involve hydride transfer to one aldehyde carbonyl from the carbonyl-addition product of the other aldehyde and hydroxide. The Leuckart reaction, formation of a tertiary amine from formic acid, a primary amine and either a ketone or an aldehyde, seems to procede via hydride transfer from formate to an iminium ion. And the Meervein-Ponndorf-Verley-Oppenauer reaction, the reversible transfer of hydrogen between ketones and secondary alcohols in the presence of excess aluminum isopropoxide, is almost certainly a hydride-transfer reaction. This latter process is of particular interest to us because it requires a metal, just as GI does. The aluminum acts as a Lewis acid, coordinating the carbonyl oxygen and... 

The analogy has been drawn between the chemistry catalyzed by dehydrogenases and the base-catalyzed hydride transfer chemistry of Meerwein-Ponndon-Verley (MPV) reductions or the Cannizzaro reaction (for recent reviews of the chemistry of pyridine nucleotides see Refs. 1,3, and 5). In MPV reductions [reaction (2)] aluminum or lithium salts of the alkoxide activate the C-H bond for transfer of hydrogen to suitable acceptors. Both direct hydride transfer (52) and radical intermediates (55) have been suggested for this reac-... 

Consider the Cannizzaro reaction. Here, aldehydes with no a-hydrogens undergo self-oxidation-and-reduction to produce a mixture of an alcohol and a salt of a carboxylic acid. Two aldehydes will generally undergo a Cannizzaro reaction to yield all possible products. However, if one aldehyde is formaldehyde, the reaction almost exclusively yields sodium formate and the alcohol corresponding to the other aldehyde. For example. 

This means that if step 1 of the Cannizzaro reaction is rate-limiting, HCHO is the chief hydride donor (and not any other aldehyde in solution), since (from the steric and electronic factors discussed) it will react with 01 faster thcin any other aldehyde. The equilibrium will be positioned farther to the right. Note how the carboxylate salt will derive only from the hydride donor. 

The only other noticeable effect of variation of the experimental parameters shown (Table I) is a negative effect of high alkali concentration on oil yield, when the sodium carbonate concentration is raised to 2.37 N (12.6%) at 270-343 C. This is counter to Elliott and Giacoletto s results (10). The effect of alkali on cellulose chain peeling and cleavage was found to be directly proportional to alkali concentration at lower temperatures (185 C) (47). Since high alkali concentrations favor the hydride- transfer mediated Cannizzaro reaction to yield acid salts and alcohols from aldehydes and some ketones, we suggest that perhaps the lower oil yield may be due to removal of carbonyl intermediates from the reaction. 

Purpose To demonstrate the oxidation-reduction of an aromatic aldehyde to give the corresponding alcohol and carboxylic acid salt by the Cannizzaro reaction. 

---