Cannizzarro reactions

Because vanillin is a phenol aldehyde, it is stable to autooxidation and does not undergo the Cannizzarro reaction. Numerous derivatives can be prepared by etherification or esterification of the hydroxy group and by aldol condensation at the aldehyde group. AH three functional groups in vanillin are... 

In addition to the health hazards mentioned above, it is important be aware of the potential for explosions due to the Cannizzarro reaction ([77], pp. 36-37). When strong alkali is mixed with formaldehyde solutions, the Cannizzarro reaction will result in a rapid and spontaneous reaction even at relatively low temperatures. Depending on conditions, an induction period may be seen. The main organic products of this reaction are methanol and formic acid (salt form). In addition, significant amounts of hydrogen are evolved. The potential for explosions in closed containers is high, and even open containers will often erupt. 

Properties. Vanillin is a colorless crystalline solid mp 82-83 °C) with a typical vanilla odor. Because it possesses aldehyde and hydroxyl substituents, it undergoes many reactions. Additional reactions are possible due to the reactivity of the aromatic nucleus. Vanillyl alcohol and 2-methoxy-4-methylphenol are obtained by catalytic hydrogenation vanillic acid derivatives are formed after oxidation and protection of the phenolic hydroxyl group. Since vanillin is a phenol aldehyde, it is stable to autoxidation and does not undergo the Cannizzarro reaction. Numerous derivatives can be prepared by etherification or esterification of the hydroxyl group and by aldol condensation at the aldehyde group. Several of these derivatives are intermediates, for example, in the synthesis of pharmaceuticals. 

The reaction is an aldol condensation followed by a Cannizzarro reaction. 

An important intermediate for synthetic p-ionone (36) is the C8 building block methyl heptenone (37). In addition to the synthesis shown above, two further processes are known for its industrial production. In the process of Rhodia INC 36), the starting material is isoprene, and methyl heptenone (37) is obtained via prenyl chloride. At BASF, methyl heptenone (37) is produced, for economic reasons, in the form of its double bond isomer (37 a) by thermal condensation of isobutylene, formaldehyde and acetone 37) (see page 13). By suitable choice of the reaction conditions, various side-reactions, such as the Cannizzarro reaction of formaldehyde, the oligomerization of isobutene and aldol condensation between formaldehyde and acetone, can largely be suppressed. 

Habermehl and Schunk289 have drawn attention to the analogy between the pseudobase disproportionation and the Cannizzarro reaction of aldehydes, which can be considered to be a disproportionation of the aldehyde hydrate to a carboxylic acid and alcohol. This reaction is usually considered to involve hydride transfer from either the mono- or dianion (i.e., 143 or 144) of the aldehyde hydrate to the carbonyl group of another aldehyde molecule. The anions 143 and 144 are clearly quite similar electronically... 

Examples Cannizzarro (reaction of aromatic aldehydes under alkaline conditions)... 

Further indirect evidence for the oxidation of the primary alcohol in 5 and the formation of glycoside 6 during the course of the reaction was obtained by electrospray mass spectrometry. Towards this end, excess formaldehyde was added to the reaction mixture after the oxidation of 5 into 6, and the resulting solution stirred for an additional 30 min at ambient temperature to form the instable intermediate 7 (eq 6). The unnatural sugar 5-hydroxymethyl-a-methylglucoside (8) is spontaneously derived from 7 at ambient temperature via a Cannizzarro-like reaction in the presence of excess formaldehyde (eq. 7). 

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