Formaldehyde hydrate polymerisation

A powerfully reducing and reactive solid (m.p., 15°C) of high vapour pressure (b.p., 50°C). Mixtures with air may explode, and contact with water causes violent polymerisation [1], More usually encountered polymeric or as a hydrate. Like formaldehyde, pure glyoxal may polymerise exothermally and ignite in storage [2],... 

The hydrate of formaldehyde, HOCH2OH, may under certain conditions polymerise in aqueous solution to form paraformaldehyde, H0CH2(0CH2) 0CH20H, which appears as a white deposit in the solution. The polymerisation may be prevented by adding to the solution 10-15% of methanol. 

The addition of water to the carbonyl group in aqueous solutions can lead to the formation of hydrates. The reactions and stability of hydrates depend primarily on the inductive effect of substituents. Hydration of formaldehyde readily yields methylene glycol (methanediol), which polymerises to linear oligomers and also to polymers known as paraformaldehyde. Hydrates of a-dicarbonyl and a-hydroxycarbonyl compounds spontaneously dimerise into various cyclic 1,4-dioxanes (see Figure 4.62). These hydrates are intermediates of other a-dicarbonyl and a-hydroxycarbonyl compounds in the oxidation-reduction reactions and precursors of carboxylic acids. Dialkyl ketones do not form hydrates. 

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