Demethylolation reaction

The urea - formaldehyde (UF) and melamine-formaldehyde systems represent similar hazards. Free formaldehyde, which can be present in trace amounts, may be liberated to the air when resins are processed or even slowly afterwards, which can irritate the mucous membranes. Formaldehyde is a metabolite occurring normally in the human body and is converted to formic acid by enzymic oxidation. Formaldehyde in the cured resin is believed to be due to the unreacted free formaldehyde left (there are also claims that it may be due to demethylolation reaction and/or cleavage of methylene-ether bridges as well). A model specification to set out the health hazards is presented for polymer mortar surfacings (out of epoxy, polyester and PU thermosets), intended for their use as indoor floor tappings [39]. 

The formation of 1,1-dinitroethene (150) as an intermediate also accounts for the formation of potassium 2,2,4,4-tetranitrobutanol (158) when a solution of potassium 2,2-dinitroethanol (20) is partially acidifled. Klager and co-workers posmlated that 1,1-dinitroethene is formed via elimination of water from 2,2-dinitroethanol and this rapidly undergoes Michael 1,4-addition with any potassium 2,2-dinitroethanol still present in the reaction mixture. Demethylolation of (158) with potassium hydroxide yields the dipotassium salt of 1,1,3,3-tetranitropropane. 

Polynitroaliphatic alcohols are invaluable intermediates for the synthesis of energetic materials (see Section 1.11). The most important route to /i-nitroalcohols is via the Henry reaction where a mixture of the aldehyde and nitroalkane is treated with a catalytic amount of base, or the nitronate salt of the nitroalkane is used directly, in which case, on reaction completion, the reaction mixture is acidified with a weak acid. Reactions are reversible and in the presence of base the salt of the nitroalkane and the free aldehyde are reformed. This reverse reaction is known as demethylolation if formaldehyde is formed. 

Both the Henry reaction and the reverse demethylolation are synthetically useful in the chemistry of polynitroaliphatic compounds. The Henry reaction is commonly used to mask the natural chemistry of an aliphatic nitro or terminal em-dinitro group by removing the acidic a -proton(s). In Section 1.7 we discussed the conversion of Q ,ty-dinitroalkanes to their bis-methylol derivatives before subjecting them to oxidative nitration and subsequent demethylolation with base, a procedure which results in the formation of Q ,Q , y, y-tetranitroalkanes. ... 

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