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REACTIONS OF FORMALDEHYDE WITH PHEXOLS 163
Fundamental Characteristics of Phenol-Formaldehyde Reactions
In general, phenols react readily with formaldehyde in the presence of
both alkaline and acidic catalysts, producing a variety of substances ranging
from simple methylol and methylene derivatives to the complex resins
in which large numbers of phenolic molecules are linked together by
methylene groups. These reactions are shared by formaldehyde polymers,
such as paraformaldehyde and the linear polj'oxy methylenes, which
(Jeporymeiize under reaction conditions. Trioxane (symmetrical-trioxymethylene)
is unique in that it does not react under neutral or alkaline
conditions. When trioxane crystals are mixed with crystalline phenol at
ordinary temperatures, liquefaction takes place, heat is absorbed, and a
colorless solution is obtained. Reaction takes place only when a strongly
acidic depolymerization catalyst is added to the phenol-trioxane solution 56 ,
In the absence of added catalysts, anhydrous formaldehyde and paraformaldehyde
dissolve in molten phenol without apparent reaction to give
clear, colorless solutions which smell strongly of formaldehyde. In such
solutions, it is probable that the dissolved formaldehyde is present in the
form of hemi-formals such as C6H5OCH2OH and CaH6OCHsOCH2OH.
The analogy of these solutions to alcoholic formalderryde solutions is clearly
apparent (page 138). According to Heychler 47 , a small percentage of
sodium phenate catalyses the solution of linear formaldehyde polymers
in phenol, just as sodium alcoholates catalyze solution in methanol, ethanol,
and other alcohols. That hemi-formals are produced is also indicated by
the isolation of methyl phenyl formal from an acid-catalyzed reaction of
phenol with formaldehyde solution containing methanol 14 .
^^y-on CH * 0(aq i> -OCHSOH 5>