A new method has been developed for the determination of the heat of p
henolic resol synthesis carried out in an aqueous solution. This heat
is determined as the difference in the heats of syntheses of the resit
ol from the mixture of raw materials and from the resol studied. Heats
of resitol syntheses were determined by DSC at constant heating rate
using high-pressure crucibles, i.e. under isochoric conditions for the
liquid-vapour sample. The heat of synthesis of resols, obtained at fo
rmaldehyde-to-phenol molar ratio equal to 3.0 and using NaOH as cataly
st, were determined. The relevant values were calculated on the basis
of the chemical composition of the resols and the molar enthalpies of
the aromatic ring substitution and methylene bridge formation reaction
s. The experimentally determined heats were consistent with the calcul
ated ones, not when free formaldehyde (CH2O) but its monohydrate, CH2O
.H2O (methylene glycol, HO-CH2-OH) was assumed to be the reactive form
of formaldehyde in an aqueous medium (formalin). (C) 1998 Elsevier Sc
ience B.V.