A NEW APPROACH TO THE DETERMINATION OF THE HEAT OF PHENOLIC RESOL SYNTHESIS

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.