The present invention is directed to a process for preparing a condensation product of a glyoxylic reactant and a hydrocarbyl-substituted aromatic compound having at least one hydroxy functionality, which includes (a) providing the glyoxylic reactant in the form of a compound represented by the formula ##STR1## or its reactive equivalent, wherein R.sup.1 and R.sup.3 independently are hydrogen or hydrocarbyl group of 1 to about 4 carbon atoms; and R.sup.2 and R.sup.4 independently are hydrocarbyl groups of 1 to about 4 carbon atoms; (b) mixing the aromatic compound with the glyoxylic reactant; and (c) heating the mixture to a temperature of about 50.degree. C. to about 200.degree. C. in the presence of an acid catalyst for a sufficient time to form the condensation product.