Process for preparing aromatic hydroxyaldehydes

The process for the preparation of an aromatic hydroxyaldehyde of the formula ##STR1## wherein R is methyl or ethyl, which comprises condensing a phenol of the formula ##STR2## with glyoxylic acid to produce a substituted glyoxylic acid of the formula ##STR3## and oxidizing said substituted glyoxylic in aqueous acid at a pH at most 5 with an oxidizing agent having a redox potential in the range of from E=+0.17 to +1.84 volts wherein the oxidizing agent is potassium chlorate or sodium chlorate in admixture with copper, iron, cobalt or nickel sulphate or chloride, whereby the aromatic hydroxyaldehyde is produced in high yield based on starting phenol.