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The sulfonic acid resin Dowex ® 50W × 8 can be used to replace mineral acids in the reaction between p -hydroxymandelic acid and urea in water or NaCl solutions. The synthesis of p -hydroxymandelic acid is efficiently carried out using NaOH to promote the reaction between phenol and glyoxylic acid. Alternatively, KF/alumina can be used to obtain methyl p -hydroxymandelate by reaction of phenol with methyl 2-hydroxy-2-methoxyacetate, although, this process is carried out in an organic solvent and gives a lower yield. A comparison between the three alternative methods for the synthesis of 5-(4-hydroxyphenyl)hydantoin shows that the direct route from glyoxylic acid, urea and phenol is the most efficient method, although the p -hydroxymandelic acid route would be an interesting alternative if its heterogeneous synthesis were optimized.

Clays, zeolites and organic polymers bearing sulfonic acid groups are used to promote the direct synthesis of dl-5-(4-hydroxyphenyl)hydantoin from urea, phenol and glyoxylic acid. Only organic polymers lead to good results, in particular a sulfonic polystyrene-divinylbenzene resin with a small particle size, whereas very poor results are obtained when clays or zeolites are used to promote this amidoalkylation reaction. A possible explanation for these rather surprising differences in behavior involves the different hydrophilic/hydrophobic character of the solids, particularly given the aqueous reaction medium. The pre-treatment of the resin and the particle size are important factors that influence the final result. Although the results are no better than those obtained with hydrochloric acid in the homogeneous phase, these resins do represent the only environmentally friendly alternative., We are indebted to DSM Deretil for financial support and providing some of the reagents and products.