Linear anhydrides are formed by the action of acetic anhydride on p-toluene-sulphonylglycine and carbobenzyloxy-glycine, -phenylalanine, and -β-alanine. The anhydrides from the first two acids yield the corresponding 2-thiohydantoin with ammonium thiocyanate in acetic acid. Other methods for the preparation of l-p-toluenesulphonylglycine anhydride, and its 2-thiohydantoin, are also given. Hippuric acid, with ethyl chlorocarbonate and triethylamine yields ethyl hippurate, probably via the mixed anhydride and 2-phenyloxazol-5-one. The inclusion of ammonium thiocyanate gives 1-benzoyl-2-thiohydantoin in high yield. The N-carboxy anhydride of phenylalanine (4-benzyloxazolid-2,5-dione) also reacts with ammonium thiocyanate to give carbon dioxide and 5-benzyl-2-thiohydantoin.