360 PRACTICAL ORGANIC CHEMISTRY CRYSTALLINE DERIVATIVES FOR IDENTIFICATION. (A) Acids. The ammonium salts of aromatic acids when acidified in cold aqueous solution will deposit the crystalline acid. (B) Benzylthiouronium salts. Cold aqueous solutions of ammonium salts, when treated with benzylthiouronium chloride, usually deposit the benzylthiouronium salt (cf. p. 349), and the intermediate formation of the sodium salt is unnecessary. (M.ps., pp. 543-545.) (C) Phenacyl and p-Bromophenacyl esters. Ammonium salts in aqueous-ethanolic solution do not however usually condense satisfac-torily with phenacyl and p-bromophenacyl bromide. The aqueous solution of the ammonium salt should therefore be boiled with a slight excess of sodium hydroxide to remove ammonia, and the solution then cooled, treated with hydrochloric acid until just alkaline to phenol-phthalein, and then evaporated to dryness. The sodium salt is then treated as described (p. 349) to give the ester. Filter the ester, and wash
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