This progress report is concerned primarily with problems relating to the structure and reactions of hydroxamic acids and N-hydroxyimides, and also surveys some of the biological activities of these compounds. Particular significance attaches to the Lossen rearrangement of 0-acylated hydroxamic acids, which leads to isocyanates or their reaction products.

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Direct rearrangement of monohydroxamic acids without the necessity of isolating a dihydroxamic acid occurs on reaction of the monohydroxamic salts with arenesulfonyl chlorides. The product from benzohydroxamic acid is benzo-(phenylcarbamylhydroxamic) acid, that from hydrocinnamohydroxamic acid is hydrocinnamo-(phenethylcarbamylhydroxamic) acid, and that from succinohydroxamic acid (with benzenesulfonyl chloride) is 3-benzenesulfonoxy-5,6-dihydrouracil. The steps leading to the formation of these substances are discussed, and certain of their reactions are developed.The Lossen rearrangement of a hydroxamic acid as usually performed involves acylation and heating a salt of the acyl derivative RCONHOH -RCONHOCOR' -*--R'COONa H20RCONNaOCOR'-->-RNCO -> RNHCONHR (or RNH2)