Sodium salts of drazoxolon and related 4-arylhydrazono-3- methylisoxazol-5-ones react with acyl chlorides in dry acetone to form 2-acyl-4-arylazo-3-methylisoxazol-5-ones, the structures of which were deduced from their i.r. and u.v. spectra. Several 2-acyl-4- arylazo-3- methylisoxazol-5-ones show considerable fungicidal activity against a number of plant pathogens.

From a study of the isotropic proton hyperfine interaction constants for a series of metal dithiocarbamates, and their redox behaviour, it is shown that for iron(111) and manganese(111) dithiocarbamates there is a simple relationship between E1/2 and the NCH2 proton hyperfine interaction constant in the 6Al state. Hence the redox process for these compounds is inferred to take place through the nitrogen atom.

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Drazoxolon and related 3-methyl-4-arylhydrazono-5-isoxazolones are hydrolysed by acid to 2-arylhydrazono-3-oxobutyric acids and by alkali to l-arylhydrazono-2-hydroxyiminopropanes and 2-arylhydrazono-3-hydroxyiminobutyric acids. Although many of the hydrolysis products show good antifungal activity in spore germination tests they are inferior to drazoxolon as protectants for the control of Uromyces fabae on broad bean and as protectants and eradicants against Erysiphe graminis on wheat. Neither drazoxolon nor its hydrolysis products show much activity as therapeutants. 357

Esters of 2-bromo-, 4-bromo-, 2-iodo-and 4-iodo-3,s-dinitrobenzoic acids show considerable antifungal activity in spore germination tests against Alternariu brassicicola, Botrytis cinerea, Septoria nodorum and Uromyces fabae. They act as protectant fungicides against Erysiphe graminis, Puccinia recondita and Septoria nodorum on wheat and Botrytis fabae on broad bean. The most active compounds are methyl and ethyl 4-bromo-3,s-dinitrobenzoates which give better control of wheat rust than oxycarboxin and methyl 4-iod0-3,5-dinitrobenzoate which is at least as effective as captan against Septoria leaf spot on wheat. Several of the esters are superior to captan in controlling chocolate spot on broad bean. 0 Abbreviations used: A h . = Alternaria brassicicola; B.c. = Botrytis cinerea; S.n. = Septoria nodorum; U. f. = Uromyces fabae; E,g. = Erysiphegraminis; P.r. = Puccinia recondita; B.f. = Botrytis fabae; -= Not tested. * N-Trichloromethylthio-4-cyclohexene-1 ,Zdicarboximide. ' Mixed 2,4-dinitro-doctylphenyl crotonates and 4,6-dinitro-2-octylphenyl crotonates. 2,3-dihydro-6-methyl-5-phenylcarbamoyl-1,4-oxathiin 4,4-dioxide.