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THE method of Norris, Easter, Fuller and Kucharl for the colorimetric analysis of malathion proved unreliable when applied to residues in rice bran, unless chromatographic purification of the extracts on Fuller's earth was introduced.2 It has been noted, however, in this and other laboratories (private communication from Border and Hill) that, without this chromatographic step, the divergence between the amount of insecticide found and that actually present varied markedly with different samples of rice bran (see Table I). As previously reported,2 low recoveries were recorded when considerably less than the theoretical amount of 6 N hydrochloric acid (1 ml) was required for neutralisation after alkaline hydrolysis during the analysis.

A number of compounds related to SKF 525A were tested for synergism with pyrethrins, using Lesser Mealworm beetles, Alphitobius laevigatus, and houseflies, Musca domeslica, as test insects. SKF 525A had previously been shown to be active, whereas 2.2-diphenyl-n-pentanoic acid and 2-diethylaminoethanol were inactive. Several active compounds resulted from esterification of 2-diethylaminoethanol with diphenylacetic acid and I-substituted diphenylacetic acids. Most modifications of the alcoholic moiety of active 2-diethylaminoethyl esters destroyed activity. Active compounds resulted when a a-diethylamino group was joined to a diphenylmethyl group through an ester, ketone or ether linkage, but the analogous amide was inactive. 2-Diethylaminoethyl piperonylate probably owed its activity to its piperonyl group. None of the compounds investigated approached piperonyl butoxide in synergistic activity. IntroductionThe ester 2-diethylaminoethyl z,z-diphenyl-n-pentanoate (SKF 525A, see Table I) ,is well known to increase the effects on mammals of drugs of a number of different types.1 Moreover, it has been shown to synergise the action of pyrethrins on certain insects2 In the work described here, a number of compounds related to SKF525A have been tested for action as pyrethrin synergists on insects, in order to relate chemical structure to biological activity. Variation of the acid and alcohol components established sufficient conditions for synergism in esters. The effects of different linkages between the terminal moieties of the molecule were then examined.

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SUMMARYThe in vitro fungicidal activity of 2‐methyl‐4,6‐dinitrophenol (DNC) and fifteen of its esters was determined in mycelial growth tests. The aliphatic esters possessed similar activity to that of DNC and the aromatic esters were much less fungitoxic. The benzoic ester was only weakly active against mycelial growth and in preventing spore germination but as a protectant fungicide in vivo it was very effective. It was established that DNC‐benzoate is stable in light, under conditions of high humidity and in the presence of fungal spores, but it was shown that some degree of hydrolysis occurs on the leaves of broad bean to yield the parent cresol. This hydrolysis does not lead to phytotoxicity but the small quantities of DNC produced could account for the protectant fungicidal activity of this compound.