synthetic esters of chrysanthemumic acid; analogs of pyrethrins.

Pyrethroids are obtained either by the reaction of chrysanthemumyl chloride with an alcoholic moiety in the presence of a tertiary amine or by transesterification of the ethyl ester of chrysanthemumic acid in the presence of sodium. The pyrethroids that are most toxic to insects are esters of cyclopentenolones, of substituted benzyl alcohols, and of N-hydroxymethylimides.

Pyrethroids produced today include allethrin (2-allyl-3-meth-yl-2-cyclopenten-4-oI-l-onyl chrysanthemumate), furethrin (2-furfury 1 -3-methyl -2- cyclopenten - 4 -ol -1 - ony 1 chrysanthemum-ate), cyclethrin (2-cyclopentenyl-3-methyl-2-cyclopenten-4-ol-1 -onyl chrysanthemumate), barthrin (6-chloropiperonyl chrysanthemumate), dimethrin (2,4-dimethylbenzyl chrysanthemumate), and tetrametrine [N-(3,4,5,6-tetrahydrophthalimido)-methyl chrysanthemumate]. These compounds, usually in the form of aerosols, are used against household insects.