Chemical and Fungicidal Reactions of 3,5-Dimethyltetrahydro-1,3,5-thiadiazine-2-thione (3,5-D). A Comparison with Sodium N-Methyl Dithiocarbamate and Methyl Isothiocyanate.

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Abstract
Methyl-isothiocyanate inhibits the acetate respiration in baker''s yeast at pH values above 6, but not at pH below 5. At the pH values where the inhibitory action is shown, methyl-isothiocyanate reacts with cysteine to form a compound with a dithiocarbamate spectrum. The same kind of reaction could also be demonstrated in intact yeast cells. Sodium N-methyl-dithiocarbamate acts inhibitory on the acetate respiration at lower pH values, but not at higher. At higher pH values, cupric ions act strongly synergistic. Spectrpphotometric studies did not show any reaction between sodium N-methyl-dithiocarbamate and cysteine. The spectra showed, however, that the compound is very unstable in dilute aqueous solutions. 3,5-D in aqueous solution is rapidly hydrolyzed to form a N-methyl-dithiocarbamate ester, and probably more slowly to form free N-methyl-dithiocarbamate ion. In aged solutions (24-48 hr. old), methyl-isothiocyanate is present. This could be spectrophotometrically detected by the reaction with cysteine. Freshly prepared 3,5-D solutions showed less toxicity than 24 hr. old ones. In both cases cupric ions acted synergistically at pH 6.5. This effect was most pronounced in the fresh solution. In the old solution, the effect of pH was not pronounced. The inhibitory effect at pH 6.5 was, however, variable from one experiment to the other. In both kinds of solution, ether extraction reduced the toxicity in the absence of cupric sulfate at pH 6.5 to practically sero. It is concluded that 3,5-D acts as a mixture of N-methyl dithiocarbamate and its decomposition product, methyl-isothiocyanate. In practical use, the effect of formaldehyde must not be overlooked, but this compound and other possible decomposition products, such as carbon-disulfide and dithiocarbamate, had no effect of the acetate respiration of yeast.

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