Analysis of dithiocarbamate fungicides. Reaction products of the thiuram disulphide fungicide thiram (TMTD) during acid hydrolysis.
The acid hydrolysis products (CS2, COS, and H2S) of thiram (tetramethylthiram disulphide, TMTD) absorbed in a methanolic amine reagent (ethylenediamine, piperidine) were investigated by second derivative UV spectroscopy. When the hydrolysis temperatures are below the boiling point the formation of the side products COS and H2S at the expense of CS2 is unavoidable. Failure to carefully scrub the liberated gases with a lead acetate solution leads to the absorption of H2S also in the amine reagent and, like COS, causes an absorption at 230 nm that is erroneously attributed to COS. With the second-derivative technique it has been undoubtedly proved that, under the conditions of the Deutsche Forschungsgemeinschaft method S 15, thiram liberates CS2 and COS in a molar ratio of 1.92 to 0.06 (average of eight determinations) but not in a molar ratio of 1.5 to 0.5, as previously reported by some workers. Under these conditions it is impossible, contrary to earlier claims, to differentiate thiram from other dithiocarbamates based on the ratio of the hydrolysis products in residue analysis.
Schwack
W
W
Institut für Lebensmittelchemie, Universität Karlsruhe, Germany.
Nyanzi
S
S
D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D013893:Thiram / Q000737:chemistry*
D013893:Thiram