The thermal behaviour of the ethylenebis-dithiocarbamates Maneb, Zineb and Mancozeb

Mechanism of thermal decomposition of a pesticide for safety concerns: Case of Mancozeb

“…Fig. 3 reveals that decomposition of Mancozeb occurs in three main steps with gaseous emissions of SO 2 , H 2 S and CS 2 at 200 • C. H 2 S is also observed until 500 • C. This thermal behaviour under nitrogen atmosphere differs from this previously obtained by Wang et al [21]. He mainly observed an additional mass loss at high temperature between 750 • C and 850 • C. The amount of emitted SO 2 is low and corresponds to 0.6% of the sulphur present in initial product.…”

“…First weight loss occurs between 25 • C and 200 • C. This weight loss of 26.5% is mainly associated with CS 2 and H 2 S emissions with few amounts of SO 2 and CO. CS 2 formation was already observed by Wang who suggested the emission of 1 mol of CS 2 per mole of Mancozeb and the formation of ETU during the first step of thermal decomposition of Mancozeb under nitrogen atmosphere [21]. The loss of 1 mol of CS 2 per mole of Mancozeb represents in theory 24 wt.% of the technical product which is consistent with the observed weight loss of 26.5%.…”

“…The active ingredient (Mancozeb-85 wt.%) is composed of zinc ethylene bis-dithiocarbamate (Zineb) and manganese ethylene bisdithiocarbamate (Maneb) as shown in Fig. 2 [21]. Mancozeb was used as received under powder form.…”

“…Metallic sulphides were not found in the final solid residues. This fact points out a discrepancy in mechanism of thermal decomposition of metallic-DTC suggested by Wang et al [21].…”

“…A fourstep decomposition was described but it was not clear whether the tested pesticide was pure or a commercial mixture. Decomposition under inert atmosphere leads to the formation of oxidized minerals whereas the pure materials have not oxygen atom [21]. Four steps mechanisms have been pointed out for both Maneb and Zineb.…”