Methyldithiocarbamate 
Metham Sodium (Vapam) [Sodium N-methyldithiocarbamate ] 
The principal product of decomposition of metham-sodium, when applied 
to soil, has been shown to be methyl isothiocyanate. This can then react 
with sulfhydryls or with ammonia to form N-methylthiourea. However, under 
outdoor conditions, this latter reaction is not significant (36, 37, 279, 
702, 890, 1310). 
In dilute aqueous solutions, at pH 9.5, vapam decomposes to methyl 
isothiocyanate and sulfur. Under acid conditions, carbon disulfide, 
hydrogen sulfide, N,N'-dimethylthiuram disulfide, methylamine, and methyl 
isothiocyanate formed. Methylamine and carbon disulfide can react to form 
methyl isothiocyanate. This may then react with vapam to produce dimethyl- 
thiuram disulfide and with methylamine or hydrogen sulfide to form 
dimethylthiourea. (1432). 
‘3 
CH,-N-U-S-Na + CH ,-N=C=S 
3 3 
Metham-sodium Methyl isothiocyanate 
RSH NH. 
i 
cH,-N-C-s-R NH 
CH..-N-—C- 
34 Z 
N-Methyl Thiourea 
191 
