Photochemical transformation of thiophanate‐methyl and thiophanate to alkyl benzimidazol‐2‐yl carbamates

The systemic fungicides thiophanate‐methyl (TPM) and thiophanate (TPE) were transformed in aqueous solutions on glass by irradiation with u.v. and sunlight to the more effective fungitoxic substances methyl benzimidazol‐2‐yl carbamate (MBC) and ethyl benzimidazol‐2‐yl carbamate (EBC), respectively. The thiophanate fungicides were not converted when incubated in the dark. The photochemical transformation of TPM and TPE to the corresponding alkyl benzimidazol‐2‐yl carbamates increased with the exposure time of u.v. irradiation. However, no light catalysed reactions occurred when both fungicides were irradiated with u.v. light in the solid state. The residue of TPM and TPE on leaves of cotton plants following spray application were transformed by the energy of sunlight to the more fungitoxic MBC and EBC.