Chemistry Reference
In-Depth Information
Following the above general synthetic scheme, the majority of crop protection
products are made from the starting substrate (''raw material A'', Table 5.2) by
''activating'' it through a phosgenation process to give an isocyanate, chlorofor-
mate,orcarbamoyl chloride as a ''phosgenation intermediate'', followed by addi-
tion of ''raw material B'' to form the desired ''agro product''.
Aromatic and aliphatic isocyanates are the key intermediates. Table 5.3 lists a
number of pesticides with structures suggestive of an isocyanate intermediate, but
which are probably not necessarily synthesized by employing a purchased iso-
cyanate.
A series of fungicides are prepared with isocyanates. Addition of oximes 285 to
MIC is the main process stage for the manufacture of N-methyl carbamate in-
secticides such as Aldicarb, Methomyl, Oxamyl, and Thiopanox.
S
S
H
N
+
Me
NCO
O
OH
N
N
O
285
Methomyl
Addition of substituted phenol 286 to MIC generates Methiocarb. Mexacarbate,
Promecarb, Propoxur, and Trimethacarb are produced in a similar fashion.
H
N
OH
O
+
Me
NCO
O
S
S
CH
3
286
Methiocarb
The herbicide Methazole was traditionally manufactured by the addition of 3,4-
dichlorophenyl hydroxylamine to MIC, followed by treatment with methyl chloro-
formate or phosgene and cyclization.
OH
H
N
NO
2
N
NHOH
H
2
MIC
O
Pd-C
poisoned
Cl
Cl
Cl
Cl
Cl
Cl
CH
3
OCOCl
or
COCl
2
O
N
N
O
O
Cl
Methazole
Cl
