Chemical Properties
Light Brown Solid
Uses
Carbamate herbicide; folic acid biosynthesis inhibitor.
Definition
ChEBI: A carbamate ester that is methyl carbamate substituted by a (4-aminophenyl)sulfonyl group at the nitrogen atom.
Description
Asulam is a sulfonamide and can be formulated as a
sodium salt. It is very water soluble and is a very
systemic herbicide following foliar and root uptake, owing
to its physicochemical properties (Table 1). The Log P
(Kow) of 1.01 and pKa of 4.82 are optimal for phloem
mobility in the plant (4). These properties contribute
to the herbicidal effectiveness against perennial weeds
where translocation to underground meristematic organs
is essential for effective control.
Health Hazard
Low order of toxicity; no adverse effect onskin reported; ingestion of large dose couldproduce cholinergic effects.
LD50 oral (rat): 2000 mg/kg.
Pharmacology
Asulam-induced
growth inhibition of carrot cell cultures was reversed by
4-aminobenzoic acid (8), and depletion of folate derivatives
in treated plants (7) provides further evidence that
the synthesis of folic acid is the primary target of
asulam. Furthermore, asulam is structurally related to
sulfonilamide and to sulfonamide antimicrobial drugs,
which are competitive inhibitors of 7,8-dihydropteroate
synthase (DHPS) (5,9).
Environmental Fate
Soil. It is not persistent in soils since its half-life is approximately 6–14 days (Hartley
and Kidd, 1987). The short persistence time is affected by soil temperature and moisture
content. The half-life of asulam in a heavy clay soil having a moisture content of 34%
and maintained at 20°C was 7 days (Smith and Walker, 1977). In soil, sulfanilamide was
reported as a product of hydrolysis. In non-sterile soils, this compound further degraded
to unidentifiable products (Smith, 1988) which may include substituted anilines (Bartha,
1971).
Photolytic. The reported photolytic half-lives for asulam in water at pH 3 and 9 were
2.5 and 9 days, respectively (Humburg et al., 1989)
Chemical/Physical. Forms water-soluble salts (Hartley and Kidd, 1987). When heated
to 75°C, asulam decomposed to sulfanilic acid, carbamic acid and sulfanilamide. At 90°C,
4-nitro- and 4-nitrosobenzene sulfonic acids were released (Rajagopal et a
