Description
Benazolin is a post-emergence herbicide. It has a moderate aqueous solubility, is semi-volatile with a high potential to leach to groundwater. It is not persistent in soil systems but may possibly be persistent in water. Benazolin has a low mammalian toxicity and is not expected to bioaccumulation. It has a low to moderate toxicity to most aquatic organisms, honeybees and earthworms.
Uses
Benazolin is a selective systemic herbicide developed
in the 1960s that has growth-regulatory action in
susceptible plants. Structurally, it is a benzothiazolacetic
acid and is unrelated to the four major groups of synthetic
auxins discussed thus far. Benazolin controls a range of
annual broadleaf weeds in alfalfa (Medicago sativa), canola
(Brassica spp.), cereals, clover (Trifolium spp.), corn (Zea
mays), grassland, and flax (Linum usitatissimum), and it
has a relatively low persistence in the environment.
Definition
ChEBI: A member of the class of benzothiazoles that is 4-chloro-1,3-benzothiazol-2(3H)-one which is substituted on the nitrogen by a carboxymethyl group and at position 4 by chlorine. A post-emergence herbicide used (generally as a salt or este
) for the control of annual weeds in wheat and oilseed rape. It is not approved for use with the European Union.
Production Methods
Benazolin is commercially synthesised through a controlled multi-step process that begins with the formation of a benzoxazinone intermediate, which is then reacted with appropriate substituents to introduce herbicidal functionality. A key innovation in the process involves lowering the reaction temperature and adding a catalyst, which significantly reduces the formation of unwanted byproducts and improves safety.
Mechanism of action
Selective, systemic growth-regulation action. It disrupts the normal hormonal balance in susceptible plants by mimicking the action of the natural plant hormone indole-3 acetic acid (IAA). This leads to abnormal growth and eventual death of the plant species.
Safety Profile
Moderately toxic by ingestion. Anherbicide. When heated to decomposition it emits toxicfumes of SOx, Cl-, and NOx.
Metabolism
Because benazolin is not degraded
by light and is not readily volatilized, the most important
factors affecting its persistence in the environment are
microbial breakdown and leaching. However, because
the microbial breakdown is so rapid, significant leaching
may not occur unless the rainfall within a few days of
application is large.
Toxicity evaluation
Benazolin is primarily excreted in
the urine as N-[2-chloro-6-(methylsulfinyl)phenyl]glycine
and N-[N-[2-chloro-6-(methylthio)phenyl]glycinyl]aniline.
Acid-labile conjugates of benazolin acid and N-[2-chloro-
6-(methylthio)phenylglycine] are also formed in small amounts. The acute oral LD50 for rat and mice are
>5000 mg/kg and >4000 mg/kg, respectively. See Table 21
for a list of toxicological data for benazolin.
