Chemical Properties
White Solid
Uses
Agricultural fungicide and plant growth regulator.
Uses
Hymexazol is used to control soil-borne diseases caused by
Fusarium, Aphanomyces, Pythium, Corficium and Typhula spp. in rice, sugar
beet, fodder beet, vegetables, cucurbits, ornamentals, carnations and
forest tree seedlings. It is also used as a seed dressing and stimulates some
plant growth.
Definition
ChEBI: A member of the class of isoxazoles carrying hydroxy and methyl substituents at positions 3 and 5 respectively. It is used worldwide as a systemic soil and seed fungicide for the control of diseases caused by Fusarium, Aphanomyces
Pythium, and Corticium spp. in rice, sugarbeet, fodderbeet, vegetables, cucurbits, and ornamentals.
Production Methods
Hymexazol is synthesised through a water-phase process that begins with the reaction of hydroxylamine salts, typically hydroxylamine sulphate or hydrochloride, with methyl or ethyl acetoacetate to form a hydroxamic acid intermediate. This intermediate undergoes ring closure to form the oxazole ring, which is central to hymexazol’s structure. The reaction mixture is then acidified using hydrochloric acid to stabilize the product, followed by extraction with an organic solvent such as chloroform. The crude product is isolated through precipitation and centrifugation, and finally dried to yield hymexazol with an active content typically between 95% and 98%.
Mechanism of action
Hymexazol works by inhibiting RNA synthesis in pathogenic fungi, disrupting their growth and reproduction.
Metabolic pathway
Degradation of hymexazol in soil gave acetoacetamide and the product
of rearrangement, 5-methyl-2(3H)-oxazolone.H owever, in plants the fungicide
was principally converted into its O- and N-glucoside conjugates in
the roots and shoots. The two main metabolites of hymexazol found in the
urine of rats were the O-glucuronide and sulfate conjugates.
Degradation
Hymexazol is stable under alkaline conditions and relatively stable in
acidic conditions. It is stable to sunlight and heat (PM). It should be noted
that the parent molecule is tautomeric. Hymexazol is highly volatile and
will be lost by volatilisation unless it is covered or incorporated into soil.
The fungicide was completely biodegraded in natural water at 30 °C in
2 weeks and at 10-13 °C in 2 months (Rebenok and Kolesnikova, 1983).
Hymexazol is stable in sunlight but it is readily degraded by ultraviolet
light. Photolysis of an aqueous solution of the fungicide at 253.7 nm, using
a low pressure Hg lamp, afforded the oxazolinone (2) as the major product
and at least two unidentified minor components. The oxazolinone (2)
has been found in soil studies as described below and is a product of
rearrangement formed via an aziridinone intermediate as shown in
Scheme 1 (Nakagawa et al., 1974).
