DICHLOFLUANID

Description

Dichlofluanid is solid sparingly soluble in water, soluble in most organic solvents, and decomposes in alkaline media.

The Uses of DICHLOFLUANID

Dichlofluanid is used to control a wide range of fungal diseases including storage diseases on many crops.

The Uses of DICHLOFLUANID

Fungicide.

Definition

ChEBI: A member of the class of sulfamides that is sulfamide in which the hydrogens attached to one of the nitrogens are replaced by methyl groups, while those attached to the other nitrogen are replaced by a phenyl and a [dichloro(fluoro)methyl]sulfanediyl group A fungicide introduced in 1965 and used in the cultivation of fruit and vegetables, as well as in wood preservatives, it is no longer approved for use in the European Union.

Metabolic pathway

Dichlofluanid contains an unstable dichlorofluoromethylthio (sulfenyl) moiety that has been shown to undergo rapid hydrolytic and metabolic degradation to N',N'-dimethyl-N-phenylsulfamide (2) (dimethylsulfanilide). By analogy with captan, presumably the dichlorofluoromethylthio moiety can be transferred to the sulfur atoms of cellular thiols such as cysteine and glutathione. Thus in the presence of thiols, dichlofluanid is probably cleaved at the N-S bond to form thiophosgene (3) or its monofluoro analogue and other gaseous products such as hydrogen sulfide, hydrogen chloride and carbonyl sulfide. Thiophosgene or its monofluoro analogue is rapidly hydrolysed by water. The dichlorofluoromethylthio group and thiophosgene may be intermediates in the formation of addition products such as thiazolidine-2-thione-4-carboxylic acid (4) by addition to cysteine. A thiazolidine derivative of glutathione may also be formed (5).

Degradation

Dichlofluanid is hydrolysed rapidly in alkaline conditions to form N',N'- dimethyl-N-phenylsulfamide (2). The hydrolytic DT₅₀ is >15 days, >18 hours and <10 minutes at pH 4,7 and 9, respectively, at 22 °C (PM).
Dichlofluanid is unstable to light and its fungitoxicity decreases on exposure, albeit to a lesser extent than for captan. Dichlofluanid does not absorb light of wavelength of >295 nm and so photodegradation is unlikely to occur in the absence of photosensitisers. Dichlofluanid was reacted in vitru with glutathone or cysteine in water/methanol solutions. The reaction was carried out in a closed system at 40 °C using traps for COS and CO2 and analysis by TLC. The proposed route of degradation is given in Scheme 1. Short-lived intermediates are proposed that were not detected. It is not clear whether thiophosgene (3) or its monofluoro analogue were formed (Schuphan ef al., 1981).
The photolysis of dichlofluanid was studied under artificial conditions that may not be relevant to typical environmental circumstances. Unlabelled dichlofluanid in methanol, benzene or acetone solution was irradiated with a medium pressure UV lamp (100 W) but the emission wavelengths were not given. As they photodegraded, the methanol and benzene solutions gave a brown solid and the acetone solution darkened. Products were separated and identified using IR, GC and MS methods. The products from acetone solution were N',N'-dimethyl-Nphenylsulfamide (2), phenyl isocyanate (6), phenyl isothiocyanate (7) and dimethylamidosulfonyl chloride (8). Studies using GC-MS indicated the presence of bis(dichlorofluoromethyl) disulfide (9). It was concluded that irradiation of dichlofluanid produced mainly the hydrolysis product dimethylsulfanilide (2) and the very active dichlorofluoromethyl sulfide radical (.SCCl2F), the latter reacting with other compounds in solution.
For example, 1-(dichlorofluoromethylthio)propan-2-one (10), and 1- (dichlorofluoromethylsulfonyl)propan-2-one(11) were formed in acetone solution by reaction with solvent. The phenyl isothiocyanate (12) was also isolated In vitro tests against Botrytis cinerea showed that irradiation decreased the fungicidal activity of dichlofluanid (Clark and Watkins, 1978).