Pestic. Sci. 1978, 9, 225-228

Photolysis of Dichlofluanid

Terence Clark and David A. M. Watkins

Long Ashton Research Station, University of Bristol, Long Ashton, Bristol, BS18 YAF

(Manuscript received 28 November 1977)

Dichlofluanid was found to be degraded by ultraviolet light in methanol, benzene and acetone solution. The products from acetone solution included N,N-dimethyl-N’-phe- nylsulphamide, phenyl isocyanate, phenyl isothiocyanate and dimethylamidosulphonyl chloride. G.c.-m.s. studies further indicated the presence of bis(dich1orofluoro- methyl) disulphide, l-(dichlorofluoromethylthio)propan-2-one and 1-(dichloro- fluoromethylsulphonyl)propan-2-one. In-vitro tests against Botrytis cinerea showed that irradiation decreased the activity of dichlofluanid and that synergism did not occur.

1. Introduction

The part that light plays in the fate of pesticides has been increasingly investigated in the past decadeel If decomposition by light does occur there is a need to identify the products and to see if there is either a loss or an increase in biological activity. It may be necessary to include a check for these products in residue analysis.

Dichlofluanid (I) (N-dichlorofluoromethylthio-N’,N’-dimethyl-N-phenylsulphamide) is used as a fungicide, in particular against Botrytis cinereu on strawberries. It is light sensitive and dis- coloration occurs without effect on its biological activity.2 In discussing the influence of light on the activity of fungicides Kaspers3 mentions that dichlofluanid is much less sensitive to light than captan. It is hydrolysed easily in sodium hydroxide solution to N,N-dimethyl-N’-phenylsulphamide (11) and this compound is found under field conditions.4 T s ~ g e , ~ in a paper on the thermal stability of dichlofluanid, reports the formation of (11) on photolysis. The presence of isothiocyanates in a photolysis mixture has also been rep0rted.l.

2. Experimental

2.1. Materials Dichlofluanid, obtained by extracting ‘Elvaron’ (50 % w.P.) with dry benzene, was recrystallised from methanol and had a m.p. 105-106°C. Phenyl isothiocyanate and phenyl isocyanate were purchased from Koch-Light ; dimethylamidosulphonyl chloride (VI) was a gift from Bayer (UK) Ltd. Distilled solvents were used in irradiation experiments.

2.2. Chromatography Column chromatography was carried out on silica gel (Merck 0.05-0.2 mm) packed in light petro- leum (b.p. 40-60°C). Gas chromatographic analyses were made on a stainless steel column (1.83 m x 3.17 mm) containing 2 % ‘OV17’ on ‘Gas Chrom Q’ using an FID. The temperature was programmed from 40 to 260°C at 6°C min-l; the carrier gas was nitrogen (30 ml min-1).

G.c.-m.s. was carried out on an LKB 9000 instrument at 70 eV using helium as the carrier gas. Mass spectrum of component C (m/e values and relative abundance of ions greater than 4% ot

the total ion amount): 133 (19: 2-C1), 107 (20), 101 (100: 2-CI), 98 (14), 92 (6), 90 (4), 79 (6), 66 (3, 64 (17), 63 (32), 48 (4), 47 (6), 45 (8), 44 (14), 43 (50), 42 (lo), 41 (5).

0031-613X/78/06W0225 $02.00 0 1978 Society of Chemical Industry 225

226 T. Clark and D. A. M. Watkins

Mass spectrum of component D (rn/e>4'j/,): 222 (8: 2-C1), 123 (4), 101 (9: 2 4 3 , 98 (18: I-Cl),

Mass spectrum of component F (rn/e>4%): 190 (4: 2 4 3 , 119 (7), 116 ( 3 , 112 (5: 1-Cl), 101 89 (lo), 63 (19 , 46 (4), 45 (6), 44 (15), 43 (loo), 42 (7), 36 (6).

(7: 2-CI), 97 (10: 2-C1), 77 (4), 75 (9, 73 (lo), 63 ( 5 ) , 57 (6), 46 (4), 45 ( 1 9 , 44 (9), 43 (loo), 42 ( 9 , 41 (4). 40 (4), 39 (6), 36 (5).

2.3. Photolysis Magnetically stirred solutions of dichlofluanid were irradiated using a Hanovia (100 W) medium pressure lamp in a quartz apparatus. Solutions in methanol or benzene darkened, and a brown solid deposited on the lamp surface stopping the reaction. An acetone solution (250 mi; 0.5 g) darkened but no solid separated. The irradiation was stopped after 1 h and the solution concentrated on a rotary evaporator (at 40°C) to give a brown oil. Quantitation by g.c. was from a further experiment, and the solution concentrated four-fold ; a sample was methylated by diazomethane and the hydro- lysis product quantified as its methylated derivative.

2.4. Biological testing In-vitro tests were made using a modification of the method of Edgington et aL7 Test solutions (3 PI), absorbed on filter paper discs, were placed on agar strips seeded with B. cinerea spores. These were incubated at 25°C and zones of inhibition measured after 2 days. A photolysis mixture was adjusted to contain 100 PM unchanged dichlofluanid (as determined by g.c.). A synthetic mixture of I, 11, 111, IV and VI, was made up in the proportions estimated to be present in the photolysis mixture and adjusted to contain 100 PM dichlofluanid.

3. Results and discussion

The brown oil had a characteristic smell and the infrared spectrum (film) had a strong broad band centred at 2100 cm-1 which reached a maximum and then decreased in size with increased irradiation time. The photolyses used for analysis were those in which this band was at a maximum. The soh- tion spectrum in carbon tetrachloride showed a band at 2050 cm-l which in chloroform shifted to 2100 cm-1. This shift is characteristic of the isothiocyanate group.8

Column chromatography of this oil gave an early fraction, eluted by light petroleum, which contained a volatile clear oil showing one major peak on g.c. at 18 min. The oil had an infrared spectrum and g.c. retention time identical to that of an authentic specimen of phenyl isothiocyanate (111). A trace of oil from a later fraction had an infrared spectrum similar to phenyl isothiocyanate; but with additional bands at 805 and 830 cm-l indicating a substituent in the benzene ring. The mass spectrum showed a parent ion of m/e 267 with a typical isotope pattern for two chlorine atoms. The fragmentation pattern suggested the presence of a compound of formula C~H~(NCS)(SCCIZF) (V) but the orientation was not deduced.

Infrared spectra of further fractions from the column, obtained by elution with light petroleum containing increasing proportions of diethyl ether showed similar bands at 2100 cm-1. This indica- ted the presence of other isothiocyanates or thiocyanates but these were in small amounts and were shown by g.c. to be mixtures.

On treatment of the acetone distillate with ammonia a white precipitate was obtained. By com- paring the physical properties of this solid with an authentic specimen it was shown to be ammo- nium chloride. This suggests the presence of hydrogen chloride in the distillate.

Gas chromatography of the brown oil (Table 1) showed two major peaks, six minor ones and many small peaks. The major ones were identified as unchanged dichlofluanid (12%; component H) and the hydrolysis product (I 1 %; component G). Quantitation of the latter was carried out on the methylated derivative since another unidentified minor component was eluted in the same fraction. Quantitation of the other peaks was not possible due to their incomplete resolution and varying size from run to run. This may have been due to loss during work-up caused by their volatile nature. Because column chromatography did not give a clear separation g.c.-m.s. studies were made.

Photolysis of dichlofluanid 221

Table 1. G.c. and m.s. data of the main photolysis products obtained by irradiation of dichlofluanid in acetone

Peak time Identified Component (min) Parent ion (rn/e) structure

7 9

1 1 16 18 22 34 44

119 143 (1-Cl pattern) 266 (4-CI pattern) 190 (2-C1 pattern)

135 222 (2-C1 pattern)

200 332 (2-C1 pattern)

Components A, B and E were identified, by comparison with spectra of authentic specimens, as phenyl isocyanate (Iv), dimethylamidosulphonyl chloride (VI) and phenyl isothiocyanate 011).

Component C showed a parent ion m/e 266 (< 4%) with a 4-C1 pattern. The ion at m/e 133 (half the parent ion) had a 2-CI pattern and the further loss of 32 (-S) gave the base peak at m/e 101. This again had a two-chlorine pattern and was possibly due to .CChF. This suggested the presence of (VII) in the mixture. It is a likely product as it is known that sulphenyl halides can, under the influence of ultraviolet light, give such disulphides.9

The next component D had a parent ion m/e 190 with a 2-C1 pattern and also a peak at mle 101 ( . CC12F). Minor peaks ( < 4 %) at 155 (1-C1) and 154 (1 -CI) are possibly due to loss of CI and HCl respectively. The loss of 43 (.CH3CO) to 147 (c4%) followed by 46 (.CH&) to 101 suggests the presence of an acetone substitution product (VIII). It is known that sulphenyl halides react with active methylenes in this manner.10

A later component F with a molecular ion m/e 222 had a 2-C1 pattern. Its fragmentation pattern indicates it to be the sulphone of the acetone addition product, (IX).

In-vitro tests against Botrytis cinerea, using dichlofluanid as a standard at 100 p~ showed the photolysis mixture to be less active. The photolysis mixture and a synthetic mixture (both adjusted

228 T. Clark and D. A. M. Watkins

to 100 PM dichlofluanid) with photolysis mixture proportions showed no significant difference in activity from the standard. Individual testing of (II), (111), (IV) and (VI) at 10 mM showed them to be inactive against this fungus.

The main result of the ultraviolet irradiation on dichlofluanid seems to be the production of the hydrolysis product (11) and the very active .SCCIzF radical; this reacts with other chemicals present.

Acknowledgements

We thank Dr D. Woodcock for encouragement, Mr D. Puckey for obtaining the mass spectra data and Miss H. McDonald for carrying out the biological tests.

References

1. 2. 3. 4. 5. 6. 7. 8. 9.

10.

Watkins, D. A. M. Chemy Ind. 1974, p. 185. In Pesticide Manual(Martin, H.; Worthing, C. R., Eds) British Crop Protection Council, 1977, 5th edn, p. 168. Kaspers, H. PflSchutzNachr. Bayer 1974, 21, I . Vogeler, K.; Niessen, H. PflSchutzNachr. Bayer 1967, 20, 534. Tsuge, S.; Mesaki, T.; Suzeki, K.; Kashiwa, T. Noyaku Kagoku 1975, 3, 27; Chrm. Absrr. 1976, 84, 26844. Clark, T.; Watkins, D. A. M. Rep. Long Ashton Res. Stn for I972 1973, p. 86. Edgington, L.; Buchenauer, H.; Grossrnann, F. Pesric. Sci. 1973, 4, 747. Caldow, G. L.; Thompson, H. W. Spectrochim. Acta 1958, 13, 212. Prey, V.; Gutschik, E.; Berbalk, H. Mh. Chem. 1960, 91, 556. Fuson, R. C.; Price, C. C. ; Baurnan, R. A.; Bullitt, 0. H.; Hatchard, W. R.; Maynert, E. W. J . org. Chrm. 1946, 11, 469.