Dichloroethylene photolysis

The trans isomer is more reactive than the cis isomer ia 1,2-addition reactions (5). The cis and trans isomers also undergo ben2yne, C H, cycloaddition (6). The isomers dimerize to tetrachlorobutene ia the presence of organic peroxides. Photolysis of each isomer produces a different excited state (7,8). Oxidation of 1,2-dichloroethylene ia the presence of a free-radical iaitiator or concentrated sulfuric acid produces the corresponding epoxide [60336-63-2] which then rearranges to form chloroacetyl chloride [79-04-9] (9). 

The formation and reaction of peroxyl radicals derived by reaction of tervalent phosphorus compounds with oxygen have attracted interest. Photolysis of trialkyl phosphites in oxygenated solutions of aromatic hydrocarbons gives phenols. " Phosphorus trichloride reacts with 1,2-dichloroethylene, in the presence of oxygen, to give (17). It is tempting to suggest that both reactions occur via similar intermediates, e.g. (15) and (16). 

Photolytic. In air-saturated distilled water, direct photolysis of methoxychlor by >280 nm light produced l,l-bis(p-methoxyphenyl)-2,2-dichloroethylene (DMDE), which photolyzed to p-meth-oxybenzaldehyde. The photolysis half-life was estimated to be 4.5 months (Zepp et al., 1976). 

Relatively little work has been done on the photochemistry of the halogenated alkenes. The isomerisation of liquid 1,2-dichloroethylenes irradiated in the singlet-triplet band (A 3130-3660 A) has been studied by Grabowski and Bylina a single triplet state is favoured for both cis and trans isomers. Experiments on the continuous photolysis of gaseous dj-l,2-dichloroethylene with full mercury arc indicate two primary processes, viz., molecular detachment of HCl, and rupture of the C-Cl bond, viz. 

Z pp and co-workers (1976) found that photolysis of methoxychlor, although much more rapid than that of DDT, is still a very slow environmental process. The major product of light-induced transformation is l,l-bis(p-methoxyphenyl)-2,2-dichloroethylene (DMDE, 24). This product is subject to rapid photodegradation in both aqueous and hydrocarboi) media. 

In highly methylated ethylene the (N,V) and 3s bands separate and the Rydberg band is definitely at lower frequencies . The same applies to most fluoroethy-lenes In the chloroethylenes conditions are likely to be similar althou some problems remain with the band assignments Now, in a recent paper Ausubel and Wijnen have shown that the photolysis of both cis and tram 1,2-dichloroethylenes (between 200 and 240 nm) involve two excited states. For the trans isomer they obtained, from the lower excited state, the following primary steps ... 

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