Thiophenes 2.5- dichlorination

Phosphorus pentachloride at 180°C converted benzoxazole, substituted at C-2 by 3,4-dihydroxy-2-(p-nitrophenyl)thiophene, into the 3,4-dichlorinated thiophene derivative only (91JHC1449). 

Electrophilic substitution reactions of 5-hydroxybenzo[6]thiophene have been investigated in some detail. The 4-position is the most reactive toward nitration,152 nitrosation,497 bromination,422 and formylation (Duff procedure).338 Dibromination in the presence of acetate ion affords 4,6-dibromo-5-hydroxybenzo[6]thiophene,421,422, 497 and not the 3,4-dibromo derivative, as previously believed.542 Dichlorination similarly affords the 4,6-dichloro derivative,421 and not 4,4-dich loro-4,5-dihydrobenzo[6]thiophen-5-one, as reported earlier by Fries d al.542 An interesting comparison can be made between the behavior of 5-hydroxy benzo[6]thiophene and 2-naphthol in electrophilic substitution reactions. It is clear that both positions ortho to the hydroxyl group in 5-hydroxybenzo[6]thiophene are attacked, in contrast to 2-naphthol, where only the 1-position is attacked even in the presence of an excess of the reagent. Disubstitu-... 

A second study characterizing a huge groundwater contamination caused by chemicals used for wood impregnation revealed mono- and dichlorinated naphthalenes, chlorobenzo(b)thiophene, acenaphthene and methylated naphthalenes as the main pollutants. Anaerobic microbial degradation of the main pollutant 1-chloronaphthalene was evident from identification of 1 -chloro-4-naphthol and 1-chloronaphthoic acid as biotic transformation products. In contrast inorganic and compound specific stable carbon isotope analyses indicated only a minor degree of microbial transformation. Thus, sorption seemed to be the main attenuation process within the aquifer affected by the coal tar based contamination described above. 

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