Dihydroxybenzenes chlorination

Chlorinated dihydroxybenzenes, see Pentachlorophenol Chlorine, see Allidochlor. Anilazine. Bromacil. Chlordane, 2,4-D, Dalapon-sodium. p.p -DDT, Dicamba. Dieldrin, Diuron, Malathion, Monuron. Pentachloronitrobenzene. Picloram. Propachlor. 

Diazotization in the presence of boron trifluoride enables diazonium tetrafluoroborates to be isolated from the reaction mixture and purified. Subsequent controlled decomposition produces the required fluoroaromatic. Although explosion hazards and the toxicity of the isolated salts are significant concerns with this process, known as the Balz-Schiemann process, 4,4 -di-fluorobenzophenone (BDF. 6) has been prepared by this route as a monomer for the production of the engineering plastic poly(ether ether ketone) , or PEEK , by condensation with 1,4-dihydroxybenzene in the presence of potassium carbonate. BDF 6 is superior to its chlorine analog because in aromatic systems the nucleophilic displacement of fluorine is more facile than that of chlorine, leading to a shorter polymerization time and a better quality product containing less degradation impurities. 

The transformation of chlorophenols upon irradiation of nitrate mainly yields hydroxylated derivatives, while no nitration was observed. The absence of nitro derivatives can be attributed to the electron-withdrawing character of the chlorine atoms, inhibiting nitration. Dihydroxybenzenes and benzoquinone were also observed implying that a dechlorination process, induced by either hydroxyl or light, takes place in the system [123]. 

D.O. Martire, S.E. Braslavsky, N.A. Garcia (1991). Sensitized photooxidation of dihydroxybenzenes and chlorinated derivatives. A kinetic study. J. Photochem. Photobiol., A, 61, 113-124. 

The questions raised by Kekule s interpretation of the mechanism of this reaction led to a number of investigations which involved a further study of the oxidation of aromatic phenols and quinones. Thus, for example, Zincke in collaboration with Kuster48 and Rabinowitch 4 undertook a systematic investigation of the action of chlorine (potassium chlorate plus hydrochloric acid) on various derivatives of the three dihydroxybenzenes. The results of these experiments showed that these classes of benzene derivatives split up under conditions to give aliphatic compounds. The intermediate compounds which were formed from tetrahydrobenzene during these transfonnations, were identified as the hexachloro-o-diketone derivative (I) and the pentachloro-m-diketone derivative (II). 

CHEMICAL PROPERTIES highly reactive polymerizes and copolymerizes readily dimerizes to 4-vinylcyclohexene reacts vigorously with phenol, chlorine dioxide, copper and crotonaldehyde stabilization with o-dihydroxybenzene FP (-76°C, -105°F) LFL/UFL (2.0%, 11.5%) AT (420°C, 788°F). 

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