engleski

Dehalogenation of organic compounds by reductive radicals

-Radiolysis and measurements of halide ions by means of ion chromatography have been employed to investigate reductive dehalogenation of chloro-, bromo-, and iodophenols, halogenated aliphatic compounds and 5-bromouracil by carbon-centred radicals, •CH(CH3)OH, •CH2OH, and •CO2, in air-free aqueous solutions in the presence of ethanol, methanol or sodium formate as precursors of reductive organic radicals. The influence of different bases on the reaction efficiency has also been investigated. The presence of sodium hydrogencarbonate and ammonium acetate significantly influences reduction power of carbon-centred radicals (except •CO2), while presence of stronger base, potassium hydrogenphosphate, does not improve reduction power of those radicals which is otherwise insufficient for dehalogenation of brominated and chlorinated compounds. In systems where reduction is operative, dehalogenation has been observed to occur by a chain process. Additionally, complex between base and reductive radical is formed in case of •CH(CH3)OH and •CH2OH. Mechanisms of the abovementioned reduction reactions, simple electron transfer mechanism for •CO2 and proton-coupled electron transfer for •CH(CH3)OH and •CH2OH, have been investigated. System with the concentration of NaHCO3 of 10 mmol/dm3 gives the optimal outcome, i.e. the highest yield of halide ions with as low concentration of other components as possible but even better rate constants have been achieved with •CO2 (for one to two orders of magnitude). Equilibrium constants of complexes observed in this work has been estimated to be (almost) the same.

radicals; radiolysis

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