Reductive dechlorination of chlorophenols by vitamin B[sub 12]

Miscellaneous · Fri Jan 01 00:00:00 EST 1993

OSTI ID:6980652

Smith, M H

The reductive dechlorination of chlorinated phenols by vitamin B[sub 12], supported by the reductant Ti(III) citrate, was examined. Procedures were developed, including a novel reactor system, for conducting these experiments. Most of the experiments were conducted in either hermetically-sealed glass ampoules, which could maintain vitamin B[sub 12] in the fully-reduced vitamin B[sub 12s] state for months, or in the novel two-chambered reactor (TCR), which could also support vitamin B[sub 12s] for extended periods, and could easily be sampled to perform kinetic studies. Vitamin B[sub 12s] reductively dechlorinates chlorinated phenols by nucleophilic aromatic substitution of the cobalamin for a chlorine, followed by reductive cleavage of the arylcobalamin to form the reductively-dechlorinated product. Dechlorination occurs chiefly at positions ortho to another chlorine, but the 2 and 6 positions are extremely recalcitrant, even when another chlorine is adjacent. The proposed mechanism accounts for the observed regiospecificity, consistent with bond charge density and thermodynamic considerations. Pentachlorophenol, all of the tetrachlorophenols, and all of the trichlorophenols were challenged with vitamin B[sub 12s], and all were reductively dechlorinated to some extent. A sequential dechlorination pathway was constructed and compared to patterns exhibited by anaerobic microbial consortia. On the basis of this comparison, it was concluded that any involvement of vitamin B[sub 12] in biological reductive dechlorination of chlorinated phenols requires the intimate participation of apoenzymes to direct the regiospecificity toward the 2 and 6 chlorines on the ring. The observed kinetics of the reductive dechlorination of pentachlorophenol by vitamin B[sub 12s] can be described with a first order approximation. A threefold variability in rate constants was observed.

• Research Organization: Oregon State Univ., Corvallis, OR (United States)
• OSTI ID: 6980652
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
CHLORINATED AROMATIC HYDROCARBONS
BIODEGRADATION
DECHLORINATION
PHENOLS
VITAMIN B-12
BIOCHEMICAL REACTION KINETICS
AROMATICS
CHEMICAL REACTIONS
DECOMPOSITION
DEHALOGENATION
DRUGS
HALOGENATED AROMATIC HYDROCARBONS
HEMATINICS
HEMATOLOGIC AGENTS
HYDROXY COMPOUNDS
KINETICS
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
REACTION KINETICS
VITAMIN B GROUP
VITAMINS
400201* - Chemical & Physicochemical Properties
550200 - Biochemistry
550700 - Microbiology