Kinetic studies of organocobalt compounds related to vitamin B/sub 12/ coenzymes. [B12s]
The decomposition of the unstable alkylcobaloxime, ..cap alpha..-phenylethyl-(aquo)cobaloxime, proceeds rapidly in acidic, aqueous methanol leading to the formation of styrene and dimeric organic products. Kinetic studies were carried out at ..mu.. = 1.0 M in the (H/sup +/) range 0.0014 to 1.0 M. The results obeyed the rate expression -d(C/sub 6/H/sub 5/CH(CH/sub 3/)Co(dmgH)/sub 2/(OH/sub 2/))-/dt = (k/sub b/ + K/sub a/K/sub H/(H/sup +/)/1 + K/sub H/(H/sup +/)) with k/sub b/ = (3.27 +- 0.21) x 10/sup -3/ s/sup -1/, k/sub a/ + (1.48 +- 0.14) x 10/sup -2/ s/sup -1/, and k/sub H/ = 8.13 +- 0.38 M/sup -1/ at 25.0/sup 0/C. Activation parameters have been evaluated for k/sub b/ and k/sub a/. The rate of decomposition of ..cap alpha..-phenylethyl(aquo)cobaloxime is independent of added oxidants, such as H/sub 2/O/sub 2/ and Co(NH/sub 3/)/sub 5/Br/sup 2 +/. A mass law retardation effect is observed in the presence of Co(en)/sub 3//sup 3 +/ in neutral solution. The kinetic and product anlaysis data are used to show that decomposition of ..cap alpha..-phenylethyl(aquo)cobaloxime involves concurrent homolytic and ..beta..-elimination pathways in acidic media. Vitiman B/sub 12s/ has been generated electrochemically at pH 2.5 to 3.2 in aqueous glycine buffers to yield reasonably stable solutions under strictly oxygen-free conditions. The reaction of B/sub 12s/ and a series of chromium(III) complexes, (H/sub 2/O)/sub 5/CrX/sup 2 +/ with X = F/sup -/, Cl/sup -/, Br/sup -/, N/sub 3//sup -/, NCS/sup -/, SH/sup -/, and OH/sup -/, occurs rapidly to produce B/sub 12r/ and Cr/sup 2 +/. The kinetic results follow a second-order rate dxpression -d(B/sub 12s)/dt = k/sub x/(B/sub 12s)(CrX/sup 2 +/). Electron transfer is proposed to occur by an innersphere mechanism. 22 figures, 17 tables.
- Research Organization:
- Ames Lab., IA (USA)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 6577024
- Report Number(s):
- IS-T-964; ON: DE83004864
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
Similar Records
Concurrent and competitive homolysis and elimination reactions of (. cap alpha. -phenylethyl)aquocobaloxime
Kinetics and mechanisms of the reactions of aliphatic free radicals with organocobaloximes and fluoropentaamminecobalt(III) ion, and of iron(III) with methylrhodoxime. [C(CH/sub 3/)/sub 2/OH and C(CH/sub 3/)OC/sub 2/H/sub 5/ radicals]
Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CHROMIUM COMPLEXES
ELECTROCHEMISTRY
COBALT COMPLEXES
DECOMPOSITION
ORGANOMETALLIC COMPOUNDS
OXIMES
VITAMIN B-12
CHEMICAL PREPARATION
AQUEOUS SOLUTIONS
AROMATICS
BUFFERS
CHEMICAL REACTION KINETICS
ELECTRON TRANSFER
EXPERIMENTAL DATA
HYDRATES
MEDIUM TEMPERATURE
METHANOL
PH VALUE
STYRENE
ALCOHOLS
AMINES
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DATA
DISPERSIONS
DRUGS
HEMATINICS
HEMATOLOGIC AGENTS
HYDROCARBONS
HYDROXY COMPOUNDS
INFORMATION
KINETICS
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
REACTION KINETICS
SOLUTIONS
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
VITAMIN B GROUP
VITAMINS
400201* - Chemical & Physicochemical Properties
400301 - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)
400400 - Electrochemistry