Reduction and alkylation of cobalt(II) tetrakis(4-sulfonatophenyl)porphyrin in aqueous solutions. A kinetic spectrophotometric study. [Pulsed irradiation]
The reactions of Co/sup II/TPPS (TPPS = tetrakis(4-sulfonatophenyl)prophyrin) with alkyl and hydroxyalkyl radicals have been studied by pulse radiolysis. The alkyl radicals undergo axial addition with rate constants of (1.2 to 1.9) x 10/sup 9/ M/sup -1/s/sup -1/ to form R-Co/sup III/TPPS complexes which either are stable (R = CH/sub 3/) or undergo decomposition R = CH(CH/sub 3/)/sub 2/) to Co/sup I/TPPS and an olefin via a ..beta..-proton elimination mechanism (k/sub 1/ = 0.3 s/sup -1/ at pH 8 and 3 s/sup -1/ at pH 13). The hydroxyalkyl radicals also form R-Co/sup III/TPPS with rate constants of (1.1 to 1.2) x 10/sup 9/ M/sup -1/ s/sup -1/. These adducts undergo heterolytic cleavage of the cobalt-carbon bond to form Co/sup I/TPPS and a carbonyl compound, with rate constants of 3.6 x 10/sup 2/s/sup -1/ (R = CH/sub 2/OH) and 6.2 x 10/sup 3/ s/sup -1/ (R = C(OH)(CH/sub 3/)/sub 2/). The radicals (CH/sub 3/)/sub 2/CO/sup -/ and CO/sub 2//sup -/ reduce CO/sup II/TPPS to Co/sup I/TPPS by an outer-sphere mechanism with rate constants 7 x 10/sup 8/ and 2 x 10/sup 8/ M/sup -1/ s/sup -1/, respectively. Co/sup I/TPPS is oxidized to CH/sub 3/Co/sup III/TPPS by CH/sub 3/I (k/sub 2/ = 3 x 10/sup 5/ M/sup -1/ s/sup -1/) and to Co/sup II/TPPS (probably through intermediate formation of Co/sup III/TPPS) by N/sub 2/O (k/sub 2/ less than or equal to 3 x 10/sup 2/ M/sup -1/ s/sup -1/). The reactivities of the present systems have been compared with those of other models suggested for vitamin B/sub 12/ like cobaloximes, cobalamins, and other macrocyclic Co/sup II/ complexes. 36 references, 6 figures, 1 table.
- Research Organization:
- Univ. of Notre Dame, IN
- OSTI ID:
- 5939263
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 87:9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COBALT COMPLEXES
ALKYLATION
OXIDATION
REDUCTION
WATER
RADIOLYSIS
ABSORPTION SPECTROSCOPY
ADDUCTS
ALKYL RADICALS
AQUEOUS SOLUTIONS
AROMATICS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CORRELATIONS
DATA ANALYSIS
EXPERIMENTAL DATA
HYDROXYL RADICALS
MATHEMATICAL MODELS
NITROUS OXIDE
PH VALUE
PORPHYRINS
PROPANOLS
REAGENTS
SULFONIC ACID ESTERS
VITAMIN B-12
ALCOHOLS
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL RADIATION EFFECTS
CHEMISTRY
COMPLEXES
DATA
DECOMPOSITION
DISPERSIONS
DRUGS
ESTERS
HEMATINICS
HEMATOLOGIC AGENTS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INFORMATION
KINETICS
MIXTURES
NITROGEN COMPOUNDS
NITROGEN OXIDES
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADICALS
REACTION KINETICS
SOLUTIONS
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES
VITAMIN B GROUP
VITAMINS
400600* - Radiation Chemistry