Reduction and alkylation of cobalt(II) tetrakis(4-sulfonatophenyl)porphyrin in aqueous solutions. A kinetic spectrophotometric study
The reactions of Co/sup II/TPPS (TPPS = tetrakis(4-sulfonatophenyl)porphyrin) with alkyl and hydroxyalkyl radicals have been studied by pulse radiolysis. The alkyl radicals undergo axial addition with rate constants of (1.2-1.9) 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 (1.1-1.2) 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.
- Research Organization:
- Univ. of Notre Dame, IN
- OSTI ID:
- 5340229
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 87:9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COBALT COMPOUNDS
ALKYLATION
RADIOLYSIS
AQUEOUS SOLUTIONS
CHEMICAL REACTION KINETICS
ORGANIC SULFUR COMPOUNDS
ORGANOMETALLIC COMPOUNDS
PORPHYRINS
PULSE TECHNIQUES
REDUCTION
CARBOXYLIC ACIDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
DISPERSIONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
MIXTURES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
RADIATION CHEMISTRY
RADIATION EFFECTS
REACTION KINETICS
SOLUTIONS
TRANSITION ELEMENT COMPOUNDS
400600* - Radiation Chemistry