Relationship between porphyrin basicity and thiocyanate anation rates of cobalt(III) porphyrins in neutral detergent solutions

Journal Article · Fri Sep 01 04:00:00 EDT 1978 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic50187a066· OSTI ID:6626151

Williams, G N; Hambright, P

Authors report (a) a comparison of equilibrium and kinetic parameters for the complexation of thiocyanate by synthetic water-soluble cobalt(III) porphyrins both in the presence and in the absence of a neutral detergent, and (b) anation studies of water-insoluble cobalt(III) porphyrins of varying basicity in the same detergent media. The equilibrium constants, K, for SCN/sup -/ addition to the cobalt(III) porphyrins were determined spectrophotometrically. By using an excess of SCN/sup -/ over total porphyrin, the anation rate law was found to be first order in porphyrin. The observed rate constant, k/sub obsd/, was of the form k/sub obsd/ = K/sub f/(SCN/sup -/). Typical linear k/sub obsd/ vs. (SCN/sup -/) plots are shown. The observed anation rate constants for cobalt uroporphyrin I were independent of pH between pH 1 and 2.5. Since pK/sub a/ values for the H/sub 2/O-Co/sup (III)/-P/HO/Co/sup (III)/-P reactions are above 4, H/sub 2/O-Co/sup (III)/-P is considered the reactant at pH 1.5. Co/sup (III)/-P-(SCN)/sub 2/ forms at much higher SCN/sup -/ concentrations than those used in this study, and k/sub f/ for the first SCN/sup -/ addition is orders of magnitude smaller than that for the second SCN/sup -/ process. Table I shows a comparison of equilibrium and kinetic results measured for three water-soluble porphyrins with and without the neutral detergent. Table II is a summary of the cobalt(III)-porphyrin anation data measured in the detergent. 2 figures, 2 tables.

• Research Organization: Howard Univ., Washington, DC
• OSTI ID: 6626151
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 17:9; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ADDITIVES
AQUEOUS SOLUTIONS
CARBONIC ACID DERIVATIVES
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
COBALT COMPLEXES
COMPARATIVE EVALUATIONS
COMPLEXES
DETERGENTS
DISPERSIONS
EMULSIFIERS
EQUILIBRIUM
KINETICS
MIXTURES
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PH VALUE
QUANTITY RATIO
REACTION KINETICS
SOLUBILITY
SOLUTIONS
SURFACTANTS
THIOCYANATES
TRANSITION ELEMENT COMPLEXES
WETTING AGENTS
YIELDS