Advisor(s) - Committee Chair
Robert Farina, Darwin Dall, John Reasoner
Department of Chemistry
Master of Science
Spectral and kinetic studies made on CoPc over a concentration range of 1.72 x 10-6M – 1.00 x 10-5M in DMSO are consistent with a monomer-dimer equilibrium at 303 K. The dimerization constant obtained at 303 K is 1.67 x 104M-1 and is two to three orders of magnitude smaller than those of several tetrasulfonated metallophthalocyanines in aqueous solution. The rate constants for the formation and dissociation of the CoPc dimer in DMSO at 303 K are 1.29 x 102M-1s-1 and 7.20 x 10-3s-1, respectively. The low dimerization constant for CoPc in DMSO is attributed to its relatively slow rate of dimer formation. Introduction of cyanide, detergents, and salts to solutions of CoPc in DMSO all enhanced the dissociation of the CoPc dimer. Furthermore, both cyanide and the catonic detergent cetyl trimethylammonium bromide (CTAB) at concentrations of 6.0 x 10-2M and higher, facilitate oxidation of cobalt in CoPc. For cyanide, this is accomplished by destabilization of the metal eg electrons by back-bonding in the axial positions of CoPc while the CTAB detergent forms a micelle which encapsulates a CoPc monomer striping the dye of axial DMSO molecules in the process. Thus, oxygen can bind to the vacant axial positions on the metal.
Kinetic studies of the interactions between cyanide and CoPc in DMSO show two fast reactions which are attributed to the addition of cyanide to the axial positions of CoPc. The rate constants for the addition of the first and second cyanide ligands to CoPc are 7.72 x 105M-1s-1 and 5.51 x 104M-1s-1, respectively, at 299 K. Activation parameters, ΔHs* and ΔSs* for the second cyanide addition are 9.9 kcal/mol and -4.0 e.u., respectively. Both additions are faster than the corresponding reactions with CoTSPc4- in DMSO. The three detergents sodium dodecyl sulfate (SDS), Triton X-100, and cetyl trimethylammonium bromide (CTAB) dissociate the CoPc dimer more than by dilution with DMSO. Furthermore, Triton X-100 dissociates the CoPc dimer at about the same rate as CTAB while SDS is not as efficient at comparable concentrations to CTAB. The critical micelle concentration for the CTAB-DMSO system is reached at a CTAB concentration of 6.0 x 10-2M where the CoPc dimer dissociation rate nearly triples compared to solvent dilution and oxidation of the metal in CoPc is observed. The addition of tetraethylammonium bromide, tetrapropylammonium bromide and tetrabutylammonium bromide to CoPc in DMSO increases the dimer dissociation rate by a factor of two compared to dilution with DMSO. All salts dissociate the CoPc dimer at similar rates suggesting the hydrocarbon chain is of insufficient length to be as effective as CTAB. Finally, oxygen does not seem to effect the dissociation of the CoPc dimer in DMSO
King, Harry M. Jr., "Spectral and Kinetic Studies of the Interaction of Cyanide and Detergents with Cobalt (II) Phthalocyanine in DMSO" (1988). Masters Theses & Specialist Projects. Paper 1765.