| dc.description.abstract | In a bicontinuous conductive media of 23 :34:43 didodecyldimethylammonium bromide
DDAB/n-dodecane/water microemulsion (% by wt.), controlled potential electrolysis was
performed at the two diffusion controlled reduction waves of copper phthalocyanine
tetrasulphonic acid, tetrasodium (CuPcTS) In absence and in presence of added 1,2-
dibromobutane as substrate. From the data obtained, it is possible to establish the
mechanism for electro catalytic reduction of vicinal dihalides in surfactant media. The
results suggest that vicinal dihalides are reduced to the olefin and the mediator is
reoxidized from the active CuPcTS6- state to the CuPcTS5- or CuPcTS4.- state. In the
presence of catalyst the reduction of the organohalides occurs at potentials lower than that
of direct reduction.
Linear sweep voltammetric study indicate that p-chlorophenol is better reduced in
isotropic water/acetonitrile media than in the DDAB microemulsion media by copper
phthalocyanine mediated electro catalytic dehalogenation. A tentative reason is that in
microemulsion reaction occurs via adsorbed film of the surfactant containing both the
catalyst and the substrate. In acetonitrile/water media such an environment is not present.
A new approach to studies involving destruction of toxic recalcitrant organohalide
pollutants has been suggested. This involves fl correlation between molecular mechanics
and quantum mechanics calculated parameters with observed voltammetric half-wave
potentials. Such an approach has been applied for a few model organohalides. A linear
relationship has been-obtained between voltammetric half-wave potentials and theoretically
calculated parameters such as heats of formation and lowest unoccupied molecular orbitals
(LUMOs). A forward step suggested for the future involves understanding the lowering
of the overpotential phenomena by mediators (catalysts) for reductive dehalogenation of
organohalides.
UV/VIS spectroscopic studies for copper phthalocyanine tetrasulphonic acid,
tetrasodium in both aqueous and microemulsion media reflected a high degree of
aggregation for this complex in water as compared to microemulsion media. This
suggests possible compartmentalization of CuPcTS catalyst in microemulsion. A higher
extent of aggregation was found for CuPcTS catalyst in aqueous media, in presence of
added tetraethylammonium bromide salt.
In buffered aqueous media, voltammetric reduction of copper phthalocyanine
tetrasulphonic acid tetrascdiurn was found to be pH dependent. A positive shift in
reduction potentials was found with decrease in pH. Thus, control of pH could give
another handle on lowering of the overpotential phenomena for reduction of toxic
orghanohalides by copper phthalocyanine tetrasulphonate mediator (catalyst). | en |
