Recent Advancement on Kinetic and Mechanistic Studies on the Selective Oxidation of Primary Aliphatic Alcohols under Phase Transfer Catalysis

Chromate and permanganate ions in various forms are used as powerful oxidising agents in organic
and inorganic oxidations in polar media. Kinetic studies on the oxidation of primary aliphatic alcohols
such as 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol and 1-decanol has been
carried out using phase transferred monochromate in benzene. Tetrabutylammonium bromide and
tetrabutylphosphonium bromide are used as phase transfer catalysts. The reaction showed first order
dependence on both [alcohol] and [monochromate ion]. The oxidation leads to the formation of
corresponding aldehyde and no traces of carboxylic acid has been detected. The reaction mixture
failed to induce the polymerization of added acrylonitrile which rules out the presence radical
intermediates in the reaction. Various thermodynamic parameters such as activation energy, enthalpy
of activation, entropy of activation and Gibb’s free energy have been evaluated. A suitable mechanism
has been proposed as per the experimental results obtained. The selective oxidation of primary
aliphatic alcohols involves the formation of chromate ester which on decomposition giving the product.
It is not possible to carry out the reaction in organic media without using PT catalysts. So, this method
involving PT catalysts can be used for the selective oxidation of primary alcohols in non-polar solvents
and hence kinetics and mechanism can be easily studied.