The Effect of Additives (pyrazine, Pyrazole and Their Derivatives) in the Oxidation of 2-Butanol with FeCl3‒H2O2 in Aqueous Solutions

In the present paper we described the oxidation of 2-butanol as a representative of secondary aliphatic alcohols. The oxidizing system FeCl3-H2O2 was used. A kinetic study of the oxidation reaction has been carried out. Different substituted pyrazines and pyrazoles, namely 2-pyrazinecarboxylic acid (PCA), 5-methyl-2-pyrazinecarboxylic acid (5MPCA), 2-methylpyrazine (2MPZINE), 3-(trifluoromethyl)pyrazole (3TFMPZOLE), 3-methylpyrazole (3MPZOLE) and 1-methylpyrazole (1MPZOLE) were added as cooperating ligands in aqueous solutions. DFT based calculations were also used in order to evaluate the different results obtained. Addition of PCA, 5MPCA and 3TFMPZOLE led to a better reaction performance, while the other ligands led to lower accumulation of products than the reaction without additives. Performed DFT studies suggested that the metal-ligand pi-back-bonding might be responsible for the reaction activity increase, while ligands more strongly bonded to Fe make it more difficult the access to the metal, leading to lower yields.