INTERRELATION BETWEEN CATALYTIC REDUCTION RATE AND SOLUBILITY OF NITROBENZOIC ACID ISOMERS

Abstract

The solubility of nitrobenzoic acid isomers is determined from the concentration of solution in equilibrium with the solid phase at a temperature of 303 K in an azeotropic aqueous solution of 2-propanol, including additives of acetic acid and sodium hydroxide, with an error of no more than 5%. It is shown that the lowest solubility in all these media is observed for para-nitrobenzoic acid, and the maximum for the meta-isomer. The addition of acid or base to the liquid phase assists an increase in solubility for all isomers of nitrobenzoic acid. The most significant changes in solubility occur in the presence of sodium hydroxide in the water-alcohol solvent. The shift of the maxima in the absorption spectra was compared with the change in the solubility value. It has been established that with increasing solubility, the rate of liquid phase catalytic hydrogenation of nitrobenzoic acid isomers on the skeletal nickel catalyst decreases. А linear correlation between the solubility of reagents and the rate of their reduction is revealed. The observed interrelation for para- and meta-isomers in neutral and acidic aqueous-alcoholic media is mostly caused by the influence of solubility on the adsorption ability of the hydrogenated compound on the surface of the nickel catalyst. Deviations from this dependence in the presence of sodium hydroxide can be explained by ionization of the of nitrobenzoic acid isomers molecules and by redistribution of the forms of hydrogen adsorbed on the surface of the nickel catalyst. The reason of the distinction in a similar correlation for isomers with a substituent in the ortho-position relative to the nitrogroup is the possibility for forming an intramolecular hydrogen bond in all used media.