Kinetics of solid acids catalysed nitration of toluene: Change in selectivity by triphase (liquid–liquid–solid) catalysis

Abstract

Nitrotoluenes are precursors to a variety of commercially important products such as dyes, pharmaceuticals, and plastics. The protonated form of Y, ZSM-5, and mordenite zeolites as well as strongly acidic cation exchange resin (Amberlite IR-120) were examined as triphase catalyst (liquid-liquid-solid) for the nitration of toluene to produce mainly mononitrotoluenes. Among the solid acid catalysts tested, zeolites were found to be more active than cation exchange resin with highest activity for H-mordenite followed by HZSM-5 and HY zeolites. The reaction was found to be free from external diffusional resistance. The effects of other parameters (temperature, catalyst loading, and nitric acid concentration) on the rate of toluene nitration over H-mordenite catalyst were also investigated. The selectivity for p-nitrotoluene increases with temperature but decreases with increase in nitric acid concentration. The acidity level of the catalyst determines the product distribution; the stronger the acidity, the lower the ortho/para ratio is in the product mixture. The triphasic nitration reaction is kinetically controlled with an activation energy of 24.24 kJ/mol. The catalyst could be reused for several cycles with negligible loss in activity.

Preparation of Solid Superacid SO42–/ZrO2 and SO42–/ZrO2-MxOy (M═Ce, Co, Mn, and Zn) and Its Application in Toluene Nitration

“…Henceforth, numerous studies have confirmed the existence of the nitronium ion . The presence of a catalyst facilitates the dissociation of nitric acid, shifting the equilibrium toward the formation of NO 2+ that reacts with the benzene ring to produce nitrotoluene. The basic mechanism is shown in the following equation normalH normalN normalO 3 + H + ⇌ H 2 normalN normalO 3 + ⇌ normalN normalO 2 + + H 2 normalO A r H + normalN normalO 2 + ⇌ normalA normalr + ( H ) normalN normalO 2 ⇌ normalA normalr normalN normalO 2 + H + …”

“…Henceforth, numerous studies have confirmed the existence of the nitronium ion. 7 The presence of a catalyst facilitates the dissociation of nitric acid, shifting the equilibrium toward the formation of NO 2+ 8 that reacts with the benzene ring to produce nitrotoluene. The basic mechanism is shown in the following equation …”