Selective dinitration of toluene over zeolites

The aim of this study was to develop a new greener and cleaner system for the dinitration of toluene to produce high yield in good selectivity of the desired product. Chapter one represents an introduction to the use of inorganic solid catalysts such as zeolites. The structure, acidity and selectivity of such solids were discussed. Chapter two described the latest examples in nitration reactions using various nitrating reagents. Dinitration of toluene with nitric acid and acetic anhydride and zeolite H0 was discussed in Chapter three initially. This study involves pushing the reaction to completion towards 2,4-dinitrotoluene by varying the reaction conditions. The effect of quantity of zeolite, reaction time, quantity of acetic anhydride, quantity of nitric acid, variation of nitrating reagent proportions and reaction temperature were studied. Also, use of two steps technique by adding extra zeolite and/or nitrating reagent in the second step. By using this system in dinitration of toluene 2,4-dinitrotoluene yield could not exceed 90% even when large excess of nitrating reagent was added and the reaction stopped at the mono-nitro stage. Therefore, in an attempt to push the reaction to completion, various acid anhydrides were used. Acid anhydrides with different carbon chain length, halogenated acetic anhydrides, aliphatic anhydrides of different steric bulk and aromatic and/or cyclic anhydrides containing rings were used. The most promising anhydrides were found to be propionic anhydrides and chloroacetic anhydride. Chloroacetic anhydride produced 98% of 2,4-dinitrotoluene in which 2,4-:2,6-dinitrotoluene was 49:1. In addition, propionic anhydride produced 98% in excellent selectivity (2,4-:2,6-dinitrotoluene = 123:1). This result is simply the highest for direct dinitration of toluene ever recorded. In contrast to traditional method, this system gives excellent yield with excellent selectivity and the only by-product produced during the process is the acid which can recycle easily. Also, the zeolite can easily remove from the reaction mixture by filtration, activated and reused to give good results. These systems were applied successfully to various mono-substituted benzenes with various activities.