Example C Synthesis of 2-chloro-4,6-dimethylnicotinic acid: 15 g of 2-chloro-3-cyano-4,6-dimethylpyridine [Jahine, J. prakt. Chem. 316, 337 (1974)] was mixed with 40 ml of concentrated sulphuric acid and 13 ml of fuming nitric acid, and heated with stirring to 95° C to initiate an exothermic reaction. The reaction temperature was maintained between 95 °C and 100 °C by cooling with ice water. After the exothermic reaction subsided, stirring was continued at 100°C for 30 minutes. Subsequently, the reaction mixture was decanted into ice and the pH was adjusted with ammonia to 3-4. The precipitate was collected by filtration and washed with water. The resulting solid was dehydrated by azeotropy with toluene in a device fitted with a water trap and finally recrystallized by toluene to give the target compound in 80% yield of the theoretical value with a melting point of 159-160°C. The results of elemental analysis were as follows: molecular formula C8H8ClNO2, molecular weight 185.6; calculated values: C 51.77%, H 4.34%, Cl 19.10%, N 7.55%; measured values: C 51.85%, H 4.36%, Cl 19.25%, N 7.56%.
