How is 3,4-Dichloropyridine (CAS: 55934-00-4) typically synthesized?

3,4-Dichloropyridine is commonly synthesized via the reaction of 2-chloropyridine with chlorine gas. This process involves the substitution of a hydrogen atom with a chlorine atom at the 3 and 4 positions. Other methods include the chlorination of pyridine using thionyl chloride as a catalyst, which provides high selectivity and yield.