Reaction of excess acetyl chloride on 4-nitro-2-picoline 1-oxide (I) with cooling results in the formation of 4-chloro-2-picoline 1-oxide (II) in 68% yield, together with formation of 4-chloropicolinaldehyde 1-oxide oxime (V) in 12% yield. If this reaction is carried out on a water bath, yield of II decreases to 4.2% with concurrent formation of 57% of 4-chloropicolinonitrile 1-oxide III and 6.3% of 4-chloropicolinic acid (IV).
When equimolar mixture of I and acetyl chloride in chloroform is allowed to stand at room temperature, 17% of II is obtained besides 42% recovery of I. If this reaction is carried out by warming on a water bath, 20-33% of II, 7-9% of III, 17% of 4-nitropicolinaldehyde 1-oxide oxime (VI), and 7.8% of 4-nitropicolinonitrile 1-oxide (VII) are obtained. This latter reaction is considered to be due to the nitrosation reaction of acetyl nitrite, formed by the reaction of I and acetyl chloride at the time of formation of II, on the active methyl group in α-position.