“…It is advantageous, however, for oxidation of tetrachloro-4-methoxypyridine to its N-oxide, in which case cleavage to the 4-hydroxy compound is avoided [172,353]. Whereas Alkyl-or aryl-thiopolychloropyridines are oxidized to the corresponding sulphoxide by concentrated nitric acid [293,[355][356][357][358][359][360] , or peroxyacetic acid [270,361] and to the corresponding sulphone by peroxyacetic acid [232a, 269, 270, 292-294, 296, 355-359, 361], concentrated nitric acid [293,[355][356][357][358], potassium dichromate and acid [355][356][357][358], alkaline potassium permanganate [355][356][357][358], or chlorine water [362].…”