Recent progress in the manufacture of alkanesulfonates: Photosulfochlorination of single‐chain length (C12−C16) n‐alkanes using SO2Cl2 at high conversion rates in pure phase and in the presence of solvent

Abstract

AbstractIncreasing concentration of sulfuryl chloride during the photosulfochlorination reaction under visible light shows that under these conditions n‐alkanes react at high conversion rates instead of the conversion rate of 15% reported in the literature. This photosulfochlorination with sulfuryl chloride leads to better and more interesting results compared with those of photosulfochlorination by gas mixture. Indeed, nearly total conversion of n‐alkanes, specifically n‐heptane, n‐dodecane, n‐tetradecane, and n‐hexadecane, occurred in pure phase, with a quantitative global yield, a sulfochlorination‐to‐chlorination molar ratio of about 1, and a relative reactivity of secondary to primary hydrogen of about 2.5, at a reaction temperature of 30°C and a reaction time of 120 min, using 2×10−2 mol L−1 of pyridine. Under these conditions, no polysulfochlorinated compounds are detected. These results are further improved using chlorobenzene as the solvent, instead of benzene. Indeed, the sulfochlorination of n‐heptane at a conversion rate of 80% in the presence of chlorobenzene leads also to a quantitative reaction yield, a higher RSO2Cl/RCl molar ratio, and, as expected, a high selectivity of secondary over primary hydrogen. Under these conditions, sulfochlorination of long‐chain n‐alkanes leads to the highest RSO2Cl/RCl molar ratio for n‐dodecane, n‐tetradecane, and n‐hexadecane belonging to detergent range, and the value of the molar ratio for these is between 1.45 and 1.7. The isomeric distribution of sulfochlorinated compounds obtained during sulfochlorination in the presence of solvent resembles that of secondary alkanesul‐fonates produced by sulfoxidation reaction, whereas that obtained in pure phase has a similar conversion rate, is rich in primary isomer, and thus is different from that of classic radical reactions such as photochlorination or photosulfochlorination with gas mixture.