THERMODYNAMICS OF METHANESULFONIC-ACID, METHANESULFONYL CHLORIDE, ANDMETHYL METHANESULFONATE

The heat of formation of liquid methanesulfonic acid, -178.09 +/- 1.48 , was determined by measuring the heat of reaction of methyl thiolacet ate with aqueous hypochlorite solution to give aqueous methanesulfonat e and acetate. The heats of formation of liquid methanesulfonyl chlori de, -126.91 +/- 1.54, and methyl methanesulfonate, -164.34 +/- 1.58, w ere determined by measuring the heats of reaction of methanesulfonyl c hloride with water or methanol in the presence of a suitable basic cat alyst. Heats of vaporization (based on vapor-pressure data), entropies (based on ab initio molecular orbital calculations), and free energie s of transfer from gas phase to aqueous solution were calculated leadi ng to values for the free energies of formation in aqueous solution. T he free energies of formation so determined were methanesulfonic acid, -151.72 +/- 2.68, methanesulfonyl chloride, -101.29 +/- 1.96, and met hyl methanesulfonate, -127.28 +/- 2.08. From these values the free ene rgies of hydrolysis (leading to unionized methanesulfonic acid) are me thanesulfonyl chloride, -25.11 +/- 3.04, and methyl methanesulfonate, -9.90 +/- 2.48.