Effects of Solvent Acidity on the Free-Radical-Initiated Synthesis of Methanesulfonic Acid from CH4and SO3

Sudip Mukhopadhyay, Alexis T. Bell
2002 Industrial & Engineering Chemistry Research  
The effects of solvent acidity on K 2 S 2 O 8 -initiated synthesis of methanesulfonic acid (MSA) from CH 4 and SO 3 have been investigated. Dimethyl sulfoxide, sulfuric acid, and trifluromethanesulfonic acid were used as the solvents. The initial rate of MSA synthesis increased with solvent acidity, being lowest in DMSO and highest in triflic acid. This effect is attributed to the influence of solvent acidity on the extent of decompostion of the S 2 O 8 2anion, which dissociates to form SO 4 -•
more » ... tes to form SO 4 -• . The latter species is responsible for activation of CH 4 to form CH 3 • . The maximum conversion of SO 3 to MSA also depends on the solvent, increasing in the order DMSO < TFMSA < H 2 SO 4 . The highest conversion of SO 3 to MSA observed for the conditions of these studies was 87% when H 2 SO 4 containing 0.2 M TFMSA was used as the solvent. The limit on the maximum conversion of SO 3 to MSA is set by the reaction CH 3 SO 3 H + SO 3 h CH 3 (SO 3 ) 2 H, which removes unconverted SO 3 from solution as MSA is formed. Although the extent to which this reaction proceeds decreases with increasing solvent acidity, the use of TFMSA as the solvent is detrimental because it appears to stabilize the formation of CH 3 (SO 3 ) 2 H, possibly in the form of CH 3 (SO 3 ) 2 H'(CF 3 SO 3 H) 2 . The influences of the initial concentrations of SO 3 and K 2 S 2 O 8 and of the reaction temperature on the maximum conversion of SO 3 to MSA are discussed in terms of a proposed mechanism for MSA synthesis.
doi:10.1021/ie020392d fatcat:vjej7jjssfgd7hckeflskiz77y