[CH2:1]([O:4][C:5]1[CH:13]=[CH:12][CH:11]=[CH:10][C:6]=1[C:7]([OH:9])=[O:8])[CH2:2][CH3:3].[Cl:14][S:15](O)(=[O:17])=[O:16].S(Cl)(Cl)=O>C(Cl)Cl>[Cl:14][S:15]([C:11]1[CH:12]=[CH:13][C:5]([O:4][CH2:1][CH2:2][CH3:3])=[C:6]([CH:10]=1)[C:7]([OH:9])=[O:8])(=[O:17])=[O:16]A solution of 2-n-propoxybenzoic acid (20 g, 111 mmol) in DCM (40 ml) was added dropwise over 30 min to a mixture of chlorosulphonic acid (30 ml, 440 mmol) and thionyl chloride (8.1 ml, 110 mmol) at −10° C. whilst keeping the temperature below 0° C. The mixture was slowly warmed to 20° C. and stirred for 18 h. The reaction mixture was cautiously poured onto crushed ice (260 g), keeping the temperature below 0° C. The ice slurry was stirred for 20 min and then the precipitated white solid was filtered, washed with H2O (20 ml), dissolved in DCM (200 ml), dried (MgSO4), filtered and concentrated in vacuo to afford the title compound as a yellow solid (31.2 g, 103 mmol, 92%); mp 121-124° C.
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