[S:1]([C:5]1[CH:6]=[C:7]([CH:11]=[CH:12][CH:13]=1)[C:8]([OH:10])=[O:9])([OH:4])(=[O:3])=[O:2].[OH:14]O>ClCCl.S(=O)(=O)(O)O>[S:1]([C:5]1[CH:6]=[C:7]([CH:11]=[CH:12][CH:13]=1)[C:8]([O:10][OH:14])=[O:9])([OH:4])(=[O:3])=[O:2]To a suspension of 3-sulphobenzoic acid (5 g, 2.5×10-2 moles) in dichloromethane (60 ml) containing a trace of sulphuric acid (5×10-5 moles) was slowly added hydrogen peroxide (3 g; 85%). The suspension was boiled under reflux (42° C.) for 1 hour after which it was cooled to room temperature, the dichloromethane was decanted off and the residue treated with saturated aqueous magnesium nitrate (25 ml). The resultant precipitate was filtered off, dried over phosphorous pentoxide under vacuum to yield the magnesium salt of 3-sulphoperoxybenzoic acid (3.5 g; 5.31% Avox as O; Magnesium content of 4.7%) compared with a theoretical yield of 5.67 g. The IR spectrum was again substantially the same as for the other preparations.
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