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Abstract

A multi stage process for the conversion of 2-chloro-4-sulphotoluene (SCT) to 2-chloro-4-sulphobenzoic acid (SCUBA). Stage (a) comprises a process S1 for the selective side chain bromination of SCT to 2-chloro-4-sulpho-dibromotoluene (SCDBT) or 2-chloro-4-sulpho-bromotoluene (SCMBT) by contacting the starting material with bromine in chloroform or trichloroethane and irradiating the mixture with light that dissociates bromine. Subsequently, in stage (b), process S2, the product of S1 can be hydrolysed at elevated temperature after separation from the organic solvent to the corresponding alcohol (SCOL) or aldehyde (SCAB). In stage (c), the product of S2 can be oxidized to SCUBA either by oxidation with a peroxyacid, optionally generated in situ, provided that the aqueous solution has previously been stripped of bromide/bromine in process S3. The oxidation can also be carried out using bromine, preferably generated in situ in process S5 by oxidation of residual bromide with hydrogen peroxide, which can then be followed by process S3 to strip out the bromine/bromide. A combination of processes S1, S2, S5 and S3 in that order provides a closed loop process cycle which recycles the environmentally harmful reagent, bromine.

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