The invention relates to a process for purifying 4,4′-dichlorodiphenyl sulfoxide comprising: (a) providing a suspension comprising particulate 4,4′-dichlorodiphenyl sulfoxide in monochlorobenzene, (b) solid-liquid separation of the suspension to obtain residual moisture containing 4,4′-dichlorodiphenyl sulfoxide, (c) washing residual moisture containing 4,4′-dichlorodiphenyl sulfoxide with monochlorobenzene, (d) optionally repeating steps (a) to (c).

The invention relates to a process for purifying 4,4′-dichlorodiphenyl sulfoxide comprising: (a) providing a suspension comprising particulate 4,4′-dichlorodiphenyl sulfoxide in monochlorobenzene, (b) solid-liquid separation of the suspension to obtain residual moisture containing 4,4′-dichlorodiphenyl sulfoxide, (c) washing residual moisture containing 4,4′-dichlorodiphenyl sulfoxide with monochlorobenzene, (d) optionally repeating steps (a) to (c).

The invention relates to a process for purifying 4,4′-dichlorodiphenyl sulfoxide comprising: (a) providing a suspension comprising particulate 4,4′-dichlorodiphenyl sulfoxide in monochlorobenzene, (b) solid-liquid separation of the suspension to obtain residual moisture containing 4,4′-dichlorodiphenyl sulfoxide, (c) washing residual moisture containing 4,4′-dichlorodiphenyl sulfoxide with monochlorobenzene, (d) optionally repeating steps (a) to (c).

The invention relates to a crystal (C) consisting of at least 95% by weight of 4,4′-dichlorodiphenylsulfoxide, 0 to 2% by weight of impurities and 0 to 3% by weight of an organic solvent (os). Moreover, the present invention relates to a crystal composition (CC) comprising crystals (C) and a process for the production of the crystal composition (CC) and the crystal (C).

The invention relates to a crystal (C) consisting of at least 95% by weight of 4,4′-dichlorodiphenylsulfoxide, 0 to 2% by weight of impurities and 0 to 3% by weight of an organic solvent (os). Moreover, the present invention relates to a crystal composition (CC) comprising crystals (C) and a process for the production of the crystal composition (CC) and the crystal (C).

The invention relates to a crystal (C) consisting of at least 95% by weight of 4,4′-dichlorodiphenylsulfoxide, 0 to 2% by weight of impurities and 0 to 3% by weight of an organic solvent (os). Moreover, the present invention relates to a crystal composition (CC) comprising crystals (C) and a process for the production of the crystal composition (CC) and the crystal (C).

A process for synthesizing a compound of formula (I)

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including: (a) condensing the benzaldehyde compound of formula (II) with the dialkylaniline of formula (III) to give the triphenylmethane of formula (IV); (b) treating the triphenylmethane of formula (IV) with sulfuric acid to form the triphenylmethane sulfone of the formula (V); and (c) oxidizing the triphenylmethane sulfone of formula (V) with a quinone. Such a process may be used to prepare patent blue.

A process for synthesizing a compound of formula (I)

##STR00001##

including: (a) condensing the benzaldehyde compound of formula (II) with the dialkylaniline of formula (III) to give the triphenylmethane of formula (IV); (b) treating the triphenylmethane of formula (IV) with sulfuric acid to form the triphenylmethane sulfone of the formula (V); and (c) oxidizing the triphenylmethane sulfone of formula (V) with a quinone. Such a process may be used to prepare patent blue.

The invention relates to a process for producing 4,4′-dichlorodiphenyl sulfone, comprising: (a) reacting 4,4′-dichlorodiphenyl sulfoxide and an oxidizing agent in at least one carboxylic acid as solvent to obtain a reaction mixture comprising 4,4′-dichlorodiphenyl sulfone and carboxylic acid; (b) separating the reaction mixture into a first stream comprising 4,4′-dichlorodiphenyl sulfone and a second stream comprising carboxylic acid; (c) purifying the second stream comprising carboxylic acid by distilling a part of the second stream comprising carboxylic acid stripping low boilers from at least a part of the second stream comprising carboxylic acid (d) recycling the purified carboxylic acid into the reaction (a).

The invention relates to a process for producing 4,4′-dichlorodiphenyl sulfone, comprising: (a) reacting 4,4′-dichlorodiphenyl sulfoxide and an oxidizing agent in at least one carboxylic acid as solvent to obtain a reaction mixture comprising 4,4′-dichlorodiphenyl sulfone and carboxylic acid; (b) separating the reaction mixture into a first stream comprising 4,4′-dichlorodiphenyl sulfone and a second stream comprising carboxylic acid; (c) purifying the second stream comprising carboxylic acid by distilling a part of the second stream comprising carboxylic acid stripping low boilers from at least a part of the second stream comprising carboxylic acid (d) recycling the purified carboxylic acid into the reaction (a).