Method for producing 1-naphthol-4-sulphonic acid
AssigneeSandoz Ltd.
InventorWerner Veit
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Abstract
Disclosed is a method for producing 1-naphthol-4-sulphonic acid in free acid form and contaminated with less than 2% by weight of the isomeric 1-naphthol-2-sulphonic acid.
Claims20
A method for producing 1-naphthol-4-sulphonic acid in free acid form contaminated with less than 2% by weight of 1-naphthol-2-sulphonic acid, by sulphonating 1-naphthol in a solvent which is substantially inert towards the sulphonating agent and in which 1-naphthol-4-sulphonic acid has a solubility at a temperature >50.degree. C. of from 0.01 to 5.0% by weight, which comprises the step of separating the 1-naphthol-4-sulphonic acid from the reaction mixture by filtration at a temperature >50.degree. C. directly after completion of the sulphonation.
A method for producing 1-naphthol-4-sulphonic acid in free acid form contaminated with less than 2% by weight of 1-naphthol-2-sulphonic acid which comprises dissolving 1-naphthol in a solvent selected from the group consisting of aromatic monocyclic hydrocarbons, which may be nitrated or halogenated, and halogenated aliphatic hydrocarbons and in which 1-naphthol-4-sulphonic acid has a solubility of from 0.01 to 5.0%, by weight, at a temperature >50.degree. C., adding chlorosulphonic acid to the dissolved 1-naphthol in an amount ranging from stoichiometric to 20%, by weight, in excess of stoichiometric and at a temperature of -20.degree. to 120.degree. C., heating the resulting reaction mixture for 1-12 hours at a temperature >50.degree. C. after completing addition of the chlorosulphonic acid and, directly thereafter, filtering the reaction mixture at a temperature >50.degree. C. at which 1-naphthol-4-sulphonic acid has the said solubility in said solvent.
Dependencies are inferred from the claim text.