Processes for the preparation of 2,5-dihydroxybenzenesulfonic acid salts
Processes for the preparation of 2,5-dihydroxybenzenesulfonic acid salts of formula (I) and a crystalline form of potassium 2,5 2,5-dihydroxybenzenesulfonic acid are provided.
1. A process for the preparation of compounds of formula (I)
wherein X is potassium, and m is 1 and n is 1, said process comprising:
i) sulfonation of hydroquinone of formula (II) in the presence of a solvent selected from the group consisting of n-heptane, n-hexane, n-octane, dichloromethane and 1,2-dichloroethane, to provide a compound of formula (III);
ii) treating the compound of formula (III) with potassium 2-ethylhexanoate in a suitable solvent selected from the group consisting of C 5 -C 12 alkanes, C 5 -C 12 cycloalkanes, C 1 -C 12 haloalkanes, C 7 -C 8 alkyl acetates, C 2 -C 12 alkyl ethers, C 5 -C 10 cycloalkyl ethers and mixtures thereof; and
iii) precipitating the product of formula (I).
2. The process according to claim 1 , wherein the sulfonation is carried out using sulfuric acid, fuming sulfuric acid, or a halosulfonic acid.
3. A process for the preparation of a compound of formula (I)
wherein X is potassium, and m and n are each 1, said process comprising:
i) sulfonation of hydroquinone of formula (II) using sulfuric acid in the absence of a solvent or in the presence of a solvent selected from the group consisting of n-heptane, n-hexane, n-octane, dichloromethane and 1,2-dichloroethane to provide a compound of formula (III);
ii) treating the compound of formula (III) with potassium 2-ethylhexanoate; and
iii) precipitating the product of formula (I),
wherein the compound of formula I is prepared in greater than 75% yield.
4. A method for the removal of inorganics formed during the process of claim 1 , which method comprises:
i) dissolving the crude compound of formula (I) in water;
ii) adding a water-miscible solvent selected from the group consisting of alcohols, ketones, and nitriles to precipitate the inorganics; and
iii) isolating the product of formula (I).
5. The process of claim 3 , wherein a solution of the compound of formula (III) is treated with a solution of potassium 2-ethylhexanoate.
6. The process of claim 5 , wherein a solution comprises ethyl acetate.
7. The process of claim 1 , wherein the compound of formula I is prepared in greater than 75% yield.
8. The process of claim 1 , wherein the solvent used in (ii) is selected from the group consisting of ethyl acetate, n-heptane, and n-butyl acetate.