Process for preparing sulfonated arylphosphines

1. A process for preparing solutions of sulfonated arylphosphines comprising reacting arylphosphines with oleum to form a sulfonation mixture, diluting the sulfonation mixture with water, extrating the diluted sulfonation mixture with a solution of a water-insoluble amine in a water-insoluble organic solvent, reacting the resulting water-imiscible organic phase with a solution of an inorganic base in water, adjusting the resulting aqueous solution of sulfonated arylphosphines of pH of up to 3 by addition of an acid, and passing an inert gas stream through the aqueous solution comprising sulfonated arylphosphines until sulfur dioxide is no longer liberated from the aqueous solution of sulfonated arylphosphines.

2. The process of claim 1 , wherein the arylphosphines are selected from the group consisting of monophosphines, diphosphines, oligophosphines and polyphosphines containing at least one aromatic ring.

3. The process of claim 1 , wherein the monophosphine is selected from the group consisting of methyldiphenylphosphine and triphenylphosphine.

4. The process of claim 1 , wherein the aqueous solution comprising sulfonated arylphosphines is adjusted to a pH of 0-2 by addition of an acid.

5. The process of claim 1 , wherein the aqueous solution comprising sulfonated arylphosphines is admixed with inorganic or organic acids to adjust the pH to 3.

6. The process of claim 5 , wherein the acid is selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, formic acid and acetic acid.

7. The process of claim 1 , therein an inert gas stream is passed continuously or discontinuously through the aqueous solution comprising sulfonated arylphosphines.

8. The process of claim 1 , wherein the inert gas is at least one member of the group consisting of nitrogen, helium, neon, argon, xenon and krypton, carbon dioxide, carbon monoxide and hydrogen.

9. The process of claim 1 , wherein the inert gas treatment is carried out for 2 to 100 minutes and the amount of an insert gas per kg of aqueous solution comprising the sulfonated arylphosphine is 5 to 500 liters of inert gas, the sulfite content in the aqueous solution comprising sulfonated arylphosphines being <0.1% by weight.

10. The process of claim 1 , wherein the inert gas treatment is carried out for 1 to 100 hours and the amount of inert gas per kg of aqueous solution comprising the sulfonated arylphosphine is 5 to 1000 liter of inert gas, the sulfite content in the aqueous solution comprising sulfonated arylphosphines being <0.1% by weight.

11. The process of claim 1 , wherein the inert gas stream laden with sulfur dioxide is passed through a scrubbing solution into which sulfur dioxide is absorbed, with the scrubbing solution being a basic liquid.