Process for the preparation of highly purified, dialkydithiophosphinic compounds

1. A process for the production of dialkyldithiophosphinic acid comprising sulfurizing a purified dialkylphosphinic acid whereby said purified dialkylphosphinic acid is formed by:

a) reacting a hypophosphorous acid or salt with a stoichiometric excess of an alpha olefin in the presence of a free radical initiator to form a reaction product comprising monoalkylphosphinic acid and dialkylphosphinic acid;

b) adding sufficient aqueous base to the reaction product to i) form the salts of the phosphinic acids, and ii) establish an aqueous phase and an organic phase, wherein a monoalkylphosphinic acid solubilizes into an aqueous phase;

c) separating the organic phase from the aqueous phase;

d) acidifying the organic phase;

e) removing the olefin from the organic phase; and

f) isolating the purified dialkylphosphinic acid product.

2. The process of claim 1 , wherein the dialkylphosphinic acid is of the following formula:

wherein R 1 and R 2 are each independently an alkyl radical having from 2 to 22 carbon atoms.

3. The process of claim 2 , wherein R 1 and R 2 are each independently a substituted alkyl radical having from 2 to 12 carbon atoms.

4. The process of claim 3 , wherein the R 1 and R 2 are each independently a substituted alkyl radical having from 2 to 9 carbon atoms.

5. The process of claim 2 , wherein the alkyl radicals are each independently substituted by two or more radicals selected from the group consisting of chloro-, bromo, alkyl, alkoxy groups and mixtures thereof.

6. The process of claim 3 , wherein the alkyl radicals are each independently substituted by two or more radicals selected from the group consisting of chloro-, bromo, alkyl, alkoxy groups and mixtures thereof.

7. The process of claim 4 wherein the alkyl radicals are each independently substituted by two or more radicals selected from the group consisting of chloro-, bromo, alkyl, alkoxy groups and mixtures thereof.

8. The process of claim 1 , wherein the dialkyldithiophosphinic acid is of the following formula:

wherein R 1 and R 2 are each independently an alkyl radical having from 2 to 22 carbon atoms.

9. The process of claim 1 , wherein the dialkyldithiophosphinic acid is of the following formula:

wherein R 1 and R 2 are each independently an alkyl radical having from 2 to 22 carbon atoms.

10. The process of claim 1 , wherein the reaction to form the reaction product composition takes place in the presence of an acid solution.

11. The process of claim 10 , wherein the acid solution is selected from the group consisting of hydrochloric acid, sulfuric acid, acetic acid and mixtures thereof.

12. The process of claim 11 , wherein the acid solution is an acetic acid solution.

13. The process of claim 1 , wherein the hypophosphorous salt is sodium hypophosphite monohydrate.

14. The process of claim 1 , wherein the molar ratio of the alpha olefin to the hypophosphorous acid or salt is greater than 2:1.

15. The process of claim 14 , wherein the molar ratio of the alpha olefin to the hypophosphorous acid or salt is greater than 2.5 to 1.

16. The process of claim 1 , wherein the aqueous base which is added to the reaction product composition is an aqueous sodium hydroxide solution or an aqueous sodium carbonate solution.

17. The process of claim 1 , wherein the acid in the acidification step comprises an inorganic acid solution.

18. The process of claim 17 , wherein the inorganic acid solution is a sulfuric acid solution.

19. The process of claim 1 , wherein said sulfurizing is performed using a sulfurizing agent.

20. The process of claim 19 , wherein said sulfurizing agent comprises elemental sulfur, sulfur chlorides, P 2 S 5 , or a combination thereof.