Method for preparing methyl 2-diphenylmethylsulfinylacetate

1. Method for preparing methyl 2-diphenylmethylsulfinylacetate (MDMSA) comprising the steps of:

(i) conversion of benzhydrol into methyldiphenylmethylthioacetate; and

(ii) conversion of methyldiphenylmethylthioacetate into methyl-2-diphenylmethylsulfinylacetate.

2. Method according to claim 1 , in which step (i) comprises the following steps:

a1) conversion of benzhydrol to benzhydrol carboxylate in an appropriate solvent;

b1) conversion of the benzhydrol carboxylate to methyl diphenylmethylthioacetate.

3. Method according to claim 2 , in which the step (a1) comprises reacting benzhydrol and an acid anhydride in the presence of an inorganic acid and in an appropriate solvent.

4. Method according to claim 3 , in which the solvent is an aprotic solvent.

5. Method according to claim 4 , in which the aprotic solvent is chosen from chlorinated solvents, aromatic solvents, hydrocarbon solvents and ethereal solvents.

6. Method according to claim 5 , in which the aprotic solvent is chosen from chlorinated solvents.

7. Method according to claim 6 , in which the solvent is dichloromethane.

8. Method according to claim 3 , in which the acid anhydride is chosen from acetic anhydride, propanoic anhydride and butyric anhydride.

9. Method according to claim 8 , in which the acid anhydride is acetic anhydride.

10. Method according to claim 3 , in which the inorganic acid is chosen from hydrochloric acid, butyric acid, o-phosphoric acid and sulfuric acid.

11. Method according to claim 10 , in which the inorganic acid is sulfuric acid.

12. Method according to claim 3 , in which the quantity of inorganic acid used is from 0.02 to 0.3 molar equivalents relative to the benzhydrol.

13. Method according to claim 3 , in which the reaction temperature in step a) is between +5° C. and +5° C.

14. Method according to claim 2 , in which step b1) comprises bringing the solution obtained in step a) into contact with methyl thioglycolate.

15. Method according to claim 14 , in which the contact time used in step b1) is between 2 and 3 hours.

16. Method according to claim 14 , in which the contact temperature used in step b1) is between 15° C. and 25° C.

17. Method according to claim 1 , in which the oxidizing agent is chosen from oxone, potassium permanganate, sodium percarbonate, and peroxides.

18. Method according to claim 17 , in which the oxidizing agent is hydrogen peroxide.

19. Method according to claim 18 , in which the hydrogen peroxide is added in the form of a 35% aqueous solution.

20. Method according to claim 1 , in which the oxidizing agent is used in an amount of 1 to 1.1 molar equivalent.

21. Method according to claim 1 , in which the reaction temperature in step (ii) is between 28° C. and 37° C.

22. Method according to claim 3 , in which an additional quantity of inorganic acid is added in step (ii).

23. Method according to claim 22 , in which the additional quantity of inorganic acid is from 0.02 to 0.3 molar equivalents.

24. Method according to claim 22 , in which the contact time in step (ii) is between 10 and 13 hours.

25. Method according to claim 1 , which comprises an additional step (iii) recovering the methyl 2-diphenyl-methylsulfinylacetate obtained.

26. Method according to claim 25 , in which step (iii) comprises a distillation of the solvent to dryness.

27. Method according to claim 25 , in which step (iii) comprises a step of direct crystallization.

28. Method according to claim 27 , in which the crystallization solvent is chosen from methanol, ethanol, ethyl acetate, isopropyl acetate and toluene.

29. Method according to claim 28 , in which the crystallization solvent is isopropyl acetate.

30. Method according to claim 1 , in which the successive steps are carried out in the same reactor without isolation of the intermediate compounds.

31. Method for preparing modafinil comprising preparing MDMSA according to claim 1 .