Preparation of 6,6′-((3,3′-di-tert-butyl-5,5′-dimethoxy-[1,1′-biphenyl]-2,2′-diyl)bis(oxy))bis(2,4,8,10-tetramethyldibenzo[d,f][1,3,2]dioxaphosphepine)

1. A process for preparing a compound of formula (I):

the process comprising:

a) reacting 3,3′,5,5′-tetramethyl-2,2′-dihydroxybiphenyl with PCl 3 in an inert gas atmosphere to obtain a phosphorochloridite derivative;

b) reacting at least 2 equivalents of the phosphorochloridite derivative obtained in a) with 1 equivalent of 5,5′-dimethoxy-3,3′-di-tert-butyl-2,2′-dihydroxybiphenyl in an inert gas atmosphere to obtain a crude product;

c) adding to the crude product from b) a solvent or a solvent mixture comprising at least one solvent selected from the group consisting of: o-xylene, toluene, methanol, ethanol, butanol and isopropanol to obtain a crude product mixture;

d) heating the crude product mixture from c) to dissolve the crude product and obtain a solution;

e) cooling down the solution from d) to precipitate the compound according to formula (I) from the solution; and

f) filtering-off the precipitated compound according to formula (I).

2. The process according to claim 1 wherein process operations c) to f) are repeated.

3. The process according to claim 1 , wherein the cooling down in e) comprises cooling the solution to room temperature.

4. The process according to claim 1 , wherein the solvent in c) comprises o-xylene.

5. The process according to claim 1 , wherein the mixture is heated to a temperature in the range of from 80° C. to 140° C. in d).

6. The process according to claim 1 , wherein the reacting in b) is carried out in the presence of at least one base.

7. The process according to claim 6 , wherein the base is an amine selected from the group consisting of triethylamine, dimethylaminopyridine, pyridine and tributylamine.