Method for producing 6-chlorodibenzo[D,F] [1,3,2] dioxaphosphepin

1. A process for preparing 6-chlorodibenzo[d,f]-[1,3,2]dioxaphosphepin, which comprises:

a) adding a suspension of 2,2′-dihydroxybiphenyl in an inert solvent to an excess of phosphorus trichloride under inert gas in a reactor and stirring, to obtain a reaction mixture and resulting gas;

b) discharging and neutralizing the at least one resulting gas from the reaction mixture;

c) removing excess phosphorus trichloride and also the solvent; and

d) isolating 6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin.

2. The process of claim 1 , wherein the suspension comprising 2,2′-dihydroxybiphenyl has a solids content in a range from 10 to 60% by mass.

3. The process of claim 1 , wherein at least 90% of particles of the 2,2′-dihydroxybiphenyl in the suspension have a particle size of from 1 to 1000 microns.

4. The process of claim 1 , wherein the inert solvent comprises an aromatic hydrocarbon or hydrocarbon mixture.

5. The process of claim 4 , wherein the aromatic hydrocarbon mixture is present and comprises predominantly toluene.

6. The process of claim 1 , wherein the removing of excess phosphorus trichloride and the solvent, comprising an aromatic hydrocarbon mixture, is carried out by distillation under subatmospheric pressure.

7. The process of claim 1 , further comprising:

reusing phosphorus trichloride and aromatic hydrocarbon removed by fractional distillation in the process.

8. The process of claim 2 , wherein at least 90% of particles of the 2,2′-dihydroxybiphenyl in the suspension have a particle size of from 1 to 1000 microns.

9. The process of claim 1 , wherein the inert solvent comprises an aromatic hydrocarbon.

10. The process of claim 1 , wherein the inert solvent comprises a hydrocarbon mixture.

11. The process of claim 1 , wherein the inert solvent comprises more than 50% toluene.

12. The process of claim 1 , wherein the inert solvent is toluene.

13. The process of claim 1 , wherein the inert solvent comprises xylenes.

14. The process of claim 1 , wherein the inert solvent is xylenes.

15. The process of claim 1 , wherein the phosphorus trichloride is present in a 2- to 25-fold excess in the adding a), based on molar ratios.

16. The process of claim 1 , wherein the phosphorus trichloride is present in a 10- to 15-fold excess in the adding a), based on molar ratios.

17. The process of claim 1 , wherein the isolating d) does not comprise distilling 6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin.

18. The process of claim 1 , wherein equilibration or cooling operation are not employed.

19. The process of claim 1 , wherein tetrahydrofuran is not employed as solvent.