GB684835A - Improvements in or relating to a process and apparatus for the manufacture of dialkyl phosphites and chlorinated derivatives thereof - Google Patents

Abstract

<PICT:0684835/IV (b)/1> Dialkyl phosphites are obtained by continuously flowing a thin film of an intimate admixture of phosphorus trichloride and an aqueous aliphatic alcohol containing not more than three carbon atoms in the molecule over a cooled surface whilst removing evolved hydrogen chloride by means of a stream of gas, said intimate admixture being formed by mixing together separate streams of phosphorus trichloride and the aqueous alcohol either on the cooled surface or immediately prior to contact therewith. Dialkylchloro phosphonates may be obtained by direct chlorination of the crude dialkyl phosphites obtained by the process of the invention. The invention also comprises apparatus for use in the manufacture of dialkyl phosphites comprising a substantially vertical tube provided with a jacket for coolant fluid, a rotatable horizontal disc mounted within said tube, two pipes for conducting liquid reagents to the upper surface of said disc and means for passing a stream of gas through or past the end of said jacketed tube for carrying away gaseous reaction products. In the production of the dialkyl phosphite the molar ratio of water to alcohol is preferably about 1 : 2, and the reaction temperature, particularly when using ethanol or methanol should not exceed 25 DEG C. The mixing of the phosphorus trichloride with the aqueous p alcohol may be effected by flowing separate streams of the liquids on to the surface of a rapidly rotating horizontal disc from which the liquids are flung on to a substantially vertical cooled cylindrical surface surrounding the rotating disc. The process may be carried out with the apparatus shown in the Figure, a solution of water (1 mol.) in alcohol (2 mols.) being admitted through a supply tube 8 and phosphorus trichloride being admitted through supply tube 9 so that the liquids fall as separate streams on to the upper surface of a horizontal rapidly-rotating disc 7. The liquids are flung on to the inner surface of a jacketed tube 1 through the jacket of which a coolant fluid is passed and the mixed liquid flows down the cooled surface in a thin film and then down a vertical column 17 connected by means of a connector 12 to the jacketed tube 1. The vertical column is packed with glass helices and surrounded by a cooling jacket 19, the bottom of the column being attached to a receiver (not shown) for the reacted liquid. A current of dry air or other gas is passed upwardly through the packed column. With methanol the hourly throughput should be restricted so that the temperature at the exit from the jacketed tube does not exceed 20 DEG C. but with ethanol and propanol the temperature may be up to 25 DEG and 30 DEG C., respectively. In examples: (1) a stream of aqueous ethyl alcohol and of phosphorus trichloride are reacted in the apparatus described, a stream of dry air being drawn through the column and the temperature being 14.5 DEG C. at the exit from the jacketed tube and 10 DEG C. in the receiver at the bottom of the packed column. Pure diethyl phosphite is obtained by distillation of the collected reaction mixture; (2) the crude diethyl phosphite which collects in the receiver used in (1) is chlorinated by treatment with a stream of chlorine at 0-10 DEG C. After removing dissolved chlorine and hydrogen chloride by sucking dry air through the liquid at reduced pressure the liquid is distilled to yield diethylchlorophosphonate; (3) and (4) di-isopropyl phosphite and dimethyl phosphite are obtained by reacting phosphorus trichloride with aqueous isopropyl alcohol and aqueous methanol, respectively, using the apparatus as in (1).