HU207334B - Continuous process for producing dialkyl-phosphites - Google Patents

Abstract

Continuous prepn of dialkyl-phosphites from phosphorus-trichloride and alcohol at 80-150deg.C pref 100-120deg.C. and at 1.2-5atm. pressure. As the prod is formed it is allowed to expand in steps to near atmos. pressure and sepd into a gaseous and a liq. phase. Hydrochloric acid is removed by vacuum distn. from the liq. phase within 1-5secs. Raw dialkyl phosphate is finally purified by vacuum distn

Description

The present invention relates to a process for the preparation of dialkyl phosphites. Dialkyl phosphites are the starting materials for various organic syntheses.

Numerous processes for the preparation of dialkyl phosphites are known in the art. The vast majority of these are based on the exothermic reaction of phosphorus trichloride and alcohol.

PC1 ₃ + 3 ROH -> HPO (OR) ₂ + ROH + 2 HCl

Hydrochloric acid and alkyl halide are formed as by-products of the reaction. Processes based on this method differ mainly in the removal of reaction heat and the removal of hydrochloric acid which is detrimental to the quality of the product.

One of the processes involves the removal of heat generated by the reaction by evaporation of the organic solvent. Such a procedure is described e.g. No. 2570512; U.S. Pat.

The disadvantage of solvent-based processes is that large amounts of organic solvents have to be treated which require considerable effort to regenerate and purify.

A solvent-free process is described in U.S. Patent No. 3,331,895. U.S. Pat. No. 4,198, wherein excess alcohol is reacted with phosphorus trichloride at a pressure of 3 to 10 kPa and the excess heat is removed by evaporation of the excess alcohol.

The disadvantage of this method is that complicated equipment has to be used to recover the alcohol and the yields are not adequate.

The solvent-free process is also described in U.S. Pat. U.S. Pat. Phosphorus trichloride and alcohol are introduced into a reactor through a special mixing nozzle, the bottom of which is cooled to suppress the decomposition of the resulting dialkyl phosphite by hydrochloric acid. The cooled reaction mixture is stripped of hydrochloric acid on a stripping column. The disadvantage of the method is that the reaction mixture must be cooled significantly to prevent the decomposition of the dialkyl phosphites and then reheated to remove the hydrochloric acid by distillation, which requires a significant excess of energy.

Accordingly, it has been an object of the present invention to provide a process for the preparation of dialkyl phosphites which is free from the above-mentioned disadvantages and which is capable of continuously producing dialkyl phosphites by reaction of phosphorus trichloride and alcohols without the use of a separate solvent.

In the process of the present invention, it has now been unexpectedly discovered that the reaction between phosphorus trichloride and alcohol is advantageously carried out at a temperature of 80-150 ° C, preferably 100-120 ° C, at a pressure above atmospheric such that the reaction the products are stepwise expanded to near atmospheric pressure, separated into liquid and gaseous phases, the hydrochloric acid is removed from the liquid phase under vacuum, and the crude dialkyl phosphite obtained is purified in vacuo.

This discovery is unexpected because none of the processes for the preparation of dialkyl phosphites undergo reaction of phosphorus trichloride and alcohol at elevated atmospheric pressures and, moreover, it is generally preferred to use vacuum (cf. U.S. Patent 3,331,895).

It is also unexpected that the reaction between phosphorus trichloride and alcohols can be advantageously carried out at temperatures above 100 ° C. Nowhere in the literature are reaction temperatures above 100 ° C. It is believed that at such high temperatures, the decomposition of dialkyl phosphites by hydrochloric acid is already significant.

Accordingly, the present invention provides a continuous process for the preparation of dialkyl phosphites from phosphorus trichloride and alcohol by reacting phosphorus trichloride and alcohol at a temperature of 80-150 ° C, preferably 100-120 ° C and a pressure of 120-500 kPa. After expansion to near atmospheric pressure, the liquid and gaseous phases are separated, the liquid phase is decontaminated in vacuo within 1-5 seconds, and the resulting crude dialkyl phosphite is purified in vacuo.

The alcohol of the present invention may be any linear or branched, unsaturated aliphatic alcohol of any number of carbon atoms. Examples of alcohols which can be used in the process are methyl, ethyl, isopropyl, butyl, isobutyl alcohol and the like.

The molar ratio of alcohol to phosphorus trichloride used in the process of the invention is between 3: 4 and 1. Above these values, the likelihood of side reactions increases, while above this, the risk of product decomposition by hydrochloric acid is increased, since excess alcohol is good for dissolving hydrochloric acid. In addition, removing excess alcohol from the product requires extra energy and increases the burden of the alcohol.

A typical embodiment of the present invention is illustrated in Figure 1. Of course, other embodiments are contemplated within the scope of the present invention. Symbols in Figure 1:

reactor expansion slots mixing chamber separation section hydrochloric acid desalination column alcohol desalting column vacuum distillation column

In carrying out the process of the invention, the alcohol and phosphorus trichloride are continuously introduced in a 3-4: 1 molar ratio into the mixing chamber (3) of reactor (1), where the reaction is carried out at 80-150 ° C, preferably 100-120 ° C. on and at a pressure of 120-500 kPa. The reaction products expand gradually through the expansion slots (2) to near atmospheric pressure and then decompose into a liquid and gaseous phase in the separation section of the reactor (1). The gaseous phase containing hydrochloric acid and alkyl chloride is removed from the upper part of the separation section of the reactor. The liquid phase from the lower part of the separation section, including the dialkyl phosphite, is introduced into the charged column (5) at 510 kPa under a pressure of 510 kPa. Hydrochloric acid is discharged at the top of the column and dialkylphosphite, which may be free of hydrochloric acid at the bottom, is removed. The liquid phase exiting the bottom of the column enters the distillation column (6) with 4 to 10 kPa

The alcohol leaves at a pressure of 33 334 Β. The crude dialkyl phosphite exiting from the bottom of the column is then transferred to a vacuum distillation column (7) at 0.2-1.0 kPa, leaving a distillation residue containing mainly phosphoric acid at the bottom and pure dialkyl phosphite at the top.

An advantageous feature of the process of the present invention is that phosphorus trichloride and alcohol react very rapidly with each other at 0.1 to 3.0 seconds at the pressure and temperature used. The reaction mixture obtained in the course of the reaction is then transferred to the hydrochloric acid desalination in a very short time. Together, these conditions ensure that the product is minimized.

The following examples illustrate the invention.

Example 1

Preparation of dimethyl phosphite

In the apparatus of Figure 1, methanol and phosphorus trichloride were continuously introduced in a 3.5: 1 molar ratio. The reaction is carried out at 105 ° C and 120-500 kPa. The liquid phase of the resulting reaction mixture was passed through a dehydrogenation column (810 kPa) with a bottom temperature of 50-80 ° C and a head temperature of 20-40 ° C. The fluid exiting the bottom of the desiccator is discharged to the methanol depressurizer operating at 5 to 6 kPa, where the excess methanol used is removed. The crude dimethylphosphite leaving the bottom of the column was purified by vacuum distillation. The resulting dimethylphosphite is 98.0% pure and has a refractive index of 1.4030 at 20 ° C. The yield calculated for phosphorus trichloride is 89.3%.

Example 2

Preparation of diethyl phosphite

Example 1, except that ethanol was used instead of methanol, was carried out at 105 ° C.

The resulting diethyl phosphite was 98.7% pure and had a refractive index at 20 ° C of 1.4076. The yield calculated for phosphorus trichloride is 95.6%.

Example 3

Preparation of diisopropyl phosphite

Example 1 was repeated except that isopropyl alcohol was used in place of methanol and the reaction was carried out at 105 ° C.

The resulting diisopropylphosphite was 98.9% pure and had a refractive index at 20 ° C of 1.4080. The yield calculated for phosphorus trichloride was 96.8%.

Example 4

Preparation of di-n-butyl phosphite

The procedure of Example 1 was followed except that n-butanol was used instead of methanol and the reaction was carried out at 120 ° C with a bottom temperature of 70-90 ° C and a head temperature of 30-40 ° C.

The resulting di-n-butyl phosphite is 98.2% pure and has a refractive index of 1.4240 at 20 ° C. The yield calculated for phosphorus trichloride was 96.2%.

Claims (3)

PATENT CLAIMS A continuous process for the preparation of dialkyl phosphites from phosphorus trichloride and aliphatic alcohol by separating the resulting reaction product into a gas phase and a liquid phase and deprotecting the liquid phase in a vacuum, characterized in that the phosphorus trichloride and alcohol are 80-150 ° C, preferably At a temperature of 100-120 ° C, the reaction product is expanded stepwise to near atmospheric pressure and processed in a known manner. Process for the preparation of dimethylphosphite according to claim 1, characterized in that the phosphorus trichloride and the methanol are reacted at a pressure of 200 to 500 kPa at a temperature of 100 to 120 ° C. 3. A process according to claim 1 wherein the alcohol is isopropyl alcohol.