HU199149B - Process for producing dialkylphosphites - Google Patents

Abstract

Di:alkyl-phosphites are prepd. from alkanols and phosphorus-tri:chloride in 3:1 molar ratio. No acid scavenger is used but a solvent namely chloroform or di:chloro-ethane is present. A phosphorus-tri:chloride soln. is added during agitation to a soln. of alkanol at 0-40 deg.C.

Description

The present invention relates to the preparation of dialkyl phosphites. Phosphoric esters of various orders, such as dialkyl phosphites, are valuable intermediates which are widely used in organic chemical synthesis. For example, dimethyl phosphite can be used to prepare N-phosphonomethylglycine (Hungarian Patent No. 184,601).

The preparation of dialkyl phosphites can be accomplished by direct esterification of phosphorous acid. (Bull.Soc.Chim. Francé 27, 216, 1,670,368, U.S. Patent No. 699,154) They may also be prepared, inter alia, by reaction of dialkyl phosphites with phosphorus (III) oxide and alcohols (U.S. Patent No. 2,661,364). U.S. Pat.

Phosphorus (III) halides, by reaction with epoxyalkanes and hydroxy compounds, make it possible to obtain di-trialkyl phosphites and phosphoric acid ester halides. Phosphoric acid esters and ester halides can be converted in the most varied manner into esters of various orders (U.S. Patent Nos. 2,669,890, 2,570,512, 2,490,573, and 2,853,508, 1,012,611, 1,088,955, and 1,078). Publication Documents No. 136 in the Federal Republic of Germany, Org. Synth. 31: 111; and J.Chem.Soc. (1962) 2521).

Methods have also been known in which dialkyl phosphites are prepared by reacting alkanol and phosphorus trichloride in a 3: 1 molar ratio without an acid scavenger. (U.S. Patent No. 2,669,890 and Inorg.Synth. Vol IV (1953) pages 58-61). In these embodiments, alkanol or its solution (also referred to as pentane or ether as the solvent) is added to a solution of phosphorus trichloride in hexane or carbon tetrachloride. The dialkyl phosphites are obtained in a yield of 40-80% based on phosphorus trichloride. In these processes, a large excess of phosphorus trichloride is present at the time of the reaction compared to the alkanol, whereby the three chlorine atoms are gradually substituted, favoring the formation of many by-products. This is referred to in U.S. Patent No. 154,225. also in the Hungarian patent where O, O-dimethyl-2,2,2-trichlorohydroxyethylphosphonic acid ester is prepared not directly from dimethyl phosphite, but directly from phosphorus trichloride, chlorinated and methanol in hot benzene or toluene 70-80 The reagents are added at such a rate that it can evacuate at a minimum rate per ml of reaction mixture per ml of reaction mixture. Finally, O, O-dimethyl-2,2,2-trichlorohydroxyethylphosphonic acid ester is isolated from the reaction mixture. Among the undesirable by-products are phosphorous acid or monoalkyl phosphite, pyrophosphorous acid tetraester, phosphonic acid trichloride and then phosphonic acid diester. The latter are highly toxic compounds, which are recognizable by their characteristic phosphine salt, which are present in very small quantities in the final product. In the literature cited above, it is emphasized that in the case of double distillation, others were able to produce only an odorless product (by another method Bér. 57 (1924) p.

7-9. row).

The present invention relates to a process for the preparation of C 1 -C 6 dialkyl phosphites by reacting alkanol and phosphorus trichloride in a 3: 1 molar ratio without acid scavenger in the presence of an organic solvent by adding phosphorus to a solution of alkanol and solvent trichloride and solvent, and the solvent used is chloroform or dichloroethane.

The addition temperature is 0-5 ° C for dimethylphosphite and 20-40 ° C for higher dialkyl phosphites. Meanwhile, alkyl chloride gas is removed from the mixture. After addition, the mixture is heated to reflux and the hydrochloric acid present in the mixture is spun out.

The reaction mixture is suitably worked up by distillation. Once distilled, dialkyl phosphite is a pure, substantially odorless product.

It is an important discovery of the present invention that the reaction pathway without acid scavenger is the one in which the phosphorus trichloride ratio of the previously used 3: 1 alcohol phosphorus trichloride was always high in excess of the alkanol, leading to a number of disadvantageous by-products. . It has been found that these can be avoided or minimized by providing excess alkanol throughout the reaction while phosphorus trichloride is present. The formation of by-products can be further reduced if, together with the aforementioned provision of excess alkanol, the hydrochloric acid formed in the reaction is retained in the reaction mixture with the formation of water and alkyl chloride. The resulting water preferably decomposes the starting or intermediate phosphorus trichloride, dialkylphosphorous acid chloride and monoalkylphosphorous acid dichloride. No mono-alkyl phosphate is formed.

The process of the present invention provides high purity dialkyl phosphites in very good yields (about 90% and above) in a simple manner. The production of dialkyl phosphite yields an odorless product which has been achieved only by multiple distillation in the prior art.

Details of our procedure are given in the Examples.

General Method for the Preparation of Dialkyl Phosphites A mole of anhydrous alkanol is dissolved in 150-200 mL of solvent with stirring and ca. a solution of 1 mol of phosphorus trichloride in 100 ml of solvent was added dropwise over half an hour (optionally with cooling). Meanwhile, alkylchloride gas is removed from the mixture. The reaction mixture is then heated to reflux while hydrogen chloride gas is evolved. After completion of the reaction (about 1-3 hours), the solvent was evaporated at atmospheric pressure and the residue was fractionated. No. 1 The following table describes the reaction conditions and results used.

TABLE I

Example feed temperature C ° alkanol solvent: product: product boiling point mining PClj to: First 0-5 methanol dichloroethane dimethyl phosphite 30-40 ° C / bar 9J X Second 40 ethanol chloroform diethyl phosphite 186-188 ° C 90 X Third 40 ethanol dichloro-Etu diethyl phosphite 186-IBS ° C 95 X 4. 40 n-propanol chloroform di-n-propyl phosphite 84-92 ° C / 12 bar 95 X 5th 40 i-propanol dichloroethane .di-i-propyl phosphite 79-83 ° C / 14 bar 07 X 6th 40 n-butanol dichloroethane di-n-butyl phosphite 125-128 ° C / 18 bar 89 X 7th 40 n-butanol chloroform di-n-butyl phosphite 125-128 ° C / 18 bar 85 X

Patent Claim Point

Claims (1)

A process for the preparation of C 1-6 dialkyl phosphites by reacting alkanol with phosphorus trichloride in a 3: 1 molar ratio without an acid acceptor in the presence of an organic solvent. characterized in that a solution of the phosphorus trichloride ²⁵ and the solvent is added to the solution of the alkanol and solvent at 0-40 [deg.] C. with the aid of chloroform or dichloroethane.