Process for the preparation of phosphinic acids esters

The present invention relates to a process for the preparation of phosphinic acid esters and the use of the phosphinic acid esters prepared by this process.

Phosphinic acid esters are valuable synthetic building blocks and can be used, for example, in the production of polymers and plastics in order to obtain flame-retardant materials.

DE 26 52 007 A1 describes flame-retardant epoxy resins by incorporating carboxy-functional phosphinic acids. No. 5,399,428 A1 describes flame-retardant linear polyesters by incorporating carboxy-functional phosphinic acids.

DE 25 40 283 A1 describes the addition of phosphines to α, β-unsaturated carboxylic acids in the presence of aqueous hydrochloric acid and subsequent oxidation.

DE 28 49 003 describes the preparation of phosphorus-containing cyanohydrin derivatives by adding phosphonous esters to acrolein cyanohydrin derivatives.

Phosphinic acid esters are obtained by adding phosphonous acid monoesters to 1-olefins in the presence of peroxidic catalysts. However, the yields are low. The addition of phosphonous monoesters to activated double bonds in the presence of alcoholates as the catalyst is better. Suitable unsaturated compounds are α, β-unsaturated carboxylic acid esters or nitriles, α, β-unsaturated ketones as well as alkyl vinyl sulfones and vinyl acetate (Houben-Weyl, Volume 12/1, p. 258-259).

The phosphonous acid monoesters themselves are prepared from phosphonous dihalides by reaction with alcohols or by hydrolysis and subsequent esterification.

Functional phosphinic acids are obtained by reacting phosphonous acid dihalides (dihalophosphines) with activated olefinic compounds such as acrylic or methacrylic acid derivatives and then hydrolyzing them (Houben-Weyl, volume 12/1, p. 230; KK Khairullin, TI Sobchuk, AN Pudovik , Zh. Obshch. Khim. 37, 710 (1967)). Halides are obtained as by-products in the hydrolysis with organic acids.

In addition, phosphonous acid dihalides can also be reacted with alkyl halides in the presence of aluminum chloride (Houben-Weyl, volume 12/1, p. 232). Phosphinic acid esters can also be prepared from phosphonous dialkyl esters by the Michaelis-Arbuzov reaction. Dialkyl phosphonates, in turn, are produced from phosphonyl dihalides and hydroxy compounds.

The aforementioned phosphonous acid dihalides, for example methyldichlorophosphine, which can be used as starting materials for other syntheses, have themselves been prepared in a complex synthesis from phosphorus trihalides and alkyl halides in the presence of aluminum chloride (Houben-Weyl, volume 12/1, p. 306). The reaction is highly exothermic and difficult to master technically. In addition, various by-products are formed which, like some of the aforementioned starting products, are toxic and / or corrosive, that is to say highly undesirable.

There is therefore a need for processes for the preparation of phosphinic acid esters which can be carried out in a simple manner and in which uniform products are obtained in high yield. Such a method should also be clearly superior to the previously known environmental technology.

The invention is therefore based on the object of providing a process for the preparation of phosphinic acid esters which avoids the abovementioned disadvantages and starts from elemental yellow phosphorus as a starting material.

This object is achieved by a method of the type described in the introduction, characterized in that<ul id="ul0001" list-style="none" compact="compact"><li>a) elemental yellow phosphorus with alkyl halides in the presence of alkali or alkaline earth metal hydroxide to form a mixture which contains the main constituents of the alkali metal and / or alkaline earth metal salts of alkylphosphonous, phosphorous and hypophosphorous acid</li><li>b) the alkylphosphonous acid is removed from the mixture obtained according to a)</li><li>c) esterifying the alkylphosphonous acid</li><li>d) the ester of alkylphosphonous acid thus obtained is added to a compound having at least one C = C double bond.</li></ul>

The process according to the invention has considerable advantages over the processes known hitherto, since, among other things, it avoids phosphonous acid dihalides as starting materials and also has a positive balance in the product distribution.

Methyl chloride or methyl bromide are preferably used as alkyl halides.

The reaction in step a) is preferably carried out in a two-phase system composed of aqueous alkali metal or alkaline earth metal hydroxide or mixtures thereof and an organic solvent.

Straight-chain or branched alkanes, alkyl-substituted aromatic solvents, alcohols or ethers which are immiscible or only partially miscible with water, alone or in combination with one another, are preferably used as organic solvents.

Toluene, alone or in combination with alcohols, is particularly preferably used as the organic solvent.

The reaction is preferably carried out in the presence of a phase transfer catalyst.

The phase transfer catalyst is preferably tetraalkylphosphonium halide, triphenylalkylphosphonium halide or tetraorganylammonium halide.

The temperature in the reaction is preferably from -20 to +60 ° C.

The temperature is particularly preferably 0 to 30 ° C.

The reaction is preferably carried out under a pressure of 0 to 10 bar.

The process according to the invention is preferably carried out by suspending the yellow phosphorus in a solvent or a solvent mixture and then using alkyl halide and a compound of the formula MOH or M '(OH)₂ or mixtures thereof, in which M represents an alkali metal and M 'represents an alkaline earth metal.

The yellow phosphorus and the alkyl halide are preferably reacted with one another in a molar ratio of 1: 1 to 1: 3, the molar ratio of yellow phosphorus to the compound of the formula MOH or M '(OH)₂ 1: 1 to 1: 5.

In step b), the alkylphosphonous acid is preferably removed by distillation.

In step c) it is preferred to esterify by means of oxethylation.

An oxirane such as ethylene oxide, propylene oxide or longer-chain oxiranes is preferably used for the oxethylation after step c). Alternatively, ethylene carbonate can also be used. However, it can also be esterified directly with an alcohol with elimination of water.

The esterification of the phosphonous acid to the corresponding monoester can be achieved, for example, by reaction with higher-boiling alcohols with removal of the water formed by azeotropic distillation.

Examples of suitable alcohols are butanol, hexanol, octanol, ethylhexanol, ethylene glycol, diethylene glycol and / or glycerin.

In step d) it is preferred to add in the presence of catalysts.

These are preferably basic catalysts. Alternatively, acids or radical initiators can also be used.

The basic catalysts are preferably alkali and / or alkaline earth alcoholates.

Among the compounds mentioned in step d) with at least one C =C double bond, particular mention should be made of the olefins.

The olefins are preferably linear or branched α-olefins. The α-olefins are preferably ethylene, n-, i-propylene, n-, i-butene, n-, i-pentene, n-, i-hexene, n-, i-octene, 1-decene , 1-dodecene, 1-tetradecene, 1-hexadecene, n-eicosen, and / or 2,4,4-tri-methylpentene isomer mixture.

Compounds of the general formula are olefins<chemistry id="chem0001" num="0001"><img file="EP0969008A2_D0001.tif" /></chemistry> in the R¹-R⁴ may be the same or different and represent hydrogen, an alkyl group having 1 to 18 carbon atoms, phenyl, benzyl or alkyl-substituted aromatics.

Cycloolefins of the formula are also suitable<chemistry id="chem0002" num="0002"><img file="EP0969008A2_D0002.tif" /></chemistry> especially cyclopentene, cyclohexene, cyclooctene and cyclodecene.

Open-chain dienes of the formula can also be used<chemistry id="chem0003" num="0003"><img file="EP0969008A2_D0003.tif" /></chemistry> in the R⁵ - R¹⁰ are the same or different and represent hydrogen or a C₁ to C₆ - alkyl group and R¹¹ for (CH₂)_n with n = 0 to 6. Butadiene, isoprene and 1,5-hexadiene are preferred.

As cyclodienes, 1,3 cyclopentadiene, dicyclopentadiene and 1,5-cyclooctadiene and norbornadiene are preferred.

Preferred olefins are those having an internal double bond, cyclic or open-chain dienes and / or polyenes having 4 to 20 carbon atoms.

The olefins preferably carry a functional group.

The olefins with functional groups are preferably α, β-unsaturated carboxylic acid esters, amides or nitriles, α, β-unsaturated ketones as well as alkyl vinyl sulfones and vinyl acetate.

The olefins with functional groups are preferably α, β-unsaturated carboxylic acid esters of aliphatic or cycloaliphatic alcohols with 1 to 20 C atoms or carboxylic acid esters of polyhydric alcohols with 2 to 4 hydroxyl groups and 2 to 20 C atoms.

The olefins with functional groups are preferably derivatives of acrylic acid according to the general formula (I),<chemistry id="chem0004" num="0004"><img file="EP0969008A2_D0004.tif" /></chemistry> where R1 CH₃ or H and R2 represents an ester group of mono- or polyhydric alcohols with 1-12 C atoms or an amine group.

The olefins with functional groups are preferably acrolein cyanohydrin compounds of the formula (II)<chemistry id="chem0005" num="0005"><img file="EP0969008A2_D0005.tif" /></chemistry> with R3 = acetyl or propionyl.

The olefins with functional groups are preferably itaconic acid derivatives of the general formula (III) with R '= alkyl group with 1-12 C atoms.<chemistry id="chem0006" num="0006"><img file="EP0969008A2_D0006.tif" /></chemistry>

The olefin with a functional group is preferably hydroxyethyl acrylate, methyl acrylate, ethyl acrylate, hydroxyethyl methacrylate, methyl methacrylate, methyl methacrylate, dimethyl itaconate, diethyl itaconate or acrolein cyanohydrin acetate.

The olefin with a functional group is preferably hydroxyethyl acrylate or hydroxyethyl methacrylate.

The alkylphosphonous acid is preferably methanephosphonous acid.

The invention also relates to the use of the phosphinic acid esters produced by the process according to the invention as reactive flame retardants for polymers.

The invention also relates to the use of the phosphinic acid esters produced by the process according to the invention as reactive flame retardants for thermoplastic polymers such as polyethylene terephthalate, polybutylene terephthalate or polyamide.

The invention also relates to the use of the phosphinic acid esters produced by the process according to the invention as reactive flame retardants for thermosetting resins such as unsaturated polyester resins, epoxy resins, polyurethanes or acrylates.

The invention also relates to the use of the phosphinic acid esters produced by the process according to the invention as precursors for the chemical synthesis of other phosphorus-containing compounds.

The invention is illustrated by the following examples:

Example 1: Reaction of yellow phosphorus with alkyl halide

<chemistry id="chem0007" num="0007"><img file="EP0969008A2_D0007.tif" /></chemistry>

2 l of toluene, in which 25 g (0.05 mol) of tributylhexadecylphosphonium bromide had previously been dissolved, are placed in a 5 l stainless steel pressure reactor and preheated to 60.degree. 62 g (2 mol) of molten yellow phosphorus are introduced into the reactor, cooled to 0 ° C. with vigorous stirring and then 202 g (4 mol) of methyl chloride are condensed in. Thereafter, 1000 g of a solution of 600 g of KOH in 400 g of water are introduced over the course of 1 h, the temperature being kept at 0 ° C. and the mixture reacted at this temperature for 1 h. The product mixture is warmed to room temperature, diluted with 400 ml of water and then the reactor is depressurized by combustion. You get two phases. The aqueous phase contains 64.2 mol% methanephosphonous acid in the form of its potassium salt. After neutralization with hydrochloric acid, the methanephosphonous acid was distilled off in vacuo.

Example 2: Oxethylation of methanephosphonous acid

<chemistry id="chem0008" num="0008"><img file="EP0969008A2_D0008.tif" /></chemistry>

80.3 g (1 mol) of methanephosphonous acid are placed in a 500 ml five-necked flask with gas inlet tube, thermometer, intensive stirrer and reflux condenser with gas combustion. Ethylene oxide is introduced at room temperature. A reaction temperature of 70 ° C. is set with cooling. After the absorption of ethylene oxide has ended, the mixture is left to react for another hour at 80 ° C. The ethylene oxide uptake is 65.7 g corresponding to 1.5 mol. The acid number of the product is mine 1 mg KOH / g. A colorless, water-clear product is obtained. ³¹P-NMR: 38 ppm

Example 3: Addition of methanephosphonous hydroxyethyl ester to acrylic acid hydroxyethyl ester

<chemistry id="chem0009" num="0009"><img file="EP0969008A2_D0009.tif" /></chemistry>

67 g (0.46 mol) of methyl methanephosphonate and 53.2 g of hydroxyethyl acrylate are placed in a 500 ml five-necked flask equipped with a thermometer, reflux condenser, intensive stirrer and dropping funnel. While stirring, 25 ml of sodium methylate (30%) are added dropwise at a rate such that a reaction temperature of 60 ° C. is reached. The mixture is then left to react for a further 10 minutes at 80 ° C. A pale yellow colored liquid is obtained. The phosphorus content is 11.0%, the carbon content is 40.3% and the hydroxyl number is 148 mg / g. ³¹P NMR (CHCl₃): 64 ppm

Example 4: Addition of methanephosphonous hydroxyethyl ester to acrylamide

65 g (0.445 mol) of methyl methanephosphonate and 31.6 g of acrylamide are placed in a 500 ml five-necked flask equipped with a thermometer, reflux condenser, intensive stirrer and dropping funnel. 40 ml of sodium methylate (30%) are added dropwise with stirring at a rate such that a reaction temperature of 80 ° C. is established. The mixture is then left to react for a further 10 minutes at 80 ° C. A pale yellow colored liquid is obtained.³¹P NMR (CHCl₃): 55 ppm

Example 5: Addition of methanephosphonous hydroxyethyl ester to acrylonitrile

81.6 g (0.559 mol) of methyl methanephosphonate and 37.4 g of acrylonitrile are placed in a 500 ml five-necked flask equipped with a thermometer, reflux condenser, intensive stirrer and dropping funnel. 40 ml of sodium methylate (30%) are added dropwise with stirring at a rate such that a reaction temperature of 70 ° C. is established.

The mixture is then left to react for a further 10 minutes at 80 ° C. A pale yellow colored liquid is obtained.³¹P NMR (CHCl₃): 53-54 ppm

Example 6: Addition of methanephosphonous hydroxyethyl ester to acrylic acid methyl ester

In a 500 ml five-necked flask with thermometer, reflux condenser, intensive stirrer and dropping funnel, 73 g (0.445 mol) of methyl methanephosphonate and 43 g of methyl acrylate are introduced. 40 ml of sodium methylate (30%) are added dropwise with stirring at a rate such that a reaction temperature of 80 ° C. is established. A pale yellow colored liquid is obtained. ³¹P NMR (CHCl₃): 58 ppm

Example 7: Addition of methanephosphonous hydroxyethyl ester to dimethyl itaconate

43.8 g (0.3 mol) of methyl methanephosphonate and 47.4 g of dimethyl itaconic acid (0.3 mol) are placed in a 500 ml five-necked flask equipped with a thermometer, reflux condenser, intensive stirrer and dropping funnel. 3 ml of sodium methylate (30%) are added dropwise with stirring at such a rate that a reaction temperature of max. 90 ° C. The mixture is then left to react for a further 1 h at 50-70 ° C. A pale yellow colored liquid is obtained.³¹P NMR (CHCl₃): 55-56 ppm

Example 8: Reaction of methanephosphonous acid with n-butanol

43.8 g (0.3 mol) of methanephosphonous hydroxyethyl ester and 37.1 g of n-butanol (0.5 mol) are placed in a 250 ml three-necked flask equipped with a thermometer, water separator and intensive stirrer. At a reaction temperature of 90-110 ° C, the water formed is removed by azeotropic distillation. The product is then purified by distillation at 1 mbar.

Example 9: Reaction of methanephosphonous acid with isobutanol

43.8 g (0.3 mol) of methyl methanephosphonate and 37.1 g of isobutanol (0.5 mol) are placed in a 250 ml three-necked flask with thermometer, water separator and intensive stirrer. At a reaction temperature of 80-110 ° C, the water formed is removed by azeotropic distillation. The product is then purified by distillation at 1 mbar.

Example 10: Addition of isobutyl methanephosphonate to acroleincyanhydrin acetate

110 g of isobutyl methanephosphonate are placed in a 500 ml five-necked flask with thermometer, reflux condenser, intensive stirrer and dropping funnel. 50 g of acrolein cyanohydrin acetate and 4 g of t-butyl peroctoate are added dropwise with stirring at 130.degree. The mixture is then left to react for a further 15 minutes at 120 ° C. and then the product is distilled off in a high vacuum at 170 ° C. and 0.4 mbar. 94 g of 3-acetoxy-3-cyano-propyl) methylphosphinic acid isobutyl ester are obtained, corresponding to a yield of 89.5% of theory.

Example 11: Addition of isobutyl methanephosphonate to acrolein cyanohydrin propionate

110 g of isobutyl methanephosphonate are placed in a 500 ml five-necked flask equipped with a thermometer, reflux condenser, intensive stirrer and dropping funnel. 50 g of acrolein cyanohydrin propionate and 4 g of t-butyl peroctoate are added dropwise with stirring at 130 ° C. over an hour. The mixture is then left to react for a further 15 minutes at 120 ° C. and then the product is distilled off in a high vacuum at 180 ° C. and 0.4 mbar. 94 g of 3-acetoxy-3-cyano-propyl) methylphosphinic acid isobutyl ester are obtained, corresponding to a yield of 84.5% of theory.