DE1285988B - Process for the preparation of phosphoryl tri-isocyanate - Google Patents

Description

GSForbes and HHAnderson describe in Journ. At the. Chem. Soc., Vol. 62 (1940), p. 762, the preparation of phosphorus tri-isoeyanate from phosphorus trichloride and 3 mol of silver cyanate in benzene. In the USA. Patent 2,835,652 Xvird the production of organic radicals bound to phosphorus-containing Isoeyanaten, z. B. C, H5P (NCO) "mentioned from the corresponding halides and silver cyanate in acetonitrile. In the USA. Patentschrift2-873,171 it is indicated that potassium cyanate in the reaction with phosphorus trichloride little or no Phosphortri isocyanate yields, even in various inert Solvents, for example carbon tetrachloride, and with the addition of catalytic amounts of copper chloride and silver isocyanate, and that good yields of phosphorus tri-isocyanate can only be obtained when lithium isocyanate is used cumbersome manner carbonate Li-by double decomposition with sodium carbonate to and from it by means of urea-melt, the Li-cyanate must be regenerated. Accordingly, there is provided an improved manufacturing process of phosphorus tri-isocyanate from phosphorus trichloride and alkali cyanates in British Patent 907,029, working in polar solvents such as organic nitriles, especially acetonitrile , Ketones, nitro compounds and esters enables good yields. However, this process has the disadvantage that these solvents are very flammable and require special precautionary measures. Therefore, it is described an improved process for the preparation of phosphorus-tri-isoeyanat in German patent 1,161,541, where the reaction of alkali cyanate and in Pkosphortrichlorid - preferably liquid - sulfur dioxide is carried out. When working with liquid sulfur dioxide, however, extensive cooling measures are necessary, especially since the alkali metal chloride formed must be washed out with sulfur dioxide after being filtered off.

Surprisingly, the above-mentioned disadvantages and difficulties in a new process for the preparation of phosphoryl tri-isoeyanate from phosphorus trichloride and inorganic cyanates could be avoided by converting phosphorus trichloride and sodium cyanate at high temperature in medium-boiling, non-flammable chlorohydrocarbons with the addition of catalytic amounts of organic nitriles and then the phosphorus tri-isoeyanate obtained is oxidized with SO in perchlorinated liquid hydrocarbons in the cold.

The chlorinated hydrocarbons in which, as has been found, P (NCO) is soluble, are those with a flaming point above 30 ° C, if possible above 54 ° C. Accordingly, 1,2,3-trichloropropane, 1,1,2-trichloroethane, trichlorethylene, chloroform, methylene chloride, tetrachloroethane, chlorobenzene, o-dichlorobenzene, dichloropentane mixtures, 1,4-dichlorobutane, dichlorocyclohexane, especially carbon tetrachloride and perchlorethylene are suitable. An auxiliary combustible solvent is indifferent to the extent possible, is maintained as the condition with respect to the flame point. Accordingly, phosphorus trichloride and 3 moles of sodium yanate are refluxed for several hours in these solvents, advantageously with vigorous stirring. The reaction temperature should usually be between about 40 and about 180.degree. C. , preferably between 70 and 120.degree . To accelerate the reaction, about 0.1 to about 2 percent by weight of an organic nitrile, preferably a low molecular weight aliphatic nitrile, e.g. B. acetonitrile, propionitrile, acrylonitrile, glutaric acid di-nitrile, cyanoacetic ester are added. The end of the reaction can be recognized by the fact that a filtered sample of the reaction suspension becomes chlorine-free in the filtrate. The sodium chloride formed is then separated off, expediently by filtering or centrifuging, or by distilling off solvents and phosphorus tri-isocyanate, finally expediently in vacuo.

The phosphorus tri-isoeyanate can be oxidized directly with sulfur trioxide to phosphoryl tri-isoeyanate in the cold, it being advantageous that the perchlorinated solvents required for the preparation of the phosphorus tri-isoeyanate in the cold, i.e. H. in the temperature range between about -30 and + 10'C, are sufficiently resistant to sulfur trioxide. The oxidation is preferably carried out in the temperature range mentioned, advantageously below O'C, temperatures lower than −30 ° C. being unsuitable because of the solidification of the solvents and the decrease in the reaction rate. The oxidation is usually carried out in the range between about 0 and -20 ° C. It is advisable to use the theoretically necessary amount of sulfur trioxide or only a very small excess of it in order to avoid side reactions with the solvent during the subsequent heating after the oxidation. Heating to temperatures around 70 ° C is advisable to drive off the sulfur dioxide that has formed. After the sulfur dioxide has been degassed, the solvent is distilled off from the oxidation mixture at normal pressure or slightly reduced pressure, the phosphoryl tri-isoeyanate remaining in oily form. The phosphoryl tri-isocyanate can be distilled in vacuo and is then obtained as a colorless oil in very good yield.

Phosphoryl-tri-isoeyanate. Is used directly or as a preliminary product for the production of flame retardants for textiles, pesticides and additives for lubricants. Example a) 208 g of sodium cyanate are mixed with 800 g of carbon tetrachloride, 137 g of phosphorus trichloride and 10 g of acetonitrile are added and the suspension is heated to the boil on the reflux condenser. After two hours of boiling a filtered sample of the suspension in the filtrate was only 0.6 0 /, ionogenic chlorine, other about 3 hours boiling "which corresponds to only 0.3 0 / about 3 0 /, the amount employed, therefore, a 970 The reaction suspension is then filtered off with suction and the residue is washed out with carbon tetrachloride. After drying, the precipitate weighs 205 g, with a yield of sodium chloride of 97 l) /, theoretically.

The carbon tetrachloride is formed first from the entire filtrate Normal pressure distilled off; it can be reused as such.

On distillation in vacuo, the oily residue gives 135 g of phosphorus tri-isocyanate with a boiling point of 70 ° C./12 mm as a colorless oil (yield: 88 % of theory). If you use the same amount of chloroform or perchlorethylene instead of carbon tetrachloride and work in the same way, you get the same result in twice or half the reaction time.

One can also use the same in place of acetonitrile with the same success Use amount of propionitrile.

b) Working in carbon tetrachloride and perchlorethylene is advantageous because, as has been found, they are sufficiently resistant to sulfur trioxide at about -30 to + 10'C to immediately oxidize the phosphorus tri-isoeyanate to phosphoryl tri- to perform isoeyanat in the cold. Then 0.9 mol of sulfur trioxide can be added dropwise to the total filtrate obtained above of 0.9 mol of phosphorus tri-isocyanate in carbon tetrachloride at about -25 ° C. with stirring over the course of one hour. The strong heat of reaction is dissipated by external cooling so that the internal temperature does not rise above about -9'C. The reaction solution is then heated to 70 ° C. with stirring, the sulfur dioxide formed escaping. The solvent is then distilled off at normal pressure or slightly reduced pressure. Pure phosphoryl tri-isoeyanate as colorless oil is distilled from the oily residue at 66 ° C./1 mm or 80 ° C./3 mm with a theoretical yield of 90% .

Claims (1)

Claim: Process for the production of phosphoryl triisoeyanate of phosphorus trichloride and inorganic cyanates, characterized in that one Phosphorus trichloride with sodium cyanate in the heat in medium-boiling incombustible Chlorinated hydrocarbons with the addition of catalytic amounts of organic nitriles converts and the phosphorus tri-isocyanate obtained with sulfur trioxide in perchlorinated liquid hydrocarbons are oxidized in the cold.