Patent GB-865454-A (GB)
Title: Manufacture of trialkyl phosphites
IPC: C07F9/142
Filed: 1957-07-02
Abstract: Trialkyl phosphites are obtained by reaction of phosphorus trichloride with low molecular saturated aliphatic alcohols containing 1 to 4 carbon atoms in the presence of a tertiary amine and an inert organic solvent with formation of solid tertiary amine hydrochloride at least a part of the reaction mixture being led continuously from the reaction zone into a zone where the solid amine hydrochloride formed is separated from the reaction mixture.  The reaction mixture is preferably recycled and the solid amine hydrochloride separated continuously from the reaction mixture and the amount of amine hydrochloride in the reaction mixture should preferably always be less than quantity of amine hydrochloride equivalent to a concentration of 8% by weight of trialkyl phosphite calculated on the quantity of the inert solvent.  In one embodiment the alcohol, the amine and the phosphorous trichloride are added gradually to the reaction mixture or to the solvent, the reaction mixture being continuously circulated from the reaction vessel through a filter, e.g. by means of a pump, to remove the separated amine hydrochloride and then returned to the reaction vessel, the solid residue of amine salt after washing with a further quantity of the inert solvent used in the reaction being removed either continuously or discontinuously and the free base regenerated.  When the concentration of trialkyl phosphite in the circulating mixture has attained the desired value a suitable quantity of the solution is continuously withdrawn at such a rate that the concentration of the reaction product in the recycling mixture remains approximately constant.  The wash liquid is also returned to the reaction mixture. In another embodiment at the commencement of an operation cycle the total quantity of alcohol and amine are introduced into the reaction mixture and only the phosphorus trichloride is added gradually and in this case only the filtration takes place continuously and special care must be taken towards the end of the reaction that no excess of phosphorus trichloride occurs in the reaction mixture.  This may be achieved by pH control of the reaction medium by means of an indicator or a glass electrode.  It is also possible to operate without recycling by introducing the three starting materials continuously at one end of the reaction vessel and continuously drawing off the reaction mixture at the other end and removing therefrom the solid amine hydrochloride formed.  Suitable tertiary amines are those of the aliphatic, alicyclic, aliphatic-aromatic or heterocyclic series having sufficiently strong basic properties and the hydrochlorides of which are sufficiently difficultly soluble or are insoluble in the inert solvent used and it is preferred to use trialkylamines in which the alkyl groups contain 2 to 4 carbon atoms, e.g. tributylamine or tripropylamine and more especially triethylamine.  The inert solvent may be an aliphatic, aromatic, araliphatic or cycloaliphatic hydrocarbon, e.g. petroleum ether, benzene, or decahydronaphthalene or may be trichlorobenzene. Examples are given for the production of trimethyl and triethyl phosphates.  Other specified trialkyl phosphites obtainable by the process are tri-n-propyl, triisopropyl, tri-n-butyl and tri-isobutyl phosphites.