PREPARATION OF SUBSTITUTED PHOSPHIDE SALTS

Abstract: Substituted sodium salts of phosphides are prepared by reacting a triarylphosphine with sodium in an aliphatic amine or diamine as solvent or co-solvent. The resultant phosphides may be further treated with appropriate halides to produce unsymmetrical phosphines.

Description: TITLE: Preparation of substituted phosphide salts. DESCRIPTION The present invention relates to a process for preparing substituted sodium salts of phosphides and use of such salts in preparing phosphines. The preparation of alkali metal diarylphosphides and their subsequent conversion to unsymmetrical triarylphosphines is well-known in the literature. Triarylphosphines are widely used as ligands to transition metals to afford useful catalysts for many different chemical reactions. Examples of these reactions, which are carried out on an industrial scale, include the hydroformylation reaction to produce aldehydes from alkenes, the reaction of aryl halides or alkenes to produce esters and the metathesis of simple alkenes to higher olefms. Although triphenylphosphine is frequently used as such a ligand, better specificity is often encountered if unsymmetrical triarylphosphines or diarylalkyl are used. Methods which have been used to produce alkali metal diphenylphosphides are low yielding, difficult to carry out on a large scale, and/or expensive. For example, Hewertson and Watson (J. Chem. Soc. 1962. 1490) teach that sodium diphenylphosphide may be prepared in > 75% yield by the cleavage of triphenylphosphine with sodium metal at -75 ° C in liquid ammonia. Whilst such reactions are common place in the laboratory, large scale production is hampered by the need of special (and very expensive) plant which can work at these low temperatures. Issleib and Frohlich (Z. Naturforsch, 1959, 14b, 349) have shown that the reaction may be carried out with sodium metal in dioxane. However, in this case the yield is only 25% . Clearly such a low yield is unacceptable for industrial production. Finally, metallic sodium may be reacted with chlorodiphenylphosphine (Hewertson, ibid). However, chlorodiphenylphosphine, although commercially available, is somewhat expensive and is only used because there is little alternative. There is thus a need for a method of preparing alkali metal diarylphosphides which is high yielding, uses inexpensive and readily available raw materials and uses what may be termed "conventional" chemical plant. It has now been surprisingly found that these requirements may be met if a reaction is carried out between a readily available triarylphosphine, typically triphenyl phosphine, and an alkali metal, typically sodium, in either a primary aliphatic amine or diamine either alone or diluted with a co-solvent. According to the present invention there is provided a process for preparing sodium diaryl salts of phosphides of general formula (I) R 2 P - Na + (I) where R is a phenyl or substituted phenyl group, by reaction of a triarylphosphine with sodium in an aliphatic amine or diamine as solvent or co-solvent. The sodium used in the process of the invention is preferably finely dispersed in a carrier liquid. The liquid carrier may be an inert organic solvent whose boiling point is above the melting point of sodium such as, for example, toluene, xylene and petroleum ethers. Alternatively, the carrier liquid may be a mineral oil such as, for example, selected from die Shell Ordina or BP Enerpar range of high grande mineral oils. The dispersion of sodium may be prepared by melting sodium metal in the carrier liquid and stirring rapidly. The sodium in the dispersion preferably has an average particle size in the range of 0.1 to 1000 microns, especially 0.1 to 20 microns. The sodium is preferably dispersed in an amount of lg of sodium per 0.1 to 100 cm 3 , especially 0.1 to 5 cm 3 of liquid carrier. A preferred solvent is ethylenediamine. A preferred co-solvent when used is selected from hydrocarbons and ethers. The hydrocarbon co-solvent may be aromatic or aliphatic. Toluene is an example of a suitable aromatic hydrocarbon co-solvent and hexane is an example of a suitable aliphatic hydrocarbon co-solvent. Examples of suitable ether co-solvents for use in the process of the invention include tetrahydrofuran, methy '-butyl ether and glyme ethers. The reaction may be carried out in the temperature range of about 0 ° C to about 120 ° C, preferably in the range of 50-70 ° C. The sodium diaryl of phosphides prepared according to the invention may be further treated by reaction with a compound of the general formula R'X, where R 1 is selected from hydrogen, phenyl or substituted phenyl (aryl) groups, naphthyl or substituted naphthyl groups, heterocyclic rings, C πo carbon chains optionally containing branches or unsaturated linkages, or -(CR'R'^PRR where n = 1 to 10 and X is a suitable leaving group, such as halide, methoxide or nitro, to produce phosphines of the general formula. R \ P - R 1 (II) / R The reaction temperature for producing unsymmetrical phosphines is preferably in the range of 0-120 ° C, especially 20-30 ° C. The by-product from this cleavage is phenyl sodium which is a very strong base. Since this strong base may interfere with subsequent reactions, it is preferable to destroy this reagent before further chemistry is carried out. This has been carried out in the literature by d e addition of ammonium salts such as ammonium chloride. In our case this is not convenient since such ammonium salts are insoluble in the reaction medium. A more convenient method of destruction is by the addition of an alcohol, such as n-butanol. Although this procedure produces sodium alkoxides and benzene these by-products do not appear to interfere with subsequent reactions. The use of ethylenediamine has a further benefit in the subsequent reaction of the sodium diarylphosphide with a suitable electrophile in that it is an excellent solvent for conducting such reactions. Thus, the reaction may be brought about by adding the relevant alkyl or activated aryl halide, either alone or in a suitable co- solvent, to the reaction mixture and heating for an appropriate time to complete the reaction. Work-up of the final product is particularly easy by the cautious addition of water to the reaction medium. The solvent, ethylenediamine, and the inorganic byproducts are soluble in water and the product simply precipitates from solution. The product may be isolated in a high degree of purity by simple filtration, washing and drying. A particular advantage of the process of the invention is that cryogenic plant is not required and the process is easily operable in standard chemical plant on a large scale. The invention is particularly useful for preparing sodium salts of diary lphosphides, especially sodium diphenylphosphides, and then further treatment to produce unsymmetrical triarylphosphides. An advantage of the invention in relation to sodium salts is that sodium diphenylphosphide is soluble in the ethylenediamine solvent and so is tractable in subsequent reactions to give the corresponding unsymmetrical phosphine. The invention will now be further described by means of the following Examples. Example 1 : Preparation of sodium diphenylphosphide A dispersion of sodium in mineral oil (25.4g of 33%w/w dispersion, 0.364 mol) was added portionwise over 30 mins to a stirred suspension of triphenylphosphine (44.0g, 0.168 mol) in ethylenediamine (50 cm 3 ) under nitrogen at 30 ° C. On initial addition of die dispersion an immediate exotherm occurred and the reaction mixture turned orange in colour. On addition of further portions of die dispersion, the exothermic reaction caused the internal reaction mixture temperature to rise to 70 ° C and the reaction mixture to turn deep red in colour. Upon completion of dispersion addition die reaction mixture was stirred for a further 1 to 2 hours at 50- 70 C to ensure completion of reaction to afford a diick, deep red mobile reaction mixture containing sodium diphenylphosphide and phenyl sodium. The reaction mixture was then treated dropwise with butanol (12.0g) at 50 ° C to destroy phenyl sodium and stirred at 40-50 C for a further hour. The reaction mixture produced in this way may be used direcdy in further reactions without any further treatment. Example 2: Preparation of 2-(Diphenylphosphino) Pyridine A solution of 2-chloropyridine (19. Og, 0.167mol) in toluene was added dropwise to die material produced in Example 1 at 15-25 ° C over 30 mins. The resulting exod erm was controlled by means of an ice badi. The colour of the reaction first turned dark brown before turning beige. On completion of d e reaction, the mixture was stirred for a further 30 mins to ensure completion of reaction. Water (150 cm 3 ) was then cautiously added to afford a creamy yellow reaction mixture. The mixture was cooled to 0-5 ° C and then filtered, washed wid water and dried. The product was obtained as a cream coloured solid which was fairly pure. Yield = 31.0g (70% based on triphenylphosphine). Example 3 : Preparation of sodium dipehylphosphide In Uiis Example a co-solvent is used in the process. A dispersion of sodium in mineral oil (25.4g of 33%w/w dispersion, 0.364 mol was added portionwise over 30 mins to a stirred suspension of triphenylphosphine (44. Og, 0.168 mol) in ediylenediamine (90 cm 3 ) and toluene (30 cm 3 ) under nitrogen at 30 ° C. On initial addition of die dispersion an immediate exotherm occurred and the mixture turned orange in colour. On addition of further portions of the dispersion, die exotiiermic reaction caused die internal reaction mixture temperature to rise to 70 ° C and the reaction mixture turn deep red in colour. Upon completion of dispersion addition die reaction mixture was stirred for a further 1 to 2 hours at 50- 70 C to ensure completion of reaction, to afford a thin deep red mobile reaction mixture containing sodium diphenylphosphide and phenyl sodium. The reaction mixture was tiien treated with butanol (12.0g) at 50 C to quench phenyl sodium and stirred at 40-50 C for a further hour. The reaction mixture produced in this way may be reacted witii compounds of die general formula R'X to prepare unsymmetrical phosphines in good yield without any further treatment. Example 4: Preparation of sodium diphenylphosphide In this Example the mode of reagent addition is reversed and a co-solvent is used. Thus ethylenediamine (90 cm 3 ) was added dropwise over 30 mins to a stirred suspension of a dispersion of sodium in mineral oil (25.4g of 33%w/w dispersion, 0.364 mol), triphenylphosphine (44. Og, 0.168 mol) and metiiyl '- butyl etiier (30 cm 3 ) under nitrogen at 30 ° C. On initial addition ethylenediamine an immediate exotiierm occurred and die mixture turned orange in colour. On addition of further portions of ethylenediamine, the exotiiermic reaction caused die internal reaction mixture temperature to rise to 70 ° C and die reaction mixture turn deep red in colour. Upon completion of ethylenediamine addition d e reaction mixture was stirred for a further 1 to 2 hours at 50-70 ° C to ensure completion of reaction, to afford a deep red mobile reaction mixture containing sodium diphenylphosphide and phenyl sodium. The reaction mixture was tiien treated witii butanol (12.0g) at 50 ° C to quench phenyl sodium and stirred at 40-50 ° C for a further hour. The reaction mixture produced in this way may be reacted with compounds of the general formula R'X to prepare unsymmetrical phosphines in good yield widiout any further treatment.

Claims: CLAIMS 1. A process for preparing alkali metal diaryl phosphides of general formula (I) R 2 P Na + (I) where R is a phenyl or substituted phenyl group, by reaction of the corresponding triarylphosphine with sodium in an aliphatic amine or diamine as solvent or co- solvent. 2. A process as claimed in claim 1, wherein the sodium is finely dispersed in a carrier liquid. 3. A process as claimed in claim 2, wherein die carrier liquid is an inert organic solvent whose boiling point is above the melting point of sodium. 4. A process as claimed in claim 2, wherein d e carrier liquid is selected from toluene, xylene and petroleum ethers. 5. A process as claimed in claim 2, wherein the liquid carrier is a mineral oil. 6. A process as claimed in any one of claims 2 to 5, wherein die dispersion of sodium is made by melting sodium metal in die carrier liquid and stirring rapidly. 7. A process as claimed in any one of claims 2 to 6, wherein the sodium has an average particle size in the range of 0.1 to 1000 microns. 8. A process as claimed in claim 7, wherein die sodium has an average particle size of 0.1 to 20 microns. 9. A process as claimed in any one of claims 2 to 8, wherein the sodium is dispersed in an amount of from l of sodium per 0.1 to 100 cm 3 of liquid. 10. A process as claimed in claim 9, wherein die sodium is dispersed in an amount of lg of sodium per 0.1 to 5 cm 3 of liquid carrier. 11. A process as claimed in any one of claims 1 to 1.0, wherein the aliphatic diamine is etiiylenediamine. 12. A process as claimed in any one of claims 1 to 11 , wherein the diamine is diluted with a co-solvent. 13. A process as claimed in claim 12, wherein the co-solvent is selected from hydrocarbons and eώers. 14. A process as claimed in claim 13, wherein the hydrocarbon co-solvent is aromatic. 15. A process as claimed in claim 14, wherein die aromatic hydrocarbon is toluene. 16. A process as claimed in claim 15, wherein the hydrocarbon co-solvent is an aliphatic hydrocarbon. 17. A process as claimed in claim 16, wherein d e aliphatic co-solvent is hexane. 18. A process as claimed in claim 13 where the ether co-solvent is selected from tetrahydrofuran, metiiyl '-butyl etiier and glyme ethers. 19. A process as claimed in any one of claims 1 to 18, wherein the reaction temperature is in the range of 0-120 ° C. 20. A process as claimed in claim 19, wherein the reaction temperature is in the range of 50-70 ° C. 21. A process as claimed in any one of claims 1 to 20 including die step of adding an alcohol to die reaction medium after formation of die sodium diarylphosphide. 22. A process as claimed in claim 21, wherein die alcohol is n-butanol. 23. A process as claimed in any one of claims 1 to 19, wherein the triarylphosphine is triphenylphosphine. 24. A process for preparing an unsymmetrical phosphine comprising reacting a sodium diarylphosphide as prepared by a process as claimed in any one of claims 1 to 23 with a compound of die general formula R'X, where R' is selected from hydrogen, phenyl or substituted phenyl (aryl) groups, naphthyl or substituted naphthyl groups, heterocyclic rings, C M . carbon chains, optionally containing branches or unsaturated linkages, or CR'R' l) a PRR, where n is 1 to 10 and X is a suitable leaving group. 25. A process as claimed in claim 24, wherein in the formula R'X, X is selected from halide, metiioxide and nitrogroups. 26. A process as claimed in claim 24 or 25, wherein die reaction temperature is in the range 0-120 ° C. 27. A process as claimed in claim 26, wherein the reaction temperature is in the range 20-30 ° C. 28. A process as claimed in claim 1 and substantially as hereinbefore described witii reference to Example 1 , 3 or 4. 29. A process as claimed in claim 24 and substantially as hereinbefore described with reference to Example 2, 3 or 4.

Inventors: CREMINS PETER JOHN, GANDY ROBERT, TIMMS ALLAN WILLIAM, CREMINS, PETER, JOHN, GANDY, ROBERT, TIMMS, ALLAN, WILLIAM
Applicants: CREMINS PETER JOHN, GANDY ROBERT, GREAT LAKES FINE CHEM LTD, TIMMS ALLAN WILLIAM, CREMINS, PETER, JOHN, GANDY, ROBERT, GREAT LAKES FINE CHEMICALS LIMITED, TIMMS, ALLAN, WILLIAM
Application year: 1998
Main classification: C07F9
IPC codes: C07F9