PROCESS FOR PURIFYING TRIHYDROCARBYLPHOSPHINES USING METHANOL

Abstract: A process for the purification of trihydrocarbylphosphine having at least one aryl group and at least one alkyl or cycloalkyl group in the molecule, from a reaction mass comprising the trihydrocarbylphosphine, the process comprising crystallizing the reaction mass using a solvent consisting essentially of methanol. The process provides for the unexpectedly efficient production of trihydrocarbylphosphine compounds having purities of at least 97 mol%, and more preferably at least about 99 mol%. Another embodiment of the invention is neomenthyldiphenylphosphine having a purity of at least 97 mol% produced by crystallizing neomenthyldiphenylphosphine having a purity of less than 97 mol% using a solvent consisting essentially of methanol.

Description: PROCESS FOR PURIFYING TRIHYDROCARBYLPHOSPHINES USING METHANOL TECHNICAL FIELD This invention relates to recrystallization processes for purifying certain trihydrocarbylphosphines . BACKGROUND Methods for the production of air-sensitive phosphines such as, for example, trihydrocarbylphosphines having at least one aryl group and at least one alkyl or cycloalkyl group in the molecule, have been reported in the literature. Prior methods for the purification of reaction products containing desired forms of these phosphines have involved recrystallization in which ethanol was used as a solvent. However, these previous methods result in purity levels of no greater than 95% as measured by gas chromatography, purity levels which have proven to be inadequate in commercial applications of trihydrocarbylphosphines which are important catalyst components such as, e.g. , neomenthyldiphenylphosphine. Thus, a need exists for a way to produce highly pure (at least 97 mol% as measured by 31 P NMR analysis) trihydrocarbylphosphines. This invention is deemed to fulfill this important need in a surprisingly efficient and effective manner. DESCRIPTION OF THE INVENTION In one embodiment, this invention provides a new, surprisingly effective process for producing certain highly pure trihydrocarbylphosphines. More particularly, this invention provides a process for the purification of a trihydrocarbylphosphine having at least one aryl or alkyl-substituted aryl group and at least one alkyl or cycloalkyl group in the molecule, from a reaction mass comprising the trihydrocarbylphosphine, the process comprising crystallizing the reaction mass using a solvent consisting essentially of methanol. Preferably, the purity of the crystallized trihydrocarbylphosphine is at least 97 mol%, and more preferably at least about 99 mol%, measured by 31 P NMR analysis. This process reveals that methanol achieves unexpectedly superior results as a crystallization solvent for trihydrocarbylphosphines having at least one aryl or alkyl- substituted group and at least one alkyl or cycloalkyl group in the molecule, as compared to results achieved when ethanol is employed as a solvent in the crystallization process. Another embodiment of this invention is neomenthyldiphenylphosphine (also referred to herein as NMDPP) having a purity of at least 97 mol% as measured by 31 P NMR analysis produced by crystallizing neomenthyldiphenylphosphine having a purity of less than 97 mol% as measured by 31 P NMR analysis using a solvent consisting essentially of methanol. NMDPP of this invention has a solubility in methanol of less than 2.0% by weight at 25 °C and of less than 9.0% by weight at 60°C. In a preferred embodiment, the NMDPP has a purity of at least 99 mol% measured by 31 P NMR analysis produced by crystallizing NMDPP having a purity of less than 99 mol% measured by 31 P analysis using a solvent consisting essentially of methanol. The trihydrocarbylphosphine of this invention has the formula where R 1 , R 2 , and R 3 are the same or different and are selected from alkyl, aryl, aralkyl, and cycloalkyl, at least one of R 1 , R 2 , and R 3 being aryl and at least one of R 1 , R 2 , and R 3 is alkyl or cycloalkyl. A highly preferred type of trihydrocarbylphosphine is one or more tertiary phosphines of the formula R ' A ^ C H-P ( A r ) 2 ( C H 2 ) n I „ _ C H- where R' and R" are the same or different and are individually hydrogen, alkyl, or aryl, wherein Ar is phenyl, naphthyl, alkyl-substituted phenyl or alkyl-substituted naphthyl and wherein n is an integer from 3 to 6. Preferably, R' and R" are the same or different and are C, to alkyl, Ar is phenyl or naphthyl and n is 3 or 4. Most preferably, R' is methyl or ethyl, R" is C 3 to branched alkyl, Ar is phenyl and n is 4. Especially preferred as the trihydrocarbylphosphine is neomenthyldiphenylphosphine. The reaction mass used in this invention is typically a mixture comprised of the trihydrocarbylphosphine compound and from 2 to 30 weight percent of one or more impurities including oxide derivatives of the trihydrocarbylphosphine compound. The step of crystallization in this invention is conducted using degassed solvent in which the reaction mass is dissolved. The purified product is removed from the resulting solution as a crystalline precipitate by heating the solution to a temperature in the range of 40 to 65 °C, slowly cooling the solution to form the crystalline precipitate, and then removing the precipitate by filtration. In this way, the impurities substantially remain in solution so that the resulting crystalline precipitate is highly pure. Recrystallization may be employed to achieve even higher levels of purity, if desired. In such cases, the crystallization step is repeated by using the crystalline precipitate of each previous crystallization as the reaction mass for a subsequent crystallization until the desired level of purity is attained. The solvent used consists essentially of methanol, but may include small amounts of impurities such as, for example, water and ethanol, so long as the impurities do not negatively affect the level of purity attained in the process. The amount of solvent used is typically in the range of 1 to50 mL of solvent per gram of crude reaction mass, although other amounts of solvent may be used, if desired, to optimize the yield of purified NMDPP. The following comparative examples serve to illustrate this invention, but do not limit it. All parts are by weight unless otherwise indicated. Example 1 (Comparative) Diphenylphosphine (140 g, 0.75 mol) was charged into a 2-L, 3-neck, round- bottom flask in a glove box under a nitrogen atmosphere. The reactor was connected to a nitrogen manifold. Freshly distilled tetrahydrofuran (400 mL) was added to the mixture and the mixture was cooled to -20°C. Normal butyllithium (1.6 M in hexanes, 468 mL, 0.75 mol) was added over a 2 hour period. The cold bath was removed and the orange solution was warmed to room temperature. After stirring at room temperature for 0.5 hour, (-)-menthyl chloride (129 g, 0.74 mol) was added. The mixture was stirred at room temperature for 21 hours and then heated at reflux for 40 hours. The reaction mixture was cooled to room temperature and quenched with H 2 0 (125 mL). After stirring for 2 hours, the organic layer was separated, washed with H 2 0 (125 mL) and concentrated to an oil. The resulting material was distilled under vacuum until crystal formation was observed in the distillation condenser to give about 130 g of crude NMDPP in the pot. Crystallization of the crude NMDPP from ethanol (700 mL) gave a white solid (75 g). Analysis by 31 P NMR showed 83 mol% NMDPP, 10 mol% NMDPP oxide, and 3 mol% diphenylphosphine oxide. The mother liquor was cooled to -40 °C and yielded another 23 g of product. Analysis by 31 P NMR showed 77 mol% NMDPP, 14 mol% NMDPP oxide, and 4 mol% diphenylphosphine oxide. In this and each of the examples which follow, the 31 P NMR analysis was conducted using a General Electric QE300 NMR machine set at 121.7 MHz, each sample having been prepared under nitrogen in a glove box. Example 2 (Comparative) NMDPP (85% , 1 g) was chromatographed on silica gel (230-400 mesh, 30 g, eluted with a degassed 20.1 hexanes/EtOAc solvent) in a nitrogen glove box. The solvent was removed under vacuum to give a white solid. Analysis by 31 P NMR showed 92 mol% NMDPP and 7 mol% NMDPP oxide. Example 3 Recrystallization of NMDPP (3 gms of 83 % pure NMDPP from Example 1) from methanol (degassed, 60 mL) under a nitrogen atmosphere gave a crystalline solid (1.8 g). Analysis by 31 P NMR showed greater than 99 mol% NMDPP. Example 4 In a 2-L, three-necked round-bottom flask, diphenylphosphine (164.9 gms, 0.885 mols) was dissolved in degassed THF (500 mL) and cooled to -20°C in a nitrogen glove box. The reactor was connected to a nitrogen manifold. A solution of normal butyllithium in pentane (0.885 mol) was added dropwise to the solution. The cold bath was removed, and the orange colored solution was warmed to room temperature. The solution then was added to a solution of menthyl chloride (0.885 mol) in degassed THF (100 mL) at 60°C. The reaction was refluxed for 60 hours and then cooled. Degassed water (200 ml) was then added and the solution was stirred for 30 minutes. The organic phase was separated and concentrated to a thick oil. The oil was distilled under vacuum until crystal formation was observed in the distillation condenser, and the residue was dissolved in degassed methanol. Upon cooling, NMDPP was precipitated as a white solid. The purity of the precipitate was measured by gas chromatography to be greater than 96 area% . Example 5 A solution of menthyl mesylate (22.2 g, 0.095 mol) in tetrahydrofuran (50 mL) was placed in a flame-dried, 3-neck flask fitted with a dropping funnel, condenser, and an over-head stirrer. An equivalent amount of sodium diphenylphosphide in tetrahydrofuran was added and the mixture was heated to reflux for 30 minutes. The mixture was cooled to room temperature and 100 mL of degassed, distilled water was added. After stirring for 20 minutes, the organic layer was separated and stripped to remove the solvent. The resulting crude solid was dissolved in degassed methanol (50 mL) at reflux and cooled to 0°C to precipitate NMDPP as beige crystals. The yield was 80% and the purity by 31 P NMR analysis was greater than 95 mol% . In the following examples, the solubility of crude NMDPP in methanol was compared to the solubility of purified NMDPP in methanol. Example 6 Solubility was determined for crude NMDPP made in accordance with Example 4 in methanol which was degassed with nitrogen for 2 hours. The solubility tests were carried out under nitrogen in a glove box and the results are set forth in Table 1 below. Table 1 Example 7 Solubility of NMDPP purified through crystallization in methanol degassed with mtrogen for 2 hours was measured. The solubility tests were carried out under nitrogen in a glove box and the results are set forth in Table 2 below. Table 2 As may be seen from these examples, an unexpected, surprisingly beneficial result is achieved when methanol is used as a solvent in the crystallization of the trihydrocarbylphosphine compound. This purity is exemplified by the substantially reduced solubility of the pure trihydrocarbylphosphine in methanol after crystallization as compared to the solubility of the crude trihydrocarbylphosphine compound. This invention is susceptible to considerable variation in its practice. Therefore the foregoing description is not intended to limit, and should not be construed as limiting, the invention to the particular exemplifications presented hereinabove. Rather, what is intended to be covered is as set forth in the ensuing claims and the equivalents thereof permitted as a matter of law.

Claims: CLAIMS 1. A process for the purification of a trihydrocarbylphosphine having at least one aryl group and at least one alkyl or cycloalkyl group in the molecule, from a reaction mass comprising the trihydrocarbylphosphine, the process comprising crystallizing the reaction mass using a solvent consisting essentially of methanol. 2. A process according to Claim 1 wherein the trihydrocarbylphosphine has two aryl groups in the molecule. 3. A process according to Claim 1 wherein the trihydrocarbylphosphine is a diphenylcycloalkylphosphine . 4. A process according to Claim 3 wherein the diphenylcycloalkylphosphine is neomenthyldiphenylphosphine. 5. A process according to Claim 4 wherein the purity of the crystallized trihydrocarbylphosphine is at least 97 mol% . 6. Neomenthyldiphenylphosphine having a purity of at least 97 mol% produced by crystallizing neomenthyldiphenylphosphine having a purity of less than 97 mol% using a solvent consisting essentially of methanol. 7. The compound of Claim 6 having a purity of at least about 99 mol% produced by crystallizing neomenthyldiphenylphosphine having a purity of less than about 99 mol% .

Inventors: SENARATNE K PUSHPANANDA A, WU TSE-CHONG, SENARATNE, K., PUSHPANANDA, A., WU, TSE-CHONG
Applicants: ALBEMARLE CORP, ALBEMARLE CORPORATION
Application year: 1998
Main classification: C07F9
IPC codes: C07F9