Method for producing triphenylphosphine from diphenylphosphonium chloride by removing phenylphosphonium dichloride during heat treatment

Abstract

The invention relates to a method for preparing triphenylphosphine, which comprises the following steps: a diphenylphosphine chloride raw material is subjected to heat treatment at the temperature of 280-420 DEG C to prepare triphenylphosphine, and at least part of phenylphosphine dichloride is removed in the heat treatment process.

Description

Technical Field

[0001] The present invention relates to a method for preparing triphenylphosphine by heat treatment of diphenylphosphine chloride feedstock, wherein at least a portion of phenyl diphosphine chloride is removed during the heat treatment process. Technical Background

[0002] Triphenylphosphine has a wide range of applications in the chemical industry. It is an important catalyst for the synthesis of fine chemicals; a catalyst for petroleum processing; a novel biocatalytic technology and catalyst; a novel and efficient catalyst for environmental protection; a novel catalyst for organic synthesis; a novel and efficient catalyst for polyolefins; a new material for catalyst supports and various novel co-catalytic materials; it can also be used as a functional fine chemical; a novel papermaking chemical; a novel oilfield chemical suitable for protective extraction and enhanced oil recovery; a novel surfactant; a high-performance, water-based functional coating and auxiliaries; a novel textile dyeing and finishing auxiliaries; a high-performance environmentally friendly adhesive; a novel safe and environmentally friendly pigment and dye; and a high-performance environmentally friendly leather chemical. Triphenylphosphine can also serve as an intermediate in the chemical synthesis of various important chemical products, such as β-carotene, cefprozil, and cefdinir.

[0003] The main methods for industrial production of triphenylphosphine include (1) the Grignard method (sodium method): using metallic sodium, which is stirred at high speed, to react with chlorobenzene and phosphorus trichloride to produce triphenylphosphine. This method is technically demanding, especially the sodium sand equipment. It is necessary to solve the problem of sodium dispersion and avoid the presence of water during operation, as highly reactive sodium is prone to violent reaction with water and explosion. Therefore, there are significant safety hazards and high risk in the production process. (2) the Grignard reagent method (Grignard method): this method uses phenyl magnesium halide and phosphorus trichloride as raw materials. The reactants are heated to produce triphenylphosphine through the reaction, accompanied by a small amount of byproduct - triphenylphosphine oxide. This method has disadvantages such as high cost, low yield, and poor economic benefits. (3) the Friedel-Cloughs method: this method uses thiophosphonochloride to react with benzene in the presence of excess aluminum trichloride to produce triphenylphosphine sulfur, which is then desulfurized (reduced) with iron filings or sodium naphthalene to obtain triphenylphosphine. However, the triphenylphosphine product reduced by iron powder is of poor quality and has a yellowish color. Furthermore, the use of aluminum trichloride and iron powder as catalysts will generate a large amount of solid waste that is difficult to treat and will cause environmental pollution. (4) Triphenylphosphine oxide reduction method, but the reducing agent used in the triphenylphosphine oxide reduction method is relatively expensive.

[0004] In conclusion, there is an urgent need to develop a green, environmentally friendly, low-cost, high-quality, and simple method for synthesizing triphenylphosphine. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing triphenylphosphine, which is green, environmentally friendly, safe, low-cost, high-quality and simple to operate. Furthermore, this method does not require the use of solvents or co-solvents and the raw materials are readily available.

[0006] The technical solution for achieving the above-mentioned objectives of this invention can be summarized as follows:

[0007] 1. A method for preparing triphenylphosphine, comprising heat-treating a diphenylphosphine chloride feedstock at a temperature of 280-420°C to prepare triphenylphosphine, wherein at least a portion of the phenyl diphosphine chloride is removed during the heat treatment.

[0008] 2. The method according to embodiment 1, wherein during the heat treatment process, at least 20% by weight, preferably at least 40% by weight, more preferably at least 60% by weight, or even at least 75% by weight of phenyl dichloride is removed, based on the total amount of phenyl dichloride present in the reaction mixture after the heat treatment and the amount of phenyl dichloride removed.

[0009] 3. The method according to embodiment 1 or 2, wherein during the heat treatment process, 20-98% by weight, preferably 40-95% by weight, more preferably 60-95% by weight, of phenyl dichloride is removed, based on the total amount of phenyl dichloride present in the reaction mixture after the heat treatment and the amount of phenyl dichloride removed.

[0010] 4. The method according to any one of embodiments 1-3, wherein during the heat treatment process, at least 80% by weight, preferably at least 90% by weight, more preferably at least 98% by weight, and even more preferably at least 99.5% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed.

[0011] 5. The method according to any one of embodiments 1-4, wherein during the heat treatment process, no more than 50% by weight, preferably no more than 40% by weight, for example no more than 30% by weight, of diphenylphosphine chloride is removed, based on the total amount of diphenylphosphine chloride present in the reaction mixture after the heat treatment and the total amount of diphenylphosphine chloride removed.

[0012] 6. According to any one of the embodiments 1-5, the content of phenyl dichloride in the diphenylphosphine raw material is not more than 35% by weight, preferably not more than 30% by weight, more preferably not more than 20% by weight, even more preferably not more than 15% by weight, especially not more than 8% by weight, particularly not more than 3% by weight, most preferably not more than 1% by weight, for example not more than 0.5% by weight, based on the total weight of the diphenylphosphine raw material.

[0013] 7. The method according to any one of embodiments 1-6, wherein the content of the diphenylphosphine chloride in the diphenylphosphine chloride raw material is at least 65% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, even more preferably at least 88% by weight, and even more preferably at least 95% by weight, for example at least 98% by weight, based on the total weight of the diphenylphosphine chloride raw material.

[0014] 8. The method according to any one of embodiments 1-7, wherein the heat treatment temperature is 290-400°C, preferably 300-400°C, and more preferably 300-350°C.

[0015] 9. The method according to any one of embodiments 1-8, wherein the heat treatment temperature is particularly 300-320°C, most preferably 310-320°C.

[0016] 10. The method according to any one of embodiments 1-9, wherein the heat treatment time is at least 1.5 hours, preferably 1.5-12 hours, more preferably 1.5-8 hours, especially 2-6 hours, and most preferably 3-6 hours.

[0017] 11. The method according to any one of embodiments 1-10, wherein the phosphorus trichloride content in the diphenylphosphine chloride raw material is not more than 5% by weight, preferably not more than 2% by weight, more preferably not more than 1% by weight, for example not more than 0.5% by weight or not more than 0.1% by weight, based on the total weight of the diphenylphosphine chloride raw material.

[0018] 12. The method according to any one of embodiments 1-11, wherein the method comprises heat-treating the diphenylphosphine chloride raw material at a temperature of 310-320°C for 3-6 hours, and

[0019] The diphenylphosphine chloride raw material contains at least 98% by weight of diphenylphosphine chloride, no more than 1% by weight of phenylphosphine dichloride, and no more than 0.1% by weight of phosphorus trichloride (preferably free of phosphorus trichloride), based on the total weight of the diphenylphosphine chloride raw material.

[0020] 13. The method according to any one of embodiments 1-12, wherein phenylphosphine dichloride is removed by distillation, preferably atmospheric distillation.

[0021] 14. The method according to any one of embodiments 1-13 further includes repeating the heat treatment of the reaction mixture obtained after heat treatment 1-5 times, preferably 1-4 times, more preferably 2 or 3 times, as defined in any one of embodiments 1-5, 8-10 and 13.

[0022] 15. The method according to embodiment 14, which includes adding diphenylphosphine chloride to the reaction mixture obtained after the previous heat treatment before repeating the heat treatment, preferably adding at least 5% by weight, preferably at least 10% by weight or at least 20% by weight, for example 10-80% by weight, based on the total weight of the reaction mixture obtained after the previous heat treatment.

[0023] 16. The method according to implementation scheme 14 or 15, wherein the time for each heat treatment is 1.5-2.5 hours or 3-6 hours.

[0024] 17. The method according to any one of embodiments 1-16, wherein at least 75% by weight of phenylphosphine dichloride is removed during the heat treatment, based on the total amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the amount of phenylphosphine dichloride removed, and the heat treatment time is 3-6 hours.

[0025] or

[0026] During the heat treatment, at least 75% by weight of phenyl dichloride is removed, based on the total amount of phenyl dichloride present in the reaction mixture after heat treatment and the amount of phenyl dichloride removed. The reaction mixture obtained after heat treatment is then subjected to heat treatment 1 to 5 times as defined in any one of embodiments 1-5, 8-10 and 13, and the sum of the time of the heat treatment and the time of the repeated heat treatments is 4-20 hours or 4-10 hours.

[0027] The beneficial effects of this invention are as follows:

[0028] (1) The method of the present invention is green, environmentally friendly, safe, low-cost, high-quality and simple to operate.

[0029] (2) The method of the present invention uses diphenylphosphine chloride as raw material, without the need to add other co-solvents, and the raw material is simple and easy to obtain.

[0030] (3) Diphenylphosphine chloride is a liquid, which is easy to handle and does not require the use of solvents, thus avoiding solvent pollution.

[0031] (4) By removing phenyl dichloride during the heat treatment process, the present invention can obtain triphenylphosphine with a higher yield and a higher triphenylphosphine / feed weight ratio. Triphenylphosphine is much more expensive than diphenylphosphine chloride, thus the method of the present invention has extremely high industrial value. Furthermore, removing phenyl dichloride during the heat treatment process can also lower the heat treatment temperature, thereby reducing energy consumption and risk. Detailed Implementation

[0032] This invention relates to a method for preparing triphenylphosphine, which includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 280-420°C to prepare triphenylphosphine, wherein at least a portion of the phenyl diphosphine chloride is removed during the heat treatment process.

[0033] The inventors of this invention discovered that diphenylphosphine chloride produces phenylphosphine dichloride during heat treatment. Furthermore, the diphenylphosphine chloride raw material may also contain phenylphosphine dichloride. By removing at least part of the phenylphosphine dichloride from the system during heat treatment, the yield of triphenylphosphine was further improved.

[0034] In one embodiment, during the heat treatment process, at least 20% by weight (e.g., 25% by weight, 30% by weight, 35% by weight, 40% by weight, 45% by weight, 50% by weight, 55% by weight, 60% by weight, 65% by weight, 70% by weight, 75% by weight, 80% by weight, 85% by weight, 90% by weight, 95% by weight, 98% by weight, 99% by weight, or 100% by weight), preferably at least 40% by weight, more preferably at least 60% by weight, or even at least 75% by weight of phenylphosphine dichloride, are removed based on the total amount of phenylphosphine dichloride present in the reaction mixture after the heat treatment and the total amount of phenylphosphine dichloride removed.

[0035] In one embodiment, during the heat treatment process, 20-98 wt% (e.g., 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 95 wt%, or 98 wt%), preferably 40-95 wt%, more preferably 60-95 wt%, such as 70-95 wt%, 80-95 wt%, 80-93 wt%, or 80-90 wt%, is removed based on the total amount of phenylphosphine dichloride present in the reaction mixture after the heat treatment and the total amount of phenylphosphine dichloride removed.

[0036] The heat treatment process generates some light components, such as chlorobenzene and phosphorus trichloride. The yield of triphenylphosphine can be further improved by removing at least some of these light components.

[0037] In one embodiment, during the heat treatment process, at least 80% by weight or at least 85% by weight, preferably at least 90% by weight or 95% by weight, more preferably at least 98% by weight, and even more preferably at least 99.5% by weight or 100% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed. Preferably, all chlorobenzene and phosphorus trichloride are removed.

[0038] In one embodiment, during the heat treatment process, no more than 50% by weight (e.g., 45% by weight, 40% by weight, 35% by weight, 30% by weight, 25% by weight, 20% by weight, 15% by weight, 10% by weight, 5% by weight, 2% by weight, or 1% by weight), preferably no more than 40% by weight, such as no more than 30% by weight, of diphenylphosphine chloride is removed based on the total amount of diphenylphosphine chloride present in the reaction mixture after the heat treatment and the total amount of diphenylphosphine chloride removed.

[0039] For example, during the heat treatment process, 1-50% by weight, preferably 2-40% by weight, such as 5-30% by weight or 10-25% by weight, of diphenylphosphine chloride is removed, based on the total amount of diphenylphosphine chloride present in the reaction mixture after the heat treatment and the amount of diphenylphosphine chloride removed.

[0040] In one embodiment, the content of phenyl dichloride in the diphenylphosphine raw material is not more than 35% by weight (e.g., 32% by weight, 30% by weight, 28% by weight, 26% by weight, 25% by weight, 22% by weight, 20% by weight, 18% by weight, 15% by weight, 12% by weight, 10% by weight, 8% by weight, 5% by weight, 3% by weight, 2% by weight, 1% by weight, 0.5% by weight, or 0.1% by weight), preferably not more than 30% by weight or 28% by weight, more preferably not more than 22% by weight or 20% by weight, even more preferably not more than 15% by weight, especially not more than 8% by weight, particularly not more than 3% by weight, most preferably not more than 1% by weight, for example not more than 0.5% by weight, based on the total weight of the diphenylphosphine raw material.

[0041] In one embodiment, the content of diphenylphosphine chloride in the diphenylphosphine chloride feedstock is at least 65% by weight (e.g., 68% by weight, 70% by weight, 75% by weight, 80% by weight, 85% by weight, 88% by weight, 90% by weight, 91% by weight, 92% by weight, 93% by weight, 95% by weight, 98% by weight, 99% by weight, 99.5% by weight, or 99.9% by weight), preferably at least 70% by weight, more preferably at least 80% by weight, even more preferably at least 88% by weight, and even more preferably at least 95% by weight, for example at least 98% by weight, 99% by weight, or 99.5% by weight, based on the total weight of the diphenylphosphine chloride feedstock.

[0042] In one embodiment, the phosphorus trichloride content in the diphenylphosphine chloride feedstock is no more than 5% by weight (e.g., 4% by weight, 3% by weight, 2% by weight, 1% by weight, 0.5% by weight, 0.2% by weight, 0.1% by weight, or 0.05% by weight), preferably no more than 2% by weight, more preferably no more than 1% by weight, for example, no more than 0.5% by weight or no more than 0.1% by weight, based on the total weight of the diphenylphosphine chloride feedstock. In one embodiment, the diphenylphosphine chloride feedstock is free of phosphorus trichloride.

[0043] In one embodiment, the triphenylphosphine content in the diphenylphosphine chloride feedstock is no more than 6% by weight (e.g., 5% by weight, 4% by weight, 3% by weight, 2% by weight, 1% by weight, 0.5% by weight, 0.2% by weight or 0.1% by weight), preferably no more than 5% by weight, more preferably no more than 1% by weight, for example no more than 0.5% by weight or no more than 0.1% by weight, based on the total weight of the diphenylphosphine chloride feedstock.

[0044] According to the present invention, the heat treatment temperature is 280-420°C, for example 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 345°C, 350°C, 355°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, or 420°C. In one embodiment, the heat treatment temperature is 290-400°C, preferably 300-400°C, more preferably 300-350°C. In a preferred embodiment, the heat treatment temperature is particularly 300-320°C, especially 310-320°C.

[0045] In one embodiment, the heat treatment is performed at atmospheric pressure. If necessary, the heat treatment can also be performed under negative or elevated pressure. For example, the heat treatment can be performed at -5 kPa or lower (i.e., 5 kPa or lower than atmospheric pressure), -10 kPa or lower, -20 kPa or lower, -50 kPa or lower, or -80 kPa or lower. Alternatively, the heat treatment can be performed at a pressure (gauge pressure) of at least 0.05 MPa (e.g., 0.08 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.5 MPa, 0.8 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa), at least 0.08 MPa, or at least 0.1 MPa. In one embodiment, the pressure is carried out at -80 kPa to 4 MPa, or -20 kPa to 2 MPa, or -10 kPa to 1 MPa, or -10 kPa to 0.5 MPa, or atmospheric pressure to 0.5 MPa.

[0046] In one embodiment, the heat treatment time is at least 1.5 hours (e.g., 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours), preferably 1.5-12 hours, more preferably 1.5-8 hours, and especially 1.5-6 hours, 3-6 hours or 1.5-3 hours.

[0047] In one embodiment, the heat treatment is carried out under stirring. The stirring rate can be, for example, 50-700 r / min, such as 100-600 r / min, or 200-500 r / min or 300-450 r / min.

[0048] Before stirring, the diphenylphosphine chloride feedstock can be preheated, for example to 40-90°C, preferably to 50-80°C, such as 60-80°C.

[0049] In one embodiment, the product mixture obtained by the method comprises triphenylphosphine, phenylphosphine dichloride, and diphenylphosphine chloride, as well as optionally chlorobenzene and phosphorus trichloride.

[0050] According to the present invention, phenylphosphine dichloride can be removed by distillation, preferably by atmospheric distillation.

[0051] According to the present invention, light components (such as chlorobenzene and phosphorus trichloride) can be removed by distillation, preferably by atmospheric distillation.

[0052] In one embodiment, at least a portion of phenylphosphine dichloride is continuously removed during the heat treatment process.

[0053] In a preferred embodiment of the present invention, the method further includes repeatedly subjecting the reaction mixture obtained after heat treatment to the heat treatment as defined above 1-5 times, preferably 1-4 times, more preferably 2 or 3 times. For example, if the heat treatment is repeated once, the method of the present invention includes heat treatment and repeated heat treatment 1; if the heat treatment is repeated twice, the method of the present invention includes heat treatment and repeated heat treatment 1 and 2; if the heat treatment is repeated three times, the method of the present invention includes heat treatment and repeated heat treatment 1, 2 and 3; if the heat treatment is repeated four times, the method of the present invention includes heat treatment and repeated heat treatment 1, 2, 3 and 4; if the heat treatment is repeated five times, the method of the present invention includes heat treatment and repeated heat treatment 1, 2, 3, 4 and 5.

[0054] The conditions for each heat treatment can be the same or different, and the conditions for repeated heat treatments (such as time, temperature, amount of phenylphosphine removed, amount of chlorobenzene and phosphorus trichloride removed, and amount of diphenylphosphine removed) have the above-mentioned preferred meanings.

[0055] For example, the repeated heat treatment can be carried out at 300-400°C, preferably 300-350°C, especially 300-320°C, and most preferably 310-320°C; and / or

[0056] The repeated heat treatment can be performed for 1.5-8 hours, preferably 1.5-8 hours, especially 1.5-6 hours, 3-6 hours, or 1.5-3 hours; and / or

[0057] During the repeated heat treatment process, at least 40% by weight, more preferably at least 60% by weight, or even at least 75% by weight of phenylphosphine dichloride is removed, and / or

[0058] During the repeated heat treatment process, at least 90% by weight, more preferably at least 98% by weight, and even more preferably at least 99.5% by weight of chlorobenzene and phosphorus trichloride are removed, and / or

[0059] During the repeated heat treatment process, no more than 40% by weight, for example no more than 30% by weight or 10-25% by weight, of diphenylphosphine chloride is removed.

[0060] The basis for each weight percentage is as described above.

[0061] In a preferred embodiment, the method of the present invention includes adding diphenylphosphine chloride to the reaction mixture obtained after the previous heat treatment before repeated heat treatment. Preferably, the amount of diphenylphosphine chloride added is at least 5% by weight (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% by weight), more preferably at least 10% by weight or at least 20% by weight, for example, 10-80% by weight, 10-60% by weight, or 20-60% by weight. If the heat treatment is repeated more than once, for example, 2, 3, 4, or 5 times, the amount of diphenylphosphine chloride added each time may be the same or different. Adding diphenylphosphine chloride to the reaction mixture obtained after the previous heat treatment can further increase the triphenylphosphine content in the product.

[0062] When the heat treatment is repeated, the time for each heat treatment (including the heat treatment and repeated heat treatment) can be 1.5-2.5 hours or 3-6 hours, preferably 1.5-2.5 hours.

[0063] According to the present invention, when the heat treatment is repeated, a shorter heat treatment time can be used, for example, 1.5-2.5 hours (e.g., 1.8 hours, 2 hours, or 2.2 hours). Compared with the case where the heat treatment is not repeated, repeated heat treatment can obtain a higher triphenylphosphine yield with the same or similar total heat treatment time. Alternatively, compared with the case where the heat treatment is not repeated, repeated heat treatment can obtain the same or similar triphenylphosphine yield with a shorter total heat treatment time.

[0064] In one embodiment, the content of phenylphosphine dichloride in the reaction mixture after heat treatment is no more than 8% by weight (e.g., 7% by weight, 6% by weight, 5% by weight, 4% by weight, 3% by weight, 2% by weight or 1% by weight), preferably no more than 6% by weight or no more than 4% by weight or no more than 3% by weight or no more than 2% by weight, for example 0.5-8% by weight, or 1-6% by weight, or 1-5% by weight, or 1-4% by weight, or 1-3% by weight, based on the total weight of the reaction mixture after heat treatment.

[0065] In one embodiment, the total content of chlorobenzene and phosphorus trichloride in the reaction mixture after heat treatment is no more than 5% by weight, preferably no more than 3% by weight, more preferably no more than 1% by weight, and particularly no more than 0.5% by weight, based on the total weight of the reaction mixture after heat treatment. Particularly preferred is that the reaction mixture after heat treatment is free of chlorine and phosphorus trichloride.

[0066] In one embodiment, the triphenylphosphine content in the reaction mixture after heat treatment is at least 20% by weight (e.g., 21% by weight, 25% by weight, 30% by weight, 35% by weight, 40% by weight, 50% by weight, 60% by weight, 70% by weight, or 80% by weight), preferably at least 30% by weight or at least 35% by weight, or even at least 40% by weight, for example 20-80% by weight, 30-70% by weight, 35-70% by weight, 40-70% by weight, based on the total weight of the reaction mixture after heat treatment.

[0067] In one embodiment, the weight ratio of the amount of triphenylphosphine in the reaction mixture to the total amount of diphenylphosphine chloride in the diphenylphosphine chloride feedstock after heat treatment can be at least 0.15 (e.g., 0.16, 0.18, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, or 0.6), preferably at least 0.15, at least 0.2, or at least 0.25, or even at least 0.3 or 0.4, for example, 0.15-0.6, 0.2-0.6, 0.2-0.5, 0.25-0.45, or 0.35-0.45.

[0068] In the context of this disclosure, the content of phenyl diphosphine chloride, the total content of chlorobenzene and phosphorus trichloride, the content of triphenylphosphine, and / or the weight ratio of the amount of triphenylphosphine to the total amount of diphenylphosphine chloride in the diphenylphosphine chloride feedstock in the reaction mixture after heat treatment can refer to the reaction mixture obtained after a single heat treatment or to the reaction mixture obtained after repeated heat treatments.

[0069] In a preferred embodiment, the method of the present invention further includes repeating the heat treatment as defined above on the reaction mixture obtained after heat treatment 1 to 5 times, preferably 1 to 4 times, more preferably 2 or 3 times, wherein the content of triphenylphosphine in the final reaction mixture is at least 40% by weight (e.g., 50% by weight, 60% by weight, 70% by weight or 80% by weight), preferably at least 50% by weight or at least 60% by weight, for example 40-80% by weight, 50-70% by weight, based on the total weight of the reaction mixture after heat treatment.

[0070] In a preferred embodiment, the method of the present invention further includes repeatedly subjecting the reaction mixture obtained after heat treatment to the heat treatment as defined above 1-5 times, preferably 1-4 times, more preferably 2 or 3 times, wherein the weight ratio of the amount of triphenylphosphine in the final reaction mixture to the total amount of diphenylphosphine chloride in the diphenylphosphine chloride raw material can be at least 0.3 (e.g., 0.35, 0.38, 0.40, 0.45, 0.50, 0.55 or 0.6), preferably at least 0.35 or at least 0.38, for example 0.3-0.6, 0.35-0.6 or 0.3-0.5 or 0.35-0.45.

[0071] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 280-420°C, wherein at least some of the phenylphosphine dichloride is removed during the heat treatment, and the heat treatment time is 1.5-12 hours.

[0072] The diphenylphosphine chloride raw material contains at least 65% by weight of diphenylphosphine chloride, no more than 30% by weight of phenylphosphine dichloride, and no more than 5% by weight of phosphorus trichloride, based on the total weight of the diphenylphosphine chloride raw material.

[0073] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 290-400°C, wherein during the heat treatment, at least 20% by weight of phenylphosphine dichloride is removed, based on the amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the total amount of phenylphosphine dichloride removed, and

[0074] The diphenylphosphine chloride raw material contains at least 70% by weight of diphenylphosphine chloride, no more than 20% by weight of phenylphosphine dichloride, and no more than 2% by weight of phosphorus trichloride, based on the total weight of the diphenylphosphine chloride raw material.

[0075] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 300-350°C, wherein during the heat treatment, at least 20% by weight of phenylphosphine dichloride is removed, based on the total amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the total amount of phenylphosphine dichloride removed.

[0076] The heat treatment time is at least 1.5 hours, and

[0077] The diphenylphosphine chloride raw material contains at least 70% by weight of diphenylphosphine chloride, no more than 20% by weight of phenylphosphine dichloride, and no more than 2% by weight of phosphorus trichloride, based on the total weight of the diphenylphosphine chloride raw material.

[0078] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 300-350°C, wherein during the heat treatment, at least 20% by weight of phenylphosphine dichloride is removed, based on the total amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the total amount of phenylphosphine dichloride removed.

[0079] During the heat treatment process, at least 80% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed.

[0080] The heat treatment time is at least 1.5 hours, and

[0081] The diphenylphosphine chloride raw material contains at least 70% by weight of diphenylphosphine chloride, no more than 20% by weight of phenylphosphine dichloride, and no more than 2% by weight of phosphorus trichloride, based on the total weight of the diphenylphosphine chloride raw material.

[0082] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 300-350°C, wherein at least 40% by weight of phenylphosphine dichloride is removed during the heat treatment, based on the total amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the total amount of phenylphosphine dichloride removed.

[0083] During the heat treatment process, at least 90% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed.

[0084] The heat treatment time is 1.5-12 hours, and

[0085] The diphenylphosphine chloride raw material contains at least 80% by weight of diphenylphosphine chloride, no more than 15% by weight of phenylphosphine dichloride, and no more than 1% by weight of phosphorus trichloride, based on the total weight of the diphenylphosphine chloride raw material.

[0086] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 300-350°C, wherein at least 40% by weight of phenylphosphine dichloride is removed during the heat treatment, based on the total amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the total amount of phenylphosphine dichloride removed.

[0087] During the heat treatment process, at least 90% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed.

[0088] During the heat treatment process, no more than 50% by weight of diphenylphosphine chloride is removed, based on the total amount of diphenylphosphine chloride present in the reaction mixture after the heat treatment and the amount of diphenylphosphine chloride removed.

[0089] The heat treatment time is 1.5-12 hours, and

[0090] The diphenylphosphine chloride raw material contains at least 80% by weight of diphenylphosphine chloride, no more than 15% by weight of phenylphosphine dichloride, and no more than 1% by weight of phosphorus trichloride, based on the total weight of the diphenylphosphine chloride raw material.

[0091] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 300-320°C, wherein at least 60% by weight of phenylphosphine dichloride is removed during the heat treatment, based on the amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the total amount of phenylphosphine dichloride removed.

[0092] During the heat treatment process, at least 98% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed.

[0093] During the heat treatment process, no more than 40% by weight of diphenylphosphine chloride is removed, based on the total amount of diphenylphosphine chloride present in the reaction mixture after the heat treatment and the amount of diphenylphosphine chloride removed.

[0094] The heat treatment time is 1.5-8 hours, and

[0095] The diphenylphosphine chloride raw material contains at least 88% by weight of diphenylphosphine chloride, no more than 8% by weight of phenylphosphine dichloride, and no more than 0.5% by weight of phosphorus trichloride, based on the total weight of the diphenylphosphine chloride raw material.

[0096] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 310-320°C, wherein at least 75% by weight of phenylphosphine dichloride is removed during the heat treatment, based on the total amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the total amount of phenylphosphine dichloride removed.

[0097] During the heat treatment process, at least 99.5% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed.

[0098] During the heat treatment process, no more than 30% by weight of diphenylphosphine chloride is removed, based on the total amount of diphenylphosphine chloride present in the reaction mixture after the heat treatment and the amount of diphenylphosphine chloride removed.

[0099] The heat treatment time is 1.5-6 hours, and

[0100] The diphenylphosphine chloride raw material contains at least 95% by weight of diphenylphosphine chloride, no more than 3% by weight of phenylphosphine dichloride, and no more than 0.1% by weight of phosphorus trichloride (preferably free of phosphorus trichloride), based on the total weight of the diphenylphosphine chloride raw material.

[0101] In one embodiment, the method includes heat-treating a diphenylphosphine chloride feedstock at a temperature of 310-320°C, wherein at least 75% by weight of phenylphosphine dichloride is removed during the heat treatment, based on the total amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the total amount of phenylphosphine dichloride removed.

[0102] During the heat treatment process, at least 99.5% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed.

[0103] During the heat treatment process, no more than 30% by weight of diphenylphosphine chloride is removed, based on the total amount of diphenylphosphine chloride present in the reaction mixture after the heat treatment and the amount of diphenylphosphine chloride removed.

[0104] The heat treatment time is 1.5-2.5 hours.

[0105] The diphenylphosphine chloride raw material contains at least 95% by weight of diphenylphosphine chloride, no more than 3% by weight of phenylphosphine dichloride, and no more than 0.1% by weight of phosphorus trichloride (preferably free of phosphorus trichloride), based on the total weight of the diphenylphosphine chloride raw material, and

[0106] The method includes repeating the heat treatment as defined above on the reaction mixture obtained after the heat treatment 1 to 5 times, preferably 1 to 4 times, more preferably 2 or 3 times, especially before repeating the heat treatment, by adding diphenylphosphine chloride to the reaction mixture obtained after the previous heat treatment, preferably the amount of diphenylphosphine chloride added is at least 5% by weight, preferably at least 10% by weight or at least 20% by weight, for example 10-80% by weight, based on the total weight of the reaction mixture obtained after the previous heat treatment.

[0107] In one embodiment, during the heat treatment process, at least 75% by weight of phenyl dichloride is removed, based on the total amount of phenyl dichloride present in the reaction mixture after heat treatment and the amount of phenyl dichloride removed, and the heat treatment time is 3-6 hours.

[0108] In one embodiment, during the heat treatment process, at least 75% by weight of phenyl dichloride is removed based on the total amount of phenyl dichloride present in the reaction mixture after heat treatment and the amount of phenyl dichloride removed, and the reaction mixture obtained after heat treatment is repeated 1-5 times as defined above, and the sum of the heat treatment time and the repeated heat treatment time is 4-20 hours or 4-10 hours.

[0109] The method of the present invention is carried out under the protection of an inert gas, such as nitrogen. Before carrying out the method of the present invention, the reactor is purged with an inert gas (such as nitrogen), for example, purging 2-5 times, preferably 3-5 times.

[0110] The product mixture of the method of the present invention can be separated by post-processing, such as distillation.

[0111] In one embodiment, the diphenylphosphine chloride feedstock can be prepared using chlorobenzene and yellow phosphorus as feedstocks. The resulting reaction mixture typically contains light components, such as chlorobenzene and phosphorus trichloride, as well as phenylphosphine dichloride, diphenylphosphine chloride, and triphenylphosphine. In the reaction mixture, the amount of triphenylphosphine typically does not exceed 6% by weight, for example, 1-6% by weight or 2-6% by weight, based on the total weight of phenylphosphine dichloride, diphenylphosphine chloride, and triphenylphosphine. The reaction is carried out at high temperatures (e.g., 300-500°C or 300-400°C) and elevated pressures (e.g., 0.01-8.0 MPa or 0.01-6.0 MPa, preferably autogenous pressure). The diphenylphosphine chloride feedstock of the present invention can be prepared by removing chlorobenzene, phosphorus trichloride, and most of the phenylphosphine dichloride from the reaction mixture, or by additionally adding diphenylphosphine chloride to a diphenylphosphine-rich product mixture obtained after removing chlorobenzene, phosphorus trichloride, and most of the phenylphosphine dichloride from the reaction mixture.

[0112] In this technical solution, purification costs are saved because there is no need to purify diphenylphosphine chloride.

[0113] Example

[0114] The features of the present invention are further illustrated below through examples, but these examples do not constitute a limitation thereof. Unless otherwise specified, specific conditions were applied in the examples. Reagents or instruments used, unless otherwise specified, are all commercially available products. Pressures mentioned in the examples are gauge pressures.

[0115] raw material:

[0116] Diphenylphosphine chloride: Hubei Gurun Technology Co., Ltd., purity ≥99.5%, triphenylphosphine content 0.1%-0.3%, does not contain phosphorus trichloride.

[0117] Content determination:

[0118] Gas chromatography was used to analyze each component, and quantification was performed using the correction and normalization method.

[0119] Example 1 (Comparative):

[0120] The 5L synthesis reactor was purged with nitrogen three times. 500g of diphenylphosphine chloride was added to the reactor, the reactor valve was closed, and stirring was started at a rate of 350-400 r / min. After 70-80 min, the temperature was raised to a maximum of 300℃ and held for 2.0 h. The maximum pressure during the reaction was 0.05 MPa. The reaction yielded 495g of reaction liquid, including 21g of phenyl diphosphine chloride, 431g of diphenylphosphine chloride, and 41g of triphenylphosphine, with triphenylphosphine accounting for 8.3 wt%.

[0121] Example 2:

[0122] The 5L synthesis reactor was purged with nitrogen three times. 500g of diphenylphosphine chloride was added to the reactor without closing the valve, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 300-310℃ and held for about 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 4 hours, yielding 15g of the fraction containing 2g of light components (chlorobenzene, phosphorus trichloride), 8g of phenylphosphine dichloride, and 4g of diphenylphosphine chloride. The reactor produced 458g of reaction liquid (bottom material), containing 24g of phenylphosphine dichloride, 334g of diphenylphosphine chloride, and 97g of triphenylphosphine. Triphenylphosphine accounted for 21.1 wt% and did not contain the light components (chlorobenzene and phosphorus trichloride).

[0123] Example 3:

[0124] The 5L synthesis reactor was purged with nitrogen three times. 800g of diphenylphosphine chloride was added to the reactor without closing the valves, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 310-320℃ and held for about 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 4 hours, yielding 232g of the fraction, containing 5g of light components (chlorobenzene, phosphorus trichloride), 87g of phenylphosphine dichloride, and 130g of diphenylphosphine chloride. The reactor produced 564g of reaction liquid (bottom material), containing 16g of phenylphosphine dichloride, 328g of diphenylphosphine chloride, and 216g of triphenylphosphine. Triphenylphosphine accounted for 38.3 wt% and did not contain the light components (chlorobenzene and phosphorus trichloride).

[0125] Example 4:

[0126] The 5L synthesis reactor was purged with nitrogen three times. 800g of diphenylphosphine chloride was added to the reactor without closing the valve, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 310-320℃ and held for about 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 5 hours, yielding 273g of distillate, containing 4g of light components (chlorobenzene, phosphorus trichloride), 91g of phenylphosphine dichloride, and 168g of diphenylphosphine chloride. The reactor contained 520g of bottom material, including 12g of phenylphosphine dichloride, 283g of diphenylphosphine chloride, and 220g of triphenylphosphine. Triphenylphosphine comprised 42.4 wt% and did not contain the light components (chlorobenzene and phosphorus trichloride).

[0127] The aforementioned 520g of base material and 280g of diphenylphosphine chloride were added to the synthesis reactor. The reactor valve was not closed, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 310℃-320℃ and held for approximately 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 5 hours, yielding 151g of distillate, containing 7g of light components (chlorobenzene, phosphorus trichloride), 76g of phenylphosphine dichloride, and 61g of diphenylphosphine chloride. The reactor contained 645g of base material, including 12g of phenylphosphine dichloride, 228g of diphenylphosphine chloride, and 404g of triphenylphosphine. Triphenylphosphine comprised 62.6 wt% and did not contain any light components (chlorobenzene and phosphorus trichloride).

[0128] The aforementioned 645g of base material and 155g of diphenylphosphine chloride were added to the synthesis reactor. The reactor valve was not closed, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 310℃-320℃ and held for approximately 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 5 hours, yielding 34g of the fraction, containing 3g of light components (chlorobenzene, phosphorus trichloride), 20g of phenylphosphine dichloride, and 8g of diphenylphosphine chloride. The reactor contained 743g of base material, including 4g of phenylphosphine dichloride, 219g of diphenylphosphine chloride, and 498g of triphenylphosphine. Triphenylphosphine comprised 67.0 wt% and did not contain the light components (chlorobenzene and phosphorus trichloride).

[0129] Example 5:

[0130] The 5L synthesis reactor was purged with nitrogen three times. 800g of diphenylphosphine chloride was added to the reactor without closing the valve, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 310-320℃ and held for about 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 2 hours, yielding 114g of distillate, containing 4g of light components (chlorobenzene, phosphorus trichloride), 56g of phenylphosphine dichloride, and 50g of diphenylphosphine chloride. The reactor contained 685g of bottom material, including 10g of phenylphosphine dichloride, 505g of diphenylphosphine chloride, and 160g of triphenylphosphine. Triphenylphosphine comprised 23.4 wt% and did not contain the light components (chlorobenzene and phosphorus trichloride).

[0131] The aforementioned 685g of base material and 115g of diphenylphosphine chloride were added to the synthesis reactor. The reactor valve was not closed, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 310℃-320℃ and held for approximately 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 2 hours, yielding 180g of the fraction, containing 5g of light components (chlorobenzene, phosphorus trichloride), 65g of phenylphosphine dichloride, and 100g of diphenylphosphine chloride. The reactor contained 620g of base material, containing 5g of phenylphosphine dichloride, 327g of diphenylphosphine chloride, and 283g of triphenylphosphine. Triphenylphosphine comprised 45.6 wt% and did not contain the light components (chlorobenzene and phosphorus trichloride).

[0132] The aforementioned 620g of base material and 180g of diphenylphosphine chloride were added to the synthesis reactor. The reactor valve was not closed, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 310℃-320℃ and held for approximately 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 2 hours, yielding 79g of the fraction, containing 4g of light components (chlorobenzene, phosphorus trichloride), 43g of phenylphosphine dichloride, and 24g of diphenylphosphine chloride. The reactor contained 720g of base material, containing 4g of phenylphosphine dichloride, 276g of diphenylphosphine chloride, and 425g of triphenylphosphine. Triphenylphosphine comprised 59.0 wt% and did not contain the light components (chlorobenzene and phosphorus trichloride).

[0133] The aforementioned 720g of base material and 80g of diphenylphosphine chloride were added to the synthesis reactor. The reactor valve was not closed, and stirring was started at a rate of 350-400 rpm. After 70-80 minutes, the temperature was raised to a maximum of 310℃-320℃ and held for approximately 1 hour. Distillation began, and the fraction was collected by atmospheric distillation for 2 hours, yielding 42g of the fraction, containing 4g of light components (chlorobenzene, phosphorus trichloride), 25g of phenylphosphine dichloride, and 11g of diphenylphosphine chloride. The reactor contained 756g of base material, including 7g of phenylphosphine dichloride, 236g of diphenylphosphine chloride, and 494g of triphenylphosphine. Triphenylphosphine comprised 65.3 wt% and did not contain the light components (chlorobenzene and phosphorus trichloride).

[0134] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing triphenylphosphine, comprising heat-treating a diphenylphosphine chloride feedstock at a temperature of 280-420°C to prepare triphenylphosphine, wherein at least a portion of the phenyl diphosphine chloride is removed during the heat treatment.

2. The method of claim 1, wherein during the heat treatment, at least 20% by weight, preferably at least 40% by weight, more preferably at least 60% by weight, or even at least 75% by weight of phenyl dichloride is removed, based on the total amount of phenyl dichloride present in the reaction mixture after the heat treatment and the amount of phenyl dichloride removed.

3. The method according to claim 1 or 2, wherein during the heat treatment, 20-98% by weight, preferably 40-95% by weight, more preferably 60-95% by weight, of phenylphosphine dichloride is removed, based on the total amount of phenylphosphine dichloride present in the reaction mixture after the heat treatment and the amount of phenylphosphine dichloride removed.

4. The method according to any one of claims 1-3, wherein during the heat treatment, at least 80% by weight, preferably at least 90% by weight, more preferably at least 98% by weight, and even more preferably at least 99.5% by weight of chlorobenzene and phosphorus trichloride are removed, based on the total amount of chlorobenzene and phosphorus trichloride present in the reaction mixture after the heat treatment and the total amount of chlorobenzene and phosphorus trichloride removed.

5. The method according to any one of claims 1-4, wherein during the heat treatment, no more than 50% by weight, preferably no more than 40% by weight, for example no more than 30% by weight, of diphenylphosphine chloride is removed, based on the total amount of diphenylphosphine chloride present in the reaction mixture after the heat treatment and the amount of diphenylphosphine chloride removed.

6. The method according to any one of claims 1-5, wherein the content of phenyl dichloride in the diphenylphosphine raw material is not more than 35% by weight, preferably not more than 30% by weight, more preferably not more than 20% by weight, even more preferably not more than 15% by weight, especially not more than 8% by weight, particularly not more than 3% by weight, most preferably not more than 1% by weight, for example not more than 0.5% by weight, based on the total weight of the diphenylphosphine raw material.

7. The method according to any one of claims 1-6, wherein the content of the diphenylphosphine chloride in the diphenylphosphine chloride raw material is at least 65% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, even more preferably at least 88% by weight, and even more preferably at least 95% by weight, for example at least 98% by weight, based on the total weight of the diphenylphosphine chloride raw material.

8. The method according to any one of claims 1-7, wherein the heat treatment temperature is 290-400°C, preferably 300-400°C, more preferably 300-350°C.

9. The method according to any one of claims 1-8, wherein the heat treatment temperature is particularly 300-320°C, most preferably 310-320°C.

10. The method according to any one of claims 1-9, wherein the heat treatment time is at least 1.5 hours, preferably 1.5-12 hours, more preferably 1.5-8 hours, especially 2-6 hours, and most preferably 3-6 hours.

11. The method according to any one of claims 1-10, wherein the phosphorus trichloride content in the diphenylphosphine chloride raw material is not more than 5% by weight, preferably not more than 2% by weight, more preferably not more than 1% by weight, for example not more than 0.5% by weight or not more than 0.1% by weight, based on the total weight of the diphenylphosphine chloride raw material.

12. The method according to any one of claims 1-11, wherein the method comprises heat-treating the diphenylphosphine chloride raw material at a temperature of 310-320°C for 3-6 hours, and The diphenylphosphine chloride raw material contains at least 98% by weight of diphenylphosphine chloride, no more than 1% by weight of phenylphosphine dichloride, and no more than 0.1% by weight of phosphorus trichloride (preferably free of phosphorus trichloride), based on the total weight of the diphenylphosphine chloride raw material.

13. The method according to any one of claims 1-12, wherein phenylphosphine dichloride is removed by distillation, preferably atmospheric distillation.

14. The method according to any one of claims 1-13, further comprising repeating the heat treatment of the reaction mixture obtained after heat treatment 1-5 times, preferably 1-4 times, more preferably 2 or 3 times, as defined in any one of claims 1-5, 8-10 and 13.

15. The method of claim 14, further comprising adding diphenylphosphine chloride to the reaction mixture obtained after the previous heat treatment before repeating the heat treatment, preferably adding at least 5% by weight, preferably at least 10% by weight or at least 20% by weight, for example 10-80% by weight, based on the total weight of the reaction mixture obtained after the previous heat treatment.

16. The method according to claim 14 or 15, wherein the duration of each heat treatment is 1.5-2.5 hours or 3-6 hours.

17. The method according to any one of claims 1-16, wherein at least 75% by weight of phenylphosphine dichloride is removed during the heat treatment, based on the total amount of phenylphosphine dichloride present in the reaction mixture after heat treatment and the amount of phenylphosphine dichloride removed, and the heat treatment time is 3-6 hours. or During the heat treatment, at least 75% by weight of phenyl dichloride is removed, based on the total amount of phenyl dichloride present in the reaction mixture after heat treatment and the amount of phenyl dichloride removed, and the reaction mixture obtained after heat treatment is repeated 1 to 5 times as defined in any one of claims 1-5, 8-10 and 13, and the sum of the time of the heat treatment and the time of the repeated heat treatment is 4-20 hours or 4-10 hours.