Preparation method of DOPO derivative flame retardant

Abstract

The invention discloses a preparation method of a DOPO (9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) derivative flame retardant, which belongs to the technical field of oxygen-containing acid ester of phosphorus and comprises the following steps: preparation of a monosubstituted intermediate, biphosphoramidation reaction and post-treatment. The biphosphoramidation reaction method comprises the following steps: dissolving a monosubstituted intermediate into xylene, then adding DOPO, ZnCl2 and DBU, stirring for 20-30 minutes at 50-60 DEG C, then adding DBU-imidazolium salt, stirring and reacting for 3.2-3.8 hours at 80-90 DEG C, gradually turning the solution into light yellow along with the proceeding of the reaction, and carrying out reduced pressure distillation to remove xylene to obtain a crude product. The target product prepared by the method is high in selectivity, the generation of byproducts is reduced, and the purity of the product is improved; the yield of the prepared DOPO derivative is 91.2 to 92.4 percent, and the purity of the prepared DOPO derivative is 93.9 to 95.8 percent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic phosphorus flame retardant synthesis technology, and particularly relates to a preparation method of a DOPO derivative flame retardant. BACKGROUND

[0002] 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives are a kind of organic phosphorus flame retardants with excellent performance, which have the advantages of high flame retardant efficiency, good thermal stability, low toxicity, low smoke, etc., and are widely used in the flame-retardant modification of high polymer materials.

[0003] Among the numerous DOPO derivatives, disubstituted DOPO derivatives are of great concern due to the two phosphaphenanthrene structural units in their molecular structure. These compounds usually have higher phosphorus content and can provide more excellent flame retardant performance. Among them, disubstituted DOPO derivatives containing nitrogen-phosphorus (N-P) bonds (the general structure can be represented as DOPO-N(R)-DOPO) exhibit unique value. The introduction of N-P bonds not only endows the molecule with higher thermal stability and chemical stability, but more importantly, can produce a significant nitrogen-phosphorus synergistic flame-retardant effect. This synergistic effect usually means higher flame-retardant efficiency, lower addition amount, and better comprehensive performance than single phosphorus-based flame retardants, making it an important direction for the development of high-performance and environmentally friendly flame retardants.

[0004] However, in the prior art, the main difficulty in the high-efficiency and high-selectivity synthesis of such disubstituted DOPO derivatives containing N-P bonds is concentrated on the successful introduction of the second DOPO group.

[0005] After DOPO successfully introduces the first nitrogen-containing substituent to form a monosubstituted intermediate, the spatial environment around the phosphorus atom of the intermediate becomes highly crowded due to the connection of a relatively large group, and the steric hindrance significantly increases. At the same time, the P-N bond formed changes the electron cloud distribution of the phosphorus atom, usually reducing its electrophilicity. These two key factors work together to make the nucleophilic addition reaction of the second DOPO molecule (through its active P-H bond) to the phosphorus atom of the monosubstituted intermediate extremely difficult, with a high reaction energy barrier and a slow rate.

[0006] In the article "Thermal stability and flame retarding properties in epoxy resins" by Klinkowski et al. in Polymer Degradation and Stability, Vol. 106, 2014, pp. 122-128, a nucleophilic substitution reaction was performed using DOPO-Cl and m-phenylenediamine, but only monosubstituted phosphonamide products were selectively generated. Even if an excess of DOPO-Cl was used, the disubstituted product was not successfully synthesized.

[0007] The introduction of the second DOPO in the monosubstituted DOPO derivative is attempted, and the reaction often has the problems of low conversion rate, long reaction time and many by-products (such as unreacted monosubstituted intermediates, hydrolysis products, over-reaction products or isomers, etc.). This directly leads to the difficulty of the yield and purity of the target disubstituted product to reach the ideal level.

[0008] Therefore, developing a green synthesis method capable of effectively overcoming the steric hindrance and electronic effect limitation and realizing efficient and high-selectivity synthesis of disubstituted DOPO derivatives containing N-P bonds is a technical problem to be solved urgently in the field of flame retardants. SUMMARY

[0009] In view of the deficiencies in the prior art, the present application provides a preparation method of a DOPO derivative flame retardant, and provides a synthesis method for preparing a disubstituted DOPO derivative through a step-by-step phosphoramide reaction. The synthesis method can realize efficient, high-yield and high-selectivity synthesis of the disubstituted DOPO derivative, and the structural formula of the DOPO derivative is as follows:

[0010] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a preparation method of a DOPO derivative flame retardant, comprising the following steps: monosubstituted intermediate preparation, double phosphoramide reaction and post-treatment.

[0011] Step one: monosubstituted intermediate preparation DOPO, benzylamine and triethylamine are dissolved in dichloromethane, and carbon tetrachloride is then added dropwise, with the dropwise addition time being controlled to be 1-1.5 hours. After the dropwise addition is completed, the reaction is stirred under reflux at 50-55 DEG C for 4-4.5 hours. After the reaction is completed, triethylamine hydrochloride is removed by filtration, and low-boiling-point dichloromethane is recovered by one-time reduced-pressure distillation. Then, carbon tetrachloride is recovered by two-time reduced-pressure distillation after being heated, to obtain a solid monosubstituted intermediate; The molar ratio of DOPO to benzylamine is 1:1.05-1.1; The molar ratio of DOPO to triethylamine is 1:1.2-1.3; The mass ratio of DOPO to dichloromethane is 1:4-5; The mass ratio of DOPO to carbon tetrachloride is 1:1.05-1.1; The vacuum degree of the one-time reduced-pressure distillation is 0.05-0.06 MPa, and the temperature is 30-35 DEG C; The vacuum degree of the two-time reduced-pressure distillation is 0.05-0.06 MPa, and the temperature is 60-65 DEG C.

[0012] Step two: double phosphoramide reaction The monosubstituted intermediate is dissolved in xylene, then DOPO is added, followed by ZnCl2 and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), stirring at 50-60 DEG C for 20-30 min, then adding DBU-imidazole salt, stirring at 80-90 DEG C for 3.2-3.8 hours, as the reaction proceeds, the solution gradually turns into light yellow, removing xylene by distillation under reduced pressure to obtain a crude product; The mass ratio of the monosubstituted intermediate to xylene is 1:5-7; The molar ratio of the monosubstituted intermediate to DOPO is 1:1.05-1.1; The molar ratio of the monosubstituted intermediate to ZnCl2, DBU, DBU-imidazole salt is 1:0.05-0.07:0.3-0.4:0.3-0.4.

[0013] The preparation method of the DBU-imidazole salt is as follows: under a nitrogen atmosphere, imidazole and acetonitrile are added to a reaction kettle, nitrogen is replaced, DBU is added dropwise, temperature is controlled at 25-30 DEG C, stirring is carried out for 30-35 min, and then concentrated under reduced pressure at 55-60 DEG C until crystals are precipitated, and then recrystallized with cold acetonitrile, and dried under vacuum at 55-60 DEG C to obtain the DBU-imidazole salt; The molar ratio of the DBU to imidazole is 1:1.05-1.1; The mass ratio of the DBU to acetonitrile is 1:2.5-3.5; The temperature of the cold acetonitrile is 0-5 DEG C.

[0014] Step three: post-treatment The crude product is cooled to room temperature, washed with an ethanol / water mixed solution for 3-4 times, then dissolved in toluene at 50-60 DEG C to a saturated state, recrystallized by cooling, and the obtained crystals are dried at 80-85 DEG C for 4-5 hours to obtain a DOPO derivative; The mass ratio of ethanol to water in the ethanol / water mixed solution is 1:0.9-1.1; The amount of the ethanol / water mixed solution used for each washing is 1-1.5 times the mass of the crude product; The DOPO derivative is DOPO-N(BZA)-DOPO, and the structural formula is as follows:

[0015] Compared with the prior art, the present application has the following beneficial effects: (1) During the preparation of the monosubstituted intermediate, the PH bond in DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) is reactive. In the presence of carbon tetrachloride and triethylamine, the PH bond is chlorinated to generate the intermediate P-Cl bond. The generated DOPO-Cl undergoes a nucleophilic substitution reaction with benzylamine (BnNH2). The amino group (-NH2) of benzylamine attacks the P-Cl bond, replacing the chlorine atom to form a phosphoramide bond (PN), generating the monosubstituted intermediate DOPO-N(H)-BZA. The increased steric hindrance around the monosubstituted intermediate hinders the second nucleophilic attack, and the reduced electron cloud density of the P atom weakens its electrophilicity. This makes it difficult for the monosubstituted intermediate to undergo a second nucleophilic addition with the PH bond of DOPO. In the bisphosphamidation reaction, this application uses ZnCl2, DBU and DBU-imidazolium salt as co-catalysts to solve the technical problem that the monosubstituted intermediate is difficult to undergo a second nucleophilic addition with the PH bond of DOPO, and prepares the disubstituted DOPO derivative DOPO-N(BZA)-DOPO. In the bisphosphatization reaction, ZnCl2, DBU, and DBU-imidazolium salt activate the reactants from different angles. ZnCl2 activates reactants containing PH and NH bonds through Lewis acid interaction; DBU abstracts a proton from the NH bond in the monosubstituted intermediate (structure P-NH-BZA) through basic interaction, generating a highly reactive nitrogen anion nucleophilic center (PN). - -BZA); DOPO phosphorus center (P + Partially positively charged, P=O bond (O - The DBU-imidazolium salt carries a partially negative charge and has the structure [DBUH]. + [Im] - The imidazole anion of this salt (Im - The P region preferentially binds to DOPO via electrostatic interactions. + Near the center, make DOPO's P + The site is "exposed" and in an activated state, with [DBUH] of DBU-imidazolium salt. + Combined PN - -BZA was "pulled" towards the nearby Im due to electrostatic attraction. - And Im - P already anchored at DOPO + site, thereby making N - Precisely targeting phosphorus atoms reduces non-specific contact between them and solvents or other potential sites, thus improving the selectivity of generating the target product.

[0016] (2) The preparation method of the double-substituted DOPO derivative DOPO-N(BZA)-DOPO of the application has high selectivity in preparing the target product, reduces the generation of by-products, and improves the purity of the product; the yield of the DOPO derivative DOPO-N(BZA)-DOPO prepared by the method of the application is 91.2-92.4%, and the purity is 93.9-95.8%. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 FTIR curve of the DOPO derivative prepared in Example 1. DETAILED DESCRIPTION

[0018] In order to have a clearer understanding of the technical features, objectives and effects of the application, the specific embodiments of the application will be described.

[0019] Example 1 A preparation method of a DOPO derivative flame retardant, comprising the following steps: Step one: preparation of a single-substituted intermediate 21.6g of DOPO, 11.77g of benzylamine and 13.1g of triethylamine are dissolved in 108g of dichloromethane, and then 23.76g of carbon tetrachloride is added dropwise, the dropwise adding time is controlled to be 1.5 hours, after the dropwise adding is completed, stirring reflux reaction is carried out at 55℃ for 4 hours, after the reaction is completed, triethylamine hydrochloride is removed by filtration, low-boiling-point dichloromethane is recovered by once vacuum distillation (0.06MPa, 35℃), and then carbon tetrachloride is recovered by twice vacuum distillation (0.06MPa, 65℃) after temperature rising, to obtain a solid single-substituted intermediate.

[0020] Step two: phosphoramidation reaction The single-substituted intermediate is dissolved in xylene, then DOPO is added, followed by the addition of ZnCl2 and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), stirring is carried out at 60℃ for 20min, then DBU-imidazole salt is added, and stirring reaction is carried out at 90℃ for 3.2 hours, along with the reaction, the solution gradually turns into light yellow, and xylene is removed by vacuum distillation to obtain a crude product; The mass ratio of the single-substituted intermediate to xylene is 1:8; The molar ratio of the single-substituted intermediate to DOPO, ZnCl2, DBU, DBU-imidazole salt is 1:1.1:0.07:0.4:0.4; The preparation method of the DBU-imidazole salt is that, under a nitrogen atmosphere, imidazole and acetonitrile are added into a reaction kettle, nitrogen is replaced, DBU is added dropwise, the temperature is controlled to be 30℃, stirring reaction is carried out for 30min, then vacuum concentration is carried out at 60℃ until crystals are precipitated, the crystals are recrystallized with cold acetonitrile, and vacuum drying is carried out at 60℃ to obtain the DBU-imidazole salt; The molar ratio of the DBU to the imidazole is 1:1.1; The mass ratio of the DBU to the acetonitrile is 1:3.5; The temperature of the cold acetonitrile is 5℃.

[0021] Step three: post-treatment The crude product is cooled to room temperature, washed with an ethanol / water mixed solution 4 times, dissolved in toluene at 60℃ to saturation, recrystallized by cooling, and the obtained crystals are dried at 85℃ for 4 hours to obtain the DOPO derivative; The mass ratio of the ethanol to the water in the ethanol / water mixed solution is 1:1.1; The amount of the ethanol / water mixed solution used in each washing is 1.5 times the mass of the crude product.

[0022] The yield of the DOPO derivative prepared in Example 1 is 92.4%, and the purity is 95.8%.

[0023] Example 2 A preparation method of a DOPO derivative flame retardant, comprising the following steps: Step one: preparation of a mono-substituted intermediate 21.6g of DOPO, 11.56g of benzylamine, and 12.6g of triethylamine are dissolved in 97.2g of dichloromethane, and then 23.3g of carbon tetrachloride is added dropwise, with the dropwise addition time controlled to be 1.2 hours. After the dropwise addition is completed, the reaction is stirred and refluxed at 52℃ for 4.2 hours. After the reaction is completed, the triethylamine hydrochloride is removed by filtration, and then low-boiling dichloromethane is recovered by first reducing pressure distillation (0.055 MPa, 32℃), and then carbon tetrachloride is recovered by second reducing pressure distillation (0.055 MPa, 62℃) after the temperature is increased, to obtain a solid mono-substituted intermediate.

[0024] Step two: phosphoramidation reaction The mono-substituted intermediate is dissolved in xylene, and then DOPO is added, followed by the addition of ZnCl2 and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The solution is stirred at 55℃ for 25 min, and then DBU-imidazole salt is added. The reaction is stirred at 85℃ for 3.5 hours. As the reaction proceeds, the solution gradually turns yellow. Xylene is removed by reducing pressure distillation to obtain a crude product; The mass ratio of the mono-substituted intermediate to the xylene is 1:6; The molar ratio of the mono-substituted intermediate to DOPO, ZnCl2, DBU, DBU-imidazole salt is 1:1.08:0.06:0.35:0.35; The preparation method of the DBU-imidazole salt is as follows: under a nitrogen atmosphere, imidazole and acetonitrile are added into a reaction kettle, nitrogen is replaced, DBU is added dropwise, temperature is controlled at 28°C, and after stirring for 32 min, the solution is concentrated under reduced pressure at 58°C until crystals are precipitated, the crystals are recrystallized with cold acetonitrile, and after vacuum drying at 58°C, the DBU-imidazole salt is obtained. The molar ratio of the DBU to the imidazole is 1:1.08. The mass ratio of the DBU to the acetonitrile is 1:3. The temperature of the cold acetonitrile is 2°C.

[0025] Step three: post-treatment The crude product is cooled to room temperature, washed with an ethanol / water mixed solution for 3 times, dissolved in toluene at 55°C until saturated, recrystallized by cooling, and the obtained crystals are dried at 82°C for 4.5 hours to obtain the DOPO derivative. The mass ratio of ethanol to water in the ethanol / water mixed solution is 1:1. The amount of the ethanol / water mixed solution used in each washing is 1.2 times of the mass of the crude product.

[0026] The yield of the DOPO derivative prepared in Example 2 is 91.2%, and the purity is 95.2%.

[0027] Example 3 A preparation method of a DOPO derivative flame retardant, comprising the following steps: Step one: preparation of a mono-substituted intermediate 21.6g of DOPO, 11.2g of benzylamine and 12.1g of triethylamine are dissolved in 86.4g of dichloromethane, and then 22.7g of carbon tetrachloride is added dropwise, the dropwise adding time is controlled for 1 hour, after the dropwise adding is completed, the solution is stirred and refluxed at 50°C for 4.5 hours, after the reaction is completed, the triethylamine hydrochloride is removed by filtration, and then low-boiling dichloromethane is recovered by once vacuum distillation (0.05 MPa, 30°C), and then carbon tetrachloride is recovered by twice vacuum distillation (0.05 MPa, 60°C) after the temperature is increased, to obtain the solid mono-substituted intermediate.

[0028] Step two: phosphoramidation reaction The mono-substituted intermediate is dissolved in xylene, then DOPO is added, followed by the addition of ZnCl2 and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), the solution is stirred at 50°C for 30 min, then DBU-imidazole salt is added, and the solution is stirred at 80°C for 3.8 hours, as the reaction proceeds, the solution gradually turns into light yellow, and then xylene is removed by vacuum distillation to obtain the crude product; The mass ratio of the mono-substituted intermediate to xylene is 1:5. The molar ratio of the monosubstituted intermediate to DOPO, ZnCl2, DBU, DBU-imidazole salt is 1:1.05:0.05:0.3:0.3; The preparation method of the DBU-imidazole salt is as follows: under a nitrogen atmosphere, imidazole and acetonitrile are added into a reaction kettle, nitrogen is replaced, DBU is added dropwise, the temperature is controlled at 25°C, and after stirring for 35 min, the reaction kettle is concentrated under reduced pressure at 55°C until crystals are precipitated, the crystals are recrystallized with cold acetonitrile, and after vacuum drying at 55°C, the DBU-imidazole salt is obtained. The molar ratio of the DBU to imidazole is 1:1.05. The mass ratio of the DBU to acetonitrile is 1:2.5. The temperature of the cold acetonitrile is 0°C.

[0029] Step three: post-treatment The crude product is cooled to room temperature, washed with an ethanol / water mixed solution three times, dissolved in toluene at 50°C until saturated, recrystallized by cooling, and the obtained crystals are dried at 80°C for 5 hours to obtain the DOPO derivative. The mass ratio of ethanol to water in the ethanol / water mixed solution is 1:0.9. The amount of the ethanol / water mixed solution used for each washing is 1 times the mass of the crude product.

[0030] The yield of the DOPO derivative prepared in Example 3 is 92.1%, and the purity is 93.9%.

[0031] Example 4 A preparation method of a DOPO derivative flame retardant, comprising the following steps: Step one: preparation of a monosubstituted intermediate 21.6g of DOPO, 11.77g of benzylamine, and 13.1g of triethylamine are dissolved in 108g of dichloromethane, and then 23.76g of carbon tetrachloride is added dropwise, the dropwise addition time is controlled for 1.5 hours, after the dropwise addition is completed, the reaction is stirred and refluxed at 55°C for 4 hours, after the reaction is completed, the triethylamine hydrochloride is removed by filtration, and then low-boiling dichloromethane is recovered by one-stage reduced pressure distillation (0.06MPa, 35°C), and then carbon tetrachloride is recovered by two-stage reduced pressure distillation (0.06MPa, 65°C) after the temperature is increased, to obtain a solid monosubstituted intermediate.

[0032] Step two: phosphoramidation reaction The monosubstituted intermediate is dissolved in xylene, then DOPO is added, followed by the addition of ZnCl2 and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), the mixture is stirred at 60°C for 20 min, and then stirred at 90°C for 3.2 hours, after the reaction is completed, xylene is removed by reduced pressure distillation to obtain a crude product; The mass ratio of the monosubstituted intermediate to xylene is 1:8. The molar ratio of the monosubstituted intermediate to DOPO, ZnCl2, DBU, DBU-imidazole salt is 1:1.1:0.07:0.4:0.4; The preparation method of the DBU-imidazole salt is as follows: under a nitrogen atmosphere, imidazole and acetonitrile are added into a reaction kettle, nitrogen is replaced, DBU is added dropwise, temperature is controlled at 30°C, stirring is carried out for 30 min, then concentrated under reduced pressure at 60°C until crystals are precipitated, then recrystallized with cold acetonitrile, dried under vacuum at 60°C to obtain the DBU-imidazole salt; The molar ratio of the DBU to imidazole is 1:1.1; The mass ratio of the DBU to acetonitrile is 1:3.5; The temperature of the cold acetonitrile is 5°C.

[0033] Step three: post-treatment The crude product is cooled to room temperature, washed with an ethanol / water mixed solution for 4 times, then dissolved in toluene at 60°C until saturated, recrystallized by cooling, and the obtained crystals are dried at 85°C for 4 hours to obtain the DOPO derivative; The mass ratio of ethanol to water in the ethanol / water mixed solution is 1:1.1; The amount of the ethanol / water mixed solution used in each washing is 1.5 times of the mass of the crude product.

[0034] Example 4 omits the addition of DBU-imidazole salt based on Example 1, and the yield of the prepared DOPO derivative is 78.1% and the purity is 91.7%.

[0035] The DBU-imidazole salt plays a certain directional guiding role in the bisphosphamidation reaction. After omitting the DBU-imidazole salt, due to the lack of directional role, the probability of effective collision of the nitrogen negative ion with the P + of DOPO decreases, the reaction is incomplete, the residual amount of unreacted raw materials (intermediate, DOPO) increases, and due to the lack of the stabilizing effect of the DBU-imidazole salt on the N - negative ion (P-N - -BZA), the high-activity amide negative ion is in a free state, and the N - can rotate 360°, which may attack the P=O bond in the molecule itself to generate a cyclic byproduct, or attack any position of the adjacent DOPO molecule, such as the benzene ring and O atom, to generate other byproducts, resulting in an increase in the content of byproducts in the product, the byproducts are similar in structure to the target product, and it is difficult to separate and purify, thereby reducing the purity of the final product.

[0036] Example 5 A preparation method of a DOPO derivative flame retardant, comprising the following steps: Step one: preparation of a monosubstituted intermediate The 21.6g of DOPO, 11.77g of benzylamine and 13.1g of triethylamine were dissolved in 108g of dichloromethane, and then 23.76g of carbon tetrachloride was added dropwise, the dropwise adding time was controlled to be 1.5 hours, after the dropwise adding was completed, the reaction was stirred and refluxed at 55℃ for 4 hours, after the reaction was completed, the triethylamine hydrochloride was removed by filtration, and then low-boiling dichloromethane was recovered by one-time reduced pressure distillation (0.06MPa, 35℃), and then carbon tetrachloride was recovered by two-time reduced pressure distillation (0.06MPa, 65℃) after the temperature was increased, and a solid-state mono-substituted intermediate was obtained.

[0037] Step two: bisphosphoramidation reaction The mono-substituted intermediate was dissolved in xylene, then DOPO was added, and then ZnCl2 and triethylamine were added, the mixture was stirred at 60℃ for 20min, and then DBU-imidazole salt was added, the mixture was stirred at 90℃ for 3.2 hours, and as the reaction proceeded, the solution gradually turned yellow, and then xylene was removed by reduced pressure distillation to obtain a crude product; The mass ratio of the mono-substituted intermediate to xylene was 1:8; The molar ratio of the mono-substituted intermediate to DOPO, ZnCl2, triethylamine, DBU-imidazole salt was 1:1.1:0.07:0.4:0.4; The DBU-imidazole salt was prepared by adding imidazole and acetonitrile into a reaction kettle under a nitrogen atmosphere, replacing nitrogen, adding DBU dropwise, controlling the temperature to be 30℃, stirring for 30min, and then concentrating under reduced pressure at 60℃ until crystals were precipitated, and then the crystals were recrystallized with cold acetonitrile, and then the DBU-imidazole salt was obtained after being dried under vacuum at 60℃; The molar ratio of the DBU to imidazole was 1:1.1; The mass ratio of the DBU to acetonitrile was 1:3.5; The temperature of the cold acetonitrile was 5℃.

[0038] Step three: post-treatment The crude product was cooled to room temperature, washed with an ethanol / water mixed solution for 4 times, then dissolved in 60℃ toluene to a saturated state, and then recrystallized by cooling, and then the obtained crystals were dried at 85℃ for 4 hours to obtain a DOPO derivative; The mass ratio of ethanol to water in the ethanol / water mixed solution was 1:1.1; The amount of the ethanol / water mixed solution used for each washing was 1.5 times of the mass of the crude product.

[0039] In Example 5, triethylamine was used instead of DBU on the basis of Example 1, and the yield and purity of the DOPO derivative were significantly reduced, the yield of the prepared DOPO derivative was 52.7%, and the purity was 86.2%.

[0040] The product yield and purity decrease, which is probably due to the insufficient basicity of triethylamine, the difficulty in efficient abstraction of active proton, the slow rate of nucleophilic reaction of monosubstituted intermediate with DOPO, the incomplete reaction and the increased residue of unreacted raw material; and the small steric hindrance of triethylamine, the easy excessive coordination with ZnCl2 to form stable complex, and the weakened activation of ZnCl2 on the reaction site.

[0041] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing detailed description of the present application is made with reference to the foregoing embodiments, for those skilled in the art, it still can be modified, or the equivalent replacement of part of the technical features of the technical solutions recorded in the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the preparation of a DOPO derivative flame retardant, characterized by, The preparation method comprises the following steps: single-substituted intermediate preparation, bis-phosphoramidation reaction, post-treatment. The method of the bis-phosphoramidation reaction is as follows: the single-substituted intermediate is dissolved in xylene, then DOPO is added, followed by the addition of ZnCl2 and DBU, stirring at 50-60 DEG C for 20-30 min, the addition of DBU-imidazole salt, and stirring at 80-90 DEG C for 3.2-3.8 hours; as the reaction proceeds, the solution gradually turns yellow, and xylene is removed by distillation under reduced pressure to obtain a crude product.

2. A process for the preparation of a DOPO derivative flame retardant according to claim 1, characterized by, The method of the single-substituted intermediate preparation is as follows: DOPO, benzylamine and triethylamine are dissolved in dichloromethane, and carbon tetrachloride is added dropwise, with the dropwise addition time being controlled at 1-1.5 hours; after the dropwise addition is completed, reflux stirring is carried out at 50-55 DEG C for 4-4.5 hours; after the reaction is completed, triethylamine hydrochloride is removed by filtration, low-boiling dichloromethane is recovered by one-time distillation under reduced pressure, and carbon tetrachloride is recovered by two-time distillation under reduced pressure to obtain a solid single-substituted intermediate.

3. The method for preparing a DOPO derivative flame retardant according to claim 1, characterized in that, In the bis-phosphoramidation reaction step, The mass ratio of the single-substituted intermediate to xylene is 1:5-7; The molar ratio of the single-substituted intermediate to DOPO is 1:1.05-1.1; The molar ratio of the single-substituted intermediate to ZnCl2, DBU, DBU-imidazole salt is 1:0.05-0.07:0.3-0.4:0.3-0.

4.

4. The method for preparing a DOPO derivative flame retardant according to claim 2, characterized in that, In the single-substituted intermediate preparation step, The molar ratio of DOPO to benzylamine is 1:1.05-1.1; The molar ratio of DOPO to triethylamine is 1:1.2-1.3; The mass ratio of DOPO to dichloromethane is 1:4-5; The mass ratio of DOPO to carbon tetrachloride is 1:1.05-1.

1.

5. The method for preparing a DOPO derivative flame retardant according to claim 1, characterized in that, The method of preparing the DBU-imidazole salt is as follows: under a nitrogen atmosphere, imidazole and acetonitrile are added to a reaction kettle, nitrogen is replaced, DBU is added dropwise, the temperature is controlled at 25-30 DEG C, stirring is carried out for 30-35 min, and the reaction kettle is concentrated under reduced pressure at 55-60 DEG C until crystals are precipitated; the crystals are recrystallized with cold acetonitrile, and DBU-imidazole salt is obtained after vacuum drying at 55-60 DEG C.

6. A process for the preparation of a DOPO derivative flame retardant according to claim 5, characterized by, In the DBU-imidazole salt preparation step, the molar ratio of DBU to imidazole is 1:1.05-1.1, the mass ratio of DBU to acetonitrile is 1:2.5-3.5, and the temperature of the cold acetonitrile is 0-5 DEG C.

7. The method for preparing a DOPO derivative flame retardant according to claim 1, characterized in that, The method of the post-treatment is as follows: the crude product is cooled to room temperature, washed with an ethanol / water mixed solution for 3-4 times, dissolved in toluene at 50-60 DEG C until saturation, recrystallized by cooling, and the obtained crystals are dried at 80-85 DEG C for 4-5 hours to obtain a DOPO derivative.

8. A process for the preparation of a DOPO derivative flame retardant according to claim 7, characterized by, In the post-treatment step, The mass ratio of ethanol to water in the ethanol / water mixed solution is 1:0.9-1.1; The amount of the ethanol / water mixed solution used for each washing is 1-1.5 times the mass of the crude product.

Images