Nitrogen-phosphorus synergistic flame retardant and preparation method thereof

Abstract

The invention belongs to the technical field of flame retardants, and particularly relates to a nitrogen-phosphorus synergistic flame retardant and a preparation method thereof, and the nitrogen-phosphorus synergistic flame retardant has a chemical structure as shown in a formula (I). According to the preparation method, a transition metal catalyst is not used, and coupling of the DOPO and the hydrazide compound is achieved through the Atherton-Todd reaction of the compound A and the DOPO. The nitrogen-phosphorus synergistic flame retardant prepared by the preparation method disclosed by the invention has excellent flame retardant property, and the flame retardant property of the material can be remarkably improved by adding a small amount of the nitrogen-phosphorus synergistic flame retardant. The preparation method of the nitrogen-phosphorus synergistic flame retardant is simple, raw materials are cheap and easy to obtain, and the nitrogen-phosphorus synergistic flame retardant is suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardants, and specifically relates to a nitrogen-phosphorus synergistic flame retardant and a preparation method thereof. Background Art

[0002] The advantage of phosphorus-based flame retardants is that they have the dual functions of flame retardancy and plasticization, with abundant raw material resources and low cost; the disadvantage is that most phosphorus-containing products are lipophilic oils and are difficult to add to high molecular polymers during synthesis. The advantage of nitrogen-based flame retardants is that after thermal decomposition, they easily release non-combustible gases such as ammonia, nitrogen, deep nitrogen oxides, and water vapor. The generation of these gases and the decomposition of flame retardants absorb most of the heat, greatly reducing the surface temperature of the polymer. In addition, these non-combustible gases, such as nitrogen, not only play a role in diluting the oxygen in the air and the concentration of combustible gases produced by thermal decomposition of polymers, but also react with oxygen in the air to consume oxygen on the surface of the material, while achieving a good flame retardant effect.

[0003] Nitrogen-phosphorus flame retardants are widely used in production and life because they have the advantages of both nitrogen-based flame retardants and phosphorus-based flame retardants. They have strong thermal stability and little impact on materials. Adding a small amount of flame retardants can exert greater flame retardant properties. Nitrogen-phosphorus flame retardants are mostly intumescent flame retardants, which are flame retardants that combine nitrogen (N), phosphorus (P), and carbon (C) in the same molecule. The compounds are halogen-free, have good hydrolysis stability, high decomposition temperature, low hygroscopicity, and have good nitrogen-phosphorus synergistic effects. In addition, this type of flame retardant has the advantages of high thermal stability and less impact on the environment during combustion. It is a type of flame retardant with great development potential.

[0004] Common nitrogen-phosphorus synergistic flame retardants on the market include aminophosphate flame retardants, such as ammonium polyphosphate (APP), melamine phosphate flame retardants, and phosphazene flame retardants, such as hexaphenoxy cyclotriphosphazene. In the reaction of synthesizing nitrogen-phosphorus synergistic flame retardants DOPO derivatives, there are many reports on the reaction of DOPO with compounds containing functional groups such as imine, carbonyl, amino, double bond, and hydroxyl. The reaction of DOPO with amide groups is rare. At present, there is only one report on the patent of the reaction of DOPO with amide compounds. The reaction uses transition metals (cuprous oxide or (2,2'-bipyridine) bis(1,10-phenanthroline) ruthenium (II) bis(hexafluorophosphate)) as catalysts, and room temperature N 2 The photocatalytic reaction of DOPO and benzamide under protective conditions had a yield of 57%-73%.

[0005] ; However, the yield of the patented synthesis route is low, and the flame retardant effect of the resulting flame retardant is not good. Summary of the invention

[0006] In order to solve the defects of the existing technology that the types of nitrogen-phosphorus synergistic flame retardants are relatively single, the preparation method is complicated, and the flame retardant effect of the flame retardant is not good. The present invention proposes a new flame retardant based on DOPO that has not been reported before. It does not use a transition metal catalyst, but achieves the coupling of DOPO and hydrazide compounds through the Atherton-Todd reaction of phthalic hydrazide and DOPO, thereby obtaining a new type of nitrogen-phosphorus synergistic flame retardant. Specifically, the present invention provides the following technical solutions to solve the above technical problems: A nitrogen-phosphorus synergistic flame retardant having the chemical structure of the following formula (I): (I) Where R 1 , R 2 is independently selected from at least one of H, C1-6 alkyl, C1-6 alkoxy, C6-15 aryl, hydroxyl, and nitro; or R 1 , R 2 Connected into C6-15 aromatic ring; DOPO is , * indicates a chemical bond connected to N.

[0007] Furthermore, the C1-6 alkyl is chain or cyclic and is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclobutyl, cyclopentyl or cyclohexyl; the C1-6 alkoxy is selected from methoxy, ethoxy, propoxy, butoxy, pentyloxy or hexyl; and the C6-15 aryl is selected from phenyl, biphenyl, naphthyl or anthracenyl.

[0008] Furthermore, the nitrogen-phosphorus synergistic flame retardant has a chemical structure of the following formula (II): (II) R 1 , R 2 They can be connected to form an aromatic ring, such as a benzene ring, and the resulting nitrogen-phosphorus synergistic flame retardant has the chemical structure of the following formula (III): (III) The present invention also provides a method for preparing the nitrogen-phosphorus synergistic flame retardant represented by the above formula (I), and the synthesis route is as follows: .

[0009] R 1 , R 2 , DOPO is defined as above; the reaction conditions are in the presence of a halogenating agent and an acid binding agent, at 50-80°C for 5-10 hours. The reaction solvent is a halogenated hydrocarbon and / or a C1-3 alcohol; the halogenated hydrocarbon is selected from at least one of dichloromethane and dichloroethane; the C1-3 alcohol is selected from at least one of methanol, ethanol, isopropanol, and ethylene glycol.

[0010] Furthermore, the preparation method of the nitrogen-phosphorus synergistic flame retardant comprises the following steps: compound A, a reaction solvent, DOPO, and a halogenating agent are uniformly mixed, an acid binding agent is added, and the mixture is reacted at 50-80° C. for 5-10 hours; further, after the reaction is completed, the solvent and the halogenating agent are evaporated, and the remaining product is purified by ethanol pulping to remove salts (such as triethylamine hydrochloride) formed by the acid binding agent and other impurities.

[0011] The preparation method of the present invention is an extension of the classic Atherton-Todd reaction. Under room temperature conditions, DOPO first obtains phosphorus oxychloride under the action of a halogenating agent such as carbon tetrachloride, and then couples with compound A (such as phthalic acid hydrazide, maleic acid hydrazide), and an acid binding agent neutralizes hydrogen chloride to promote the reaction to proceed in the forward direction.

[0012] Furthermore, the molar ratio of compound A to DOPO is 1:2-3, such as 1:2.1, 1:2.2, 1:2.5.

[0013] Furthermore, the acid-binding agent is selected from at least one of tertiary amines (such as triethylamine, N,N-diisopropylethylamine), pyridine, and tetramethylguanidine. The amount of the acid-binding agent is 5-100 times the molar amount of compound A, preferably 50-100 times; the halogenating agent is carbon tetrachloride, and the amount of the halogenating agent is 10-100 times the molar amount of DOPO; preferably 20-50 times. Choosing carbon tetrachloride as the halogenating agent instead of sulfonyl chloride or N-chlorosuccinimide with higher reaction activity can improve the yield.

[0014] Furthermore, compound A is selected from maleic hydrazide and phthalic hydrazide; correspondingly, the obtained nitrogen-phosphorus synergistic flame retardants are compounds of formula (II) and formula (III), respectively.

[0015] Furthermore, in the above preparation method, when compound A is added, a halogenated salt (such as lithium chloride, zinc chloride, ferric chloride, aluminum chloride) with a molar amount of 5-10% of compound A is also added, and the solvent is a mixed solvent of halogenated hydrocarbons and alcohols in a volume ratio of 10:1-2, which can significantly improve the yield of the di-DOPO product. In particular, when compound A is phthaloyl hydrazide, due to the influence of the benzene ring on the planar structure and rigidity of the overall compound, after one of the amino groups (NH) reacts, due to the large steric effect of DOPO and the increase in the rigidity of the parent structure, the remaining amino groups will be hindered from continuing to react with DOPO. Even if DOPO is in excess and the reaction time is extended, the yield of the disubstituted product is not high. The inventors have also tried to add inorganic strong bases, such as sodium hydroxide, sodium hydride, etc., and organic strong bases, such as DBU, to promote the protonation of NH and increase the nucleophilic reaction activity, but the results were not ideal. This low yield of the disubstituted product is caused by the R of compound A. 1 , R 2 The connection situation is particularly serious, indicating that R 1 , R2 The connection to form a ring has an impact on the di-substitution reaction. The inventor unexpectedly found that when a small amount of halogenated salt is added at the same time as compound A, and the solvent is a combination of halogenated hydrocarbons and low-carbon alcohols, the yield of the DOPO substitution product can be significantly improved. The inventor speculates that the possible reason is that the halogenated salt can accelerate the formation of the first-stage acyl chloride and react with another substrate faster; in addition, it can increase the nucleophilicity of hydroxylamine in hydrazide, which helps to generate di-substitution products.

[0016] The present invention also provides a method for preparing the compound of formula III, comprising the following steps: ; Add halogenated hydrocarbon, C1-3 alcohol, carbon tetrachloride, DOPO, phthalic acid hydrazide, halogenated salt and acid binding agent into the reaction vessel, and react at 50-80° C. for 6-15 hours. After the reaction, remove the solvent and carbon tetrachloride by rotary evaporation. Purify the remaining solid by ethanol slurry twice, separate by column chromatography, and purify by recrystallization to obtain a white powder sample, which is the product compound of formula III.

[0017] Furthermore, the volume ratio of the halogenated hydrocarbon to the C1-3 alcohol is 10:1-2; the molar ratio of DOPO, phthalic acid hydrazide, carbon tetrachloride, and the halogenated salt is 2.1-2.5:1:50-100:50-100.

[0018] When preparing the compound of formula III, the yield of the di-DOPO substituted product is low, while the mono-substituted product has poor flame retardant properties. The inventors unexpectedly found that adding a small amount of halide salt, such as lithium chloride, in a mixed solvent of halogenated hydrocarbons and C1-3 alcohols can significantly increase the yield of the di-DOPO product.

[0019] The present invention also provides a flame retardant engineering plastic, which is obtained by melt co-extrusion of engineering plastic and flame retardant, and optionally, auxiliary materials. Further, the flame retardant accounts for 5-15wt% of the flame retardant engineering plastic, preferably 6-10wt%, more preferably 8-10wt%; the auxiliary material is selected from at least one of an anti-ultraviolet agent, a toughening agent, an antioxidant, a pigment, and an inorganic filler.

[0020] The nitrogen-phosphorus synergistic flame retardant prepared by the present invention has excellent flame retardant performance, and can significantly improve the flame retardant performance of the material with a relatively small addition amount. The preparation method of the nitrogen-phosphorus synergistic flame retardant of the present invention is simple, the raw materials are cheap and readily available, and it is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The product obtained in Example 1 1 H NMR spectra; Figure 2 The product obtained in Example 1 31 P NMR spectra; Figure 3 is the mass spectrum of the product obtained in Example 1; Figure 4 is the DSC graph of the product obtained in Example 2; Figure 5 is the TGA diagram of the product obtained in Example 2; Figure 6 The product obtained in Example 5 1 H NMR spectra; Figure 7 The product obtained in Example 5 31 P NMR spectra; Figure 8 is the mass spectrum of the product obtained in Example 5; Fig. 9 is the DSC graph of the product obtained in Example 5; Fig.10 This is the TGA chart of the product obtained in Example 5. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further explained and illustrated by specific embodiments below.

[0023] Example 1 ; 10 ml of dichloromethane, 0.5 mol of carbon tetrachloride, 11 mmol of DOPO, and 5 mmol of phthalic acid hydrazide were added to the reaction vessel, and 0.5 mol of triethylamine was added dropwise, and the reaction was carried out at 60°C for 6 hours. After the reaction, dichloromethane and carbon tetrachloride were removed by rotary evaporation, and the remaining solid was purified by ethanol beating twice to remove triethylamine hydrochloride and other impurities, and then separated by column chromatography and purified by recrystallization to obtain a white powder sample with a yield of 74.3% and an HPLC purity of 98.4%.

[0024] Figure 1 The product obtained in Example 1 1 H NMR spectra. Figure 2 The product obtained in Example 1 31 P NMR spectrum. Figure 3 is the mass spectrum of the product obtained in Example 1. The characteristic peak of aromatic hydrogen appears at 7.3-8.4 ppm. 31 The presence of a single peak at 6.33 ppm in the P NMR spectrum indicates that the compound contains a phosphorus atom, further confirming that DOPO is attached to phthaloyl hydrazide. According to the theoretical relative molecular weight of the compound of 590.4, there is a corresponding molecular ion peak in the mass spectrum, and the structure of the compound is finally determined to be shown in formula (III). There is also a small amount of ion peaks at 376.3 in the mass spectrum, which is a DOPO monosubstituted product.

[0025] Example 2 10 ml of dichloroethane, 1 mL of methanol, 0.5 mol of carbon tetrachloride, 11 mmol of DOPO, 5 mmol of phthalic acid hydrazide, and 0.5 mmol of lithium chloride were added to the reaction vessel, and 0.5 mol of triethylamine was added dropwise, and the reaction was carried out at 60°C for 6 hours. After the reaction, dichloroethane and carbon tetrachloride were removed by rotary evaporation, and the remaining solid was purified by ethanol beating twice to remove triethylamine hydrochloride and other impurities, and then separated by column chromatography and recrystallized to obtain a white powder sample with a yield of 88.6% and an HPLC purity of 99.3%.

[0026] Compared with Example 1, a small amount of lithium chloride was added in Example 2. As a result, the yield and purity of the product were significantly improved, indicating that the presence of lithium chloride is beneficial to the preparation of the disubstituted product.

[0027] Figure 4 It is the DSC chart of the product obtained in Example 2. Figure 5 This is the TGA graph of the product obtained in Example 2. The obtained compound has a relatively high melting point (266.4°C) and thermogravimetric analysis results, which meet the test standards of the current mainstream flame retardants on the market and have potential commercial application value.

[0028] Example 3 The other conditions were the same as those in Example 2, except that 1 mL of methanol was not added. After final recrystallization, the product yield was 83.1% and the HPLC purity was 99.2%. This indicated that in order to increase the yield, not only lithium chloride but also an alcohol solvent needed to be added.

[0029] Example 4 The other conditions were the same as those in Example 2, except that 10 ml of dichloroethane and 1 ml of methanol were replaced by 10 ml of methanol. After final recrystallization, the product yield was 80.4% and the HPLC purity was 98.3%. This indicates that a mixed solvent of a halogenated hydrocarbon and a small amount of alcohol is necessary to improve the yield and purity.

[0030] Example 5 ; 10 ml of dichloromethane, 0.5 mol of carbon tetrachloride, 5 mmol of maleic hydrazide, and 11 mmol of DOPO were added to the reaction vessel, and 0.5 mol of triethylamine was added dropwise at room temperature, and the reaction was carried out at 70 °C for 6 h. After the reaction, dichloromethane and carbon tetrachloride were removed by rotary evaporation, and the remaining solid was purified twice by ethanol slurry to remove triethylamine hydrochloride and other impurities, and a white powder sample was obtained with a yield of 86.3% and an HPLC purity of 99.4%.

[0031] Figure 6 The product obtained in Example 5 1 H NMR spectra. Figure 7 The product obtained in Example 531 The P NMR spectrum showed double peaks at 6.52 ppm and 6.72 ppm with similar chemical shifts, indicating that the compound was a group of diastereoisomers. Figure 8 This is the mass spectrum of the product obtained in Example 5, with a molecular ion peak having a mass-to-charge ratio (m / z) of 541.1, and the relative molecular weight of the compound was finally determined, and two DOPOs were coupled to the maleic hydrazide. Fig. 9 This is the DSC chart of the product obtained in Example 5. Fig.10 This is the TGA diagram of the product obtained in Example 5. The compound has two melting points, which further indicates that the compound is a group of diastereomers. The compound structure contains a carbon-carbon double bond, so it is easy to break and decompose at the carbon-carbon double bond in thermal gravimetric analysis. The compound contains a carbon-carbon double bond structure and can be considered as a reactive flame retardant in practical applications.

[0032] Application Examples The compound of formula III prepared in Example 2 and the compound of formula II prepared in Example 5 were used as flame retardants and thermoplastic polyester PBT (intrinsic viscosity 1.07 dl / g) was extruded through a twin-screw extruder to prepare specimens of different specifications, and the specimens were tested to obtain their combustion flame retardant properties. The compound of formula (III) was added to PBT as a flame retardant, and the flame retardant properties were shown in Table 1; the compound of formula (II) was added to PBT as a flame retardant, and the flame retardant properties were shown in Table 2.

[0033] Table 1. Combustion test of the reaction product of phthalic acid hydrazide and DOPO added to PBT .

[0034] Table 2. Combustion test of the reaction product of maleic hydrazide and DOPO added to PBT .

[0035] It can be seen from the data in Table 1 and Table 2 that the nitrogen-phosphorus synergistic flame retardant prepared by the present invention has excellent flame retardant effect, and the PBT material can achieve a good flame retardant effect when the addition amount is 8wt%. The preparation method of the nitrogen-phosphorus synergistic flame retardant of the present invention is simple, has high yield, and is suitable for industrial production.

Claims

1. A nitrogen-phosphorus synergistic flame retardant, characterized in that: It has the chemical structure of formula (I): (I) wherein R1 and R2 are independently selected from at least one of H, C1-6 alkyl, C1-6 alkoxy, C6-15 aryl, hydroxyl, and nitro; or R1 and R2 are connected to form a C6-15 aromatic ring; DOPO is , * indicates a chemical bond connected to N.

2. The nitrogen-phosphorus synergistic flame retardant according to claim 1, characterized in that: The C1-6 alkyl group is chain or cyclic and is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclobutyl, cyclopentyl or cyclohexyl; the C1-6 alkoxy group is selected from methoxy, ethoxy, propoxy, butoxy, pentyloxy or hexyl; the C6-15 aryl group is selected from phenyl, biphenyl, naphthyl or anthracenyl.

3. The nitrogen-phosphorus synergistic flame retardant according to claim 1, characterized in that: The nitrogen-phosphorus synergistic flame retardant has the chemical structure of the following formula (II): (II)。 4. The nitrogen-phosphorus synergistic flame retardant according to claim 1, characterized in that: R1 and R2 are connected to form a benzene ring.

5. The nitrogen-phosphorus synergistic flame retardant according to claim 1, characterized in that: The obtained nitrogen-phosphorus synergistic flame retardant has the chemical structure of the following formula (III): (III)。 6. The method for preparing the nitrogen-phosphorus synergistic flame retardant according to any one of claims 1 to 5, characterized in that: The synthetic route is as follows: ； The reaction conditions are to react in the presence of a halogenating agent and an acid-binding agent, and to react at 50-80° C. for 5-10 hours; the reaction solvent is a halogenated hydrocarbon and / or a C1-3 alcohol.

7. The preparation method according to claim 6, characterized in that: The following steps are involved: Compound A, reaction solvent, DOPO and halogenation reagent are mixed evenly, and the acid binding agent is slowly added, and the reaction is carried out at 50-80° C. for 5-10 hours.

8. The preparation method according to claim 6, characterized in that: The molar ratio of compound A to DOPO is 1:2-3; the acid-binding agent is selected from at least one of tertiary amine and pyridine, and the amount of the acid-binding agent is 5-100 times the molar amount of compound A; the halogenating agent is carbon tetrachloride, and the amount of the halogenating agent is 10-100 times the molar amount of DOPO.

9. The preparation method according to claim 6, characterized in that: Compound A is selected from maleic hydrazide and phthalic hydrazide.

10. The preparation method according to claim 6, characterized in that: When compound A is added, a halogenated salt of 5-10% molar amount of compound A is also added, and the halogenated salt is selected from at least one of lithium chloride, zinc chloride, ferric chloride, and aluminum chloride; the solvent is a mixed solvent of halogenated hydrocarbons and C1-3 alcohols in a volume ratio of 10:1-2.

Images