A nitrogen-phosphorus synergistic flame retardant and its preparation method

Abstract

The present invention belongs to the technical field of flame retardants, and particularly relates to a nitrogen-phosphorus synergistic flame retardant and a preparation method thereof. The nitrogen-phosphorus synergistic flame retardant has a chemical structure as shown in the following formula (I). The preparation method of the present invention does not use a transition metal catalyst, and realizes the coupling of DOPO and hydrazide compounds through the Atherton-Todd reaction of compound A and DOPO. The nitrogen-phosphorus synergistic flame retardant prepared by the present invention has excellent flame retardant properties, and can significantly improve the flame retardant properties of materials with less addition amount. The preparation method of the nitrogen-phosphorus synergistic flame retardant of the present invention is simple, the raw materials are cheap and easy to obtain, and it 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] At present, common nitrogen-phosphorus synergistic flame retardants in 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 retardant 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 photocatalyzes the reaction of DOPO and benzamide under N2 protection at room temperature, with a yield of 57%-73%.

[0005] ;

[0006] 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

[0007] To solve the defects in the prior art that the types of nitrogen-phosphorus synergistic flame retardants are relatively single, the preparation methods are complicated, and the flame retardant effect of the flame retardants is not good. The present invention proposes a novel DOPO-based flame retardant that has not been reported. Without using a transition metal catalyst, the coupling of DOPO with hydrazide compounds is achieved through the Atherton-Todd reaction of phthalohydrazide and DOPO, obtaining a novel type of nitrogen-phosphorus synergistic flame retardant. Specifically, the present invention provides the following technical solutions to solve the above technical problems:

[0008] A nitrogen-phosphorus synergistic flame retardant having the chemical structure of the following formula (I):

[0009] (I)

[0010] 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 , * represents the chemical bond connected to N.

[0011] Further, the C1-6 alkyl is linear 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 hexyloxy; the C6-15 aryl is selected from phenyl, biphenyl, naphthyl or anthracenyl.

[0012] Further, the nitrogen-phosphorus synergistic flame retardant has the chemical structure of the following formula (II):

[0013] (II)

[0014] R1 and R2 can be connected to form an aromatic ring, such as forming a benzene ring, and the obtained nitrogen-phosphorus synergistic flame retardant has the chemical structure of the following formula (III):

[0015] (III)

[0016] The present invention also provides a preparation method of the nitrogen-phosphorus synergistic flame retardant shown in the above formula (I), and the synthesis route is as follows:

[0017] .

[0018] R1, R2, and DOPO are defined as above; the reaction conditions are to react at 50-80 °C for 5-10 h in the presence of a halogenating reagent and a deacidifying agent. 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.

[0019] Further, the preparation method of the nitrogen-phosphorus synergistic flame retardant comprises the following steps: Compound A, reaction solvent, DOPO, and halogenating reagent are mixed evenly, a deacidifying agent is added, and the reaction is carried out at 50-80 °C for 5-10 h; Further, after the reaction is completed, the solvent and halogenating reagent are evaporated, and the remaining product is slurried and purified with ethanol to remove the salts formed by the deacidifying agent (such as triethylamine hydrochloride) and other impurities.

[0020] The preparation method of the present invention is an extension of the classical Atherton-Todd reaction. Under room temperature conditions, DOPO first obtains phosphoryl chloride under the action of a halogenating reagent such as carbon tetrachloride, and then couples with Compound A (such as phthalic hydrazide, maleic hydrazide). The deacidifying agent neutralizes hydrogen chloride to promote the forward progress of the reaction.

[0021] Further, the molar ratio of Compound A to DOPO is 1:2-3, such as 1:2.1, 1:2.2, 1:2.5.

[0022] Further, the deacidifying agent is selected from at least one of tertiary amines (such as triethylamine, N,N-diisopropylethylamine), pyridine, and tetramethylguanidine. The dosage of the deacidifying agent is 5-100 times the molar amount of Compound A, preferably 50-100 times; the halogenating reagent is carbon tetrachloride, and the dosage of the halogenating reagent is 10-100 times the molar amount of DOPO; preferably 20-50 times. Selecting carbon tetrachloride as the halogenating reagent instead of sulfonyl chloride or N-chlorosuccinimide with higher reaction activity can improve the yield.

[0023] Further, Compound A is selected from maleic hydrazide and phthalic hydrazide; correspondingly, the obtained nitrogen-phosphorus synergistic flame retardants are the compounds of formula (II) and formula (III) respectively.

[0024] Further, in the above preparation method, when adding compound A, a halogenated salt in an amount of 5-10% of the molar amount of compound A (such as lithium chloride, zinc chloride, ferric trichloride, aluminum trichloride) is also added, and the solvent is a mixed solvent of a halogenated hydrocarbon and an alcohol in a volume ratio of 10:1-2, which can significantly improve the yield of the bis-DOPO product. Especially when compound A is phthalohydrazide, due to the influence of the benzene ring on the planar structure and rigidity of the overall compound, after one amino group (NH) reacts, due to the large steric hindrance effect of DOPO and the increase in the rigidity of the parent structure, it will hinder the remaining amino group 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 also once tried to add inorganic strong bases such as sodium hydroxide and sodium hydride, and organic strong bases such as DBU to promote the protonation of N-H to improve the nucleophilic reaction activity, but the results were not satisfactory. This low yield of the disubstituted product is particularly serious in the case of the connection of R1 and R2 of compound A, indicating that the ring formation of R1 and R2 has an impact on the disubstitution reaction. Unexpectedly, the inventors found that when adding a small amount of halogenated salt while adding compound A and using a mixed solvent of a halogenated hydrocarbon and a lower alcohol, the yield of the bis-DOPO substitution product can be significantly improved. The inventors speculate that the possible reason is that the halogenated salt can accelerate the formation of acyl chloride in the first stage and can react with another substrate faster; in addition, it can also increase the nucleophilicity of hydroxylamine in acylhydrazide, which helps to form the disubstituted product.

[0025] The present invention also provides a preparation method of a compound of formula III, comprising the following steps:

[0026] ;

[0027] Add a halogenated hydrocarbon, a C1-3 alcohol, carbon tetrachloride, DOPO, phthalohydrazide, a halogenated salt, and an acid-binding agent to a reaction vessel, react at 50-80 °C for 6-15 h. After the reaction is completed, rotary evaporate to remove the solvent and carbon tetrachloride, and the remaining solid is slurried and purified twice with ethanol, separated by column chromatography, and recrystallized and purified to obtain a white powdery sample, which is the product compound of formula III.

[0028] Further, the volume ratio of the halogenated hydrocarbon to the C1-3 alcohol is 10:1-2; the molar ratio of DOPO, phthalohydrazide, carbon tetrachloride, and the halogenated salt is 2.1-2.5:1:50-100:50-100.

[0029] When preparing the compound of formula III, the yield of the bis-DOPO substitution product is relatively low, and the flame retardant performance of the monosubstituted product is not good. Unexpectedly, the inventors found that adding a small amount of halogen salt, such as lithium chloride, under the condition of a mixed solvent of a halogenated hydrocarbon and a C1-3 alcohol, can significantly improve the yield of the bis-DOPO product.

[0030] The present invention also provides a flame-retardant engineering plastic, which is obtained by melt co-extrusion of an engineering plastic and a flame retardant, and optionally, an auxiliary material is further added. Further, the flame retardant accounts for 5-15 wt% of the flame-retardant engineering plastic, preferably 6-10 wt%, more preferably 8-10 wt%; the auxiliary material is selected from at least one of an ultraviolet absorber, a toughening agent, an antioxidant, a pigment, and an inorganic filler.

[0031] The nitrogen-phosphorus synergistic flame retardant prepared by the present invention has excellent flame retardancy, and can significantly improve the flame retardancy of materials with a small addition amount. The preparation method of the nitrogen-phosphorus synergistic flame retardant of the present invention is simple, and the raw materials are cheap and easy to obtain, which is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the 1 1H NMR spectrum of the product obtained in Example 1;

[0033] Figure 2 is the 31 31P NMR spectrum of the product obtained in Example 1;

[0034] Figure 3 is the mass spectrum of the product obtained in Example 1;

[0035] Figure 4 is the DSC chart of the product obtained in Example 2;

[0036] Figure 5 is the TGA chart of the product obtained in Example 2;

[0037] Figure 6 is the 1 1H NMR spectrum of the product obtained in Example 5;

[0038] Figure 7 is the 31 31P NMR spectrum of the product obtained in Example 5;

[0039] Figure 8 is the mass spectrum of the product obtained in Example 5;

[0040] Figure 9 is the DSC chart of the product obtained in Example 5;

[0041] Figure 10 is the TGA chart of the product obtained in Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0042] The following specific examples are used to further explain and illustrate the technical solutions of the present invention.

[0043] Example 1

[0044] ;

[0045] Add 10 mL of dichloromethane, 0.5 mol of carbon tetrachloride, 11 mmol of DOPO, and 5 mmol of phthalhydrazide into the reaction vessel, and dropwise add 0.5 mol of triethylamine. React at 60 °C for 6 h. After the reaction is completed, rotary evaporate to remove dichloromethane and carbon tetrachloride. The remaining solid is slurried with ethanol and purified twice to remove triethylamine hydrochloride and other impurities. Separate by column chromatography and purify by recrystallization to obtain a white powdery sample with a yield of 74.3% and an HPLC purity of 98.4%.

[0046] Figure 1 is the product obtained in Example 1 1 1H NMR spectrum. Figure 2 is the product obtained in Example 1 31 31P NMR spectrum. Figure 3 is the mass spectrum of the product obtained in Example 1. The characteristic peaks of aromatic hydrogens appear at 7.3 - 8.4 ppm. Its 31 single peak appears at 6.33 ppm in the 31P NMR spectrum, indicating that the compound contains a phosphorus atom, further confirming that DOPO is attached to phthalhydrazide. According to the theoretical relative molecular weight of the compound, 590.4, there is a corresponding molecular ion peak in the mass spectrum, and finally the structure of the compound is determined as shown in formula (III). There is also a small amount of ion peak at 376.3 in the mass spectrum, which is the DOPO monosubstituted product.

[0047] Example 2

[0048] Add 10 mL of dichloroethane, 1 mL of methanol, 0.5 mol of carbon tetrachloride, 11 mmol of DOPO, 5 mmol of phthalhydrazide, and 0.5 mmol of lithium chloride into the reaction vessel, and dropwise add 0.5 mol of triethylamine. React at 60 °C for 6 h. After the reaction is completed, rotary evaporate to remove dichloroethane and carbon tetrachloride. The remaining solid is slurried with ethanol and purified twice to remove triethylamine hydrochloride and other impurities. Separate by column chromatography and purify by recrystallization to obtain a white powdery sample with a yield of 88.6% and an HPLC purity of 99.3%.

[0049] Compared with Example 1, a small amount of lithium chloride was added in Example 2. As a result, both the yield and purity of the product were significantly improved. It shows that the presence of lithium chloride is beneficial to the preparation of the disubstituted product.

[0050] Figure 4 is the DSC diagram of the product obtained in Example 2. Figure 5 is the TGA diagram of the product obtained in Example 2. The obtained compound has a relatively high melting point (266.4 °C) and thermogravimetric analysis results, meeting the test standards of current commercially available mainstream flame retardants and having potential commercial application value.

[0051] Example 3

[0052] Other conditions were the same as 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 indicates that to increase the yield, not only lithium chloride but also an alcohol solvent needs to be added.

[0053] Example 4

[0054] Other conditions were the same as in Example 2, except that 10 mL of dichloroethane and 1 mL of methanol were replaced with 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 halogenated hydrocarbon and a small amount of alcohol is necessary to increase the yield and purity.

[0055] Example 5

[0056] ;

[0057] 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. 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. The remaining solid was purified by ethanol pulping twice to remove triethylamine hydrochloride and other impurities, and a white powdery sample was obtained with a yield of 86.3% and an HPLC purity of 99.4%.

[0058] Figure 6 is the 1 1H NMR spectrum of the product obtained in Example 5. Figure 7 is the 31 31P NMR spectrum of the product prepared in Example 5. Doublets appear at 6.52 ppm and 6.72 ppm with similar chemical shifts, indicating that the compound is a pair of diastereoisomers. Figure 8 is the mass spectrum of the product prepared in Example 5. The molecular ion peak with a mass-to-charge ratio (m / z) of 541.1 was finally used to determine the relative molecular weight of the compound, with two DOPOs coupled to maleic hydrazide. Figure 9 is the DSC chart of the product obtained in Example 5. Figure 10 is the TGA chart of the product obtained in Example 5. The compound has two melting points, further indicating that the compound is a pair of diastereoisomers. The compound structure contains a carbon-carbon double bond, so it is prone to break and decompose at the carbon-carbon double bond during thermogravimetric analysis. The compound contains a carbon-carbon double bond structure and can be considered for use as a reactive flame retardant in practical applications.

[0059] Application Example

[0060] The compound of Formula III prepared in Example 2 above and the compound of Formula II prepared in Example 5 were used as flame retardants, and were extruded with thermoplastic polyester PBT (intrinsic viscosity 1.07 dl / g) through a twin-screw extruder to prepare splines of different specifications, and the combustion flame retardant properties of the splines were tested. When the compound of Formula (III) was added as a flame retardant to PBT, the flame retardant properties are shown in Table 1; when the compound of Formula (II) was added as a flame retardant to PBT, the flame retardant properties are shown in Table 2.

[0061] Table 1. Combustion test of the reaction product of phthalohydrazide and DOPO added to PBT

[0062] 。

[0063] Table 2. Combustion test of the reaction product of maleic hydrazide and DOPO added to PBT

[0064] 。

[0065] From the data in Table 1 and Table 2, it can be seen that the nitrogen-phosphorus synergistic flame retardant prepared in the present invention has excellent flame retardant effect, and can make the PBT material achieve good flame retardant effect at an addition amount of 8 wt%. The preparation method of the nitrogen-phosphorus synergistic flame retardant of the present invention is simple, has a 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 the following formula (I): (I) wherein R1 and R2 are independently selected from H and C1-6 alkyl; or R1 and R2 are connected to form a benzene ring; DOPO is , * represents a chemical bond connected to N.

2. The nitrogen-phosphorus synergistic flame retardant according to claim 1, wherein C1-6 alkyl is selected from methyl, ethyl, propyl, butyl, pentyl, and hexyl.

3. The nitrogen-phosphorus synergistic flame retardant according to claim 1, wherein 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, The obtained nitrogen-phosphorus synergistic flame retardant has the chemical structure of the following formula (III): (III).

5. The preparation method of the nitrogen-phosphorus synergistic flame retardant according to any one of claims 1-4, characterized in that, The synthesis route is as follows: ； The reaction conditions are to react in the presence of a halogenating reagent and a deacidifying agent, and the reaction conditions are to react at 50-80 °C for 5-10 h; the reaction solvent is a halogenated hydrocarbon and / or a C1-3 alcohol.

6. The preparation method according to claim 5, wherein It includes the following steps: Compound A, the reaction solvent, DOPO, and the halogenating reagent are mixed evenly, and the deacidifying agent is slowly added, and the reaction is carried out at 50-80 °C for 5-10 h.

7. The preparation method according to claim 5, wherein The molar ratio of compound A to DOPO is 1:2-3; the deacidifying agent is selected from at least one of tertiary amines and pyridine, and the amount of the deacidifying agent used is 5-100 times the molar amount of compound A; the halogenating reagent is carbon tetrachloride, and the amount of the halogenating reagent used is 10-100 times the molar amount of DOPO.

8. The preparation method according to claim 5, characterized in that, Compound A is selected from maleic hydrazide and phthalic hydrazide.

9. The preparation method according to claim 5, wherein When adding compound A, a halogenated salt with a molar amount of 5-10% of compound A is also added. The halogenated salt is selected from at least one of lithium chloride, zinc chloride, ferric trichloride, and aluminum trichloride; the solvent is a mixed solvent of a halogenated hydrocarbon and a C1-3 alcohol in a volume ratio of 10:1-2.

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