DE102023000325B3 - Thiazole compounds as flame retardants containing phosphorus, nitrogen and sulfur and their use - Google Patents

Abstract

The present invention provides thiazole compounds with phosphorus, nitrogen and sulfur and their use as halogen-free flame retardants for plastics.

Description

The present invention relates to thiazole compounds with phosphorus, nitrogen and sulfur and their use as halogen-free flame retardants for plastics.

It is state of the art to use flame-retardant plastics for certain applications. In the event of a fire, the flame retardant prevents or delays the ignition of the plastic, reduces the speed of fire and inhibits the spread of fire.

The selection of the flame retardant is specific to the material and takes into account the planned product application. Well-known flame retardants are metal hydroxides, halogen-containing organic compounds and organophosphorus compounds. In addition to their fire-protecting effect, these flame retardants often have undesirable effects on the processing process or the treated plastic.

Out of DE100 35 647 A1 Flame-retardant plastic mixtures are known containing magnesium hydroxide or aluminum hydroxide. These compounds must be used in high mass proportions of 60 - 150 phr in order to achieve a flame-retardant effect on plastics. This makes it more difficult to process the plastics and impairs the mechanical properties of the products.

However, phosphorus-containing flame retardants, which are less likely to have these undesirable properties of the halogen-containing compounds, preferably include, in addition to red phosphorus and inorganic phosphorus compounds, low molecular weight organic phosphorus compounds.

In EP1837338A1 , EP1837339A1 and EP1837340A1 Low molecular weight phosphorus-containing flame retardants based on phosphorus-containing mixtures of phosphorus-containing ethylenically unsaturated monomers, their production and their use are described. The flame retardant effect is based on the decomposition products of the phosphorus compound.

Synergy effects between phosphorus, nitrogen and sulfur in flame retardants are known, which, due to their increased effectiveness, are effective even when used in small quantities ( CN110128702A ).

Flame retardants containing nitrogen and sulfur form nitrogen- and sulfur-containing decomposition products in the gas phase and contribute to the dilution of the flame. The primary products formed further decompose into gases containing nitrogen and sulfur. ( Jian et al. (2016) Industrial & Engineering Chemistry Research, 55(44), 11520-11527 )

The radicals (PO*) containing oxygen and phosphorus stop the chemical reaction in the flame in the gas phase. ( Jian et al. (2016) Industrial & Engineering Chemistry Research, 55(44), 11520-11527 )

CN106009040A discloses a flame retardant containing phosphorus, nitrogen and sulfur used for epoxy resins, characterized by preparation from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and aminothiazole in an Atherton-Todd Reaction. When the phosphorus content of the epoxy curing system reaches 0.43 wt% to 1.23 wt%, a UL-94 V-0 rating is achieved. The oxygen index LOI is up to 36%.

CN106749413A discloses a flame retardant containing phosphorus, nitrogen and sulfur used for epoxy resins, characterized by a reaction of parahydroxybenzaldehyde, aminothiazole and DOPO. If the phosphorus content of the cured epoxy resin product is 0.94% by weight or more, a classification according to UL-94 V-0 is achieved. The oxygen index LOI is up to 33.3%.

Out of CN106751470A a production process of a fire-retardant epoxy resin with DOPO-aminothiazole derivatives is known. DOPO aminothiazole derivatives with 5 - 15 parts by weight are used in the epoxy resin system.

In CN109400649A is an application of a flame retardant in an epoxy resin with mass proportions of 0 - 30 phr. The flame retardant was synthesized from thiazolamine or 2-aminobenzothiazole in a mixture with neopentyl glycol-phosphoryl chloride-phosphorus oxychloride.

In CN109721727A The production of a DOPO-poly(aryl ether ketone) flame retardant is described. In the reaction, 4-fluorobenzaldehyde or p-chlorobenzaldehyde and thiazolamine or 2-aminobenzothiazole are reacted in a solvent, preferably dichloromethane. DOPO is then added. In the third reaction step, the DOPO derivative is introduced as a side group into the poly(aryl ether ketone).

Out of CN111253437A A P/N/Si-containing reactive multi-element epoxy resin flame retardant and its two-stage manufacturing process are described. In the first step, 2-aminothiazole or 2-aminoimidazole is reacted with vinyldichlorosilane, yielding vinyldiaminothiazole or vinyldiaminoimidazole. In the second step, DOPO and vinyldiaminothiazole or vinyldiaminoimidazole react to form the P/N/Si-containing flame retardant.

In CN111690171A A flame retardant is produced using the following process. The aminothiazole compound is mixed with triethylenediamine and reacted. An alkenylhalosilane compound is then added, resulting in an intermediate product. In a second reaction step, the intermediate product is reacted with DOPO to form a flame retardant. With 7% by weight of flame retardant in polycarbonate, an oxygen index LOI of up to 35.7% is achieved.

CN113234103A discloses a phosphazene flame retardant. Hexachlorocyclotriphosphazene is reacted with a base and 2-aminothiazole in an organic solvent. In epoxy resins, the flame retardant reaches UL-94 V-1 at a mass fraction of 3% and UL-94 V-0 at more than 5%. The synthesis of phosphazene flame retardants requires bases such as triethylamine, which have a strong odor and pose a risk of chemical burns.

Out of WO 2008/026215 A2 is a process for producing polybrominated compounds characterized by the chemical formula C ₆ Br ₅ -XC ₆ Br ₅ , where X = O or C ₂ H ₄ . In the event of a fire, these compounds lead to the formation of harmful and corrosive gases (e.g. dioxins, hydrogen halides), tend to be released unintentionally and are often harmful to health.

In Jian et al. (2016) Industrial & Engineering Chemistry Research, 55(44), 11520-11527 An aminobenzothiazole-DOPO derivative was incorporated into epoxy resins and the flame retardant effect was investigated. UL-94 V-1 was achieved with 5% additive. With 10% flame retardant, a UL-94 V-0 rating was achieved.

In Jian et al. (2017) Journal of Materials Science, 52(16), 9907-9921 An aminothiazole-DOPO derivative was incorporated into epoxy resins and the flame-retardant effect was investigated. At 5% additive content, UL-94 V-0 was achieved.

In the publication Yang et al. (2020) Royal Society open Science, 7(9), 200800, a nitrogen-containing alkyl phosphinate and its aluminum salt were synthesized. The flame retardant effect in ABS has been tested. With 20% flame retardant, UL-94 V-2 was achieved with an LOI of 24%. A high amount of additive is required for flame retardants that do not have synergistic effects. A large amount of additives significantly affects the mechanical properties of the flame-retardant plastics.

Against the background of the prior art described above, the object of the present invention is to provide thiazole compounds with phosphorus, nitrogen and sulfur, which can be produced in a simple manner, are non-volatile, act as flame retardants even at low mass contents and in many plastics, in particular Thermoplastics can be used.

und

worin

• R₁ = C_1-6-Alkyl oder Phenyl
• R₂ = H oder C_1-6-Alkyl (ein bis zwei Substituenten)
• R₃ = H
• Mⁿ⁺ = Metallionen mit n = 1,2,3
• bedeuten, gelöst.

The task is accomplished by providing thiazole compounds with phosphorus, nitrogen and sulfur, characterized by the chemical formulas

and

wherein

• R ₁ = C _1-6 alkyl or phenyl
• R ₂ = H or C _1-6 alkyl (one to two substituents)
• R ₃ = H
• M ⁿ⁺ = metal ions with n = 1,2,3
• mean solved.

und

According to the invention, the compounds are characterized in that R ₁ is preferably a methyl group, all R ₂ are preferably hydrogen atoms, R ₃ is preferably a hydrogen atom or aluminum cation and a carboxamide structure is present.

and

wobei R₁ C_1-6-Alkyl oder Phenyl bedeutet, bei 20 - 150 °C, bevorzugt bei 30 - 120 °C, besonders bevorzugt bei 50 - 100 °C umgesetzt wird.According to the invention, the compounds can be prepared by a process in which 2-aminothiazole derivatives or 2-aminobenzothiazole derivatives are reacted with a chemical compound of the formula

where R ₁ is C _1-6 -alkyl or phenyl, is reacted at 20 - 150 ° C, preferably at 30 - 120 ° C, particularly preferably at 50 - 100 ° C.

The compounds I and II according to the invention are prepared in a one-step process. The starting materials are mixed together at a temperature of 50 ° C in 1,4-dioxane, with the 2-aminothiazole derivatives or 2-aminobenzothiazole derivatives being slowly added dropwise as a solid or dissolved in 1,4-dioxane. During the reaction the product precipitates as a fine precipitate. After cooling, the compound according to the invention is obtained as a suspension in 1,4-dioxane. It is filtered off and washed several times with ethanol. After drying the compounds I and II according to the invention, a white to beige powder is obtained.

This method has several advantages over the prior art methods. It only uses commercially available starting materials, requires simple experimental setups and takes place in one reaction step. This is advantageous compared to multi-stage syntheses of flame retardants from the field of DOPO derivatives with aminothiazoles or aminobenzothiazoles. Furthermore, no additional reactants, such as catalysts or bases/acids, are required in the process described.

The compounds III according to the invention are prepared using the compounds I and II according to the invention. These are dissolved in water in the presence of a base. After adding the metal ions, compound III precipitates as a fine precipitate. After cooling, the compound III according to the invention is obtained as a suspension in water. It is filtered off and washed several times with water. After drying the compound III according to the invention, a white powder is obtained.

The compounds III according to the invention are obtained as a fine, filterable precipitate. The simple processing is an advantage over complex purification steps, such as the removal of solvents or the removal of by-products such as triethylamine hydrochloride.

The compounds according to the invention can be used as flame retardants or for producing flame retardant compositions. They have further advantages over existing flame retardants. The synergism between phosphorus, nitrogen and sulfur allows a lower percentage of flame retardants in plastics compared to flame retardants that only rely on one mechanism of action.

According to their chemical formulas, the compounds according to the invention are free of halogens. In the event of a fire, no corrosive or toxic hydrogen halides can be released. This is advantageous compared to halogen-containing flame retardants.

The compounds according to the invention can be used to produce flame-retardant plastics or plastic mixtures. Since the compounds according to the invention contain phosphorus, nitrogen and sulfur, they are highly effective in plastics or plastic mixtures even when small proportions by mass are added. This is advantageous over inorganic flame retardants containing aluminum hydroxide or magnesium hydroxide. On the other hand, small amounts of additives, up to 5% by weight, influence the mechanical and optical properties of plastics to a negligible extent.

1. a) 99,9 bis 25,0 Masseprozent eines Kunststoffs oder Kunststoffgemisches,
2. b) 0,1 bis 50,0 Masseprozent einer Verbindung nach mindestens einem der Ansprüche 1 bis 7 und
3. c) 0,0 bis 25,0 Masseprozent eines oder mehrerer Additive oder Füllstoffe, wie z.B., aber nicht ausschließlich Weichmacher, Ruß, Graphit, Talkum, Stärke, Quarz, Zinkoxid, Glasfasern, Kreide und Kieselgur.

enthalten, wobei die Summe der Komponenten immer 100,0 Masseprozent beträgt.A characteristic feature of flame-retardant plastics or plastic mixtures is that they

1. a) 99.9 to 25.0 percent by mass of a plastic or plastic mixture,
2. b) 0.1 to 50.0 percent by mass of a compound according to at least one of claims 1 to 7 and
3. c) 0.0 to 25.0 percent by weight of one or more additives or fillers, such as, but not limited to, plasticizers, carbon black, graphite, talc, starch, quartz, zinc oxide, glass fibers, chalk and diatomaceous earth.

included, whereby the sum of the components is always 100.0 percent by mass.

The flame-retardant plastics or plastic mixtures can be those from the group of thermoplastics.

The flame-retardant thermoplastics can be produced using a kneader. The processing temperature is determined by the thermoplastic selected. For execution, the thermoplastic is melted in the kneader. The flame retardant is added to the melt. After kneading for up to 15 minutes, the mixture is removed and cooled.

The thermoplastics can be those from the group of polyolefins, preferably polypropylene, polyamides, and polyacrylates, preferably polymethyl methacrylate.

What is particularly surprising in this context is the high thermal stability of the compounds according to the invention, whose thermal decomposition in mixtures only takes place above 250 ° C. The compounds according to the invention can therefore also be used as flame retardants for plastics with high processing temperatures, e.g. B. polyamides can be used.

The present invention is illustrated by the following examples.

The following chemicals were used: 2-aminothiazole (Sigma-Aldrich), 2-aminobenzothiazole (Sigma-Aldrich), 2-methyl-1,2-oxaphospholane-5-one-2-oxide (Exolit PE110), ammonium hydrogen carbonate (BASF), Aluminum chloride hexahydrate (Carl-Roth), polyamide-6 (Durethan B35FA, Lanxess), polymethyl methacrylate (Lucryl, BASF), polypropylene (DH789, Braskem).

The following processing techniques were used: A 1 L three-necked flask with a reflux condenser, dropping funnel and gas connection was used to prepare the compounds I, II and III according to the invention. To process the compounds I, II and III according to the invention as flame retardants in plastics, a measuring kneader from Brabender (model 835205) and a plate press from Campana Ing. Benedetto were used.

Analyzes were performed as follows: IR spectra were recorded using a Nicolet™ iS™ 10 from ThermoScientific in ATR mode. TG analyzes were carried out on a Mettler Toledo TGA/SDTA 851 at a heating rate of 10 K min ^-1 in a flowing nitrogen atmosphere (40 mL min ^-1 ). DSC measurements were carried out using a DSC1 STAR system from Mettler Toledo with a heating rate of 10 K min ^-1 in a flowing nitrogen atmosphere (30 mL min ^-1 ).

Fire tests were carried out as follows: For the vertical fire test according to UL-94, 5 samples (125 mm x 13 mm x 1 mm) were flamed on their underside with a propane gas flame (20 mm). The fire time and fire behavior (burning drippings, complete burning) were assessed. To measure the oxygen index (Wazau Instrument) according to DIN EN ISO 4589, samples (80 mm x 100 mm x 1 mm) were flamed on their top side. The oxygen index was determined by increasing or decreasing the oxygen content.

Example 1: Preparation of the compound I according to the invention

In a 1-L flask with a stirrer, 2-methyl-1,2-oxaphospholane-5-one-2-oxide (134.07 g, 1 mol) was dissolved in 1,4-dioxane (400 mL) under protective gas (N ₂ ). Heated to 50 °C. 2-Aminothiazole (100.14 g, 1 mol) was dissolved in 1,4-dioxane (200 mL) and slowly added dropwise. The mixture was stirred at 90 °C for 3 h. A fine precipitate falls out during the reaction. After the reaction mixture had cooled, the solid obtained was filtered off. It was then washed with ethanol (99%). The powder obtained was pre-dried in air and dried in vacuo until a residual moisture content was <1%. A beige powder is obtained with a yield of 90%.

Example 2: Preparation of the compound II according to the invention

In a 1-L flask with a stirrer, 2-methyl-1,2-oxaphospholane-5-one-2-oxide (134.07 g, 1 mol) was dissolved in 1,4-dioxane (400 mL) under protective gas (N ₂ ). Heated to 50 °C. 2-Aminobenzothiazole (150.20 g, 1 mol) suspended in 1,4-dioxane (400 mL) was slowly added dropwise. The mixture was stirred at 90 °C for 3 h. A fine precipitate falls out during the reaction. After the reaction mixture had cooled, it was filtered. The solid was washed with ethanol. The powder was pre-dried in air and dried in vacuo until a residual moisture content was <1%. A white powder was obtained with a yield of 86%.

Example 3: Preparation of the compound III according to the invention

The compound I according to the invention (1.4 g, 6 mmol) was suspended in water (10 mL) in a 50 mL flask. An aqueous solution of ammonium bicarbonate (474 mg, 6 mmol, in 5 mL water) was slowly added dropwise. After the gas formation had ended, the solution was heated to 70 °C. A solution of aluminum chloride hexahydrate (483 mg, 2 mmol) in water (5 mL) was slowly added dropwise to precipitate a white solid. The mixture was stirred at 90 °C for 60 minutes. The solid was filtered off and washed with warm water. Drying took place in a vacuum at 120 °C. The yield of the white powder was 93%.

Example 4: Application of the compound I according to the invention as a flame retardant for polypropylene

In a Brabender W 50 EHT laboratory kneader, 38.0 g or 36.0 g of polypropylene (DH789, Braskem) were melted at 200 ° C, mixed with 2.0 g or 4.0 g of flame retardant I and left for approx. 8 min knead tet. The mixtures were removed and pressed into a plate at 200 °C for approx. 5 min. The polypropylene samples produced contained flame retardant I in 5% by weight and 10% by weight.

Example 5: Application of the compound I according to the invention as a flame retardant for polyamide-6

In a Brabender W 50 EHT laboratory kneader, 38.0 g or 36.0 g of polyamide-6 (Durethan B35FA, Lanxess) were melted at 230 ° C, mixed with 2.0 g or 4.0 g of flame retardant I and left for approx .Kneaded for 5 minutes. The mixtures were removed and pressed into a plate at 250 °C for approx. 5 min. The polyamide samples produced contained flame retardant I in 5% by weight and 10% by weight.

Example 6: Use of a compound I according to the invention as a flame retardant for polymethyl methacrylate

In a Brabender W 50 EHT laboratory kneader, 38.0 g or 36.0 g of polymethyl methacrylate (Lucryl, BASF) were melted at 170 ° C, mixed with 2.0 g or 4.0 g of flame retardant I and left for approx. 8 min kneaded. The mixtures were removed and each pressed into a plate at 170 °C for about 5 minutes. The polymethyl methacrylate samples produced contained flame retardant I in 5% by weight and 10% by weight.

Example 7: Application of the compound II according to the invention as a flame retardant for polypropylene

In a Brabender W 50 EHT laboratory kneader, 38.0 g or 36.0 g of polypropylene (DH789, Braskem) were melted at 200 ° C, mixed with 2.0 g or 4.0 g of flame retardant II and left for approx. 15 min kneaded. The mixtures were removed and each pressed into a plate at 200 °C for about 5 minutes. The polypropylene samples produced contained flame retardant II in 5% by weight and 10% by weight.

Example 8: Application of the compound II according to the invention as a flame retardant for polyamide-6

In a Brabender W 50 EHT laboratory kneader, 38.0 g or 36.0 g of polyamide-6 (Durethan B35FA, Lanxess) were melted at 230 ° C, mixed with 2.0 g or 4.0 g of flame retardant II and left for approx .Kneaded for 12 minutes. The mixtures were removed and pressed into a plate at 250 °C for approx. 5 min. The polyamide samples produced contained flame retardant II in 5% by weight and 10% by weight.

Example 9: Application of the compound II according to the invention as a flame retardant for polymethyl methacrylate

In a Brabender W 50 EHT laboratory kneader, 38.0 g or 36.0 g of polymethyl methacrylate (Lucryl, BASF) were melted at 170 ° C, mixed with 2.0 g or 4.0 g of flame retardant II and left for approx. 8 min kneaded. The mixtures were removed and each pressed into a plate at 170 °C for approx. 5 min. The polymethyl methacrylate samples produced contained the flame retardant II in 5% by weight and 10% by weight.

Example 10: Application of the compound III according to the invention as a flame retardant for polyamide-6

In a Brabender W 50 EHT laboratory kneader, 38.0 g or 36.0 g of polyamide-6 (Durethan B35FA, Lanxess) were melted at 230 ° C, mixed with 2.0 g or 4.0 g of flame retardant III and left for approx .Kneaded for 12 minutes. The mixtures were removed and pressed into a plate at 250 °C for approx. 5 min. The polyamide samples produced contained flame retardant III in 5% by weight and 10% by weight.

The results from Examples 1 to 10 are listed in Table 1. Table 1: Properties of flame-retardant plastics. Plastic_FSM Example Mass fraction of flame retardant [%] Result of the vertical fire test according to UL-94 LOI [%] Fire time [s] classification Polypropylene 0 Burned down No 17 ^a Polyamide-6 0 >150 No 24 ^a Polymethyl methacrylate 0 Burned down No 17 ^a Polypropylene_I 4 5 56 V-2 21 Polypropylene_I 4 10 28 V-2 22 Polyamide-6_I 5 5 4 V-0 29 Polyamide-6_I 5 10 0 V-0 40 Polymethyl methacrylate_I 6 5 Burned down No 21 Polymethyl methacrylate_I 6 10 41 V-2 22 Polypropylene_II 7 5 49 V-2 20 Polypropylene_II 7 10 29 V-2 22 Polyamide-6_II 8th 5 7 V-2 29 Polyamide-6_II 8th 10 0 V-0 31 Polymethyl methacrylate_I 9 5 Burned down No 20 Polymethyl methacrylate_I 9 10 53 V-2 21 Polyamide-6_III 10 5 Burned down No 24 Polyamide-6_III 10 10 22 V-2 26
Notes: UL-94: Underwriters Laboratories: “Tests for Flammability of Plastic Materials for Parts in Devices and Appliances”, LOI: Limiting Oxygen Index, measured according to DIN EN ISO 4589 . ^a) Literature values for LOI from: Reis Bernardes, Felipe, et al. Polymers 11.12 (2019): 2110.; Liu, Ke, et al. RSC advances 8.17 (2018): 9261-9271 .; Ebdon, John R., et al. Polymer Degradation and Stability 69.3 (2000): 267-277.)

Claims (4)

Thiazole compounds containing phosphorus, nitrogen and sulfur, characterized by the chemical formula

and

where R ₁ = C _1-6 alkyl or phenyl R ₂ = H or C _1-6 alkyl (one to two substituents) R ₃ = H M ⁿ⁺ = metal ions with n = 1,2,3. Connections to Claim 1 , characterized in that R ₁ represents a methyl group, R ₂ represents hydrogen atoms and R ₃ represents a hydrogen atom and there is a carboxamide structure. Connections to Claim 1 , characterized in that R ₁ represents a methyl group, R ₂ represents hydrogen atoms, M ⁿ⁺ represents an aluminum cation and a carboxamide structure is present. Use of compounds according to at least one of the Claims 1 until 3 as a flame retardant or for the production of flame retardant compositions.