Synthetic method for preparing trifluoromethyl TDI (toluene diisocynate) by one-step method

Abstract

The invention discloses a synthetic method for preparing trifluoromethyl TDI (toluene diisocynate) by a one-step method, which adopts trifluoromethyl DNT (dinitrotoluene) as a reaction raw material, utilizes a one-step metal catalytic reaction, and obtains the trifluoromethyl TDI through recrystallization and distillation separation. The method is easy to operate, economical and environmentally friendly, and the prepared isocyanate can be applied to the fields of macromolecules, polyurethane, propellants and the like.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis and polymers, and relates to a one-step method for preparing trifluoromethyl TDI. Background Art

[0002] Polyurethane (PU) is a general term for polymers with urethane binding groups. It is formed by the chemical reaction of isocyanate groups and compounds with active hydrogen such as hydroxyl groups. It was produced by Bayer and others in 1937. Polyurethane mainly includes two major categories: polyester type and polyether type. It can be made into polyurethane plastics (mainly foam plastics), polyurethane fibers (spandex), polyurethane rubbers and elastomers. Polyurethane appeared in the 1930s. After nearly 80 years of technological development, it has been widely used in defense, aerospace, light industry, chemical industry, petroleum, textiles, transportation, automobiles, medical and other fields. Polyurethane has both the elasticity of rubber and the strength and excellent processing properties of plastics. It has advantages that other synthetic materials cannot match in terms of heat insulation, sound insulation, wear resistance, oil resistance, elasticity, etc. It is the sixth largest plastic after polyethylene, polyvinyl chloride, polypropylene, polystyrene and polyacrylonitrile-butadiene-styrene resin (ABS), and has become an indispensable emerging material for economic development and people's lives.

[0003] Toluene diisocyanate (TDI) is internationally recognized as a fine chemical product with "two major and one high", that is, large engineering investment, difficult production control, and high technical content. TDI has two isomers, 2,4-toluene diisocyanate and 2,6-toluene diisocyanate. Most of the products are mixtures of the two isomers, which can form three TDI varieties, namely TDI-65 / 35 (TDI-65), TDI-80 / 20 (TDI-80) and TDI-100. The first domestic TDI unit was put into production in 1958, and the research and development of isocyanates began. By 1988, the national annual production capacity was only 1,600 tons. With the rapid development of the polyurethane industry, the demand for TDI has continued to grow, promoting the transformation and rapid maturity of the TDI industry, reaching 1.19 million tons by 2019, and is widely used in automobiles, aerospace, electronics and other fields.

[0004] At present, isocyanate is an important organic synthesis intermediate that can undergo nucleophilic addition reactions, such as substituted urea herbicides, sulfonylureas and thioureas. The main synthesis methods include trichloromethyl carbonate non-phosgene method, oxalyl chloride method, sodium azide method, lead tetraacetate method, etc.

[0005] In the field of raw materials for chemical production, TDI is an important organic compound, widely used in polyurethane foam, coatings, elastomers and adhesives. The industrial methods for manufacturing TDI mainly include phosgenation, nitration and carbodiimide method. A large amount of by-products and waste will be produced during the phosgenation process, causing certain pollution to the environment. A large amount of acidic wastewater and waste gas will be produced during the nitration process, causing great pollution to the environment. The activity of the catalyst in the carbodiimide method has a great influence on the reaction, and the reaction conditions need to be strictly controlled.

[0006] In summary, there are many methods for preparing TDI, but they all involve multi-step reactions, mainly including nitration, reduction and phosgenation reactions, involving many steps, complex and toxic raw materials, so it is particularly necessary to develop an economical and efficient synthesis method. In addition, TDI is limited in further application due to its shortcomings such as single category and easy yellowing. Therefore, it is of great significance to use new methods to synthesize new TDI series compounds to make up for the defects of TDI. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a one-step method for preparing trifluoromethyl TDI, so as to solve the technical problems such as few TDI derivatives, complex synthesis reaction steps, poor environmental protection, high risk, limited product performance, and narrow application scenarios.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0009] A one-step method for preparing trifluoromethyl TDI, wherein trifluoromethyl DNT is used as a reaction raw material, and under the action of a transition metal catalyst and a ligand, the reaction is carried out in one step with an isocyanate raw material, and the trifluoromethyl TDI is obtained by recrystallization and distillation.

[0010] The present invention also includes the following technical features:

[0011] Specifically, the method comprises the following steps: under nitrogen protection, adding trifluoromethyl DNT, isocyanate raw materials, transition metal catalysts, ligands and base into a reaction container, evacuating and filling with nitrogen three times; adding solvent by using a syringe, heating in an oil bath, cooling to room temperature after reaction, monitoring by TLC, filtering and obtaining TDI product by distillation and separation.

[0012] Specifically, the transition metal catalyst is any one of Pd(acac)2, Pd(OAc)2, Pd2(dba)3, Pd(TFA)2, Pd2(allyl)2Cl2, Ni(COD)2, and NiCl2(PCy3)2.

[0013] Specifically, the ligand is any one of BrettPhos, IPr, IMes, SIMes, XPhos, RuPhos, DPPF, PCy3, and BINAP.

[0014] Specifically, the isocyanate raw material is one of NaOCN, KOCN, AgOCN, and NH4OCN.

[0015] Specifically, the solvent is any one of toluene, xylene, dioxane, and trifluorotoluene.

[0016] Specifically, the base is any one of potassium tert-butoxide, lithium tert-butoxide, sodium ethoxide, anhydrous potassium phosphate, potassium carbonate, cesium carbonate, potassium acetate, potassium pivalate, and cesium fluoride.

[0017] Specifically, the reaction temperature is 80-150° C. and the reaction time is 12-48 hours.

[0018] Specifically, the mass ratio of the isocyanate raw material, the catalyst and the ligand is 1:(0.01-0.5):(0.01-0.8).

[0019] Compared with the prior art, the present invention has the following technical effects:

[0020] The method of the invention proposes a one-step method for preparing trifluoromethyl TDI for the first time, and the reaction steps are simple, the raw materials are non-toxic and harmless, the sources are wide, the economy is environmentally friendly, and the safety is high.

[0021] The method of the present invention is the first to carry out trifluoromethylation of TDI, expanding the types of TDI-based isocyanate materials. The material properties are greatly improved in terms of chemical stability, surface free energy, friction coefficient, refractive index, dielectric constant and power consumption factor through fluorine atom substitution, laying a material foundation for material application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The following is the H NMR spectrum of trifluoromethyl TDI prepared in Example.

[0023] Figure 2 The carbon NMR spectrum of trifluoromethyl TDI prepared in Example.

[0024] Figure 3 The figure is the NMR fluorine spectrum of trifluoromethyl TDI prepared in Example. DETAILED DESCRIPTION

[0025] The present invention provides a one-step method for preparing trifluoromethyl TDI. The method uses trifluoromethyl DNT as a reaction raw material, utilizes a one-step metal catalytic reaction, and obtains trifluoromethyl TDI through recrystallization and distillation separation, thereby solving the problems of few TDI derivatives, complex synthesis reaction steps, poor environmental protection, high risk, limited product performance, and narrow application scenarios. Among them, the metal catalysis uses a transition metal catalyst, and the transition metal-catalyzed coupling reaction is one of the most effective and most commonly used synthesis methods for constructing carbon-carbon (hetero) bonds; the traditional coupling reaction usually uses (quasi) halogenated aromatic hydrocarbons as electrophilic coupling components, and undergoes multiple coupling reactions with metal reagents, nucleophilic reagents, olefins or alkynes to construct multiple carbon-carbon or carbon-hetero bonds; aryl diazonium salts, aryl hydrazines, aromatic carboxylic acids and aromatic sulfinic acids are also used as electrophilic coupling components to participate in multiple coupling reactions; although the above-mentioned electrophilic coupling components have been widely used in coupling reactions, it is very meaningful for the present invention to expand more efficient, inexpensive and easily available electrophilic components. Aromatic nitro compounds are important raw materials for the preparation of aromatic compounds. They are widely available and cheap. At the same time, they are also precursors of energetic compounds and can be used as new electrophiles to replace halogenated aromatics. In addition, fluorine atoms have strong electronegativity, high CF bond energy (540kJ / mol), the smallest van der Waals radius except for hydrogen, and the shielding and protective effect of fluorine on the carbon chain, which endow fluorinated polymers with excellent thermal stability, weather resistance and chemical inertness, as well as unique properties such as low surface free energy, low friction coefficient, low refractive index, low dielectric constant and low power consumption factor. In addition, the low surface energy and low friction coefficient of fluorinated polymers make them have outstanding hydrophobic and anti-adhesive properties. Introducing fluorinated groups into polyurethane can combine the excellent mechanical properties and two-phase microstructure characteristics of polyurethane, and can greatly improve the surface properties and overall properties of polyurethane. This is mainly because ① due to the special nature of the CF bond, it will affect the physical and chemical properties of organic molecules; ② the C-F bond strength is high, so the metabolism of the fluorinated active site is inhibited; ③ the strong electron absorption of fluorine will greatly affect the properties of other functional groups in the molecule. Therefore, it is particularly important to develop a one-step method for preparing trifluoromethyl TDI using transition metal catalysis in the present invention.

[0026] The method of the present invention uses trifluoromethyl DNT as a reaction raw material, and reacts with an isocyanate raw material under certain conditions in a one-step reaction under the action of a transition metal catalyst and a ligand, and obtains trifluoromethyl TDI by recrystallization and distillation. The reaction equation is:

[0027]

[0028] Specifically, the process comprises the following steps: under nitrogen protection, adding trifluoromethyl DNT, isocyanate raw materials, transition metal catalysts, ligands and base into a reaction container, evacuating and filling with nitrogen three times; adding solvent by means of a syringe, heating in an oil bath, cooling to room temperature after reaction, monitoring by TLC, filtering and obtaining a TDI product by distillation and separation.

[0029] The transition metal catalyst is any one of Pd(acac)2, Pd(OAc)2, Pd2(dba)3, Pd(TFA)2, Pd2(allyl)2Cl2, Ni(COD)2, and NiCl2(PCy3)2.

[0030] The ligand is any one of BrettPhos, IPr, IMes, SIMes, XPhos, RuPhos, DPPF, PCy3, and BINAP.

[0031] The isocyanate-based raw material is one of NaOCN, KOCN, AgOCN, and NH4OCN.

[0032] The solvent is any one of toluene, xylene, dioxane, and trifluorotoluene.

[0033] The base is any one of potassium tert-butoxide, lithium tert-butoxide, sodium ethoxide, anhydrous potassium phosphate, potassium carbonate, cesium carbonate, potassium acetate, potassium pivalate, and cesium fluoride.

[0034] The reaction temperature is 80-150°C and the reaction time is 12-48 hours.

[0035] The mass ratio of the isocyanate raw material, the catalyst and the ligand is 1:(0.01-0.5):(0.01-0.8).

[0036] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0037] Embodiment 1:

[0038] The present embodiment provides a one-step method for preparing trifluoromethyl TDI. Under nitrogen protection, 0.5 mmol trifluoromethyl DNT, 2 mmol NaOCN, 10 mol% Pd2(allyl)2Cl2, 25 mol% RuPhos, and 1.5 mmol potassium acetate are added, and the mixture is evacuated and filled with nitrogen three times; 3 mL of dioxane is added by a syringe, and the oil bath is heated to 150° C. and reacted for 24 hours; the mixture is cooled to room temperature, monitored by TLC, filtered, and separated by distillation to obtain a light yellow solid with a yield of 45%.

[0039] Embodiment 2:

[0040] Under nitrogen protection, add 0.5mmol trifluoromethyl DNT, 2mmol KOCN, 10mol% Ni(COD)2, 40mol% SIMes, 1.5mmol potassium phosphate, evacuate and fill with nitrogen three times; add 3mL trifluorotoluene via a syringe, heat to 150°C in an oil bath, and react for 24h; cool to room temperature, monitor by TLC, filter, and separate by distillation to obtain a light yellow solid with a yield of 30%.

[0041] Embodiment 3:

[0042] Under nitrogen protection, 0.5mmol trifluoromethyl DNT, 2mmol AgOCN, 10mol% Pd2(dba)3, 35mol% BrettPhos, and 1.5mmol cesium fluoride were added, and the mixture was evacuated and filled with nitrogen three times; 3mL dioxane was added using a syringe, and the oil bath was heated to 140°C and reacted for 24h; the mixture was cooled to room temperature, monitored by TLC, filtered, and separated by distillation to obtain a light yellow solid with a yield of 40%.

[0043] Figure 1 The NMR hydrogen spectrum of trifluoromethyl TDI prepared in Example is as follows: Figure 2 The NMR carbon spectrum of trifluoromethyl TDI prepared in Example, Figure 3 This is the NMR fluorine spectrum of trifluoromethyl TDI prepared in Example; it can be seen from the figure that the synthesized compound has a correct structure and good purity.

[0044] Based on the structural determination, trifluoromethyl TDI and TDI were tested for stability. The same mass of trifluoromethyl TDI and TDI were placed in an oven with a humidity of 50% and kept at 40°C for 24 hours. The samples were taken out for weighing and nuclear magnetic resonance analysis. The loss of trifluoromethyl TDI was 20%, while the loss of TDI was nearly 95%.

[0045] The polyurethane material was prepared by curing with terminal hydroxyl polybutadiene (HTPB) and trifluoromethyl TDI and TDI. The mechanical properties were tested according to GB / T528-2009. The operation method and test results are as follows:

[0046] Add 15g HTPB, 1.21g trifluoromethyl TDI and 10mL dichloromethane or tetrahydrofuran or ethyl acetate to a 100mL beaker for dissolution, add 0.0015g dibutyltin dilaurate or dimethylcyclohexylamine or triphenylbismuth, stir for 15min, vacuum to remove solvent and bubbles, pour the reactants into a polytetrafluoroethylene mold, vacuum exhaust for 30min, and then cure in a 70℃ oven for 3 days. After demolding, use a cutter to cut dumbbell-shaped specimens for mechanical property testing according to GB / T 528-2009. The measured tensile strength is 1.70234MPa and the elongation at break is 602.658%.

[0047] Add 15g HTPB, 0.87g TDI and 10mL dichloromethane or tetrahydrofuran or ethyl acetate to a 100mL beaker for dissolution, add 0.0015g dibutyltin dilaurate or dimethylcyclohexylamine or triphenylbismuth, stir for 15min, vacuum to remove solvent and bubbles, pour the reactants into a polytetrafluoroethylene mold, vacuum exhaust for 30min, and then cure in a 70℃ oven for 3 days. After demolding, use a cutter to cut dumbbell-shaped specimens for mechanical property testing according to GB / T 528-2009. The measured tensile strength is 1.31879MPa and the elongation at break is 323.940%.

Claims

1. A one-step method for preparing trifluoromethyl TDI, characterized in that: The method uses trifluoromethyl DNT as a reaction raw material, and reacts it with an isocyanate raw material in a one-step manner under the action of a transition metal catalyst and a ligand, and obtains trifluoromethyl TDI by recrystallization and distillation.

2. The one-step method for preparing trifluoromethyl TDI according to claim 1, characterized in that: The method comprises the following steps: under nitrogen protection, adding trifluoromethyl DNT, isocyanate raw materials, transition metal catalysts, ligands and base into a reaction container, evacuating and filling with nitrogen three times; adding solvent by using a syringe, heating in an oil bath, cooling to room temperature after reaction, monitoring by TLC, filtering and obtaining a TDI product by distillation and separation.

3. The one-step method for preparing trifluoromethyl TDI as claimed in claim 2, characterized in that: The transition metal catalyst is any one of Pd(acac)2, Pd(OAc)2, Pd2(dba)3, Pd(TFA)2, Pd2(allyl)2Cl2, Ni(COD)2, and NiCl2(PCy3)2.

4. The one-step method for preparing trifluoromethyl TDI as claimed in claim 2, characterized in that: The ligand is any one of BrettPhos, IPr, IMes, SIMes, XPhos, RuPhos, DPPF, PCy3, and BINAP.

5. The one-step method for preparing trifluoromethyl TDI as claimed in claim 2, characterized in that: The isocyanate raw material is one of NaOCN, KOCN, AgOCN and NH4OCN.

6. The one-step method for preparing trifluoromethyl TDI according to claim 2, characterized in that: The solvent is any one of toluene, xylene, dioxane and trifluorotoluene.

7. The one-step method for preparing trifluoromethyl TDI according to claim 2, characterized in that: The base is any one of potassium tert-butoxide, lithium tert-butoxide, sodium ethoxide, anhydrous potassium phosphate, potassium carbonate, cesium carbonate, potassium acetate, potassium pivalate, and cesium fluoride.

8. The one-step method for preparing trifluoromethyl TDI according to claim 2, characterized in that: The reaction temperature is 80-150°C and the reaction time is 12-48 hours.

9. The one-step method for preparing trifluoromethyl TDI according to claim 1, characterized in that: The mass ratio of the isocyanate raw material, the catalyst and the ligand is 1:(0.01-0.5):(0.01-0.8).

Images