A method for preparing diisothiocyanate

Abstract

The invention discloses a method for preparing diisothiocyanate, comprising the following steps: adding elemental sulfur and diisobutylaluminum hydride to an organic solvent, heating for reaction; and then adding diisocyanate for heating for reaction to obtain the product diisothiocyanate. The preparation method of the invention is simple and easy to implement, and the raw materials are easily available. Starting from elemental sulfur, diisobutylaluminum hydride ( i Bu2AlH2) was used as a reducing agent to directly replace the oxygen atom of diisocyanate (O=C=N‑R‑N=C=O) with a sulfur atom, and diisothiocyanate (S=C=N‑R‑N=C=S) was prepared by a simple "one-pot method" with a product yield of more than 75%.

Description

Technical Field

[0001] The invention relates to a method for preparing a compound, in particular to a method for preparing diisothiocyanate. Background Art

[0002] Diisothiocyanate is the basic raw material for preparing polythiourea. As a new type of sulfur-containing functional polymer material, polythiourea has received widespread attention. Since polythiourea has excellent dielectric properties and high refractive index performance, the thiourea group can also produce coordination with heavy metal ions to enable it to adsorb heavy metal ions. In addition, the reorganization of the covalent bonds of polythiourea and the hydrogen bonding effect can achieve self-healing. Therefore, polythiourea has great application potential in dielectric materials, high refractive materials, metal coordination materials and self-healing materials. Patent CN110922618B reports a method for preparing an insulating medium by reacting p-phenylene diisothiocyanate with diamine to prepare polythiourea, and then forming a copolymer with polyamic acid to improve the energy storage density. Patent CN110372978B uses p-phenylene diisothiocyanate and 4,4'-diaminodiphenylmethane to react in N-methylpyrrolidone to prepare an N-methylpyrrolidone solution of a linear high molecular weight polymer polythiourea, which is then mixed with an N-methylpyrrolidone solvent solution of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) and formed into a film on a quartz glass substrate using a solution casting method, thereby effectively improving the stability and dielectric properties of the organic composite dielectric film.

[0003] Polythiourea can be obtained by polymerization reaction of diisothiocyanate and organic diamine in solvent. At present, the synthesis methods of isothiocyanate mainly include: thiophosgene method, phenyl chlorothioformate method, substituted thiourea method, carbon disulfide method, etc. In the prior art, a one-pot synthesis of isothiocyanate [J]. Applied Chemistry, 2019, 36(8):5. A one-pot synthesis method of isothiocyanate is disclosed, which uses N,N-ethylethylamine (Et 3 N) is a base, toluene is a solvent, primary amine and CS 2 As raw material, tert-butyl carbonate diethyl phosphate (3) as desulfurization reagent, in n (primary amine): n (CS 2 ):n(Et 3 N):n(3)=1:1.1:3.3:1.1, the reaction temperature of the dithioformate synthesis stage is room temperature, and the desulfurization reaction stage is -5℃ to room temperature. A series of alkyl, aryl and bifunctional isothiocyanate compounds were synthesized under the experimental conditions. The preparation process is relatively complicated. Moreover, the preparation method of one isothiocyanate N=C=S in one molecule cannot be directly used for diisothiocyanate (two N=C=S exist in one molecule at the same time). The development and application of polythiourea materials urgently need to develop the preparation method of diisothiocyanate. Summary of the invention

[0004] Purpose of the invention: The present invention aims to provide a simple method for preparing diisothiocyanates in one pot.

[0005] Technical solution: The method for preparing diisothiocyanate of the present invention is based on the principle of using diisobutylaluminum hydride ( i Bu 2 AlH) has a strong reducing property, reducing elemental sulfur to negative divalent sulfur (S 2- ), the Al-S bond energy is relatively high (373 kJ / mol), aluminum and sulfur have a strong affinity, and sulfur-aluminum bonds are easily formed, forming unstable active intermediates [ i Bu 2 AlSH], and then react with diisocyanate. Since aluminum has a stronger affinity with oxygen (Al-O bond energy 512 kJ / mol), the oxygen atom of diisocyanate (O=C=NRN=C=O) is replaced by a sulfur atom, and diisothiocyanate (S=C=NRN=C=S) is prepared by a "one-pot method". The preparation method includes: adding elemental sulfur and diisobutylaluminum hydride to an organic solvent, heating to react; then adding diisocyanate to heat to react, and obtaining the product diisothiocyanate; the reaction equation is:

[0006] 2S+2 i Bu 2 AlH→2[ i Bu 2 AlSH]

[0007] 2[ i Bu 2 AlSH]+O=C=NRN=C=O→S=C=NRN=C=S+2[ i Bu 2 AlOH]

[0008] By-products i Bu 2 AlOH, due to the strong affinity between aluminum atoms and oxygen atoms, forms a complex substance and is removed in the chromatography stage. R is a phenyl or alkyl group.

[0009] Furthermore, the temperature for the heating reaction of elemental sulfur and diisobutylaluminum hydride is 120-130° C., the heating reaction time is 1-2 hours, the molar ratio of elemental sulfur, diisobutylaluminum hydride and diisocyanate is 2:2-2.2:1-1.1, and the organic solvent is toluene.

[0010] Furthermore, before the reaction starts, the reactor is replaced with nitrogen to remove air and moisture. After heating and reacting elemental sulfur and diisobutylaluminum hydride, the mixture is cooled to room temperature and then diisocyanate is added to react. After adding diisocyanate, the reaction is continued at 60-70° C. for 3-5 hours. After the reaction is completed, the materials in the reactor are transferred to a chromatography column and chromatographic separation is performed using n-hexane as a solvent. The yield of the product is higher than 75%.

[0011] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the method is simple and easy to implement, the raw materials are easily available, starting from elemental sulfur, diisobutylaluminum hydride ( i Bu 2 AlH) is used as a reducing agent to directly replace the oxygen atom of diisocyanate (O=C=NRN=C=O) with a sulfur atom, and diisothiocyanate (S=C=NRN=C=S) is prepared by a simple "one-pot method", with a product yield of more than 75%. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is the infrared spectrum of the product of Example 1;

[0013] Figure 2 is the H NMR spectrum of the product of Example 1;

[0014] Figure 3 is the infrared spectrum of the product of Example 2;

[0015] Figure 4 This is the H NMR spectrum of the product of Example 2. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0017] Example 1

[0018] Aromatic diisothiocyanate: p-phenylene diisothiocyanate (S=C=NC 6 H 4 -N=C=S), the steps are as follows:

[0019] The reactor was replaced with nitrogen to remove air and moisture; 1.5 mol of elemental sulfur (48.1 g) and diisobutylaluminum hydride (1 L of toluene solution, 1.5 mol) were added in sequence, heated to 120-130°C, reacted for 1 hour, and cooled to room temperature; 122 g (0.76 mol) of p-phenylene diisocyanate was added, and the reaction was carried out at 60-70°C for 3 hours; the reaction was concentrated under reduced pressure, the solvent was recovered (reused), and the material in the reactor was kept fluid, and the material in the reactor was transferred to a chromatography column, and chromatographic separation was performed using n-hexane as the solvent.

[0020] The solid was collected and concentrated to obtain 129 g (yield 89%) of p-phenylene diisothiocyanate, and the recovered solvent was used next time.

[0021] Test melting point mp129.6℃, infrared spectrum, nuclear magnetic resonance (see Figure 2 ), elemental analysis.

[0022] like Figure 1 As shown in the infrared spectrum, 2067cm -1 、2139cm -1 and 2189cm -1 It is the characteristic absorption peak of N=C=S. Elemental analysis (C 8 H 4 N 2 S 2 , molecular weight 192.26), the measured results are consistent with the theoretical calculations.

[0023] element C，％ H，％ N，％ S，％ Theoretical calculations 49.97 2.1 14.57 33.36 Test results 50.42 2.11 14.80 33.47

[0024] Example 2

[0025] Aliphatic diisothiocyanate: 1,4-butane diisothiocyanate (S=C=N-CH 2 CH 2 CH 2 CH 2 -N=C=S)

[0026] The reactor was replaced with nitrogen to remove air and moisture; 1.5 mol of elemental sulfur (48.1 g) and diisobutylaluminum hydride (1 L of toluene solution, 1.5 mol) were added in sequence, heated to 120-130°C, reacted for 2 hours, and cooled to room temperature; 112 g (0.8 mol) of 1,4-butane diisocyanate was added, reacted at 60-70°C for 3 hours, concentrated under reduced pressure, and the solvent was recovered (reused) to maintain the fluidity of the materials in the reactor. The materials in the reactor were transferred to a chromatography column and chromatographically separated using n-hexane as the solvent.

[0027] The resulting solution was collected and concentrated to obtain 103 g (yield 79.7%) of 1,4-butane diisothiocyanate in liquid form (solidified at low temperature, melting point mp 32°C). The recovered solvent was used next time.

[0028] Test infrared spectrum, nuclear magnetic resonance (see Figure 4 ), elemental analysis.

[0029] like Figure 3 As shown, infrared spectrum, 2120cm -1 and 2190cm -1 It is the characteristic absorption peak of N=C=S. Elemental analysis (C 6 H 8 N 2S 2 , molecular weight 172.27), the measured results are consistent with the theoretical calculations.

[0030] element C，％ H，％ N，％ S，％ Theoretical calculations 41.83 4.68 16.26 37.23 Test results 41.10 4.27 16.37 37.71

Claims

1. A method for preparing diisothiocyanate, characterized in that: The steps include: Adding elemental sulfur and diisobutylaluminum hydride to an organic solvent for heating reaction, the heating reaction temperature is 120-130° C., and the heating reaction time is 1-2 hours; cooling to room temperature after the heating reaction, adding diisocyanate and reacting at 60-70° C. for 3-5 hours to obtain a product diisothiocyanate; the molar ratio of elemental sulfur, diisobutylaluminum hydride and diisocyanate is 2:2-2.2:1-1.1; The reaction formula is as follows: , , R is phenyl or butyl.

2. The method for preparing diisothiocyanate according to claim 1, characterized in that: The organic solvent is toluene.

3. The method for preparing diisothiocyanate according to claim 1, characterized in that: Before the reaction started, the reactor was purged with nitrogen to remove air and moisture.

4. The method for preparing diisothiocyanate according to claim 1, characterized in that: After the reaction was completed, the materials in the reactor were transferred to a chromatography column and chromatographic separation was performed using n-hexane as a solvent.

5. The method for preparing diisothiocyanate according to claim 1, characterized in that: The yield of the product was higher than 75%.

Images