Method for catalytic synthesis of symmetrical dialkyl disulfide

Abstract

The present invention belongs to the field of preparation methods of aliphatic disulfides, and particularly relates to a method for catalytic synthesis of symmetrical dialkyl disulfides, which is implemented according to the following steps: (1) Place a magnetic stirrer bar, measured thiol, sulfur, and an organic superbase catalyst into a reaction flask; (2) Place the reaction flask in an oil bath of a magnetic heating stirrer, install a condenser, and connect the condenser to a drainage bottle through a silicone rubber tube. A saturated aqueous solution of H<subgt;2< / subgt;S is pre-added to the drainage bottle; (3) Start heating and begin stirring the reaction, start timing, and determine the amount of H<subgt;2< / subgt;S released and the reaction termination time by the drainage method to obtain the target product. The reaction conditions of the present invention are mild, the reaction rate is fast, the atomic utilization rate and the yield are high, and the by-product H<subgt;2< / subgt;S gas is easily separated and utilized.

Description

Technical Field

[0001] The invention belongs to the field of preparation methods of aliphatic disulfides, and in particular relates to a method for catalytically synthesizing symmetrical dialkyl disulfides. Background Art

[0002] Compounds containing sulfur-sulfur (SS) bonds, commonly known as disulfides or disulfanes, are among the most valuable functional groups in organic synthetic chemistry and represent an important class of organosulfur compounds. Disulfides are widely present in nature and exhibit significant biological activities. Furthermore, synthetic disulfides have found widespread application as synthetic intermediates in various organic transformations, flavors and fragrances, biochemistry, pharmacology, industrial polymers, and peptide mimetics. Because thiols are commercially available or easily synthesized materials, and their use as starting materials for the synthesis of organosulfur compounds has been widely reported, the oxidative coupling of thiols is the best and simplest route to prepare disulfide compounds.

[0003] The oxidative coupling of alkyl thiols using inorganic or organic oxidants has a good effect. These oxidants generate an equal amount of reduced products after the oxidative coupling reaction. If they cannot be effectively recycled or the treatment cost is high, they can only become waste. Therefore, these oxidants are called stoichiometric oxidants. Despite this, people continue to be interested in developing new, highly selective and efficient oxidants for RSH oxidative coupling. Both aromatic thiols and alkyl thiols have good applicability and are particularly suitable for the preparation of commercially unavailable disulfides such as dibutyl disulfide and dioctyl disulfide. These stoichiometric oxidants include: KMnO4, 4,4'-azopyridine, N-fluorobisbenzenesulfonamide, hexachlorotriphosphazene, diacetyloxyiodobenzene, tribromoacetophenone, dimethyl sulfoxide / hydrohalic acid, urea peroxide, 1,2-dioxetane compounds, ICl2 - Anionic ionic liquids, CCl4, (Me)2SO / [(Me)3Si]2NH, graphene oxide and bromotrichloromethane.

[0004] Molecular oxygen or molecular air is an ideal oxidant that is highly atom-economical, environmentally friendly, cheap, and readily available, and can minimize the generation of harmful substances (Reaction Formula I).

[0005]

[0006] Although molecular oxygen is theoretically an ideal oxidant for the oxidative coupling of thiols, its oxidative performance towards alkyl thiols is generally poor in practice. Catalytic or non-catalytic oxidative coupling methods of thiols with air oxygen are currently only applicable to laboratory synthesis, and the synthesis scale is limited to 1 mmol to 10 mmol. If RSSR is prepared on a large scale, there will be problems of insufficient oxygen supply or extremely long reaction times. If air or pure oxygen is in excess, especially under pressure, there is a risk of explosion. The selectivity, conversion rate and rate of the thiol oxidative coupling reaction are greatly related to the solvent type, temperature and nano-catalyst. From the perspective of the reaction mechanism, aryl sulfur radicals ArS· are easier to generate than alkyl sulfur radicals RS·. Therefore, the yield of R2S2 formed by radical dimerization is relatively low.

[0007] Molecular oxygen O2 and elemental sulfur (S8, cyclooctasulfur) both belong to Group VIA chalcogens. Therefore, using S8 as an oxidant for the oxidative coupling of RSH is another alternative method (Reaction II). Although thiols can be easily oxidized to disulfides using elemental sulfur and a base catalyst, a major problem with this method is that a large amount of trisulfides and other polysulfides are also produced. Therefore, choosing suitable catalysts and reaction conditions is a key factor in improving the selectivity of R2S2.

[0008]

[0009] Early on, Vineyard conducted a systematic study on the oxidative coupling of RSH with sulfur catalyzed by organic amines. Using methanol as the solvent, at room temperature, n-C4H9 (the molar ratio of n-C4H9SH / S was 2.5, with n-C4H9SH being 25 mol% in excess) was added to a sulfur slurry and a n-butylamine catalyst and refluxed for 3 h. The selectivities of (n-C4H9)2S2 and (n-C4H9)2S3 were 97.5% and 2.5% respectively [Vineyard BD. Versatility and the mechanism of the n-butyl-amine-catalyzed reaction of thiols with sulfur[J]. The Journal of Organic Chemistry, 1967, 32(12): 3833-3836.]. Under solvent-free conditions, with NaOH and fatty alcohol polyoxyethylene ether ( Using 15-S-7 as the catalyst, the oxidation reaction of RSH with elemental sulfur (the molar ratio of RSH / S is 4.0, and RSH is in 100 mol% excess) can prepare dialkyl disulfide [Shaw J E, McAfee M G. Oxidation of Thiols to Disulfides by Elemental Sulfur Without Contamination by Higher Polysulfides[J]. Phosphorus, Sulfur, and Silicon and the Related Elements, 1998, 143(1): 125-131.]. The dosage of NaOH is 2.0 mol% (based on sulfur). The dosage of 15-S-7 is 34 wt%. When primary and secondary alkyl thiols such as 1-propanethiol, 1-octanethiol, 2-propanethiol, and 2-butanethiol are used as raw materials, the ratio of R2S2 to R2S3 is between 10 / 0 and 99.6 / 0.4. When tertiary alkyl thiol such as tert-butyl thiol is used as the raw material, the ratio of R2S2, R2S3, and R2S4 is 2.5 / 95.8 / 1.7.

[0010] The deficiencies of the prior art are as follows: The oxidation of thiols by molecular oxygen to couple and prepare disulfide is better for aryl thiols. However, when oxidizing alkyl thiols, the yield of disulfide is generally low, the synthesis scale is small, and there is a risk of explosion. There is also a problem of deep oxidation (the by-products are sulfinic esters and sulfonic esters); the main problem in preparing dialkyl disulfide by the oxidation of sulfur by sulfur is the generation of more trisulfide and other polysulfide by-products. Summary of the Invention

[0011] The present invention aims to overcome the deficiencies of the prior art and provide a method for catalytically synthesizing dialkyl disulfide with mild reaction conditions, fast reaction rate, high atomic utilization rate and yield, and the by-product H2S gas is easily separated and utilized.

[0012] To solve the above technical problems, the present invention is realized as follows:

[0013] A method for catalytically synthesizing symmetric dialkyl disulfide is implemented according to the following steps:

[0014] (1) Place a magnetic stir bar and the measured thiol, sulfur, and organic superbase catalyst into a reaction flask.

[0015] (2) Place the reaction flask described in step (1) into an oil bath of a magnetic heating stirrer, install a condenser, and connect the condenser to a drainage bottle through a silicone rubber tube. A saturated aqueous solution of H2S is pre-added to the drainage bottle.

[0016] (3) Start heating and begin stirring the reaction. Start timing. Determine the H2S release amount and the reaction termination time through the water displacement method to obtain the target product.

[0017] Further, in step (1), the molar ratio of the thiol to sulfur is 2.1 - 3.0:1.

[0018] Further, in step (1), the organic superbase catalyst is one or a mixture of two or more of 1,8 - diazabicycloundec - 7 - ene (DBU), 1,5 - diazabicyclo[4.3.0]non - 5 - ene (DBN), 1,1,3,3 - tetramethylguanidine (TMG), 2 - tert - butyl - 1,1,3,3 - tetramethylguanidine (BTMG), 1,5,7 - triazabicyclo[4.4.0]dec - 5 - ene (TBD), or 7 - methyl - 1,5,7 - triazabicyclo[4.4.0]dec - 5 - ene (MTBD).

[0019] Further, in step (1), the thiol is one or a mixture of two or more of n - hexyl mercaptan, n - octyl mercaptan, n - dodecyl mercaptan, cyclohexyl mercaptan, 2 - mercaptoethanol, benzyl mercaptan, or furfuryl mercaptan.

[0020] Further, in step (1), the dosage ratio of the organic superbase catalyst to the sulfur dosage is 0.001 - 0.1 mol%.

[0021] Further, in step (3), the reaction pressure is normal pressure.

[0022] Further, in step (3), the initial reaction temperature is 15 - 25 °C.

[0023] Further, in step (3), the maximum oil bath temperature is set at 90 °C, and the heating rate is 3.3 °C / min.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) Compared with conventional organic base catalysts, the organic superbase has a fast catalytic reaction rate and a high yield of dialkyl disulfide.

[0026] (2) The molar ratio of thiol to sulfur can be as low as 2.1 (the thiol is 5 mol% in excess), and the yield of dialkyl disulfide can reach 91 - 99.3%.

[0027] (3) The catalyst dosage is small. When the dosage of the organic superbase is as low as 0.001 mol% (one ten - thousandth of the amount of substance of sulfur), the catalytic activity is still very high, and the yield of dialkyl disulfide can still reach more than 95%.

[0028] (4) The reaction is carried out under solvent - free conditions, which is conducive to simplifying the subsequent product separation and purification procedures.

[0029] (5) The reaction conditions of this reaction are mild (room temperature and atmospheric pressure) and are not limited by the reaction scale, and it is very easy to achieve kg - scale preparation.

[0030] (6) Sulfur is cheap, easily available and has good stability, and is easy to store and use. Compared with oxidation by stoichiometric oxidants or molecular oxygen, this reaction has no problem of deep oxidation (the by - products are sulfinic acid esters and sulfonic acid esters) and has no impact on other active functional groups in the thiol raw material molecules.

[0031] (7) Similar to the oxidation by molecular oxygen, the atom utilization rate of the oxidative coupling reaction of thiols using sulfur as the oxidant is also relatively high, but its application range is wider. Whether it is the oxidative coupling of aryl thiols or alkyl thiols, a relatively high yield of disulfide can be obtained.

[0032] (8) The by - product H2S gas is very easy to separate and can be recycled, for example, by means of alkali washing to produce products such as NaHS or Na2S, or compressed into a liquid as a raw material for producing thiols. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic structural diagram of the drainage bottle of the present invention.

[0034] In the figure: 1. H2S gas inlet; 2. Water outlet; 3. Valve; 4. Cover; 5. H2S saturated aqueous solution.

[0035] Figure 2 This is a possible mechanism diagram of the oxidative coupling reaction of RSH and sulfur catalyzed by an organic superbase proposed by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. These embodiments should be understood as only for explaining the present invention and not for limiting the protection scope of the present invention. After reading the content recorded in the present invention, all other embodiments obtained by making various changes or modifications to the present invention based on the technical solutions and embodiments of the present invention also fall within the scope protected by the claims of the present invention.

[0037] To prevent the reaction from occurring violently, in step (3) of the present invention, at the initial stage of the reaction, it must be carried out at a relatively low temperature (room temperature), and the temperature is gradually increased, and the heating rate is controlled at 3.3 °C / min.

[0038] The release amount of by-product H2S was monitored by the drainage method to observe the reaction rate and judge the reaction end point. The schematic diagram of the drainage bottle is shown in Figure 1 , a 5000 ml screw-thread glass stopper bottle was used, and the bottle mouth was equipped with a two-hole stainless steel vent pipe ( -10 mm) and a screw-thread bottle cap (matched with the standard GL45 cap). A silicone rubber washer was used to seal the bottle mouth of the glass stopper bottle and the two-hole stainless steel cover body. One of the two holes was used as the air inlet, and the lower end of the other hole was connected to the bottom of the drainage bottle through a silicone rubber tube as the drainage port. The drainage bottle was filled with about 3 liters of distilled water, and an excessive amount of hydrogen sulfide was pre-introduced to form a saturated hydrogen sulfide aqueous solution.

[0039] After the reaction was completed, the discharged saturated hydrogen sulfide aqueous solution was replenished back into the drainage bottle through the drainage pipe, and the hydrogen sulfide gas discharged from the drainage bottle was absorbed by the KOH aqueous solution absorption bottle.

[0040] It must be pointed out that H2S is toxic, and the reaction operation should be carried out in a fume hood.

[0041] The composition of the product was analyzed by gas chromatography. A Scion 436 gas chromatograph was used to analyze the filtered crude product, and the peak area normalization method was directly used to calculate and analyze the content (weight percentage) of each component in the test sample (judging from the product data obtained by separation, although the response factors of each component were not considered, the test results of disulfide and trisulfide were close to the actual composition). The specific analysis test conditions are as follows: the chromatographic column is a SCION-WAXMS capillary column (SC32434, 30 m * 0.32 mm ID * 0.50 μm df, VF-WAXms); FID detector, the vaporization chamber temperature was set at 280 °C, the detector temperature was 260 °C, and the split ratio was 40:1. The initial column temperature was 160 °C, with an initial residence time of 0.3 min, and then it was heated to 240 °C at a heating rate of 30 °C / min and held for 5.53 min. High-purity nitrogen was used as the carrier gas, and the carrier gas flow rate was 4 mL / min. A 5 μL manual injection syringe ( 75N syringe) was used for injection, and the injection volume was 0.4 μL.

[0042] Considering that trisulfides and tetrasulfides may be unstable and may decompose in the high-temperature vaporization chamber and chromatographic column of gas chromatography, thus affecting the accuracy of the analysis results. Therefore, nuclear magnetic resonance hydrogen spectroscopy (1H NMR) was used for analysis and verification. Since 1H NMR measurement is carried out under room temperature conditions, there is no problem of thermal decomposition. 1H NMR was performed using an Ascend 400 nuclear magnetic resonance spectrometer (Bruker, 400 MHz). Deuterochloroform (99.8% atomic D, containing 0.03% V / V tetramethylsilane (TMS), containing silver foil stabilizer) was used as the solvent. The chemical shift was determined by the parts per million (ppm) of the low field relative to the position of the internal standard TMS (δ = 0). For normal aliphatic dialkyl disulfides (di-n-hexyl disulfide, di-n-octyl disulfide, and di-n-dodecyl disulfide), the chemical shift of the methylene group (-CH2-SS-CH2-) connected to sulfur was 2.68 ppm; for normal aliphatic dialkyl trisulfides (di-n-hexyl trisulfide, di-n-octyl trisulfide, and di-n-dodecyl trisulfide), the chemical shift of the methylene group (-CH2-SSS-CH2-) connected to sulfur was 2.87 ppm; for normal aliphatic dialkyl tetrasulfides (di-n-hexyl tetrasulfide, di-n-octyl tetrasulfide, and di-n-dodecyl tetrasulfide), the chemical shift of the methylene group (-CH2-SSSS-CH2-) connected to sulfur was 2.95 ppm. Therefore, direct 1H NMR measurement was performed on the reaction mixture, the peak areas of the three methylene groups connected to sulfur were integrated, and the molar percentages of disulfide, trisulfide, and tetrasulfide were obtained by the normalization method. Experiments have proved that the 1H NMR analysis results are completely consistent with the gas chromatography analysis results, confirming that dialkyl polysulfides (R-Sn-R, n = 2-4) can exist stably in the high-temperature vaporization chamber and chromatographic column and will not decompose. Detailed implementation mode

[0044] Example 1

[0045] 3.20 g of sublimed sulfur (0.1 mol), 43.89 g of n-octanethiol (0.3 mol), and a magnetic stir bar were placed in a 100 mL single-neck reaction flask. 11.5 mg of TMG (the dosage of TMG based on sulfur is 0.1 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, a condenser was installed and the condenser was connected to the drainage system. The maximum temperature of the oil bath was set to 90 °C, and the heating rate of the oil bath was 3.3 °C / min. Stirring and heating the reaction started from room temperature of 16 °C and timing began. When the temperature rose to 22.6 °C, hydrogen sulfide started to be released. When the temperature rose to 90 °C, hydrogen sulfide was still slowly released. When the reaction reached 41 minutes, hydrogen sulfide stopped being released, and at this time the reaction was stopped and cooled to room temperature. The yields of di-n-octyl disulfide and di-n-octyl trisulfide analyzed by gas chromatography were 98.0% and 2.0% respectively; 1The yields of di-n-octyl disulfide and di-n-octyl trisulfide determined by \(^{1}H\) NMR were 97.5% and 2.5% respectively. The boiling point of di-n-octyl disulfide is 369 °C (760 mmHg).

[0046] Example 2

[0047] 3.20 g of sublimed sulfur (0.1 mol), 43.89 g of n-octyl mercaptan (0.3 mol) and a magnetic stir bar were placed in a 100 mL single-neck reaction flask, and 1.24 mg of DBN (the amount of DBN based on sulfur is 0.01 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, a condenser was installed and the condenser was connected to the drainage system. Stirring and heating the reaction started from room temperature of 17 °C, the heating rate of the oil bath was 3.3 °C / min. Hydrogen sulfide started to be released when the temperature rose to 33.5 °C, and hydrogen sulfide stopped being released when the temperature rose to 83 °C. At this time, the reaction was stopped and cooled to room temperature. The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide analyzed by gas chromatography were 97.6% and 2.4% respectively; 1 The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide determined by \(^{1}H\) NMR were 97.2% and 2.8% respectively. The boiling point of di-n-octyl disulfide is 369 °C (760 mmHg).

[0048] Example 3

[0049] 3.20 g of sublimed sulfur (0.1 mol), 43.89 g of n-octyl mercaptan (0.3 mol) and a magnetic stir bar were placed in a 100 mL single-neck reaction flask, and 1.24 mg of DBN (the amount of DBN based on sulfur is 0.01 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, a condenser was installed and the condenser was connected to the drainage system. Stirring and heating the reaction started from room temperature of 17 °C, the heating rate of the oil bath was 3.3 °C / min. Hydrogen sulfide started to be released when the temperature rose to 33.5 °C, and hydrogen sulfide stopped being released when the temperature rose to 83 °C. At this time, the reaction was stopped and cooled to room temperature. The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide analyzed by gas chromatography were 97.6% and 2.4% respectively; 1 The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide determined by \(^{1}H\) NMR were 97.2% and 2.8% respectively. The boiling point of di-n-octyl disulfide is 369 °C (760 mmHg).

[0050] Example 4

[0051] 3.20 g of sublimed sulfur (0.1 mol), 43.89 g of n-octyl mercaptan (0.3 mol) and a magnetic stir bar were placed in a 100 mL single-neck reaction flask, and 1.52 mg of DBU (the amount of DBU based on sulfur was 0.01 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, a condenser was installed and the condenser was connected to the drainage system. Stirring and heating the reaction were started from room temperature of 16 °C and timing was started (the maximum oil bath temperature was set at 90 °C, and the oil bath heating rate was 3.3 °C / min). When the temperature rose to 46 °C, hydrogen sulfide began to be released. When the reaction reached 29 minutes, hydrogen sulfide stopped being released, and at this time the reaction was stopped and cooled to room temperature. The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide by gas chromatography analysis were 98.1% and 1.9% respectively; 1 The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide determined by HNMR were 97.8% and 2.2% respectively. The boiling point of di-n-octyl disulfide is 369 °C (760 mmHg).

[0052] Example 5

[0053] 3.20 g of sublimed sulfur (0.1 mol), 43.89 g of n-octyl mercaptan (0.3 mol) and a magnetic stir bar were placed in a 100 mL single-neck reaction flask, and 0.17 mg of BTMG (the amount of BTMG based on sulfur was 0.001 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, a condenser was installed and the condenser was connected to the drainage system. The maximum oil bath temperature was set at 90 °C (the oil bath heating rate was 3.3 °C / min). Stirring and heating the reaction were started from room temperature of 15 °C and timing was started. When the temperature rose to 38 °C, hydrogen sulfide began to be released. When the reaction reached 40 minutes, hydrogen sulfide stopped being released, and at this time the reaction was stopped and cooled to room temperature. The yields of di-n-octyl disulfide and di-n-octyl trisulfide by gas chromatography analysis were 97.2% and 2.8% respectively; 1 The yields of di-n-octyl disulfide and di-n-octyl trisulfide determined by HNMR were 96.8% and 3.2% respectively. The boiling point of di-n-octyl disulfide is 369 °C (760 mmHg).

[0054] Example 6

[0055] 3.20 g of sublimed sulfur (0.1 mol), 43.89 g of n-octanethiol (0.3 mol) and a magnetic stir bar were placed in a 100 mL single-neck reaction flask, and 0.15 mg of MTBD (the amount of MTBD based on sulfur was 0.001 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a thermostatic heating magnetic stirrer with a condenser installed and the condenser connected to the drainage system. Stirring and heating the reaction were started from room temperature of 15 °C and timing was started. The maximum temperature of the oil bath was set at 90 °C (the heating rate of the oil bath was 3.3 °C / min). When the temperature reached 38 °C, hydrogen sulfide began to be released. When the reaction reached 40 minutes, the release of hydrogen sulfide stopped, and at this time the reaction was stopped and cooled to room temperature. The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide by gas chromatography analysis were 96.6% and 3.4% respectively; 1 The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide determined by HNMR were 96.2% and 3.8% respectively. The boiling point of di-n-octyl disulfide was 369 °C (760 mmHg).

[0056] Comparative Example 1

[0057] 3.20 g of sublimed sulfur (0.1 mol), 43.89 g of n-octanethiol (0.3 mol) and a magnetic stir bar were placed in a 100 mL single-neck reaction flask, and 101.2 mg of triethylamine (the amount of triethylamine based on sulfur was 1.0 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a thermostatic heating magnetic stirrer with a condenser installed and the condenser connected to the drainage system. The maximum temperature of the oil bath was set at 90 °C and the heating rate of the oil bath was 3.3 °C / min. Stirring and heating the reaction were started from room temperature of 16 °C and timing was started. When the temperature reached 20 °C, hydrogen sulfide began to be released. When the reaction reached 25 minutes, the release of hydrogen sulfide stopped, and at this time the reaction was stopped and cooled to room temperature. The selectivities of di-n-octyl disulfide and di-n-octyl trisulfide by gas chromatography analysis were 87.2% and 12.8% respectively. Under the condition of the same catalyst dosage, the yields of di-n-octyl disulfide of DBU, TMG, BTMG, DBN and MTBD were 99.8, 99.8, 100, 99.6 and 99.2% respectively.

[0058] Comparative Example 2

[0059] 3.20 g of sublimed sulfur (0.1 mol), 43.89 g of n-octanethiol (0.3 mol) and a magnetic stir bar were placed in a 100 mL single-neck reaction flask, and 112.2 mg of triethylenediamine (the amount of triethylenediamine based on sulfur was 1.0 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a heating magnetic stirrer with a constant temperature, a condenser was installed and the condenser was connected to the drainage system. The maximum temperature of the oil bath was set at 90 °C and the heating rate of the oil bath was 3.3 °C / min. Stirring and heating the reaction started from room temperature of 16 °C and timing began. Hydrogen sulfide started to be released when the temperature rose to 26 °C, and hydrogen sulfide stopped being released when the reaction reached 58 minutes. At this time, the reaction was stopped and cooled to room temperature. The yields of di-n-octyl disulfide and di-n-octyl trisulfide analyzed by gas chromatography were 90.0% and 10.0% respectively. Under the condition of the same catalyst dosage, the yields of di-n-octyl disulfide of DBU, TMG, BTMG, DBN and MTBD were 99.8, 99.8, 100, 99.6 and 99.2% respectively.

[0060] Example 7

[0061] 3.20 g of sublimed sulfur (0.1 mol), 30.72 g of n-octanethiol (0.21 mol) and a magnetic stir bar were placed in a 100 mL single-neck reaction flask, and 17.1 mg of BTMG (the amount of BTMG based on sulfur was 0.1 mol%) was added. The reaction flask was placed in the heat-conducting oil bath of a heating magnetic stirrer with a constant temperature, a condenser was installed and the condenser was connected to the drainage system. The maximum temperature of the oil bath was set at 90 °C (the heating rate of the oil bath was 3.3 °C / min). Stirring and heating the reaction started from room temperature of 15 °C and timing began. Hydrogen sulfide started to be released when the temperature rose to 18 °C, and hydrogen sulfide stopped being released when the temperature rose to 74 °C. At this time, the reaction was stopped and cooled to room temperature. The yields of di-n-octyl disulfide and di-n-octyl trisulfide analyzed by gas chromatography were 91.0% and 9.0% respectively. The boiling point of di-n-octyl disulfide is 369 °C (760 mmHg).

[0062] Example 8

[0063] Place 3.20 g of sublimed sulfur (0.1 mol), 24.83 g of n-hexanethiol (0.21 mol) and a magnetic stir bar into a 100 mL single-neck reaction flask, add 17.1 mg of BTMG (the dosage of BTMG based on sulfur is 0.1 mol%), place the reaction flask into the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, install a condenser and connect the condenser to the drainage system. Set the maximum temperature of the oil bath to 90 °C (the heating rate of the oil bath is 3.3 °C / min), start stirring and heating the reaction from room temperature of 14 °C and start timing. When the temperature rises to 22 °C, hydrogen sulfide starts to be released. When the temperature rises to 84 °C, hydrogen sulfide stops being released. At this time, stop the reaction and cool it to room temperature. The yields of di-n-hexyl disulfide and di-n-hexyl trisulfide analyzed by gas chromatography are 92.8% and 7.2% respectively. The boiling point of di-n-hexyl disulfide is 230 °C (760 mmHg).

[0064] Example 9

[0065] Place 3.20 g of sublimed sulfur (0.1 mol), 42.50 g of n-dodecanethiol (0.21 mol) and a magnetic stir bar into a 100 mL single-neck reaction flask, add 17.1 mg of BTMG (the dosage of BTMG based on sulfur is 0.1 mol%), place the reaction flask into the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, install a condenser and connect the condenser to the drainage system. Set the maximum temperature of the oil bath to 90 °C (the heating rate of the oil bath is 3.3 °C / min), start stirring and heating the reaction from room temperature of 14 °C and start timing. When the temperature rises to 27 °C, hydrogen sulfide starts to be released. When the temperature rises to 83 °C, hydrogen sulfide stops being released. At this time, stop the reaction and cool it to room temperature. The yield of bis-dodecyl disulfide analyzed by gas chromatography is 100%, and no bis-dodecyl trisulfide is formed. The melting point of bis-dodecyl disulfide is 30.8–34.5 °C

[0066] Example 10

[0067] Place 3.20 g of sublimed sulfur (0.1 mol), 24.83 g of cyclohexanethiol (0.21 mol) and a magnetic stir bar into a 100 mL single-neck reaction flask, add 17.1 mg of BTMG (the dosage of BTMG based on sulfur is 0.1 mol%), place the reaction flask into the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, install a condenser and connect the condenser to the drainage system. Set the maximum temperature of the oil bath to 90 °C (the heating rate of the oil bath is 3.3 °C / min), start stirring and heating the reaction from room temperature of 15 °C and start timing. When the temperature rises to 25 °C, hydrogen sulfide starts to be released. When the temperature rises to 89 °C, hydrogen sulfide stops being released. At this time, stop the reaction and cool it to room temperature. The yields of dicyclohexyl disulfide and dicyclohexyl trisulfide analyzed by gas chromatography are 96.1% and 3.9% respectively. The boiling point of dicyclohexyl disulfide is 115-118 °C (1.0 mmHg).

[0068] Example 11

[0069] Place 3.20 g of sublimed sulfur (0.1 mol), 23.97 g of furfuryl mercaptan (0.21 mol) and a magnetic stir bar in a 100 mL single-neck reaction flask, add 17.1 mg of BTMG (the dosage of BTMG based on sulfur is 0.1 mol%), place the reaction flask in the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, install a condenser and connect the condenser to the drainage system. Set the maximum temperature of the oil bath to 90 °C (the heating rate of the oil bath is 3.3 °C / min), start stirring and heating the reaction from room temperature of 15 °C and start timing. Hydrogen sulfide starts to be released immediately at 15 °C. When the temperature rises to 65 °C, the release of hydrogen sulfide stops. At this time, stop the reaction and cool it to room temperature. 1 The yields of bis(furfuryl) disulfide and bis(furfuryl) trisulfide analyzed by HNMR are 98.8% and 1.2% respectively. The boiling point of bis(furfuryl) disulfide is 112 - 115 °C (0.5 mmHg).

[0070] Example 12

[0071] Place 3.20 g of sublimed sulfur (0.1 mol), 26.08 g of benzyl mercaptan (0.21 mol) and a magnetic stir bar in a 100 mL single-neck reaction flask, add 17.1 mg of BTMG (the dosage of BTMG based on sulfur is 0.1 mol%), place the reaction flask in the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, install a condenser and connect the condenser to the drainage system. Set the maximum temperature of the oil bath to 90 °C (the heating rate of the oil bath is 3.3 °C / min), start stirring and heating the reaction from room temperature of 15 °C and start timing. Hydrogen sulfide starts to be released immediately at 15 °C. When the temperature rises to 32 °C, the release of hydrogen sulfide stops. At this time, stop the reaction and cool it to room temperature. 1 The yields of dibenzyl disulfide and dibenzyl trisulfide analyzed by HNMR are 97.2% and 2.8% respectively. The melting point of dibenzyl disulfide is 72.4 °C.

[0072] Example 13

[0073] Place 3.20 g of sublimed sulfur (0.1 mol), 16.41 g of 2-mercaptoethanol (0.21 mol) and a magnetic stir bar in a 100 mL single-neck reaction flask, add 17.1 mg of BTMG (the dosage of BTMG based on sulfur is 0.1 mol%), place the reaction flask in the heat-conducting oil bath of a collecting heat type constant temperature heating magnetic stirrer, install a condenser and connect the condenser to the drainage system. Set the maximum temperature of the oil bath to 90 °C (the heating rate of the oil bath is 3.3 °C / min), start stirring and heating the reaction from room temperature of 15 °C and start timing. When the temperature rises to 18.1 The yields of bis(2-hydroxyethyl) disulfide and bis(2-hydroxyethyl) trisulfide analyzed by 1H NMR were 96.1% and 3.9% respectively. The boiling point of bis(2-hydroxyethyl) disulfide was 152-157 °C (3 mmHg).

[0074] It can be understood that the above specific description of the present invention is only for explaining the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced to achieve the same technical effect; as long as it meets the usage requirements, it is within the protection scope of the present invention.

Claims

1. A method for catalytically synthesizing symmetrical dialkyl disulfides, characterized in that: Follow these steps to implement: (1) A magnetic stirrer and measured thiol, sulfur and organic superbase catalyst are placed in a reaction flask; the molar ratio of the thiol to the sulfur is 2.1 to 3.0:1; the organic superbase catalyst is 1,8-diazabicycloundec-7-ene, 1,5-diazabicyclo[4.3.0]ketone-5-ene, 1,1,3,3-tetramethylguanidine, 2-tert-butyl-1,1,3,3-tetramethylguanidine, 1,5,7-triazide Bicyclo(4.4.0)dec-5-ene or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, or a mixture of two or more thereof; the mercaptan is n-hexylmercaptan, n-octylmercaptan, n-dodecylmercaptan, cyclohexylmercaptan, 2-mercaptoethanol, benzylmercaptan, or furfurylmercaptan, or a mixture of two or more thereof; the amount of the organic superbase catalyst used is 0.001 to 0.1 mol% relative to the amount of sulfur used; (2) Place the reaction bottle described in step (1) in an oil bath pot with a magnetic heating stirrer, install a condenser, and connect the condenser to a drainage bottle through a silicone rubber tube. Saturated H2S aqueous solution is pre-added to the drainage bottle; (3) Start heating and stirring the reaction, start timing, and determine the amount of H2S released and the time when the reaction ends by the water displacement method to obtain the target product; the reaction pressure is normal pressure; the initial reaction temperature is 15-25°C; the oil bath temperature is set to a maximum of 90°C, and the heating rate is 3.3°C / min.

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