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2-Mercaptobenzothiazole is a chemical substance with the molecular formula C7H5NS2, CAS 149-30-4. Pale yellow monoclinic needle like or leaf like crystals. It is soluble in glacial acetic acid and has an unpleasant smell. Insoluble in water and gasoline, soluble in ethanol, ether, acetone, ethyl acetate, benzene, chloroform and dilute alkali. In addition, the product is also used to prepare pesticide fungicide, nitrogen fertilizer synergist, cutting oil and lubricating additive, organic anti ashing agent in photographic chemistry, metal corrosion inhibitor, etc. In addition, it is also a reagent for chemical analysis. This product is low toxic and irritating to skin and mucosa.
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Chemical Formula |
C7H5NS2 |
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Exact Mass |
167 |
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Molecular Weight |
167 |
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m/z |
167 (100.0%), 169 (9.0%), 168 (7.6%), 168 (1.6%) |
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Elemental Analysis |
C, 50.27; H, 3.01; N, 8.38; S, 38.34 |
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There are many production methods for 2-Mercaptobenzothiazol, but there are mainly three methods using aniline, o-nitrochlorobenzene and diphenylthiourea as raw materals.
Final Solution
1. Using aniline as raw material
Aniline, carbon disulfide and sulfur are usually directly reacted in an autoclave. Aliphatic amine, dimethylformamide, triazolidine and formaldehyde can also be used instead of carbon disulfide to make aniline and sulfur react under high pressure. The reaction pressure of the method using aniline as raw materal is high, generally above 4MPa and up to 15MPa, so it is also called high pressure method.
2. Using o-nitrochlorobenzene as raw material
O-nitrochlorobenzene can be reduced to o-aminothiophenol by reaction with reducing agent sodium hydrosulfide, sodium polysulfide or hydrogen sulfide. And further reacted with carbon disulfide to prepare accelerator M. Some of these methods have a long reaction time (sodium hydrosulfide takes about 20h), but they can be carried out under normal pressure or lower pressure, also known as atmospheric pressure method.
3. Using diphenylthiourea as raw material
The reaction pressure of this method is between the two methods, below 4MPa, which is generally referred to as medium pressure method.
The preparation method is to take o-chloronitrobenzene, sodium polysulfide and carbon disulfide as raw materals to produce 2-Mercaptobenzothiazole sodium salt, and then acidify with sulfuric acid and wash with water to obtain the product. It can also be reacted with aniline, carbon disulfide and sulfur to obtain 2-Mercaptobenzothiazol, dissolved into sodium salt with sodium hydroxide, filtered, neutralized, washed with water and dried to obtain the product.
Add aniline, carbon disulfide and sulfur into the condensation kettle in turn and heat. The condensation reaction was completed after 2H. To obtain crude 2-Mercaptobenzothiazol. Cool down and transfer it to the neutralization kettle. Neutralize with alkali solution, filter, discard impurities, transfer the filtrate into the acidification kettle, and add sulfuric acid for acidification. Filter, dry, smash, sift and pack the finished product.
MBT with the chemical formula C7H5NS2, is a light yellow crystalline powder with a unique odor. As an organic chemical intermediate, it has demonstrated extensive application value in various fields such as rubber industry, metal corrosion prevention, analytical chemistry, pesticides and pharmaceuticals.
As the core component of rubber vulcanization accelerators, MBT occupies an irreplaceable position in the fied of rubber processing. Its mechanism of action is to significantly enhance the physical properties of rubber products by forming an elastic cross-linked structure with unsaturated vulcanized polymers.
1. Sulfurization promoting properties
MBT has a rapid vulcanization promoting effect on general rubber systems such as natural rubber (NR), isoprene rubber (IR), and styrene butadiene rubber (SBR). The critical temperature for vulcanization is as low as 120-130 ℃. At a typical dosage of 0.5-2 phr, the tensile strength of rubber products can be increased by 20% -30%, and the hardness can be increased by 5-10 Shore A units. When used in combination with activators such as zinc oxide and stearic acid, the vulcanization efficiency can be increased by more than 40%, and the vulcanization plateau can be extended by 30%, effectively avoiding early vulcanization phenomena.
2. Composite promotion system
In the butyl rubber (IIR) system, the combination of MBT and dithiothiuram (TMTD) in a ratio of 1:0.5 can shorten the vulcanization time to 60% of the traditional formula while maintaining the airtightness index of the product (≤ 0.5 cm ³/(cm ² · 24h · atm)). A light colored rubber product with a water resistance of 720 hours (50 ℃ water bath) can be prepared in the chlorosulfonated polyethylene (CSM) rubber compound by combining it with lead trisulfate, which is particularly suitable for marine engineering seals.
3. Application of latex vulcanization
In natural rubber latex, 2-Mercaptobenzothiazole is combined with diethyldithiocarbamate diethylamine (ZDC) in a ratio of 1:1.2 to achieve room temperature vulcanization (25 ± 2 ℃).
The vulcanization time is controlled within 8-12 hours, and the tensile strength of the product can reach 18-22 MPa. This system can reduce vulcanization energy consumption by 65% in the production of medical rubber gloves, while maintaining the biocompatibility index of the product (cytotoxicity ≤ level 1).
4. Intermediate conversion value
MBT, as a key intermediate, can derive various high-performance accelerators:
The accelerator CZ (N-cyclohexyl-2-benzothiazole sulfonamide) was prepared by reacting with cyclohexylamine, and the sulfurization activity was increased by 2.5 times
Reacting with morpholine to generate promoter NOBS (N-oxydiethylene-2-benzothiazole sulfonamide), with a 40% extension in calcination time
The oxidation product MBTS (dibenzothiazole disulfide) in EPDM rubber can improve the heat aging resistance (150 ℃ × 70h) of the product by 50%
Innovative applications in the field of metal corrosion prevention
The thiol group (- SH) of MBT forms a dense protective film on the metal surface, effectively inhibiting electrochemical corrosion.
1. Copper based material protection
In the circulating cooling water system, when the concentration of copper ions reaches 0.5 mg/L, adding 5-10 mg/L MBT can reduce the corrosion rate of copper pipes from 0.25 mm/a to 0.03 mm/a. The mechanism of action is that the S atom in the MBT molecule forms a stable five membered ring chelate with Cu ⁺, and the protective film thickness can reach 50-80 nm. In the copper plating process of electronic components, using it as a brightener (0.05-0.10 g/L) can refine the copper layer crystallization to 0.5-1.0 μ m and reduce the porosity by 80%.
2. Industrial application of mineral processing
As a flotation collector for sulfide ores, MBT can achieve a recovery rate of 92% -95% (pH=6-8) for pyrite. The selective adsorption mechanism is that the benzothiazole ring in MBT molecules forms a π - d complex bond with Fe ² ⁺ on the surface of pyrite, with an adsorption energy of -45 kJ/mol. In copper molybdenum separation flotation, adjusting the pH to 10-11 with lime can increase the grade of molybdenum concentrate from 0.8% to 4.2% and improve the recovery rate by 15 percentage points.
3. Electroplating additive function
In the acidic copper plating system, MBT, as an auxiliary brightener (0.02-0.05 g/L), can increase the cathodic polarization by 15-20 mV and improve the crystal orientation and alignment of the coating to over 90%. In the cyanide silver plating process, adding 0.5 g/L MBT can increase the hardness of the silver layer from HV 60 to HV 120, and improve the wear resistance (Taber 500g load) by three times.
Accurate applications in the field of analytical chemistry
The metal chelating properties of MBT make it an important tool for trace metal analysis.
1. Color reaction system
In an ammonia buffer solution with pH=9, MBT forms a 1:2 red complex with Ag ⁺, with a molar absorptivity of 1.2 × 10 ⁵ L/(mol · cm) and a detection limit of 0.02 μ g/mL. The system has a relative standard deviation (RSD) of ≤ 2.5% and a recovery rate of 98% -102% in the determination of mercury content in electroplating waste. The yellow complex formed with Pb ² ⁺ (λ max=410 nm) can lower the determination limit of lead to 0.5 μ g/g in ore analysis.
2. Extraction and Separation Technology
In the system of propanol sodium chloride water (volume ratio 3:1:6), the complex formed by MBT and SnCl ₂ has a distribution coefficient of 1500 for Rh ³ ⁺. This system can increase the recovery rate of rhodium from 65% to 92% and achieve a purity of 99.95% in platinum group metal separation. In the treatment of copper smelting wastewater, MBT Cu ² ⁺ complex can be quantitatively adsorbed by ion exchange resin (D401 type) with a desorption rate of ≥ 95%.
3. Electrochemical sensors
Based on MBT modified glassy carbon electrode, the linear range for detecting Cd ² ⁺ is 1 × 10 ⁻⁸ -1 × 10 ⁻⁵ mol/L, and the detection limit is 3 × 10 ⁻⁹ mol/L. In the monitoring of heavy metals in seawater, the response deviation of the sensor after continuous operation for 30 days is ≤ 5%, and the anti-interference ability (selectivity coefficient for Zn ² ⁺ and Pb ² ⁺) reaches the order of 10 ³.
Other special application areas
1. Dye industry
MBT and 1-amino-4-nitroanthraquinone can be refluxed in DMF to produce Disperse Brilliant Red S-GL (C.I. Disperse Red 121). Under high temperature and high pressure dyeing conditions at 130 ℃, the dye has a dye uptake rate of 96% on polyester fibers and a color fastness (ISO 105-B02) of ≥ 4 levels. The benzothiazole group in its molecular structure forms hydrogen bonds and van der Waals forces with fibers, endowing the dye with excellent enhancement and compatibility.
2. Optoelectronic materials
The photodetector prepared by MBT and CdS quantum dots composite exhibits an on/off ratio of 10 ⁴ and a response time (τ r/τ f) of 120/150 μ s under 365 nm illumination. This materal has a sensitivity three times higher than pure CdS devices in the fied of ultraviolet detection, and a decrease of two orders of magnitude in dark current. The band matching mechanism lies in the formation of a 0.5 eV potential barrier between the LUMO energy level of MBT (-3.2 eV) and the conduction band energy level of CdS (-3.7 eV), effectively promoting the separation of photogenerated carriers.
2-mercaptobenzothiazole, with its unique molecular structure and reactivity, has formed a cross application network in multiple industrial fieds. With the advancement of the green chemistry concept, its production process is being optimized towards atomic economy (yield increased to 92%), solvent recovery rate (≥ 95%), and three waste emissions (reduced by 80% compared to traditional processes). In the future, MBT and its derivatives will continue to play a key role in promoting technological upgrades in related industries such as high-performance rubber materals, intelligent anti-corrosion coatings, and precision medical diagnosis.
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