Oxidative synthesis of dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is a sulfur-containing organic compound, colorless odorless transparent liquid at room temperature, is a hygroscopic liquid. It has the characteristics of high polarity, high boiling point, good thermal stability and miscibility with water, and can dissolve in most organic matter such as ethanol, benzene and chloroform, known as “universal solvent”. Dimethyl sulfoxide is widely used as extraction solvent, pharmaceutical intermediate, pesticide additive, antifreeze, degreaser, rare metal extractant, cosmetic additive, dyeing agent and modifier of synthetic fiber, etc.

Basic information

CAS number: 67-68-5

English name: dimethylsulfoxide

Description: Colorless liquid, flammable, almost odorless, with bitter taste. Melting point 18.4℃, boiling point 189.0±9.0℃, density of 1.1±0.1g/cm³. The product is a weak oxidizing agent, non-aqueous dimethyl sulfoxide is not corrosive to metals, and it is corrosive to iron, copper and other metals when it is hydrated, but it is not corrosive to aluminum.

Use and market demand

Dimethyl sulfoxide can be divided into industrial grade dimethyl sulfoxide, pharmaceutical grade dimethyl sulfoxide and agricultural grade dimethyl sulfoxide according to its application fields and uses, and different grades of dimethyl sulfoxide may have differences in purity, purity and quality standards.

1. Industrial dimethyl sulfoxide

It is mainly used as solvent and intermediate in organic synthesis. It is widely used in the chemical industry to dissolve, extract and synthesize organic compounds. In organic synthesis, dimethyl sulfoxide can also be used as an oxidizing agent in many oxidation reactions.

2. Pharmaceutical grade dimethyl sulfoxide

Mainly used in pharmaceutical and medical fields, it is used as a solvent, carrier and absorbent of drugs, for the preparation of injections, topical drugs, eye drops and so on. Due to its anti-inflammatory and active oxygen scavenging effects, DMSO has been used in the treatment of a variety of intestinal diseases. In addition, DMSO is also used as a cryoprotectant, which can reduce the freezing point of aqueous solutions and inhibit the formation of ice crystals, and is widely used in the storage and transportation of frozen cells. DMSO is a promising compound for clinical application due to its wide pharmacological spectrum and non-accumulation effect.

3. Agricultural grade DSO

Mainly used in the field of agriculture and plant protection, it is used as a solvent and penetration agent for pesticides, which is used to improve the permeability and absorption of pesticides.

China is currently the world’s largest dimethyl sulfoxide production and marketing market, the product development is early, the production technology is relatively mature, not only to meet the domestic downstream market demand, but also a large number of exports to overseas markets. With the large-scale production of DSO leading enterprises such as Xingfa Group, Cangzhou Dongli and Lunan Chemical Industry in recent years, the overall production of DSO in China has increased to 75,000 tons in 2022, and the market size has reached more than 2 billion yuan.

At present, the market price of dimethyl sulfoxide is 30,000 to 35,000 yuan/ton, with the wide application in the downstream field, the market demand for dimethyl sulfoxide is about 100,000 tons, and the consumer market maintains an average annual growth of more than 5%, with a broad space for development and good prospects for development.

Synthesis methods review

At present, DMSO synthesis methods mainly include nitrogen dioxide method, hydrogen peroxide method and ozone method.

1. Nitrogen dioxide method

At present, dimethyl sulfoxide is produced by nitrogen dioxide method in industry. The dimethyl sulfide and nitrogen dioxide gas and oxygen enter the dimethyl sulfide oxidation tower, in which the dimethyl sulfide and the oxidizing agent nitrogen dioxide are oxidized at 60-80℃. The essence of the reaction process is to oxidize dimethyl sulfide by air, and NO2 is the catalyst of the oxidation reaction process.

This method mainly has production safety problems and environmental pollution risks of nitrogen oxides. Domestic factories that use this method have experienced varying degrees of explosion, mainly because DME sulfide raw materials and air are easy to form explosive mixtures.

Taking into account the safety of N2O4 transportation, general enterprises need to support NO2 production devices, resulting in cumbersome processes.

2. Hydrogen peroxide method

The current research mainly uses hydrogen peroxide as oxidant, titanium silicon molecular sieve as catalyst, methanol as solvent to carry out liquid phase oxidation reaction of dimethyl sulfide. Under relatively mild conditions, the conversion rate of dimethyl sulfide is more than 99%, and the selectivity of dimethyl sulfoxide is more than 90%.

However, this method needs to use 2 times the organic solvent of dimethyl sulfide, resulting in low efficiency and increased recovery cost, and the titanium silicon molecular sieve used is expensive and the production cost is high.

3. Ozone method

Under a certain temperature (20-100℃) and pressure (2MPa), using acetone or acetonitrile as solvent, under the action of titanium-containing catalyst, the conversion rate of dimethyl sulfide is about 40%-80%, the selectivity of dimethyl sulfoxide can reach 80-90%, but the ozone utilization rate is 60-80%.

The catalyst of this method is expensive, and there are harsh conditions such as high pressure, low conversion rate, high energy consumption, high cost, and difficult to industrialization.

The development and use of catalysts with high catalytic activity and low cost can improve the conversion and selectivity of the reaction and increase the yield under the premise of ensuring safety and green. Promoting the application of this method in industrial production has important economic significance for promoting the development of DSO related industries in China.