Articles / Dipolar Aprotic Solvents DMSO and NMP IN CROP PROTECTION FORMULATIONS

DIPOLAR APROTIC SOLVENTS DMSO AND NMP IN CROP PROTECTION FORMULATIONS

2 May, 2023

Abstract

The article is devoted to two aprotic solvents widely used in plant protection preparations, despite severe regulatory limitations for both.

DIMETHYL SULFOXIDE

  1. Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula (CH3)2SO, CAS Number 67-68-5. This colorless liquid is the most widely commercially used sulfoxide. It is a very important non classified polar aprotic solvent safe for man and for the environment.

  2. Physico-Chemical properties of DMSO. It dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as in water. Density 1.1 g/cm3, Melting point 19°C/66°F, Boiling point 189°C/372°F, pH (50/50 in water) 8.5. It is combustible liquid with ignition temperature 300-302°C/572-576°F.

  3. Safety. DMSO has an excellent toxicological and ecotoxicological profile. It is not classified as skin or eye irritant, not skin sensitizer, not suspected to be carcinogenic, it is safe for environment. However, application of 1 % DMSO to the soil proved to be severely phytotoxic for plant growth and dry matter accumulation. Its use in agriculture is limited in the USA.

  4. DMSO application. Wide use of DMSO is based on its unique physical, chemical, biological and safety properties. In agrochemicals, DMSO is used as inert and non-classified less toxic solvent for agricultural formulations of crop protection products (pesticides) and for chemical synthesis of active ingredients for such formulations. For liquid formulations DMSO is used due to its high solvency power and miscibility with most inert substances applied in the formulations. DMSO is used to dissolve Active substances when water or other solvents fail. It is widely used for crop protection products in such formulation types as: SL - Soluble Liquids, EC – Emulsion Concentrates, DC – Dispersion Concentrates, ULV – Ultra Low Volume formulations, the last is for application from airplanes and drones. However, there is still a restriction of use in agrichemical products: only for formulations used before crops emergence or prior to formation of edible parts. Additional potential problems of use of DMSO in the crop protection formulations are due to its specific physicochemical and biological properties. For example, the relatively high freezing point of DMSO, 18.5°C (65°F), means that at or below room temperature it is a solid, and that can limit its utility and requires pre-heating when it is used in production lines. This also requires relatively warm conditions for the storage of liquid products based on DMSO.
    Despite its toxigenic nature, DMSO gets microbially contaminated easily. So, it must be aseptically sterilized (filtered), before packing. The container of DMSO should be airtight. Microbially contaminated DMSO has a strong nasty smell.
    For synthesis of active ingredients of pesticide formulations, DMSO is used as a powerful polar aprotic solvent which can be effective for many chemical reactions, increasing reaction speed and yield. There is a long list of active ingredients for agriculture for which synthesis DMSO is used. However, because of its high boiling point, 189°C (372°F), DMSO evaporates slowly at normal atmospheric pressure. Substances dissolved in DMSO cannot be as easily recovered compared to other solvents, as it is very difficult to remove all traces of DMSO by conventional evaporation. Such an operation requires the application of special techniques, which is expensive. Among the largest consumers of DMSO in agrochemical industry there are such companies as Syngenta group, BASF, DOW AgroSciences (today Corteva Agriscience), ADAMA, Nufarm, Sumitomo, UPL, Nutrichem, etc.

  5. DMSO manufacturers. Among largest manufacturers of DMSO there are Arkema Group, Gaylord Chemical Company LLC, Hubei Xingfa Chemicals Group Co. Ltd., Eastman, Parchem Fine & Specialty Chemicals, Sigma Aldrich Co. LLC, Toray Fine Chemicals Co. Ltd., Zhuzhou Hansen Chemicals Co. Ltd., etc.

NMP

  1. N-Methyl-2-pyrrolidone (NMP) is produced in huge quantities across the world. It is a polar solvent with the formula C5H9NO and outstanding characteristics, CAS No. 872-50-4. It is a clear colorless liquid with a faint amine smell.

  2. Physicochemical properties of NMP. It has a wide range of uses due to its excellent physicochemical characteristics. NMP is highly polar and miscible with most organic solvents (alcohols, ethers, ketones, aromatic hydrocarbons, chlorinated hydrocarbons, etc.). Organic and inorganic substances are highly soluble in it. It mixes with water in all proportions. Its specific gravity is 1.027. It has a high flash point compared to similar solvents FP 86°C/187°F (closed cap). The boiling point is high BP 202°C/396°F, the freezing point is low -23°C/-9°F, and handling is easy. It is chemically and thermally stable, and not corrosive.

  3. Safety. N-Methylpyrrolidone is toxic to the reproductive system of male and female animals. Based on the animal tests, NMP should be considered as a potential human reproductive hazard. Prolonged exposure to NMP may cause skin, eye irritation, and other health issues which are expected to limit the use of N-Methyl-2-Pyrrolidone. That’s why NMP is prohibited for use in agrochemical products in EC, USA and in most Western countries. However, a lot of old agrochemical products with NMP yet are on the market, although many countries require to replace it in the crop protection products.

  4. NMP application. NMP is widely used due to its excellent solvency for a wide range of organic and inorganic chemical compounds. Yet it has the most massive use in agricultural formulations. It has high thermal and chemical stability and low surface tension. However, side-effects associated with the prolonged exposure to NMP are expected to restrict the use of the product which in turn limits the market growth. Nevertheless, there is a strong trend of growing demand for NMP.

  5. NMP manufacturers. In USA, the NMP Producers Group consists of BASF Corporation, Ashland, and Lyondell Chemical Company. The other big manufacturers of NMP are Shandong, Hefei TNJ, Puyang Guangming, Zhejiang Realsun Chemical, etc.
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