N,N-dimethylformamide is an organic compound with the chemical formula of C3H7NO. It is a colorless transparent liquid. It is miscible with water and is miscible with most organic solvents. It is not only a widely used chemical raw material, but also a widely used excellent solvent. In addition to halogenated hydrocarbons, it can be mixed with water and most organic solvents at will, and has good solubility for a variety of organic and inorganic compounds.
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Chemical Property:
1. It is an aprotic polar solvent, which has good solubility for many organic and inorganic compounds, and has good chemical stability in the absence of alkali, acid and water.
2. Chemical properties: in the absence of acid, alkali and water, it is relatively stable even when heated to the boiling point. It is decomposed into formic acid and dimethylamine under the action of acid, while it is decomposed into formate and dimethylamine under the action of base.
3. It is decomposed into dimethylamine and formaldehyde under the action of ultraviolet rays, and then decomposed into dimethylamine and carbon monoxide when heated to about 350 ℃. It forms a relatively stable equimolar adduct with hydrochloric acid, with a melting point of 40 ° C and a boiling point of 110 ° C. It can also form crystalline adducts with SO3, with a melting point of 138 ° C and a boiling point of 145 ° C. dmf-so3 can be used as a mild sulfonating agent and sulfating agent. The adducts formed with POCl3, CoCl2, SOCl2, etc. can introduce Cho groups on aromatic rings with high electron density (Vilsmeier reaction). P2O5 is insoluble in N, N-dimethylformamide at room temperature, but it can dissolve at room temperature without precipitation after forming a stable complex above 40 ℃. When heated in the presence of metallic sodium, a violent reaction occurs and hydrogen gas is released. It can also react violently with triethylaluminum at 0 ℃. It can also react with Grignard reagent. When reacting with acyl chloride and anhydride, a derivative of dicarbonamide is formed.
4. It belongs to low toxicity. Animal experiments show that continuous administration of a large amount of N, N-dimethylformamide causes weight loss and hinders hematopoietic function. It has a strong irritating effect on eyes, skin and mucosa, and its liquid or vapor can cause liver disorders after being absorbed by the skin. Inhalation of high concentration of vapor can cause acute poisoning. The main symptoms are severe irritation, general spasm, painful constipation, nausea and vomiting. In addition to skin and mucous membrane irritation, chronic poisoning also includes nausea, vomiting, chest tightness, headache, general discomfort, decreased appetite, stomachache, constipation, hepatomegaly and liver function changes, and urobilinogen and urobilin can also be increased. During use, the average vapor concentration is required to be below 29.9mg/m3, and poisoning symptoms (central nerve injury) occur when the concentration is 59.8mg/m3. The oral toxicity LD50 of rats and mice was 3000-7000mg / kg. The olfactory threshold concentration is 0.14mg/m3, and TJ 36-79 stipulates that the maximum allowable concentration in the air of the workshop is 10mg / m3.
5. Stability: stable
6. Prohibited substances: strong oxidant, acyl chloride, chloroform, strong reductant, halogen, chlorinated hydrocarbon, concentrated sulfuric acid and fuming nitric acid
7. Polymerization hazard: non polymerization.
Since the first synthesis of dimethylformamide with formic acid and dimethylamine in 1899, the process methods of synthesizing dimethylformamide with different raw materials have been developed, such as dimethylamine carbon monoxide method, formamide dimethylamine method, cyanohydric acid methanol method, acetonitrile methanol method, methyl formate dimethylamine method, trichloroacetal dimethylamine method, etc. However, the industrial production abroad is still dominated by dimethylamine carbon monoxide method.
1. Methyl formate dimethylamine method: methyl formate is formed by esterification of formic acid and methanol, and then reacted with dimethylamine in gas phase to form dimethylformamide. Then, methanol and unreacted methyl formate are recovered by distillation, and the finished product is prepared by vacuum rectification.
2. Dimethylamine carbon monoxide method: it is obtained by direct reaction of dimethylamine and carbon monoxide under the action of sodium methoxide. The reaction conditions are 1.5-2.5mpa and 110-150 ℃. The crude product is rectified to obtain the finished product.
3. Methyl formate is synthesized by carbonylation of carbon monoxide and methanol under high pressure and temperature of 80-100 ℃, and then reacts with dimethylamine to produce dimethylformamide, and the finished product is obtained after rectification.
4. Trichloroacetal method: it is obtained by reacting trichloroacetal with dimethylamine.
Add chloroform and 0.52 parts of Trichloroacetaldehyde into the reaction kettle, cool it to below 30 ℃, and then introduce gaseous dimethylamine. At the same time, drop 0.78 parts of Trichloroacetaldehyde into the reaction kettle for reaction. After the reaction is completed, the distillation operation is carried out. When the top temperature of the rectification column is 58-64 ℃, the fraction is chloroform, and the fraction at 64-150 ℃ is the mixture of chloroform and dimethylformamide. The mixture is distilled under reduced pressure to obtain crude dimethylformamide, and then the crude crystal is rectified to obtain the finished product.
Consumption quota (kg / T): dimethylamine (40%) 2372; Trichloroacetaldehyde (95%) 2543.
Refining method: n, N-dimethylformamide often contains impurities such as water, ethanol, primary amine and secondary amine, and can form hcon (CH3) 2 · 2H2O with 2 molecules of water. To obtain high-purity products, the method of combining desiccant and distillation can be used. First, 1 / 10 volume of benzene was added and azeotropic distillation was carried out under normal pressure to remove water. And then refined according to the following methods:
① Add anhydrous magnesium sulfate (25g / L) to dry and distill under reduced pressure at 2 ~ 2.67kpa.
② Add powdered barium oxide, pour out the liquid after stirring, and distill under reduced pressure.
③ Add alumina powder (50g / L, fired at 500 ~ 600 ℃), mix and shake, and distill under reduced pressure (0.67 ~ 1.33kpa).
④ Add triphenylchlorosilane (5 ~ 10g / L), heat at 120 ~ 140 ℃ for 24 hours, and then distill under reduced pressure (0.67kpa). Conductivity of the product obtained by the above method: (1) (0.9 ~ 1.5) × 10 -7 S/m； (2) (0.4~1.0) × 10 -7 S/m； (3) (0.3~0.9) × 10 -7 S/m； (4) (0.2~0.5) × 10 -7 S/m。
5. The reagent dimethylformamide was obtained from the industrial product dimethylformamide through purification. If a small amount of water is contained in industrial products, it can be removed by 4A molecular sieve. If the moisture content is high, appropriate amount of granular potassium hydroxide can be added without shaking and fully standing for layering. After separating the water layer containing formic acid and other impurities, add 1 / 5 of reagent grade benzene in the volume of dimethylformamide for atmospheric rectification. When the gas phase temperature reaches 130 ℃, add appropriate amount of phosphorus pentoxide to the residual liquid, cover and shake for 3.5H, filter out the solid after standing, and then dehydrate with potassium hydroxide under nitrogen filling conditions, Then, under the protection of dry nitrogen, vacuum rectification is carried out to collect the middle distillate to obtain a high-purity product.
6. Dimethylamine and carbon dioxide are synthesized under pressure under the catalysis of sodium methoxide, or dimethylamine and methyl formate are prepared by gas phase reaction, or dimethylamine and Trichloroacetaldehyde are also prepared.