N,N-Dimethylaniline

Also known as dimethyl tiphenylamine, colorless to light yellow oily liquid, with a pungent odor, easy to oxidize in the air or under the sun and use the ze darkened. Relative density (20 ℃ / 4 ℃) 0.9555, freezing point 2.0 ℃, boiling point 193 ℃, flash point (opening) 77 ℃, flash point 317 ℃, viscosity (25 ℃) 1.528mpa-s, refractive index (n20D) 1.5584. Soluble in ethanol, ether, chloroform, benzene and other organic solvents. Soluble in a variety of organic compounds. Slightly soluble in water. It is combustible and will burn in case of an open flame. The vapor and air will form an explosive mixture with an explosive limit of 1.2%~7.0% (vol). It is highly toxic, and toxic aniline gas is released by high heat energy decomposition. It can be absorbed through the skin and cause poisoning, LD501410mg/kg, the maximum permissible concentration in air is 5mg/m3.
Storage method
1.Storage Precautions[25] Store in a cool, well-ventilated storehouse. Keep away from fire and heat sources. Keep the container sealed. It should be stored separately from acids, halogens, and edible chemicals, and never mixed. Equipped with corresponding varieties and quantity of fire-fighting equipment. The storage area should be equipped with emergency treatment equipment for leaks and suitable shelter materials.

2. Adopt iron drum sealed packing, 180kg per drum, and store in cool and ventilated place. Store and transport according to the regulations of flammable and toxic materials.
synthesis method
1. It is obtained by the reaction between aniline and methanol in the presence of sulfuric acid at high temperature and high pressure. Process flow:1. 790kg of aniline, 625kg of methanol, 85kg of sulfuric acid (ammonium 100%) are added into the reaction kettle, control temperature 210-215℃, pressure 3.1MPa, react for 4h, then release the pressure, the material is discharged to the separator, neutralized by 30% sodium hydroxide, static, and the lower quaternary ammonium salt is separated. Then at 160 ℃, 0.7-0.9MPa hydrolysis reaction for 3h, the hydrolysis products and the upper layer of oily materials combined by washing after vacuum distillation of the finished product.

2. Using methanol and aniline as raw materials, it is synthesized by alumina catalyst under the condition of 200-250℃ with excess methanol and atmospheric pressure. The raw material consumption quota: aniline 790kg/t, methanol 625kg/t, sulfuric acid 85kg/t. The laboratory preparation can react aniline with trimethyl phosphate.

3, aniline and methanol mixed (n aniline: n methanol ≈ 1:3), and through the reciprocating non-pulse metering pump injected at 0.5h-1 air speed into the reactor equipped with a catalyst, the reaction outflow first into the glass gas-liquid separator, the separator under the liquid collected at regular intervals removed for chromatographic analysis.

In 2001, Nankai University and Tianjin Ruikai Technology Development Co., Ltd. jointly developed a highly efficient aniline methylation catalyst, and realized the gas-phase synthesis of N,N-dimethyl aniline. The process is as follows: Liquid aniline is mixed with methanol, vaporized in the vaporization tower, and then entered into a tubular reactor with an air velocity of 0.5-1.0h-1 (the fixed bed of the tubular reactor is equipped with loaded nano-solid catalyst), and continuously produced at 250-300℃ under atmospheric pressure, with a DMA yield of over 96%.

Refining method: It often contains impurities such as aniline and N-methyl aniline. N,N-dimethylaniline is dissolved in 40% sulfuric acid and distilled by water vapor. Sodium hydroxide is added to make it alkaline. The distillation is continued with water vapor. The distillate is separated into aqueous layers and dried with potassium hydroxide. Normal pressure distillation is carried out in the presence of acetic anhydride. The distillate is washed with water to remove traces of acetic anhydride, dried with potassium hydroxide, followed by barium oxide, and distilled under reduced pressure in the presence of a stream of nitrogen. Other methods of refining the distillate include adding 10% acetic anhydride and refluxing for a few hours to remove the primary and secondary amines. After cooling, an excess of 20% hydrochloric acid is added and extracted with ether. The hydrochloric acid layer is alkaline with alkali and then extracted with ether, and the ether layer is dried with potassium hydroxide and distilled under reduced pressure under a stream of nitrogen. N,N-dimethylaniline can also be converted to picric acid salts, recrystallized to a constant melting point and then decomposed with a warm 10% aqueous solution of sodium hydroxide. It is then extracted with ether, washed and dried, and distilled under reduced pressure.

5. Aniline, methanol and sulfuric acid mixed in proportion, condensation reaction in the autoclave, the reaction products by the pressure relief recovery of methanol, add alkali neutralization, separation and then distillation by reduced pressure to obtain the product.

6. N,N-dimethylaniline can be generated by the methylation reaction of aniline and trimethyl phosphate, and then extracted by ether, dried and distilled.

7. N,N-dimethylaniline can be synthesized on the catalytic bed of Ziegler catalyst in copper-manganese system or copper-zinc-chromium system at 280℃ with the mixture of aniline and methanol at the ratio of 1:3.5. The obtained N,N-dimethylaniline was collected at 193-195℃ on a 54-tab column distillation device and packed into brown glass bottles. For the preparation of pure N,N-dimethylaniline, the N,N-dimethylaniline can be injected with nitrogen gas as carrier gas into the preparation gas chromatograph which has a metal phosphate column.