5 New Methods for the Preparation of N,N-Dimethylacetamide

Dimethylacetamide (DMA), also known as N,N-dimethylacetamide or acetic dimethylamine, is less commonly discussed compared to its chemical counterpart dimethylformamide (DMF) in the field of chemical production. DMA, with the English name Dimethylacetamide (abbreviated as DMAC or DMA), is a colorless and transparent liquid that can be mixed with water, alcohols, ethers, and other organic solvents. It is a polar solvent with high thermal stability, resistance to hydrolysis, low corrosiveness, and low toxicity.

Dimethylacetamide
Dimethylacetamide

Dimethylacetamide Uses

DMA serves as an excellent polar solvent for the synthesis of natural resins. It is widely used in the synthesis of polyimides, polysulfonamides, and other high molecular weight compounds. Additionally, DMA is employed in resin film formation, fiber spinning, crystallization and purification of aromatic dicarboxylic acids (such as terephthalic acid), and as a catalyst in certain organic reactions. Compared to its chemical analogue, DMF, DMA exhibits higher thermal stability, greater resistance to hydrolysis, lower corrosiveness, and lower toxicity, making it a viable alternative to DMF.

5 New Methods for the Preparation of N,N-Dimethylacetamide
Packaging of N,N-Dimethylacetamide

Production Methods of Dimethylacetamide (DMA)

The production methods of dimethylacetamide (DMA) in China currently mainly include the acetic anhydride method, acetyl chloride method, and acetic acid method. Additionally, DMA can be synthesized by reacting ethyl acetate with dimethylamine, acetic acid with ammonia and methanol, or methyl acetate with dimethylamine. Another method involves the one-step carbonylation of trimethylamine with carbon monoxide.

1. Acetic Anhydride Method:

Dimethylacetamide is prepared by the reaction of acetic anhydride with dimethylamine:

First, an aqueous solution of dimethylamine is heated to vaporize the gas. After dehydration and purification of the gas, it is introduced into acetic anhydride at room temperature for acylation. The reaction is exothermic, and the acylation endpoint is reached when the reaction temperature no longer rises (170°C). Then, the acylation mixture is controlled at 0-20°C and neutralized by adding an alkaline solution. Sodium acetate is formed during the reaction, and it is separated when the pH reaches 8-9. After alkali washing of the neutralization liquid, ethyl acetate is added, and the mixture is subjected to azeotropic dehydration. After crude distillation, a fraction at 164-166.5°C is collected to obtain the final product, dimethylacetamide.

2. Acetic Acid Method:

Dimethylacetamide is prepared by the reaction of acetic acid with dimethylamine:

First, an aqueous solution of dimethylamine is heated to vaporize the gas. The gaseous dimethylamine is introduced into acetic acid for acylation. The reaction is exothermic and continues continuously. The crude product obtained is subjected to distillation, and a fraction at 164-166.5°C is collected to obtain the final product, dimethylacetamide. In China, successful synthesis has been achieved using catalytic distillation technology, utilizing the reaction heat and reducing energy consumption. Since the reaction and distillation are carried out in the same process, the process flow is greatly shortened, and the separation efficiency and product yield are significantly improved, with no discharge of waste.

3. Acetyl Chloride Method:

Dimethylacetamide is prepared by the reaction of dimethylamine with acetyl chloride:

Under cooling conditions, dimethylamine is introduced into ethyl ether, followed by the slow addition of a mixture of acetyl chloride and ethyl ether with stirring. White solid dimethylamine hydrochloride immediately precipitates, which is filtered. The filtrate is subjected to ether recovery using a water bath, followed by distillation. The fraction at 164-166.5°C is collected to obtain the final product, dimethylacetamide.

4. Ethyl Acetate Method:

Dimethylacetamide is prepared by the reaction of ethyl acetate and dimethylamine at 30°C, with a yield of 98%.

5. Methyl Acetate Method:

Dimethylacetamide is prepared by the reaction of methyl acetate and dimethylamine at a temperature of 140-170°C and a pressure of 2.0-2.5 MPa. This method has low corrosiveness, high product yield, and low production cost, and it has reached industrial conditions.

It is important to note that the choice of method depends on factors such as the desired scale of production, availability of starting materials, reaction conditions, and desired purity of the final DMA product.

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