CN110845415A

CN110845415A - Environment-friendly synthesis method of 2-ethyl-4-methylimidazole

Info

Publication number: CN110845415A
Application number: CN201911080429.5A
Authority: CN
Inventors: 康富春; 唐增花; 刘海明
Original assignee: Guangzhou Guyan Electronic Material Co Ltd
Current assignee: Guangdong Guyan Electronic Materials Co ltd
Priority date: 2019-11-07
Filing date: 2019-11-07
Publication date: 2020-02-28
Anticipated expiration: 2039-11-07
Also published as: CN110845415B

Abstract

The invention discloses a green synthesis method of 2-ethyl-4-methylimidazole, belonging to the technical field of organic synthesis; the invention adopts low-toxicity methyl propionate and 1, 2-propane diamine to generate aminopropyl propionamide at a proper reaction ratio at the temperature of 80 ℃, and then uses aromatic hydrocarbon with water to close ring to generate 2-ethyl-4-methylimidazoline in the presence of a catalyst; dehydrogenating 2-ethyl-4-methylimidazoline at 120-140 ℃ in the presence of pd/c catalyst to obtain 2-ethyl-4-methylimidazole; the method for preparing the 2-ethyl-4-methylimidazole not only avoids using high-toxicity propionitrile, high-pollution aldehyde and ammonia and a high-risk Raney nickel catalyst burnt in air, but also does not generate waste ammonia in the production process, and belongs to an environment-friendly method for preparing the 2-ethyl-4-methylimidazole.

Description

Environment-friendly synthesis method of 2-ethyl-4-methylimidazole

Technical Field

The invention relates to a preparation method of environment-friendly 2-ethyl-4-methylimidazole, belonging to the technical field of organic synthesis.

Background

The 2-ethyl-4-methylimidazole is an epoxy resin curing agent with excellent performance. The epoxy resin is liquid at normal temperature, the dosage is less, the epoxy resin can be easily mixed with the epoxy resin, the mixture has long working life, and the curing temperature is not high; the cured product has excellent heat resistance, adhesiveness and insulativity, and is widely applied to the fields of adhesives, coatings, composite materials and the like. There are three main methods for producing 2-ethyl-4-methylimidazole: the first is aldehyde ammonia process, which adopts n-propyl aldehyde, acetone aldehyde water solution and ammonia water as material to prepare 2-ethyl-4-methyl imidazole in one pot, and has low yield, complicated purification and great amount of aldehyde ammonia effluent incapable of being treated. The other is imidazoline dehydrogenation, which is to prepare 2-ethyl-4-methylimidazoline by 1, 2-propane diamine and propionitrile under the catalysis of sulfur and then prepare 2-ethyl-4-methylimidazole through the catalytic dehydrogenation of raney nickel. The propionitrile in the method belongs to a highly toxic pipe product, the labor protection requirement is strict, a large amount of solid waste is generated by sulfur and sulfur-removing zinc powder, the ammonia gas discharged by the reaction pollutes the atmosphere, a large amount of impure ammonia-containing wastewater can be generated even if the ammonia gas is absorbed by water, and the operation risk is increased by using Raney nickel which spontaneously combusts when meeting air. Thirdly, cuprous salt is used as a catalyst, propionitrile and 2-aminopropionaldehyde diglycol are firstly reacted to generate an intermediate, alcohol and hydrochloric acid are then added to decompose the intermediate to generate 2-ethyl-4-methylimidazole, and the method not only uses virulent propionitrile and expensive 2-aminopropionaldehyde glycol, but also generates a large amount of wastewater in the acidolysis process. In summary, the existing preparation method of 2-ethyl-4-methylimidazole has the production difficulties of high toxicity, high pollution, dangerous operation and the like, and is also the reason that the price of 2-ethyl-4-methylimidazole is high.

Disclosure of Invention

The invention aims to provide a preparation method of 2-ethyl-4-methylimidazole, which abandons high-toxicity and dangerous raw materials, generates few three wastes in the production process and belongs to an environment-friendly preparation method.

In order to achieve the purpose, the invention adopts the technical scheme that:

methyl propionate and 1, 2-propane diamine in proper proportion are refluxed to generate aminopropyl propionamide, a ring closing catalyst and aromatic hydrocarbon are added to perform dehydration and ring closing reaction to generate 2-ethyl-4-methylimidazoline, a pd/c catalyst is added to perform medium-temperature dehydrogenation reaction, and the 2-ethyl-4-methylimidazole is prepared by reduced pressure distillation after filtration. The preparation method does not use high-toxicity propionitrile, high-pollution aldehyde ammonia and flammable Raney nickel, and no waste ammonia is discharged in the reaction process;

the ratio of the methyl propionate to the 1, 2-propane diamine is 1: 2 to 4 (molar ratio);

the reaction of the methyl propionate with 1, 2-propanediamine is carried out under reflux (about 80 ℃);

the ring closing catalyst is active alumina or dibutyl tin oxide or a 5A molecular sieve;

the medium-temperature dehydrogenation reaction refers to dehydrogenation reaction at 120-140 ℃;

the aromatic hydrocarbon is toluene, xylene and trimethylbenzene;

the specifications of the palladium-carbon catalyst are 5% and 10%.

The invention adopts methyl propionate to react with excessive 1, 2-propane diamine to firstly generate aminopropyl propionamide, and the purpose of excessive 1, 2-propane diamine is to reduce the generation of dipropionamide by-product. The aminopropyl propionamide generates dehydration ring-closing reaction in the presence of a catalyst, and the released water molecules are azeotropically taken away by aromatic hydrocarbon, so that the reaction equilibrium is moved to the product. The yield of the ring-closing product, namely 2-ethyl-4-methylimidazoline, can reach over 90 percent. The dehydrogenation catalyst of imidazoline is Raney nickel as conventional catalyst, but the Raney nickel is spontaneously combusted when meeting air, which causes great hidden trouble to production, so that the invention adopts a relatively stable palladium-carbon catalyst as the dehydrogenation catalyst of imidazoline. Dehydrogenating 2-ethyl-4-methylimidazoline with palladium-carbon catalyst to obtain 2-ethyl-4-methylimidazole with yield over 80%. The method for preparing the 2-ethyl-4-methylimidazole has the advantages of high yield, non-toxic and non-dangerous raw materials, belonging to conventional chemical raw materials, and little discharge of three wastes in the production process, and belonging to an environment-friendly preparation process.

Detailed Description

The present invention is further illustrated by the following examples, which are provided only for illustrating the present invention and are not intended to limit the scope of the present invention.

Example 1

Putting 88g of methyl propionate and 222g of 1, 2-propane diamine into a flask, carrying out reflux reaction at 80 ℃ for 3 hours, adding 3g of dibutyltin oxide and 176g of trimethylbenzene, distilling out unreacted reactants with low boiling point at low temperature, heating to 180 ℃, carrying out reflux for 3 hours with water, and distilling off anhydrous components. Vacuum distillation is carried out, 102-112 ℃/2.0kpa of fraction is collected, 98g of 2-ethyl-4-methylimidazoline is prepared, and the yield is 87.5%.

Example 2

88g of methyl propionate and 296g of 1, 2-propanediamine are placed in a flask and refluxed for 3 hours at 80 ℃, unreacted substances are distilled off, and then 5g of 5A molecular sieve and 176g of toluene are added to carry out reflux reaction with water until anhydrous fractions are distilled off. And finally, carrying out reduced pressure distillation, and collecting 102-112 ℃/2.0kpa of fraction to prepare 92g of 2-ethyl-4-methylimidazoline with the yield of 82%.

Example 3

Putting 88g of methyl propionate and 148g of 1, 2-propane diamine into a flask, carrying out reflux reaction for 3 hours at the temperature of 80 ℃, adding 3g of activated alumina and 176g of dimethylbenzene, distilling out unreacted reactants at low temperature, heating up, carrying out reflux dehydration reaction until anhydrous components are distilled out. Carrying out reduced pressure distillation, and collecting 102-112 ℃/2.0kpa of fraction to obtain 101g of 2-ethyl-4-methylimidazoline with the yield of 90%.

Example 4

112g of the prepared 2-ethyl-4-methylimidazoline was placed in a flask, 1.1g of 10% pd/c catalyst was added thereto, and the mixture was slowly heated to 120 ℃ to conduct dehydrogenation reaction for about 6 hours until no bubbles were released. Suction filtering, reduced pressure distillation, and collection of 91g of fraction with boiling point of 150-160 ℃/1.33kpa, yield 82.7%.

Example 5

112g of the 2-ethyl-4-methylimidazoline prepared above was taken, 2.2g of 5% pd/c catalyst was added, the mixture was slowly heated to 140 ℃ and the dehydrogenation reaction was continued for about 10 hours until no bubbles were released. Filtering by suction, distilling under reduced pressure, and collecting 95.5g of fraction with the boiling point of 150-160 ℃/1.33kpa, wherein the yield is 86.8%.

Claims

1. An environment-friendly synthesis method of 2-ethyl-4-methylimidazole, which is characterized by comprising the following steps: methyl propionate and 1, 2-propane diamine are used as starting materials, the starting materials react at 80 ℃ according to a proportion to generate aminopropyl propionamide, then aromatic hydrocarbon with water is used for generating a 2-ethyl-4-methylimidazoline intermediate in the presence of a ring closing catalyst, the intermediate is subjected to dehydrogenation reaction at 120-140 ℃ in the presence of a pd/c catalyst, and then the 2-ethyl-4-methylimidazole is prepared through filtration and reduced pressure distillation.

2. The method of synthesis according to claim 1, characterized in that: the ratio of the methyl propionate to the 1, 2-propane diamine is that the molar ratio is 1: 2 to 4.

3. The method of synthesis according to claim 1, characterized in that: the ring closing catalyst is dibutyl tin oxide, active alumina or 5A molecular sieve.

4. The method of synthesis according to claim 1, characterized in that: the aromatic hydrocarbon is toluene, xylene and trimethylbenzene.

5. The method of synthesis according to claim 1, characterized in that: the pd/c catalyst was 5% and 10% specification.

6. The method of synthesis according to claim 1, characterized in that: the filtration comprises vacuum filtration, vacuum filtration or pressure filtration.