Patent Application
20210363076
The invention relates to a dehydrochlorination reaction of organic matters, belongs to the field of organic synthesis reactions, and more particularly relates to a method for preparing 2-methylallyl chloride by dehydrochlorination of 1,2-dichloro-tert-butane.
2-Methylallyl chloride is an important intermediate for organic synthesis and is widely used in medicine, pesticides, perfume monomers, polymer materials and other fields.
2-Methylallyl chloride is generally obtained by a gas-phase chlorination reaction of isobutylene with chlorine gas. For example, in DE3402446, CN1030407, CN1288119, CN101182279, and CN202044960, an isobutylene gas-phase chlorination reaction is adopted to prepare 2-methylallyl chloride.
Various side reactions occur during the chlorination reaction. In addition to the main product 2-methylallyl chloride, the reaction products usually include a certain amount of chloro-tert-butane, isobutenyl chloride, 1,2-dichloro-tert-butane and 3,3′-dichloro-isobutylene and other side products. Among them, 1,2-dichloro-tert-butane and 3,3′-dichloro-isobutylene are polychlorinated by-products, are free of direct application field, and need to be treated as hazardous wastes. In the separation process of chlorination reaction liquid, the polychloride is generally discharged as a high-boiling-point component from the tower bottom of the last tower of a multi-tower continuous rectifying tower.
The simplest separation process is two-tower continuous rectification, which separates low-boiling-point substances from the top of the first tower and separates high-boiling-point substances from the second tower (“Industrial Production Technology of Methallyl Chloride with an Annual Output of 1,000 tons”, Nanjing Meishan Chemical Plant, 1995).
CN1288119 employs a five-tower process to discharge high-boiling-point substances from a fifth tower.
None of the existing literatures mentions the effective use of high-boiling-point substances.
In view of the problem of effective utilization of high-boiling-point substances, the inventors of the present invention propose a method to separate 1,2-dichloro-tert-butane from high-boiling-point substances, and then prepare 2-methyl 3-chloro-allyl from 1,2-dichloro-tert-butane and a sodium hydroxide aqueous solution. This method can not only realize waste utilization, but also has high reaction selectivity.
A method for preparing 2-methyl 3-chloro-allyl from 1,2-dichloro-tert-butane, wherein 1,2-dichloro-tert-butane and a sodium hydroxide aqueous solution are used as raw materials, and react in a rectifying tower to eliminate hydrogen chloride, and the product 2-methyl 3-chloro-allyl is rectified from the top of the rectifying tower.
The sodium hydroxide aqueous solution has a concentration of 10˜20%; and a mass ratio of the sodium hydroxide aqueous solution to the 1,2-dichloro-tert-butane is 1.6-3.5:1.
An azeotrope of the 2-methyl-3-chloro-allyl and water is obtained from the top of the rectifying tower, and is layered by cooling to obtain the 2-methyl 3-chloro-allyl.
The rectifying tower is a combined rectifying tower, wherein a plate type tower is provided at the lower part of the combined rectifying tower; a packing tower is provided at the upper part of the combined rectifying tower; an inner reflux condenser is provided at the top of the tower top; and a reboiler is provided at the bottom of the combined rectifying tower to provide a heat source.
The number of plates in the plate type tower on the lower part of the combined rectifying tower is 10-20; and the upper packing tower has 10-20 theoretical plates.
A tray of the plate type tower is a sieve tray, a bubble tray or a float valve tray; and the packing tower is structured packing or random packing.
The sodium hydroxide aqueous solution is added from a first plate of the plate type tower of the combined rectifying tower, and the 1,2-chloro-tert-butane is added from the fifth to fifteenth plates in the middle of the plate type tower on the lower part of the combined rectifying tower.
The reflux ratio of a reflux in the tower top is controlled to 1-5.
The inventors of the present invention have through researches found that in the presence of alkaline, chlorine on the tertiary carbon of 1,2-dichloro-tert-butane is more likely to undergo a elimination reaction than chlorine on a 1-position, and the eliminated hydrogen chloride reacts with sodium hydroxide to generate sodium chloride, and the reaction product is 2-methyl 3-chloro-allyl (i.e., 2-methylallyl chloride). However, if the formed 2-methylallyl chloride cannot leave a basic reaction system in time, it will continue to undergo hydrolysis and etherification reactions to form 2-methylallyl alcohol and 2-methylallyl ether, thereby reducing the reaction selectivity. To this end, the present invention proposes to adopt a reactive rectification method (a reaction in a rectifying tower) to carry out the elimination reaction. The product 2-methylallyl chloride is removed from the reaction system in time by taking advantage of the fact that the boiling point of the product is about 30° C. lower than that of the reactants and the product can form a binary azeotrope with water, thereby greatly improving the selectivity of the elimination reaction. After the binary azeotrope is cooled, the organic phase is layered into an organic phase, i.e., 2-methyl 3-chloro-allyl. Studies have also found that this elimination reaction requires a certain residence time. Therefore, the present invention uses the plate type tower as a reactor for the elimination reaction.
According to the present invention, reactive rectification is adopted, such that 1,2-dichlorot-butane and a sodium hydroxide aqueous solution are subjected to a hydrogen chloride elimination reaction to obtain 2-methylallyl chloride. The reaction selectivity is high, and the by-product 1,2-dichloro-tert-butane is converted into the product 2-methylallyl chloride.
The technical solution of the present invention will be further described below with reference to the examples.
The separation process of 1,2-dichloro-tert-butane feedstock required by the present invention is as follows:
high-boiling-point substances (about 80% of 1,2-dichloro-tert-butane and about 20% of 3,3′-dichloro-isobutene) are continuously added to the middle of a continuous rectifying tower with 20 theoretical plates, and a ratio ratio on the tower top is controlled to about 1.0. The 1,2-dichloro-tert-butane produced from the tower top accounts for 79.8% of the feed, has a content of 99.8% or more. 3,3′-Dichloro-isobutylene is obtained from the tower bottom with a content of about 99%.
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| Number | Date | Country | Kind |
|---|---|---|---|
| 201810134166.0 | Feb 2018 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2018/109598 | 10/10/2018 | WO | 00 |
