CN109824466B - Method for preparing 2-methyl-1, 3-pentadiene - Google Patents
Method for preparing 2-methyl-1, 3-pentadiene Download PDFInfo
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- CN109824466B CN109824466B CN201910201904.3A CN201910201904A CN109824466B CN 109824466 B CN109824466 B CN 109824466B CN 201910201904 A CN201910201904 A CN 201910201904A CN 109824466 B CN109824466 B CN 109824466B
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Abstract
A method for preparing 2-methyl-1, 3-pentadiene relates to 2-methyl-1, 3-pentadiene. Removing one molecule of water from 2-methyl-2, 4-pentanediol to obtain 4-methyl-4-pentene-2-ol; removing one molecule of water from 4-methyl-4-pentene-2-ol to obtain 2-methyl-1, 3-pentadiene. The yield of 2-methyl-1, 3-pentadiene is improved, and the ratio of 2-methyl-1, 3-pentadiene to 4-methyl-1, 3-pentadiene can be improved to 9: 1, and the yield of 2-methyl-1, 3-pentadiene is more than 80%. The weakly acidic catalyst is used, so that the loss of equipment is reduced. The mild catalyst is selected, so that the loss of equipment is reduced, and the environmental friendliness of the reaction is improved. The method of step-by-step dehydration is adopted, so that the generation of 4-methyl-1, 3 pentadiene is greatly reduced, and the yield of 2-methyl-1, 3 pentadiene is improved.
Description
Technical Field
The invention relates to 2-methyl-1, 3-pentadiene, in particular to a method for preparing 2-methyl-1, 3-pentadiene.
Background
2-methyl-1, 3-pentadiene is an important intermediate for synthesizing perfume, and can be subjected to Diels-Alder reaction with other unsaturated olefin to synthesize cyclohexene derivative perfume molecules, such as ligustral. Ligustral has strong fragrance of green grass and grass, and can be used in daily chemical essence formula, especially in soap, synthetic detergent, and cosmetic essence formula. Can increase the fresh feeling and the diffusibility of the essence. The worldwide demand is about 2000 tons/year at present, and the incense belongs to an important incense raw material. Therefore, the preparation of the precursor 2-methyl-1, 3-pentadiene of the ligustral is particularly important.
The current method for preparing 2-methyl-1, 3-pentadiene is mainly obtained by dehydrating 2-methyl-2, 4-pentanediol which is obtained by condensing acetone, and British patent GB572602 discloses that 2-methyl-2, 4-pentanediol is dehydrated under the action of iodine or hydrochloric acid to prepare a mixture of 2-methyl-1, 3-pentadiene and 4-methyl-1, 3-pentadiene, but a catalyst of strong acid has strong corrosivity to reaction equipment. U.S. Pat. No. 20060058561 uses inorganic acid salt as catalyst to proceed dehydration reaction of 2-methyl-2, 4 pentanediol. A mixture of 2-methyl-1, 3-pentadiene and 4-methyl-1, 3-pentadiene is obtained. Polyethylene glycol auxiliary agents are also needed to be added in the reaction to bring away the reaction heat. Industrial application is difficult due to the high reaction temperature. SU1759825 dehydrates under the catalysis of inorganic acid in the presence of solvent such as ethylene glycol to obtain an isomer mixture of 2-methyl-1, 3-pentadiene and 4-methyl-1, 3-pentadiene, wherein the ratio of the two isomers is 3: 1 to 4: 1.
From the above, 2-methyl-1, 3-pentadiene is generally obtained by dehydrating 2-methyl-2, 4-pentanediol as an intermediate for producing ligustral, and there have been many problems in the prior art such as strong acidity, corrosiveness, and high reaction temperature of the catalyst for reaction. And the dehydration of 2-methyl-2, 4-pentanediol, in addition to obtaining 2-methyl-1, 3-pentadiene, inevitably produces the corresponding isomer, 4-methyl-1, 3-pentadiene, with the ratio of the two alkenes being between 3: 1 and 4: 1. Since 4-methyl-1, 3-pentadiene cannot undergo a Diels-Alder reaction with other unsaturated olefins and is often disposed of only as a waste by-product, the yield of 2-methyl-1, 3-pentadiene is limited.
Disclosure of Invention
The invention aims to provide a method for preparing 2-methyl-1, 3-pentadiene through two-step dehydration catalyzed by a weakly acidic catalyst aiming at the defects of the existing method for preparing 2-methyl-1, 3-pentadiene through dehydrating 2-methyl-2, 4-pentanediol.
The invention comprises the following steps:
1) removing one molecule of water from 2-methyl-2, 4-pentanediol to obtain 4-methyl-4-pentene-2-ol;
2) removing one molecule of water from 4-methyl-4-pentene-2-ol to obtain 2-methyl-1, 3-pentadiene.
In step 1), the specific method for removing one molecule of water from 2-methyl-2, 4-pentanediol can be as follows: in a reactor with a thorn-shaped fractionating column and a condensing tube connected at the top, 2-methyl-2, 4 pentanediol reacts and simultaneously the product 4-methyl-4-penten-2-ol is distilled out; the reaction temperature can be 110-140 ℃; the catalyst for the reaction can be loaded on montmorillonite ferric chloride, and the mass ratio of the ferric chloride to the montmorillonite can be (0.05-0.5): 1.
In step 2), the specific method for removing one molecule of water from 4-methyl-4-penten-2-ol can be as follows: in a reactor with a thorn-shaped fractionating column and a condensing tube connected at the top, 4-methyl-4-pentene-2-ol reacts while the product 2-methyl-1, 3-pentadiene is distilled out; the reaction temperature can be 120-150 ℃, and the catalyst for the reaction can be at least one of oxalic acid, citric acid, potassium hydrogen sulfate, ferric chloride and the like.
The reaction process of the invention is as follows:
the invention improves the yield of 2-methyl-1, 3-pentadiene, and the ratio of the 2-methyl-1, 3-pentadiene to the 4-methyl-1, 3-pentadiene can be improved to 9: 1, and the yield of the 2-methyl-1, 3-pentadiene is more than 80 percent. The invention uses weak acidic catalyst to reduce the loss of equipment.
The invention adopts a two-step dehydration method and selects a mild catalyst to obtain higher yield of the 2-methyl-1, 3 pentadiene. Compared with other prior art, the invention has the following advantages:
1) the mild catalyst is selected, so that the loss of equipment is reduced, and the environmental friendliness of the reaction is improved.
2) The method of step-by-step dehydration is adopted, so that the generation of 4-methyl-1, 3 pentadiene is greatly reduced, and the yield of 2-methyl-1, 3 pentadiene is improved.
Detailed Description
The following examples further illustrate the invention.
Example 1
(1) Preparation of 4-methyl-4-penten-2-ol
Adding 300g of 2-methyl-2, 4-pentanediol into a 500ml three-necked flask with stirring magnetons, adding 3g of ferric chloride catalyst loaded on montmorillonite (the mass ratio of ferric chloride to montmorillonite is 0.1: 1), connecting a thorn-shaped fractionating column, a condensing tube and a receiving bottle on the three-necked flask, carrying out reaction at the temperature of 110-140 ℃, extracting a product 4-methyl-4-pentene-2-ol during the reaction process, and analyzing the content of the 4-methyl-4-pentene-2-ol to be more than 90% by gas chromatography. 4-methyl-4-penten-2-ol is reacted (2).
(2) Preparation of 2-methyl-1, 3 pentadiene
Adding 300g of 4-methyl-4-penten-2-ol, 6g of a mixture of oxalic acid and ferric chloride (mass ratio is 3: 2) into a 500ml three-neck flask with a stirring magneton, connecting a thorn-shaped fractionating column, a condenser pipe and a receiving flask to the three-neck flask, reacting at 120-150 ℃, extracting a product 2-methyl-1, 3 pentadiene during the reaction, and analyzing the content of the 2-methyl-1, 3 pentadiene to be more than 90% and a small amount of 4-methyl-1, 3 pentene by gas chromatography.
The total yield of 2-methyl-1, 3 pentadiene in two steps was 83%.
Example 2
(1) Preparation of 4-methyl-4-penten-2-ol
Adding 300g of 2-methyl-2, 4-pentanediol into a 500ml three-necked flask with stirring magnetons, adding 3g of ferric chloride catalyst loaded on montmorillonite (the mass ratio of ferric chloride to montmorillonite is 0.3: 1), connecting a thorn-shaped fractionating column, a condensing tube and a receiving bottle on the three-necked flask, carrying out reaction at the temperature of 110-130 ℃, extracting a product 4-methyl-4-pentene-2-ol during the reaction process, and analyzing the content of the 4-methyl-4-pentene-2-ol to be more than 90% by gas chromatography. 4-methyl-4-penten-2-ol is reacted (2).
(2) Preparation of 2-methyl-1, 3 pentadiene
Adding 300g of 4-methyl-4-penten-2-ol, 6g of a mixture of oxalic acid and citric acid (mass ratio is 1: 1) into a 500ml three-necked bottle with a stirring magneton, connecting a thorn-shaped fractionating column, a condensing tube and a receiving bottle to the three-necked bottle, reacting at 120-150 ℃, extracting a product 2-methyl-1, 3 pentadiene during the reaction, analyzing the content of the 2-methyl-1, 3 pentadiene to be more than 90% by gas chromatography, and only a small amount of 4-methyl-1, 3 pentene in the extracted product.
The yield of 2-methyl-1, 3 pentadiene was 82%.
Example 3
(1) Preparation of 4-methyl-4-penten-2-ol
Adding 300g of 2-methyl-2, 4-pentanediol into a 500ml three-mouth bottle with stirring magnetons, adding 3g of ferric chloride catalyst loaded on montmorillonite (the mass ratio of ferric chloride to montmorillonite is 0.5: 1), connecting a thorn-shaped fractionating column, a condensing tube and a receiving bottle on the three-mouth bottle, carrying out reaction at the temperature of 110-130 ℃, extracting a product 4-methyl-4-pentene-2-ol during the reaction process, and analyzing the content of the 4-methyl-4-pentene-2-ol to be more than 90% by gas chromatography. 4-methyl-4-penten-2-ol is reacted (2).
(2) Preparation of 2-methyl-1, 3 pentadiene
Adding 300g of 4-methyl-4-pentene-2-ol, 6g of a mixture of potassium bisulfate and citric acid (mass ratio is 1: 2) into a 500ml three-neck flask with a stirring magneton, connecting a thorn-shaped fractionating column, a condensing tube and a receiving flask to the three-neck flask, carrying out reaction at 120-150 ℃, extracting a product 2-methyl-1, 3 pentadiene during the reaction, analyzing the content of the 2-methyl-1, 3 pentadiene by gas chromatography to be more than 92%, and only a small amount of 4-methyl-1, 3 pentene in the extracted product.
The yield of 2-methyl-1, 3 pentadiene was 85%.
Claims (4)
1. A process for the preparation of 2-methyl-1, 3-pentadiene characterised by the steps of:
1) removing one molecule of water from 2-methyl-2, 4-pentanediol to obtain 4-methyl-4-pentene-2-ol; the specific method for removing one molecule of water from 2-methyl-2, 4 pentanediol comprises the following steps: in a reactor with a thorn-shaped fractionating column and a condensing tube connected at the top, 2-methyl-2, 4 pentanediol reacts and simultaneously the product 4-methyl-4-penten-2-ol is distilled out; the catalyst for the reaction is loaded on montmorillonite ferric chloride, and the mass ratio of the ferric chloride to the montmorillonite is (0.05-0.5): 1;
2) removing one molecule of water from 4-methyl-4-pentene-2-ol to obtain 2-methyl-1, 3-pentadiene; the specific method for removing one molecule of water from 4-methyl-4-pentene-2-ol comprises the following steps: in a reactor with a thorn-shaped fractionating column and a condensing tube connected at the top, 4-methyl-4-pentene-2-ol reacts while the product 2-methyl-1, 3-pentadiene is distilled out; the catalyst for the reaction is at least one of oxalic acid, citric acid, potassium bisulfate and ferric chloride.
2. The process for preparing 2-methyl-1, 3-pentadiene according to claim 1, wherein in step 1), the reaction temperature is 110 to 140 ℃.
3. The process for preparing 2-methyl-1, 3-pentadiene according to claim 1, wherein in step 2), the reaction temperature is 120 to 150 ℃.
4. The process for preparing 2-methyl-1, 3-pentadiene according to claim 1, characterized by the following reaction sequence:
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB572602A (en) * | 1942-07-04 | 1945-10-16 | Shell Dev | Production of methyl pentadienes |
| SU1759825A1 (en) * | 1990-07-26 | 1992-09-07 | Всесоюзный научно-исследовательский институт синтетических и натуральных душистых веществ | Method of producing a mixture of 2-methyl- and 4-methylpenta-1,3-dienes |
| US20060058561A1 (en) * | 2004-09-11 | 2006-03-16 | Celanese Chemicals Europe Gmbh | Process for dehydrating 2-methylpentane-2,4-diol |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6157525A (en) * | 1984-08-28 | 1986-03-24 | Kao Corp | Production of methylpentadiene |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB572602A (en) * | 1942-07-04 | 1945-10-16 | Shell Dev | Production of methyl pentadienes |
| SU1759825A1 (en) * | 1990-07-26 | 1992-09-07 | Всесоюзный научно-исследовательский институт синтетических и натуральных душистых веществ | Method of producing a mixture of 2-methyl- and 4-methylpenta-1,3-dienes |
| US20060058561A1 (en) * | 2004-09-11 | 2006-03-16 | Celanese Chemicals Europe Gmbh | Process for dehydrating 2-methylpentane-2,4-diol |
Non-Patent Citations (3)
| Title |
|---|
| Dehydration of 2-methyl-2,4-pentanediol and 4-methyl-x-penten-2-ol under;Ipatief, V. N.et al.,;《JACS》;19451231;第67卷;第1200-1202页 * |
| Dehydration of alcohols, diols, and related compounds in dimethyl;Traynelis, Vincent J. et al.,;《Journal of Organic Chemistry》;19641231;第29卷(第1期);第123-129页 * |
| Dehydration of diols catalyzed by CeO2;Satoshi Sato, et al.,;《Journal of Molecular Catalysis A:Chemical》;20040807;第221卷;第177-183页 * |
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