Method for continuously and efficiently synthesizing citral based on one-pot method

Abstract

The invention discloses a method for continuously and efficiently synthesizing citral based on a one-pot method. According to the method disclosed by the invention, efficient synthesis from acetal to citral is realized in a reaction container by utilizing a metal supported catalyst. Wherein the preparation of the used metal supported catalyst is realized by loading one or more of common metals or transition metals such as iron, sodium, potassium, aluminum, magnesium, copper, zinc, titanium, gold, platinum, palladium, nickel, rhodium, osmium, ruthenium, vanadium, cobalt, chromium, molybdenum and the like into aluminum oxide, magnesium oxide, ceramic, diatomite or a molecular sieve carrier through an impregnation method or a coprecipitation method. The reaction raw material is acetal, and the cracking reaction and the rearrangement reaction are carried out in one reaction container. According to the present invention, the complex multi-step process is reduced to the one-pot continuous reaction, the intermediate rectification cracking process is reduced, the time is shortened by more than 50%, and the high-purity citral can be rapidly and massively obtained.

Description

Technical Field

[0001] The invention relates to the field of organic chemical industry and pharmaceutical intermediate synthesis, and specifically to realizing one-pot continuous and efficient synthesis of citral through a certain supported metal catalyst. Background Art

[0002] Citral is a colorless to pale yellow oily liquid with a strong lemon aroma. 10 H 16 O, its fragrance helps to concentrate and improves people's mood. Citral has a wide range of uses, mainly used in the preparation of lemon, citrus and assorted fruit flavors, and is also the main raw material for synthesizing ionones and vitamins. Citral has a relatively active chemical property and is prone to redox reactions to produce geranic acid or geraniol / nerol.

[0003] Citral can be separated and extracted from plant essential oils and prepared by chemical synthesis. It is obtained by vacuum distillation of Litsea cubeba oil. This method has harsh process conditions, a long production process and a low extraction rate. Especially with the expansion of the use of citral, citral made from natural resources can no longer meet the needs of market development and is not suitable for large-scale production. The chemical synthesis method can be divided into the dehydrogenation linalool transposition method and the condensation rearrangement synthesis method of 2 C5 enols and enal. At present, the industrial production of citral is mainly chemical synthesis. The reaction process is as follows Figure 1 shown.

[0004] The dehydrolinalool transposition method can be divided into the following according to the catalyst: 1) dehydrolinalool is first esterified with acetic anhydride to obtain dehydrolinalyl acetate, and then rearranged and hydrolyzed under the catalysis of silver or copper ions to obtain citral, and the yield of this method is 70% to 90%. This production process has a long reaction step, uses acetic anhydride, and has a high production cost; 2) using vanadium-containing oxide as the main catalyst, silanol as the co-catalyst, and high-boiling point paraffin oil as the solvent for reaction, the yield is about 78%, but the price of silanol is relatively high, and the production cost is also relatively high; 3) in a mixed reaction system composed of titanium tetrachloride or titanium tetrabutoxide and copper or silver halide, dehydrolinalool can be catalytically rearranged to obtain citral, and the process of this method is simple, but the yield is low, only 64%.

[0005] The synthesis method based on the condensation and rearrangement of two C5 enols and enals uses isopentenol and isopentenal as raw materials, condenses to obtain acetal, and then obtains citral through cracking and rearrangement. Although the yield exceeds 95%, this process is an intermittent production process, which has the disadvantages of large floor space, long synthesis time, and complicated synthesis steps.

[0006] US Pat. No. 5,177,265A discloses a method for preparing citral by condensation, cracking and rearrangement using isopentanal and isopentanol as raw materials and phosphoric acid as a catalyst. The method uses toluene as a solvent, and the conversion rate of isopentanal is 83% under the conditions of a reaction temperature of 60-90° C. and a pressure of 8000-14000 Pa (absolute pressure). The disadvantages are that the excess acid after the reaction needs to be neutralized by adding alkaline salt, which increases the "three wastes", the post-processing process is cumbersome, and the reaction cannot be carried out continuously.

[0007] In summary, in the reaction of preparing citral by condensation of isopentanol and isopentanal using an acidic catalyst, the catalytic conversion rate is low, side reactions are prone to occur, affecting the product yield, and the acidic substance is corrosive to the equipment, requiring high equipment materials, increasing equipment investment in industrial production, and the reaction process is complicated and equipment cleaning is cumbersome. In addition, the reaction is catalyzed by an acidic catalyst, and the reaction solution is acidic. After the reaction is completed, the reaction solution needs to be neutralized, which will produce a large amount of wastewater, which does not meet the development concept of economic and environmental protection in modern industrial production.

[0008] Therefore, there is an urgent need to research and develop a citral synthesis system with high activity, good selectivity, easy separation, high production efficiency, economy and environmental protection. Summary of the invention

[0009] The purpose of the present invention is to provide a method for continuously and efficiently synthesizing citral based on a one-pot process in view of the deficiencies in the prior art.

[0010] The present invention adopts the following technical solution:

[0011] Based on the one-pot continuous and efficient synthesis method of citral, a metal-supported catalyst is used to achieve efficient synthesis from acetal to citral in one reaction vessel.

[0012] The preparation of metal supported catalysts is achieved as follows:

[0013] One or more common metals or transition metals such as iron, sodium, potassium, aluminum, magnesium, copper, zinc, titanium, gold, platinum, palladium, nickel, rhodium, osmium, ruthenium, vanadium, cobalt, chromium, molybdenum, etc. are loaded into alumina, magnesium oxide, ceramics, diatomaceous earth, or molecular sieve carriers by impregnation or co-precipitation.

[0014] The citral synthesis process of the present invention comprises placing isopentenyl acetal and a catalyst in a reaction container, and reacting under certain conditions to directly and efficiently obtain citral. The reaction raw material is acetal, and the cracking and rearrangement reactions are both carried out in one reaction container.

[0015] The reaction temperature is controlled at 100-300°C, the reaction pressure is -1.0-0 MPa, the rotation speed is 300-400 rpm, the reaction time is controlled at 0.5-5.0 h, and the mass ratio of the reaction raw materials to the catalyst is 26-50:0.45. The reaction process is as follows Figure 2 shown.

[0016] The invention adds raw materials and catalysts into a reaction container, and reacts at a suitable temperature for a period of time to directly obtain a citral product without requiring intermittent distillation treatment in the middle.

[0017] The beneficial effects of the present invention are as follows:

[0018] The existing system for synthesizing citral has problems such as low conversion rate and cumbersome discontinuous process operation. The present invention reduces the complex multi-step process to a one-pot continuous reaction in the synthesis process of citral by using a supported metal catalyst, reduces the refining process of the intermediate, shortens the time by at least 50%, and can efficiently prepare high-purity citral. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the reaction process of citral.

[0020] Figure 2 Schematic diagram of the one-pot continuous synthesis of citral. DETAILED DESCRIPTION

[0021] The following description is only a preferred embodiment of the present invention and does not limit the present invention. For those skilled in the art, various changes and variations are possible. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0022] Example 1

[0023] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.1 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and the reaction was continued for 1.5 hours to obtain the light component citral with a purity of 94.1% and a yield of 87.5%.

[0024] Example 2

[0025] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 220 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.1 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and the reaction was continued for 1.5 hours to obtain the light component citral with a purity of 91.5% and a yield of 87.5%.

[0026] Example 3

[0027] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 180 ° C and the heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.1 MPa, and the low-temperature cooling circulation pump was set to -30 ° C for circulation cooling. After reacting for 1.5 hours, the light component citral was obtained with a purity of 93.2% and a yield of 77.8%.

[0028] Example 4

[0029] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.04 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and the reaction was continued for 1.5 hours to obtain the light component citral with a purity of 84.2% and a yield of 81.8%.

[0030] Example 5

[0031] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.08 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and the reaction was continued for 1.5 hours to obtain the light component citral with a purity of 83.2% and a yield of 84.1%.

[0032] Example 6

[0033] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.06 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and the reaction was continued for 1.5 hours to obtain the light component citral with a purity of 96.2% and a yield of 96.1%.

[0034] Example 7

[0035] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.06 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and the reaction was continued for 2.5 hours to obtain the light component citral with a purity of 88.4% and a yield of 95.1%.

[0036] Example 8

[0037] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 400 rpm, the pressure was adjusted to -0.06 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and the reaction was continued for 1.5 hours to obtain the light component citral with a purity of 86.4% and a yield of 85.3%.

[0038] Example 9

[0039] 30 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.06 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and after reacting for 0.5 h, the light component citral was obtained with a purity of 78.4% and a yield of 85.3%.

[0040] Example 10

[0041] 50 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.06 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and after reacting for 1.5 hours, the light component citral was obtained with a purity of 75.4% and a yield of 78.7%.

[0042] Embodiment 11

[0043] 50 ml of acetal and 0.45 g of catalyst were added to the reaction vessel, the oil bath temperature was set to 200 °C and heating was turned on, the speed was set to 300 rpm, the pressure was adjusted to -0.06 MPa, the low-temperature cooling circulation pump was set to -30 °C for circulation cooling, and after reacting for 5.0 hours, the light component citral was obtained with a purity of 80.4% and a yield of 85.3%.

[0044] Summary of Examples

[0045]

[0046]

[0047] As can be seen from the tables of Examples 1-11, the existing system for synthesizing citral has problems such as low conversion rate and cumbersome discontinuous process operation. The present invention reduces the complex multi-step process to a one-pot continuous reaction in the synthesis process of citral by using a supported metal catalyst, reduces the process of distillation and cracking intermediates, shortens the time by at least 50%, and can efficiently and massively prepare high-purity citral.

Claims

1. A method for continuously and efficiently synthesizing citral based on a one-pot process, characterized in that: Using metal-supported catalysts, efficient synthesis from acetal to citral can be achieved in one reaction vessel.

2. The method according to claim 1, characterized in that The metal element of the supported metal catalyst includes one or more common metals or transition metals including iron, sodium, potassium, aluminum, magnesium, copper, zinc, titanium, gold, platinum, palladium, nickel, rhodium, osmium, ruthenium, vanadium, cobalt, chromium, and molybdenum.

3. The method according to claim 1, characterized in that The carrier of the metal-supported catalyst is one of aluminum oxide, magnesium oxide, ceramics, diatomaceous earth and molecular sieve.

4. The citral synthesis method according to claim 2 or 3, characterized in that The reaction raw material is acetal.

5. The method according to claim 4, characterized in that The cleavage and rearrangement reactions are all carried out in one reaction vessel.

6. The method according to claim 5, characterized in that The reaction temperature is controlled at 100-300° C., the reaction pressure is -1.0-0 MPa, the rotation speed is 300-400 rpm, and the reaction time is controlled at 0.5-5.0 h.

7. The method according to claim 6, characterized in that The mass ratio of the reaction raw material acetal to the metal-supported catalyst is 26-50:0.45.

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