Storage-stable citral and preparation method thereof

Abstract

According to the storage-stable citral and the production method thereof provided by the invention, the purpose of improving the storage stability is achieved by controlling the key component isomenthenol in a citral product to be within a certain content range.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical intermediate synthesis, specifically relating to a method for producing storage-stable citral. Background Technology

[0002] Citral, also known as 3,7-dimethyl-2,6-octadien-1-aldehyde, is a widely used fragrance in daily chemical products and a key chemical intermediate. It is a raw material for synthesizing fragrances such as ionone and methyl ionone, and can also be widely used as a fragrance ingredient in tableware detergents, soaps, and toilet waters. In nutritional chemicals, it is used to manufacture vitamins A and E.

[0003] To date, published patent documents related to citral, such as CN112619692B and CN112058313B, mainly focus on improvements in the synthesis process. However, the impact of trace components on the storage stability of citral products is currently a blank area of ​​research. Summary of the Invention

[0004] The purpose of this invention is to provide a storage-stable citral product and its production method.

[0005] The synthesis process using isobutylene and formaldehyde as raw materials is currently the mainstream process for commercially available citral products. The crude citral product obtained by this process is purified by conventional distillation, but the resulting citral product has poor storage stability. To further improve the storage stability of citral and meet the high-end needs of downstream fragrance and flavor customers, it is necessary to control the trace impurities in the citral product.

[0006] Further research revealed that when the isomentheneol content in citral products was high, the TD24 temperature of the samples, as measured by instruments, was low, indicating poor storage stability. This is because the isomentheneol molecule has a one-carbon double bond at the terminal position, which is chemically reactive. This terminal double bond induces an exothermic coupling polymerization reaction between isomentheneol molecules, causing heat accumulation and an increase in temperature, leading to the deterioration of the citral product. The molecular formula of isomentheneol is as follows:

[0007]

[0008] Based on the above findings, the technical solution adopted by the present invention to achieve the aforementioned objectives is as follows:

[0009] In a first aspect, the present invention provides a storage-stable citral.

[0010] A storage-stable citral comprising citral and isomentheneol, wherein the isomentheneol content is 0.22% to 2.09% by mass, preferably 0.5% to 1.8%; and the citral content is 96.5% or more by mass.

[0011] Secondly, the present invention provides a method for producing storage-stable citral, comprising:

[0012] (1) The crude citral product is pretreated to obtain crude citral liquid.

[0013] (2) The pretreated crude citral liquid was separated by distillation to obtain citral product.

[0014] In this invention, the crude citral product is obtained by reacting isobutylene and formaldehyde under high temperature and high pressure (T > 250℃, P > 20MPaA) with Prins reaction to obtain 3-methyl-3-buten-1-ol, followed by isomerization, oxidation, condensation, cleavage and rearrangement. The process route is shown below:

[0015]

[0016] The isomenthene alcohol content in the crude citral product typically ranges from 3.5% to 5.5%.

[0017] In this invention, in order to control the content of the key component isomentheneol to be 0.22% to 2.09%, the crude citral product is first pretreated. One specific treatment scheme is to mix the crude citral product with an azeotropic additive evenly. The azeotropic additive can form the highest azeotrope with isomentheneol without affecting the distillation separation sequence of other components.

[0018] Specifically, the aforementioned azeotropic additive is a high-boiling-point fatty alcohol, preferably a C15-C25 saturated fatty alcohol, and more preferably a C18-C22 saturated fatty alcohol. The amount of the azeotropic additive is 0.5%-4.5% of the crude citral product, preferably 1.0%-3.5%.

[0019] In this invention, the distillation conditions are not particularly limited, generally the pressure range is 30 to 6500 PaA, preferably 40 to 2500 PaA, the number of trays is 10 to 50, and the reflux ratio is 0.3 / 1 to 2.5 / 1.

[0020] In the method of this invention, storage stability is characterized by the parameter TD24, which physically represents the lowest temperature corresponding to the maximum reaction rate after 24 hours under adiabatic conditions. Generally speaking, chemically reactive components in a material undergo trace chemical reactions under certain conditions, releasing heat and causing a continuous accumulation of heat in the material, thereby accelerating the reaction and heat accumulation. This is the main factor affecting the TD24 value. The storage temperature of most materials is much lower than their TD24 value; the higher the TD24 value of a material, the better its storage stability.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention provides a method for preparing storage-stable citral. By controlling the content of isomentheneol in the crude product within a reasonable range, the storage stability of the product citral is improved. Moreover, after being stored at room temperature (25°C) for 730 days, the purity decreases by less than 2%, meeting the high-end market demand for storage-stable citral. Detailed Implementation

[0023] The method provided by the present invention will be further illustrated by the following embodiments, but the present invention is not limited to the listed embodiments and should also include any other known modifications within the scope of the claims of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0026] Raw material source:

[0027] Citral crude product (GC purity: 83%–94%) was sourced from Wanhua Chemical Group.

[0028] Eicosanol (GC purity: >99%), Beijing Innocare Reagent Co., Ltd.

[0029] In this invention, the purity of raw materials and the content of isomentheneol were determined by gas chromatography.

[0030] Analytical instruments:

[0031] GC gas chromatograph: Agilent 7890, column DB-5, injection port temperature: 260℃; split ratio 40:1; carrier gas flow rate: 30ml / min; temperature program: 80~230℃, 3℃ / min; detector temperature: 280℃.

[0032] Storage stability test: measured using an adiabatic accelerated calorimeter (ARC), brand and model: THT-ARC.

[0033] Example 1

[0034] 700g of crude citral (containing 86.0% citral and 6.5% isomentheneol) and 10g of eicosanol were added to a 1000mL glass buffer tank. The crude citral was then transferred by siphon to the bottom of a conventional distillation column (28 plates, reflux ratio 1.2 / 1, and top pressure 490PaA). After the distillation column was running stably, 45g of the first fraction (boiling range 81.0℃~83.9℃) was collected from the top. Then, the receiving flask was switched to collect 530g of the fraction (boiling range 83.9~85.3℃). Analysis showed that the citral purity was 96.8% and the isomentheneol purity was 1.73%.

[0035] According to the accelerated calorimeter (ARC) test, its TD24 = 160℃, after being stored at room temperature (25℃) for 730 days, its purity decreased to 95.2%, a decrease of 1.6%.

[0036] Example 2

[0037] 700g of crude citral (containing 88.4% citral and 5.3% isomentheneol) and 12g of eicosanol were added to a 1000mL glass buffer tank. The crude citral was then transferred by siphon to the bottom of a conventional distillation column (32 plates, reflux ratio 1.1 / 1, top pressure 520PaA). After the distillation column was running stably, 43g of the first fraction (boiling range 81.7℃~84.2℃) was collected from the top. Then, the receiving flask was switched to collect 538g of the fraction (boiling range 84.2~86.3℃). Analysis showed that the purity of citral was 97.9% and the isomentheneol was 1.09%.

[0038] According to the accelerated calorimeter (ARC) test, its TD24 = 168℃. After being stored at room temperature (25℃) for 730 days, its purity decreased to 96.9%, a decrease of 1.0%.

[0039] Example 3

[0040] 700g of crude citral (containing 93.0% citral and 2.5% isomentheneol) and 12g of eicosanol were added to a 1000mL glass buffer tank. The crude citral was then transferred by siphon to the bottom of a conventional distillation column (29 plates, reflux ratio 1.2 / 1, and top pressure 510PaA). After the distillation column was running stably, 41g of the first fraction (boiling range 83.6℃~84.7℃) was collected from the top. Then, the receiving flask was switched to collect 542g of the fraction (boiling range 84.7~86.9℃). Analysis showed that the purity of citral was 98.7% and the isomentheneol was 0.53%.

[0041] According to the accelerated calorimeter (ARC) test, its TD24 = 175℃. After being stored at room temperature (25℃) for 730 days, its purity decreased to 98.2%, a decrease of 0.5%.

[0042] Comparative Example 1

[0043] Isomentrenol was added to the citral product in Example 2 above, so that its citral content was 97.8% and its isomentrenol content was 2.53%. It was directly tested by accelerated calorimeter (ARC) and its TD24 was 154°C. After being stored at room temperature (25°C) for 730 days, its purity decreased to 95.6%, a decrease of 2.2%.

[0044] Comparative Example 2

[0045] 700g of crude citral (containing 93.0% citral and 2.5% isomentheneol) and 15g of eicosanol were added to a 1000mL glass buffer tank. The crude citral was then transferred by siphon to the bottom of a conventional distillation column (39 plates, reflux ratio 1.2 / 1, and top pressure 480PaA). After the distillation column was running stably, 41g of the first fraction (boiling range 83.6℃~84.7℃) was collected from the top. Then, the receiving flask was switched to collect 542g of the fraction (boiling range 84.7~86.9℃). Analysis showed that the citral purity was 99.3% and the isomentheneol content was 0.15%.

[0046] According to the accelerated calorimeter (ARC) test, its TD24 = 163℃. After being stored at room temperature (25℃) for 730 days, its purity decreased to 97.6%, a decrease of 1.7%.

[0047] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A storage stable citral, which comprises citral and isomenthol, the mass content of isomenthol being 0.22% to 2.09%, preferably 0.5% to 1.8%, and the mass content of citral being 96.5% or more.

2. A method for preparing the citral according to claim 1, comprising: (1) pretreating a citral crude product to obtain a citral crude liquid; and (2) subjecting the citral crude liquid to rectification separation to obtain a citral product. The citral crude product is obtained by the Prins reaction of isobutylene and formaldehyde under high temperature and high pressure to obtain 3-methyl-3-buten-1-ol, followed by isomerization, oxidation, condensation, cleavage and rearrangement. The method for the pretreatment is to mix the citral crude product with a co-boiling additive uniformly, the co-boiling additive being a saturated aliphatic alcohol with a carbon number of C15 to C25, and further preferably a saturated aliphatic alcohol with a carbon number of C18 to C22.

3. The production method according to claim 2, wherein, The amount of the co-boiling additive is 0.5% to 4.5% of the mass of the citral crude product, and preferably 1.0% to 3.5%.

4. The production method according to claim 2, wherein, The pressure range for the rectification is 30 to 6500 PaA, and preferably 40 to 2500 PaA.

5. The production method according to claim 4, wherein, The number of the plates for the rectification is 10 to 50.

6. The production method according to claim 2, wherein The reflux ratio for the rectification is 0.3 / 1 to 2.5 / 1.

7. The production method according to claim 2 or 6, wherein ​ 8. The production method according to claim 2 or 6 or 7, wherein, ​

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