A method for purifying melatonin and its crystallization mother solution

Abstract

The invention discloses a method for purifying melatonin and a crystallization mother liquor thereof. Deoxygenated water is added during the ethanol purification process and nitrogen filling protection is performed throughout the process, thereby greatly improving the purity and recovery rate of melatonin. Furthermore, the crystallization mother liquor is alkaline hydrolyzed to reduce melatonin and its self-condensation impurities into a synthetic precursor 5-methoxytryptamine, and the synthetic precursor is acylated to obtain a mother liquor material product having a purity equivalent to that of a crude melatonin product. This method can effectively improve the recovery rate and total purification yield of melatonin in the mother liquor, and also reduce the processing volume of the final mother liquor, alleviate the pressure of three wastes treatment, and help increase the competitiveness of the product.

Description

Technical Field

[0001] The invention relates to the technical field of chemical separation, and in particular to a method for purifying melatonin and its crystallization mother liquor. Background Art

[0002] Melatonin, also known as pineal hormone and melatonin, has powerful neuroendocrine immunomodulatory activity and free radical scavenging antioxidant ability. It is the strongest endogenous free radical scavenger discovered so far. It has a significant effect in preventing diseases, regulating circadian rhythms, and delaying aging. At the same time, melatonin has a significant regulatory effect on the central nervous system, immune system, and cardiovascular system.

[0003] Melatonin has a variety of chemical synthesis methods. The better route is to use 5-methoxytryptamine as a raw material, obtain crude melatonin through an acylation reaction, and obtain refined melatonin after recrystallization of the crude melatonin. At present, the crystallization method of melatonin in industrial production mainly uses ethanol as a solvent for crystallization, and the crystallization process inevitably produces mother liquor. In the prior art, ethanol is mostly used as a solvent for the purification of melatonin, but the purification yield is low. For this reason, ethanol aqueous solution is also used, such as using an ethanol aqueous solution with a concentration of 15-20% to purify the crude melatonin, the purification yield is 90-93%, and the product purity can reach more than 99.5%, but the impurity content of the peak with a retention time of 12.398 minutes is 0.13%, which exceeds the USP ≤ 0.1% requirement and does not meet the USP43 standard; and the use of an ethanol aqueous solution with a concentration that is too low results in a large amount of subsequent mother liquor processing and high processing energy consumption. For example, the pineal glands of animals are used to extract melatonin from the crystallization mother liquor, but the source of the pineal glands of the raw animals is the biggest problem.

[0004] In addition, the ethanol solvent used in the existing melatonin purification technology has a relatively large solubility of melatonin in ethanol, and the melatonin ethanol mother liquor will decompose during the concentration process, producing a self-condensation impurity that cannot be purified by ethanol, resulting in a single impurity>0.1% (USP43 standard: single impurity≤0.1%), which does not meet the USP standard. Therefore, how to extract melatonin dissolved in the ethanol mother liquor will be the key to improving the overall yield of melatonin purification technology. At the same time, how to remove the self-condensation impurities generated during the concentration of the melatonin ethanol mother liquor to improve the purity of melatonin extracted from the mother liquor will help increase the competitiveness of the product. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for purifying melatonin and its crystallization mother liquor, so as to solve the problems of low yield in the current melatonin ethanol purification process, large amount of melatonin residue in the crystallization mother liquor, and impurities caused by melatonin self-condensation during the mother liquor treatment process.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for purifying melatonin and its crystallization mother solution, comprising the following steps:

[0008] (1) Purification of crude melatonin

[0009] (1-1) Mixing crude melatonin with an ethanol aqueous solution having a concentration of 30 to 95% at a mass ratio of crude melatonin to ethanol aqueous solution = 1:1 to 5 to obtain a dissolving solution, wherein the water used in the ethanol aqueous solution is deoxygenated water; preferably, the concentration of the ethanol aqueous solution is 40 to 60%, and the mass ratio of crude melatonin to ethanol aqueous solution is 1:2 to 3;

[0010] (1-2) adding activated carbon in an amount of 1 to 3 wt % of the crude melatonin to the solution, replacing the air in the system with nitrogen, heating the system to 50 to 75° C. to dissolve the decolorized solution, and filtering and separating the activated carbon to obtain a melatonin filtrate;

[0011] (1-3) The melatonin filtrate is cooled to -10 to 10°C at a rate of 10°C / h and then crystallized for 4 to 8 hours to obtain a crystal liquid, which is centrifuged to obtain a melatonin fine material and a melatonin crystal mother liquor; the melatonin fine material is vacuum dried to obtain a melatonin fine material; preferably, the temperature is cooled to 0 to 5°C;

[0012] (2) Treatment of melatonin crystallization mother liquor

[0013] (2-1) mixing the melatonin crystal mother liquor with an alkaline catalyst, controlling the pH value of the system to be 10 to 14, and refluxing at 60 to 80° C. for 2 to 8 hours to obtain an alkaline hydrolyzate;

[0014] (2-2) vacuum concentrating the alkaline hydrolysis solution to precipitate a solid fraction, adding acid to adjust the pH value to 1 to 4, preferably 1 to 2, and stirring until the solid is completely dissolved to obtain an acidified solution;

[0015] (2-3) adding activated carbon in an amount of 0.1 to 0.3 wt % of the acidified liquid to decolorize the obtained decolorized liquid, and separating the activated carbon to obtain a filtrate;

[0016] (2-4) adding alkali to the filtrate to adjust the pH value to 10-14, preferably 12-13, and obtaining the melatonin precursor 5-methoxytryptamine after centrifugation, and obtaining a mother liquor material with a purity of >99.5% after acylation; and recycling the mother liquor material to add the crude melatonin product for purification.

[0017] Furthermore, in the step (2-1) of the present invention, the alkaline catalyst is sodium hydroxide, potassium hydroxide, sodium methoxide, sodium tert-butoxide, or triethylamine; preferably, the system pH value is 12 to 13, the reflux temperature is 70 to 75° C., and the reflux time is 4 to 5 hours;

[0018] In the above scheme, the purity of the crude melatonin in step (1-1) of the present invention is above 99.50%. The purity of the refined melatonin in step (1-3) is above 99.70%, the single impurity is below 0.05%, and the yield is above 88%. The purity of the mother liquor in step (2-4) is above 99.50%.

[0019] The present invention has the following beneficial effects:

[0020] (1) In the process of melatonin purification, the prior art mostly uses ethanol as a solvent. The solubility of melatonin in ethanol is relatively large, up to about 20%, so the purification yield is relatively low. The present invention adds deoxygenated water during the purification process and uses nitrogen protection throughout the process. Since melatonin is slightly soluble in water, the solubility of melatonin in ethanol can be reduced, thereby reducing the content of melatonin in the crystallization mother liquor, which helps to greatly improve the recovery rate in the melatonin purification technology; at the same time, by reducing the oxygen content in the purification system, the self-condensation impurities generated during the purification process are reduced, which helps to improve the purity of the melatonin product, so that the purity of the melatonin product reaches more than 99.7%, and the single impurity is less than 0.1%.

[0021] (2) The present invention reduces melatonin and its self-condensation impurities in the melatonin crystallization mother liquor to 5-methoxytryptamine, a synthetic precursor of melatonin, by alkaline hydrolysis reduction. The synthetic precursor is subjected to secondary purification by acidification and alkali, and finally acylated to obtain a mother liquor material with a purity equivalent to that of a crude melatonin product. The purity of the mother liquor material can reach more than 99.5%, thereby improving the recovery rate of melatonin in the mother liquor, and the total purification yield can reach more than 95%. The amount of mother liquor treatment is reduced, thereby alleviating the pressure of three waste treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings:

[0023] Figure 1 is a processing flow chart of an embodiment of the present invention;

[0024] Figure 2 This is the purity detection spectrum of the melatonin product according to the first embodiment of the present invention;

[0025] Figure 3 This is a purity detection spectrum of the mother liquor material obtained after the melatonin crystallization mother liquor is treated in Example 1 of the present invention;

[0026] Figure 4It is a purity detection spectrum of mother liquor material obtained by using the existing technology (concentration, crystallization and recrystallization) of melatonin crystal mother liquor. DETAILED DESCRIPTION

[0027] Embodiment 1:

[0028] This embodiment provides a method for purifying melatonin and its crystallization mother solution, such as Figure 1 As shown, the steps are as follows:

[0029] (1) Purification of crude melatonin

[0030] (1-1) 300 g of crude melatonin with a purity of 99.63% is mixed with 900 g of 40% ethanol aqueous solution to obtain a dissolving solution, wherein the water used in the ethanol aqueous solution is deoxygenated water;

[0031] (1-2) Add 5 g of activated carbon to the above solution, replace the air in the system with nitrogen, heat to 70° C. to dissolve and decolorize for 30 min, and filter to separate the activated carbon to obtain a melatonin filtrate;

[0032] (1-3) The melatonin filtrate was cooled to 5°C at a rate of 10°C / h and then continued to crystallize for 4h to obtain a crystal solution, which was centrifuged to obtain 280g of melatonin fine wet material and 913g of melatonin crystal mother liquor; the melatonin fine wet material was vacuum dried to obtain a purity of 99.87% and a single impurity of 0.04% (see Figure 2 ) of melatonin fine product 273g, the yield is 91.0%;

[0033] (2) Treatment of melatonin crystallization mother liquor

[0034] (2-1) Mixing the above melatonin crystallization mother liquor with sodium methoxide, controlling the pH value of the system to 12, and refluxing at 70° C. for 4 h to obtain an alkaline hydrolyzate;

[0035] (2-2) The alkaline hydrolyzate was concentrated in vacuo to obtain 411 g of a solid fraction, and an acid was added to adjust the pH value to 2. The acidified solution was obtained by stirring for 20 min until the solid was completely dissolved.

[0036] (2-3) adding 0.5 g of activated carbon to the above acidified liquid to obtain a decolorized liquid, and separating the activated carbon to obtain a filtrate;

[0037] (2-4) Base was added to the filtrate to adjust the pH value to 12, and 18 g of melatonin precursor 5-methoxytryptamine was obtained after centrifugation. After acylation, 18.7 g of mother liquor material with a purity of 99.57% was obtained. The mother liquor material was recycled and added to the crude melatonin for purification.

[0038] Embodiment 2:

[0039] This embodiment provides a method for purifying melatonin and its crystallization mother solution, such as Figure 1 As shown, the steps are as follows:

[0040] (1) Purification of crude melatonin

[0041] (1-1) 300 g of crude melatonin with a purity of 99.58% was mixed with 720 g of 50% ethanol aqueous solution to obtain a dissolving solution, wherein the water used in the ethanol aqueous solution was deoxygenated water;

[0042] (1-2) Add 5 g of activated carbon to the above solution, replace the air in the system with nitrogen, heat to 65° C. to dissolve and decolorize for 30 min, and filter to separate the activated carbon to obtain a melatonin filtrate;

[0043] (1-3) The melatonin filtrate was cooled to 0°C at a rate of 10°C / h and then crystallized for 5h to obtain a crystal solution, which was centrifuged to obtain 272g of melatonin fine material and 729g of melatonin crystal mother liquor; the melatonin fine material was vacuum dried to obtain 268g of melatonin fine material with a purity of 99.81% and a single impurity of 0.03%, with a yield of 89.3%;

[0044] (2) Treatment of melatonin crystallization mother liquor

[0045] (2-1) The above melatonin crystallization mother liquor was mixed with sodium tert-butoxide, the pH value of the system was controlled to be 13, and refluxed at 75° C. for 4 h to obtain an alkaline hydrolyzate;

[0046] (2-2) The alkaline hydrolyzate was concentrated in vacuo to obtain 380 g of a solid fraction, acid was added to adjust the pH value to 1, and the mixture was stirred for 20 min until the solid was completely dissolved to obtain an acidified solution;

[0047] (2-3) adding 0.5 g of activated carbon to the above acidified liquid to obtain a decolorized liquid, and separating the activated carbon to obtain a filtrate;

[0048] (2-4) Base was added to the filtrate to adjust the pH value to 13, and 21.8 g of melatonin precursor 5-methoxytryptamine was obtained after centrifugation. After acylation, 22.5 g of mother liquor with a purity of 99.62% was obtained. The mother liquor was recycled and added to the crude melatonin for purification.

[0049] Embodiment three:

[0050] This embodiment provides a method for purifying melatonin and its crystallization mother solution, such as Figure 1 As shown, the steps are as follows:

[0051] (1) Purification of crude melatonin

[0052] (1-1) 300 g of crude melatonin with a purity of 99.60% is mixed with 600 g of 60% ethanol aqueous solution to obtain a dissolving solution, wherein the water used in the ethanol aqueous solution is deoxygenated water;

[0053] (1-2) Add 5 g of activated carbon to the above solution, replace the air in the system with nitrogen, heat to 60° C. to dissolve and decolorize for 30 min, and filter to separate the activated carbon to obtain a melatonin filtrate;

[0054] (1-3) The melatonin filtrate was cooled to -5°C at a rate of 10°C / h and then crystallized for 8h to obtain a crystal solution, which was centrifuged to obtain 265g of melatonin fine material and 611g of melatonin crystal mother liquor; the melatonin fine material was vacuum dried to obtain 266g of melatonin fine material with a purity of 99.83% and a single impurity of 0.03%, with a yield of 88.6%;

[0055] (2) Treatment of melatonin crystallization mother liquor

[0056] (2-1) mixing the above melatonin crystallization mother liquor with potassium hydroxide, controlling the system pH value to 14, and refluxing at 75° C. for 6 h to obtain an alkaline hydrolyzate;

[0057] (2-2) The alkaline hydrolyzate was concentrated in vacuo to obtain 375 g of a solid fraction, acid was added to adjust the pH to 1, and the mixture was stirred for 20 min until the solid was completely dissolved to obtain an acidified solution;

[0058] (2-3) adding 0.5 g of activated carbon to the above acidified liquid to obtain a decolorized liquid, and separating the activated carbon to obtain a filtrate;

[0059] (2-4) Base was added to the filtrate to adjust the pH value to 14, and 23.0 g of melatonin precursor 5-methoxytryptamine was obtained after centrifugation. After acylation, 24.1 g of mother liquor with a purity of 99.67% was obtained. The mother liquor was recycled and added to the crude melatonin for purification.

[0060] The present invention is based on the detection method for melatonin purity and impurities in the United States Pharmacopoeia USP43. The melatonin crystal mother liquor purification process of the present invention has better product quality than the conventional purification process of the prior art (see Figure 3 and Figure 4 ).

Claims

1. A method for purifying melatonin and its crystallization mother solution, characterized in that The following steps are involved: (1) Purification of crude melatonin (1-1) a crude melatonin product having a purity of 99.50% or more and an ethanol aqueous solution having a concentration of 30 to 95% are mixed at a mass ratio of crude melatonin product to ethanol aqueous solution of 1:1 to 5 to obtain a dissolving solution, wherein the water used in the ethanol aqueous solution is deoxygenated water; (1-2) adding activated carbon in an amount of 1 to 3 wt % of the crude melatonin to the solution, replacing the air in the system with nitrogen, heating the system to 50 to 75° C. to dissolve the decolorized solution, and filtering and separating the activated carbon to obtain a melatonin filtrate; (1-3) The melatonin filtrate is cooled to -10 to 10°C at a rate of 10°C / h and then crystallized for 4 to 8 hours to obtain a crystal liquid, which is centrifuged to obtain a melatonin fine material and a melatonin crystal mother liquor; the melatonin fine material is vacuum dried to obtain a melatonin fine material; (2) Treatment of melatonin crystallization mother liquor (2-1) mixing the melatonin crystallization mother liquor with an alkaline catalyst, controlling the pH value of the system to be 10 to 14, and refluxing at 60 to 80° C. for 2 to 8 hours to obtain an alkaline hydrolyzate; (2-2) vacuum concentrating the alkaline hydrolyzate to precipitate a solid fraction, adding acid to adjust the pH value to 1 to 4, and stirring until the solid is completely dissolved to obtain an acidified solution; (2-3) adding activated carbon in an amount of 0.1 to 0.3 wt % of the acidified liquid to decolorize the obtained decolorized liquid, and separating the activated carbon to obtain a filtrate; (2-4) adding alkali to the filtrate to adjust the pH value to 10-14, and obtaining the melatonin precursor 5-methoxytryptamine after centrifugation, and obtaining a mother liquor material with a purity of >99.5% after acylation; and the mother liquor material is recycled and added to the crude melatonin product for purification.

2. The method for purifying melatonin and its crystallization mother solution according to claim 1, characterized in that: The concentration of the ethanol aqueous solution in the step (1-1) is 40-60%, and the mass ratio of crude melatonin: ethanol aqueous solution is 1:2-3.

3. The method for purifying melatonin and its crystallization mother solution according to claim 1, characterized in that: The crystallization temperature in the step (1-3) is 0 to 5°C.

4. The method for purifying melatonin and its crystallization mother solution according to claim 1, characterized in that: The alkaline catalyst in the step (2-1) is sodium hydroxide, potassium hydroxide, sodium methoxide, sodium tert-butoxide, or triethylamine.

5. The method for purifying melatonin and its crystallization mother solution according to claim 1 or 4, characterized in that: The pH value of the system in step (2-1) is 12-13, the reflux temperature is 70-75° C., and the reflux time is 4-5 hours.

6. The method for purifying melatonin and its crystallization mother solution according to claim 1, characterized in that: The pH value in the step (2-2) is 1 to 2.

7. The method for purifying melatonin and its crystallization mother solution according to claim 1, characterized in that: The pH value in the step (2-4) is 12-13.

8. The method for purifying melatonin and its crystallization mother solution according to claim 1, characterized in that: The purity of the melatonin product in step (1-3) is above 99.70%, the single impurity is below 0.05%, and the yield is above 88.0%.

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