阅读说明：本技术 一种硝西泮的制备方法 (Preparation method of nitrazepam ) 是由 付林 廖俊 曾建华 邬德琦 徐明琴 冯蕾 于 2020-12-22 设计创作，主要内容包括：本发明公开一种硝西泮的制备方法,包括如下步骤：(1)将2-氯乙酰胺基-5-硝基二苯甲酮、六次甲基四胺、氯化铵、乙醇投入反应容器中,升温回流反应。反应结束后降温,加入保护溶剂,再加入活性炭和吸附剂,保温搅拌1小时,过滤,滤液减压浓缩,降温,过滤、水洗、丙酮淋洗得到硝西泮粗品；(2)将粗品在混合溶剂中打浆精制,得到硝西泮。本发明工艺制备工艺简洁,生产成本低,有助于改善成品外观,适用于工业化生产,收率提高了20％。(The invention discloses a preparation method of nitrazepam, which comprises the following steps: (1) putting 2-chloroacetamide-5-nitrobenzophenone, hexamethylenetetramine, ammonium chloride and ethanol into a reaction vessel, and heating for reflux reaction. Cooling after the reaction is finished, adding a protective solvent, adding active carbon and an adsorbent, keeping the temperature and stirring for 1 hour, filtering, concentrating the filtrate under reduced pressure, cooling, filtering, washing with water, and leaching with acetone to obtain a crude product of nitrazepam; (2) and pulping and refining the crude product in a mixed solvent to obtain the nitrazepam. The preparation process is simple, low in production cost, beneficial to improving the appearance of the finished product, suitable for industrial production and capable of improving the yield by 20%.)

1. A preparation method of nitrazepam is characterized by comprising the following steps:

(1) putting 2-chloroacetamide-5-nitrobenzophenone, hexamethylenetetramine, ammonium chloride and ethanol into a reaction vessel, and heating for reflux reaction; cooling after the reaction is finished, adding a protective solvent, adding active carbon and an adsorbent, heating, refluxing, preserving heat, stirring, filtering, concentrating the filtrate under reduced pressure, cooling, filtering, washing with water, and leaching with acetone to obtain a crude product of nitrazepam;

(2) and (2) pulping and refining the nitrazepam crude product in the step (1) in a mixed solvent to obtain the nitrazepam.

2. A method for preparing nitrazepam according to claim 1, characterized in that the ratio of the volume of the protective solvent in step (1) to the mass of 2-chloroacetamidol-5-nitrobenzophenone is 2.0 ml: 1.0 g-5.0 ml: 1.0 g.

3. A method for preparing nitrazepam according to claim 2, characterized in that the mass ratio of the added adsorbent in step (1) to the mass of 2-chloroacetamidol-5-nitrobenzophenone is 0.2: 1-0.6: 1.

4. A method for preparing nitrazepam according to claim 1 or 2, characterized in that the mass ratio of the 2-chloroacetamidol-5-nitrobenzophenone, hexamethylenetetramine and ammonium chloride in step (1) is 1: 0.9-1.2: 0.5 to 0.8.

5. A method for preparing nitrazepam according to claim 1, wherein the volume of ethanol in step (1) and the mass ratio of 2-chloroacetamidol-5-nitrobenzophenone are 18.0 ml: 1.0 g-25.0 ml: 1.0 g; the mass ratio of the volume of the mixed solvent in the step (2) to the 2-chloroacetamido-5-nitrobenzophenone is 2.0 ml: 1.0 g-3.0 ml: 1.0 g.

6. A preparation method of nitrazepam according to claim 1, characterized in that, the filtrate obtained in step (1) is reduced in pressure, concentrated and then cooled to 0 ℃ to 5 ℃; and (3) the mixed solvent in the step (2) is a mixture of alcohol and ethyl acetate.

7. A preparation method of nitrazepam according to claim 6, characterized in that the mass ratio of the activated carbon to the adsorbent in step (1) is 1: 1-1: 3; the volume ratio of the alcohol to the ethyl acetate in the mixed solvent in the step (2) is 0.8: 1-1.2: 1.

8. a method of preparing nitrazepam according to claim 7, wherein the alcohol is methanol or ethanol; the protective solvent in the step (1) is ethyl acetate or dichloromethane; the adsorbent in the step (1) is one or more than two of chromatographic silica gel, neutral alumina and diatomite.

9. A preparation method of nitrazepam according to claim 1, characterized in that, the temperature of the temperature-rising reflux reaction in step (1) is 75-78 ℃, and the time of the temperature-rising reflux reaction is 6-8 hours; after the reaction in the step (1) is finished, cooling to 40-65 ℃; the time for heating, refluxing, heat preservation and stirring in the step (1) is 45 minutes to 1.5 hours.

10. The preparation method of nitrazepam of claim 1, wherein the pulping refining mode of step (2) is as follows: adding the nitrazepam crude product in the step (1) into a mixed solvent, heating to 55 ℃, then keeping the temperature at 55-60 ℃, stirring for 1-1.5 hours, cooling to 0-10 ℃, filtering, and drying to obtain the nitrazepam.

Technical Field

The invention belongs to the technical field of pharmaceutical chemicals, and particularly relates to a preparation method of nitrazepam.

Background

Nitrazepam is a common Benzodiazepine (BZDs) sedative hypnotic drug, has the effects of sedative hypnosis, antianxiety, anticonvulsant, antiepileptic and central muscle relaxation and the like, is mainly used for treating insomnia clinically, and is used for treating epilepsy by being combined with antiepileptic drugs. The pharmaceutical raw materials of nitrazepam are collected in the Chinese pharmacopoeia, the Indian pharmacopoeia, the British pharmacopoeia, the European pharmacopoeia, the Japanese pharmacopoeia and the Korean pharmacopoeia, and the structural formula of 4 known impurities A, B, C, D in the European pharmacopoeia under the term of nitrazepam is as follows:

an unknown impurity is reported in the literature, namely the confirmation of the structure of an unknown impurity in nitrazepam (Tianjin pharmacy, 2017,29,1-5), and structural analysis is carried out, wherein the unknown impurity and the 7-aminonitrazepam are both nitrazepam degradation impurities, and the specific structural formula of the unknown impurity is as follows:

nitrazepam contains an unstable seven-membered ring structure, and easily generates degradation impurities under the conditions of acid, alkali, heating, oxidation and the like; during the preparation process, various process impurities such as residual raw materials, intermediates, reagents, reaction byproducts and the like exist, and the organic impurities, inorganic impurities and solvent residues directly influence the product quality of the nitrazepam. The Chinese pharmacopoeia, the Japanese pharmacopoeia, the Korean pharmacopoeia and the Indian pharmacopoeia adopt a TLC method to judge related substances, the European pharmacopoeia adopts an HPLC method with higher sensitivity to judge, 4 known impurities A, B, C, D are collected in the European pharmacopoeia EP8.0, and the limit of a single impurity is defined to be 0.1 percent, and the limit of total impurities is defined to be 0.2 percent. With the gradual expansion of the market of the imitation pharmaceuticals and the progress of the evaluation of the consistency of the imitation pharmaceuticals in China, pharmaceutical enterprises make higher enterprise standards for the limit of impurities under related substance items, and pharmaceutical research and development institutions and pharmaceutical enterprises in China establish HPLC (high performance liquid chromatography) methods to research the quality of nitrazepam so as to better meet higher quality requirements of customers at home and abroad. The document 'HPLC method determination of nitrazepam and related substances in tablets' (J. drug analysis, 2010,30(8), 1477-.

In the prior art, 2-amino-5-nitrobenzophenone and chloroacetyl chloride are subjected to acylation reaction in a toluene solvent to obtain 2-chloroacetamide-5-nitrobenzophenone; carrying out cyclization reaction with hexamethylenetetramine in an ethanol solvent to obtain a nitrazepam crude product; in the refining and purifying step, the nitrazepam is prepared by ethanol recrystallization, wherein the total yield of cyclization and refining is 28.5-40%. The preparation process comprises the following steps:

in the process, no catalyst is used in the cyclization step, and the cyclization reaction lasts for 20 hours; in the refining process, 20 times of ethanol is adopted for refluxing and dissolving, then the temperature is directly reduced to separate out crystals, and the phenomenon of reworking and refining again due to yellow appearance of the product frequently occurs in the production process, so that impurities are taken away in a large amount of solvent, and the refining and purification yield is inevitably sacrificed; nitrazepam is active in nature and is easily degraded by heating in alcohol solvents. In the cyclization step, after-treatment concentration and the refining step, the nitrazepam crystal material is darkened in color and specific impurities are increased by long-term heating in an ethanol solvent, so that the improvement of the liquid phase purity of the nitrazepam is influenced.

In the synthesis of nitro diazepam (journal of Chinese medical industry, 1994,25,531-533), under the catalysis of ammonium chloride, 2-chloroacetamido-5-nitrobenzophenone and hexamethylenetetramine are subjected to cyclization reaction in an ethanol solvent to obtain a crude product of nitrazepam; and (3) the crude product is salified with nitric acid in a chloroform solvent, and then is dissociated in a saturated sodium bicarbonate aqueous solution to obtain the nitrazepam, wherein the total yield of cyclization and refining is 28-32%. The cyclization procedure in the process is catalyzed by ammonium chloride, so that the cyclization reaction time is greatly shortened. However, in the cyclization step, the post-treatment concentration operation needs to be carried out in an unstable nitrazepam ethanol system for a long time, and in the concentration process, particularly in the later stage of concentration, along with most of the solvent evaporated, the temperature of the system is higher, the crystallization material is in a more unstable state, yellow pigment impurities are easy to produce, and the color of the separated crystallization material is gradually deepened; in the refining process, nitric acid is used for salifying in a chloroform solvent, then the salified substance is suspended in water and purified in a free mode of a saturated sodium bicarbonate solution, and the heating reflux and distillation processes in alcohol solvents such as ethanol and the like are removed in the refining process, so that the material safety of the nitrazepam product is facilitated. However, the solvent is about 20 times as much as the solvent, salt substances generated in the process of dissociating, neutralizing and separating materials need to be thoroughly washed and removed, and the refining flow is complicated: the steps of material separation, solvent recovery and the like are required twice, and the conditions of salification again, dissociation and rework purification are also required because the product is yellow in appearance. The refining process route is as follows:

both of the above-mentioned methods for the preparation of nitrazepam have limitations: the concentration process of cyclization after-treatment is carried out by heating in an unstable nitrazepam ethanol system for a long time, the color of a nitrazepam crystallization material is gradually darkened in the concentration process, and the situations that excessive colloidal materials in a product are easy to separate and remove due to excessive concentration and evaporation solvents are easy to occur; in the refining process, the solvent consumption is large, the nitrazepam product obtained by one-time refining is yellow in appearance and is difficult to meet the quality standard of faint yellow crystalline powder of Chinese pharmacopoeia, and the total yield of cyclization and refining is low due to the re-refining.

Disclosure of Invention

The invention aims to provide a preparation method of nitrazepam, aiming at the defects of the prior art. The method greatly improves the safety of materials in the concentration process after cyclization, effectively removes yellow pigment impurities in precipitated crystal materials, has simple refining and purification process, low production cost and higher yield, and is suitable for industrial production.

In order to achieve the purpose, the purpose of the invention is realized by the following technical scheme:

a preparation method of nitrazepam comprises the following steps:

(1) putting 2-chloroacetamide-5-nitrobenzophenone, hexamethylenetetramine, ammonium chloride and ethanol into a reaction vessel, and heating for reflux reaction; cooling after the reaction is finished, adding a protective solvent, adding active carbon and an adsorbent, heating, refluxing, preserving heat, stirring, filtering, concentrating the filtrate under reduced pressure, cooling, filtering, washing with water, and leaching with acetone to obtain a crude product of nitrazepam;

(2) and (2) pulping and refining the nitrazepam crude product in the step (1) in a mixed solvent to obtain the nitrazepam.

Preferably, the protective solvent in step (1) is ethyl acetate or dichloromethane.

Preferably, the mass ratio of the volume of the protective solvent in the step (1) to the 2-chloroacetamido-5-nitrobenzophenone is 2.0 ml: 1.0 g-5.0 ml: 1.0 g.

Preferably, the mass ratio of the added adsorbent in the step (1) to the mass of the 2-chloroacetamido-5-nitrobenzophenone is 0.2: 1-0.6: 1.

Preferably, the adsorbent in step (1) is chromatographic silica gel, neutral alumina or kieselguhr, and more preferably chromatographic silica gel.

Preferably, the mass ratio of the 2-chloroacetamide-5-nitrobenzophenone, the hexamethylenetetramine and the ammonium chloride in the step (1) is 1: 0.9-1.2: 0.5 to 0.8.

Preferably, the mass ratio of the volume of the ethanol in the step (1) to the 2-chloroacetamido-5-nitrobenzophenone is 18.0 ml: 1.0 g-25.0 ml: 1.0 g.

Preferably, the temperature of the temperature-rising reflux reaction in the step (1) is 75-78 ℃, and the time of the temperature-rising reflux reaction is 6-8 hours.

Preferably, the temperature is reduced to 40-65 ℃ after the reaction in the step (1) is finished.

Preferably, the mass ratio of the activated carbon and the adsorbent in the step (1) is 1: 1-1: 3.

preferably, the time for heating, refluxing, heat preservation and stirring in the step (1) is 45 minutes to 1.5 hours.

Preferably, the filtrate obtained in the step (1) is reduced in pressure, concentrated and then cooled to 0-5 ℃.

Preferably, the mixed solvent in the step (2) is a mixture of alcohol and ethyl acetate.

Preferably, the alcohol is methanol or ethanol.

Preferably, the volume ratio of the alcohol to the ethyl acetate is 0.8: 1-1.2: 1.

preferably, the mass ratio of the volume of the mixed solvent in the step (2) to the 2-chloroacetamido-5-nitrobenzophenone is 2.0 ml: 1.0 g-3.0 ml: 1.0 g.

Preferably, the pulping refining mode in the step (2) is as follows: adding the nitrazepam crude product in the step (1) into a mixed solvent, heating to 55 ℃, then keeping the temperature at 55-60 ℃, stirring for 1-1.5 hours, cooling to 0-10 ℃, filtering, and drying to obtain the nitrazepam.

The mechanism of the invention is as follows: the nitrazepam is easy to degrade in alcohol solvents including methanol, ethanol and the like, and a crystalline material separated out in the post-treatment concentration process of a cyclization procedure is gradually deepened to generate yellow pigment impurities. The literature "HPLC method for determining nitrazepam and related substances in tablets" also clearly indicates that the methanol solution of nitrazepam is obviously degraded after being stored. In experiments, the aim of preventing the color of a precipitated crystal material from becoming dark cannot be achieved by reducing the system temperature by improving the concentration vacuum degree of treatment after cyclization. By further investigation, the applicant found that: a certain amount of dichloromethane is added before concentration, so that the color of the precipitated crystal material can be effectively prevented from being darkened; a certain amount of adsorbent is added before concentration, so that organic impurities generated in the reaction process can be effectively removed, the color of the filtered filtrate is improved, and the appearance of the product of nitrazepam can meet pharmacopoeia standards.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) in the cyclization procedure, after the cyclization reaction is completed, a protective solvent is added into the cyclization reaction liquid and then concentration is carried out, so that the color of the precipitated crystal material is effectively prevented from being darkened, and the condition that the cyclization reaction liquid is not stable enough in a single ethanol solvent system and easily generates degradation impurities is avoided;

(2) in the cyclization procedure, after the cyclization reaction is completed, an adsorbent is added into a system, so that organic impurities generated in the reaction process can be effectively removed, the system color of a cyclization reaction liquid before concentration is further improved, and the appearance of a nitrazepam product is more favorable to accord with pharmacopoeia standards;

(3) the refining process greatly reduces the dosage of the refining solvent, has simple purification process, reduces the production cost, improves the total yield of cyclization and refining by 20 percent, and is suitable for industrial production.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Examples the preparation of 2-chloroacetamido-5-nitrobenzophenone is described in Nitro-Stable Synthesis (journal of the Chinese medical industry, 1994,25, 531-533).

Example 1

20g of 2-chloroacetamide-5-nitrobenzophenone, 24g of hexamethylenetetramine, 12g of ammonium chloride and 500ml of ethanol are put into a reaction bottle, and the temperature is increased to 75-78 ℃ for reflux reaction for 6 hours. And after the reaction is finished, cooling to 65 ℃, adding 40ml of ethyl acetate, adding 4g of active carbon and 10g of chromatographic silica gel, heating, refluxing, keeping the temperature and stirring for 1 hour, filtering while hot, concentrating the filtrate under reduced pressure, cooling to 5 ℃, filtering, washing with water, and leaching with acetone to obtain a crude product of nitrazepam. And adding the crude product into a mixed solvent of 20ml of ethanol and 20ml of ethyl acetate, heating to 55 ℃, then keeping the temperature at 55-60 ℃, stirring for 1 hour, cooling to 0 ℃, filtering, and drying to obtain a light yellow crystal product, namely nitrazepam, 11.6g, with the HPLC purity of 99.93% and the yield of 65.72%.

Example 2

30g of 2-chloroacetamide-5-nitrobenzophenone, 30g of hexamethylenetetramine, 24g of ammonium chloride and 600ml of ethanol are put into a reaction bottle, and the temperature is increased to 75-78 ℃ for reflux reaction for 7 hours. And after the reaction is finished, cooling to 40 ℃, adding 150ml of dichloromethane, adding 6g of activated carbon and 6g of neutral alumina, heating, refluxing, keeping the temperature and stirring for 45 minutes, filtering while hot, concentrating the filtrate under reduced pressure, cooling to 0 ℃, filtering, washing with water, and leaching with acetone to obtain a crude product of nitrazepam. Adding the crude product into a mixed solvent of 40ml of ethanol and 50ml of ethyl acetate, heating to 55 ℃, then keeping the temperature at 55-60 ℃, stirring for 1 hour, cooling to 10 ℃, filtering, and drying to obtain a light yellow crystal product, namely nitrazepam, 16.4g, with the HPLC purity of 99.90% and the yield of 61.96%.

Example 3

30g of 2-chloroacetamide-5-nitrobenzophenone, 27g of hexamethylenetetramine, 15g of ammonium chloride and 600ml of ethanol are put into a reaction bottle, and the temperature is increased to 75-78 ℃ for reflux reaction for 8 hours. And after the reaction is finished, cooling to 60 ℃, adding 90ml of ethyl acetate, adding 6g of active carbon and 18g of diatomite, heating, refluxing, keeping the temperature and stirring for 1.5 hours, filtering while hot, concentrating the filtrate under reduced pressure, cooling to 2 ℃, filtering, washing with water, and leaching with acetone to obtain a crude product of nitrazepam. Adding the crude product into a mixed solvent of 36ml of methanol and 30ml of ethyl acetate, heating to 55 ℃, then keeping the temperature at 55-60 ℃, stirring for 1 hour, cooling to 5 ℃, filtering, and drying to obtain a light yellow crystal product, namely nitrazepam, 16.7g, with the HPLC purity of 99.91% and the yield of 63.09%.

Example 4

30g of 2-chloroacetamide-5-nitrobenzophenone, 33g of hexamethylenetetramine, 18g of ammonium chloride and 540ml of ethanol are put into a reaction bottle, and the temperature is raised to 75-78 ℃ for reflux reaction for 6.5 hours. And after the reaction is finished, cooling to 55 ℃, adding 120ml of ethyl acetate, adding 6g of activated carbon and 9g of neutral alumina, heating, refluxing, keeping the temperature and stirring for 45 minutes, filtering while hot, concentrating the filtrate under reduced pressure, cooling to 5 ℃, filtering, washing with water, and leaching with acetone to obtain a crude product of nitrazepam. Adding the crude product into a mixed solvent of 40ml of ethanol and 40ml of ethyl acetate, heating to 55 ℃, then keeping the temperature at 55-60 ℃, stirring for 1.5 hours, cooling to 0 ℃, filtering, and drying to obtain a light yellow crystal product, namely nitrazepam, 16.6g, with the HPLC purity of 99.93% and the yield of 62.71%.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by the present specification, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.