CN113861131B

CN113861131B - Preparation method of cetirizine impurity C

Info

Publication number: CN113861131B
Application number: CN202111316145.9A
Authority: CN
Inventors: 周伟; 刘孟良
Original assignee: Shenzhen Phystandard Biotechnology Co ltd
Current assignee: Shenzhen Phystandard Biotechnology Co ltd
Filing date: 2021-11-08
Publication date: 2024-04-19
Anticipated expiration: 2041-11-08

Abstract

The invention relates to the technical field of pharmaceutical chemicals, in particular to a preparation method of cetirizine impurity C. The method uses 1-chloro-2- (chlorophenyl methyl) benzene to directly react with hydroxyethyl piperazine to prepare a key intermediate 4- { (2-chlorophenyl) phenyl } -1-hydroxyethyl piperazine, then uses 4- { (2-chlorophenyl) phenyl } -1-hydroxyethyl piperazine and tert-butyl bromoacetate as reaction substrates, uses alkali metal hydroxide as a catalyst, mixes dichloromethane and water as a solvent, reacts at room temperature, stands for layering after the reaction is finished, and the organic layer is purified by silica gel column chromatography to obtain the product. The method has the advantages of low cost and easy acquisition of raw materials, low toxicity and little pollution; the reaction steps are few, and the preparation period is short; the product is single, the purity is high, the yield is good, and the total yield can reach more than 70%. The prepared cetirizine impurity C standard has great significance for quality research of cetirizine.

Description

Preparation method of cetirizine impurity C

Technical Field

The invention relates to the technical field of pharmaceutical chemicals, in particular to a preparation method of cetirizine impurity C.

Background

Cetirizine (Cetirizine) is a second generation H ₁ antihistamine, which is used as a long-acting selective oral potent antiallergic agent for treating seasonal or perennial allergic rhinitis, urticaria and skin itch caused by allergen, and has the following structural formula:

At present, the preparation method of cetirizine generally comprises the steps of reacting 1-chloro-4- (chlorophenyl methyl) benzene with piperazine, then reacting with 2-chloroethanol to synthesize a key intermediate 4- { (2-chlorophenyl) phenyl } -1-hydroxyethyl piperazine, condensing with sodium chloroacetate in an inert organic solvent under the action of a catalyst, and performing a series of post-treatments to obtain cetirizine.

Among the numerous impurities of cetirizine, cetirizine impurity C (chemical name: 2- [ 2- {4- [ (2-chlorophenyl) (phenyl) methyl ] piperazin-1-yl } ethoxy ] acetic acid dihydrochloride) is a more important one, and has the following structural formula:

The impurity can be used for quantitative and qualitative analysis in the processes of cetirizine production, transportation and storage, so that the quality standard of cetirizine is improved, and important basis and guidance are provided for safe medication of cetirizine. Therefore, the preparation of the cetirizine impurity C standard substance has great significance for the quality research of cetirizine. The impurity is similar to cetirizine in structure, can be improved on the existing preparation process of cetirizine, and discusses the synthesis process of cetirizine impurity C.

Chinese patent CN101492430a discloses a method for preparing cetirizine hydrochloride, which uses 4- { (4-chlorophenyl) phenyl } -1-hydroxyethyl piperazine and sodium chloroacetate as reaction substrates, uses alkali metal hydroxide as catalyst, uses DMF or DMSO as solvent, and makes reaction at 5-40 ℃. However, the product of the reaction exists in the form of sodium salt, has large polarity and good water solubility, and is difficult to extract from water; secondly, DMF is preferably used as a solvent, so that the product is more difficult to extract from water, and the DMF is difficult to wash off by water, and the extracted product contains a large amount of DMF, which is unfavorable for purification and separation; in the post-treatment, the method preferably uses toluene as a toxic reagent as a washing solvent, so that the danger of experimenters is increased, the post-treatment of waste liquid is difficult, and the environment is polluted.

Disclosure of Invention

The invention aims to provide a preparation method of cetirizine impurity C, which can simplify the reaction steps, reduce the energy consumption and obtain a high-purity product under mild reaction conditions.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A method for preparing cetirizine impurity C, comprising the steps of:

(1) Preparation of Compound a: adding 2-chlorobenzophenone into a reaction bottle, adding a solvent I, stirring at the temperature of-10-10 ℃, slowly adding sodium borohydride, slowly heating to room temperature for reacting for 2-4 hours, adding a small amount of water for quenching reaction, spin-drying the solvent I, extracting, drying, and spin-drying to obtain a compound a;

Preferably, the temperature T1 is 0 ℃;

preferably, the first solvent is methanol;

Preferably, the extracting agent for extraction is ethyl acetate;

Preferably, the drying agent is anhydrous sodium sulfate;

wherein the molar mass ratio of the 2-chlorobenzophenone to the sodium borohydride is 1:0.6-0.7,

Preferably, the molar mass ratio of the 2-chlorobenzophenone to the sodium borohydride is 1:0.6.

(2) Preparation of compound b: adding a compound a into a reaction bottle, adding a solvent II, adding concentrated hydrochloric acid, reacting for 2-4 hours at 40-50 ℃, adding water after the reaction is finished, extracting, washing an organic layer, drying and spin-drying to obtain a compound b;

Preferably, the second solvent is 1, 4-dioxane;

Preferably, the extracting agent for extraction is ethyl acetate;

preferably, the organic layer is washed with brine;

preferably, the drying is anhydrous sodium sulfate drying;

wherein the molar mass ratio of the compound a to the concentrated hydrochloric acid is 1:5-6,

Preferably, the molar mass ratio of the compound a to the concentrated hydrochloric acid is 1:5.

(3) Preparation of compound c: adding a compound b into a reaction bottle, dissolving in a solvent III, adding potassium carbonate, adding 1- (2-hydroxyethyl) piperazine, heating to 80-90 ℃ for reaction for 8-12h, cooling to room temperature after the reaction is finished, filtering, and evaporating filtrate to obtain a compound c which is colorless oily substance;

Wherein the molar mass ratio of the compound b to the potassium carbonate to the 1- (2-hydroxyethyl) piperazine is 1:2-3:1-2,

Preferably, the molar mass ratio of the compound b, the potassium carbonate and the 1- (2-hydroxyethyl) piperazine is 1:2:1;

Wherein the third solvent is acetone or acetonitrile.

(4) Preparation of compound d: adding a compound c into a reaction bottle, dissolving in dichloromethane, adding tetrabutylammonium bromide, 35% sodium hydroxide solution and tert-butyl bromoacetate, reacting for 6-10h at room temperature, standing for layering after the reaction is finished, spin-drying an organic layer, purifying by silica gel column chromatography, wherein the silica gel column uses dichloromethane: washing with methanol=100:1 to obtain a compound d, wherein the compound d is colorless oily matter;

Wherein the molar mass ratio of the compound c to the tetrabutylammonium chloride to the tert-butyl bromoacetate is 1:0.4-0.5:2-3, and preferably the molar mass ratio of the compound c to the tetrabutylammonium chloride to the tert-butyl bromoacetate is 1:0.5:2.

(5) Preparation of cetirizine impurity C: adding a compound d into a reaction bottle, dissolving in dichloromethane, then adding a dioxane hydrochloride solution, reacting for 3-4 hours at room temperature, removing dichloromethane under reduced pressure after the reaction is finished, adding ethyl acetate, stirring for 1-2 hours, filtering, washing and drying a generated white solid to obtain cetirizine impurity C.

Preferably, the washed detergent is ethyl acetate.

The reaction process structural formula of the preparation method provided by the invention is as follows:

The above preparation method and the selection of reactants, solvents, extractants, desiccants, detergents, etc. in the preparation steps thereof, and the selection of reaction conditions such as temperature, time, etc. are all preferable, and are not limited to the above selection, and may be replaced and omitted as appropriate according to effects.

Compared with the prior art, the invention has the following advantages:

(1) The reaction conditions are conventional and basically carried out at room temperature, the highest reaction temperature is not more than 100 ℃, and the energy consumption is low;

(2) The raw materials are cheap and easy to obtain, and the toxicity and pollution are low;

(3) The product is single, the purity is high, the yield is good, and the total yield can reach more than 70 percent;

(4) The reaction steps are reduced, the preparation period can be greatly shortened, and the preparation cost is reduced.

Drawings

FIG. 1 is a structural formula of cetirizine impurity C;

FIG. 2 is a route for the preparation of cetirizine impurity C;

FIG. 3 is a hydrogen nuclear magnetic resonance spectrum of cetirizine impurity C;

FIG. 4 is an HPLC plot of cetirizine impurity C;

Fig. 5 is a C mass spectrum of cetirizine impurity.

Detailed Description

The term as used herein:

"prepared from … …" is synonymous with "comprising". The terms "comprising," "including," "having," "containing," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

When an equivalent, concentration, or other value or parameter is expressed as a range, preferred range, or a range bounded by a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when ranges of "1 to 5" are disclosed, the described ranges should be construed to include ranges of "1 to 4", "1 to 3", "1 to 2 and 4 to 5", "1 to 3 and 5", and the like. When a numerical range is described herein, unless otherwise indicated, the range is intended to include its endpoints and all integers and fractions within the range.

"And/or" is used to indicate that one or both of the illustrated cases may occur, e.g., a and/or B include (a and B) and (a or B).

The technical solution of the present invention will be described in detail with reference to specific examples, but it will be understood by those skilled in the art that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention.

Example 1

As shown in fig. 2, a preparation method of cetirizine impurity C includes the following steps:

(1) Preparation of Compound a: 5g of 2-chlorobenzophenone (23.15 mmol) was added to a dry reaction flask, 30mL of anhydrous methanol was added, 525mg of sodium borohydride (13.89 mmol) was slowly added with stirring at-10℃and the temperature was slowly raised to room temperature for 2 hours, after the reaction was completed, a small amount of water was added to quench the reaction, the methanol was dried by swirling, the residue was added with 100mL of water, washed 3 times with 100mL of ethyl acetate, the ethyl acetate layer after delamination was washed with brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to give 5g of colorless oily compound a in 100% yield.

(2) Preparation of compound b: 5g of Compound a (22.93 mmol) was added to a dry reaction flask, 30mL of 1, 4-dioxane was added, and finally 9.6mL of concentrated hydrochloric acid (115 mmol) was added, the temperature was raised to 40℃for 2 hours, after completion of the reaction, 100mL of water was added, washing 3 times with 100mL of ethyl acetate, the ethyl acetate layer after delamination was washed with brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to give 5.1g of colorless oily Compound b in 94% yield.

(3) Preparation of compound c: 5.1g of compound b (21.61 mmol) was added to a dry reaction flask, 50mL of acetone was added, then 6.1g of anhydrous potassium carbonate (44 mmol) was added, finally 2.8 g of N-hydroxyethyl piperazine (21.61 mmol) was added under stirring, the reaction was mixed and refluxed at 80℃for 8 hours, after the reaction was completed, cooled to room temperature, filtered, the solvent was removed under reduced pressure, 150mL of ethyl acetate was added to the residue, washed 3 times with 150mL of water, the organic layer was washed with brine, dried over anhydrous sodium sulfate, the solvent was removed under reduced pressure, and the residue was purified by silica gel column chromatography using methylene chloride: methanol=50: 1 column chromatography gave 6.1g of compound c as a colorless oil in 85% yield.

The compound b (chemical name: 1-chloro-2- (chlorophenyl methyl) benzene) is directly reacted with hydroxyethyl piperazine to obtain a key intermediate, and the key intermediate can be prepared by the prior art that 1-chloro-4- (chlorophenyl methyl) benzene is reacted with piperazine and then reacted with 2-chloroethanol, so that the reaction step and energy consumption are increased, more time is consumed, and the yield is reduced instead.

(4) Preparation of compound d: 6.1g of compound c (18.48 mmol) are introduced into a dry reaction flask, 50mL of dichloromethane are added, then 50mL of 35% sodium hydroxide solution and 1.44g of tetrabutylammonium chloride (7.4 mmol) are added, finally 7.22g of tert-butyl bromoacetate (37 mmol) are added with stirring, the mixture is reacted at room temperature for 6 hours, after completion of the reaction, the mixture is allowed to stand for delamination, the solvent is removed under reduced pressure from the organic layer, and the residue is purified by column chromatography on silica gel with dichloromethane: methanol=100: 1 column chromatography gave 7.2g of compound d as a colorless oil in 87% yield.

The method comprises the steps of taking a compound d (chemical name: 4- { (2-chlorophenyl) phenyl } -1-hydroxyethyl piperazine) and bromoacetic acid tert-butyl ester as reaction substrates, taking alkali metal hydroxide as a catalyst, mixing dichloromethane and water, reacting at room temperature, directly standing for layering, and purifying an organic layer by silica gel column chromatography to obtain a product; the polarity of the product is smaller, the extraction is simple, repeated extraction is not needed, and toluene with high toxicity is not needed to be used as a detergent. The product in the prior art exists in the form of sodium salt, has large polarity and good water solubility, and is difficult to extract from water; in addition, DMF is used as a solvent in the prior art, so that the product is more difficult to extract from water, and is difficult to wash away DMF by water, and the extracted product contains a large amount of DMF, which is unfavorable for purification and separation and needs to be repeatedly extracted by using toxic toluene.

(5) Preparation of cetirizine impurity C: 7.2g of compound d (16.21 mmol) was added to a dry reaction flask, 50mL of methylene chloride was added, then 20mL of dioxane hydrochloride (4.0 moL/L) was added under stirring, the reaction was carried out at room temperature for 3 hours, after the completion of the reaction, most of the solvent was removed under reduced pressure, 100mL of ethyl acetate was added to the residue, stirring was continued for 1 hour, a white solid was produced, filtration was carried out, and the solid was washed with ethyl acetate and dried to obtain cetirizine impurity C (structural formula shown in FIG. 1) in 100% yield.

The cetirizine impurity C was characterized by a spectrum as shown in fig. 3 by nuclear magnetic resonance hydrogen spectrum (1H NMR (600 mhz, chroman-d) d ppm 2.53-2.76 (m, 4H) 2.95 (d, j=5.45 hz, 2H) 3.10 (br.s., 4H)

3.71-3.85(m,2H)3.93-4.06(m,2H)4.90(s,1H)7.13(td,J＝7.63,1.45Hz,1H)7.18-7.23(m,1H)7.24-7.27(m,2H)7.28-7.31(m,2H)7.41(d,J＝7.45Hz,2H)7.78(dd,J＝7.72,1.00Hz,1H)12.49(br.s.,1H)), HPLC profile as shown in fig. 4; as shown in the mass spectrum of FIG. 5, the product prepared by the method is very pure and has very low content of other substances.

Example 2

A method for preparing cetirizine impurity C, comprising the steps of:

(1) Preparation of Compound a: 5 g of 2-chlorobenzophenone (23.15 mmol) was added to a dry reaction flask, 40mL of anhydrous methanol was added, 612mg of sodium borohydride (16.2 mmol) was slowly added under stirring at 0℃and the temperature was slowly raised to room temperature for 3 hours, after the reaction was completed, a small amount of water was added to quench the reaction, the methanol was dried by swirling, the residue was added with 120mL of water, washed with 120mL of ethyl acetate for 2 times, the ethyl acetate layer after delamination was washed with brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to give 4.8g of colorless oily compound a in 98% yield.

(2) Preparation of compound b: 4.8g of Compound a (22.02 mmol) was added to a dry reaction flask, 30mL of 1, 4-dioxane was added, and finally 10.97mL of concentrated hydrochloric acid (132 mmol) was added, the temperature was raised to 45℃for 3 hours, after completion of the reaction, 100mL of water was added, washing 3 times with 100mL of ethyl acetate, the ethyl acetate layer after delamination was washed with brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to give 5g of colorless oily Compound b in 95% yield.

(3) Preparation of compound c: 5g of compound b (21.19 mmol) was added to a dry reaction flask, 50mL of acetonitrile was added, then 8.83g of anhydrous potassium carbonate (63.57 mmol) was added, finally 5.5 g of N-hydroxyethyl piperazine (42.38 mmol) was added under stirring, the mixture was refluxed for 10 hours at 85 ℃, after the reaction was completed, cooled to room temperature, filtered, the solvent was removed under reduced pressure, 150mL of ethyl acetate was added to the residue, washed 3 times with 150mL of water, the organic layer was washed with brine, dried over anhydrous sodium sulfate, the solvent was removed under reduced pressure, and the residue was purified by silica gel column chromatography using methylene chloride: methanol=50: 1 column chromatography gave 6g of compound c as a colorless oil in 88% yield.

(4) Preparation of compound d: 6g of compound c (18.18 mmol) are introduced into a dry reaction flask, 50mL of dichloromethane are added, 50mL of 35% sodium hydroxide solution and 1.77g of tetrabutylammonium chloride (9.09 mmol) are then added, finally 10.63g of tert-butyl bromoacetate (54.54 mmol) are added with stirring, the mixture is reacted at room temperature for 8 hours, after completion of the reaction, the mixture is allowed to stand for delamination, the solvent is removed under reduced pressure from the organic layer, and the residue is purified by column chromatography on silica gel with dichloromethane: methanol=100: 1 column chromatography gave 7g of compound d as a colorless oil in 88% yield.

(5) Preparation of cetirizine impurity C: 7g of compound d (15.76 mmol) was added to a dry reaction flask, 50mL of methylene chloride was added, then 20mL of dioxane hydrochloride (4.0 moL/L) was added under stirring, the reaction was carried out at room temperature for 3.5 hours, after the completion of the reaction, most of the solvent was removed under reduced pressure, 100mL of ethyl acetate was added to the residue, stirring was continued for 1.5 hours, a white solid was produced, filtration was carried out, the solid was washed with ethyl acetate, and drying was carried out, to obtain cetirizine impurity C in 100% yield.

Example 3

A method for preparing cetirizine impurity C, comprising the steps of:

(1) Preparation of Compound a: 5g of 2-chlorobenzophenone (23.15 mmol) was added to a dry reaction flask, 50mL of anhydrous methanol was added, 567mg of sodium borohydride (15 mmol) was slowly added under stirring at 10℃and the temperature was slowly raised to room temperature for 4 hours, after completion of the reaction, a small amount of water was added to quench the reaction, the methanol was dried by swirling, the residue was added with 120mL of water, washed 3 times with 120mL of ethyl acetate, the ethyl acetate layer after delamination was washed with brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to give 4.9g of colorless oily compound a in 99% yield.

(2) Preparation of compound b: 4.9g of Compound a (22.47 mmol) was added to a dry reaction flask, 30mL of 1, 4-dioxane was added, and finally 10.29mL of concentrated hydrochloric acid (123.58 mmol) was added, the temperature was raised to 50℃for 4 hours, after completion of the reaction, 100mL of water was added, washing 3 times with 100mL of ethyl acetate, the ethyl acetate layer after delamination was washed with brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure to give 5g of colorless oily Compound b in 95% yield.

(3) Preparation of compound c: 5g of compound b (21.18 mmol) were added to a dry reaction flask, 50mL of acetone was added, then 7.35g of anhydrous potassium carbonate (52.95 mmol) was added, finally 4.13 g of N-hydroxyethyl piperazine (31.77 mmol) was added with stirring, the reaction was mixed and refluxed at 90℃for 12 hours, after the reaction was completed, cooled to room temperature, filtered, the solvent was removed under reduced pressure, 150mL of ethyl acetate was added to the residue, washed 1 time with 150mL of water, the organic layer was washed with brine, dried over anhydrous sodium sulfate, the solvent was removed under reduced pressure, and the residue was purified by silica gel column chromatography using methylene chloride: methanol=50: 1 column chromatography gave 6.1g of compound c as a colorless oil in 87% yield.

(4) Preparation of compound d: 6.1g of compound c (18.48 mmol) are introduced into a dry reaction flask, 50mL of dichloromethane are added, then 50mL of 35% sodium hydroxide solution and 1.62g of tetrabutylammonium chloride (8.32 mmol) are added, finally 9g of tert-butyl bromoacetate (46.2 mmol) are added with stirring, the mixture is reacted at room temperature for 10 hours, after completion of the reaction, the mixture is allowed to stand for delamination, the solvent is removed under reduced pressure from the organic layer, and the residue is purified by column chromatography on silica gel with dichloromethane: methanol=100: 1 column chromatography gave 7g of compound d as a colorless oil in 84% yield.

(5) Preparation of cetirizine impurity C: 7g of compound d (15.76 mmol) was added to a dry reaction flask, 50mL of methylene chloride was added, then 20mL of dioxane hydrochloride (4.0 moL/L) was added under stirring, the reaction was carried out at room temperature for 4 hours, after the completion of the reaction, most of the solvent was removed under reduced pressure, 100mL of ethyl acetate was added to the residue, stirring was continued for 2 hours to give a white solid, filtration was carried out, and the solid was washed with ethyl acetate and dried to obtain cetirizine impurity C in 100% yield.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features but not others included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims below, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Claims

1. The preparation method of cetirizine impurity C is characterized by comprising the following steps:

(1) Preparation of Compound a: dissolving 2-chlorobenzophenone in a solvent I, stirring and adding sodium borohydride at a temperature T1, heating, reacting for T1 time, extracting, drying and spin-drying to obtain a compound a;

(2) Preparation of compound b: dissolving the compound a in a solvent II, adding concentrated hydrochloric acid, reacting for T2 time at a temperature T2, adding water after the reaction is finished, extracting, washing an organic layer, drying and spin-drying to obtain a compound b;

(3) Preparation of compound c: dissolving the compound b in a solvent III, adding potassium carbonate, adding 1- (2-hydroxyethyl) piperazine, reacting for T3 time at a temperature T3, cooling and filtering after the reaction is finished, and evaporating filtrate to obtain a compound c;

(4) Preparation of compound d: dissolving a compound c in dichloromethane, adding tetrabutylammonium bromide, 35% sodium hydroxide solution and tert-butyl bromoacetate, reacting for T4 time at a temperature T4, standing for layering after the reaction is finished, spin-drying an organic layer, and purifying by silica gel column chromatography to obtain a compound d;

(5) Preparation of cetirizine impurity C: dissolving a compound d in dichloromethane, then adding dioxane hydrochloride solution, reacting for T5 time at a temperature of T5, removing dichloromethane under reduced pressure after the reaction is finished, adding ethyl acetate, stirring for a period of time, filtering, washing and drying to obtain cetirizine impurity C;

the structural formula of the cetirizine impurity C is as follows:

The structural formula of the compound a is The structural formula of the compound b is

Compound c has the structural formula/>Compound d has the structural formula/>

2. The method for preparing cetirizine impurity C according to claim 1, wherein the step (1) satisfies one or more of the following conditions:

A. The molar mass ratio of the 2-chlorobenzophenone to the sodium borohydride is 1:0.6-0.7,

B. the temperature T1 is-10 to 10 ℃,

C. the temperature is slowly raised to the room temperature;

D. The reaction time t1 is 2-4h.

3. The method for preparing cetirizine impurity C according to claim 2, wherein in the step (1), the molar mass ratio of the 2-chlorobenzophenone to the sodium borohydride is 1:0.6.

4. The method for producing cetirizine impurity C according to claim 2, wherein in the step (1), the temperature T1 is 0 ℃.

5. The method for preparing cetirizine impurity C according to claim 1, wherein the step (1) further satisfies one or more of the following conditions:

E. The first solvent is methanol;

F. The extracting agent for extraction is ethyl acetate;

G. The drying agent is anhydrous sodium sulfate.

6. The method for preparing cetirizine impurity C according to claim 1, wherein the step (2) satisfies one or more of the following conditions:

H. The molar mass ratio of the compound a to the concentrated hydrochloric acid is 1:5-6,

I. the temperature T2 is 40-50 ℃;

J. the reaction time t2 is 2-4h.

7. The method for preparing cetirizine impurity C according to claim 6, wherein in the step (2), the molar mass ratio of the compound a to the concentrated hydrochloric acid is 1:5.

8. The method for preparing cetirizine impurity C according to claim 1, wherein the step (2) further satisfies one or more of the following conditions:

K. The second solvent is 1, 4-dioxane;

L, the extracting agent for extraction is ethyl acetate;

M. the organic layer is washed with brine;

and N. the drying is drying with anhydrous sodium sulfate.

9. The method for preparing cetirizine impurity C according to claim 1, wherein the step (3) satisfies one or more of the following conditions:

the molar mass ratio of the compound b to the potassium carbonate to the 1- (2-hydroxyethyl) piperazine is 1:2-3:1-2;

P, the temperature T3 is 80-90 ℃;

q. the reaction time t3 is 8-12h.

10. The method for preparing cetirizine impurity C according to claim 9, wherein in the step (3), the molar mass ratio of the compound b, potassium carbonate and 1- (2-hydroxyethyl) piperazine is 1:2:1.

11. The method for preparing cetirizine impurity C according to claim 1, wherein the third solvent in step (3) is acetone or acetonitrile.

12. The method for preparing cetirizine impurity C according to claim 1, wherein the step (4) satisfies one or more of the following conditions:

the molar mass ratio of the compound c to the tetrabutylammonium chloride to the tert-butyl bromoacetate is 1:0.4-0.5:2-3,

S, the temperature T4 is room temperature;

t, the reaction time t4 is 6-10h;

and U, flushing the silica gel column by using a mixed solution of dichloromethane and methanol with the molar ratio of 100:1.

13. The method for preparing cetirizine impurity C according to claim 12, wherein in the step (4), the molar mass ratio of the compound C, tetrabutylammonium chloride and tert-butyl bromoacetate is 1:0.5:2.

14. The method for preparing cetirizine impurity C according to claim 1, wherein the step (5) satisfies one or more of the following conditions:

V. the temperature T5 is room temperature;

W. the reaction time t5 is 3-4h;

x, stirring for 1-2h;

And Y, the washed detergent is ethyl acetate.