DESC:FIELD OF THE INVENTION

The present invention is directed to a process for the preparation of cytosine. More particularly, the present invention provides a process for the preparation of cytosine without using organic solvent but with high yield and quality.

BACKGROUND OF THE INVENTION

Cytosine is a pyrimidine derivative, with a heterocyclic, aromatic ring, and two substituents attached (an amine group at position four and a keto group at position two). IUPAC name of cytosine is 4-aminopyrimidin-2(1H)-one and the structure is given below:
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Cytosine is a white crystalline powder, slightly soluble in water and ethanol, and insoluble in ether. Cytosine is involved in synthesis of DNA and RNA. Cytosine is used as important fine chemical intermediates, pesticides and pharmaceuticals, with a wide range of applications. In pesticides, cytosine is efficient with low toxic residue in agricultural broad-spectrum antibiotics. In the medical field, cytosine is a nucleic acid species, an antiviral drug, mainly used for the synthesis of anti-HBV and anti-HIV drugs, anticancer drug and 5-fluoro-cells pyrimidine and the like.

There are various commercially available preparations of Cytosine. Prior art provides various processes for the preparation of cytosine, some of them are given below:

J. Org. Chem. 1957, 22, 2, 192-193 by Peter et al., discloses a new method for the preparation of cytosine. Isoxazole is prepared by the reaction of malonaldehyde tetraethyl acetal with hydroxylamine hydrochloride. ß-ethoxyacrylonitrile is prepared by reaction of isoxazole with diethyl sulfate in alkaline solution. Cytosine is prepared by condensing ß-ethoxyacrylonitrile with urea in a sodium alcoholate solution. This document describes only 43.7% yield based on Ethoxy acrylonitrile using Sodium butylate generated by n-butanol and Sodium metal. That Sodium butylate, Urea and Ethoxy acrylonitrile refluxed (112-115°C) for 2 hours resulted the desired product in very less yield. The use of sodium metal creates handling and safety issue during manufacturing at bulk scale.

US2892840 relates to the utilization of an acrylonitrile derivative as a starting material and includes correlated improvements and discoveries whereby the preparation of cytosine is enhanced. In US ’840 sodium methoxide has been prepared by using sodium metal and methanol. More specifically, using methanolic solution for in-situ reaction at 75-85°C for six hours. In US’840, no yield and quality reported for finished product, i.e., Cytosine. Moreover, the inventors of the present application have reproduced this experiment at lab and observed inferior quality material with very less yield.

US5026852A relates to a process for the preparation of cytosines, which may optionally be substituted in the 5-position, from ß-alkoxy-acrylonitriles and/or ß,ß-dialkoxy-propionitriles and urea in the presence of alcoholates and subsequent neutralization.

CN103992278A discloses a synthesis method of cytosine. According to the method, ethyl cyanoacetate, urea and triethyl orthoformate are utilized as raw materials, ethyl 3-cyano-2-ureido-acrylate, 5-ethoxycarbonyl cytosine, and 5-carboxyl cytosine are sequentially synthesized, decarboxylation is performed to synthesize cytosine and refining, correction, perfection and other various process steps are sequentially performed.

CN102816123A discloses a preparation method for cytosine, comprises the following steps of: (1) mixing sodium ethoxide, dimethylbenzene, and carbamide, stirring the mixture at a temperature of 85°C to 95°C for 0.3-0.5 hours, dropping 3,3-diethoxy propionitrile, controlling the temperature between 100°C and 105°C, after finishing dropping, back-flow reacting for 8-10 hours, concentrating the mixture to be dried after finishing the reaction, adding distilled water to dissolve condensate, standing for stratification, dropping hydrochloric acid on a water layer and uniformly mixing, adjusting a pH value to equal to 7.0-7.5, cooling, crystallizing and centrifuging to obtain a crude product; and (2) adding the crude product in water and activated carbon, decoloring at the temperature of 70°C to 80°C, filtering and removing the activated carbon, cooling and crystallizing filter liquid, centrifuging to obtain a wet end product, and drying to obtain the cytosine.

CN103880758A discloses a synthesis method of cytosine, comprises the following steps: selecting 3-hydroxy acrylonitrile sodium salt and thiourea as raw materials; when preparing, adding a catalyst and an organic solvent to a reaction kettle, uniformly stirring, and sequentially adding the 3-hydroxy acrylonitrile sodium salt and the thiourea; raising temperature to 50-90°C and carrying out a cyclization reaction for 6-10 hours to obtain a cyclization reaction solution; evaporating out the solvent in the cyclization reaction solution, and adding water and hydrochloric acid to obtain an intermediate product solution; dropping hydrogen peroxide to the intermediate product solution, raising temperature to 60-90°C and preserving heat for 18-24 hours; regulating pH value through a sodium hydroxide solution, and cooling to 10-15°C when the pH value is 7.0-7.5; and after cooling, filtering, washing and drying to obtain the cytosine.

DE3434142A1 discloses preparation of cytosine by a simplified process in which in a first reaction step urea and an alkoxide are reacted and freed from the solvent used and only then is a reaction with alkoxyacrylonitriles or dialkoxypropionitriles carried out. This procedure increases the yield. Methanol and methoxides, which give very low yields when reacted jointly, can now be used if methanol is avoided in the second reaction step.

Yet, there exists an unmet need of providing a process for the preparation of cytosine without using any organic solvent with higher yield and quality.

The present invention addresses said problems existing in the prior-art documents in an economic and effective way. The present invention provides a process for the preparation of cytosine without using organic solvent with higher yield (=70%) and quality (=99.9%).
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OBJECTIVES OF THE INVENTION

The principal object of the present invention is to provide an improved process for the preparation of cytosine.

Another object of the present invention is the provision of a process for the preparation of cytosine without employing an organic solvent.

A further object of the invention is to provide a procedure for the preparation of cytosine in which an alkoxy acrylonitrile and urea serve as the intermediates.

A still further object of the invention is the provision for the preparation of effective and economical/safe preparation of cytosine.

SUMMARY OF THE INVENTION

In an aspect of the present invention, the present invention discloses a process for preparation of cytosine, comprising: mixing of urea and sodium methoxide to obtain a reaction mass, and methanol as a by-product; distilling out the methanol from the reaction mass followed by slow charging of (Z)-3-ethoxy acrylonitrile in the reaction mass and collecting ethanol as a by-product of the reaction; raising the reaction mass temperature and maintaining the reaction temperature for another two hours to get complete conversion; cooling the reaction mass temperature to 30-35°C and charging with water followed by adjusting the pH in a range of 6.5-7.0 by using sulfuric acid solution; heating the reaction mass to 80-85°C and stirring for two hours followed by slow cooling to 30-35°C and filtering to obtain the cytosine.

In a feature of the present invention, amount of the urea is in the range of 50-150 grams, more preferably in the range of 70-120 grams, and most preferably in the range of 85-95 grams.

In a feature of the present invention, amount of the sodium methoxide is in the range of 20-80 grams, more preferably in the range of 30-70 grams, and most preferably in the range of 45-55 grams.

In a feature of the present invention, the mixture of urea and sodium methoxide is heated to a temperature in the range of 20-80°C, more preferably in the range of 40-70°C, and most preferably in the range of 60-65°C.

In a feature of the present invention, amount of the (Z)-3-ethoxy acrylonitrile is in the range of 50-150 grams, more preferably in the range of 70-120 grams, and most preferably in the range of 90-110 grams.

In a feature of the present invention, the reaction mass in step (c) is heated to a temperature in the range of 40-100°C, more preferably in the range of 60-90°C, and most preferably in the range of 70-75°C.

In a feature of the present invention, amount of the water charged in the reaction mass is in the range of 300-1000 ml, more preferably in the range of 400-800 ml, and most preferably in the range of 450-550 ml.

The process as claimed in claim 1, wherein amount of the sulfuric acid solution added in the reaction mass to adjust pH is in a range of 50-130 ml, more preferably in a range of 70-120 ml, and most preferably in a range of 90-110 ml.

DETAILED DESCRIPTION OF THE INVENTION

As used herein and in the appended claims, the singular forms “a,” “and,” and “the” include plural referents unless the context clearly dictates otherwise.
Also, the use of “or” means “and/or” unless stated otherwise. Similarly, “comprise,” “comprises,” “comprising” “include,” “includes,” and “including” are interchangeable and not intended to be limiting.
It is to be further understood that where descriptions of various embodiments use the term “comprising,” those skilled in the art would understand that in some specific instances, an embodiment can be alternatively described using language “consisting essentially of” or “consisting of.”
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices and materials are described herein.
The publications discussed above and throughout the text are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior disclosure.

The term “urea” herein also known as carbamide, is an organic compound with chemical formula CO(NH2)2. This amide has two –NH2 groups joined by a carbonyl (C=O) functional group. It is a colorless, odorless solid, highly soluble in water, and practically non-toxic (LD50 is 15 g/kg for rats). After dissolution in water, it is neither acidic nor alkaline. Various commercial urea processes are characterized by the conditions under which urea forms and the way that unconverted reactants are further processed. The process consists of two main equilibrium reactions, with incomplete conversion of the reactants. The first is carbamate formation: the fast exothermic reaction of liquid ammonia with gaseous carbon dioxide (CO2) at high temperature and pressure to form ammonium carbamate (H2N-COONH4). The second is urea conversion: the slower endothermic decomposition of ammonium carbamate into urea and water.

The term “(Z)-3-ethoxy acrylonitrile” having IUPAC name as (Z)-3-ethoxyprop-2-enenitrile with molecular formula of C5H7NO.

The term “sulfuric acid” herein (alternative spelling sulphuric acid), also known as vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with molecular formula H2SO4. It is a colorless, odorless, and viscous liquid that is soluble in water and is synthesized in reactions that are highly exothermic. It has a role as a catalyst and as pH controlling agent. It is a conjugate acid of a hydrogensulfate. Sulfuric acid is also a key substance in the chemical industry. It is most commonly used in fertilizer manufacture, but is also important in mineral processing, oil refining, wastewater processing, and chemical synthesis.

The term “sodium methoxide” herein is a chemical compound with the formula CH3ONa. It is a white solid formed by the deprotonation of methanol. It is a caustic base. Broadly, sodium methoxide or sodium methylate is a sodium alkoxide.

The present invention provides a process for the preparation of cytosine without using organic solvent.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others thereof, which will be exemplified in the process hereinafter disclosed, and the scope of the invention will be indicated in the claims.

In one aspect, the present invention provides a process for the preparation of cytosine.

In another aspect, the present invention provides a process for the preparation of cytosine without using organic solvent.

In another aspect, the present invention provides a process for the preparation of cytosine by mixing of urea and sodium methoxide followed by heating to 60-65°C and observe the methanol formation in the reaction as a by-product; distilling out the total solvent followed by slow charging of (Z)-3-ethoxy acrylonitrile which leads to exothermicity of in the reaction mass and ethanol is collected as a by-product of the reaction; raising the reaction mass temperature to 70-75°C after end of the exothermic reaction and maintains the reaction temperature for another two hours to get complete conversion; cooling the mass temperature to 30-35°C and charging of water followed by adjustment of the pH to neutral (6.5-7.0) by using 50% sulfuric acid solution; heating the reaction mass to 80-85°C and stirred for 2 hours followed by slow cooling to 30-35°C and filter to get the final product.

In one embodiment of the present invention, the amount of urea is present in the range of 50-150 grams, more preferably in the range of 70-120 grams, and most preferably in the range of 85-95 grams.

In another embodiment of the present invention, the amount of sodium methoxide is present in the range of 20-80 grams, more preferably in the range of 30-70 grams, and most preferably in the range of 45-55 grams.

In one another embodiment of the present invention, the mixture of urea and sodium methoxide is heated to a temperature in the range of 20-80°C, more preferably in the range of 40-70°C, and most preferably in the range of 55-65°C.

In still another embodiment of the present invention, the amount of (Z)-3-ethoxy acrylonitrile is present in the range of 50-150 grams, more preferably in the range of 70-120 grams, and most preferably in the range of 90-110 grams.

In still one another embodiment of the present invention, the reaction mass after end of exothermic is heated to a temperature in the range of 40-100°C, more preferably in the range of 60-90°C, and most preferably in the range of 65-85°C.

In yet another embodiment of the present invention, the amount of water charged after completion of reaction in the reaction mass is in the range of 300-1000ml, more preferably in the range of 400-800 ml, and most preferably in the range of 450-550 ml.

In yet another embodiment of the present invention, the amount of sulfuric acid added in the reaction mass to adjust pH is in the range of 50-130 ml, more preferably in the range of 70-120 ml, and most preferably in the range of 90-110 ml.

In yet one another embodiment of the present invention, the amount of 50wt% sulfuric acid in the composition of the present invention is in amount of sufficient quantity so as to adjust the pH of the composition preferably in the range of 6-10, more preferably the range of 7-9 and most preferably in the range of 6.5-7.5.

In one another aspect of the present invention, the present invention discloses a process for the preparation of cytosine, comprising: mixing of urea and sodium methoxide to obtain a reaction mass and observe the methanol formation in the reaction as a by-product; distilling out completely the solvent from the reaction mass followed by slow charging of (Z)-3-ethoxy acrylonitrile which leads to exothermicity in the reaction mass and ethanol is collected as a by-product of the reaction; raising the reaction mass temperature after end of the exothermic reaction and maintains the reaction temperature for another two hours to get complete conversion; cooling the reaction mass temperature to 30-35°C and charging of water followed by adjustment of the pH in a range of 6.5-7.0 by using sulfuric acid solution; heating the reaction mass to 80-85°C and stirred for two hours followed by slow cooling to 30-35°C and filter to get the cytosine as a final product.

In a feature of the present invention, amount of the urea is in the range of 50-150 grams, more preferably in the range of 70-120 grams, and most preferably in the range of 85-95 grams.
In a feature of the present invention, amount of the sodium methoxide is in the range of 20-80 grams, more preferably in the range of 30-70 grams, and most preferably in the range of 45-55 grams.

In a feature of the present invention, the mixture of urea and sodium methoxide is heated to a temperature in the range of 20-80°C, more preferably in the range of 40-70°C, and most preferably in the range of 60-65°C.

In a feature of the present invention, amount of the (Z)-3-ethoxy acrylonitrile is in the range of 50-150 grams, more preferably in the range of 70-120 grams, and most preferably in the range of 90-110 grams.

In a feature of the present invention, the reaction mass after end of the exothermicity is heated to a temperature in the range of 40-100°C, more preferably in the range of 60-90°C, and most preferably in the range of 70-75°C.

In a feature of the present invention, quantity of the water charged after completion of reaction in the reaction mass is in the range of 300-1000 ml, more preferably in the range of 400-800 ml, and most preferably in the range of 450-550 ml.

In a feature of the present invention, amount of the sulfuric acid solution added in the reaction mass to adjust pH is in a range of 50-130 ml, more preferably in a range of 70-120 ml, and most preferably in a range of 90-110 ml.

Some illustrative non-limiting examples of the present invention are described below.

EXAMPLES
Comparative Example 1
To a cooled solution of 23 gram of sodium in 690 ml. dry butanol, was added 60 g. (1 mole) of dry urea and 97.0 g. (1.0 mole) of ß-ethoxyacrylonitrile. The mixture was refluxed (112-115°C) for 2 hours and cooled to 20°C. Sulfuric acid (128.0 gram) in 1250 ml. water was added and the mixture was stirred for 0.5 hour. The aqueous layer was separated from the butanol, heated to 80°C and 2500 ml. alcohol was added. The mixture was chilled to 0°C and the crude cytosine sulfate filtered off. The cytosine sulfate was added to 1 liter of H2O and alkalized with concentrated ammonium hydroxide until the mixture was slightly alkaline to alkacid paper. The crude cytosine was filtered, added to 1 liter of water, and clarified with charcoal. On cooling, there were obtained colorless plates of cytosine. Concentration of the mother liquor yielded an additional amount of cytosine. There was obtained a total of 48.5 g. of cytosine. Yield, 43.7% based on ß-ethoxyacrylonitrile employed. Melting point 305°C (browns), 319-323°C (decomp.). The infrared spectrum of the compound obtained was identical with a known sample of cytosine. Yield: 43.7%

Comparative Example 2
The urea and nitrile were added to the previously prepared solution of sodium-n-butoxide and the mixture refluxed for two hours at 112°C to 115°C. The slurry was cooled to 20°C and the 2N sulfuric acid added. After 15 minutes agitation the butanol was separated. The aqueous acid solution was heated to 80°C and the ethyl alcohol added over an hour period to the solution kept at 80°C to 85 C. The mixture was cooled to 20°C and the cytosine sulfate filtered off. The sulfate was added to 300 cc of water and the cytosine precipitated by the addition of the ammonia solution. The crude cytosine was filtered off, added to 200cc water, and charcoaled. After filtration and cooling to 20°C, the filtrate deposited large colorless plates of cytosine. The cytosine obtained was dried at 100°C for 16 hours. Yield: 40%

Example 1
A mixture of urea (90 gm), sodium methoxide (50 gm) is heated to 60-65°C; and observes the methanol formation in the reaction as a by-product. Distil-out the total solvent and then charge slowly (Z)-3-ethoxy acrylonitrile (100 grams). Exothermic nature observed and ethanol is collected as a by-product of the reaction. After exothermicity ends, raise the reaction mass temperature to 70-75°C. Maintain the reaction for another two hours to get complete conversion. Slowly cooled the mass temperature to 30-35°C and charged water (500 ml). Adjust the pH to neutral (6.5-7.0) by using 50% sulfuric acid solution (~100 ml). Heat the reaction mass to 80-85°C and stirred for 2 hrs. Slowly cool to 30-35°C and filter to get the final product. Yield: 80 gm. (>70%) ,CLAIMS:1. A process for preparation of cytosine, comprising:
a) mixing of urea and sodium methoxide to obtain a reaction mass, and methanol as a by-product;
b) distilling out the methanol from the reaction mass followed by slow charging of (Z)-3-ethoxy acrylonitrile in the reaction mass and collecting ethanol as a by-product of the reaction;
c) raising the reaction mass temperature and maintaining the reaction mass temperature for another two hours to get complete conversion;
d) cooling the reaction mass temperature to 30-35°C and charging with water followed by adjusting pH in a range of 6.5-7.0 by using sulfuric acid solution;
e) heating the reaction mass to 80-85°C and stirring for two hours followed by slow cooling to 30-35°C and filtering to obtain the cytosine.

2. The process as claimed in claim 1, wherein amount of the urea is in a range of 50-150 grams, more preferably in a range of 70-120 grams, and most preferably in a range of 85-95 grams.

3. The process as claimed in claim 1, wherein amount of the sodium methoxide is in a range of 20-80 grams, more preferably in a range of 30-70 grams, and most preferably in a range of 45-55 grams.

4. The process as claimed in claim 1, wherein the mixture of urea and sodium methoxide is heated to a temperature in a range of 20-80°C, more preferably in a range of 40-70°C, and most preferably in a range of 60-65°C.

5. The process as claimed in claim 1, wherein amount of the (Z)-3-ethoxy acrylonitrile is in a range of 50-150 grams, more preferably in a range of 70-120 grams, and most preferably in a range of 90-110 grams.

6. The process as claimed in claim 1, wherein the reaction mass in step (c) is heated to a temperature in a range of 40-100°C, more preferably in a range of 60-90°C, and most preferably in a range of 70-75°C.

7. The process as claimed in claim 1, wherein amount of the water charged in the reaction mass is in a range of 300-1000 ml, more preferably in a range of 400-800 ml, and most preferably in a range of 450-550 ml.

8. The process as claimed in claim 1, wherein amount of the sulfuric acid solution added in step (d) is in a range of 50-130 ml, more preferably in a range of 70-120 ml, and most preferably in a range of 90-110 ml.