The field of the invention relates to processes for the preparation of 1,2-diamines, and to the use of these compounds as intermediates for the preparation of several useful compounds. More particularly, it relates to the preparation of 2-methyl-l,2- diaminopropane which is a useful intermediate for the preparation of pharmaceutically active compounds.

Background of the Invention

1,2-diamines of Formula I, or salts thereof, R1

NH NH2

R3

Formula I

wherein R1, R2 and R3 are hydrogen or C1 to C6 straight or branched chain alkyl group, are useful intermediates in the synthesis of several drugs, herbicides, agricultural products, dyes and cosmetics. Host of patents describe the use of 1,2-diamines as intermediates for example, in U.S. Patent Nos. 2,500,600; 3,725,443; 3,770,766; 3,928,412; 4,810,717; 4,935,421; 4,935,422; 3,931,218; 4,128,655; 4,303,649 4,260,626; 5,596,002; DE 2,341,289 and DE 2,408,334. U.S. Patent Application No. 2004/0039008 describes the use of 2-methyl-l,2-diaminopropane of Formula I, wherein R1 and R2 are methyl and R3 is hydrogen, in the preparation of novel anti-malarial compound OZ-277, which is a dispiro-l,2,4-trioxolane derivative.

Several processes have been reported for the preparation of 1,2-diamines for example, mBerischte 1932, 65B, 710-713 and 1933, 66B, 1330-1333. These processes disclose the preparation of 1,2-diamines by reducing α-aminonitriles using a palladium catalyst at pressures in excess of 355 pounds per square inch (PSI). Journal of Chemical Society, Abstracts, 1934, 49-50 discloses a process for the preparation of 1,2-diamines by oximation of alkylene compounds followed by reduction of the aldoximes using sodium amalgam (Na/Hg).

Journal of American Chemical Society 1948, 70, 184-186 describes a process of converting 2-cyanoalkanes to 1,2-diamines by the reaction of homologs of ethylenimine with amines and liquid ammonia in the presence of ammonium chloride as a catalyst at elevated temperatures and pressures.

Journal of American Chemical Society I960, 82, 696-698 discloses a process for the preparation of 1,2-diamines by reduction of corresponding ce-aminonitriles using alcoholic hydrogen chloride over platinum oxide at low pressures.

U.S. Patent No. 2,408,171 discloses the preparation of 2-methyl-l, 2- propanediamine by reacting 2-methyl-2-nitro-l-propanol with ammonia in the presence of a suitable hydrogenation catalyst under hydrogen pressure of about 1100 PSI at 4O0C to get 2-methyl-l, 2-diaminopropane.

U.S. Patent No. 2,413,248 describes the preparation of N-(2- aminoisobutyl)benzylamine by reducing N-(2-nitroisobutyl)-benzylamine in methanol using Raney nickel at 500 PSI hydrogen pressure.

U.S. Patent No. 2,587,043 describes a process for the preparation of 1,2- primarydiamines by acylating an alpha aminonitrile compound, forming the dihydroimidazole by catalytically hydrogenating acylated aminonitrile with gaseous hydrogen in the presence of ammonia or ammonium compounds and forming the diprimary diamine by hydrolyzing the dihydroimidazole. The process requires a hydrogen pressure of about 500 PSI to 2500 PSI at a temperature of about 90-1000C.

U.S. Patent No. 4,902,831 describes a process for the preparation of 1,2- diaminoethane compounds which comprises reacting a Schiff base with a nitroalkane in the presence of a catalytic amount of an inorganic base to form a substituted or unsubstituted l-nitro-2-aminoethane which is then hydro genated to obtain the corresponding 1,2-diaminoethane compound.

Japanese Patent Application IP 08-027072 A2 describes a process for the preparation of 2-methyl- 1 ,2-propanediamine which can be used for the preparation of compounds containing dihydroimidazole ring by hydrogenating 2-acetyl-amino-2-methyl- propanenitrile in the presence of Raney nickel catalyst and in the absence of ammonia.

These processes require high-pressure conditions usually in the range of 300 to 2500 PSI or use of nitro compounds, which are highly inflammable and toxic. The purity of 1,2-diamines obtained by above mentioned prior-art is poor, the product obtained is very hygroscopic and difficult to purify without significantly affecting the yields.

Thus, the invention provides a process which does not result in impure product; rather pure 1,2-diamines having purity more than 99% by GC is obtained. The process is simple, cost-effective, which does not require high pressure and provide pure non- hygroscopic product thus making the process amenable for commercial use.

SUMMARY OF THE INVENTION

In one general aspect there is provided a process for preparing 1,2-diamines of Formula I, or a salt thereof,

Formula I

wherein, R1, R2 and R3 are hydrogen or C1 to C6 straight or branched chain alkyl group. The process includes a) hydrogenating acetylamino-nitrile of Formula II,

Formula II wherein R1, R2 and R3 are as defined above and R4 is hydrogen or C1 to C6 straight or branched chain alkyl group, with a metal catalyst in the presence of ammonia or chemical equivalents thereof, at a hydrogen gas pressure of about 40 PSI to about 250 PSI, in an organic solvent to get a dihydroimidazole of Formula III,

Formula III wherein R1, R2, R3 and R4 are as defined above; and

b) hydrolyzing the dihydroimidazole of Formula III in the presence of a base to get 1 ,2-diamine of Formula I, or a salt thereof.

hi another general aspect there is provided a process for preparing 2-methyl-l,2- diaminopropane of Formula I, or a salt thereof, wherein R1 and R2 are methyl and R3 is hydrogen. The process includes a) hydro genating acetylamino-nitrile of Formula II, wherein R1 and R2 are methyl, R3 is hydrogen and R4 is hydrogen or C1 to C6 straight or branched chain alkyl group, with a metal catalyst in the presence of ammonia or chemical equivalents thereof, at a pressure of about 40 PSI to about 250 PSI in an organic solvent to get a dihydroimidazole of Formula III, wherein R1, R2, R3 and R4 are as defined above; and

b) hydrolyzing the dihydroimidazole of Formula III in the presence of a base to get 2- methyl-l,2-diaminopropane of Formula I, or a salt thereof, wherein R1 and R2 are methyl and R3 is hydrogen.

hi another general aspect there is provided a process for preparing pure 1 ,2- diamine of Formula I, or a salt thereof. The process includes drying 1,2-diamine over a solid base and then distilling over a solid base to get the pure 1,2-diamine having a purity of more than 99% by GC. The process may produce the pure 1,2-diamine having a purity of more than 99% by GC. In particular, it may produce 1,2-diamine having a purity of more than 99.5%, for example more than 99.8% by GC.

ha another general aspect there is provided a pure 1,2-diamine of Formula I, or a salt thereof, wherein R1 and R2 are methyl and R3 is hydrogen, having a purity of more than 99% by GC.

The pure 1,2-diamine of Formula I, or a salt thereof may have, for example moisture content less than 1% w/w. In particular, it may have moisture content less than 0.5% w/w, for example less than 0.3% w/w.

The resulting pure 1,2-diamine of Formula I, or a salt thereof, may be used as an intermediate for the preparation of dyes, enamels, varnishes, fungicides, bactericides, resins, herbicides, hypoglycemic agents, /3-adrenergic blockers, antipyretics, anti¬ depressants, anti-diabetics, anti-inflammatory, antimalarials, ulcer-inhibitors, anti¬ arrhythmic, antihypertensive, anti-secretory compounds, and the like.

The details of one or more embodiments of the inventions are set forth in the description below. Other features, objects and advantages of the inventions will be apparent from the description and claims.

Detailed Description of the Invention

The inventors have developed an efficient process for the preparation of 1,2- diamines of Formula I, or a salt thereof, wherein R1, R2 and R3 are hydrogen or C1 to C6 straight or branched chain alkyl group. The process involves hydrogenating acetylamino- nitrile of Formula II, wherein R1, R2 and R3 are as defined above and R4 is hydrogen or C1 to C6 straight or branched chain alkyl group, with a metal catalyst in the presence of ammonia or chemical equivalents thereof, at a hydrogen gas pressure of about 40 PSI to about 250 PSI, in an organic solvent to get a dihydroimidazole of Formula III, wherein R1, R2, R3 and R4 are as defined above. The dihydroimidazole of Formula III is hydrolyzed in the presence of a base to get 1,2-diamine of Formula I, or a salt thereof.

The hydrogenation reaction may be carried at a temperature from about 400C to about 18O0C. In particular, it may be carried out at a temperature from about 600C to about 15O0C. Examples of metal catalysts which can be used in the hydrogenation reaction include catalysts such as Raney nickel, platinum and ruthenium.

Suitable organic solvents which can be used in the hydrogenation reaction of compound of Formula II are conventional solvents used in the hydrogenation reactions and are known to a person of ordinary skill in the art. Examples of such solvents include alcohols, inert polar aprotic solvents, dialkyl ether, paraffin oil, dowtherm, and the like.

The term "ammonia or chemical equivalents thereof includes liquor ammonia, aqueous ammonia solution, ammonium hydroxide, ammonium chloride, ammonium sulphate, ammonium formate, and the like.

hi general, the reaction mixture may be cooled after the completion of the reaction, and may be treated with charcoal. The reaction mixture may also be concentrated to reduce the volume of solvent before cooling. The dihydroimidazole of Formula III thus obtained may be used as such for further hydrolysis. It may also be further purified by high vacuum distillation and the fractions corresponding to the pure dihydroimidazole of Formula III are collected separately and used for further hydrolysis reaction.

The hydrolysis of the dihydroimidazole of Formula III can be carried out in aqueous conditions using a base. The reaction may also be carried out in the presence of an organic solvent. The dihydroimidazole of Formula III can be treated with aqueous solution of a base at a temperature of from about 600C to 15O0C.

The organic solvents which can be used in the hydrolysis reaction include water- soluble alcohols, low boiling polar aprotic solvents, water-soluble ketones, acetonitrile, and mixtures thereof.

Examples of a base which can be used in the hydrolysis reaction of dihydroimidazole of Formula III include alkali and alkaline earth metal hydroxides, carbonates, bicarbonates and alkoxides.

After completion of the reaction, the organic solvent may be removed under vacuum and the 1,2-diamine product layer can be separated from the reaction mass by adding a solid base to the reaction mass. The separated layer can be isolated and dried over solid base for about 10-12 hours. The 1,2-diamine product may be further or additionally dried to achieve the desired moisture values. The product may be dried by removing the solid base drying agent and adding fresh solid base. The resultant mass can be stirred at about 35-4O0C to reduce the moisture content to less than 1%.

The solid base drying agents which can be used include alkali metal hydroxide such as potassium hydroxide.

The inventors have also developed a process for the preparation of 2-methyl-l,2- diaminopropane of Formula I, or a salt thereof, wherein R1 and R2 are methyl and R3 is hydrogen. The process involves hydrogenating acetylamino-nitrile of Formula II, wherein R1 and R2 are methyl, R3 is hydrogen and R4 is hydrogen or C1 to C6 straight or branched chain alkyl group, with a metal catalyst in the presence of ammonia or chemical equivalents thereof, at a pressure of about 40 PSI to about 250 PSI in an organic solvent to get dihydroimidazole of Formula III, which is hydrolyzed in the presence of a base to get 2-methyl-l,2-diaminopropane of Formula I, or a salt thereof, wherein R1 and R2 are methyl and R3 is hydrogen.

The product 1,2-diamine thus obtained may be used as an intermediate in the preparation of dyes, enamels, varnishes, fungicides, bactericides, resins, herbicides, hypoglycemic agents, /3-adrenergic- blockers, anti-depressants, anti-inflammatory, antimalarials, ulcer-inhibitors, anti-arrhythmic, antihypertensive, anti-secretory compounds, and the like.

Acetylamino-nitrile of Formula II wherein, R1, R2 and R3 are methyl and R4 is hydrogen or C1 to C6 straight or branched chain alkyl group can be prepared by methods known in the art such as the process disclosed in U.S. Patent No. 2,587,043.

The present invention is further illustrated by the following examples which are provided merely to be exemplary of the invention and do not limit the scope of the invention. Certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

Example 1: Preparation of 2,4,4-trimethyl-2,3-dihydroimidazole

In a hydrogenator, N-acetyl-2-cyano-2-methylethylamine (100 gm) and methanol (300 ml) were added followed by addition of Raney Nickel catalyst (80 gm) and liquor ammonia solution (200 ml, 22-25% w/v in water). The vessel was closed and hydrogen gas was purged to achieve 6 Kg pressure. The temperature of the reaction mass was slowly raised up to 850C. The reaction mass was stirred at 8 to 9 Kg hydrogen pressure at 85 to 90°C for 8 to 9 hrs. After confirming the completion of reaction by TLC, the reaction mass was cooled to 25 to 300C and hydrogen was vented out. The reaction mass was removed from the hydrogenator and charcoal (10 gm) was charged to it. The resultant mass was filtered through a celite bed and the bed was washed with a small amount of methanol. The filtrate was concentrated under vacuum to remove methanol and the residue was distilled under vacuum of about 10 mm of Hg and the fraction distilling between 110- 13O0C was collected and kept separately to give pure 2,4,4-trimethyl-2,3- dihydroimidazole.

Yield: 80 gm

Purity: Not less than 99% by GC

Example 2: Preparation of 2-methyl-l,2-propanediamine

2,4,4-trimethyl-2,3-dihydroimidazole (100 gm) prepared per example 1 was added to a solution of potassium hydroxide (300 ml, 30% w/v in water). The resultant mixture was refluxed for about 6 to 7 hours. The completion of reaction was monitored by TLC. After this, the reaction mass was cooled to about 25-3O0C. Solid potassium hydroxide (300 gm) was added to the cooled mass and stirred for about 30 minutes. The organic layer was separated and collected. Solid potassium hydroxide (10 gm) was added to the organic layer. The resultant mass was stirred further at 35 to 4O0C for 10 to 12 hours. Solid potassium hydroxide was filtered and the moisture content of the filtrate was checked. The process of adding solid potassium hydroxide and heating to 35-4O0C was repeated till moisture content of not more than 1% was achieved. This gave substantially pure 2- methyl- 1,2-diaminoρropane.

Yield: 85 gm

Purity: not less than 99% by GC

The above-obtained material was distilled at atmospheric pressure and the fraction boiling at 109-1110C was collected to get highly pure 2-methyl-l,2-diaminopropane.

Yield: 82.5 gm Purity: 99.9% by GC Moisture content: 0.3% w/w by Karl Fischer. While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are included within the scope of the present invention.