AN IMPROVED PROCESS FOR THE PREPARATION OF FELBAMATE
FIELD OF THE INVENTION:
The present invention relates to an improved process for the preparation of Felbamate comprisingreactingcompound of structural formula II with sodium cyanate in the presence of dry hydrochloricacid in methylene dichloride solvent andisolating Felbamate compound of structural formula I.

BACKGROUND OF THE INVENTION:
Felbamate (dicarbamate compound with the chemical name of 2-phenyl-l, 3-propanediol dicarbamate) is an antiepileptic drug and is known from U.S. Patent No. 2, 884,444.
The chemical structure of Felbamate can be represented by compound of structural formula I.

Felbamate is a well-known antiepileptic drug described in U.S. Patent Nos. 4,978,680 and 5,082,861 which are incorporated by reference.

Several processes for the preparation of Felbamate have been described; including the methods disclosed in U.S. Patent Nos. 2,884,444, 4,868,327, 4,982,016and 5,091,595 as well as PCT Publication No. 94/06737 and 94/27491, all of which are incorporated by reference. U.S. Patent No. 2,884,444 described a process for the preparation of Felbamate comprises, reducing compound of structural formula III with lithium aluminium hydride in an ether solvent to get compound of structuralformula II and reacting compound of structural formula II with ethyl urethane in presence of aluminium isopropylate in an anhydrous toluene to get Felbamate compound of structural formula I as shown below in scheme no. 1.

The above processes require costly and extremely flammable reducing agent such as lithium aluminium hydride and hazardous ethyl urethane compound. The high cost and hazardous nature of theses reducing agent and ethyl urethane compound render such process unsatisfactory for commercial use.
PCT Publication No. 94/06737 described a process for the preparation of Felbamate compound of structural formula I as shown below in scheme no. 2 wherein the compound of structural formula II is reacted with sodium cyanate in the presence of hydrochloric acid gas in acetonitrile solvent.


The reaction of compound of formula II with sodium cyanate in the presence of acid such as hydrochloric acid in acetonitrile as a solvent forms impurity having compound of structural formula IX by Pinner reaction mechanism. The formation of impurities affects the yield and purity of the Felbamate compound of structural formula I.

Accordingly there is need in the art to develop an improved process for the preparation of Felbamate compound of structural formula I, which obviates prior ail problems.

SUMMARY OF THE INVENTION:
A first aspect of the present invention is to provide an improved process for the preparation of Felbamate compound of structural formula I comprising the steps of:
a. reacting compound of structural formula II with sodium cyan ate in the presence of
hydrochloric acid in methylene dichloride solvent and
b. isolating Felbamate compound of structural formula I.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 depicts X-ray diffraction pattern of crystalline Felbamate compound of structural formula I,
DETAIL DESCRIPTION OF THE INVENTION
The compound of structural formula II may be formed by processes known in the art such as . those described herein WO94/06737,WO94/27941which is incorporated herein by reference only.
The reaction of compound of structural formula II with sodium cyanate may be carried out in methylene chloride solvent.
The reaction of compound of structural formula II with sodium cyanate may be carried out in the presence of dry hydrochloric acid gas.
The reaction of compound of structural formula II with sodium cyanate may be earned out at a temperature in the range of 0°C to 30°C.
The reaction of compound of structural formula II with sodium cyanate may be carried out for duration of 30 minutes to 6 hours.
The Felbamate compound of structural formula I may be isolated by steps of quenching, adjustment of pH, filtration, washing, suspending in water, adjustment of pH, agitation, filtration, washing, drying or the combination(s) thereof.

The isolated Felbamate compound of structural formula I may be crystalline in nature.
The Felbamate compound of structural formula I may be characterized by X-ray diffraction pattern as depicted in Figure 1.
EXAMPLES
In the following examples, the preferred embodiments of the present invention are described only by way of illustrating the process of the invention. However, these are not intended to limit the scope of the present invention in any way.
Example 1: Preparation of Felbamate
The solution of 2-phenylpropane-l, 3-diol(20.0gm) in methylene dichloride (440 ml) was stirred at 25-30°C for 15-20minutes. The reaction mixture was heated to 40-45°C and distilled out the dichloromethane atmospherically (Approximately 2 vol.) from reaction mixture at 40-45°C.The resulting reaction mixture was cooled to 25-30°C(Sample moisture content NMT-0.10%) and sodium cyanate (19.64 gm) was added at 25-30°C.Theresulting reaction mixture was cooled to -5 to 0°C and then purging of dry HC1 gas in reaction mixture was earned out at -5 to 0°C for about 5hours(HCl quantity depends on consumption and evolution). The progress of reaction wasmonitored by HPLC analysis. The resulting reaction mixture was quenched in cold water (200 ml)followed by adjusted pH 4 to 6 using sodium hydroxide solution at 10-15°C. The resulting solids were filtered and washed with coldwater (20 ml). The resulting solids were suspended in water (440 ml)at 25-30°C for 30 minutes and then resulting reaction mass was cooled to 10-15°Cand then stirred for 15-20 minutes. The pHof reaction mixture was adjusted to 2-2.5by using 2N HC1 at 10-15°C.The resulting reaction mixture was heated to 95-100°Cand agitated for 5 hours. The resulting reaction mass was slowly cooled to 10-15°C in 60 minutes. The resulting solids were filtered, washed with water (200ml) and dried at 50-55°C under reduced pressure to get title compound. Yield: 28 gm Purity: 99.61 %( By HPLC)

WE CLAIM:
1. An improved process for the preparation of Felbamate compound of structural formula I comprising the steps of:
a. reacting compound of structural formula II with sodium cyanate in the presence of hydrochloric acid in methylene dichloride solvent and

b. isolating Felbamate compound of structural formula I.
2. The process as claimed in claim Istep (a) wherein the reaction of compound of structural formula II with sodium cyanate is carried out in methylene chloride solvent.
3.The process as claimed in claim lstep(a) wherein the reaction of compound of structural formula II with sodium cyanate is carried out in the presence of dry hydrochloric acid gas.
4. The process as claimed in claim 1 step(a) wherein the reaction of compound of structural formula II with sodium cyanate is carried out at a temperature in the range of 0°C to 30°C.
5. The process as claimed in claim 1 step (a) the reaction of compound of structural formula II with sodium cyanate is earned out for duration of 30 minutes to 6 hours.
6. The process as claimed in claim lstep (b) the isolated Felbamate compound of structural formula I is crystalline in nature.

7. The process as claimed in claim 1 step (b) the isolated Felbamate compound of structural formula I is characterized by X-ray diffraction pattern as depicted in Figure no. 1.