FORM 2
The Patents Act 1970,
(39 of 1970)
&
The Patents Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
Novel method for preparation of 2- N, N-Dimethyl-1, 3-Dithiocyanatopropane
GHARDA KEKI HORMUSJI
AN INDIAN NATIONAL OF GHARDA HOUSE, 48 HILL ROAD, BANDRA (WEST), MUMBAI 400 050, INDIA
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

FIELD OF THE INVENTION
The present invention relates to a novel method for the preparation of 2-N, N-Dimethyl-1, 3-Dithiocyanatopropane which is a vital intermediate for the preparation of various insecticides such as cartap, ethiofencarb, acaricide, fenitrothion and methiocarb.
BACKGROUND
2-N,N-Dimethyl-l, 3-Dithiocyanatopropane is prepared by using Bisultap and sodium cyanide. As the process involves the use of sodium cyanide, the traces of cyanogens are likely to pass into the effluents which in turn lead to water and soil pollution. Therefore the process is environmentally toxic and requires high cost effluent treatment to make it environment friendly.
Chinese Patent No. CN1052303 discloses a preparation method for 2,3-dichloro-N,N-dimethyl propylamine which is an important intermediate for synthesis of anti-clam-worm toxin insecticide cartap, insecticidal pellet, insectisidal, insecticidal sulfo-compound and insecticidal cyclic compound.
Chinese Patent No. CN1061957 discloses process for the preparation of 2,3-dichloro-N,N-dimethylpropylamine, as an important intermediate for the synthesis of various insecticides ( for example, cartap, ethiofencarb, acaricide, fenitrothion

and methiocarb.). Before the addition of an alkali, an additive is added in to the aqueous solution of hydrochloride of the compound to adsorb and deposit colloidal ironic hydroxide, thus obtaining a pure 2,3-dichloro-N,N-dimethylpropyl amine.
Chinese Patent No. CN101103725 discloses a method for the preparation of 1,3-dithiocyanato-2-(dimethylamino) propane solution which involves mixing a catalyst and water together; leading in hydrogen chloride gas, hydrolysis at 18-25 for 15-24 h to form Cartap. The catalyst comprises benzyl trioctyl ammonium chloride, benzyl tri-Bu ammonium chloride, benzyl tri-Et ammonium bromide and Bu trioctyl ammonium bromide. The organic solvents employed in the reaction are benzene, toluene, dichloroethane, carbon tetrachloride or chloroform.
Chinese Patent No. 1830957 discloses a process for preparing 2-N,N-dimethyl-1,3-bithiocyano propane as an intermediate for Cartap from l-N,N-dimethyl-2,3-dichloropropane hydrochloride. The process includes steps such as neutralizing with alkali, proportionally adding aryl hydrocarbon solvent, proportionally dropping the alcoholic solution of salt of Na or K thiocyanate and reaction at 60-80°C for 1-5 hrs. The product yield is very low.

The processes disclosed in the prior art utilize toxic compounds such as sodium cyanide, which are difficult to handle at commercial stage, for the preparation of dithiocyanatopropane and such processes requires costly effluent treatment. Accordingly, it is desirable to develop an environment friendly and economic process for the preparation of dithiocyanatopropane.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a novel method for the preparation of 2-N, N-Dimethyl-1, 3- Dithiocyanatopropane which is an intermediate for the preparation of various insecticides like cartap, ethiofencarb, acaricide, fenitrothion and methiocarb.
It is another object of the present invention to provide a process for the preparation of 2-N, N-Dimethyl-1, 3-Dithiocyanatopropane which avoids the use toxic substances such as NaCN and KCN.
It is still another object of the invention to provide an environmental friendly process for the preparation of 2-N, N-Dimethyl-1, 3-Dithiocyanatopropane.

It is yet another object of the invention to provide a process for the preparation of 2-N, N-Dimethyl-1, 3-Dithiocyanatopropane which is simple, economic and high yielding.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a method for preparing
2-N,N-Dimethyl-l,3-Dithiocyanatopropane; said method comprising the following steps:
a. neutralizing a hydrochloride salt of l-N,N-Dimethyl-2,3-
Dichloropropane with at least one alkoxide solution and at least one
thiocyanate in a solvent system comprising at least one hydrocarbon
and at least one alcohol to obtain a mass;
b. heating the mass at a temperature of about 70°C to obtain a heated
mass;
c. stirring the heated mass at 70°C for about 15 hours followed by
removing the alcohol from the reaction mixture by distillation to
obtain a product containing inorganic impurities; and

d. filtering the product to obtain 2-N,N-Dimethy 1-1,3-Dithiocyanatopropane.
Typically, the step of neutralization is carried out at a temperature of about 20 to about 150 °C.
Typically, the step of neutralization is carried out for a period of about 6 to about 24 hours.
Typically, the alkoxide is at least one selected from the group consisting of sodium methoxide and sodium ethoxide,
Typically, the hydrocarbon is at least one selected from the group consisting of toluene, xylene and mono-chloro- benzene.
Typically, the alcohol is at least one selected from the group consisting of methanol, ethanol, isopropanol and butanol.
Typically, the proportion of alcohol to hydrocarbon is about 70:30.
Typically, the thiocyanate is at least one selected from the group consisting of sodium thiocyanate, potassium thiocyanate and ammonium thiocyanate.

Typically, the amount of the solvent system is in the range of about 400 to about 1000 ml per mole of l-N,N-Dimethyl-2,3-Dichloropropane.
Typically, the molar ratio of thiocyanate is about 2 to about 5 M/M of 1-N,N-Dimethy 1 -2,3-Dichloropropane.
DETAILED DESCRIPTION OF THE INVENTION
The process disclosed in the prior art utilizes sodium cyanide or other cyano compounds for the preparation of 2-N,N-Dimethyl-l, 3-Dithiocyanatopropane. These cyano compounds are toxic in nature and are difficult to handle at commercial stage. The disposal of the toxic waste of such process requires effluent treatment. Another drawback of the process of the prior art is that the process utilizes costly chemicals which results in high operational cost.
In accordance with the present invention there is provided a method for preparing 2-N,N-Dimethyl-l,3-Dithiocyanatopropane; said method comprising the following
steps:
In first step a hydrochloride salt of l-N,N-Dimethyl-2,3-Dichloropropane is neutralized with at least one alkoxide solution and at least one thiocyanate in a solvent system comprising at least one hydrocarbon and at least one alcohol to obtain a mass.

Typically, the hydrochloride salt of l-N,N-Dimethyl-2,3-Dichloropropane is obtained by chlorination of N,N-dimethyl allyl amine followed by reaction with sodium or potassium thiocyanate.
In accordance with the present invention the step of neutralization is carried out at a temperature of about 20 to about 150 °C for a period of about 6 to about 24 hours.
Typically, the alkoxide is at least one selected from the group consisting of sodium methoxide and sodium ethoxide.
The hydrocarbon used in the solvent system of the present invention is at least one selected from the group consisting of toluene, xylene and mono-chloro- benzene.
Typically, the alcohol is at least one selected from the group consisting of methanol, ethanol, isopropanol and butanol.
In accordance with the present invention the proportion of alcohol to hydrocarbon is about 70:30.
Typically, the thiocyanate is at least one selected from the group consisting of sodium thiocyanate, potassium thiocyanate and ammonium thiocyanate.

In accordance with the present invention the amount of the solvent system used is in the range of about 400 to about 1000 ml per mole of l-N,N-Dimethyl-2,3-Dichloropropane.
In accordance with one of the embodiments of the present invention the molar ratio of thiocyanate is about 2 to about 5 M/M of l-N,N-Dimethyl-2,3-Dichloropropane.
In accordance with the preferred embodiment of the present invention the molar ratio of thiocyanate is about 2 to about 2.5 M/M of l-N,N-Dimethyl-2,3-Dichloropropane.
In the next step the obtained mass is heated at a temperature of about 70°C to
obtain a heated mass which is then stirred at 70°C for about 15 hours followed by
removal of alcohol from the reaction mixture by distillation to obtain a product
containing inorganic impurities.
In the final step the product is filtered to obtain 2-N,N-Dimethyl-l,3-
Dithiocyanatopropane.
Following examples illustrate the invention, but are not intended to limit the scope of the present invention.

EXAMPLES EXAMPLE-1
192.5 gm of l-N,N-Dimethyl-2,3-Dichloropropane as hydrochloride salt was mixed with 500 ml of a mixture of methanol and Toluene (70:30 v/v). To this 250 ml of sodium methoxide solution (as 4.0 N solution) was added at 30°C followed by addition of 204 gm of potassium thiocyanate solids to obtain a mass. The obtained mass was heated to 70°C and stirred at 70°C for 15 hours. Then methanol was distilled out from the reaction mass and the inorganic was filtered off. 2-N,N-Dimethyl-l,3-Dithiocyanatopropane content in toluene was found to be 0.9 moles as per analysis. Yield = 89%.
EXAMPLE- 2
192.5 gm of l-N,N-Dimethyl-2,3-Dichloropropane as hydrochloride salt was mixed with 500 ml of a mixture of Ethanol and Toluene (70:30 v/v). To this 250 ml of sodium ethoxide solution (as 4.0 N solution) was added at 30°C followed by addition of 204 gm of potassium thiocyanate solids to obtain a mass. The obtained mass was heated to 70°C and stirred at 70°C for 15 hours. Then ethanol was distilled out from the reaction mass and the inorganic was filtered off. 2-N,N-Dimethyl-l,3-Dithiocyanatopropane content in toluene was found to be 0.9 moles as per analysis. Yield = 92%.

EXAMPLE- 3
192.5 gm of l-N,N-Dimethyl-2,3-Dichloropropane as hydrochloride salt was mixed with 500 ml of a mixture of methanol and Toluene (70:30 v/v). To this 250 ml of sodium ethoxide solution (as 4.0 N solution) was added at 30°C followed by addition of 204 gm of potassium thiocyanate solids to obtain a mass. The obtained mass was heated to 70°C and stirred at 70°C for 15 hours. Then methanol was distilled out from the reaction mass and the inorganic was filtered off. 2-N,N-Dimethyl-l,3-Dithiocyanatopropane content in toluene was found to be 0.9 moles as per analysis. Yield = 91%.
Technical Advancement
■ The process of the present invention avoids use of toxic substances such as NaCN and KCN.
■ The present process involves neutralization of a hydrochloride salt of 1-N,N-Dirnethyl-2,3-Dichloropropane with at least one alkoxide and at least one thiocyanate in a solvent system, wherein the solvent system comprises a particular proportion of alcohol and hydrocarbon (70:30).
■ The process of the present invention does not require effluent treatment.
■ The process of the present invention is simple, high yielding, economic and environment friendly.

While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

I claim:
1. A method for preparing 2-N,N-Dimethyl-l,3-Dithiocyanatopropane; said method comprising the following steps:
a. neutralizing a hydrochloride salt of l-N,N-Dimethyl-2,3-
Dichloropropane with at least one alkoxide solution and at least one
thiocyanate in a solvent system comprising at least one hydrocarbon
and at least one alcohol to obtain a mass;
b. heating the mass at a temperature of about 70°C to obtain a heated
mass;
c. stirring the heated mass at 70°C for about 15 hours followed by
removing the alcohol from the reaction mixture by distillation to
obtain a product containing inorganic impurities; and
d. filtering the product to obtain 2-N,N-Dimethyl-l,3-
Dithiocyanatopropane.
2. The process as claimed in claim 1, wherein the step of neutralization is carried out at a temperature of about 20 to about 150 °C.

3. The process as claimed in claim 1, wherein the step of neutralization is carried out for a period of about 6 to about 24 hours.
4. The process as claimed in claim 1, wherein the alkoxide is at least one selected from the group consisting of sodium methoxide and sodium ethoxide.
5. The process as claimed in claim 1, wherein the hydrocarbon is at least one selected from the group consisting of toluene, xylene and mono-chloro-benzene.
6. The process as claimed in claim 1, wherein the alcohol is at least one selected from the group consisting of methanol, ethanol, isopropanol and butanol.

7. The process as claimed in claim 1, wherein the proportion of alcohol to hydrocarbon is about 70:30.
8. The process as claimed in claim 1, wherein the thiocyanate is at least one selected from the group consisting of sodium thiocyanate, potassium thiocyanate and ammonium thiocyanate.
9. The process as claimed in claim 1, wherein the amount of the solvent system is
in the range of about 400 to about 1000 ml per mole of l-N,N-Dimethyl-2,3-
Dichloropropane.

10. The process as claimed in claim 1, wherein the molar ratio of thiocyanate is about 2 to about 5 M/M of l-N,N-Dimethyl-2,3-Dichloropropane.