DESC:FIELD OF THE INVENTION

The present invention relates to a novel process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I.

BACKGROUND OF THE INVENTION

Diafenthiuron is chemically known as 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea or N-[2,6-bis(1-methylethyl)-4-phenoxyphenyl]-N'-(1,1-dimethylethyl)thiourea and having chemical structure as below;

Diafenthiuron is a white to pale gray powder, pH value at room temperature 7.5, light stability. Diafenthiuron acts against pests with contact and stomach poison two effects; and exhibits a positive temperature coefficient; and good penetration in the sun.

Diafenthiuron acts after conversion by either light, or in vivo, to the corresponding carbodiimide, which is an inhibitor of mitochondrial respiration. Mode of action as insecticide and acaricide which kills larvae, nymphs and adults is by contact and/or stomach action; also shows some ovicidal action. It is commonly used as insecticide and acaricide effective against phytophagous mites (tetranychidae, tarsonemidae), aleyrodidae, aphididae and jassidae on cotton, various field and fruit crops, ornamentals and vegetables. Diafenthiuron also controls some leaf-feeding pests in cole crops (Plutella xylostella), soya beans (Anticarsia gemmatalis) and cotton (Alabama argillacea).

Diafenthiuron compound was first disclosed in US4328247. This patent also discloses process of preparation of the compound.

US4962126A disclose general preparation of Diafenthiuron. This patent discloses process of reacting 4-phenoxy-2,6-diisopropyl aniline with phosgene and thioisothiocyanate ester to obtain 4-phenoxy-2,6 diisopropyl phenyl isothiocyanate and then react with tert-butylamine to obtain Diafenthiuron.

US4997967 discloses process for preparation of isothiocyanates derivatives wherein, 4-phenoxy-2,6-diisopropyl aniline hydrochloride and sodium thiocyanate are reacted in the presence of aqueous hydrochloric acid, xylene as a solvent, the reaction of a substituted thiourea in a high boiling point aromatic solvent. The reaction mixture was heated to above 150?to obtain 4-phenoxy-2,6-diisopropylphenyl isothiocyanate. The isothiocyanates prepared is a useful intermediate for the synthesis of Diafenthiuron. Further this patent discloses reaction with mono- or dialkylamines and further optional reaction with alkyl halides into the corresponding 1,3-disubstituted thiourea or isothiourea which have pronounced insecticidal and acaracidal activity. It is also known to prepare isothiocyanates by reacting primary amines with thiophosgene [q.v. Houben-Weyl, Methoden der organischen Chemie, IX, 875 (1955)]. This method is unfavorable for an economic preparation of isothiocyanates on an industrial scale because of the high cost of thiophosgene and the difficulty of handling it.

CN100447131 discloses method for preparing 1-tert butyl-3-(2,6-diisopropyl-4-henyl cxypheny) thiourea comprising the steps of: a, 4 - phenoxy - 2,6 -diisopropyl aniline and its salts with carbon disulfide and an organic base or an inorganic base in a solvent in the reaction of the corresponding 4 - phenoxy-2 ,6 -diisopropylbenzene amino dithiocarbamate salts; b, 4 - phenoxy-2 ,6 -diisopropylphenyl group dithioformate with t-butylamine in an organic solvent to produce 1 - tert-butyl -3 - (2,6 - isopropyl-4 - phenoxyphenyl) thiourea.

CN102993075 discloses synthesis method comprises the following steps of: firstly, synthesizing an N-2,6-diisopropyl-4-phenoxylphenyl)isocyanate intermediate by taking 2,6-diisopropyl-4-aminobiphenyl ether and triphosgene as raw materials; then, subjecting the generated N-2,6-diisopropyl-4-phenoxylphenyl)isocyanate intermediate and tert-butylamine to a reaction to generate 3-(2,6-diisopropyl-4-phenoxylphenyl)-1-tert-butyl urea; and then, subjecting the 3-(2,6-diisopropyl-4-phenoxylphenyl)-1-tert-butyl urea and phosphorus pentasulfide to a reaction under the action of potassium carbonate to finally generate diafenthiuron.

CN101307016 discloses a method for synthesizing 2, 6-diisopropyl-4-pheonxy phenylthioureal, relating to a process for synthesizing an intermediate of an agriculture insecticide acaricide diafenthiuron. The 2, 6-2iso-methylpropylamine has reactions of bromination, etherification and sulfocarbamide in the action of catalysts of 8-copper quinolinate and Dimethylamino pyridine to generate the 2, 6-diisopropyl-4-pheonxy phenylthioureal. The method adopts the continuous reaction and takes the 8-copper quinolinate and the Dimethylamino pyridine as catalysts; the temperature of the etherification reaction is reduced to about 115 DEG C from 150 DEG C; meanwhile, the method adopts one solvent, integrates the three steps of bromination, etherification and sulfocarbamide into one, generates the product directly without the separation, reduces the generation of waste water, has positive significance on the practical production, reaction yield coefficient more than 83 percent and the content up to 97 percent, improves the production efficiency

It is further known to react primary amines, especially primary aromatic amines, in the form of their salts, in an inert solvent, with ammonium thiocyanates or alkali metal thiocyanates to the corresponding asymmetrically substituted thioureas [q.v. Houben-Weyl), Methoden der organischen Chemie, IX, 888 (1955)], and to convert these thioureas into the corresponding isothiocyanates by splitting off ammonia [q.v. Chemistry and Industry, 27, 785 (1954)]. Although the combination of these known process steps avoids the drawbacks involved in the use of thiophosgene, the thiourea is none the less still obtained in unsatisfactory yield even when using aromatic amines.

In the literature J.Agric.Food Chem.1992, 40,908 ~ 913 reported in 4 - phenoxy-2,6-diisopropyl aniline reaction with phosgene substituted isocyanate, and then with the corresponding tert-butylamine urea, and then by the addition of phosphorus pentoxide dehydration and hydrogen sulfide in the system to obtain Diafenthiuron. This process has multi-step approach therefore it has low yield value.

In the above methods isothiocyanate is prepared from thiosulfate phosgene which is highly toxic and difficult to maintain at large-scale preparation Diafenthiuron. Moreover in above methods 2,6-diisopropyl aniline hydrochloride and sodium thiocyanate is reacted to give Diafenthiuron. However, due to the thermal decomposition, the reaction requires a higher temperature, generally difficult to achieve low pressure steam heating, applied to industrial production of high energy consumption; reaction prone tarry by-product.

The present invention is directed to the above drawbacks, the purpose is to provide novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I which is a mild reaction conditions, simple operation, less expensive cost effective process.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide an novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula I starting from readily accessible and cheap intermediates which are easy to handle, the process makes it possible to prepare the isothiocyanates of formula I in simple manner and in good yield.

An object of the present invention is to provides a novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I comprising: reaction of tert-butyl isothiocyanate of formula (III) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (IV) in absence of solvent.

An object of the present invention is to provide novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I comprising: reaction of tert-butyl isothiocyanate with 4-phenoxy-2, 6-di (propan-2-yl) aniline in presence of solvent and phase transfer catalyst.

An object of the present invention is to provide novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I in good yields.

Another objective of the present invention is to provide a novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I and its acceptable salts thereof, which would be easy to implement on commercial scale.

Another objective of the present invention is to provide a novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I and its acceptable salts thereof, which would be further used for developing suitable dosage forms of Diafenthiuron to be used thereafter in various crops.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I.

Thus, the invention provides a simple, economically viable and efficient process for preparing a 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I.

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated and briefly described as follows.

In one embodiment the present invention provides a process for preparation of tert-butyl chloride of formula (III) comprising reacting tert-butyl alcohol (II) with hydrochloric acid in presence of a suitable solvent selected from monochlorobenzene, MDC, and EDC.

In another embodiment the present invention provides a process for preparation of tert-butyl isothiocyanate of formula (IV) comprising reacting tert-butyl chloride of formula (III) with ammonium thiocyanate in presence of zinc chloride, Phase transfer catalyst, solvent and optionally Diphenyl ether.

The reaction of tert-butyl chloride of formula (III) and ammonium thiocyanate is conveniently carried out in the temperature range from 10° to 150° C., preferably from 20° to 60° C., and further the temperature is raised in range from 40° to 100° C., in presence of zinc chloride, phase transfer catalyst and solvent and optionally diphenyl ether.

Suitable solvents in which the reaction of tert-butyl chloride of formula (III) and ammonium thiocyanate can be carried out are selected from but not limited to water, alcohols, ketones, diols, triols, esters, amides, ethers, hydrocarbons, polar aprotic solvents, polar solvents, chloro solvents, nitriles or mixtures thereof. Polar aprotic solvents such as acetone, DMF, acetonitrile, DMSO, sulfolane; alcohols such as methanol, ethanol, propanol, butanol; chloro solvents like methylene chloride, chloroform, monochlorobenzene, MDC, and ethylene dichloride (EDC) and ethylene chloride; hydrocarbon solvents like toluene, xylene, heptane, cyclohexane and hexane, more preferably ethylene dichloride (EDC). Preferred solvents in which the reaction of tert-butyl chloride of formula (III) and ammonium thiocyanate can be carried out are water, ethylene dichloride (EDC). Depending on the solvent and reaction temperature, the cleavage reaction takes from 3 to 9 hours. If the solvent is water the reaction mixture is heated at temperature 50-55°c for 4 hours and temperature is raised to about 90°c and maintained for another three hour.

Phase transfer catalyst may be selected from the group comprising of quaternary ammonium cations, quaternary phosphonium cations, and cyclic polyethers such as tricaprylylmethylammonium chloride, methyl tributyl ammonium chloride, methyl tributyl ammonium fluoride, tetrabutyl ammonium bromide, tetrabutyl ammonium fluoride, tetrabutyl ammonium hydrogen sulfate, triethyl benzyl ammonium chloride, tetrabutyl phosphonium bromide, tetrabutyl phosnhonium chloride, tetraoctylphosphonium bromide, and mixtures thereof.

In one embodiment the present invention provides a novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I comprising: reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) in absence of solvent.

The reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) is conveniently carried out in the temperature range from 100° to 200° C., preferably from 140° to 170° C., in absence of solvent.

In another embodiment the present invention provides a novel process for the preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I comprising: reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) in presence of solvent, base and phase transfer catalyst.

The reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) is carried out in the temperature range from 100° to 200° C., preferably from 140° to 170° C., in presence of solvent and optionally phase transfer catalyst. Suitable solvents in which the reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) can be carried out are aromatic hydrocarbons, preferably alkylbenzenes or mixtures thereof having a boiling range from 125° to 200° C., such as ethyl benzene, xylenes, trimethylbenzenes, ethyl methyl benzenes, toluene, heptane, cyclohexane and hexane. Further suitable solvents for the reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) are ethyl benzene, xylenes, trimethylbenzenes, ethyl methyl benzenes toluene, heptane, cyclohexane and hexane. Preferred solvents in which the reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) can be carried out is xylenes. Base may be selected from but not limited to KOH, NaOH, K2CO3 & Na2CO3 and the like.

Phase transfer catalyst may be selected from the group comprising of quaternary ammonium cations, quaternary phosphonium cations, and cyclic polyethers such as tricaprylylmethylammonium chloride, methyl tributyl ammonium chloride, methyl tributyl ammonium fluoride, tetrabutyl ammonium bromide, tetrabutyl ammonium fluoride, tetrabutyl ammonium hydrogen sulfate, triethyl benzyl ammonium chloride, tetrabutyl phosphonium bromide, tetrabutyl phosnhonium chloride, tetraoctylphosphonium bromide, and mixtures thereof.

The process is normally carried out under normal pressure. However, optionally the reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) is preferably carried out under slightly reduced pressure. It is preferred to carry out the reaction of tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) under a pressure of 0.5 to 1 bar.

The 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I can be isolated by filtration or by evaporation of the solvent. After removal of the salt by washing with solvent, the product is obtained in good purity and in a yield of 95-97% of theory. It is, however, possible to obtain 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula I immediately after its synthesis by separating the solvent present in the reaction mixture in simple manner by removing the solvent by distillation and vacuum distillation of the residue.

Therefore, in another embodiment the present invention provides a process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula (I) comprisingreacting tert-butyl alcohol reacted with hydrochloric acid to give tert-butyl chloride of formula (III), which was reacted with ammonium thiocyanate in presence of zinc chloride to tert-butyl isothiocyanate of formula (IV). Further tert-butyl isothiocyanate of formula (IV) reacted with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) to give final compound 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula (I).

The above process can be represented stepwise as shown below:

Step I

Step II

Step III

The process of this invention makes it possible to prepare the 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula (I), starting from tert-butyl isothiocyanate of formula (IV) and 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V), in simple manner and in excellent yield, while avoiding the drawbacks of the known processes.

The process of the invention is illustrated with reference to the following working Examples.

Example 1
Preparation of tert-butyl chloride from tert-butyl alcohol

Reaction Scheme:

74.12g (1mole) of tert-butyl alcohol was charged in a 4 neck round bottom flask to which 313g (3moles) of concentrated hydrochloric acid was added. The reaction mixture was kept for stirring for about half an hour at room temperature and further it was maintained for about 3 more hours at room temperature. After the completion of the reaction, the organic and the aqueous layers so formed were completely separated. The separated organic layer was properly washed with 10% of sodium bicarbonate solution and then followed by water till the litmus paper turned from neutral to moist. Later the total organic mass formed was taken into the distillation assembly and the fractions were collected. Boiling point of the fractions obtained was 49.5°C -52.5°C
Weight is 82g to 85g.
% purity of product = 98.5% to 99.5 %
% yield = 88% to 90%

Example 2
Preparation of tert-butyl isothiocyanate from tert-butyl chloride
Reaction Scheme:

93.0g (1 mole) tert.-butyl chloride, 100ml EDC, 138.0g (1.01 moles) Zinc Chloride, diphenyl ether 5.0g (0.029 mole) and 1.0g of TBAB were charged in four necked round bottom flask and were maintained at room temperature. The formed reaction mixture was heated at 40-45°C for about 3 hours. Further the temperature was raised to 50°C and maintained at the same temperature for about 3 more hours. After the completion of the reaction the organic layer was washed properly with almost 100ml of water in order to separate the organic layer from aqueous layer. The total of the organic mass formed was taken for distillation and the fractions were collected .The boiling point of the collected fraction was at 30°C -32°C at 10mm/Hg
Weight is 98 to 100 gm.
% purity of product = 98.0 to 99.0 %
% yield = 85-86 %

Example 3
Preparation of tert-butyl isothiocyanate from tert-butyl chloride
Reaction Scheme:

93.0g (1.0mole) tert.-butyl chloride, 76 gm NH4SCN, 100ml water, 138.0g (1.01moles) Zinc Chloride, and 1.0g of TBAB were charged in four necked round bottom flask. The reaction mixture was heated at 50°C -55°C for about 4 hours and further the temperatures was raised up to 90°C and maintained for another 3 hours. As the reaction gets completed the Organic layer and the aqueous layer were separated.
Weight is 98g to 100g.
% purity of product = 98.0% to 99.0%
% yield = 85%-86%

Example 4
Preparation of Diafenthiuron from tert.-butyl isothiocyanate
Reaction Scheme:

346g (3.0mole) tert.-butyl isothiocyanate and 270g (1.0 mole) 4-Phenoxy-2, 6-di (propan-2-yl) aniline were taken in four necked flask. Charged 0.3 to 0.5 mole KOH Its temperature was raised to 150°C -160°C. The temperature of reaction mixture was maintained at 140°C to 160°C for about 7 to 8 hrs. The reaction mass formed was cooled to 5°C -8°C and maintaining the same for about 2 hrs. Then the formed reaction mass was properly filtered and collected as a dried cake through suction drying under proper vacuum.
Diafenthiuron dry wt. = 368g to 373g.
% Purity =97%
% yield = 93% to 94%.

Example 5
Preparation of Diafenthiuron from tert.-butyl isothiocyanate
Reaction Scheme:

346.0g (5.0 mole) tert.-butyl isothiocyanate and 306.0g (1.0 mole) 4-Phenoxy-2, 6-di (propan-2-yl) aniline hydrochloride was taken in a four necked flask. Charged 1.3 to 1.5 mole KOH The temperatures of the reaction mixture was raised to 150°C to 160°C and was maintained at 140°C to 160°C for about 3 to 4 hrs. Then the reaction mass was cooled to 5°C to 8°C and maintaining the same for further 2 hrs. The reaction mass formed was filtered and collected as a dried cake through suction drying under proper vacuum.
Diafenthiuron dry wt. = 368g to 373g.
% Purity =97%
% yield = 93% to 94%.

Example 6
Preparation of Diafenthiuron from tert.-butyl isothiocyanate
Reaction Scheme:

115.20g (1.00 mole) tert.-butyl isothiocyanate, O-Xylene and 270.0g (1.0 mole) 4-Phenoxy-2, 6-di (propan-2-yl) aniline were charged in a four necked flask. Charged 0.3 to 0.5 mole KOH The temperature of the reaction mixture was raised to 140°C and was further maintained at 140°C to 160°C for about 7 to 8 hrs. After the completion of the reaction the solvent was recovered back under the vaccum and the resulted residue was dissolved in acetonitrile. The reaction mass was cooled to 5°C -8°C and maintaining the same for about 2 hrs. The formed mass was filtered and collected as filtrate. Dried cake was obtained through suction drying under vacuum.
Diafenthiuron dry wt. = 368g to 373g.
% Purity =97 %
% yield = 93 to 94 %.

Example 7
Preparation of Diafenthiuron from tert.-butyl isothiocyanate
Reaction Scheme:

115.20g (1.00 mole) tert.-butyl isothiocyanate, O-Xylene and 270.0g (1 mole) 4-Phenoxy-2, 6-di (propan-2-yl) aniline and (1.0 mole) hydrochloric acid were charged in a four necked flask. Charged 1.3 to 1.5 mole KOH The temperature of the formed reaction mass was raised upto 140°C and was maintained at 140°C to 160°C for 7 to 8 hrs. After the completion of the reaction the solvents were recovered back by vacuum and the resulting residue was dissolved in acetonitrile. The reaction mass was cooled to 5°C to 8°C and maintaining that for 2 hrs. The resulting mass is filtered and collected in form of cake through suction drying under vacuum.
Diafenthiuron dry wt. = 368g to 373g.
% Purity =97%
% yield = 93% to 94%.
,CLAIMS:We Claim,

1. A novel process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula (I) comprising reacting tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) to 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula (I).

2. A novel process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula (I) as claimed in claim 1 wherein the reaction is carried out in presence or absence of solvent, base and phase transfer catalyst.

3. A novel process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula (I) as claimed in claim 1 wherein suitable solvents may be selected from but not limited to aromatic hydrocarbons, preferably alkylbenzenes or mixtures thereof such as ethyl benzene, xylenes, trimethylbenzenes, ethyl methyl benzenes, toluene, heptane, cyclohexane and hexane, ethyl benzene, xylenes, trimethylbenzenes, ethyl methyl benzenes toluene, heptane, cyclohexane and hexane.

4. A novel process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula (I) as claimed in claim 1 wherein base may be selected from but not limited to KOH, NaOH, K2CO3 & Na2CO3.

5. A novel process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula (I) as claimed in claim 1 wherein Phase transfer catalyst may be selected from the group comprising of quaternary ammonium cations, quaternary phosphonium cations, and cyclic polyethers such as tricaprylylmethylammonium chloride, methyl tributyl ammonium chloride, methyl tributyl ammonium fluoride, tetrabutyl ammonium bromide, tetrabutyl ammonium fluoride, tetrabutyl ammonium hydrogen sulfate, triethyl benzyl ammonium chloride, tetrabutyl phosphonium bromide, tetrabutyl phosnhonium chloride, tetraoctylphosphonium bromide, and mixtures thereof.

6. A process for the preparation of 1 tert-butyl isothiocyanate of formula (IV) as claimed in claim 1 comprising reacting tert-butyl chloride of formula (III) with ammonium thiocyanate in presence of zinc chloride, Phase transfer catalyst, solvent and optionally Diphenyl ether.

7. A process for the preparation of 1 tert-butyl isothiocyanate of formula (IV) as claimed in claim 6 wherein suitable solvents may be selected from but not limited to water, alcohols, ketones, diols, triols, esters, amides, ethers, hydrocarbons, polar aprotic solvents, polar solvents, chloro solvents, nitriles or mixtures thereof. Polar aprotic solvents such as acetone, DMF, acetonitrile, DMSO, sulfolane; alcohols such as methanol, ethanol, propanol, butanol; chloro solvents like methylene chloride, chloroform, monochlorobenzene, MDC, and ethylene dichloride (EDC) and ethylene chloride; hydrocarbon solvents like toluene, xylene, heptane, cyclohexane and hexane, more preferably ethylene dichloride (EDC), preferably water, ethylene dichloride (EDC).

8. A process for the preparation of 1 tert-butyl isothiocyanate of formula (IV) as claimed in claim 6 wherein phase transfer catalyst may be selected from the group comprising of quaternary ammonium cations, quaternary phosphonium cations, and cyclic polyethers such as tricaprylylmethylammonium chloride, methyl tributyl ammonium chloride, methyl tributyl ammonium fluoride, tetrabutyl ammonium bromide, tetrabutyl ammonium fluoride, tetrabutyl ammonium hydrogen sulfate, triethyl benzyl ammonium chloride, tetrabutyl phosphonium bromide, tetrabutyl phosnhonium chloride, tetraoctylphosphonium bromide, and mixtures thereof.

9. A novel process for the preparation of tert-butyl chloride of formula (III) as claimed in claim 6 comprising reacting tert-butyl alcohol (II) with hydrochloric acid in presence of solvent.

10. A novel process for the preparation of tert-butyl chloride of formula (III) as claimed in claim 6 wherein the suitable solvent may be selected from but not limited to monochlorobenzene, MDC, and EDC.

11. A novel process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula (I) as claimed in any of the preceding claims comprising of steps:
a. reacting tert-butyl alcohol (II) reacted with hydrochloric acid to give tert-butyl chloride of formula (III),
b. reacting tert-butyl chloride of formula (III) with ammonium thiocyanate in presence of zinc chloride, phase transfer catalyst, solvent to tert-butyl isothiocyanate of formula (IV) and optionally diphenyl ether.
c. reacting tert-butyl isothiocyanate of formula (IV) with 4-phenoxy-2, 6-di(propan-2-yl) aniline of formula (V) to 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl)thiourea of formula (I).

12. A novel process for preparation of 1-tert-butyl-3-(2,6-di-isopropyl-4-phenoxyphenyl) thiourea of formula (I) as claimed in any of the preceding claims and further exemplified with working examples.