FIELD OF THE INVENTION
The present invention provides an industrially advantageous, safe, eco-friendly and efficient process for the preparation of substituted benzyl alcohol.

BACKGROUND OF THE INVENTION
Hydrogenation of substituted benzoate to obtain substituted benzyl alcohol is an industrially important process. The substituted benzyl alcohol is a key precursor for preparing various agrochemical compounds or for preparing pharmaceutical products.
The preparation of substituted benzyl alcohol is known in the art via reduction of substituted benzoate either by lithium aluminium hydride or by sodium borohydride along with the combination of homogeneous catalysts.
The lithium aluminium hydride is an expensive, pyrophoric and difficult to handle on large scale. Thus, lithium aluminium hydride is unsuitable for industrial applications.
The US Patent Publication No. 2015/0274621 and a Chinese Patent Publication no. CN105237342A disclose a process for the preparation of para-substituted benzyl alcohol via reduction of para-substituted benzoate with sodium borohydride along with combination of homogeneous catalysts.
The US Patent Publication No. 2015/0274621 discloses homogeneous hydrogenation of methyl benzoate with iron hydrido-borohydride catalyst complex having amino-phosphine pincer ligands at elevated temperature of 115ºC.
The Chinese Patent Publication No. 105237342A discloses a method for preparing alcohol through catalytic hydrogenation reduction of a carboxylate compound with a ruthenium complex catalyst with sodium borohydride as an additive at elevated temperature of 120ºC.
The above prior art references are agonised from drawback such as use of catalyst and elevated temperature (more than 110ºC), which are essential for reaction completion. Therefore, such processes are not industrially viable.
Eventually, the use of catalyst is expensive and hence, increases overall operational cost. Further, the use of said catalyst is not eco-friendly.
The ruthenium complexes are known to be carcinogenic. Further their recovery and effluent disposal is very challenging.
In view of the above, there is an urgent need for the development of industrially advantageous, eco-friendly and efficient process for preparing substituted benzyl alcohol by without aid of catalyst.

OBJECT OF THE INVENTION
The present invention provides an industrially advantageous, safe, eco-friendly and efficient process for the preparation of substituted benzyl alcohol by reduction of substituted benzoate.

SUMMARY OF THE INVENTION
The present invention provides an improved and industrial advantageous process for preparation of compound of formula 1,

Formula 1
wherein R is selected from substituted or unsubstituted alkyl,
comprising:
i) contacting compound of formula 2,

Formula 2
wherein R is same as defined above; R1 is selected from but not limited to alkyl,
with sodium borohydride to obtain a reaction mixture; and
ii) isolating compound of formula 1 from the step i) reaction mixture.
In another preferred embodiment, the present invention provide an industrially advantageous, safe, eco-friendly and efficient process for the preparation of para-(trifluoromethyl)benzyl alcohol comprising
i) contacting para-(trifluoromethyl)benzoic acid methyl ester with sodium borohydride to obtain a reaction mixture; and
ii) isolating para-(trifluoromethyl)benzyl alcohol from the step i) reaction mixture.

DETAILED DISCRIPTION OF THE INVENTION
The present invention provides an industrially advantageous, safe, eco-friendly and efficient process for the preparation of compound of formula 1,

Formula 1
wherein R is selected from substituted or unsubstituted alkyl, wherein substituted alkyl is halo alkyl; halo may be selected from fluorine, chlorine or bromine;
by contacting compound of formula 2 with sodium borohydride.

Formula 2
wherein R is same as defined above and
R1 is selected from but not limited to alkyl such as methyl, ethyl, propyl, isopropyl; phenyl or benzyl;
In another preferred embodiment, the present invention provide an industrially advantageous, safe, eco-friendly and efficient process for the preparation of para-(trifluoromethyl)benzyl alcohol comprising:
i) contacting para-(trifluoromethyl)benzoic acid methyl ester with sodium borohydride to obtain a reaction mixture; and
ii) isolating para-(trifluoromethyl)benzyl alcohol from the step i) reaction mixture.
The reduction step of the present invention may be carried out in the presence of solvent or mixture of solvents. The solvent may be selected from alcohol and ether solvent or mixture thereof.
The alcohol solvent may be selected from methanol, ethanol, propanol, isopropanol and mixture thereof. The ether solvent may be selected from tetrahydrofuran, 2-methyl tetrahydrofuran, diethyl ether, diisopropyl ether, tetrahydropyran, ethyl tert-butyl ether, monoglyme, diglyme and mixture thereof.
The reduction step of present invention may be carried out at a temperature in the range of 40ºC to 80ºC and time required for completion of reaction may be 1 hour to 10 hours.
The compound of formula 1 or para-(trifluoromethyl)benzyl alcohol is isolated from reaction mixture by any isolation techniques known in the art.
Isolation and purification of final compound described here in the present invention may be effected, if desired, by any suitable separation or purification procedure such as, for example, column chromatography, distillation, azeotropic distillation, filtration, extraction, slurry wash, solvent-antisolvent system, carbon treatment or combination of these procedures.

EXAMPLES
Example 1: Process for the preparation of para-(trifluoromethyl)benzyl alcohol
Para-(trifluoromethyl)benzoic acid methyl ester (100 g, 1.0 eq.) was suspended in a mixture of tetrahydrofuran and methanol (450 ml). Sodium borohydride (22.2 g) was added and the reaction mixture was heated to reflux for 3 to 5 hours. The reaction mass was cooled and hydrochloric acid (10%) was added. The aqueous layer was extracted with methylene chloride. The organic layer was washed sequentially with water, brine solution and distilled to obtain the title compound.
Purity: 99.6% (by Gas Chromatography)
Yield: 90%

Example 2: Process for the preparation of para-(trifluoromethyl)benzyl alcohol
Para-(trifluoromethyl)benzoic acid methyl ester (200 g, 0.98 eq.) was treated with a mixture of sodium borohydride (44.47 g), monoglyme (885g) and methanol (50.2 g) . Reaction mass was heated to reflux 3 hours. Monoglyme was recovered at 100oC under atmospheric pressure. The reaction mass was cooled to 50oC and water (815 g) was added to quench the reaction mass. The reaction mixture was neutralized and extracted with Methylene chloride. The organic layer was distilled to obtain the title compound.
Purity: 99.5 % (by Gas Chromatography)
Yield: 82%

Example 3: Process for the preparation of para-(trifluoromethyl)benzyl alcohol
Para-(trifluoromethyl)benzoic acid methyl ester (100 g, 0.5 eq.) was added to diglyme (624.7 g). Sodium borohydride (22.2 g) was added slowly and the reaction mixture was heated to 60-65oC for 10 hours. Diglyme was recovered at 90oC under vacuum. The reaction mass was cooled to 50oC and water (400 g) was added to quenched the reaction mass. The pH of the quenched mass was adjusted to 7.0 using sulphuric acid (50%). Methylene chloride was added and organic layer was separated. The aqueous layer was re-extracted with methylene chloride. The resulting organic layers were mixed and distilled to obtain the title compound having purity 97% by Gas Chromatography.

WE CLAIM:
1. A process for the preparation of compound of formula 1,

Formula 1
wherein R is selected from substituted or unsubstituted alkyl, wherein substituted alkyl is halo alkyl; halo group is selected from fluorine, chlorine or bromine;
comprises:
i) contacting compound of formula 2,

Formula 2
wherein R is same as defined above; and
R1 is alkyl group selected from methyl, ethyl, propyl, isopropyl; phenyl or benzyl;
with sodium borohydride to obtain a reaction mixture and
ii) isolating compound of formula 1 from the step i) mixture.
2. A process for the preparation of para-(trifluoromethyl)benzyl alcohol
comprises:
i) contacting para-(trifluoromethyl)benzoate with sodium borohydride to obtain a reaction mixture; and
ii) isolating para-(trifluoromethyl)benzyl alcohol from step i) reaction mixture.
3. The process as claimed in claims 1 and 2, wherein the step i) is carried out in the presence of solvent or mixture of solvents.
4. The process as claimed in claims 1 and 2, wherein the step i) is carried out in the presence of solvent selected from alcohol and ether or mixture thereof.
5. The process as claimed in claims 1 and 2, wherein the step i) is carried out in the presence of solvent selected from methanol, ethanol, propanol, isopropanol, tetrahydrofuran, 2-methyl tetrahydrofuran, diethyl ether, diisopropyl ether, tetrahydropyran, ethyl tert-butyl ether, monoglyme, diglyme or mixture thereof.
6. The process as claimed in claims 1 and 2, wherein the step i) is carried out at a temperature in the range of 40ºC to 80ºC.

Dated this 13th day of December 2016.

Kapil
Senior Research Associate (IPR)
SRF Limited