Description:FIELD OF THE INVENTION
The present invention relates to a cost-effective industrially advantageous process for preparing cis-alkenes by selective hydrogenation of 1,4-dienes in the presence of substituted arene chromium complex catalyst and an additive.

BACKGROUND OF THE INVENTION
Cis-Alkenes of formula I are known to be an important intermediate for the chemical industry and has versatile use.

Formula I
wherein R1, R2, R3, R4 and R5 represent, simultaneously or independently from each other, a hydrogen atom or a C1-C12 alkyl or de-conjugated alkenyl group, optionally substituted; and R1 and R3 or R3 and R4, or R2 and R5 or R4 and R5, taken together, may form a C3-10 alkanediyl or de-conjugated alkenediyl group, optionally substituted analogues

Selective transformations of 1,4-dienes of Formula II to cis-alkenes of Formula I are of considerable interest for chemical industry which prepare flavors and perfumes.

Formula II

Wherein R1, R2, R3, R4 and R5 represent same as above
Cis-3-Hexen-1-ol of Formula Ia, also known as leaf alcohol, its esters are also important raw materials for flavor and fragrance.

Formula Ia
Leaf alcohol holds a special position in the field of aroma chemicals. Its importance is due to its unique natural green qualities, although its volume of consumption places it in the area of a specialty material. Leaf alcohol and its derivatives are a symbol of the “green revolution in flavors and fragrances that developed in the industry during the 1960’s. Leaf alcohol was first used by the German firm Schimmel under the trade names “Phyllol” and “Verdalol” before the Second World War. In the area of flavors, there are no near substitutes for leaf alcohol, its esters or its isomeric alcohols and aldehydes.
Over the years many attempts have been made to develop synthetic routes of leaf alcohol. The basic route involves the selective semi-hydrogenation of 3-hexyn-1-ol, which is generated from either l-butyne or 1,2-butadiene by reaction with ethylene oxide.
Another important route involves the selective 1,4-hydrogenation of conjugated dienes into their corresponding "cis'-alkenes.
It is widely known in the literature that 2,4-hexadienol or sorbic alcohol of formula IIa can be hydrogenated into the corresponding "cis'-alkene in the presence of different catalysts; however the yields are quite low.

Formula IIa
The selective transformations of 1,4-dienes of Formula II to cis-alkenes of Formula I is very challenging because any minor impurity of E/Z isomer in Formula II will deactivate the catalyst system. Therefore, the 1,4-dienes Formula II needs to be purified by preparative liquid chromatography or crystallization before selective reduction to prepare to cis-alkenes of Formula I.
There are several publications, wherein different processes using different catalyst have been developed for selective transformations of 1,4-dienes of Formula II to cis-alkenes of Formula I.
A Japanese patent no. 5616781discloses catalytic hydrogenation of 2,4-hexadien-1-ol or its acetate in the presence of metal carbonyls i.e. hexacarbonyl chromium catalyst [Cr(CO)6], methyl benzoate tricarbonyl chromium, hexacarbonyl molybdenum catalyst [Mo(CO)6], benzene tricarbonyl molybdenum etc. In the exemplified examples, hexacarbonyl chromium and benzene tricarbonyl molybdenum have been used. The yields are quite low [84-93%] and catalyst used in higher concentration of around 5 mol%. Cis-3-hexenol composition in final product is in the range of 79-98%.

Catalyst Catalyst load temperature Cis-3-hexenol trans-3-hexenol 4-hexanol Yield
%
Cr(CO)6 5% 190-200 98 1.0 0.5 93
benzene tricarbonyl molybdenum 5% 70-100 91 2 2 84
Cr(CO)6 5% 190-200 79 2 7 --
benzene tricarbonyl molybdenum 120-140 94 2 3 89

In view of the above, since the catalyst used in very high concentration i.e. around 5 mol%, which is quite high and hence overall process becomes expensive. Further the catalyst i.e. Cr(CO)6 is highly toxic and can be used in lab scale only. The use of Cr(CO)6 has not been found suitable at large scale; therefore it is an unattractive option from industrial point of view.

An article, namely A Journal of Molecular Catalysis A: Chemical 275 (2007) 153–157 discloses selective hydrogenation of sorbic alcohol to leaf alcohol. In presence of Ruthenium catalyst precursor [Cp*RuCl2]n in solvent like methyl tert-butyl ether: ethylene glycol at temperature 20°C to 75°C. The catalyst amount used in the said hydrogenation reaction is between 3-10 wt% of the amount of sorbic alcohol. The optimal conditions for the highest selectivity (up to 98%) and the reaction rate are achieved in hydrogenation in ethylene glycol with the addition of methyl tert-butyl ether or hexane to increase the reaction rate.

The process given in said article suffers from the several drawbacks such as use of very expensive and highly moisture/air sensitive Ruthenium based catalyst, which needs extra handling precautions. Further the catalyst used in high amounts i.e., 3-10 wt%, which adds to cost and hence process is quite expensive. In addition to this, ether solvents are used during reaction. Ethers are extremely flammable chemicals that rapidly catch fire; therefore extreme cautions are required in laboratories.

Another article, Agric. Biol. Chem. 1982, 46, 1757 discloses catalytic hydrogenation of 1,4-dienes with chromium carbonyl complexes. The selectivity of the sorbic alcohol is examined with various arene ligands of tricarbonyl chromium catalyst and with hexacarbonyl chromium ligand in various solvents with around 5mol% catalyst load. It is observed that E,E isomer of 2,4-hexadiene-1-ol has been purified using preparative liquid chromatography. The hydrogenation of 2,4-hexadien-1-ol with hexacarbonyl chromium ligand in different solvents has been tried, the results are reproduced herein and tabulated in the below table.
Solvent 2,4-Hexa dien-1-ol(%) (Z)-3-Hexen-1-ol (%) (E)-3-Hexen -1-ol (%) 4-Hexen-1-ol (%) Hexanol (%)
Cyclohexane 4.8 87.2 3.6 2.5 1.9
Benzene 4.3 90.4 3.6 1.4 0.3
THF 4.0 90.3 1.8 1.8 3.1
Acetone 2.9 88.9 2.0 4.7 1.5
Methanol 3.6 95.1 1.1 0.0 0.1
Butylamine 12.4 82.6 2.8 2.2 0.0
Acetonitrile 2.3 93.8 1.5 1.4 1.0

Further, the said article discloses that there are no large differences observed between the solvents, but methanol showed relatively good selectivity and the same fact can be observed from the above tabulated results. In acetone, yield obtained is approximately 90% with selectivity of about 91%, the by-products are mainly 4-hexen-1-ol in addition to a little (E)-3-hexen-1-ol and hexanol.

The catalyst hexacarbonyl chromium and arene tricarbonyl chromium have been widely used in the prior art. It is observed that these catalysts are used with high loading i.e. 5 mol% or more than 5 mol% has been used for selective hydrogenation of 1,4-dienes to cis-akenes. The catalyst hexacarbonyl chromium is highly toxic and is not advised to use at industrial scale. Further, due to the high loading of catalyst, the process is not feasible for industrial scale.

A US patent no. 8,003,838 discloses the use of Ruthenium complexes having cyclopentadienyl derivatives and a diene as ligands, together with some acidic additives for improving the selectivity in the hydrogenation of 1,4-dienes into the corresponding “cis”-alkenes as major product, i.e. wherein the two substituents in position 2,3 of the diene are in a cis configuration in the corresponding alkene.
The said patent suffers from the drawback such as use of Ruthenium metal catalyst, which is very expensive and highly moisture/air sensitive. The use of these complexes requires expensive pre-treatment for raw material stream on industrial scale. The process is not suitable for industrial scale.

Most of the prior art references demand the absence of isomeric mixture of EZ-hexadien-1-ol in 2E,4E-hexadien-1-ol (sorbic alcohol) compound and therefore extensive purification using preparative liquid chromatography or crystallization is required. Presence of isomeric mixture of EZ-hexadien-1-ol is found to deactivate the known catalytic system using hexacarbonyl chromium or Ruthenium catalysts. The preparative liquid chromatography technique required for purification is cumbersome and cannot be performed on industrial scale. Further the catalyst loading is found to be quite high in most of the above references i.e. 5 mol % or more with respect to starting material, which adds on to the cost and hence process costs are quite expensive and not an attractive option at industrial scale.

In view of the above, there is an urgent need to develop a cost-effective process by using some different catalysts or catalytic systems for selective hydrogenation of 1,4-dienes of formula II, into the corresponding "cis'-alkenes of Formula I, wherein presence of other isomer may not cause deactivation of catalyst. The need to obtain higher selectivity, as well as to maintain a high conversion to obtain higher yield is always desired. Keeping this in mind, inventors of the present invention aim to develop an industrially advantageous process for selective hydrogenation of 1,4-dienes of formula II, into the corresponding "cis'-alkenes of Formula I with high selectivity and high conversion rate.

OBJECT OF THE INVENTION
The principal object of the present invention is to develop a cost-effective industrial advantageous process for preparing cis-alkenes of Formula I by selective hydrogenation of 1,4-dienes of Formula II, wherein other isomer can also be present.
Another object of the present invention is to develop a cost-effective industrial advantageous process for preparing cis-alkenes of Formula I by selective hydrogenation of 1,4-dienes of Formula II in the presence of a suitable catalyst system with higher selectivity.
Another object of the present invention is to develop a cost-effective industrial process for preparing cis-alkenes of Formula I in higher conversion by selective hydrogenation of 1,4-dienes of Formula II in the presence of a suitable catalyst system.
Further object of the present invention is to develop a cost-effective industrial process for preparing cis-alkenes of Formula I in high selectivity and high conversion by selective hydrogenation of 1, 4-dienes of Formula II in the presence of a suitable catalyst system

SUMMARY OF THE INVENTION
Accordingly, the present invention provides a cost-effective industrial process for preparing cis-alkenes of Formula I,

Formula I
wherein R1, R2, R3, R4 and R5 represent, simultaneously or independently from each other, a hydrogen atom or a C1-C12 alkyl or de-conjugated alkenyl group, optionally substituted; and R1 and R3 or R3and R4 or R2 and R5 or R4 and R5, taken together, may form a C3-10 alkanediyl or de-conjugated alkenediyl group, optionally substituted analogues

Which comprises the steps:
i) Hydrogenating 1,4-dienes of Formula II,

Formula II
wherein R1, R2, R3, R4 and R5 represent, simultaneously or independently from each other, a hydrogen atom or a C1-C12 alkyl or de-conjugated alkenyl group, optionally substituted; and R1 and R3or R3and R4 or R2 and R5 or R4 and R5, taken together, may form a C3-10 alkanediyl or de-conjugated alkenediyl group,
optionally substituted analogues

in the presence of substituted arene chromium complex catalyst in a suitable solvent in the presence of a suitable boron additive at suitable hydrogen pressure and a suitable temperature and
ii) Isolating the pure cis-alkenes of Formula I.

In another embodiment, the present invention provides a cost-effective industrial advantageous process for preparing leaf alcohol of Formula Ia,

Formula Ia
Comprises:
i) Hydrogenating sorbic alcohol of Formula IIa,

Formula IIa

in the presence of substituted arene chromium complex catalyst; at suitable hydrogen pressure at a suitable temperature, in a suitable solvent in the presence of boron additive and
ii) Isolating the pure leaf alcohol of Formula Ia.

In one another embodiment, the present invention provides a cost-effective industrial advantageous process for preparing leaf alcohol of Formula Ia,

Formula Ia
Comprises:
i) Hydrogenating a mixture of sorbic alcohol of Formula IIa and E/Z isomer of formula IIb,

Formula IIa

Formula IIb
in the presence of substituted arene chromium complex catalyst; at suitable hydrogen pressure at a suitable temperature, in a suitable solvent in the presence of a suitable boron additive and
ii) Isolating the pure leaf alcohol of Formula Ia.

DETAILED DISCRIPTION OF THE INVENTION
Embodiments of the present invention seek to resolve at least one of the problems existing in the prior art to at least some extent, or to provide a consumer with a useful commercial choice. The illustrative embodiments herein are used to help understand the method and core ideas about the present invention. It should be noted that many adaptations and modifications may be made without departing from the scope of the appended claims in accordance with the common general knowledge of those of ordinary skilled in the art.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials Similar or equivalent to those described herein can be used in the practice or testing of the present invention the preferred methods and materials are described. Unless stated to the contrary, any use of the words such as “including,” “containing,” “comprising,” “having and the like, means “including without limitation' and shall not be construed to limit any general Statement that it follows to the Specific or Similar items or matters immediately following it. Except where the context indicates to the contrary, all exemplary values are intended to be fictitious, unrelated to actual entities and are used for purposes of illustration only. Most of the foregoing alternative embodiments are not mutually exclusive but may be implemented in various combinations. As these and other variations and combinations of the features discussed above can be utilized without departing from the invention as defined by the claims, the foregoing description of the embodiments should be taken by way of illustration rather than by way of limitation of the invention as define by the appended claims. The purpose of the present invention, the following terms are defined below.

As defined herein the term ‘pure’ represent the compound having cis-isomer purity is greater than 98%.

The term ‘conversion’ represent: conversion of 2E,4E hexadiene-1-ol

The present invention is to develop a cost-effective industrial process for preparing cis-alkenes of Formula I by selective hydrogenation of 1,4-dienes of Formula II in the presence of substituted arene chromium complex catalyst.

Formula I Formula II

wherein R1, R2, R3, R4 and R5 represent, simultaneously or independently from each other, a hydrogen atom or a C1-C12 alkyl or de-conjugated alkenyl group, optionally substituted; and R1 and R3 or R3 and R4, or R2 and R5 or R4 and R5, taken together, may form a C3-10 alkanediyl or de-conjugated alkenediyl group, optionally substituted analogues

According to another embodiment of the invention, the substrate is a compound of formula (I) wherein R1, R4 and R5 represent each a hydrogen atom; and R2 and R3 represent, simultaneously or independently from each other, a hydrogen atom or a C1-C8 alkyl or deconjugated alkenyl group, optionally Substituted.
Possible substituents of R1 to R5 when taken alone or together are as described above.
In one embodiment, the present invention provides a cost-effective industrial process for preparing cis-alkenes of Formula I by selective hydrogenation of 1,4-dienes of Formula II in the presence of substituted arene chromium complex catalyst at a suitable hydrogen pressure in a suitable solvent.
In one embodiment, the present invention provides a cost-effective industrial process for preparing cis-alkenes of Formula I, wherein a compound of Formula II and substituted arene chromium complex catalyst may be added in a stainless-steel autoclave, in a suitable solvent under inert atmosphere at room temperature. Thereafter, hydrogen pressure is applied and the resulting reaction mixture is stirred at a suitable temperature for suitable time or till completion of the reaction.
In particular, the resulting reaction mixture can be stirred at a temperature of 125°Cfor few minutes to several hours. Preferably, the reaction mixture is stirred at a temperature of 110-200°C for 0.5 hours to 10 hours and more preferably at a temperature of 120-130°C for 0.5 hours to 24 hours.
The substituted arene chromium complex can be selected from substituted arene tricarbonyl chromium complex. The arene complex can be monosubstituted, di-substituted or tri substituted, preferably di-substituted or tri-substituted. More preferably the arene complexes having functional groups attached on 1,2; 1,4 and 1,3,5 positions. The substituted groups can be selected from alkyl and esters. Arene complex can be selected from the group comprising of xylenes, and preferably p-xylene, o-xylene, 1,4-diisopropyl benzene, 1,3,5-triisopropylbenzene, mesitylene and 1,4-dimethoxy benzene.
The inventors of the present invention after extensive experimentation have surprisingly observed that the catalyst load can be reduced and taken in nominal amount to prepare the cis-alkene of formula I. This results in cost reduction and hence process is cost effective and feasible at commercial scale.
The substituted arene chromium complexes of the invention, an essential parameter of the selective hydrogenation, can be added to the reaction medium in a different concentration. As non-limiting examples, the complex concentration may range from 0.01 mol % to 2 mol %, the molar percentage being relative to the amount of substrate i.e.1,4-dienes of Formula II. Preferably, the complex concentration may be comprised between 0.02 mol % to 1 mol% and more preferably 0.05 mol % to 0.5mol%
The suitable solvent used in the selective hydrogenation can be a ketone solvent. The ketone solvent can be selected from the group comprising of acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone and the like.
In the present invention, the starting material i.e. 1,4-dienes of Formula II may exist in pure form or it can be a mixture of isomers i.e.EE/EZ. The ratio of isomers can be in the range of 80-100/20-0 with respect to EE/EZ isomers, having the following formulas:

In one embodiment, the selective hydrogenation of 1,4-dienes of Formula II can be conducted effectively in presence of a suitable boron additive.
The suitable boron additive can be selected from but not limited to boric acid, boric acid derivative. Preferably, the boron additive can be selected from boric acid, sodium borate, potassium borate and alike or combination thereof.
It is advantageous to use the boron additive, as it acts as activator and is highly beneficial to selectivity and higher conversion rate. Further, the hydrogenation reaction may be completed under mild conditions.
The completion of the reaction can be monitored with gas chromatography or any other suitable analytical techniques.
After completion of the reaction, the reaction mixture is cooled to room temperature, and reaction mixture may be filtered to remove the catalyst and concentrated.
The desired product cis-alkenes of Formula I obtained have conversion greater than 99.5% and selectivity greater than 98%. Optionally, the resulting product can be purified through distillation, to improve the purity and have purity greater than 99.5%.
In one specific embodiment, the present invention provides a cost-effective industrial process for preparing leaf alcohol of Formula Ia by selective hydrogenation of sorbic alcohol of Formula IIa with hydrogen in the presence of di or tri substituted arene chromium complex as catalyst and ketone solvent.

In one specific embodiment, the present invention provides a cost-effective industrial process for leaf alcohol of Formula Ia, wherein a mixture of Formula IIa, di or tri chromium complex catalyst in suitable solvent is added in a stainless-steel autoclave in inert atmosphere at room temperature. Then, hydrogen pressure may be applied and the resulting reaction mixture can be stirred at suitable temperature for suitable time for sufficient time till completion of reaction.
In particular, the resulting reaction mixture can be stirred at a temperature of 125°C for few minutes to several hours. Preferably, the reaction mixture is stirred at a temperature of 110-200°C for 0.5 hours to 10 hours and more preferably at a temperature of 120-130°C for 0.5 hours to 24 hours.

In the present invention, the starting material i.e. 1,4-dienes of Formula II may exist in the form of a mixture of two isomers i.e. EE/EZ isomers as shown below:

Formula IIa

Formula IIb

In one embodiment the starting material i.e. 1,4-dienes of Formula II may exist in 80-100/20-0 EE/EZ ratio.
The reaction parameters such as catalyst, suitable solvent, temperature, pressure used in the specific embodiment are the same as defined above.
The completion of the reaction is monitored with Gas Chromatography or any other suitable analytical techniques.
After completion of the reaction, the reaction mixture is cooled to room temperature, filtered to remove the catalyst and concentrated. The resulting products have purity of greater than 98% and conversion is greater than 99.9%. The resulting product may be further purified through distillation and get desired product having purity greater than 99.5%.

The prior art disclosures suggest that the Formula II or Formula IIa should be purified, prior to 1,4 selective hydrogenations because even minor presence of the mixture of corresponding EE/EZ isomers in Formula II or Formula IIa may deactivate the catalyst activity.
However, the inventors of the present invention have observed that there is no need to purify the Formula II, if the EE/EZ isomers presents in the ratio (as discussed herein earlier) prior to 1,4 selective hydrogenations, in presence of specific catalysts system, its loading amount, solvent and boron additive invented by present inventors. Therefore, the present invention provides a technical solution to the prior art problem and the present invention is also efficient and cost-effective at industrial scale.
According to a further embodiment of the present invention, the compound of Formula I or Ia, prepared by the present invention, is used in the pharmaceutical, agrochemical or perfumery industry as final product or as an intermediate. Particularly preferred the compound of Formula I or Ia is useful in the perfumery industry as final product or as an intermediate.
The major advantage realized in the present invention is that the reduction is very selective and highly efficient when performed using a combination of specified catalyst, solvent and boron additive. Further using the combination of specified catalyst, solvent and boron additive, the deactivation effect of E,Z isomer has not been observed. Another advantage of present invention is mixture of 2E,4E-hexadien-1-ol (Formula IIa) and isomeric mixture EZ-hexadien-1-ol (Formula IIb) can be used directly without purifying 2E,4E-hexadien-1-ol for preparing leaf alcohol. Further catalyst has been used in very less quantity, which makes the process highly cost effective and attractive option for industrial scale. All these advantages make the process of present invention highly efficient and cost effective at commercial scale.
It is against this and other backgrounds, the present invention is brought out and explained in following non-limiting examples.
It will be apparent to those skilled in the art that various modifications and variation scan be made in the present invention and specific examples provided herein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention that come within the scope of any claims and their equivalents.

EXAMPLES
Example1. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-99%, EZ-0.11%), sodium borate (1 mol%) and p-xylene-Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30bar G) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction [0.5 hours]. The reaction mixture is cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 0.4 0.5 98.2 0.3 0.6 100 99.19

Example2. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-85%, EZ-15%), boric acid (1 mol%) and p-Xylene-Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:
(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 14.3 0.8 83.7 0.7 0.5 100 98.47

The resulting product is purified through distillation to obtained leaf alcohol having purity of greater than 99.5%.

Example3. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles, EE-99%, EZ-0.11%), sodium borate (1 mol%) and 1,4-diisopropyl benzene--Cr(CO)3 (0.0005 mol) in methyl ethyl ketone (125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 0.2 0.3 98.6 0.4 0.5 100 99.59

Example4. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-85%, EZ-15%) boric acid (1 mol%) and 1,4-diisopropyl benzene--Cr(CO)3 (0.0005 mol) in MEK(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:
(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 14.5 0.7 83.5 0.8 0.5 100 98.24

The resulting product is purified through distillation to obtained leaf alcohol having purity of greater than 99.5%.

Example5. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE;99%, EZ-0.11%), sodium borate (1 mol%) and 1,3,5-triisopropyl benzene--Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:
(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 0.3 0.4 98.4 0.4 0.5 100.00 99.39

Example6. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-85%, EZ-15%), boric acid (1 mol%) and 1,3,5-triisopropyl benzene--Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30bar G) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 14.5 0.7 83.5 0.8 0.5 100.00 98.24

The resulting product is purified through distillation to obtained leaf alcohol having purity of greater than 99.5%.

Example7. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-99%, EZ-0.11%), sodium borate (1 mol%) and mesitylene--Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 0.3 0.4 98.5 0.4 0.4 100 99.49

Example8. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE- 85%, EZ-15%) sodium borate (1 mol%) and mesitylene--Cr(CO)3(0.0005 mol) in acetone (125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixtures cooled to room temperature filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 14.9 0.5 83.5 0.6 0.5 100.00 98.24

The resulting product is purified through distillation to obtained leaf alcohol having purity of greater than99.5%.

Example9. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-85%, EZ-15%), boric acid (1 mol%) and mesitylene--Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and purified through distillation and get desired product i.e. Leaf alcohol and the reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 14.6 0.4 83.6 0.8 0.7 100.00 98.35

Example10. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-99%, E/Z-0.11%), sodium borate (1 mol%) and 1,4-dimethoxy benzene--Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 0.2 0.6 98.6 0.2 0.4 100 99.59

The resulting product is purified through distillation to obtained leaf alcohol having purity of greater than 99.5%.

Example11. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-85%, EZ-15%) %), sodium borate (1 mol%) and 1,4-dimethoxy benzene--Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 14.8 0.7 83.6 0.5 0.4 100 98.35

The resulting product is purified through distillation to obtained leaf alcohol having purity of greater than99.5%.

Example12. Process for the preparation of pure leaf alcohol
A mixture of sorbic alcohol (0.5 moles; EE-85%, E/Z-15%), boric acid (1 mol%) and 1,4-dimethoxybenzene--Cr(CO)3(0.0005 mol) in acetone(125mL) in a stainless steel autoclave and purged with argon three times at room temperature then added H2 and temperature increased up to 125°C, maintained H2 pressure (30barG) for 0.5 hours. The reaction is monitored with Gas Chromatography till completion of the reaction. The reaction mixture cooled to room temperature, filtered to remove the catalyst and concentrated. The reaction monitoring results are tabulated below:

(E,E)-2,4Hexadienol (%) (E,Z)-2,4Hexadienol (%) (E) -3-Hexen-1-ol (%) (Z) -3-Hexen-1-ol (%) 4-Hexen-1-ol (%) Hexanol (%) Conversion (%) Selectivity (%)
0 14.3 0.6 83.7 0.5 0.9 100.00 98.47

The resulting product is purified through distillation to obtained leaf alcohol having purity of greater than 99.5%.
, Claims:Claim1. An industrial process for preparing cis-alkenes of Formula I,

Formula I
wherein R1, R2, R3, R4 and R5 represent, simultaneously or independently from each other, a hydrogen atom or a C1-C12 alkyl or de-conjugated alkenyl group, optionally substituted; and R1 and R3 or R3 and R4, or R2 and R5 or R4 and R5, taken together, may form a C3-10 alkanediyl or de-conjugated alkenediyl group, optionally substituted

Comprising the steps:
i) Hydrogenating 1,4-dienes of Formula II,

Formula II
Wherein R1, R2, R3, R4 and R5 are same as defined above

in the presence of substituted arene chromium complex catalyst at suitable hydrogen pressure and temperature, in a suitable solvent, in the presence of a suitable boron additive and;
iii) Isolating the cis-alkenes of Formula I.
Claim2. An industrial process for preparing leaf alcohol of Formula Ia,

Formula Ia
Comprises:
i) Hydrogenating a mixture of sorbic alcohol of Formula IIa and E/Z isomer of formula IIb,

Formula IIa

Formula IIb
in the presence of substituted arene chromium complex catalyst; in a suitable solvent in the presence of a suitable boron additive at suitable hydrogen pressure and suitable temperature and
iii) Isolating the leaf alcohol of Formula Ia.
Claim3. The process as claimed in claims 1 and 2, wherein in step i) substituted arene chromium complex is di or tri substituted arene complex.

Claim4. The process as claimed in claims 3, wherein di or tri substituted arene chromium complex is selected from o-xylene; p-xylene; 1,4-diisopropylbenzene; 1,3,5-triisopropyl benzene; mesitylene and 1,4-dimethoxybenzene.
Claim5. The process as claimed in claims 1 and 2, wherein in step i) moles % of the di or tri substituted arene chromium complex catalyst used in an amount of less than 2 mole% with respect to 1,4-dienes of Formula II.
Claim6. The process as claimed in claims 1 and 2, wherein in step i) the suitable solvent is ketone.
Claim7.The process as claimed in claims 6, the ketone is comprising of acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone.
Claim8. The process as claimed in claims 1 and 2, wherein in step i) the suitable boron additive is selected from boric acid and metal salt of boric acid selected from sodium borate, potassium borate and alike or combination thereof.
Claim9. The process as claimed in claims 1 and 2, wherein in step i) suitable temperature is in the range of 120-130°C.
Claim10. The process as claimed in claims I and II, wherein Formula II or IIa have mixture of isomers with EE/EZ ratio 80-100/0-20.