FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
A PROCESS FOR DEHYDROGENATING ALKANE TO ALKADIENE
RELIANCE INDUSTRIES LIMITED
an Indian Company
of 3rd Floor, Maker Chamber-IV, 222,
Nariman Point, Mumbai 400 021,
Maharashtra, India.

Inventors
1. GHOSH RAJSHEKHAR
2. AHUJARITU
3. PILLAI MUTHUKUMARU SUBRAMANIA
4. TEMBE GOPAL LAXMAN
5. JASRA RAKSHVIR
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE DISCLOSURE:
The present disclosure relates to a process of dehydrogenating alkane to alkadiene. Particularly, the present disclosure relates to a process of dehydrogenating C4 and C5 alkane, 3-methyl pentane and cyclic alkanes having at least 7 carbon atoms into respective dienes.
BACKGROUND:
The dehydrogenation of hydrocarbons is an important commercial process
because of the wide and increasing demand for dehydrogenated hydrocarbons
for use in the manufacture of various chemical products such as detergents,
plastics, synthetic rubbers, pharmaceutical products, high octane gasoline,
perfumes, drying oils ion-exchange resins, and various other products well
known to those skilled in the art. De-hydrogenation reaction of alkane is the
reverse of hydrogenation reaction and is usually endothermic. The art has
developed and is continuing to develop a number of alternative methods to
produce dehydrogenated hydrocarbons in commercial quantities. In the
dehydrogenation reaction, selectivity in formation of the preferred product is
desirable. Accordingly, one of the problems faced in the hydrocarbon
dehydrogenation is the development of a process for maximum conversion of
starting material into the desired product. Further, hydrocarbon
dehydrogenation reactions are mostly carried out at a higher temperature requiring higher energy consumption and specialized equipment which in-turn contributes to a higher production cost. The application of higher temperature for dehydrogenation of the hydrocarbons leads to the atom loss in the form of carbon dioxide and therefore, lesser yield of the final product/s. Some of the representative patent documents which disclose dehydrogenation of hydrocarbon are discussed herein below.

US patent 6982305 discloses dehydrogenation of alkane to make an olefin in presence of Group VIII dehydrogenation catalyst (including Iridium) and then polymerizing the olefin (ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and mixtures thereof) in the presence of an olefin polymerization catalyst, and an optional hydrocarbon solvent. US6982305 does not specifically disclose preparation of butadiene from butane.
AnotherUS patent application 20040181104 discloses a process of catalytic dehydrogenation of ethyl benzene using iridium-based pincer catalyst in presence of hydrogen acceptor. However, US2004181104 patent application specifically discloses dehydrogenation of alkyl aromatic compound and not the C4 alkane. It, further, does not disclose the preparation of alkadienes from alkanes.
WO2012061272 application discloses a method of making a C5 or C6 conjugated linear diene compound involving reacting a C5 or C6 linear monoene with a hydrogen acceptor in the presence of a hydrogen transfer catalyst i.e., iridium pincer complex catalyst to produce a C5 or C6 conjugated linear diene. However, WO2012061272 application does not disclose the conversion of alkane to alkadiene. Further, it does not disclose the dehydrogenation of butane.
From the above, it is clear that none of the prior arts report single pot dehydrogenation reaction of alkane into alkadiene in high yield.
Therefore, to overcome the above shortcomings associated with the prior art the inventors of the present disclosure have provided a process for dehydrogenation of alkane into alkadiene.

Definitions:
As used in the present disclosure, the following words and phrases are generally intended to have the meanings as set forth below, except to the extent that the context in which they are used to indicate otherwise.
The expression "non-reactive medium" means a fluid that does not take part in the reaction at particular experimental conditions and only provides a medium for the reaction to occur.
The expression "Pincer ligated" means a chelating agent that binds to three adjacent coplanar sites, usually on a transition metal in a meridional configuration.
OBJECTS:
Some of the objects of the present disclosure which at least one embodiment herein satisfies are as follows:
It is another object of the present disclosure to provide a process for dehydrogenating alkane into alkadiene which is simple.
It is still another object of the present disclosure to provide a process for dehydrogenating alkane into alkadiene which is a single pot reaction.
It is still another object of the present disclosure to provide a process for dehydrogenating alkane into alkadiene in high yield.
It is still another object of the present disclosure to provide a process for dehydrogenating alkane into alkadiene which is energy efficient and therefore economic.
Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.

In one aspect of the present disclosure there is provided a process for dehydrogenating at least one alkane selected from the group consisting of C4 and C5 linear alkanes, 3-methylpentane and cyclic alkanes having at least 7 carbon atoms, said process comprising reacting said alkane and a hydrogen acceptor in the presence of a pincer ligated iridium homogeneous catalyst and a non-reactive medium at a temperature ranging between 100 °C and 190 °C to obtain alkadiene, wherein the concentration of the hydrogen acceptor ranges between 40 and 86% with respect to the total mass of the reaction mixture.
Typically, the hydrogen acceptor is at least one selected from the group consisting of t-butyl ethylene, norbornene, isobutylene and diisobutylene.
Typically, the pincer ligated iridium catalyst is at least one selected from the group represented by a formula I and II

Wherein R'= H, MeO, NR2 and R = tBu, iPr, cylopentyl, cyclohexyl
Typically, the non-reactive medium is at least one selected from the group consisting of mesitylene, 1,2,4,5 tetramethyl benzene and 2,2,4,4,6,6,8,8-octamethylnonane.
Typically, the ratio of the hydrogen acceptor to alkane ranges between 1 and 5.
Typically, the ratio of the non-reactive medium to alkane ranges between 1 and 5.

Typically, the ratio of the pincer ligated iridium homogeneous catalyst to alkane ranges between 3 x 10-4 and 3 x 10-3
Typically, the ratio of the hydrogen acceptor to the pincer ligated iridium homogeneous catalyst ranges between 800 and 1500.
Preferably, the ratio of the hydrogen acceptor to the pincer ligated iridium homogeneous catalyst ranges betweenl000 and 1200.
Typically, the pincer ligated iridium homogeneous catalyst can be supported on at least one inorganic support selected from the group consisting of alumina, silica, zeolite or metal surface through physical adsorption or covalent bond linkage.
DETAILED DESCRIPTION:
In accordance with one aspect of the present disclosure there is provided a process for dehydrogenating at least one alkane selected from the group consisting of C4 and C5 linear alkanes, 3-methyIpentane and cyclic alkanes having at least 7 carbon atoms. During the dehydrogenation of alkane, it is well know that alkenes are also formed along with alkadiene. However, the focus of the inventors of the present disclosure is to selectively enhance the conversion of alkane into alkadiene. The dehydrogenation reaction is carried out by reacting alkane and a hydrogen acceptor in the presence of pincer ligated iridium homogeneous catalyst and a non-reactive medium. The alkane is at least one selected from the group consisting of C4 to C5 linear alkanes, 3-methylpentane and cyclic alkanes having at least 7 carbon atoms.
In an exemplary embodiment C4 alkane used for dehydrogenating is selected from the group consisting of butane and isobutane. Particularly, to prepare butadiene, butane is used as a reactant.

Though any C2-C20 olefin can be employed as hydrogen acceptor in the dehydrogenation reaction of the present disclosure C4 to C8 olefins are preferred hydrogen acceptors. The hydrogen acceptor used in the process of the present disclosure is at least one selected from the group consisting of tert-butylethylene, norbornene, isobutylene and diisobutylene. The hydrogen acceptor is believed to promote the rate of the dehydrogenation reaction by accepting the hydrogen atoms from the catalyst thereby resulting in the active catalyst species which then reacts with alkane reactant. Further, the formation of the alkadiene can be regulated by controlling the quantity of the hydrogen acceptor. Up to a certain extent, increase in the quantity of the hydrogen acceptor results in the higher yield of the alkadiene. Accordingly, increase in the yield of alkadiene as a function of quantity of the hydrogen acceptor may be exponential, directly proportional or incremental Therefore, to obtain optimized results the concentration of the hydrogen acceptor ranges between 40 and 86% with respect to the total mass of the reaction mixture.

Wherein R' = H, MeO, NR2 and R = tBu, iPr, cylopentyl, cyclohexyl
The dehydrogenation reaction of the present disclosure is catalyzed by hydrogen transfer catalyst. Pincer ligated iridium homogeneous catalyst is used to transfer the hydrogen from the alkane to the hydrogen acceptor. Pincer ligated iridium catalyst is at least one selected from the group represented by a formula I and II

Depending upon the need of the reaction conditions the catalyst may be . supported on at least one inorganic support selected from the group consisting of alumina, silica, zeolites or metal surface. The catalyst and support are attached to each other either through physical adsorption or through covalent bond linkage.
The hydrogen transfer catalyst i.e., pincer ligated iridium catalyst reacts with hydrogen acceptor for example tert-butyl ethylene to give 2,2-dimethyl butane and thereby generating a co-ordinatively unsaturated catalytically active species. The catalytically active species then oxidatively reacts with alkane by activating C-H bond to give rise to the alkyl hydride. The alkyl hydride then undergoes reductive elimination to form alkadiene. The temperature condition for the dehydrogenating reaction should be such that there is barely any loss of the reactant in the form of the carbon dioxide. Therefore, the dehydrogenation reaction of C4 alkane is carried at a temperature ranging between 100 °C and 190 °C. In this temperature range the atom efficiency is close to 100% as there is no loss due to the formation of carbon dioxide that usually takes place during the dehydrogenation reaction.
The non-reactive medium means a fluid that does not take part in the reaction at particular experimental conditions and only provides a medium for the reaction to occur. Such non-reactive medium is one where C-H activation cannot occur which includes significantly substituted aromatic or aliphatic compound having high boiling points. Further, the non-reactive medium either aromatic or aliphatic is such selected that no two hydrogen atoms are adjacent to each other so that the non-reactive medium does not compete with the dehydrogenation reaction of alkane into alkadiene. Based on this criteria, the non-reactive medium is at least one selected from the group consisting of mesitylene, 1,2,4,5 tetramethyl benzene and 2,2,4,4,6,6,8,8-octamethylnonane.

Inventors of the present disclosure after extensive research have found that to drive a dehydrogenation reaction in the desired direction the components of the reaction are used in a specific proportion/ratio. The concentration of the hydrogen acceptor in the reaction mixture ranges between 40 and 86 w/w% of the total reaction mixture. The ratio of the hydrogen acceptor to alkane ranges between 0.5 and 5.0, whereas the ratio of the non-reactive medium to alkane ranges between 1 and 5.0, and the ratio of the pincer ligated iridium catalyst to alkane ranges between 3 x 10"4 and 3 x 10"3. Further, in accordance with the present disclosure the ratio of the hydrogen acceptor to the pincer ligated iridium homogeneous catalyst ranges between 800 and 1500. Preferably, the ratio of the hydrogen acceptor to the pincer ligated iridium homogeneous catalyst ranges between 1000 and 1200.
The present disclosure is further described in light of the following examples which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure.
Experimental:
Catalyst synthesis was carried out in a Glove box having argon atmosphere. All synthesis reactions were carried out using anhydrous solvents bought from . Sigma-Aldrich. 3,3-Dimethyl-l-butene (tBE) and mesitylene were obtained from Sigma-Aldrich and dried over molecular sieves prior to use. nButane was obtained locally with 99.5% purity and dried by passing through a molecular sieves column prior to use.
Reactions were carried out in 100ml PARR reactors. tBE, catalyst and mesitylene wherever specified were added to the reactor in the glove box. The reactor was brought out and n-butane as required was charged into the reactor while cooling the reactor. The reaction was heated under stirring for the required amount of time. After the reaction the reactor was cooled and vented

into a balloon for sampling the gas, the amount of gas sample obtained was weighed. Subsequently, the liquid sample was weighed and taken for analysis. Both the gas and liquid samples were analyzed by GC.
The conversion was calculated by estimating the conversion of 3,3-Dimethyl-l-butene (tBE) to 2,2-Dimethylbutane (TBA). Total olefin is the sum of 1-butene, cis 2-butene, trans 2-butene and butadiene. Butadiene selectivity is with respect to the total olefin.
Example 1:
14.4 gm of tert-butylethylene, 75 mg of pincer ligated catalyst (please specify) were mixed together into a 100 ml parr reactor.4.5 gm of n-butane was charged into the mixture. The mixture was then heated at 110 °C for 24 hours. Then the reaction mass was cooled and vented into a balloon to collect 8.gm of the gas sample. lO.gm of liquid sample was also collected. Both the gas and the liquid samples were analyzed by GC. The results are provided in Table No. 1
Example 2:
16.3 gm of tert-butylethylene, 75 mg of pincer ligated catalyst (please specify) were mixed together in presence of 3 ml of mesitylene into a 100 ml pan-reactor. 9.gm of n-butane was charged into the mixture. The mixture was then heated at 150 °C for 24 hours. Then the reaction mass was cooled and vented into a balloon to collect 2.gm of the gas sample. 26.gm of the liquid sample was also collected. Both the gas and the liquid samples were analyzed by GC. The results are provided in Table No. 1
Example 3:
14.4.gm of tert-butylethylene, 75 mg of pincer ligated catalyst (please specify) were mixed together in presence of 3 ml of mesitylene into a 100 ml parr reactor. 6 gm of n-butane was charged into the mixture. The mixture was then

heated at 170 °C for 24 hours. Then the reaction mass was cooled and vented into a balloon to collect 2.5 gm of the gas sample. 21 gm of the liquid sample was also collected. Both the gas and the liquid samples were analyzed by GC. The results are provided in Table No. 1
Example 4:
14.4 gm of tert-butylethylene, 75 mg of pincer ligated catalyst (please specify) were mixed together in presence of 3 ml of mesitylene into a 100 ml parr reactor. 5 gm of n-butane was charged into the mixture. The mixture was then heated at 190 °C for 24 hours. Then the reaction mass was cooled and vented into a balloon to collect 0.5 gm of the gas sample. 20.5 gm of the liquid sample was also collected. Both the gas and the liquid samples were analyzed by GC. The results are provided in Table No. 1
Example 5:
19.6 gm of tert-butylethylene, 100 mg of pincer ligated catalyst (please specify) were mixed together in presence of 5 ml of mesitylene into a 100 ml parr reactor. 3.5 gm of n-butane was charged into the mixture. The mixture was then heated at 170 °C for 24 hours. Then the reaction mass was cooled and 27 gm of the liquid sample was also collected. Both the gas and the liquid samples were analyzed by GC. The results are provided in Table No. 1
Example 6:
14.4 gm of tert-butylethylene, 75.mg of pincer ligated catalyst (please specify) were mixed together in presence of 3 ml of mesitylene into a 100 ml parr reactor. 6.5.gm of n-butane was charged into the mixture. The mixture was then heated at 190 °C for 24 hours. Then the reaction mass was cooled and 23 .gm of the liquid sample was also collected. Both the gas and the liquid samples were analyzed by GC. The results are provided in Table No. 1

Example 7:
14.4 gm of tert-butylethylene, 75 mg of pincer ligated catalyst (please specify) were mixed together in presence of 3 ml of mesitylene into a 100 ml pan-reactor. 6.5.gm of n-butane was charged into the mixture. The mixture was then heated at 190 °C for 48 hours. Then the reaction mass was cooled and 24.5.gm of the liquid sample was also collected. Both the gas and the liquid samples were analyzed by GC. The results are provided in Table No. 1
Example 8:
21.5.gm of tert-butylethylene, HOmg of pincer ligated catalyst (please specify) were mixed together in presence of 8.ml of mesitylene into a 100 ml pan-reactor. 7.5.gm of n-butane was charged into the mixture. The mixture was then heated at 170 °C for 48 hours. Then the reaction mass was cooled and 38.gm of the liquid sample was also collected. Both the gas and the liquid samples were analyzed by GC. The results are provided in Table No. 1
Table No. 1

Ex No tBE:
Cat tBE: nbutane Solvent
mesitylene:
nbutane Conversion
(%) Total olefin
(%) Butadiene selectivity TON
1 1187.1 3.00 0 4.9 5.2 1.2 21
2 1349.0 1.22 3 2.0 1.9 3.5 21
3 1187.1 1.61 3 36.5 40.9 6.1 300
4 1187.1 1.94 3 31.1 63.5 8.6 389
5 1214.1 3.77 5 29.5 67.3
12.6 216
6 1187.1 1.49 3 23.8 34.9 6.3 278
7 1187.1 1.49 3 44.2 55.5 5.5 442
8 1214.1 1.94 8 39.1 63.2 9.5 396

ECONOMICAL SIGNIFICANCE AND TECHNICAL ADVANCEMENT:
- The process of the present disclosure employs milder conditions for dehydrogenation of alkane as compared to the prior act processes.
- The process of the present disclosure is economic and energy efficient.
- The process of the present disclosure can be driven to desired direction. i.e. prepare only dienes.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

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 disclosure. These and other changes in the preferred embodiment of the disclosure 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 disclosure and not as a limitation.

We Claim:
1. A process for dehydrogenating at least one alkane selected from the group consisting of C4 and C5 linear alkanes, 3-methylpentane and cyclic alkanes having at least 7 carbon atoms, said process comprising reacting said alkane and a hydrogen acceptor in the presence of a pincer ligated iridium homogeneous catalyst and a non-reactive medium at a temperature ranging between 100 °C and 190 °C to obtain alkadiene, wherein the concentration of the hydrogen acceptor ranges between 40 and 86% with respect to the total mass of the reaction mixture.
2. The process as claimed in claim 1, wherein the hydrogen acceptor is at least one selected from the group consisting of t-butyl ethylene, norbornene, isobutylene and diisobutylene.
3. The process as claimed in claim 1, wherein the pincer ligated iridium catalyst is at least one selected from the group represented by a formula I and II

Wherein R' = H, MeO, NR2 and R = tBu, iPr, cylopentyl, cyclohexyl

4. The process as claimed in claim 1, wherein the non-reactive medium is at least one selected from the group consisting of mesitylene, 1,2,4,5 tetramethyl benzene and 2,2,4,4,6,6,8,8-octamethylnonane.
5. The process as claimed in claim 1, wherein the ratio of the hydrogen acceptor to alkane ranges between 1 and 5.
6. The process as claimed in claim 1, wherein the ratio of the non-reactive medium to alkane ranges between 1 and 5.
7. The process as claimed in claim 1, wherein the ratio of the pincer ligated iridium homogeneous catalyst to alkane ranges between 3 x 10-4 and 3 x
10-3
8. The process as claimed in claim 1, wherein the ratio of the hydrogen acceptor to the pincer ligated iridium homogeneous catalyst ranges between 800 and 1500, preferably, 1000 and 1200.
9. The process as claimed in claim 1, wherein the pincer ligated iridium homogeneous catalyst can be supported on at least one inorganic support selected from the group consisting of alumina, silica, zeolite or metal surface through physical adsorption or covalent bond linkage.