WO2009003085A1

WO2009003085A1 - Process for the manufacture of hydrofluoroolefins via metathesis

Info

Publication number: WO2009003085A1
Application number: PCT/US2008/068295
Authority: WO
Inventors: Maher Y. Elsheikh; Philippe Bonnet
Original assignee: Arkema Inc.
Priority date: 2007-06-27
Filing date: 2008-06-26
Publication date: 2008-12-31

Abstract

The present invention is direct toward a process for the synthesis of hydrofluoroolefins (HFO). The process is based on an olefin metathesis reaction of a hydrofluoroolefin in the presence of metathesis catalyst whereby the carbon-carbon double bonds in the olefins (alkenes) are rearranged to form three carbon hydrofluoroolefins of the formula CFa H 3-a C Fb H 1-b = C Fd H 2-d where a, b and d are as defined in the application.

Description

PROCESS FOR THE MANUFACTURE OF HYDROFLUOROOLEFINS VIA METATHESIS

Field of The Invention

The present invention relates to a process for the manufacture of hydro fluoroolefins. More particularly, the present invention relates to a process for manufacturing hydrofluoroolefins having three carbons via an olefin metathesis reaction. The olefin metathesis reaction process comprises the catalytic rearrangement of carbon-carbon double bonds in an olefin (alkene) to form three carbon hydrofluoroolefins.

Background of the Invention

The Montreal Protocol for the protection of the ozone layer, signed in October 1987, mandate the phase out of the use of chlorofluorocarbons (CFCs). Materials more "friendly" to the ozone layer, such as hydrofluorocarbons (HFCs) eg HFC- 134a replaced chlorofluorocarbons. The latter compounds have proven to be green house gases, causing global warming and were regulated by the Kyoto Protocol on Climate Change, signed in 1998. The emerging replacement materials, hydro fluoropropene, were shown to be environmentally acceptable ie has zero ozone depletion potential (ODP) and acceptable low GWP. This present invention describes process for manufacturing of hydro fluoropropenes. The process of the present invention is based on a catalytic olefin metathesis transformation of two fluoroolefins to produce the desirable fluoroolefins.

Synthesis of 2,3,3,3-tetrafluoropropene (HFO-1234yf) via the cycloaddition reaction of hexafiuoropropene to ethylene followed by pyro lysis of the resulting cyclobutene to HFO-1234yf and vinylidene is described in U.S. Patent No. 4,086,407 which discloses a multi-step process wherein hexafluoropropylene and ethylene are cyclodimerized to form l-trifluoromethyl-l,2,2-trifluorocyclobutane which is then cracked to produce 2,3,3,3-tetrafluorpropylene and vinylidene fluoride. . Description of the Invention

The present invention is directed towards a process for the synthesis of hydrofluoroolefins (HFOs) of the formula CF₃ H _3-a C F_b H _1-b = C F_d H _2-d where a= 0,1,2,3 b = 0,1 and d= 0,1,2, where a+b+d is greater than or equal to 1 by reacting, in the presence of an olefin metathasis catalyst, a propylene compound such as CF_aH _3-a CF_b H _\-_b = CF_C H ₂-_c where c= 0,1,2 and an ethylenic compound such as CFdH ₂-d = CF_eH ₂-_e- The product obtained, CF_C H _2-c = C F_e H _2-e where e=0,l,2 as shown in Equation 1. The reaction can take place in a homogeneous or heterogeneous mixture.

CF_aH _3-a CF_b H _!__b = CF_C H _2-c + CF_<jH ₂-_<j ⁼ CF_eH _2-e -^ CF_a H _3-a C F_b H i-_b = C F_<j H 2-_d + CF_C H ₂-_C = C F₆ H 2-e Equation 1

An olefin metathesis reaction is a reaction in which all of the carbon-carbon double bonds in an olefin (alkene) are cut and then rearranged in a statistical fashion: If this process is repeated enough, eventually an equilibrium mixture of olefins will be obtained. If one of the end product alkenes is volatile or easily removed, than the reaction can be driven completely to the right.

The commonly accepted mechanism for the olefin metathesis reaction involves a 2+2 cycloaddition reaction between a transition metal alkylidene complex and the olefin to form an intermediate metallacyclobutane. This metallacycle then breaks up in the opposite fashion to afford a new alkylidene and a new olefin, for example:

hi equation 1, when a= 3, b=l, c=2, d=0 and e=0, the two reactants are hexafluoropropene and ethylene. The two products formed are HFO-1234yf and vinylidene fluoride, as shown below: CF₃CF=CF₂ + CH₂=CH₂ →* ⁽F₃C⁾FC-CF₂ →- CF₃CF=CH₂ + CH₂=CF₂

H 2C -—--—** Q (-(2

Other examples of olefin metathasis include: I T olefin methasis CF₃CF=CH₂ + CHF=CF₂ ■*► CF₃CF=CHF + CH₂=CF₂

CF₃CF=CF₂ + CHF=CF₂ (F₃C)FC- -CF₂ CF₃CF=HF + CF₂=CF₂

FHC h CF₂

CF₃CF=CF₂ + CHF=CH₂ -~^> -→~ CF₃CF=HF + CH₂=CF₂

The olefin metathesis reaction can be catalyzed with four distinct generations of catalyst. First, a heterogeneous catalyst consisting of a high valent transition metal halide, oxide or oxo-halide with an alkylating co-catalyst such as an alkyl zinc or alkyl aluminum. Some of these catalyst systems are placed on an alumina or silica support. Examples include WCVSnMe₄ and Re₂O₇Al₂O₃. While these catalysts are exceedingly active, they have an exceedingly low tolerance for functional groups because of their Lewis acidic nature. Likewise, less than one percent of the material is an active catalyst, and nothing is known about the nature of the actual catalytic species on these systems. Second, titanocene based catalyst formed form the reaction of (C₅H₅ )₂TiC12 with two equivalents of A1(CH₃)₃ to yield (C₅H₅)₂TiCH₂ClAl(CH₃)₂, commonly called Tebbe's Reagent. In the presence of a strong base such as pyridine, the reagent is functionally equivalent to "(C₅H₅ )₂Ti=CH₂". Such Ti-=based catalyst are not early as active or tolerant of carbonyl functionalities as the later catalyst, but it has been shown that the Ti complexes undergo stoichiometric Wittin-like reactions with ketones, aldehydes and other carbonyls to form the corresponding methylene derivatives. The mechanism of this reaction is identical to that of the olefin metathesis reaction except that the final step is not reversible. Third, a variety of catalyst based upon W, Mo and Re are known. The most important of these are the acrylimido complexes of Mo with the general formula (Ar⁵N)(RO)₂Mo=CHR' where Ar' is typically 2,6-diisopropylphenyl, R' can be virtually anything and R is neopentyl or neophyl (CMe₂Ph). These catalyst are exceedingly active, metathesizing over 1,000 equivalents of cis-pentene to equilibrium in less than one minute for R = CMe(CF₃)₂. The reactivity of these catalysts can be tuned very easily by changing the nature of the alkoxide ligands. For example when R-tert-butyl, the complex reacts only with strained cyclic olefins. These catalysts have a high tolerance for functionality, although they are air and water-sensitive. Two important features of these catalysts are that they are 100% active and have been fully characterized by NMR and X-ray crystallography. The success of these catalyst stems from their coordinative and electronic insaturation (making them electrophilic) and their bulky ligands (prevents bimolecular decomposition). Finally, a series of Ru based catalyst have been developed that differ from the previous versions in several distinct ways. First, the metal is not in its highest oxidation state and is supported by phosphine ligands. Second, these catalysts are so tolerant of functionality that some of them can operate in water. Such functional group tolerance comes at the expense of lower metathesis rates than the W, Mo and Re catalysts.

The metathesis reaction of an olefin according to the present invention is facilitated using such catalysts. Any catalyst compatible with the methods of the invention may be used. By varying the catalyst employed for a particular metathesis reaction within the invention, it may be possible to increase product yields and reduce reaction times. For example, if a catalyst exhibiting greater thermal stability is selected, it may be possible to increase the reaction rate by increasing the temperature of the reaction mixture without the catalyst decomposing. Other reaction conditions, such as choice of solvent (e.g., solvent with higher boiling points might be used) might be varied as well. Based on the teaching herein, suitable catalysts for particular metathesis condensation reactions can be determined by examining the catalytic activity of a number of different catalysts in the particular reaction, and selecting as suitable those displaying any catalytic activity. Those particular catalysts that display higher levels of activity are preferred, and those that display the highest levels of activity are more preferred.

One or more solvents can be added to the reaction mixture to help dissolve the substrate and catalyst of the reaction mixture into a homogeneous state (e.g., substrate and catalyst dissolved together in a liquid phase). Those solvents capable of both dissolving the constituents of the process and not significantly hindering the reaction are acceptable for use with the invention. Typically, the choice of the solvent depends upon the particular constituents used, as, for example, one particular solvent may be capable of dissolving one set of constituents but not another. As such, many types of solvents can be used with this process. A non-exhaustive list of examples of solvents that might be used include various hydrocarbon-based solvents such as aliphatic hydrocarbons (e.g., hexane and heptane), aromatic hydrocarbons (e.g., benzene, toluene, naphthalene, phenol, and aniline), alicyclic and heterocyclic hydrocarbons (e.g., cyclohexane), cyclic ethers, and derivatives of any of the foregoing (e.g., halogenated derivatives of the foregoing such as chloroform and dichloromethane). In the experiments presented below, dichloromethane, benzene, tetrahydrofuran (THF), dimethoxyethane (DME), and acetone were used as solvents. Mixtures of two or more solvents might also be used. The suitability of a particular solvent for a particular reaction can be determined empirically by the methods taught herein. For example, a given solvent can be selected for a particular reaction based on the ability of the solvent to dissolve the constituents of the reaction and the boiling point of the solvent (which should be above the temperature of the reaction). A candidate solvent can be used in the reaction to determine whether it is suitable.

The amount of solvent used in a particular application of the invention will vary depending on the particular substrate, catalyst, and reaction conditions employed. The amount of solvent used should be in excess of the amount needed to (a) dissolve the substrate and catalyst under the reaction conditions selected and (b) allow that reaction to proceed. Based on the results obtained below, 1 ml of solvent for up to about 300 mg of substrate/catalyst mixture can be a sufficient amount. For other applications, a solvent to substrate-catalyst ratio of between about 1 ml:0.1 to 1000 mg can be an appropriate ratio for carrying out the reaction.

The efficiency of the subject metathesis reaction can be adjusted by varying the amount of substrate per amount of catalyst used in the reaction. The substratexatalyst ratio used in the invention can be any that result in the formation of the desired olefin product. This ratio will vary widely depending on factors such as the particular catalyst selected, the particular reaction to be catalyzed, the quantity or concentration of substrate present, the solvent selected, and the particular reaction conditions (e.g., pressure, temperature, etc.) utilized. Such substrate: catalyst ratios can be determined empirically by comparing the amount of desired product produced using a range of different ratios. Those that produce more of the product are typically preferred; and those that produce the most product are typically the most preferred. In general, the ratio of substrate to catalyst (mol:mol) can be varied from about 1:1 to 1000:1. Too much catalyst might be disadvantageous from an economic standpoint (catalysts generally being relatively expensive), while too little catalyst might be disadvantageous from an efficiency standpoint (i.e., too little product results). Accordingly, a preferred substrate: catalyst ratio is also one that produces the most economically efficient reaction.

A variety of different reaction conditions will result in the metathesis of an olefin. The particular conditions to be employed will vary depending on the particular olefin substrate used, the particular catalyst used, the substratexatalyst ratio used, and the solvent in which the reaction takes place. Suitable conditions are described below. Other suitable conditions, however, are within the invention and can be determined empirically using the information provided below.

Methods within the invention include a step of placing the substrate/catalyst/solvent mixture under conditions that result in the production of the olefin product in the reaction mixture. This step typically (but not always, as the reaction can proceed at room temperature in many cases) includes adjusting the temperature of the reaction mixture to a temperature suitable for the reaction to proceed. The particular temperature or range of temperatures chosen will vary according to several parameters including the particular reaction selected, the concentration of the reactants in the reaction mixture, the pressure of the reaction mixture, etc. Suitable temperatures can be determined by extrapolation from temperatures known to be optimal for reactions similar to those of the selected reaction (i.e., from conventional metathesis methods or from similar methods using conventional catalysts) to get a general range of suitable temperatures. Experiments can then be performed using a catalyst described herein in an adaptation of the conventional methods, and the temperature can be varied around the extrapolated general range of suitable temperatures to identify suitable and/or optimal temperature(s) for the processes of the invention.

Generally, those temperatures at which the greatest amount of chemical product is produced are preferred. In some cases, those temperatures which do not necessarily result in the greatest amount of chemical product are preferred for other reasons (e.g., from an economic standpoint it may be preferred to run the reaction at lower temperatures to avoid the costs associated with heating a reaction mixture or to avoid decomposition of expensive catalysts). For many reactions, suitable temperatures can range from about 10° C. to about 70° C, although this range can vary substantially.

The reaction of the invention can be performed under any atmosphere that allows the reaction to proceed. For catalysts that lose activity in the presence of oxygen, a deoxygenated, inert atmosphere such as nitrogen (N₂) or argon is preferred. For catalysts that lose activity in the presence of water, a dry atmosphere is preferred. For the metathesis of olefins, the reaction is preferably performed under an inert gas such as argon.

Although the substrate/catalyst/solvent mixture according to the invention can react under standard atmospheric pressure to result in the production of the olefin product, methods within the invention might also include a step of adjusting the pressure of the reaction mixture to another pressure at which the reaction can proceed. The particular pressure or range of pressures chosen will vary according to several parameters including the particular reaction selected, the concentration of the components in the reaction mixture, the temperature of the reaction mixture, etc. Suitable pressures can be determined by extrapolation from pressures known to be optimal for reactions similar to those of the selected reaction (i.e., from conventional metathesis methods or from methods using a similar combination of reaction components) to obtain a general range of suitable pressures. Experiments can then be performed by using a reaction mixture of the invention in an adaptation of the conventional methods, and the pressure can be varied around the extrapolated general range of suitable pressures to find the optimal pressure(s) for the processes of the invention. For example, those pressures at which the greatest amount of desired olefin product is produced might be optimal. Although metathesis of an olefin can take place at pressures greater than atmospheric pressure, it is generally preferred to run the reaction at about standard atmospheric pressure (because no specialized containment is necessary) or less. Where a volatile product is produced, it may be preferred to run the reaction at less than standard atmospheric pressure, as removal of the evolved volatile product is expected to drive the reaction forward (to the right as shown herein) at a higher rate.

The duration of the reaction will depend upon the particular reaction and reaction conditions selected. Generally, the amount of time for the reaction to occur will vary from the time between (a) the initiation of the reaction and the first appearance of the desired chemical product and (b) the initiation of the reaction and the termination of chemical product synthesis (e.g., due to exhaustion of substrate or production of interfering by-products). Thus the reaction can last for less than a few seconds to more than several days. The reaction can even proceed continuously by continuous removal of desired product and by-products, and continuous replenishment of substrate, catalyst, and/or solvent.

The chemical products resulting from a reaction according to the invention can be isolated from the reaction mixture by any suitable means, e.g., filtration, chromatography, distillation, etc. The isolated products can be further purified by conventional methods as well.

The products produced according to the invention can be further processed according to standard methods.

Examples

Example 1 Olefin metathesis of hexafluoropropene and ethylene gas

CF₃CF=CF₂ + CH₂=CH₂

A mixture of hexafluoropropene 2 grams, .013 moles, and ethylene gas .728 g; .026 moles, could be sealed under vacuum in a thick glass tubing, in the presence of catalytic amount of 1-Bis(tricyclohexylphosphine)benzylidene ruthenium dichloride catalyst (0.213 grams, 0.26 m.mols). Upon heating to 60° C for 18 hours, 1,1- difluoroethylene and HFO- 1234yf would be produced.

Example 2 Metathesis of HFO-1225ye (CF3CF=CHF) and ethylene

CF₃CF=CHF + CFH=CHF + CF3CF=CH2

A mixture of HFO-1225ye 2 grams, .015 mol, ethylene gas .9 grams, .032 mol and 1- (Bis(tricyclohexylphosphine)benzylidene ruthenium dichloride catalyst (0 .62 grams, 0.75 m.mol) could be placed in a thick glass tubing and heated at 60°C, for 20 hours, vinyl fluoride and HFO- 1234yf would be produced.

While the present invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

Claims

1. A process for producing a hydrofluoroolefin of the formula

CF₃H _3-a C F_b H i_-b = C F_d H _2-d where a= 0,1,2,3 b = 0,1 d= 0,1,2 and wherein a+b+d is greater than or equal to 1 comprising reacting a propylene compound of the formula CF_aH _3-a CF_b H i-_b = CF_C H _2-c where c= 0,1,2 with an ethylenic compound of the formula CF_dH _2-d = CF_eH _2-e, where e= 0,1,2 in the presence of an olefin metathesis catalyst.

2. The process of claim 1 wherein said process is carried out in a homogeneous mixture.

3. The process of claim 1 wherein said process is carried out in a heterogeneous mixture.

4. The process of claim 3 wherein said heterogeneous catalyst comprises a high valent transition metal halide, oxide or oxo-halide with an alkylating co-catalyst selected from the group consisting of alkyl zinc and alkyl aluminum.

5. The process of claim 3 wherein said catalyst is selected from the group consisting OfWCl₆ZSnMe₄ and Re₂O₇Al₂O₃.

6. The process of claim 2 wherein said homogeneous catalyst is (C₅Hs)₂TiCH₂ClAl(CH₃),.

7. The process of claim 1 wherein said reacting occurs in the presence of a solvent.

8. The process of claim 7 wherein said solvent is selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, hetrocyclic hydrocarbons, cyclic ethers, derivatives thereof and mixtures thereof.

9. The process of claim 1 wherein said reacting occurs in an inert atmosphere.

10. The process of claim 9 wherein said inert atmosphere comprises nitrogen or argon.

11. The process of claim 1 wherein said metathesis catalyst is a high valent transition metal halide, oxide or oxohalide.

12. The process of claim 11 wherein said metathesis catalyst further comprises an alkylating co-catalyst selected from alkyl zinc or alkyl aluminum.

13. The process of claim 1 wherein said metathesis catalyst comprises a titanocene catalyst.

14. The process of claim 1 wherein said metathesis catalyst comprises a catalyst based upon tungsten, molybdenum or rhenium.

15. The process of claim 1 wherein said metathesis catalyst comprises a ruthenium based catalyst.