PROCESS

The invention relates to processes for the production of fluorinated cyclopropanes. In particular, the invention relates to a process for the preparation of fluorinated cyclopropanes for use in compositions, often in heat transfer compositions.

Due to environmental concerns arising from the use of potential]}' ozone depleting refrigerants and changing legislation that requires a reduction in the use of global warming potential (GWP) substances, it has become desirable to identify new heat transfer compositions to replace the chlorinated heat transfer compositions such as chlorofiuorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) which have historically been used.

US 2006/0043330 (Honeywell International Inc) discloses non-chlorinated azeotropic compositions including 2,3,3,3-tetrafluoropropene and trifluoroiodomethane and their use in refrigeration systems, as blowing agents, in foamable compositions and aerosols. However, there remains a need for alternative compositions for use in applications of this type which may have reduced toxicity and flammability properties, in comparison to the compositions disclosed in US 2006/0043330.

The applicants have identified compounds for use in such compositions, particularly for use in heat transfer compositions. These compounds are based upon cyclopropane, which is a known refrigerant (C270). Cyclopropane has a low GWP, and is relatively non-toxic; this compound was historically used as an anaesthetic. However, there are disadvantages with the use of cyclopropane as a refrigerant; for instance, cyclopropane is highly flammable and has a lower heat capacity than fluorinated cyclopropanes. In addition, the use of a range of fluorinated cyclopropanes allows these compounds to be used alone or in combination to produce a composition with an appropriate balance of physical and thermodynamic properties; for instance, the boiling point can be precisely controlled.

Fluorocyclopropanes are known compounds and their use as anaesthetics and pesticides has been postulated. However, they have hitherto not been used in commercial heat transfer compositions, aerosols, as blowing agents or in foaming compositions. As a result the present invention provides new processes for preparing fluorinated cyclopropanes. the preferred application for these cyclopropanes being in heat transfer compositions. However, the}' are appropriate for use in each of the above described applications in addition to having uses as extraction solvents and as power cycle working fluids.

Fluorinated cyclopropanes have been widely studied, and have been prepared by a variety of methods which would be known to the person skilled in the art. These are described in, for instance. Dolbier W.R and Battiste M. A., Chem. Rev., (2003). 103, 1071 - 1096 and Millaur R ₅ Schwertfeger W. and Siegemund G., Angew. Chem. Int. Ed. Eng., (1985). 24. 161 - 179. However, it is desirable to provide improved processes which can be conveniently used on an industrial scale.

However, there remains a need for a method of preparation of fluorinated cyclopropanes which is economical, viable on an industrial scale and may. ideally utilize readily available feedstock materials. Such a method may conveniently be utilised in the preparation of heat transfer compositions.

According to a first aspect of the invention there is provided a process for the preparation of a composition comprising a fluorinated cyclopropane, the process including the step of reacting a carbene with a compound of formula (I)

R R

^{R R} (I) where R may be the same or different and is selected from fluorine, alkyl, alkoxy or hydrogen, wherein if all of the R groups are hydrogen, alkyl or alkoxy, the carbene includes at least one fluorine substituent.

It is preferred that the compounds produced by this reaction are selected from fluorocyclopropane, 1,1-difluorocyclopropane, 1,2-difluorocyclopropane, 1,1,2-

iπfluorocyclopropane. 1.2.3-trifluorocyclopropanε. 1.1.2.2- tetrafluorocyclopropane. trans- 1.1 peniafiuorocyclopropane trans- 1 , 1 ,2,3-tetrafluorocyclopropane. cis- 1.1.2,3- tetrafluorocyclopropane, trifluoromethylcyclopropane, 1 -trifluoromεthyJ-2.2- difluorocyclopropane. l-trifluoromethyl-1.2,2-trifluorocyclopropane. 1 - trifluorometh)'l-l,2,3-trifluorocyclopropane, and l-trifluoromethyl-2,2,3- trifluorocyclopropane.

It is preferred that, where an alkyl group is present on the compound of formula (I), this is selected from methyl, ethyl, n-propyl and n-butyl. Similarly, it is preferred that the alkoxy group, where present, is selected from mefhoxy. ethoxy,

D-propoxy and n-butoxy. Substituted alkyl and alkoxy groups may also be used, and fall within the scope of the terms 'alkyl' and 'alkoxy' as used herein. The substituent may, for instance, be a halogen. There may be a single halogen substituent on the alkyl or alkoxy group, however it is preferred that there be more than one halogen on each group; these may be the same or different. Where the alkyl or alkoxy groups are halogenated, they will preferably be fluorinated. It is preferred that, where present, the unsubstituted alkyl is a methyl substituent, and that should an unsubstituted alkoxy group be present, this is a methoxy substituent. It is, however, preferred that where an alkyl or alkoxy group is present, that it is substituted. The most preferred substituted alkyl and alkoxy groups are trifluoromethyl and trifiuoromethoxy substituents. Where more than one alkyl and/or alkoxy group is present these may be the same or different.

The carbene may be defined by the formula .'CX]X ₂ where X] and X ₂ will preferably be independently selected from hydrogen or a halogen. The preferred halogens are chlorine, bromine and fluorine. Fluorine is the most preferred halogen substituent because it removes the additional step of trans-halogenation after the cycloaddition reaction has occurred. The ^' inclusion of an additional step to exchange the halogen atom(s) for fluorine is undesirable as this increases costs and is damaging to the overall yield of the fluorinated cyclopropane.

It is particularly preferred thai the carbεnε is difluorocarbεnε. as dlhalocarbenes are more stable than man}' other types of carbene; difluorocarbene ma} ⁷ easier to generate than other dihalocarbenes due to the highly electron withdrawing nature of the fluorine substituents.

The carbene may be generated in a variety of ways, including heat or light stimulated decomposition, pyrolysis or in the presence of base (typically sodium hydroxide). Preferably, the carbene will be generated from a compound selected from diazo compounds, tos}'lhydrazones, ketenes, ylides, strained alkenes, alkene oxides such as hexafluoropropene oxide, aziridines, alkali metal halocarboxylates such as sodium trifluoroacetate, heterocycles or through α -elimination of haloalkanes. Further methods are described in Dolbier W.R and Battiste M.A., Chem. Rev., (2003), 103, 1071 - 1096 and Millaur H., Schwertfeger W. and Siegemund G., Angew. Chem. Int. Ed. Eng., (1985). 24, 161 - 179 which are herein, incorporated by reference.

Where the carbene is to be methylene carbene. it is preferably generated from diiodomethane in the presence of base, or diazomethane in the presence of heat or light, although other reaction conditions and reagents may be used. Fluorocarbenes are preferentially generated from dibromofluoromethane or diiodofiuoromethane (with dϋodofluoromethane being most preferred), the reaction preferably being promoted through the presence of base. Difluorocarbene is preferably generated from chlorodifluoromethane (HCFC-22), often in the presence of base.

Alternatively, the carbene may be generated using pyrolysis; however, this route is not particularly preferred as the reactions are not very selective or high yielding. An example of this is the generation of the carbene from hexafluoropropylene oxide. Hexafluoropropylene oxide is often prepared by oxidising hexafluoropropene. A common source of hexafluoropropene is via the pyrolysis of tetrafluoroetbylene or chlorodifluoromethane.

^" ftTiere the product is to be a tεtrafluorocyclopropanε. it is preferred thai two of the

R groups are fluorine and that these are reacted with difluorocarbεne. However, it is possible that the tetrafluorocyclopropane could be prepared from other combinations of carbene and alkene. For instance, if the tetrafluorocyclopropane were to include fluorine substituents only, it could be prepared from methylene carbene and 1,1,2,2-tetrafluorethylene; or from fluorocarbene and 1 ,1,2- trifluoroefrrylene. It is more preferred that the compound of formula (I) is vinylidene fluoride or 1,2-difluoroethylene: the most preferred compound falling within the scope of formula (I) for use in the invention is vinylidene fluoride as this is an inexpensive and a readily available feedstock.

The person skilled in the art will understand that similar permutations of alkene substituent and carbene substituent will be appropriate for the preparation of tri- fluorinated cyclopropanes. di-fluorinated cyclopropanes and mono-fluorinated cyclopropanes.

For instance, where the fiuorinated cyclopropane is 1,1-difluoro cyclopropane the compound of formula (I) may be ethylene and the carbene may be difhiorocarbene which has been generated from chlorodifiuoromethane.

1,1,2-trifluorocyclopropane may be prepared from fluoroethylene which is reacted, as above, with difluorocarbene which has preferably been generated from chlorodifiuoromethane. The fluoroethylene may, in some cases, be prepared by dehydrofluorination of 1,1-difluoroethane. 1,1,2-trifluorocyclopropane could also be prepared by reaction of 1,1,2-trifluoroethylene and methylene carbene. In this case, the methylene carbene is preferably generated from diazomethane and the 1,1,2-trifluoroethylene prepared, in preferred embodiments, by dehydrofluorinafion of 1,1,1,2-tetrafluoroethane.

In a further example, 1,1,2,2-tetrafluorocyclopropane may optionally be prepared from 1,1-difluoroethylene and difluorocarbene which has been generated from chlorodifiuoromethane or an alternative source. One method of preparing difluoroefhylene is by dehydrofluorination of 1,1,1 -trifluoroefhane.

Similarly, pentafiuorocyclopropanε ma) ^" be prepared from 1,1, 2 -trifluoro ethylene and difluorocarbεne which has been generated from, for instance. chJorodifluorom ethane. Optionally, the 1.1,2-trifluoroethylene ma) ^' be prepared by dehydrofiuorination of 1 , 1.1.2 -trifluoro ethane.

The dehydrofluorinations described above may be liquid or vapour phase reactions. Where dehydrofiuorination is in the liquid phase, it is preferred that the reaction occurs in the presence of base at temperatures and in solvents which promote dehydrofiuorination. Typically the solvent will be a polar aprotic solvent such as water or ethanol, however, alternative solvents may also be used, in particular alkylene glycols.

Alternatively, where the reaction is a vapour phase reaction it is preferred that a catalyst be present. The catalyst of choice is a chromia containing catalyst. although other catalysts may be used either alone or in combination with the chromia containing catalyst. Typically, these vapour phase reactions will be carried out at atmospheric pressure or higher, more preferably at atmospheric pressure.

Typical temperature ranges for the dehydrofiuorination will be in the range 100 ⁰ C to 500 ⁰ C, preferably in the range 15O ⁰ C - 400 ⁰ C.

It will be clear to the person skilled in the art from the above description and their common general knowledge that the reaction conditions are highly dependent upon the precise nature of the starting materials and the desired end product.

However, it is preferred that carbene generation occurs in the presence of base.

The bases which will typically be used in the generation of the carbene include sodium hydroxide, metal carboxylates, alkyl lithiums, alkyl zincs and potassium tertiary butoxide. However, the person skilled hi the art would understand that other bases would also be suitable for use hi carbene generation reactions.

Any solvent can be used proλ'ided it resists attack by base and the carbene intermediate, has a boiling point that does not cause excessive pressure generation or separation difficulties and at least partial!)' solubilises the reactants. Examples of such solvents include water, glycol, glycol ethers, polyalkylene glycols and dipolar aprotic solvents such as N-methyl pyrrolidone. Mixtures of solvents can be used, and in some cases may be preferred, so as to allow dissolution of both the base and the olefin and to facilitate their contacting at the phase boundary of the two. To aid contacting between the phases a phase transfer catatyst may be employed e.g. crown ethers, cryptands or perfluorinated carboxylic acid salts. It is preferred that water is used, either alone or in combination with a co-solvent. If is most preferred that water is used alone.

Typically the reaction temperature will be in the range -100 ⁰ C to í300°C, however, for pyrolytic reactions the reaction temperature may be in excess of +600°C, and will typically be in the range +600 ⁰ C to +700 ⁰ C. For non-pyrolytic reactions it is preferred that the reaction temperature be somewhere in the range — 78 ⁰ C to +200 ⁰ C, more preferably in the range +5O ⁰ C to í100°C. It is most preferred that no external heat or cooling method be applied to the reaction mixture, so that the reaction is completed at "room temperature'. However, a 'room temperature' reaction may absorb or evolve heat, or be completed at non- atmospheric pressure (i.e. raised pressure or reduced pressure when compared to atmospheric), so that the temperature inside the reaction vessel may, none-the-less be above or below the external 'room temperature'. Accordingly, the expression 'room temperature' is intended only to indicate that the reaction is neither heated nor cooled using an external source of temperature control, and is not intended to exclude reactions in which the temperature inside the reaction vessel rises or drops below this temperature due to the thermodynamic properties of the reaction itself.

The addition of the carbene to the alkene is typically a reaction in which the formation of the carbene and reaction with the alkene is either substantially simultaneous or a single step reaction. Accordingly, the reaction conditions between the carbene and alkene are typically the same as those used for the initial generation of the carbene. However, it is possible, where appropriate, to vary the

reaction temperature, or io add farther reagents once the carbene has been generated, in particular, where the carbene is the more stable difluorocarbene. Further, the addition of the carbene to the alkenε may be completed as either a continuous or batch reaction process.

According to a further aspect of the invention there is provided a process for the preparation of a composition comprising a fluorinated cyclopropane, the process including the step of reacting a compound of formula (II)

with a metal and optional^ a metal halide to generate a fluorinated cyclopropane, wherein X may be the same or different and is selected from a halogen, alkyl, alkoxy or hydrogen.

Without being bound by theory it is believed that the halide ion from the metal halide exchanges with the chlorine atoms in the compound of formula (TI), dεhalogenation and ring formation of the resulting compound being facilitated through the presence of the metal.

It is preferred that the compounds produced by this reaction are selected from fluorocyclopropane, 1,1-difluorocyclopropane, 1.2-difIuorocyclopropane. 1,1,2- trifluorocyclopropane, 1,2,3-trifluorocyclopropane, 1,1,2,2- tetrafluorocyclopropane, trans-l,l,2,3-te1rafluorocyclopropane, pentafluorocyclopropane trans- 1 ,1,2, 3-tetrafluorocyclopropane, cis- 1 , 1 ,2,3- tetrafluorocyclopropane, trifluoromethyl cyclopropane, 1 -trifiuoromethyl-2,2- difluorocyclopropane, 1 -trifluoromethyl- 1,2,2-trifluorocyclopropane, 1- trifluoromethyl-1 ,2,3-trifluorocyclopropane, and 1 -trifluoromethyl-2,2,3- trifluorocyclopropane.

It is preferred that the metal is selected from an alkali, alkaline earth or transition metal, the most preferred metals being sodium, magnesium and zinc. Typically, the metal used in this process will be zinc.

Ii is preferred thai the metal halide is selected from group (Ij metal halides. group (II) metal halides and transition metal halides and that the reaction is a Wuπz reaction. Typically these will be a sodium halide or a zinc halide. it is more preferred that the sodium halide is selected from sodium bromide or sodium iodide, with sodium iodide being the most preferred reagent, because iodine atoms are generally more labile than chlorine or bromine atoms. However, zinc chloride ma} ⁷ also optionally be used.

It is preferred that, where an alkyl group is present on the compound of formula (II). this is selected from methyl, ethyl, n-propyl and n-butyl. Similarly, it is preferred that the alkoxy group, where present, is selected from mefhoxy, ethoxy, n-propoxy and n-butoxy. Substituted alkyl and alkoxy groups ma}' also be used, for instance the substituent may be a halogen. There ma}' be a single halogen substituent on the alkyl or alkoxy group, however it is preferred that there be more than one halogen on each group: these ma} ^" be the same or different. Where the alkyl or alkoxy groups are halogenated, they will preferably be fluorinated. It is more preferred that, where present, the unsubstituted alkyl is a methyl substituent. and that should an unsubstituted alkoxy group be present, this is a methoxy substituent. It is, however, preferred that where an alkyl or alkoxy group is present, that it is substituted. The most preferred substituted alkyl and alkoxy groups are trifluoromefhyl and trifluoromethoxy substituents. Where more than one alkyl and/or alkoxy group is present, these may be the same or different.

Where X is a halogen, it is preferred that the halogen is fluorine. Where the halogen is not fluorine, it is necessary to transhalogenate the resulting cyclopropane, substituting the other halogen substituents with fluorine. This additional step is undesirable as it is difficult to control the selectivity of the reaction, reducing the overall yield. In addition, the inclusion of a further step in the reaction is commercially undesirable as any increase in the complexity of the process will also increase costs.

It is particularly preferred that the compound of formula (II) is selected from

wherein X is a halogen and each halogen may be the same or different. Preferably one or more X groups will be fluorine or chlorine, more preferably fluorine. It is most preferred thai the compound of formula (II) is selected from

Alternatively, the compound of formula (U) may be a 1,3-dichlorobutane compound of formula

wherein X may be the same or different and is selected from a halogen or hydrogen.

The process may comprise the additional step of generating the compound of formula (E) from an alkene, preferably from an ethylene, more preferably from a substituted ethylene. The ethylene may be mono-, di-, tri-, or tetra- substituted with, for instance, halogens, alkyl groups or alkoxy groups. The substituents may be the same or different. It is preferred that the alkyl and alkoxy substituents, where these are present, are as outlined above for the compound of formula (II). In particular, it is preferred that where the substituent is a halogen, that this halogen is fluorine to remove the need for a subsequent transhalogenation reaction.

The alkene is preferably telomerised using a compound of formula CCl ₂ XiX ₂ wherein Xj and X ₂ are independently selected from alkyl, alkoxy and hydrogen. It is further preferred that at least one of Xi or X ₂ is hydrogen.

Most preferably , the compound of formula (II) is prepared through the reaction of 1.1.2-trifjuoroetfjy]εne with dichlorofluoromεthane (HCFC-31). or through the reaction of tetrafluoroethylεne and dichlorom ethane. The person sldlled in the art would, however, understand that man)' alternative combinations of starting 5 materials are possible.

The generation of the compound of formula (II) ma}- be implemented as a continuous or batch process, with the batch process preferably being devised as a

'one pof reaction process. However, a two step reaction process in which the

] O compound of formula (II) is first prepared and purified, and then the cyclisation completed separately may also be used. It would be clear to the person skilled in the art that the process type selected will depend upon the particular reactants being used and products obtained. In particular, the selectivity of each reaction

(i.e. the reaction to form the compound of formula (II) and the subsequent Wurtz 5 cyclisation) and reactivity of any by-products from the formation of the compound of formula (II) will influence whether a batch or continuous process is more appropriate. For instance, " ^' clean' reactions which are highly selective and high

3'ielding with by-products of low reactivity will be better suited to continuous or single step batch processes. 0

As with the carbene chemistry described above, it will be clear to the person skilled in the art that the reaction conditions are highly dependent upon the precise nature of the starting materials and the desired end product. However, it is preferred that the reaction to prepare the compound of formula (II) occurs at the 5 reflux temperature of the solvent. Preferred reaction temperatures would be in the range 5O ⁰ C to 200 ⁰ C, more preferably in the range 5O ⁰ C to 100 ⁰ C. Preferentially, although not essentially, the cyclisation reaction occurs under inert atmosphere, optionally at a pressure greater than atmospheric pressure.

Any solvent can be used provided that the compound of formula (II) is at least partially soluble therein, that the solvent has a boiling point that does not cause excessive pressure generation or separation difficulties, and has no unfavourable interactions with the reactants. Examples of such solvents include water, glycol,

glycol ethers, polyalkylene glycols and dipolar aprotic solvents such as N-mεthyl p)ττolidone. Mixtures of solvents can be used, and in some cases may be preferred, so as to allow" dissolution of both the base and the olefin and to facilitate their contacting at the phase boundary of the two. To aid contacting between the phases a phase transfer catalyst may be employed e.g. crown ethers, cryptands or perfluorinated carboxylic acid salts. It is preferred that water is used, either alone or in combination with a co-solvent. If is most preferred that water is used alone.

The fluorinated cyclopropane produced by the inventive processes ma)' be a mono-, di-, tri-. tetra- or penta-substituted fluorocyclopropane. Of these, mono- fluorinated cyclopropanes are least preferred on stability grounds. In particular, although mono-fluorocyclopropanes may be prepared by the processes of the subject invention, they are the least preferred product. Preferred products are 1,1- difluorocyclopropane. 1,1,2 -trifhiorocyclopropane and 1,1,2,2- tetrafluorocyclopropane.

It is preferred that the process produces a tetrafluorocyclopropane as tetra- substituted cyclopropanes have a lower flammability than the mono-, di- and tri- fluorocyclopropanes. However, all of these are suitable for preparation by the inventive processes. Higher substitutions would be anticipated to exhibit reduced stability due to a high level of stereochemical hindrance resulting from the close proximity of the fluorine atoms in the composition.

Most preferably, the cyclopropane product is 1,1, 2,2 -tetrafluorocyclopropane as the starting materials for this compound are most easily obtainable and the boiling point is in an appropriate range for most of the envisaged applications, in particular for refrigeration purposes. However, 1,1,2,3-tetrafluorocyclopropanes are also considered to be suitable for use in the subject invention.

It is also preferred that the fluorocyclopropanes described herein are prepared by reaction of an alkene with a carbene as the feedstocks are easier to source, and the reactions more selective.

According to a further aspect of the invention there is provided a process for preparing a heat transfer composition comprising the step of preparing a fluorocyclopropanes according to either of the above processes. Typically, but not essentially, the fluorocyclopropanes will then be blended with an additive selected 5 from lubricants, hydrocarbons, hydrofluorocarbons. stabilisers and flame retardants. Further details regarding these additives are provided in our co- pending application entitled "Refrigerant Compositions' and of the same filing date as this application.

] O According to a further aspect of the invention there is provided a process for modifying a refrigerant system comprising removal of at least a portion of the existing refrigerant and replacement of this refrigerant with a refrigerant composition including the heat transfer composition produced according to the invention. 5

According to a further aspect of the invention there is provided a process for preparing an aerosol composition comprising the step of preparing a fluorocyclopropane by either of the above processes. Often, the process of preparing the aerosol composition will comprise the additional step of mixing the 0 fluorocyclopropane with a material to be sprayed.

In a further aspect of the invention there is provided a process for preparing a foamable composition comprising the step of preparing a fluorocyclopropane by either of the above processes. The fluorocyclopropane may then, optionally, be mixed with a surfactant.

According to an additional aspect of the invention there is provided a process for preparing a blowing agent comprising the step of preparing a fluorocyclopropane by either of the above processes.

According to a further aspect of the invention there is provided a process for preparing an extraction solvent comprising the step of preparing a fluorocyclopropane by either of the above processes.

According to another aspect of the invention there is provided a process for preparing a power cycle working fluid for use in a mechanical power generation device comprising the step of preparing a fluorocyclopropane according to either of the above processes. It is preferred that the mechanical power generation device is adapted to use a Ranldne Cycle or modification thereof to generate work from heat.

A Ranldne cycle, or "Organic Ranldne Cycles' ^" (ORCj is a method of generating mechanical or electrical power from low grade or waste heat. These cycles are similar in technology to the conventional, steam-based power generation used in large scale power stations. The cycle requires the presence of an organic fluid (e.g. a fluorocyclopropane) which permits recovery of energy from low- temperature sources of heat, particularly from so-called '"waste heat" (temperature of source below about 15O ⁰ C) or from ambient heat content of waves, soil, or air. ORC technology is normally designed around the thermophysical properties of an organic working fluid to operate at lower pressures and/or temperatures than is normal for a steam based power cycle. The higher boiling cyclopropanes prepared by the inventive processes may therefore be used in such technologies.

Examples

Example 1 - Preparation of 1,1-difluoropropane

Excess chlorodifiuoromethane and ethylene is bubbled through a solution of sodium acetate. The gas stream exiting the reactor is condensed and collected.

Example 2 - Preparation of 1,1,2-trifluoropropane

Excess chlorodifiuoromethane and vinyl fluoride is bubbled through a solution of sodium acetate. The gas stream exiting the reactor is condensed and collected.

Example 3 -Preparation of 1,1-difluoropropane

To a refluxing stirred mixTure of zinc dust and propan-1 -ol is added 1,1-difluoro- 1,3-dicliloropropane. As the product is formed it is removed from the reactor and condensed using a cold trap.

Example 4 ~ Preparation of 1,1-difluoropropane

Zinc dust, propan-1 -ol and l,l-difluoro-L3-dichloropropane are placed in an autoclave under an inert atmosphere. The autoclave is sealed and warmed to initiate reaction. When the reaction is complete, the product is vented from the reactor and condensed.

Example 5 ~ Preparation of 1,1-difluoropropane

To a refluxing stirred mixture of zinc dust and propan-1 -ol is added 1,1-difmoro- 1.3-dichloropropane and sodium iodide. As the product is formed it is removed from the reactor and condensed using a cold trap.

Example 6 - Preparation of 1,1-difluoropropane

Zinc dust, propan-1-ol and l _; l-difluoro-l,3-dichloropropane and sodium iodide are placed in an autoclave under an inert atmosphere. The autoclave is sealed and warmed to initiate reaction. When the reaction is complete, the product is vented from the reactor and condensed.