WO2004000770A1

WO2004000770A1 - Method for alkylating aromatic compounds with methane

Info

Publication number: WO2004000770A1
Application number: PCT/FR2003/001892
Authority: WO
Inventors: Jean-Marie Basset; Jean Thivolle-Cazat; Mostafa Taoufik
Original assignee: Centre National De La Recherche Scientifique (C.N.R.S)
Priority date: 2002-06-21
Filing date: 2003-06-19
Publication date: 2003-12-31
Also published as: FR2841241A1; FR2841241B1; AU2003253073A1

Abstract

The invention concerns a method for performing one or several aromatic substitutions on a compound (A) comprising at least an aromatic ring for preparing substituted aromatic compounds, which consists in: grafting an alkyl fragment on the aromatic ring of an aromatic compound (A) by coupling reaction between said aromatic compound (A) and methane, in the presence of a metal catalyst, in particular a catalyst based on a metal M, of the type known to catalyze an alkane metathesis reaction. The catalyst preferably comprises a metal M-hydrocarbyl complex, optionally in hydride form, in particular grafted and dispersed on a solid support. The metal M can be selected among transition metals, lanthanides and actinides.

Description

Process for the aikylation of aromatic compounds by methane.

The present invention relates to a process allowing one or more aromatic substitutions to be made on a compound (A) comprising at least one aromatic nucleus, in particular to a process for the alkylation of aromatic compounds.

Aromatic ring alkylation reactions have long been known as the Friedel and Crafts process (Olah: "Friedel-Crafts and related reactions", Interscience, New York, 1963-1965). These reactions are particularly advantageous for the synthesis, from benzene, of ethylbenzene, itself a precursor of styrene; these reactions also allow the production of cumene and higher alkylbenzenes. Various alkylating agents can be used, such as alkyl halides, alcohols and olefins. In all cases, catalysts based on Lewis acids are used, such as AICI ₃ , BF ₃ , FeCI ₃ , ZrCI ₄ , SnCI ₄ . By way of example, mention may be made of the ethylation of benzene in the liquid phase. Gas phase processes also exist, and catalysts based on supported H ₃ PO ₄ , aluminum silicates, BF ₃ / AI ₂ O ₃ or even zeolites, such as ZSM-5, are then used. In addition to corrosion problems, these reactions require the preparation of olefins by costly dehydrogenation processes, which has led to work whose objective was to allow direct use

, alkanes. Recent studies report the use of platinum supported on zeolite, like ZSM-5, to catalyze the direct alkylation of benzene with ethane or light alkanes from C ₂ to C. These reactions must however be carried out at elevated temperatures, from 400 to 500 ° C (US-A-4,899,008, JP-A-11199527, S. Kato et al. Catal. Lett. 2001, 73, 175).

The alkylation of aromatic rings with alkanes remains, however, a field that is poorly understood, little developed or using essentially acid catalysts; such a process supposes the formation of a carbon-carbon bond which is rarely observed in other types of reactions involving alkanes, for example with metal catalysts. A number of reactions are known to transform alkanes into other alkanes, such as for example hydrogenolysis reactions consisting of cleavage of CC bonds by hydrogen. Isomerization reactions are also known which transform an alkane into one of its isomers, for example butane into isobutane. All these reactions are generally carried out at relatively high temperatures and in the presence of catalysts based on metals, in particular of transition, in mass form or in the form of films, or even in the form of metallic particles supported on oxides. Thus, the catalyst can be of the nickel black, Ni / SiO ₂ , platinum black, Pt SiO ₂ , Pd / AI ₂ O ₃ or tungsten film or even rhodium film optionally alloyed with copper, tin , gold or silver. Under certain conditions, approval reactions have been observed transforming a given alkane into its higher counterparts. However, these homologation processes generally remain in the minority compared to parallel hydrogenolysis or isomerization reactions, and their performance is very low.

Consequently, the discovery of methods making it possible to transform the alkanes by formation of C-C bonds was necessary in order to enhance the value of the alkanes, in particular those of low molecular weight.

In this sense, patent application WO-A-9802244 describes a process for metathesis of alkanes in which an alkane reacts with itself or several alkanes react with each other, in the presence of an appropriate catalyst. A metathesis reaction is a reaction which makes it possible to transform a given alkane into a mixture of its lower and higher counterparts by concomitant stages of cleavage and of formation of C-C bonds. The reaction can be written according to the following equation (1):

2 C _n H _2n +2 C _n- jH2 (ni) +2 ⁺ Cn + iH ₂ (n + i) +2

(1) where i = 1, 2, 3, .... n-1 and n greater than or equal to 2. The catalyst is based on metal hydride grafted and dispersed on a solid oxide. The metals are chosen in particular from those of groups 5 and 6 Table of the Periodic Table (as defined by IUPAC in 1991 and illustrated in "Hawley's Condensed Chemical Dictionary", 12 ^th edition, RL Lewis, Sr., published by VN Reinhold Company, New York, 1993), as especially tantalum, chromium or tungsten. The preparation of the catalyst comprises a step of grafting a polyalkyl organometallic precursor onto the support, followed by a hydrogenolysis reaction of the alkyl ligands to form a metal hydride. WO-A-0027781 performs the metathesis of alkanes using a catalyst which is the precursor of the catalyst according to the preceding document, before its hydrogenolysis. The reaction described in these documents is a metathesis of the CC sigma bonds of the alkanes. Finally, WO-A-0104077 applies a similar method between an alkane and methane.

Against all expectations, the inventors found that it was possible to carry out an alkylation of aromatic rings, namely the grafting of a methyl group onto an sp ² carbon of an aromatic ring or structure (aromatic substitution), by reacting a compound comprising at least one aromatic ring or ring and methane. This can be carried out with great selectivity and under favorable operating conditions, at low temperature, in particular at temperatures below 400 ° C.

The invention finds applications in various fields, e.g. the field of oils, fuels, polymers, chemistry in organic synthesis, for example for obtaining substituted aromatic hydrocarbons. One of the interests is in particular to develop methane and aromatic products by forming industrially more interesting compounds.

The subject of the invention is therefore a process allowing one or more aromatic substitutions to be made on a compound (A) comprising at least one aromatic nucleus, process in which a methyl group is grafted onto the aromatic nucleus of a compound (A) by a coupling reaction between this compound (A) and methane (B), in the presence of a metal catalyst. The process of the invention relates in particular to the alkylation of an unsubstituted compound (A), that is to say that does not contain an alkyl substituent (methyl included). The catalyst is in particular a catalyst based on a metal M of the type of those which are known to catalyze alkane metathesis reactions. he it is for example a catalyst as described in WO-A-9802244, WO-A-0027781 or WO-A-0104077. The catalysts of the invention may in particular be defined as follows: catalyst comprising an M-hydrocarbyl complex, preferably grafted and dispersed on a solid support, the complex possibly being in the form of hydride, in particular by treatment of the above complex with hydrogen . The hydrocarbon ligands are essentially composed of carbon and hydrogen and can in particular be alkyl, alkylidene or alkylidyne radicals, as will be seen below.

Without wanting to be linked to theory; it seems likely that these catalysts play the role of catalytic precursors. When brought into contact with methane and the aromatic nucleus, these catalysts tend to form a new metal-aikyl complex and / or a metal-aryl complex which would be catalytically active species.

The metal M can be a transition metal, in particular chosen from those of groups 3, 4, 5 and 6 of the periodic table of the elements, as well as from the lanthanides and actinides. We can for example choose the metal from scandium, yttrium, lanthanum, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cerium and neodymium . A metal chosen from the metals of columns 4, 5 and 6 is preferred, particularly titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten.

The metal complexes according to the invention are preferably supported or grafted and dispersed on a solid support, for example oxide or sulphide. Among the oxide type supports, mention may preferably be made of crystalline or amorphous silica, mesoporous silicas, alumina, silica-aluminas, zeolites natural clays, aluminum silicates, titanium oxide, magnesium oxide, niobium or zirconium oxide. The solid support can also be a metal or refractory oxide, in particular modified by an acid such as a sulfated zirconia or a sulfated alumina. The solid support can also be a metal sulfide such as a molybdenum or tungsten sulfide, a sulfurized alumina or a sulfurized metal oxide. Among the preferred catalysts, mention may be made of tantalum, tungsten or chromium hydrides, grafted and dispersed on a silica or a silica-alumina.

Other characteristics and particularities of the catalysts which can be used in the invention will appear below.

The reaction according to the invention provides a coupling reaction leading to the grafting of a methyl group on a carbon of the aromatic nucleus, with evolution of hydrogen. For example, methane and benzene produce toluene and hydrogen. The reaction can be written in general according to equation (2):

ArH + CH ₄ > ArCH ₃ + H ₂ (2)

Ar = compound or aromatic nucleus.

In the presence of methane, the reaction can continue by grafting another methyl group onto the new methyl substituent, and so on, forming an alkyl substituent, and / or onto the aromatic nucleus, leading to compounds polysubstituted by methyls and or by alkyls.

The aromaticity of a nucleus or of a structure can be characterized by the fact that the said nucleus or the said structure comprises a total number of π electrons satisfying Hϋckel's rule that the number of π electrons is given by the formula 4r + 2 where r is an integer greater than or equal to zero (Jerry

March, Advanced Organic Chemistry (Reactions, Mechanisms, and Structure),

Third Edition, pages 37-64, see in particular page 59, I 18-21). The aromatic rings have the capacity to undergo an aromatic substitution in accordance with the invention. The compounds (A) are preferably compounds containing one or more aromatic rings, but having no hydrocarbon substituent on their aromatic nucleus (s) such as a linear or branched alkyl chain. The process allows the alkylation of the aromatic ring (s), that is to say the grafting of a methyl group on a carbon of the ring. The reaction can be continued by grafting other methyl groups onto other carbons in the nucleus, and / or by increasing the grafted substituents. When there are several aromatic rings, they can be either joined, or linked by a CC bond or by a saturated or unsaturated hydrocarbon chain. The method can also be applied to such compounds which are heterocyclic or comprising one or more heterocycles, eg with 5 or 6 atoms, comprising one or more heteroatoms such as O, S, N, Si or P.

The invention can in particular be addressed to aromatic compounds per se monocyclic or polycyclic.

These compounds can in particular be defined by the following general formula (3): compound comprising at least one aromatic cycle, in particular from 1 to 6 aromatic cycles, preferably from 1 to 2, these cycles, when there are several, being either joined or not joined and preferably linked by a CC bond (these carbons being ring carbons) or by a hydrocarbon chain, saturated or not, branched or not, comprising from 1 to 20 carbon atoms (C), in particular from 1 to 10 C, preferably from 1 to 5 C, and optionally one or more heteroatoms such as O, S, N, Si or P, the aromatic rings themselves containing in particular from 3 to 22 C, preferably from 6 at 10 C, and possibly optionally comprising one or more heteroatoms such as O, S, N, Si or P. Among the compounds corresponding to formula (3), there are aromatic compounds per se. The preferred case of the invention is benzene. Other examples are cyclodecapentaene, cyclotetradecaheptaene, annulene, naphthalene, acenaphthene, anthracene, phenanthrene, triphenylene, pyrene, coronene. In the compounds comprising several non-joined aromatic rings, biphenyl, diphenylmethane, diphenylethanes, diphenylpropanes, diphenylacetylene and cis- and trans-stilbenes may be cited as examples. The compound can also be ionic such as the cyclopropenylium or tropylium cations or the cyclopentadienide anion. Examples of compounds having a heteroatom are furan, benzofuran, thiophene, benzothiophene, pyrrole, indole, pyrazole, imidazoie, triazole, tetrazole, isoxazole, isothiazole, phosphole , pyridine, quinoline, pyridazine, pyrimidine, pyrazines, triazines, phosphorine.

Alternatively, the compounds (A) may be compounds containing one or more aromatic rings and comprising, on the or at least one of the aromatic rings, a hydrocarbon substituent such as a linear or branched alkyl chain, which may optionally include a or several heteroatoms, these, when they are present, are preferably placed in the main or secondary chain rather than at the end of the chain. When there are several aromatic rings, they can be either joined or linked by a C-C bond or even by a saturated or unsaturated hydrocarbon chain.

These compounds (A) can in particular be defined by the following general formula (4): compound corresponding to formula (3) above and further comprising at least one hydrocarbon substituent such as a linear or branched alkyl chain, comprising in total in particular from 1 to 30 C, preferably from 1 to 5 C for the linear ones and preferably from 4 to 6 C for the branched ones, and possibly possibly comprising one or more heteroatoms, these, when they are present, being preferably placed in the main or secondary chain rather than at the end of the chain. Mention may be made, by way of examples, of toluene, ethylbenzene, xylenes, propylbenzenes, phenyltoluenes, phenylethylbenzenes.

When in particular the aromatic ring comprises a linear or branched alkyl chain in substitution, the reaction makes it possible to graft a methyl group on the aromatic nucleus. The growth of the alkyl chains present on the compound can be observed. According to one embodiment of the invention, the method of the invention, applied to compounds of formula (4), in particular compounds substituted by one or more linear or branched alkyls, is used to produce a mixture of compounds containing compounds (4a) comprising at least one additional methyl substituent and compounds (4b) in which the original alkyl substituent has optionally been transformed into one of its higher or lower counterparts, in particular higher counterparts. This compound (4b) or some of these can themselves additionally comprise at least one additional methyl substituent.

The compounds with an aromatic nucleus (s) suitable for carrying out the process according to the invention can also be generated in situ, by dehydrogenation of the corresponding saturated hydrocarbons, during the use of the catalyst of the invention and in the reaction conditions of the invention. In other words, the implementation of the invention on these precursor hydrocarbons leads to the formation of the corresponding compound (A), then to its alkylation. By way of example, mention may be made of cyclohexane, cyclohexene and cyclohexadiene, precursors of benzene, methylcyclohexane, precursor of toluene, decaline and tetraline, precursors of naphthalene.

When carrying out the process of the invention, the starting compound (A) can comprise a single species of compound (A) or a mixture of at least two species.

The process according to the invention can be carried out batchwise or continuously, that is to say in a static reactor or else a recycling reactor or even a dynamic reactor. It is preferably carried out in the gas phase and in a dynamic reactor for continuous operation. Thus, a methane flow can be brought into contact with one, or brought through a bed of liquid compound (A), to take charge of the vapor pressure of this compound (A). The gaseous mixture obtained is then brought into contact with the catalyst. The solid catalyst, the liquid compound (A) and the methane gas can also be brought into direct contact, in particular in a static reactor. The catalyst may be in suspension.

As the aromatic + methane coupling reaction produces hydrogen, it may be advantageous to use a hydrogen absorber such as an olefin, for example cyclohexene or cyclohexadiene or even such as a divided metal, for example palladium or uranium on a support, or else carry out the reaction in a membrane reactor allowing hydrogen to pass, for example a palladium membrane. The process can be carried out in the presence of an inert, liquid or gaseous agent such as nitrogen, helium or argon.

The process can be carried out at a temperature ranging from -30 to 400 ° C, preferably from 0 to 300 ° C, more preferably from 100 to 250 ° C. The pressure can vary from 10 ^"3 to 30 MPa, preferably from 10 ^{" 2} to 10 MPa.

In the process according to the invention, the compound (s) (A) and the compound (B) can be added to the catalyst in one or more stages and in different ways, separately and in any order, or simultaneously or even before -Mixed. Compound a (A) and compound (B) can be used in A / B molar ratios varying from 500/1 to 1/500, preferably from 200/1 to 1/200, in particular from 100/1 to 1/100.

The proportion of catalyst present in the reaction mixture consisting of the compound (A) and the compound (B) may be such that the molar ratio of compound (A) to the metal M ranges from 10/1 to 10 ^5/1, preferably 50/1 10 ^4/1, especially from 100/1 to 10 ^3/1.

The subject of the invention is also the use of methane and a catalyst according to the invention, for the alkylation of a compound (A), allowing the grafting of a methyl substituent, on the aromatic ring. A subject of the invention is also the use of a catalyst according to the invention, based on a metal M, capable of catalyzing an alkane metathesis reaction, for the grafting of one or more methyl groups, on the aromatic nucleus of one or more compounds (A) or their saturated precursors. These other objects of the invention can take up the different characteristics described elsewhere with regard to the aikylation method. The subject of the invention is in particular such uses, for the grafting of a methyl substituent, onto the aromatic nucleus of a compound of formula (3) or of a compound of formula (4).

Most preferably, the catalysts according to the invention are obtained from an organometallic complex of formula (9) below: MR _a

(9) in which: M is a transition metal chosen in particular from those from groups 3, 4, 5 and 6 of the periodic table, as well as from lanthanides and actinides. One can for example choose the metal from scandium, ryttrium, lanthanum, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cerium and neodymium. A metal chosen from the metals of columns 4, 5 and 6 mentioned above is preferred, particularly titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten. the groups R are hydrocarbon ligands, identical or different, saturated or unsaturated, preferably aliphatic or alicyclic, in particular in C1 to C20, preferably in C1 to C10, linked to the metal M by one or more carbons, the metal bonds carbon can also be single, double or triple bonds, these ligands possibly containing atoms other than C or H, for example Si, a is less than or equal to the valence of M which can be 3, 4, 5 or 6.

The groups R may in particular be (i) radicals linked to M by a single bond, or alkyl radicals such as methyl, ethyl, propyl, neopentyl, allyl, ethynyl, benzyl, trimethylsilylmethyl (or neosilyl), bis (trimethylsilyl) methyl, cyclopentadienyl, (2i) radicals linked to M by a double bond, or alkylidene radicals, such as neopentylidene, methylidene, ethylidene, propylidene, allylidene, (3i) radicals linked to M by a triple bond, or aikylidynes radicals, such as neopentylidyne, ethylidyne, propylidyne, allylidyne, methylidyne or (5i) mixtures such as neopentyle-neopentylidene or neopentyl-neopentylidyne.

The neopentyl-neopentylidene and neopentyl-neopentylidyne mixtures are particularly advantageous in complexes with tantalum, respectively tungsten. According to an embodiment which is particularly suitable for using the solid catalyst, the compound is dispersed and grafted. organometallic on an anhydrous solid support, for example an oxide or a sulphide. The grafting reaction generally leads to the formation of one or more chemical bonds between the metal and atoms of the support, for example oxygen atoms in the case of supports of the oxide type. The solid support, for example silica, is subjected to a thorough heat treatment (with the aim of ensuring dehydration and dehydroxylation), in particular between 200 and 1100 ° C. for several hours (for example from 10 to 20 hours). Of course, a person skilled in the art will take care not to exceed the degradation temperature or the stability limit of the solid oxide which he has chosen to use. For example, for silica, the dehydration is carried out between 200 and 700 ° C, preferably around 500 ° C, for a simple dehydration reaction or at a temperature above 500 ° C if it is desired to obtain, in more, the formation of siloxane bridges on the surface.

To transfer and graft the complex onto the solid support, it is possible in particular by sublimation or by impregnation from a solution.

In the case of sublimation, the organometallic complex in the solid state is heated under vacuum and under temperature conditions ensuring its sublimation and its migration in the vapor state on the solid support, which is preferably found in it. powdery state or in the form of lozenges or the like. Sublimation is carried out in particular between 50 and 150 ° C., preferably around 80 ° C. The deposition can be checked for example by infrared spectroscopy.

The grafting is done by reaction of the complex with the functional groups of the support (for example OH, Si-O-Si, etc. for silica). The grafting will preferably be carried out at a temperature greater than or equal to ambient temperature.

It may be desirable to remove excess unreacted complex that simply adsorbed on the surface of the oxide by reverse sublimation. Thereafter, a treatment may or may not be carried out under hydrogen or in the presence of another suitable reducing agent, under conditions leading to transform all or part of the metal atoms into hydrides by hydrogenolysis or reduction of the hydrocarbon ligands. We can in particular work under a hydrogen pressure between 10 ^"3 and 10 MPa, but preferably at atmospheric pressure. As regards the temperature, one can work between 25 and 400 ° C, more generally around 150 ° C. The reaction is driving for a sufficient time, which can range, for example, from 1 hour to 24 hours, in particular from 10 to 20 hours, in particular approximately 15 hours.

In the general method which has just been described, sublimation can be replaced by a grafting reaction in solution. In this case, the organometallic complex is in solution in a conventional organic solvent, such as benzene, toluene, pentane, ether, the condition being to be in a very anhydrous medium. The reaction is carried out by suspending the solid support, preferably in powder form, in this metal complex solution, or else by any other method ensuring adequate contact between the two media. The reaction can be carried out at room temperature and more generally between 25 and 150 ° C. As in the case of sublimation, it is desirable to remove the excess of unreacted complex by washing the support with new solvent.

These catalysts have in particular the following characteristics:

- Very good dispersion of the metal on the oxide or the solid support, this dispersion being largely, mainly or completely monoatomic as regards the metal;

the bond between the metallic atom and the oxygen of the solid oxide is very strong and makes it possible to maintain the state of dispersion achieved;

- the metal fixed on the support is in a state of high unsaturation; its electronic layer d has a high electron deficit (less than 16 electrons); in the cases observed, we are around 10 electrons.

The catalyst can be prepared by other methods, using other precursors insofar as they lead to a metal hydride or a complex with hydrocarbon ligands of metal M capable of catalyzing an alkane metathesis reaction. The examples which follow illustrate the present invention without limiting it.

Example 1: Preparation of a supported tantalum hydride catalyst. The preparation of the surface tantalum hydride catalyst [Ta] _s -H can be carried out as follows: in a glass reactor, the tantalum tris (neopentyl) neopentylidene Ta [-CH ₂ -CMe ₃ ] ₃ [= CH- CMe ₃ ] is sublimated at 80 ° C on silica previously dehydroxylated at 500 ° C, so as to graft the tantalum complex by a reaction at 25 ° C with one or more hydroxyl groups of the silica surface, reaction which produces also neopentane (equation 10):

≡SiOH + Ta [-CH ₂ -CMe ₃ ] ₃ [= CH-CMe ₃ ]>

≡SiOTa [-CH ₂ -CMe ₃ ] ₂ [= CH-CMe ₃ ]

+ (≡SiO) ₂ Ta [-CH ₂ -CMe ₃ ] [= CH-CMe ₃ ] + CMe ₄ The mixture of neopentyl-neopentylidene complexes obtained: ≡SiOTa [-

CH ₂ -CMe ₃ ] ₂ [= CH-CMe ₃ ] and (≡SiO) ₂ Ta [-CH ₂ -CMe ₃ ] [= CH-CMe ₃ ] is then released from the rest of the Ta complex [-CH ₂ -CMe ₃ ] ₃ [= CH-CMe ₃ ] which has not reacted, by reverse sublimation at 80 ° C. under vacuum of about 10 ^"3 Torr (133.322 2 10 ^{" 3} Pa), then treated under hydrogen at atmospheric pressure, at 150 ° C, for 15 h, so as to form the supported tantalum hydride species; this reaction is accompanied by the hydrogenolysis of the neopentyl and neopentylidene ligands producing methane, ethane, propane, isobutane and neopentane, in the gas phase.

Example 2: Preparation of a supported tantalum hydride catalyst.

Another way of preparing the tantalum hydride catalyst Ua] _s -H is as follows: the silica is previously dehydroxylated at a temperature above 500 ° C (up to 1100 ° C) so as to make siloxane bridges appear on the surface more or less stretched from the condensation of hydroxyl groups; the tris (neopentyl) neopentylidene tantalum Ta [-CH ₂ -CMe ₃ ] ₃ [= CH-CMe ₃ ] is sublimed at 80 ° C and reacts with the remaining hydroxyl groups as well as with the siloxane bridges according to (equation 11):

sSi-O-Sis + Ta [-CH ₂ -CMe ₃ ] ₃ [= CH-CMe ₃ ] = Si-CH ₂ -CMe ₃ + ≡SiOTa [-CH ₂ -CMe ₃ ] ₂ [= CH-CMe ₃ ]

The transition from neopentyl-neopentylidene complexes to surface tantalum hydrides is carried out as previously in Example 1 by treatment under hydrogen.

EXAMPLE 3 Reaction Between Toluene and Methane

The Ta [-CH ₂ -CMe ₃ ] ₃ [= CH-CMe ₃ ] complex grafted onto the silica by impregnation (400 mg; 4.62% Ta / SiO ₂ ; 102 micromoles of Ta) is transferred to a glove box in a tubular stainless steel reactor which can be isolated from the atmosphere. After connection of the reactor to the assembly, the circuit is purged with argon, then the supported tantalum hydride catalyst [Ta] _s -H is prepared in situ by treatment, under hydrogen (3 ml / min) at 150 ° C for 15h, alkyl-alkylidene complexes grafted, similar to Example 1. After cooling, the reactor is purged with argon of excess hydrogen, then again heated to 150 ° C. under a stream of methane (3 ml / min; 25 bar). By switching a valve, the methane stream is brought upstream of the reactor through a bed of toluene liquid at room temperature to take charge of its vapor pressure (approximately 3733.016 Pa or 28 Torr) before being introduced in the reactor; the reactor is then brought quickly (rise of 20 ° C / min) to the temperature of 250 ° C. The analysis of the products is carried out online by gas chromatography (capillary column KCI / AI ₂ O ₃ 50m x 0.32 mm; detection by flame ionization). We then observe the formation mainly of xylenes (majority p-xylene) and benzene.

EXAMPLE 4 Reaction Between Benzene and Methane

The Ta [-CH ₂ -CMe ₃ ] ₃ [= CH-CMe ₃ ] complex grafted onto the silica by impregnation (400 mg; 4.62% Ta / SiO ₂ ; 102 micromoles of Ta) is transferred to a glove box in a tubular stainless steel reactor which can be isolated from the atmosphere. After connection of the reactor to the assembly, the circuit is purged with argon, then the supported tantalum hydride catalyst [Ta] _s -H is prepared in situ by treatment under hydrogen (3 ml / min) at 150 ° C for 15h, alkyl-alkylidene complexes grafted, similar to Example 1. After cooling, the reactor is purged with argon of excess hydrogen, then again heated to 150 ° C. under a stream of methane (3 ml / min ; 25 bar). By switching a valve, the methane stream is brought upstream of the reactor through a bed of liquid benzene at 10 ° C to take charge of its vapor pressure (approximately 3999.66 Pa or 30 Torr); the reactor is then brought quickly (rise of 20 ° C / min) to the temperature of 250 ° C. The analysis of the products is carried out online by gas phase chromatography (column capillary KCI / AI ₂ O ₃ 50m x 0.32 mm; flame ionization detection). The formation of toluene is then observed; we also observe the formation of ethylbenzenes and xylenes which are products of successive crossed metatheses.

It should be clearly understood that the invention defined by the appended claims is not limited to the particular embodiments indicated in the description above, but encompasses variants which do not depart from the scope or the spirit of the present. invention.

Claims

1. A process allowing one or more aromatic substitutions to be made on a compound (A) comprising at least one aromatic nucleus, in which a methyl group is grafted onto the aromatic nucleus of a compound (A) by a coupling reaction between this compound (A) and methane (B), in the presence of a metal catalyst.

2. Method according to claim 1, characterized in that the compound (A) is an aromatic compound.

3. Method according to claim 1, characterized in that the compounds

(A) comprise one or more aromatic rings, in particular from 1 to 6 aromatic rings, these rings, when there are several, being either joined or not joined and preferably linked by a CC bond or by a hydrocarbon chain, saturated or not, branched or not, comprising from 1 to 20 C and optionally one or more heteroatoms such as O, S, N, Si or P, the aromatic rings containing from 3 to 22 C and possibly optionally comprising one or more heteroatoms such that O, S, N, Si or P.

4. Method according to claim 2 or 3, characterized in that the compound (A) is chosen from benzene, cyclodecapentaene, cyclotetradecaheptaene, annulene, naphthalene, acenaphtene, anthracene, phenanthrene, triphenylene, pyrene, coronene, biphenyl, diphenylmethane, diphenylethanes, diphenylpropanes, cis- and transstilbenes, diphenylacetylene, cyclopropenylium or tropylium cations, cyclopentadienide anion, furan, thiophophen , benzothiophene, pyrrole, indole, pyrazole, imidazoie, triazole, tetrazole, isoxazole, isothiazole, phosphole, pyridine, quinoline, pyridazine, pyrimidine, pyrazines, triazines and phosphorine.

5. Method according to claim 1, characterized in that the compounds (A) comprise one or more aromatic cycles, in particular from 1 to 6 aromatic cycles, these cycles, when there are several, being either joined or not joined and preferably connected by a CC link or by a chain hydrocarbon, saturated or not, branched or not, comprising from 1 to 20 C and optionally one or more heteroatoms such as O, S, N, Si or P, the aromatic rings containing from 3 to 22 C and possibly optionally comprising one or more heteroatoms such as O, S, N, Si or P, these compounds comprising on a cycle at least one hydrocarbon substituent such as a linear or branched alkane chain, comprising in particular from 1 to 30 C, and possibly optionally comprising one or more heteroatoms .

6. Method according to claim 5, characterized in that the compound (A) is chosen from toluene, ethylbenzene, xylenes, phenyltoluenes, phenylethylbenzenes, and propylbenzenes.

7. Method according to any one of claims 1 to 6, characterized in that the compound (A) can be obtained in situ by a dehydrogenation reaction of a saturated cyclic hydrocarbon.

8. Method according to claim 7, characterized in that the compound (A) is obtained in situ by a dehydrogenation reaction of a compound chosen from cyclohexane, cyclohexene, cyclohexadiene, methylcyclohexane, decaline or tetraline.

9. Method according to any one of claims 1 to 8, characterized in that the metal M is a transition metal, a lanthanide or an actinide.

10. Method according to claim 9, characterized in that the metal M is chosen from titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten.

11. Method according to any one of claims 1 to 10, characterized in that the catalyst is an M-hydrocarbyl complex, optionally in the form of hydride, and grafted and dispersed on a solid support.

12. Method according to any one of claims 1 to 1 1, characterized in that the catalyst is as obtained from a) an organometallic complex of formula (9) below:

MRa in which:

M is a transition metal chosen from those of groups 3, 4, 5 and 6 of the periodic table of the elements or from lanthanides and actinides; the R groups are identical or different, saturated or unsaturated, preferably aliphatic or alicyclic, especially C ₁ to C ₁₀ , preferably C 1 to C ₁₀ , hydrocarbon ligands, linked to metal M by one or more carbons, the metal bonds -carbon can be single, double or triple - a is less than or equal to the valence of M which is 3, 4, 5 or 6. b) of a solid support, then optionally treatment with hydrogen to form a hydride.

13. Method according to claim 12, characterized in that the support is chosen from crystallized or amorphous silica, mesoporous silicas, alumina, silica-aluminas, zeolites, natural clays, aluminum silicates, l titanium oxide, magnesium oxide, niobium or zirconium oxide.

14. Method according to any one of claims 1 to 13, characterized in that the catalyst is a tantalum hydride, tungsten or chromium grafted on silica or silica-alumina.

15. Method according to any one of claims 1 to 14, characterized in that the reaction between the compound (A) and the compound (B) is carried out at a temperature between -30 and 400 ° C and under an absolute pressure from 10 ^"3 to 30 Mpa.

16. Method according to any one of claims 1 to 15, characterized in that the molar ratio (A) / (B) varies from 500/1 to 1/500, in particular from 200/1 to 1/200, in particular from 100/1 to 1/100.

17. Method according to any one of claims 1 to 16, characterized in that the proportion of catalyst present in the reaction mixture constituted by the compounds (A) and (B) is such that the molar ratio of the compound (A) to metal M ranges from 10/1 10 ^5/1, especially 50/1 to 10 ^4/1, especially from 100/1 to 10 ^3/1.

18. Method according to any one of claims 1 to 17, characterized in that the reaction is carried out in a static or recycling reactor or in a dynamic reactor.

19. Method according to any one of claims 1 to 18, characterized in that the reaction between the compound (A) and the compound (B) is performed in the gas phase or in the liquid phase, the catalyst then being suspended in the liquid phase.

20. Method according to any one of claims 1 to 19, characterized in that the reaction is carried out in the presence of at least one inert gas, preferably chosen from the group consisting of nitrogen, helium, argon.

21. The method of claim 5 or 6, characterized in that a mixture of compounds (4a) is produced comprising at least one additional methyl substituent and of compounds (4b) in which the original alkyl substituent has optionally been transformed into one of his senior counterparts.

22. Use of a compound as described in any one of claims 1 to 8, of methane and of a catalyst based on a metal M, capable of catalyzing an alkane metathesis reaction, for grafting of a methyl group on the aromatic ring of the compound (A).

23. Use of a catalyst based on a metal M, capable of catalyzing an alkane metathesis reaction, for the grafting of one or more methyl groups on an aromatic ring.