WO2003059514A1

WO2003059514A1 - Method for preparing solid basic wadsworth-emmons reaction catalysts

Info

Publication number: WO2003059514A1
Application number: PCT/FR2003/000009
Authority: WO
Inventors: François Figueras; Hafedh Kochkar; Lakshmi Kantam Mannepalli
Original assignee: Centre National De La Recherche Scientifique (C.N.R.S)
Priority date: 2002-01-03
Filing date: 2003-01-03
Publication date: 2003-07-24
Also published as: WO2003059514B1; AU2003216780A1; FR2834228A1

Abstract

The invention concerns a method for preparing a solid basic catalyst comprising a step which consists in heat treating a mixed magnesium hydroxide and a metal M of the rare earth family wherein the mol ratio Mg/M ranges between 1.5 and 5, said heat treatment consisting in bringing said mixed hydroxide to a temperature not less than 500 °C and not more than 1000 °C. The invention also concerns the use of the catalysts obtained by said method as heterogeneous catalysts for Wadsworth-Emmons reaction.

Description

PROCESS FOR THE PREPARATION OF SOLID BASIC CATALYSTS FOR THE REACTION OF WADWORTH-E MONS

The present invention relates to solid basic catalysts useful in particular for carrying out a heterogeneous catalysis of the Wadsworth-Emmons reaction.

By "Wadsworth-Emmons reaction" is meant, within the meaning of the present invention, a condensation reaction using (i) a carbonyl compound (aldehyde or ketone) and (ii) a phosphonic ester specifically having a labile hydrogen in α of the phosphoryl function, and whose global balance equation is generally written in the following form:

- OH (I)

(where Ri, R ₂ , Ai, A ₂ , R ₃ , and R ₄ represent any substituents, preferably not capable of leading to reactions entering into competition with the balance reaction above).

Insofar as it leads to the formation of a carbon-carbon double bond by the action of a phosphorus compound on a carbonyl compound, the Wadsworth-Emmons reaction is very analogous to the so-called Wittig reaction (condensation of a compound carbonyl and a phosphorus ylide). By abuse of language, the Wadsworth-Emmons reaction is therefore sometimes unduly designated by certain authors as a "Wittig reaction". In the present description, to avoid any confusion, the term "Wittig reaction" will be used exclusively to designate the specific condensation of a carbonyl compound and a phosphorus ylide. On this subject, it should also be emphasized that the Wadsworth-Emmons reaction is clearly to be distinguished from the Wittig reaction: it in fact constitutes an alternative to this reaction, which is generally implemented when the radical R ₃ or the radical R ₄ is a carbanion stabilizing group, of the -COOR or -CN type for example. In this case, in fact, the Wittig reaction is inhibited due to the excessive stabilization of the corresponding ylide. On this subject, we can in particular refer to Advanced Organic Chemistry - Carey Sundberg - 3 ^rd Edition - pp. 95-103 (1997) and Organic Chemistry - Allinger et al. - 10 ^th draw - p. 902 (1994).

The Wadsworth-Emmons reaction finds numerous applications in fine chemistry and in pharmacy, in particular for the preparation of nitriles or unsaturated ketones. Thus, it is for example used for the synthesis of compounds of interest in perfumery, or even for the preparation of carotenoids or certain drugs. In this regard, reference may in particular be made to US patents 5,382,732, US 4,066,692, US 5,028,615 or US 5,654,488.

The Wadsworth-Emmons reaction is generally carried out in the presence of a strong liquid base of the type of NaOH, BuLi or NaH solutions, described in particular in the articles by Hϋnig et al. in Tetrahedron Letters, vol. 36, p. 3151 (1974), of Deschamps et al. in Tetrahedron Letters, vol. 13, p. 1137 (1977) or also of Ando et al. in Tetrahedron Letters, vol. 36, pp 4105-4108 (1995).

In the context of the use of this type of base, the general mechanism of the reaction is as follows:

(1) formation of the carbanion corresponding to the phosphonic ester:

O O

A ₁ A ₂ P— CHR ₃ R4 + BM ^"1 -» ^• 6 (A ^ PC R ₃ R ₄ ) M ⁺ + BH (H.1)

(2) reaction of the carbanion with the carbonyl compound

(3) hydrolysis of the adduct obtained:

+ R ₁ R ₂ C = CR ₃ R ₄ + M ⁺ OH- (II.3)

Step (3) of obtaining the olefin is generally followed by neutralization of M ⁺ OH ^" , which leads to the formation of a corresponding salt.

In the mechanism described above, the strong liquid bases used are consumed irreversibly during step (1). Therefore, they are generally used at least in stoichiometric proportions. Thus, in the article by Ando et al. for example (see above), a NaH solution is used as basic compound at a rate of 0.65 millimoles of NaH per 0.5 millimoles of phosphonic ester and 0.55 millimoles of aldehyde.

Because of this basic quantitative use, the conventional methods of condensing a carbonyl compound and a phosphonic ester lead to a significant production of salts which it is necessary to eliminate during the purification of the products. In addition, as has been pointed out in particular in US Pat. No. 5,292,973, it should be noted that the presence of these salts makes the final step of separation of the products of the reaction extremely difficult to carry out, and all particularly on an industrial scale.

Furthermore, these processes induce a large quantity of saline effluents which, because of their impact on the environment, require subsequent treatments, which in particular induces high operating costs.

In order to avoid the problems associated with the use of strong liquid bases, numerous efforts have therefore been made in recent years to replace conventional strong liquid bases with solid compounds having a strong basic character.

Among these solid basic compounds proposed to replace the usual liquid bases in the Wadsworth-Emmons reaction, there may be mentioned in particular alumina, potassium fluoride KF impregnated on alumina, or barium hydroxide Ba (OH) ₂ . In this regard, reference may in particular be made to the article by Texier-Boullet et al. in Tetrahedron, vol. 44, p.1259 (1985) and to the publications of Sinistierra et al. in Synthesis p.1057 (1985), in Tetrahedron, vol.44, p.1431 (1988) or in the Journal of Catalysis, vol.112, p. 528 (1988).

With regard to this type of heterogeneous solid bases, one of the important parameters to be controlled is that of the porosity of the solids used. Indeed, the pore size of the solids used must be large enough to avoid inhibition of the carbanion formation reaction, in particular due to the phenomena of diffusion of chemical species on the surface of the solid.

However, once this porosity parameter has been controlled, the solid bases prove to be interesting and effective. Indeed, they first of all make it possible to avoid the formation of salts observed above, insofar as the compound of the M ⁺ OH ^"type is then obtained in the solid state and, is therefore able to be extracted without that an additional neutralization step is not necessary.

In addition, the use of these solid bases has the following advantages:

^"During the reaction, corrosion of the reactor due to the presence of a basic compound decreases due to the location of the basicity of the solid, thereby improving the safety conditions,

• at the end of the reaction, the separation of the products is carried out more easily, which results in particular in reduced operating costs.

However, it should be stressed that, although these solid bases effectively replace the usual liquid bases by avoiding the problems associated with the production of saline effluents while inducing relatively acceptable yields, the fact remains that , in the same way as liquid bases, these solid bases are used in stoichiometric proportions, insofar as they are also consumed irreversibly during the initial stage of formation of the carbanion corresponding to the phosphonic ester. In other words, the base used in the processes for condensing a carbonyl compound and a phosphonic ester described in the state of the art is always used, whether it is liquid or not, at reagent title not regenerated during the process.

Now, the inventors have now discovered that by thermally treating certain mixed hydroxides based (1 °) on magnesium and (2 °) on a lanthanide, it is possible, subject to adapting the conditions of the heat treatment, to synthesize solids with a basic character having the surprising characteristic of not being irreversibly consumed when they are engaged in a Wadsworth-Emmons reaction, which makes it possible to envisage their use in a catalytic amount in this reaction.

In this context, the inventors have moreover demonstrated that, unexpectedly, these solids, which nevertheless have a basic character clearly less marked than the heterogeneous catalysts proposed in the state of the art, prove to be particularly effective in terms of yield for the Wadsworth-Emmons reaction. The inventors' work has also made it possible to show that, in the specific context of the use of aldolisable (or ketolisable) carbonyl compounds, the use of these particular solids makes it possible to almost completely inhibit the parasitic reaction of aldolization (or ketolization). This selectivity of the catalyst for the Wadworth-Emmons reaction is particularly marked with regard to the Aldoliddes compounds.

On the basis of these discoveries, the present invention aims to provide a process for the preparation of basic solids capable of ensuring the role of heterogeneous catalyst for the Wadsworth-Emmons reaction.

Another object of the invention is to provide new solid basic catalysts obtained by this process. Another object of the invention is to provide a process for the condensation of carbonyl compounds and phosphonic esters according to the Wadsworth-Emmons reaction, which has a high yield and makes it possible to comply with pollution standards, using a solid as a basic compound, used in very small quantities.

Thus, according to a first aspect, the subject of the present invention is a process for preparing a solid basic catalyst, in particular useful for the Wadsworth-Emmons reaction, said process comprising a step of heat treatment of a mixed magnesium hydroxide and of a metal M of the rare earth family, in which the Mg / M molar ratio of the overall amount of magnesium present, relative to the overall amount of metal M present, is between 1.5 and 5. Said treatment thermal consisting in bringing said mixed hydroxide to a temperature at least equal to 500 ° C. and at most equal to 1000 ° C.

By “rare earths” is meant, within the meaning of the present description, all of the metallic elements comprising rytterbium and the metals characterized by an atomic number included inclusively between 57 and 71, namely the metals, designated by the term generic of "lanthanides", which range from lanthanum to lutetium in the periodic table.

The heat treatment implemented according to the method of the invention can be carried out by any means known to those skilled in the art, subject to respecting the aforementioned temperature conditions. Thus, this heat treatment can for example be carried out by means of an oven. This heat treatment is generally carried out in air or under nitrogen. More generally, the heat treatment implemented according to the invention can also be carried out under any type of atmosphere which is not capable of reacting with the mixed starting hydroxide or with the catalyst obtained at the end of the heat treatment, and especially under an atmosphere of inert gas such as argon. Preferably, this heat treatment is carried out under an atmosphere having the lowest possible CO ₂ concentration, and advantageously under an atmosphere substantially free of CO ₂ . Following the heat treatment, it is generally preferred that the catalyst obtained is kept far from any source of C0 ₂ , so as to avoid carbonation which would affect the efficiency of the catalyst. Thus, the catalyst obtained at the end of the heat treatment is generally maintained under an atmosphere that is substantially (or even completely) free of CO ₂ , most often from the time when it is cooled following the heat treatment. It is also advantageous to store the catalyst obtained at the end of the heat treatment under a nitrogen atmosphere, under an argon atmosphere or even under vacuum, before its use.

Preferably, the heat treatment implemented in the process of the invention is carried out so as to bring the mixed hydroxide to a temperature at least equal to 550 ° C, and more advantageously to a temperature at least equal to 600 ° vs. On the other hand, in particular so as to obtain a catalyst having a sufficiently high specific surface at the end of the process of the invention, it is often advantageous, during the heat treatment step, for the mixed hydroxide to be subjected at a temperature less than or equal to 800 ° C, preferably at a temperature less than or equal to 750 ° C, and even more advantageously at a temperature less than 700 ° C. Thus, it is typically preferred that, during the heat treatment of the process of the invention, the mixed hydroxide is brought to a temperature between 625 ° C and 675 ° C, and advantageously to a temperature between 640 ° C and 660 ° C, the temperature of the heat treatment being particularly preferably equal to 650 ° C.

By “mixed hydroxide of magnesium and of a metal M” is meant, within the meaning of the present description, any compound comprising, among other possible constituents, cations Mg ²⁺ , cations of said metal M, and hydroxide ions OH ^" . The mixed hydroxides used according to the invention may optionally include other cations, such as Al ³⁺ , N ²⁺ or K ⁺ cations, or other anions such as CO ₃ ² anions ^" , O ^{2 "} _, NO ₃ ^" or CI ^" . Thus, the mixed hydroxides used according to the invention can thus be, for example, solids having a single phase consisting of a double magnesium hydroxide and said metal M. However, so preferential, a mixed hydroxide of magnesium and of a metal M designates, within the meaning of the invention, a solid having two distinct phases, namely: - a phase based on hydroxide ions and Mg ²⁺ cations, which is most often a phase of magnesium hydroxide Mg (OH) ₂ , generally of the brucite type; and

a phase based on cations of the metal M, and optionally of hydroxide ions, which may for example be a phase of oxycarbonate of the metal M, of hydroxide of the metal M, or alternatively a phase of oxy-hydroxide of the metal Mr.

When present, these two distinct phases can in particular be highlighted by the appearance of characteristic peaks on a diffractogram obtained by X-ray diffraction on a dried sample of the mixed hydroxide.

Advantageously, when the mixed hydroxide used according to the invention comprises several phases, it is preferred that these phases are nested as intimately as possible with each other.

Whatever the exact structure of the mixed hydroxide used according to the invention, within this mixed hydroxide, the Mg / M molar ratio of the overall amount of magnesium present, relative to the overall amount of metal M present, is between 1, 5 and 5. Advantageously, this ratio is greater than or equal to 2, more preferably greater than or equal to 3, and even more preferably greater than or equal to 3.5. Furthermore, it is generally preferred that this Mg / M molar ratio be less than or equal to 4.5. Thus, this Mg / M molar ratio can typically be between 3.8 and 4.2, preferably between 3.9 and 4.1, and it is advantageously equal to 4.

The mixed hydroxides most advantageously used according to the process of the invention are obtained by a process called "co-precipitation in basic medium", consisting in carrying out the joint precipitation of a phase based on magnesium hydroxide and of a phase based on hydroxide or oxy-hydroxide of metal M, from Mg ²⁺ ions and cations of said metal M, in an aqueous or hydro-alcoholic medium brought to a value of pH suitable for carrying out this joint precipitation, ie generally a pH value (designated by the term "pH of co- precipitation ") between 8 and 11, preferably between 9 and 10.5, and advantageously between 9.8 and 10.2.

In the context of such co-precipitation in basic medium, in particular so as to obtain a mixed hydroxide as homogeneous as possible, it is generally advantageously to introduce the ions Mg ²⁺ and the cations of the metal M progressively within a reactor, preferably in the form of an aqueous solution of nitrates, and / or chlorides of magnesium and of metal M, while jointly adding a basic solution, in particular an aqueous or hydro-alcoholic solution based on soda, of potassium hydroxide, ammonia and / or potassium carbonate (typically an aqueous solution of potassium hydroxide and potassium carbonate), so as to maintain the pH of the medium in the aforementioned pH range, and advantageously by maintaining the pH of the medium at a substantially constant value throughout the duration of the co-precipitation, that is to say generally by maintaining the pH of the co-precipitation at a value not deviating from 0.2 in more or less than a vale ur average pH advantageously between 9 and 10.5, and generally equal to 10. Maintaining the co-precipitation pH at a substantially constant value throughout the duration of the addition can be carried out by any means known to the skilled in the art. Thus, one can for example use an automated administration system of the basic solution, such as for example a valve delivering the basic solution, said valve being connected to a pH probe immersed in the medium which controls the opening and closing of the valve as a function of the pH of the medium, for example by opening said valve only when the measured pH is lower than the pH value which it is desired to set for the medium.

In a co-precipitation in basic medium as defined above, whatever the pH conditions used, the Mg ²⁺ ions and the metal cations M are generally introduced in quantities such as the overall molar ratio Mg / M of the total quantity of cation Mg ²⁺ introduced relative to the total quantity of cations of the metal M introduced is substantially equal to the molar ratio which it is desired to obtain for the mixed hydroxide synthesized, that is to say generally between 1 , 5 and 6, advantageously between 3 and 5, preferably between 3.5 and 4.5, typically between 3.8 and 4.2, this ratio being advantageously equal to 4. In fact, it can be seen that, under the aforementioned pH conditions, almost all of the cations engaged in the co-precipitation reaction are integrated into the synthesized mixed hydroxide. Advantageously, the co-precipitation reaction takes place at room temperature, preferably between 15 and 30 ° C, and it is advantageous to subject the solid obtained to temperature ripening, generally between 45 and 75 ° C, and preferably between 50 and 60 ° C (typically at 55 ° C), for a period advantageously between 1 and 25 hours, and preferably between 10 and 20 hours (typically between 15 and 18 hours).

According to a particular variant, the co-precipitation in basic medium can be carried out in the presence of Al ³⁺ ions, the Al / Mg ratio of the amount of Al ³⁺ cations used relative to the amount of Mg ²⁺ cations used then preferably less than 1: 3, and advantageously between 1: 4 and 1: 2. Without wishing to be linked in any way to a particular theory, it seems to be possible to suggest that the presence of aluminum makes it possible to stabilize the structure during the subsequent heat treatment step.

Preferably, the metal M is chosen from lanthanum, Pytterbium, neodymium, cerium or europium. In particular in this case the heat treatment is preferably carried out so as to bring said mixed hydroxide to a temperature at least equal to 600 ° C., this temperature advantageously being less than or equal to 700 ° C. Typically, the heat treatment of the process of the invention consists in bringing said mixed hydroxide to a temperature between 625 and 675 ° C, preferably between 640 and 660 ° C.

Whatever the exact nature of the metal M, the solid basic catalyst obtained at the end of the process of the invention generally has a BET specific surface greater than or equal to 30 m ² / g, and, in a diffraction diagram by X-rays, this solid has the peaks characteristic of a phase based on a magnesium oxide and the peaks characteristic of a phase based on a metal oxide M. The solid basic catalysts obtained according to the process of the invention which have a BET specific surface greater than or equal to 30 m ² / g, and which has, in an X-ray diffraction diagram, the peaks characteristic of a phase to based on a magnesium oxide and the peaks characteristic of a phase based on an oxide of the metal M of the rare earth family, constitutes another particular object of the present invention.

The solid basic catalysts obtained according to the process of the present invention may have a BET specific surface greater than or equal to 35 m ² / g, or even greater than 40 m ² / g, and even greater than 50 m ² / g, this specific surface generally being less or equal to 150m ² / g. This BET specific surface is generally between 30m ² / g and 60m ² / g.

Whatever the nature of the metal M, the Mg / M molar ratio in the catalyst obtained is generally substantially identical, and most often identical, to the Mg / M molar ratio which characterizes the mixed hydroxide subjected to the heat treatment. Thus, within the solid basic catalysts obtained according to the invention, the Mg / M molar ratio is generally between 1, 5 and 5, and more preferably between 2 and 4.

As pointed out, the solid basic catalysts obtained according to the process of the invention are particularly suitable for carrying out the heterogeneous catalysis of a condensation reaction of a carbonyl compound and of a phosphonic ester according to the Wadsworth reaction. Emmons. The use of solid basic catalysts obtained according to the process defined above as a heterogeneous catalyst for this reaction constitutes another object of the present invention.

The use of a catalyst obtained according to the process of the invention has multiple advantages in the context of a Wadsworth-Emmons reaction.

Indeed, in addition to the fact that it makes it possible, in the general case, to initiate a Wadsworth-Emmons reaction with high efficiency, this catalyst also has, because of its solid character, all the advantages solid bases used in the prior art. Thus, it does not in particular lead to the formation of salts observed during the use of liquid bases, which makes it possible both to avoid the problems linked to the industrial production of saline effluents and to facilitate the purification step reaction products.

In addition, the inventors have demonstrated that, in the case where the carbonyl compound used is aldolisable or ketolisable (that is to say when it has on the same carbon atom two hydrogen atoms in the alpha position of carbonyl function), the use of the catalysts obtained according to the process of the invention makes it possible to significantly inhibit the parasitic reaction of aldolization or ketolization which is observed during the use of other known bases. state of the art. This selectivity is particularly clear in the case of aldolisable carbonyl compounds.

In addition, the solid catalysts obtained according to the process of the invention above all have the particularity of being able to be used in a catalytic amount in the condensation reaction of a carbonyl compound and a phosphonic ester. Indeed, these solids have a particular basic character, both strong enough to deprotonate the phosphonic ester in α of the phosphoryl function, but also weak enough for their protonation to be reversible, which constitutes two essential conditions for carrying out a catalysis. basic of the Wadsworth-Emmons reaction. Thus, in the context of the catalysis of a Wadsworth-Emmons reaction, the solid basic catalysts obtained according to the process of the invention can be used in a very small amount compared to the reagents used. Thus, the catalysts of the invention are generally used at a rate of 10 to 100 grams per mole of carbonyl compound, advantageously at a rate of 15 to 80 grams per mole of carbonyl compound, and even more preferably at a rate of 20 to 60 grams per mole of carbonyl compound. In general, the amount of catalyst used is such that the molar ratio of the metal M introduced relative to the amount of carbonyl compound used, is between 0.01 and 0.25, this molar ratio being advantageously less than or equal to 0.15, and preferably less than or equal to 0.10. In general, the use of the solid basic catalysts obtained according to the process of the present invention is implemented within the framework of a process for the preparation of an olefin by condensation of a carbonyl compound and of a phosphonic ester according to the Wadsworth-Emmons reaction, said method comprising the steps of:

(a) reacting said carbonyl compound and said phosphonic ester, in the presence of said solid basic catalyst, preferably in the absence of CO ₂ , and preferably in the absence of water; and

(b) subjecting, after reaction, the reaction mixture to a hydrolysis reaction.

It should be emphasized that the solid basic catalyst used according to this process has the important advantage of being able to be separated from the reaction medium before the hydrolysis step (b), which in particular has the consequence, on the one hand, of facilitating the 'final step of product purification and, on the other hand, to allow to consider the recycling of the catalyst.

It should be emphasized that this possibility of extracting the catalyst before the hydrolysis step is not only due to its solid nature. Indeed, this separation is impossible in the case of most of the other solid bases generally used in the Wadsworth-Emmons reaction, insofar as these bases, even solid, complex the adduct formed at the end of l 'step (a). On the other hand, in the case of the specific solid catalysts used according to the invention, the specific process of regeneration of the base leads to a separation between the adduct and the catalyst, which makes it possible to envisage the separation before step (b ).

Given this possibility, the catalyst is advantageously separated from the reaction medium before step (b), for example by filtration of the reaction medium, whereby the phosphonic acid formed during the hydrolysis of step is avoided. (b) irreversibly poisons the surface of the catalyst. The separated catalyst can then be subjected to recycling, to be reused later, in particular in a condensation reaction of a carbonyl compound and a phosphonic ester. This recycling is then generally carried out by washing the catalyst separated from the reaction medium (advantageously followed by possible drying), then by a heat treatment of the solid obtained at the end of the washing, at a temperature generally between 500 and 700 °. C, preferably at a temperature above 600 ° C, and typically between 625 ° C and 675 ° C, this heat treatment is preferably carried out by gradually bringing the catalyst to the temperature for implementing the process (or stages of washing and / or drying) at the heat treatment temperature, generally according to a temperature rise profile of 20 to 200 ° C per hour, preferably between 40 and 100 ° C per hour, typically at a rate of

50 ° C per hour.

Again, it is preferred that after the heat treatment, the recycled catalyst obtained is maintained in an atmosphere substantially (or even completely) free of CO ₂ , in particular under nitrogen or argon, before its subsequent use.

The catalyst obtained at the end of such recycling generally has an activity similar or identical to that of the initial catalyst, especially under the above-mentioned preferential conditions of implementation, the average number of recyclings that can be envisaged for a catalyst according to the invention before a significant loss of activity is generally at least equal to 10, and most often at least equal to 20.

The various characteristics of the present invention, as well as its multiple advantages, will appear even more clearly in the light of the various examples of implementation set out below. Example 1: Preparation of a “MgLaO” type catalyst according to the invention

An aqueous solution (S) was prepared by adding to 520 ml of deionized water: - 68 g (or 0.386 mole) of magnesium nitrate hexahydrate

Mg (NO ₃₎ _2, 6H2O; and

- 42 g (or 0.129 mole) of hydrated lanthanum nitrate sold by the company Aldrich under the formula La (N0 ₃ ) ₃ , xH2O, (x = 3-5).

In parallel, an aqueous solution (Sb) was produced by adding to 520 ml of deionized water:

- 58.8 g (or 1.05 mole) of potassium hydroxide KOH; and

- 36.2 g (or 0.262 mole) of potassium carbonate K ₂ CO ₃ .

The solution (S) was then introduced, at a temperature of 25 ° C., into a reactor consisting of a flask comprising, at the start of the addition, 500 ml of deionized water. The addition of solution (S) was carried out with a constant flow rate of 230 ml per hour, while maintaining the contents of the flask with stirring. Throughout the duration of the addition of the solution (S), the pH of the medium was kept constantly equal to 10 (to within +/- 0.1 pH unit) by an automated addition system of aqueous solution ( Sb) making it possible to continuously compensate for the decrease in pH linked to the introduction of the solution (S). The formation of a precipitate was observed.

Once all of the solution (S) introduced into the medium at a controlled pH of 10, the medium obtained was brought to a temperature of 55 ° C, and was kept at this temperature for 16 hours.

Following this temperature ripening, the medium obtained was centrifuged and the solid obtained was washed on filter with 5 times 500 ml of distilled water.

Part of the solid obtained was dried under nitrogen at 120 ° C for a period of 17 hours, whereby a solid was obtained having a residual dry matter content of 63% (after heating at 1000 ° C. for 1 hour) and containing, by mass relative to the total mass of the dry matter, 29.7% of magnesium, 39.9% of lanthanum, and 5.4% potassium. A part of this solid was then subjected to an analysis by X-ray diffraction. The diffractogram obtained shows the peaks characteristic of a brucite phase Mg (OH) ₂ , as well as the peaks characteristic of a lanthanum oxycarbonate phase La2θ (COs) ₂ - These peaks were identified by reference to diffractograms established for standard samples of brucite and lanthanum oxycarbonate phases. Given the widening observed for the diffraction lines, it has been determined that the lanthanum-based phase in the solid is in the form of crystallites of sizes between 30 and 40 nanometers.

Furthermore, 1 g of the solid obtained after centrifugation and washing was subjected to a heat treatment at 650 ° C. in air for a period of 4 hours. 0.65 g of a so-called "LaMgO" catalyst was then obtained which was allowed to cool to ambient temperature (20 ° C.) under an atmosphere of dry nitrogen. The solid "LaMgO" obtained was then kept under dry nitrogen.

The synthesized "LaMgO" solid has a BET specific surface area equal to 37.6 m ² / g. It is in the form of a porous solid where the size of the pores is between 6 and 13 nanometers.

Example 2: Use of a catalyst of “LaMgO” type according to the invention as heterogeneous basic catalyst of Wadsworth-Emmons reactions.

The catalyst "LaMgO" obtained in Example 1 was used in various condensation reactions of carbonyl compounds with ethyl cyanophosphate NCCH ₂ P (0) (OEt) ₂ , according to the reaction of

Wadsworth-Emmons. In these different reactions, the condensation reaction was carried out under the following conditions: - 2 millimoles of the carbonyl compound and 2 millimoles of the phosphonic ester were dissolved in 15 ml of dimethylformamide (DMF);

the mixture obtained was brought to 110 ° C. after stabilization of the temperature of the medium at 110 ° C., 0.05 g of the catalyst "LaMgO from Example 1 was added (maintained under dry nitrogen since it was obtained so as to avoid carbonation in air);

- the medium was then maintained at 110 ° C; during a reaction time (t) variable according to the tests. At the end of the reaction, the yield of the reaction was calculated, expressed by the molar ratio of the quantity of product obtained, compared to the quantity of carbonyl compound used in the reaction.

The results obtained are collated in table (I) below:

Table (I): Wadsworth-Emmons condensations catalyzed by the catalyst "LaMgO" of Example 1. (Phosphonic ester NCCH ₂ P (0) (OEt) ₂ ).

Example 3: Use of a “LaMgO” type catalyst according to the invention, as heterogeneous basic catalyst of Wadsworth-Emmons reactions.

The catalyst "LaMgO" obtained in Example 1 was used in various condensation reactions of carbonyl compounds with ethyl phosphonoacetate EtOCOCH ₂ P (O) (Oet) 2, according to the Wadsworth-Emmons reaction. In these different reactions, the condensation reaction was carried out under the following conditions:

- 2 millimoles of the carbonyl compound and 2 millimoles of the phosphonic ester were dissolved in 15 ml of dimethylformamide (DMF). the mixture obtained was brought to 110 ° C. after stabilization of the temperature of the medium at 110 ° C., 0.1 g of the "LaMgO" catalyst of Example 1 was added (maintained under dry nitrogen since its obtaining, so as to avoid carbonation in air);

- The medium was then kept at 110 ° C for a reaction time (t) variable according to the tests. At the end of the reaction, the yield of the reaction was calculated, expressed by the molar ratio of the quantity of product obtained, compared to the quantity of carbonyl compound used in the reaction.

Table (II): Wadsworth-Emmons condensation catalyzed by the “LaMgO” catalyst of Example 1 (Phosphonic ester: EtOCOCH ₂ P (0) (OEt) ₂ )

Claims

1- Process for the preparation of a solid basic catalyst, comprising a step of heat treatment of a mixed magnesium hydroxide and of a metal M of the rare earth family in which the molar ratio Mg / M of the overall amount of magnesium present, relative to the overall amount of metal M present, is between 1, 5 and 5, said heat treatment consisting in bringing said mixed hydroxide to a temperature at least equal to 500 ° C. and at most equal to 1000 ° C. .

2- A method according to claim 1, characterized in that the temperature to which said mixed hydroxide is brought during the heat treatment is greater than or equal to 550 ° C.

3- A method according to claim 1, characterized in that the temperature to which said mixed hydroxide is brought during the heat treatment is less than or equal to 800 ° C.

4- A method according to any one of claims 1 to 3, characterized in that, following the heat treatment, the solid basic catalyst obtained is maintained under an atmosphere substantially free of CO ₂ .

5- Method according to any one of claims 1 to 4, characterized in that the mixed hydroxide subjected to the heat treatment is a solid having two distinct phases, namely:

- a phase based on hydroxide ions and Mg ²⁺ cations; and

- a phase based on metal cations M.

6- A method according to any one of claims 1 to 5, characterized in that the mixed hydroxide of magnesium and metal M which is subjected to the heat treatment is obtained according to a process of co-precipitation in basic medium, consisting in carrying out the joint precipitation of a phase based on magnesium hydroxide and a phase based of hydroxide or oxy-hydroxide of metal M, from Mg ²⁺ ions and cations of said metal M, in an aqueous or hydro-alcoholic medium, brought to a pH value of between 8 and 11.

7- A method according to any one of claims 1 to 6 characterized in that the metal M denotes lanthanum, ytterbium, neodymium, cerium or europium.

8- A method according to any one of claims 1 to 7, characterized in that the heat treatment consists in bringing the mixed magnesium hydroxide and metal M to a temperature between 600 ° C and 700 ° C.

9- Solid basic catalyst having a BET specific surface greater than 30 m ² / g and having, in an X-ray diffraction diagram, the characteristic peaks of a phase based on a magnesium oxide and the characteristic peaks d '' a phase based on an oxide of a metal M from the rare earth family, in which the Mg / Al molar ratio is between 1, 5 and 5, said catalyst being capable of being obtained according to one any of claims 10 to 12.

10- solid basic catalyst according to claim 9, characterized in that it has a BET specific surface greater than or equal to 35 m ² / g.

11- Use of a solid basic catalyst capable of being obtained according to one of claims 1 to 8, or of a catalyst according to any one of claims 9 or 10, for carrying out a heterogeneous catalysis of the condensation of a carbonyl compound and a phosphonic ester according to the Wadsworth-Emmons reaction.

12- Use according to claim 11, characterized in that the carbonyl compound used in the Wadsworth-Emmons reaction is an aldolisable or ketolisable carbonyl compound.

13- Use according to claim 12 wherein the carbonyl compound is aldolisable.

14- Use according to one of claims 11 to 13, characterized in that said catalyst is used in an amount of 0.01 to 0.25 molar equivalent relative to the carbonyl compound used.

15- Process for the preparation of an olefin by condensation of a carbonyl compound and of a phosphonic ester according to the Wadsworth-Emmons reaction, using a solid basic catalyst capable of being obtained according to the process of one of the claims 1 to 8, or a catalyst according to any one of claims 9 or 10, said process comprising the steps consisting in:

(a) reacting said carbonyl compound and said phosphonic ester, in the presence of said basic catalyst; and

(b) subjecting, after reaction, the reaction mixture to a hydrolysis reaction.

16- Method according to claim 15, characterized in that the catalyst is separated from the reaction medium before step (b), and in that said catalyst is subjected to recycling, to be reused later in a condensation reaction of a carbonyl compound and a phosphonic ester.