PROCESS AND CATALYSTS FOR THE SELECTIVE PRODUCTION OF ALPHA-ALKYLCINNAMALDEHYDE

Abstract: The selective obtainment of α-alkyl cinnamaldehydes, such as Jasmine aldehyde is carried out by a process that involves two consecutive reactions: acetalization of an n-alkyl aldehyde by direct reaction with an alcohol or by transacetalization followed by the reaction between said acetal and aromatic aldehyde such as benzaldehyde using molecular sieves with regular pore distribution in the range of micro and mesopores and between 6 and 100 Å as acid catalysts.

Description: The present invention describes the preparation of α-alkyl cinnamaldehydes and preferably, the preparation of α-n-amylcinnamaldehyde (Jasmine aldehyde), by aldolic condensation catalyzed by acid zeolite type solids, zeotypes and molecular sieves. α-n-amylcinnamadehyde is a substance with a violet scent and it is commonly used in perfumery. The production of α-n-amylcinnamaldehyde can be carried out by aldolic condensation of heptanal and benzaldehyde using alkaline catalysts. A difficulty with aldol condensation is that both reagents can undergo side reactions giving rise to by-products that reduce the yield of alkyl cinnamaldehyde and that furthermore can confer an unpleasant scent, thus reducing the quality of the perfume. One of these undesired reactions is self-condensation of n-alkyl aldehyde, which can be inhibited to a great extent, by keeping the concentration of this reagent relative to that of the benzaldehyde in the reaction mixture very low. Therefore, this methodology requires long addition times of heptanal, leading to the use of batch reactions with long reaction times and renders impractical the use of plug-flow continuous reactors. Further by-products that are formed in these conditions are those resulting from the limited stability of benzaldehyde which tends to disproportionate via the Cannizzaro reaction to yield benzyl alcohol and benzoic acid, which in turn reacts with the alkaline catalyst, and therefore, causes neutralization of the catalyst. A. Weissenborn in DD-A-11,191 (1956) describes a process for the preparation of Jasmine aldehyde wherein the catalysts are Ni, Co or Fe salts of carboxylic acids. The reaction is carried out in the temperature range of 180-190ºC, in the presence of toluene in order to facilitate azeotropic distillation of the water and the heptanal is added slowly to the reaction mixture. Yields around 80% of Jasmine aldehyde are obtained. R. Mahrwald and H. Schick DD-A-287,712 (1991), describe a procedure wherein the aldolic condensation between heptanal and benzaldehyde is accomplished in the presence of titanium compounds (tetraisopropyltitanium) and toluene as the azeotropic agent. Yields around 56% of Jasmine aldehyde are obtained. L.S. Payne in EP-A-392,579 (1990), describes a procedure for the selective preparation of α-cinnamaldehydes by aldolic condensation in two phases, using glycols (especially ethylene glycol) as solvents and sodium or potassium hydroxides as catalysts. Yields around 90% of α-cinnamaldehyde are obtained. P. Mastagli et al. in Bull. Soc. Chim. France, 1955, p. 268, describe the preparation of Jasmine aldehyde using anionic exchange resins (IR-4B) as catalysts. The yields obtained varied between 2 and 12%. The same author describes in Compt. Rend. 1957 vol. 244, p. 207, a process starting from n-alkyl aldehyde and benzaldehyde acetals using as a catalyst a mixture of an acid catalyst (cationic exchange resin) and a basic catalyst (anionic exchange resin) in order to produce the hydrolysis and aldolic condensation respectively. The yields obtained varied between 5 and 28%. A. Sakar et al. in Ind. J. Chem., 1986, vol. 25,p. 656 accomplish aldolic condensation using potassium carbonate and a phase transfer catalyst such as benzyltriethylammonium chloride. On the other hand, D. Abenhaim et al in Synthetic Comm., 1994, vol. 24, p. 1199 carry out condensation using the same type of catalysts but under microwave effect. In both cases yields around 80% of Jasmine aldehyde are obtained. This invention refers to the selective preparation of α-alkyl cinnamaldehydes and specifically, Jasmine aldehyde, by direct reaction between the acetal of n-alkyl aldehyde (heptanal) and benzaldehyde whereby an acid form of a zeolite, zeotype or a molecular sieve, is used as an acid catalyst, the molecular sieve having a regular pore size distribution between 6 and 100Å. The process involves a first acetalization step which is carried out directly with an alcohol or by transacetalization using trialkyl orthoformate (TOF) in the presence of the above-mentioned catalysts. The second step involves the elimination of the remaining alcohol or TOF by distillation and addition of benzaldehyde. The acid catalysts cause consecutive slow hydrolysis of the acetal and mixed aldolic condensation, maintaining at all times a low concentration of the n-alkylaldhyde with respect to the benzaldehyde, whereby the α-alkyl cinnamaldehydes are obtained with high yields and selectivities. The present invention relates the use of acid zeolites, zeotypes and mesoporous molecular sieves, that in a certain way could be assimilated to zeotype materials, as selective catalysts in the aldolic condensation of acetalizated n-alkyl aldehydes and benzaldehyde, to obtain α-alkyl cinnamaldehydes with yields higher than 80%. The first stage of the process involves the acetalization of the aldehyde which takes place according to conventional procedures in a continuous or discontinuous batch reactor or in a continuous fixed or fluidized bed reactor containing the catalyst. The reaction temperature ranges from 25 to 280ºC. When the transacetalization method is used, the aldehyde and the corresponding trialkyl orthoformate molar ratio is between 1:1 and 1:10 preferably, between 1:2 and 1:5. For the first step of the reaction, the preferred alcohols are methanol, ethanol, propanol, propylene glycol and ethylene glycol. The second step of the reaction, and after distillation of the remaining alcohol or TOF, involves the addition of benzaldehyde to the reaction mixture. The ratio benzaldehyde:n-alkylaldehyde is between 1:1 and 1:10, preferably between 1:1 and 1:5, whereby when the n-alkylaldehyde is heptanal molar ratio benzaldehyde : heptanal is preferably between 1:2 and 1:5. The reaction can be accomplished in an inert atmosphere, such as nitrogen, and at a temperature ranging from 25 to 200ºC, preferably between 50 and 150ºC. The amount of catalyst used is between 2 and 30% based on the weight of the n-alkyl aldehyde acetal which preferably is a RCHO n-alkylaldehyde acetal, wherein R is a linear or branched, saturated or unsaturated chain having between 2 and 20 carbon atoms. When the reaction is carried out in a batch reactor, at the end of the reaction the catalyst is filtered, washed with dichloromethane and the solvent is evaporated. The catalysts used in the present invention are zeolites and zeotypes, preferably with 12 membered rings and molecular sieves, since the geometric constraints, due to the pore size, make it possible to obtain products with high selectivities, from mixed aldolic condensation. The zeolite catalysts that meet the previous specifications are the following (the initials between brackets being accepted by the International Zeolite Associations (see W.M. Meier and D.H. Olson in Atlas of Zeolites Structure Types, 1992) - Mordenite (MOR), Ofretite (OFF), Omega (MAZ), Beta (BEA), Y (FAU), SSZ-24 (AFI), ZSM-12 (AFI) and SSZ-42 New zeolites which combine channels of 10 MR with 12 MR (MCM-22), SSZ-26, SSZ-36, CIT-1 and zeotypes having pore sizes of 20-100 Å such as M41S and MCM-41, (Beck et al. JACS, 114, 10834, (1992)), and amorphous mesoporous silica-alumina (SAM), with pore sizes in a narrow pore range (Bellussi et al.) Stud. Surf. Sci. 84, 93 (1994)) are also applicable. Acid materials being isomorphous to Beta, Y, Mordenite, Omega, MFI, SSZ-24, SSZ-26, SSZ-33, CIT-1, SSZ-42 and MCM-22 zeolites which are substituted by trivalent ions selected from Al, B, Ga and Fe, can also be used. Acid forms of silica-aluminophopshates i.e. SAPO-5, ALPO-8, VPI-5 and SAPO-37, are also suitable for use as acid catalysts. The zeolites preferably have a framework Si/T''' ratio in the range of 6 to 400, more preferably of 10 to 200, whereby T"' refers to the trivalent ions. The catalysts, prior to be used, have to be prepared in their acid form. Preparation of the acid form The preparation of the acid form is accomplished directly by exchange with a mineral acid when this is allowed by the zeolite stability, or if this is not possible, by an indirect method which consists in an exchange of its alkaline and alkaline earth cations by NH 4 + by means of a treatment with an aqueous solution of ammonium chloride followed by calcination, following conventional methods. It can also be prepared by exchange with di- or trivalent ions, followed by thermal treatment at temperatures between 100 and 600ºC during periods of between 30 minutes and 6 hours. On the other hand, the number of acid sites, the distribution of acid strength and the hydrophilic-hydrophobic characteristics of the catalyst can be controlled by varying the Si/Al ratio of the crystalline framework. The Al content of a zeolite can be modified directly during synthesis. When this is not possible post-synthesis dealuminations which mainly consist of the extraction of aluminum from the framework by acid treatment or using a complexing agent such as EDTA, are carried out. Furthermore, if desired, it is possible to introduce silicon at the same time, by a chemical treatment with reactants such as (NH 4 )2F 6 Si or SiCl 4 . Example 1. - Acetalization of heptanal and subsequent condensation with benzaldehyde in the presence of zeolitic catalysts of different structures. Immediately before its use, the catalyst, in an amount equivalent to 10% (1.1 g) of the weight of the heptanal, is activated by heating at 100ºC, under pressure of approximately 0.00133 bar(1mm Hg) for 2 h. Therafter, the system is allowed to cool to room temperature and 11.5 g (0.1 mol) of heptanal dissolved in 150 ml. of methanol are added. The solution is heated at the reflux temperature of methanol during the time necessary to achieve an acetal (1,1-dimethoxyheptane) yield of around 90%. Thereafter, the methanol is evaporated and 10.6 g (0.1 mol) of benzaldehyde) are added. The condensation reaction is carried out under magnetic agitation at 125ºC, in a nitrogen atmosphere for a reaction time between 4 and 16 h. Therafter, the catalyst is filtered and washed repeatedly with dichloromethane. The crude of the reaction is analyzed by gas chromatography-mass spectrometry. The Jasmine aldehyde yield in molar %, for the different catalysts, is: Catalyst Jasmine Aldehyde Yield (%) MCM-41 87 SAM 83 HY 75 Example 2. Acetalization and condensation of benzaldehyde and 1,1-dimethoxyheptane in the presence of MCM-41 catalyst with different benzaldehyde/heptanal molar ratios In the same conditions as those in Example 1, the reaction is carried out in the presence of MCM-41 catalyst with a Si/Al ratio of 14, and using different benzaldehyde/heptanal molar ratios (1:1, 1:3 and 1:5). The results show that the variation in the ratio of the reactants has little influence on the selectivity for jasmine aldehyde, as final yields in the neighborhood of 85% are obtained in all cases. Example 3. Influence of the temperature on the condensation reaction in the presence of MCM-41. In the same conditions as those in Examples 1 and 2, the reaction is carried out in the presence of MCM-41 catalyst with a Si/Al ratio of 14 at different reaction temperatures. The Jasmine aldehyde yield obtained after one hour reaction time is shown in the following table: Temperature (ºC) Jasmine Aldehyde Yield (%) 100 10 125 60 140 70

Claims: A process for the selective preparation of α-alkyl cinnamaldehydes, the process comprising a first step of acetalization of an n-alkyl aldehyde by direct reaction of the aldehyde with an alcohol or transacetalization with trialkyl orthoformate for obtaining n-alkyladehyde acetal, and a second step wherein the acetal and benzaldehyde are subjected to condensation using an acid catalyst, wherein the acid catalyst is an acid form of a molecular sieve, having a regular pore distribution between 6 and 100 Å, an acid form of a microporous silica-aluminophophate, or an acid form of a zeotype material of medium and large pore. A process according to claim 1, characterized in that the molecular sieve is a zeolite selected from the group consisting of Beta, Y, Mordenite, Omega, MFI, SSZ-24, SSZ-26, SSZ-33, CIT-1, SSZ-42, MCM-22 zeolites and isomorphic substitutions thereof with trivalent ions selected from Al, B, Ga, Fe. A process according to claim 2, characterized in that the zeolite has a framework Si/T III ratio in a range of between 6 and 400, wherein T III refers to the trivalent ions selected from Al, B, Ga and Fe. A process according to claims 1, characterized in that the microporous silica-aluminophosphate is selected from the group consisting of SAPO-5, ALPO-8 and VPI-5 and SAPO-37. A process according to claim 1, characterized in that the zeotype material is selected from the group consisting of M41S, MCM-41 and SAM. A process according to claim 1, characterized in that the condensation is carried out at a temperature between 25 and 200ºC, a reaction time between 10 minutes and 24 hours and a molar ratio benzaldehyde:n-alkylaldehyde between 1:1 and 1:10. A process according to claim 1, characterized in that the alcohol used in the acetalization is selected from the group consisting of methanol, ethanol, propanol, ethylene glycol and propylene glycol. A process according to claim 1 or 6, characterized in that in the condensation, the n-alkylaldehyde is a RCHO n-alkylaldehyde, wherein R is a linear or branched, saturated or unsaturated chain having between 2 and 20 carbon atoms. A process according to claim 6, characterized in that the n-alkylaldehyde is heptanal, the reaction time is between 10 minutes and 5 hours, and the molar ratio between benzaldehyde and heptanal is between 1:2 and 1:5. A process according to claim 3, characterized in that the framework Si/T III ratio is between 10 and 200.

Inventors: CLIMENT OLMEDO M JOSE, CORMA CANOS AVELINO, GUIL LOPEZ RUT, IBORRA CHORNET SARA, PRIMO MILLO JAIME, CLIMENT OLMEDO, M JOSE, CORMA CANOS, AVELINO, GUIL LOPEZ, RUT, IBORRA CHORNET, SARA, PRIMO MILLO, JAIME, CLIMENT OLMEDO, M José, CORMA CANOS, Avelino, Instituto Tecnologia Quimica, GUIL LOPEZ, Rut, Instituto Tecnologia Quimica
Applicants: CONSEJO SUPERIOR INVESTIGACION, UNIV VALENCIA POLITECNICA, CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS, UNIVERSIDAD POLITECNICA DE VALENCIA
Application year: 1998
Main classification: C07C45
IPC codes: C07C45, C07C47, C07B61, B01J29