EP0966418A1

EP0966418A1 - Method for producing acetals

Info

Publication number: EP0966418A1
Application number: EP98916896A
Authority: EP
Inventors: Jürgen KANAND; Rocco Paciello; Michael Röper
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1997-03-17
Filing date: 1998-03-06
Publication date: 1999-12-29
Also published as: CA2284521A1; TW391955B; WO1998041493A1; AU7032298A; DE19710993A1

Abstract

The invention relates to a method for producing acetals by reacting allyl ethers with alcohols. According to said method, an allyl ether is reacted with an alcohol in liquid phase in the presence of a homogenous catalyst from an organometallic compound of an element from group VIA and/or VIIIA of the periodic table of elements or in the presence of a heterogeneous catalyst containing one or more elements from the groups IA, VIA, VIIA and/or VIIIA of the periodic table of elements in essentially water-free conditions.

Description

Process for the production of acetals

description

The present invention relates to a process for the preparation of acetals by reacting an allyl ether with an alcohol.

Acetals are widely used in industry, for example as starting materials for the preparation of the corresponding aldehydes by the hydrolysis of the acetal or as reagents for the production of acetals from aldehydes or ketones by transacetalization. In perfumery, acetals are used as fragrances [see. Fragrances, flavors, cosmetics 27 _. , 71 (1977)].

Acetals are generally prepared from the corresponding aldehydes or ketones by reacting them with an alcohol with acid catalysis [Fragrances, Flavors, Cosmetics 22, 71 (1977)]. In many cases, the aldehydes in question are not available in the desired amounts from natural sources, or the price of the aldehydes obtainable from natural raw materials is so high that it precludes extensive technical utilization of these aldehydes for the various purposes. There is therefore a need for processes which enable the economical production of acetals based on petrochemical raw materials.

US-A 4 788 325 and Chang [J. Organomet. Chem. L, 31 (1995)] describe the reaction of allyl ethers with alcohols in the presence of hydrogen and carbon monoxide with dicobalt octacarbonyl (Co (CO) β) as a catalyst. This is either used directly in the reaction as a catalyst or generated in situ in the reaction mixture by carbonylation of cobalt salts with carbon monoxide under high pressure. Under the reaction conditions, the dicobalt octacarbonyl is converted by the hydrogen into hydridocobalt tetracarbonyl (HCo (CO)), which is the actual catalytically active species. A disadvantage of this process is that the cobalt carbonyl compounds used are relatively volatile and some are discharged with the acetal during the work-up of the product mixture by distillation, which is why it has to be freed of cobalt carbonyls contained therein before it is used further, for example as a fragrance, in an elaborate decobalization step. This process is therefore not economical. US Pat. No. 4,658,069 relates to a process for converting allyl ethers which additionally contain a formyl or carboxy group into the corresponding diacetals, the allyl ether being reacted with an alkanol under anhydrous conditions in a first stage and then in this reaction water formed is removed and in a second stage, the allyl ether acetal obtained in the first stage is converted to a saturated diacetal with the aid of a ruthenium halide catalyst and an alkanol. Iridium, rhodium, osmium, palladium and platinum halides are also mentioned as suitable catalysts. Since these halides of the platinum metals are not sufficiently stable under the reaction conditions and tend to deposit the platinum metal in question on the walls of the reaction apparatus, which leads to losses of the expensive platinum metal, this process is not economical on an industrial scale.

JP-A 25114/1972 relates to a process for the preparation of acetals from allyl ethers by reacting them with an alkanol in the presence of a ruthenium (III) chloride catalyst. In the example of this application, 1-methoxy-2, 7-octadiene is reacted with methanol and using RuCl ₃ under a nitrogen atmosphere to give 1, 1-dirnethoxyoct-7-ene. This process also has the disadvantage of poor catalyst stability.

The present invention was therefore based on the object of finding an economical process for the preparation of acetals from allyl ethers which does not have the disadvantages of the prior art.

Accordingly, a process for the preparation of acetals by the reaction of allyl ethers with alcohols has been found, which is characterized in that an allyl ether with an alcohol in the liquid phase in the presence of a homogeneous catalyst from an organometallic compound of an element from the group VIA and / or VIIIA of the Periodic Table of the elements or in the presence of a heterogeneous catalyst which contains one or more elements from groups VIA, VIIA and / or VIIIA of the Periodensy ^¬ stems of the elements, is reacted under substantially anhydrous conditions.

Suitable starting materials in the process of this invention allyl ^¬ serve ether of the formula I 0 R2

in which R ^{1 is} hydrogen or an organic radical, in particular a cyclic, straight-chain or branched hydrocarbon group having 1 to 17 carbon atoms, preferably 1 to 10 carbon atoms. Examples of such hydrocarbon groups are alkyl groups, C ₃ - to Cι ₇ alkenyl whose double bond is preferably in conjugation with the allylic double bond, aryl groups such as phenyl or naphthyl, C ₃ - to Cβ-cycloalkyl or alkylaryl, or aralkyl groups. Depending on their size, these hydrocarbon groups can be substituted with 1 to 3 substituents which are inert under the reaction conditions, such as ester groups or alkoxy or aryloxy groups. R ¹ is preferably a straight-chain, branched or cyclic alkyl group. The radical R ² in the allyl ether of the formula I is an organic radical having 1 to 20, preferably 1 to 10, carbon atoms. Preferred radicals R ² are hydrocarbon groups, for example a straight-chain or branched C ₁ to C ₀ , preferably C ₁ to C 10 alkyl groups, a C ₃ to C ₈ cycloalkyl group, a C ₃ to C ₂₀ , preferably a C ₃ - To Cι ₂ alkenyl or C ₅ - to Cβ-cycloalkenyl group, where the double bond of these alkenyl groups is preferably not in the α-position to the oxygen atom of the allyl ether, a C ₆ to Cio-aryl group, such as the phenyl or naphthyl group , or a C - to Cn-aralkyl or alkylaryl group. The radical R ² is preferably bonded to the oxygen tom of the allyl ether I via a primary, secondary carbon atom. Particularly preferred radicals R ² are straight-chain or branched alkyl groups or alkenyl groups. Depending on their size, the organic radicals R ² can carry 1 to 2 substituents which are inert under the reaction conditions, for example Cχ ~ to Cιo "alkoxy groups. Depending on its size, the radical R ² can also be substituted with 1 to 2 hydroxyl groups. Preferably carries the radical R ^2, however, has no further substituents.

For illustrative purposes only, some allyl ethers I suitable as starting materials in the process according to the invention are listed below as examples: allyl methyl ether, allyl ethyl ether, allyl n-propyl ether, allyl n-butyl ether, diallyl ether, (but -2-enyl) methyl ether, (but-2-enyl) ethyl ether, (but-2-enyl) -n-propyl ether, (but -2-enyl) -n-butyl ether, di- (but -2 -enyl) ether, (octa-2, 7-dienyl) methyl ether, (octa-2, 7-dienyl) -n-butyl ether, di- (octa-2, 7 -dienyl ) ether, l-butoxydodecatriene-2, 7, 11. In alcohol R ³ OH II, which is used in the process according to the invention for producing acetals III according to reaction equation (1).

this reaction presumably via the isomerization of allyl ether I to an intermediate enol ether IV

0 R ² IV

expires, the radical R ³ can be the same or different from the radical R ² contained in the allyl ether used. Preferably, primary or secondary, more preferably primary alcohols R ³ 0H are used in the inventive method. Tertiary alcohols R ³ 0H can also be used, however, depending on the steric nature of the radical R ² , steric hindrances can occur during the course of the reaction. The alcohol R ³ OH is therefore preferably chosen so that there is no steric hindrance with the radical R ² . Aliphatic Ci to C ₄ alcohols are particularly preferably used as R ³ OH, in particular methanol, ethanol, n-propanol, isobutanol and n-butanol. Of course, as alcohols R ³ 0H and multivalent alcohols such as ethylene glycol, 1, 2 -propylene glycol, 1, 3 -propylene glycol,

1,4-butanediol or 1,6-hexanediol can be used. If the radical R ^{2 contains} a free hydroxyl group, this can react intramolecularly or intermolecularly with the double bond to form cyclic or acyclic acetals, ie in such a case the hydroxyl group present in the radical R ^{2 functions} as alcohol R ³ OH.

Homogeneous catalysts for the acetalization of the allyl ether I to the acetal III in the process according to the invention can be a large number of organometallic compounds of transition metal elements, in particular those containing elements from groups VIA and VIIIA of the Periodic Table of the Elements, preferably molybdenum, iron, cobalt, nickel, in particular the platinum metals ruthenium , Rhodium, palladium platinum, osmium and / or iridium, particularly preferably, ruthenium, rhodium, iridium or osmium. Organometallic compounds in the sense of the present application are complexes of the transition metals mentioned with organic ligands, the heteroatoms such as phosphorus, antimony, arsenic, nitrogen Contain substance, sulfur and / or oxygen, understood, which are coordinated with the transition metal via free electron pairs, for example organic amine ligands, organic phosphine ligands, chelate ligands, such as acetylacetone and dioximes, such as dimethyl dioxime, furildioxime or benzil dioxime, ureas or thioureas, 8-hydroxyquinoline, monodentate or multidentate, in particular bidentate organophosphine and organophosphite ligands, organoarsine and organostibin ligands, and aromatic, nitrogen-containing ligands for their property as complexing agents the (-N = CC = N-) structural unit is responsible, for example 2, 2 ' -Bipyridine or 1, 10-phenanthroline, as well as the ligands derived by substitution of these basic bodies, for example terpyridines. These complexes can exist as neutral complexes or can be charged and form a salt with an anion. In contrast, simple salts of these transition metals with, for example, carboxylic acid, carbonic acid, hydrocyanic acid, which do not contain any of the aforementioned organic ligands, are not considered as organometallic compounds in the sense of the present application. The same applies to carboxylato, cyano or carbonyl complexes of the transition metals, such as dicobalt octacarbonyl (C0 (CO) β) or hydridocobalt tetracarboxyl (HCo (CO) ₄ ), which do not contain any of the aforementioned organic ligands. In contrast, complexes of the transition metals with the aforementioned organic ligands, which additionally contain carboxylates, alcoholates, cyanide, carbonate or the carbonyl ligands in complex form, or which contain a carboxylate,

Alcoholate, cyanide, carbonate or sulfonate anion as a counter anion to the positively charged organometallic complex of the transition metal - contained as understood by the term organometallic compounds.

Both monodentate or multidentate, for example bidentate, phosphine ligands can be used as ligands. Suitable phosphine ligands are, for example, trialkylphosphines, triarylphosphines, alkyldiarylphosphines, aryldialkylphosphines, aryldiphosphines, alkyldiphosphines and arylalkyldiphosphines. The alkyl group-bearing phosphine ligands can contain identical or different C ₁ ~ to C ₀ , preferably C 1 to C ₆ alkyl or cycloalkyl groups. The aryl group-bearing phosphine ligands can contain the same or different C ₆ - to Cχ ₂ aryl groups, in particular the phenyl or naphthyl group but also diphenyl groups. Furthermore, phosphine ligands can be used to complex the group VIA or VIIIA elements, the heterocycloaliphatic groups such as pyrrolidine, imidazolidine, piperidine, morpholine, oxazolidine, piperazine or triazolidine groups or heteroaromatic groups, such as Pyrrole, imidazole, oxazole, indole, pyridine, quinoline, pyrimidine, pyrazole, pyrazine, pyridazine or quinoxaline groups together with other alkyl or carry aryl groups. The alkyl or aryl groups of the ligands may be unsubstituted or under the reaction conditions inert substituents, such as Cι ~ C to ₄ ~ alkoxy or di-Cι ~ to C ₄ alkylamino, Ci to _C6 alkyl, nitro, Wear cyano or sulfonate groups. Examples of suitable sulfonated phosphine ligands include triphenylphosphine trisulfonate (TPPTS) and triphenylphosphine monosulfonate (TPPMS) (Angew. Chem. S &. 1588 (1993)).

In principle, there is no restriction on the applicability of such ligands for complexing the group VIA or VIIIA elements in the process according to the invention. However, for reasons of cost, preference is given to using ligands which can be prepared in a simple manner.

A merely exemplary list of such ligands will be given below: Trimethylphosphine, triethylphosphine, tripropylphosphine, triisopropylphosphine, tributylphosphine, Trioc- tylphosphin, Tridecylphosphin hexylphosphine, tricyclopentylphosphine, tricyclo-, triphenylphosphine, tritolylphosphine, Cyclohexyldi- phenylphosphine, Tetraphenyldiphosphinomethan, 1,2-bis (diphenyl - phosphino) ethane, tetramethyldiphosphinomethane, tetraethyldiphosphinomethane, 1, 3-bis (diphenylphosphino) propane, 1, 4-bis (diphenylphosphino) butane, tetra-t-butyldiphosphinomethane, 1, 2-bis (dimethylphosphino ) ethane, 1,2-bis (diethylphosphino) ethane, 1,2-bis (dipropylphosphino) ethane, 1,2-bis (diisopropylphosphino) ethane, 1,2-bis (dibutylphosphino) ethane, 1,2-bis (di-t-butylphosphino) ethane, 1, 1-bis (dicyclohexylphosphino) methane, 1, 2-bis (dicyclohexylphosphino) ethane, 1,4-bis (dicyclohexylphosphino) butane, and those in EP-A 279 018, EP-A 311 619, WO 90/06810 and EP-A 71 281 Bisphosphine ligands. In addition to triphenylphosphine (abbreviated: PPh ₃ ), preferred phosphine ligands are bidentate phosphine ligands of the general formula which are bridged via C 1 -C ₄ -alkylene groups

(CH ₂ ) _n

in which n is an integer from 1 to 4 and the radicals A are identical or different Ci to Cio alkyl or C ₅ to C _δ 'cycloalkyl groups, some of which have been mentioned above by way of example. In addition to the processes described in the abovementioned patent applications, the alkyl or arylphosphine ligands can be prepared using conventional methods, for example according to the methods described in Houben-Weyl, Methods of Organic Chemistry, Volume XII / 1, 4th edition, p. 17 -65 and pp. 182-186, Thieme, Stuttgart, 1963 and volume E 1, 4th edition, pp. 106-199, Thieme, Stuttgart, 1982.

Suitable phosphite ligands are, for example, trialkyl phosphites, alkyl diaryl phosphites, triaryl phosphites, alkyl bisphosphites, aryl bisphosphites, alkyl aryl bisphosphites. The alkyl group-bearing phosphite ligands can contain identical or different C ~ to C ~ ~, preferably C] _ to C ₆ alkyl or cycloalkyl groups. The aryl group-bearing phosphite ligands can contain identical or different Cg to Cχ ₂ aryl groups, in particular the phenyl or naphthyl group, but also the diphenyl group or the binaphthyl group. Furthermore, phosphite ligands can be used to complex the transition metals, the heterocycloaliphatic groups such as pyrrolidine, imidazolidine, piperidine, morpholine, oxazolidine, piperazine or triazolidine groups or heteroaromatic groups such as pyrrole, imidazole, oxazole -, Indole, pyridine, quinoline, pyrimidine, pyrazole, pyrazine, pyridazine or quinoxazoline groups together with other alkyl or aryl groups. The alkyl or aryl groups of the phosphite ligands can be unsubstituted or substituents which are inert under the reaction conditions, such as C 1 -C ₄ -alkoxy, di-C 1 -C ₄ -alkyla1tu.no-, C 1 -C ₆ - Wear alkyl, hydroxy, nitro, cyano or sulfonate groups. The sulfonate-substituted phosphite ligands and their complexes are generally water-soluble. Suitable phosphite ligands are, for example, trimethyl phosphite, triethyl phosphite, tripropyl phosphite, triisopropyl phosphite, tributyl phosphite, tricyclopentyl phosphite, tricyclohexylphosphite, triphenyl phosphite and those described in EP-A 472 071, EP-A 213 639, DE-A 214 622 A 2 733 796, EP-A 2261, EP-A 2821, EP-A 9115, EP-A 155 508, EP-A 353 770, US-A 4 318 845, US-A 4 204 997 and US-A 4 362,830 described mono- and bisphosphite ligands.

In addition to phosphine or phosphite ligands, 2, 2 '-bipyridine or 1, 10-phenanthroline ligands of alkyl or aryl-substituted or fused 2, 2' -bipyridine or 1, 10- Phenanthroline derivatives which contain the (-N = CC = N-) grouping which is responsible for the complex formation property of the 2, 2'-bipyridine or 1,10-phenanthroline ligands, for example 2, 2 '-Biquinoline, 4 , 7-diphenyl-l, 10-phenanthroline, 2,9-dimethyl-4,7-diphenyl-l, 10-phenanthroline, 4,5-diazafluorene, dipyrido [3,2-a: 2 ', 3' -c ] phenazine, 2,2 ', 6', 2 '' terpyridine and others, be used. Some of these ligands are commercially available, for example 2, 2'-bipyridine or 1, 10-phenanthroline, or can be prepared according to the methods described in Synthesis 1, (1976) or Aust. J. Chem. 21, 1023 (1970).

The complexes of the elements of group VIA or VIIIA which can be used in the process according to the invention can either be generated in situ in the reaction mixture or added to the reaction mixture in preformed form. To generate these complexes in situ, the procedure is generally to use compounds of the group VIA or VIIIA elements, e.g. their halides, preferably their chlorides, bromides or iodides, the nitrates, cyanides or sulfates or, particularly preferably, complex compounds of these metals, such as acetylacetonates, carboxylates, carbonyl complexes or olefin complexes, such as ethene or butadiene complexes, together with the ligand in question feeds the reaction mixture, whereupon the complexes which can be used according to the invention form in the reaction mixture. In general, the ligand in question is added with respect to the Group VIA or VIIIA element in a molar ratio of 1 to 200, preferably 1 to 50, in particular 1 to 10.

The above-mentioned organometallic compounds of the transition metals contain phosphorus-containing ligands, in particular phosphine ligands, containing carbonyl complexes of the platinum metals, such as HRh (PPh ₃ ) ₃ (CO), IrCl (CO) (PPh ₃ ) ₃ , [Ir (cycloocta - dienyl) PPh ₃ ) _] PF ₆ , HRuCl (PPh ₃ ) ₃ (CO), HRu (CO) (CH ₃ COO) (PPh ₃ ) ₂ , H ₂ Ru (CO) (PPh ₃ ) ₃ , HRuCl ( CO) (hexyldiphenylphosphine) ₃ , RuH ₂ (PPH ₃ ) ₄ , RuCl ₂ (CO) ₂ (PPh ₃ ) ₃ or RuH (CO) (C ₉ H ₁₉ COO) (PPh ₃ ) ₂ - C ₉ H ₁₉ COO the capric acid anion - particularly preferred as homogeneous catalysts in the process according to the invention. Of these homogeneous catalysts, the halogen-free complexes are again preferred, for example those which contain the conjugate base of an OH-acidic, organic compound as ligands, OH-acidic, organic compounds being understood as meaning those compounds which give an acidic reaction in aqueous solution, such as monocarboxylic acids, monosulfonic acids or non-chelating phenols. As such ligands, C - to C ₂ o "-carboxylic acid anions, which preferably derive from a monocarboxylic acid, such as acetate, propionate, butyrate, isobutyrate,

Valerianate, pivaloate, capronate, enanthate, caprylate, 2-ethylhexanoate, 2-propylheptanoate, caprinate, laurate, myristate, palmitate, stearate, oleate, benzoate, alkylbenzoate , Naphthoat- and alkylnaphthoate anions or non-chelating phenolate anions or sulfonate anions are used. Phenolates which can advantageously be used as ligands in such transition metal-organic compounds are, for example, the phenolate and naphtholate anions and, on the aromatic nucleus, phenolate and naphtholate anions substituted with substituents which are inert under the reaction conditions, for example Ci to C ₂ o "alkyl, preferably Ci to -C ₀ alkyl-substituted phenolates or naphtholates, such as methylphenolate, nonylphenolate, 2,6-di-tert-butylphenolate or 2,6-di-butyl-4-methylphenolate anions.

Sulfonate ligands which can advantageously be used for this purpose are e.g. Alkyl sulfonates such as the methanesulfonate or octyl sulfonate, dodecyl sulfonate, octadecyl sulfonate or trifluoromethanesulfonate anion or aryl sulfonates such as the toluenesulfonate anion.

The preparation of the homogeneous catalysts which can be used according to the invention and contain ligands derived from acidic organic compounds is briefly outlined below for the above-mentioned ruthenium complex compounds on behalf of analogous complex compounds of other transition metals:

These complexes containing carboxylate ligands can, for example, starting from RuH (PPb. ₃ ) ₃ (CO), which is accessible, for example, according to Uttley et al, Inorganic Syntheses, Vol. XVII, 125 (1977), by reaction with the corresponding carboxylic acids analogously to by Robinson et al, J. Chem. Soc, Dalton Trans. 1912 (1973), Frediani et al, ib. 165 (1990), ib. 1705 (1990), ib. 3663 (1990) and Frediani et al, J. Organomet Chem. 454, C17-C19 (1993) methods developed. The corresponding complexes containing phenolate ligands can accordingly be obtained by the reaction of HRu (CO) (PPh ₃ ) ₃ with the phenols in question. Complexes containing sulfonate ligands can be obtained, for example, by the process described in US Pat. No. 4,892,955. The halogen-containing homogeneous catalysts can, for example, according to the method of Uttley et al, Inorganic Syntheses, Vol. XV, 45

(1974) by the reaction of RUCI ₃ with formaldehyde.

The aforementioned catalysts, which are added to the reaction mixture as such or - this applies in particular to the homogeneous catalysts containing carboxylate or phenolate ligands - also in situ in the reaction mixture, by reacting RuH ₂ (PPH ₃ ) ₃ (CO ) with the carboxylic acid or phenol in question. Likewise, complexes containing hydrido and / or carbonyl ligands can be generated in situ in the reaction mixture by pressing on molecular hydrogen and / or carbon monoxide, starting from complexes which have no hydrido or carbonyl ligands.

Transition organometallic compounds, especially organic ruthenium compounds, which contain carboxylate, sulfonate or phenolate ligands and contain additional phosphorus-containing ligands, in particular phosphine or phosphite ligands, preferably phosphine ligands and optionally carbonyl ligands, are characterized in the process according to the invention as homogeneous catalysts for the catalysis of acetalization both by a high activity and selectivity as well as by a high stability and thus a long service life.

The advantageous properties of these homogeneous catalysts can additionally be improved by carrying out the acetalization in the presence of an amount of the acidic compound in question which exceeds the stoichiometric amount required to form the transition metal carboxylate or phenolate complex in question, so that the acidic compound in question is released Form in equilibrium with the transition metal-organic compound serving as a homogeneous catalyst is present in the reaction mixture. For this purpose, the same acidic compound is expediently used as is bound to the transition metal in the transition metal-organic compound, but the addition of other acidic organic compounds is equivalent to this measure. In general, the acidic organic compound is used in a molar ratio of 1: 1 with respect to the transition metal-organic compound functioning as a homogeneous catalyst.

Although it is not necessary for the acetalization reaction, an addition of hydrogen to the reaction mixture, the supply of small amounts of hydrogen, substituted or less together with the supply quantities of carbon monoxide using carbonyl-homogeneous catalysts can, to an exten ^¬ tion of the service life result of these homogeneous catalysts. In practice, synthesis gas can be used for this purpose. It should be noted here that the hydrogen and / or the carbon monoxide, depending on the reaction temperature and partial pressure used, react with the transition metal complexes present as homogeneous catalysts in the reaction mixture, and consequently in the reaction mixture under these conditions, several catalytically active, organometallic transition metal complexes which are in the essentially by the number of their hydrido- and Differentiate carbonyl ligands, which may be in equilibrium with one another.

In order to improve the activity, selectivity and stability of the homogeneous catalysts, in particular the homogeneous catalysts containing phosphorus-containing ligands, the phosphine or phosphite is generally in a 2 to 100 molar, preferably in a 2 to 20 molar and, with respect to the phosphine or phosphite complex of the transition metal element particularly preferably added in a 2 to 10 molar amount. If the as

Homogeneous catalyst serving transition metal element complex generated in situ in the reaction mixture, it is expedient to use a correspondingly high excess of phosphine or phosphite ligand with respect to the transition metal element in question.

The transition metal catalysts which are homogeneously soluble in the reaction medium are generally used in amounts of from 0.001 to 1 mol%, preferably from 0.01 to 1 mol%, based on the allyl ether I fed to the reactor. It goes without saying for the person skilled in the art that the amount of homogeneous catalyst to be added depends on the catalytic activity of the homogeneous catalyst used in each case. Depending on the type of homogeneous catalyst used, a greater or lesser amount of catalyst can therefore advantageously be added to the reaction mixture. The optimum amount for the particular homogeneous catalyst used is expediently determined in a preliminary test.

The acetalization can be carried out discontinuously, e.g. in stirred tanks or continuously, e.g. in loop reactors or stirred tank cascades, at temperatures of generally from 20 to 200 ° C., preferably from 60 to 180 ° C., in particular from 80 to 160 ° C. and at a pressure of generally 1 to 100 bar, preferably from 1 to 60 cash. Acetalization can be carried out in the presence or absence of added solvents such as aliphatic or aromatic hydrocarbons e.g. Toluene, benzene or cyclohexane, ethers, e.g. Dibutyl ether, tetrahydrofuran, dioxane or liquid, low molecular weight polyalkylene glycols, halogenated aliphatic or aromatic hydrocarbons, e.g. Chloroform, dichloromethane, chlorobenzene, dichlorobenzene, sulfoxides or sulfones, e.g. Dimethyl sulfoxide or sulfolane.

The acetalization according to the invention takes place under essentially water-free conditions, ie in the absence of technically effective amounts of water, since the presence of water has a disadvantageous effect on the result of the acetalization reaction. It understands it goes without saying that the presence of small traces of water, which have no measurable influence on the yield and economy of the process according to the invention, can be tolerated.

Instead of these conventional solvents, the isomerization and acetalization of the allyl ether I to the acetal III can also take place in a phosphine melt. This procedure can advantageously be used with homogeneous catalysts containing phosphine. In principle, the phosphine which serves as a solvent can in principle be chosen arbitrarily, but preferably that melt is used in the phosphine which serves as a ligand in the transition metal element complex which serves as a homogeneous catalyst.

The addition of the alcohol R ³ OH II can be varied over a wide range. The equimolar amount required to form acetal III can, if desired, also be exceeded. In general, the alcohol R ³ OH II to the reactor, based on the allyl ether I used, in a molar ratio II / I of 1: 1 to 100: 1, preferably from 1: 1 to 10: 1, in particular from 1: 1 to 5 : 1 fed. Higher molar excesses of the alcohol R ³ OH II with respect to the allyl ether I generally do not have a disadvantageous effect on the result of the reaction, but the alcohol R ³ OH II is expediently used in the aforementioned proportions.

After the reaction has ended, the reaction product is generally worked up by distillation, it being possible for the homogeneous catalyst to be recovered from the bottom of the distillation and, if desired, to be reused. If it is desired to reuse the catalyst, a solvent which has a higher boiling point than the acetal III formed in the reaction can advantageously be added to the reaction mixture before the distillation. If the homogeneous catalyst used is thermally and chemically stable under the conditions of the distillation, the addition of a high-boiling solvent can be dispensed with and the homogeneous catalyst e.g. be returned to the reaction in a triphenylphosphine melt.

In a further embodiment of the method according to the invention the isomerization of the allyl ether and acetalization is I to acetal III leads out using a heterogeneous catalyst ^¬, the method advantageously is carried out in liquid phase. It has surprisingly been found that heterogeneous hydrogenation catalysts which are per se conventional and are essentially insoluble in the reaction medium can be used as catalysts for the conversion of the allyl ether I to the acetal III. Of these hydrogenation catalysts, preference is given to those which contain one or more elements from groups IA, VIA, VIIA or VIIIA, optionally in combination with one or more elements from group VA, from the periodic table of the elements, in particular chromium, molybdenum, tungsten, rhenium, ruthenium, Contain cobalt, nickel, rhodium, iridium, osmium, palladium and / or platinum, optionally in combination with iron and / or copper.

So-called precipitation catalysts, for example, can be used as heterogeneous catalysts in the process according to the invention. Such catalysts can be produced by removing their catalytically active components from their salt solutions, in particular from the solutions of their nitrates and / or acetates, for example by adding solutions of alkali metal and / or alkaline earth metal hydroxide and / or carbonate solutions, precipitates as, for example, poorly soluble hydroxides, oxide hydrates, basic salts or carbonates, the precipitates obtained subsequently dry and these are then calcined at generally 300 to 700 ° C., in particular 400 to 600 ° C., into the oxides, mixed oxides and / or mixed-valentines in question Converts oxides, which, for example, by treatment with reducing agents such as hydrogen or hydrogen-containing gases at 50 to 700 ° C, in particular at 100 to 400 ° C, reduced to the relevant metals and / or to oxidic compounds of low oxidation level and be converted into the actual, catalytically active form. It is usually reduced until no more water is formed. In the production of Fällungskata ^¬ catalysts containing a support material, the precipitation of the catalytically active components can take place in the presence of the support material. The catalytically active components can, however, advantageously also be precipitated from the relevant salt solutions at the same time as the support material, as is the case, for example, when the catalytically active components are precipitated by means of a water glass solution.

Catalysts which contain the catalytically active metals or metal compounds deposited on a support material are preferably used in the process according to the invention. In addition to the above-mentioned precipitation catalysts which, in addition to the catalytically active components, additionally contain a support material, support catalysts in which the catalytically active components have been applied, for example, by impregnation to a support material.

The way in which the catalytically active metals are applied to the support is generally not critical to the result of the process and can be accomplished in a variety of ways. The catalytically active metals can be applied to these carrier materials e.g. by impregnation with solutions or suspensions of the elements or salts relating to salts, drying and subsequent reduction of the metal compounds to the relevant metals or oxidic compounds of a low oxidation level by means of a reducing agent, preferably with the aid of hydrogen, hydrogen-containing gases or hydrazine. Another possibility for applying the catalytically active metals to these supports is that

Carrier with solutions of easily decomposable salts, e.g. with nitrates or with thermally easily decomposable complex compounds, e.g. To impregnate carbonyl or hydrido complexes of the catalytically active metals and to heat the support soaked in order to thermally decompose the adsorbed metal compounds to temperatures of 300 to 600 ° C. This thermal decomposition is preferably carried out under a protective gas atmosphere. Suitable protective gases are e.g. Nitrogen, carbon dioxide, hydrogen or the noble gases. Furthermore, the catalytically active metals can be deposited on the catalyst support by vapor deposition or by flame spraying.

The content of these supported catalysts in the catalytically active metals is in principle not critical for the success of the process according to the invention. It goes without saying for a person skilled in the art that higher levels of these supported catalysts in catalytically active metals lead to higher space-time conversions than lower levels. In general, however, supported catalysts are used whose content of catalytically active metals is 0.1 to 80% by weight, preferably 0.5 to 30% by weight, based on the total catalyst. Since these content data material related to the total catalyst including carrier, the different support materials, however, have surfaces very different specific gravities and specific top, this information but can be exceeded even under- or over ^¬, without this having a detrimental effect on the result of the inventive method affects. Of course, several of the catalytically active metals can also be applied to the respective carrier material. May continue to the catalytically active metals, for example, by the processes of DE-A 2519817, EP-A 147 219 and EP-A are brought to the carrier on ^¬ 285,420. In the catalysts according to the aforementioned Writings present the catalytically active metals as an alloy, which are produced by thermal treatment and / or reduction of the salts or complexes of the aforementioned metals deposited on a support, for example by impregnation.

Generally the oxides of aluminum or titanium, zirconium dioxide, silicon dioxide, diatomaceous earth, silica gel, clays, e.g. Montmorillonites, silicates such as magnesium or aluminum silicates, zeolites such as ZSM-5 or ZSM-10 zeolites and activated carbon can be used. Preferred carrier materials are aluminum oxides, titanium dioxide, zirconium dioxide and activated carbon. Mixtures of different support materials can of course also serve as supports for catalysts which can be used in the process according to the invention.

The following catalysts may be mentioned by way of example as heterogeneous catalysts for carrying out the acetalization:

Platinum dioxide, palladium on aluminum oxide, palladium on silicon dioxide, palladium on barium sulfate, palladium on

Zirconium dioxide, rhodium on activated carbon, rhodium on aluminum oxide, ruthenium on silicon dioxide or activated carbon, nickel on silicon dioxide, cobalt on silicon dioxide, cobalt on aluminum oxide, carbonyl iron powder, rhenium-palladium on activated carbon, rhenium-platinum on activated carbon, platinum oxide-rhodium oxide mixtures, platinum Palladium on activated carbon, copper chromite, barium chromite, nickel-chromium oxide on aluminum oxide, cobalt sulfide, nickel sulfide, copper-molybdenum (VI) oxide-silicon dioxide-aluminum oxide catalysts, palladium on activated carbon catalysts partially poisoned with selenium or lead as well as the catalysts according to DE-A 3 932 332, US-A 3 449 445, EP-A 44444, EP-A 147 219, DE-A 3 904 083, DE-A 2 321 101, EP-A 415 202, DE-A 2 366 264 and EP-A 100 406.

Hydrogenation catalysts which contain Bronsted and / or Lewis acidic centers can also advantageously be used in the process according to the invention.

For example, the catalytically active metals themselves can act as Bronsted or Lewis acidic centers if they are not completely reduced to the metals in question when the catalyst is activated with gases containing hydrogen or hydrogen. This applies, for example, to chromite-containing catalysts, such as copper chromite. Such Lewis or Bronsted acidic or basic centers can also be introduced into the catalyst via the support material used. ^Support materials containing Lewis ^¬ or Brönsted acidic centers are, for example, aluminum oxides, titanium dioxide, zirconium dioxide, silicon dioxide, called silicates, clays, zeolites, magnesium-aluminum mixed oxides and activated carbon.

In the process according to the invention, preference is therefore given to using supported catalysts as hydrogenation catalysts which contain elements of IA, VI., VII. And / or VIII. Subgroup of the Periodic Table of the Elements, in particular the elements of VII. And VIII. Subgroup of the Periodic Table of the Elements on a Bronsted or Lewis acidic support material deposited. Particularly advantageous catalysts are e.g. Ruthenium

Activated carbon, ruthenium on aluminum oxide, ruthenium on silicon dioxide, ruthenium on magnesium oxide, ruthenium on zirconium dioxide, ruthenium on titanium dioxide, palladium on aluminum oxide, palladium on silicon dioxide, palladium on zirconium dioxide, palladium on barium sulphate and palladium on activated carbon catalysts partially poisoned with selenium or lead.

Catalysts which themselves have no such Bronsted or Lewis acidic centers can be Lewis or Bronsted acidic components, such as zeolites, aluminum or silicon oxides,

Phosphoric acid or sulfuric acid can be added. They are generally used in amounts of from 0.01 to 5% by weight, preferably from 0.05 to 0.5% by weight and particularly preferably from 0.1 to 0.4% by weight, based on the weight of the catalyst used.

Also suitable for converting the allyl ether I to the acetal III are heterogeneous catalysts which contain the organometallic complex compounds of transition metal elements from group VIA and VIIIA of the periodic table of the elements which can be used for the homogeneous catalysis of this process step in heterogeneous form, for example those in which the corresponding Transition metal element is fixed to a polymer matrix.

Such polymeric matrices can be resins, such as styrene-divinylbenzene resins or phenol-formaldehyde resins, to which the ligands in question which serve to complex the transition metal element are preferably covalently bound, which in turn form complexes with the transition metals in question and quasi immobilize them in this way.

Such heterogenized, polymer-bonded group VIA or group VIIIA element complexes, in particular palladium and nickel complexes, are, for example, by the method of Zhuangyu et al. (Reactive Polymers £, 249 (1988)) or after

Wang et al. (J. Org. Chem. _59th, 5358 (1994)) are available. Real estate ^¬ catalyzed phosphine complexes of the Group VIA and VIIIA elements are for example by the methods of Hartley, Adv. Organomet. Chem. 15, 189 (1977), FR Hartley "Supported Metal Complexes", Riedel, Dordrecht 1985, K. Smith, "Solid Supports and Catalysis in Organic Synthesis", Ellis Horwood, Prentice Hall, NY 1992, CH Pittman "Polymer supported Reactions in Organic Synthesis ", p. 249, Wiley, Chichester 1980 and CH Pittmann J. Am. Chem. Soc. 18, 5407 (1976) and Ann. NY Acad. Be. 2_ü, 15 (1977) available. The advantage of using such heterogenized catalysts is in particular the easier and gentler separation of the catalyst from the reaction products. This can be arranged in a fixed bed and the reaction mixture can flow through it, or it can also be suspended in the reaction mixture and mechanically separated after the reaction has ended.

The heterogeneous catalyst can either be suspended in the liquid reaction medium or preferably arranged in a fixed bed or several fixed beds. The process can be carried out using a heterogeneous catalyst suspended in the liquid reaction medium, e.g. be carried out in stirred tanks or loop reactors. When using a heterogeneous catalyst arranged in a fixed bed, the reaction mixture is generally passed over the fixed catalyst bed in the bottom or trickle mode.

In general, the catalyst is loaded with the liquid reaction mixture at a space velocity of 0.001 to 2, preferably from 0.01 to 1.5 and particularly preferably from 0.05 to 1 kg of reaction mixture / 1 hour of catalyst. When using the heterogeneous catalysts, the reaction can take place in the presence or absence of a solvent. The same solvents can be used as solvents which can also be used in carrying out the process under homogeneous catalysis.

The addition of the alcohol R ³ 0H II to produce the acetal III from the allyl ether I can be varied over a wide range. The required equimolar amount can, if desired, also be exceeded. In general, the alcohol R ³ OH II is the reactor, based on the allyl ether I used in this reaction in a molar ratio II / I of 1: 1 to 100: 1, preferably from 1: 1 to 10: 1, in particular 1 : 1 to 5: 1 fed. Higher molar excesses of the alcohol with respect to the adduct generally do not have a disadvantageous effect on the result of the reaction, but the alcohol R ³ OH II is expediently used in the context of the quantitative ratios mentioned above. The isomerization and acetalization of the allyl ether to the acetal III on the heterogeneous Catalyst in the liquid phase is generally at a temperature from 20 to 300 ° C, preferably from 50 to 280 ° C and particularly preferably from 80 to 250 ° C and at a pressure of generally 1 to 100 bar, preferably from 1 to 50 bar, especially from 2 to 10 bar.

The liquid reaction product from this process stage is generally worked up by distillation in an analogous manner to that which has already been described for carrying out this process stage with homogeneous catalysts. When heterogeneous catalysts are used, there is naturally no need to recycle the catalyst, as may be expedient and advantageous when using homogeneous catalysts.

With the process according to the invention, acetals can be prepared in good yields and selectivities starting from allyl ethers. In particular, the catalysts to be used in the process according to the invention are notable for good separability from the reaction product and also for good stability, as a result of which the disadvantages of the prior art can be overcome.

Examples

example 1

A glass autoclave was charged with 0.022 g of the catalyst HRuCl (CO) (PPh ₃ ) ₃ , 0.031 g triphenylphosphine, 0.005 g decanoic acid, 3.18 g (24.8 mmol) l-butoxybut-2-ene and 1.83 g (24 , 8 mmol) filled with n-butanol. After a reaction time of 16 hours at 160 ° C. under autogenous pressure, the reaction mixture was analyzed by means of calibrated gas chromatography. With a conversion of 85%, 1,1-dibutoxybutane with a selectivity of 85.1%, 1-butoxybut-1-ene with 10.1% was formed.

Example 2

A glass autoclave was mixed with 0.10 g of the heterogeneous catalyst palladium on activated carbon (10 wt.% Pd), 3.0 g (24 mmol) 1-butoxybut-2-ene and 1.73 g (24 mmol) n -Butanol filled. After 16 stun ^¬ at 150 ° C under a hydrogen atmosphere (1 bar) the reac tion mixture was ^¬ Siert means of calibrated gas chromatography analy ^¬. With a conversion of 21%, 1, 1-dibutoxybutane with a selectivity of 42%, dibutyl ether with 25% and 1-butoxybut-l-ene with 22% was formed.

Claims

claims

1. A process for the preparation of acetals by the reaction of allyl ethers with alcohols, characterized in that an allyl ether with an alcohol in the liquid phase in the presence of a homogeneous catalyst from an organometallic compound of an element from the group VIA and / or VIIIA of the periodic table of the elements or in the presence of a heterogeneous catalyst which contains one or more elements from groups IA, VIA, VIIA and / or VIIIA of the Periodic Table of the Elements, under essentially anhydrous conditions.

2. The method according to claim 1, characterized in that an organometallic compound of an element from the group VIA and / or VIIIA of the Periodic Table of the Elements is used as a homogeneous catalyst, which contains a mono- or polydentate phosphine or phosphite ligand bound in a complex manner.

3. Process according to claims 1 and 2, characterized in that a complex of a platinum metal with a monodentate or multidentate phosphine or phosphite ligand is used as the homogeneous catalyst.

4. Process according to claims 1 to 3, characterized in that the homogeneous catalyst is generated in situ in the reaction medium.

5. The method according to claim 1, characterized in that a supported catalyst is used as the heterogeneous catalyst.

6. Process according to claims 1 and 5, characterized in that a supported catalyst is used as the heterogeneous catalyst, which contains aluminum oxide, titanium dioxide, zirconium dioxide, a silicate, an alumina, a zeolite and / or activated carbon as a support material.

7. The method is characterized according to claims 1 and 5 to 6, characterized labeled in ^¬, which comprises using a heterogeneous catalyst containing palladium.

8. The method according to claims 1 and 5 to 7, characterized in that one uses a heterogeneous catalyst which additionally contains an element from group VA of the periodic table of the elements.