GB2217318A - Process for preparation of branched aldehydes - Google Patents

Abstract

Process for the preparation of branched aldehydes comprising hydroformylation of alkene derivatives of the formula <IMAGE> wherein Z represents a lower alkyl group, optionally substituted by an aryl group, wherein n=0, 1 or 2, in the presence of a catalyst system comprising a rhodium compound and a triphenyl phosphite ligand, wherein the phenyl groups may bear one or two substituents selected from lower alkyl, lower alkoxy and hydroxy, and wherein the phosphite ligand: Rh molar ratio is in the range of from 2 to 10, in the presence of carbon monoxide and hydrogen, in an apolar solvent, at a temperature of </= 80 DEG C at a pressure in the range of from 20 to 75 bar, and subsequent recovery of the predominantly formed branched aldehyde from the obtained normal-branched-aldehyde mixture.

Description

PROCESS FOR PREPARATION OF BRANCHED ALDEHYDES The invention relates to a process for preparation of branched aldehydes. More particularly the invention relates to the manufacture on industrial scale of branched aldehydes by hydroformylation of alkene derivatives, bearing a functional group, like an ester group.

Many olefinic compounds containing various functional groups e.g. ester, nitriles, alcohols, ethers, acetals have been hydroformylated; however no commercial processes employing these substrates are operative to date, although a variety of these olefins is available in large amounts as typical petrochemical products e.g. vinylacetate, allylacetate, allyl alcohol etc.

Moreover the hydroformylation products of such substrates in particular branched products have greater synthetic interest and hence higher commercial value than those obtained from unsubstituted olefins.

It will be appreciated that there are actually some serious limitations to hydroformylation processes using olefins containing functional groups a) chemoselectivities are often low b) regioselectivities unfortunately do not always favour the formation of the isomeric product with the highest commercial value c) yields of the produced aldehydes collapse on increasing the substrate conversion d) reaction reates are lower than those found for hydrocarbon olefins.

On the other hand there is a still growing need for cheap aldehyde products formed by means of such hydroformylation processes, for the economical manufacture of industrial chemicals such as methylmetacrylate and the like.

Several rhodium complex hydroformylation catalysts for hydroformylation of alpha-olefins i.e. compounds containing the group -CH=CH2 or > C=CH2, have been proposed.

Such catalysts generally comprise rhodium in complex combination with carbon monoxide and with a ligand, such as triphenylphosphine and are used in conjunction with excess ligand.

Although such catalysts can be used under lower operating 2 pressures, e.g. about 20 kg/cm absolute (19.6 bar) or less, high n-/iso-aldehyde product ratios are formed from alpha-olefins, i.e.

an excess of the undesired n-aldehyde product is produced.

The same undesired n-/iso-aldehyde product ratio is produced by a process as disclosed in US Patent Specification No. 3,527,809, using phosphites as ligands, such as triphenylphosphite in place of triphenylphosphine.

Moreover these catalysts were found to tend to deactivate moderately rapidly, which phenomenon is found to be accompanied by disappearance of free triphenylphosphite ligand and by an increase in the rate of formation of "heavy" materials (i.e. high boiling byproducts). The rate of deactivation when using triphenylphosphite is much greater then using triphenylphosphine as ligand.

Numerous other references in the literature to the use of phosphite ligands in homogeneous rhodiumcomplex hydroformylation catalysts are known. Examples include United States Patent Specifications Nos. 3,499,933; 3,547,964; 3,560,539; 3,641,076; 3,644,446; 3,859,359; 3,907,847; 3,917,661; 3,933,919; 3,956,177; 4,096,192; 4,101,588; 4,107,079; 4,108,905; 4,135,911; 4,158,020; 4,195,042; 4,200,591; 4,200,592; 4,224,255; 4,262,142 and 4,267,383, British Patent Specifications Nos. 995,459; 1,207,561; 1,228,201; 1,243,189; 1,243,190; 1,263,720; 1,325,199; 1,338,225; 1,448,090; 1,455,645; 1,460,870; 1,461,900; 1,462,342; 1,463,947; 1,557,396; 1,586,805; 2,000,124A and 2,068,377A, European Patent Publications Nos. 0003753; 0028892; 0125567; 0131860, Japanese Patent Publications Nos. 10765/69 and 40326/73 and International Patent Publication No. WO 80/00081.

However from these publications not any teaching can be derived by a person skilled in the art to suppress the production of the undesired normal aldehyde products as main component in the final reaction mixture and to improve the yield of the desired branched iso-aldehyde products, when starting from terminal olefins, bearing a functional group.

This generally appreciated problem could also not be solved by the use of special cyclic phosphite ligands, as proposed in e.g.

European Patent Specifications Nos. 0096988 and 0096986, while moreover at least some of these cyclic phosphite ligands were found to be highly toxic, so that at least extreme care should therefore be taken in handling the phosphite ligands and reaction media containing them.

More particularly in the European Patent Specification No.

0096987 a process is diclosed for the production of an aldehyde by hydroformylation of an olefin comprising: - providing a hydroformylation zone containing a charge of a liquid reaction medium having dissolved therein a complex rhodium hydroformylation catalyst composed of rhodium in complex combination with carbon monoxide and with an organic phosphite ligand, and more preferably triphenyl phosphite, whereby the phosphite ligand:Rh molar ratio is in the range of from 1:1 to 20:1 and preferably in the range of from 5:1 to 16::1; - supplying said olefin to the hydroformylation zone; - maintaining a temperature in the range of from 40 to 160 OC and a total pressure in the range of from 4 bar to 35 bar and a partial pressure of hydrogen and of carbon monoxide each of at least 0.05 bar and a ratio of partial pressures of hydrogen and of carbon monoxide in the range of 10:1 to 1:10; - recovering from the liquid hydroformylation medium a hydroformylation product comprising at least one aldehyde; and - supplying make up phosphite ligand to the hydroformylation zone at a rate sufficient to maintain a predetermined level of free phosphite ligand in the hydroformylation medium.

Although a person skilled in the art might derive from this disclosure an efficient process for the hydroformylation of alpha-olefins, without any functional group, it does not provide in any way a suggestion or teaching for solving the hereinbefore mentioned problems with reference to the conversion of thermal olefins, bearing functional groups, as the disclosed process is only elaborated by means of experimental runs for the hydroformylation of butene-2.

Therefore there is still a need to develop an economical manufacturing process for the production of branched aldehydes from terminal alkenes bearing a functional group, the products of which can be easily transformed into highly valuable chemicals such as methylmethacrylate and the like, and the present invention seeks to provide such a process which is using auxiliaries as cheap as possible and which may not or in a minor degree cause damage to environment.

As result of extensive research and experimentation there was now found a process for the preparation of branched aldehydes comprising hydroformylation of terminal alkene derivatives of the formula:

wherein Z represents a lower alkyl group, optionally substituted by an aryl group, wherein n = 0,1 or 2, in the presence of a catalyst system comprising a rhodium compound and a triphenyl phosphite ligand, wherein the phenyl groups may bear one or more substituents selected from lower alkyl, lower alkoxy and hydroxy and more particularly alkoxy and hydroxy in the ortho and/or paraposition, and wherein the phosphite ligand:rhodium molar ratio is in the range from 2 to 10, in the presence of carbon monoxide and hydrogen, in an apolar solvent, at a temperature of < 80 "C and at a pressure in the range of from 20 to 75 bar; and subsequent recovery of the predominantly formed branched aldehyde from the obtained branched-/normal-aldehyde product mixture.

With the term "lower alkyl" and "lower alkoxy as used throughout this specification is meant alkyl groups or alkoxy groups of from 1 to 4 carbon atoms.

The organic phosphite ligands may have the general formula (RO)3P in which each R represents a phenyl group, wherein the phenyl groups may independently bear one or two substituents selected from lower alkyl and preferably methyl or ethyl, lower alkoxy and preferably methoxy or ethoxy, and hydroxy.

An especially preferred ligand has appeared to be triphenylphosphite, but other representative ligands include o-tolyl, 2-ethylphenyl, 2,6-dimethylphenyl, p-methoxyphenyl, and p-hydroxyphenyl as R radicals.

The rhodium compound to be applied may be a rhodium salt of an organic acid such as rhodium acetate, which may be combined with the ligand in the liquid phase and then treated with a mixture of carbon monoxide and hydrogen, prior to introduction of the starting alkene.

Alternatively the catalyst can be prepared from a carbon monoxide complex of rhodium such as dirhodium octacarbonyl or rhodium acetylacetonate carbonyl, by heating with the phosphite ligand, which thereby replaces one or more of carbon monoxide molecules. It is also possible to start with the elected ligand and finely divided rhodium metal, or with an oxide of rhodium (e.g.

Rh203) and the ligand and to prepare the active catalyst in situ during the course of the hydroformylation reaction.

According to a preferred embodiment of the presently proposed process, Z wil represent a lower alkyl group and more preferably a methyl group, whereas n is preferably 0 or 1. More preferably allyl acetate is hydroformylated according the present process.

According to another preferred embodiment the optionally substituted triphenylphosphite is used in a molar ratio between rhodium compound and phosphite ligand in the range of from 2 to 5.

More preferably triphenyl phosphite is used in this ratio range.

At all events the reaction medium should contain a predetermined initial level of free phosphite ligand. Typically this initial level is at least about 0.001 %w/v and preferably at least about 0.01 Zw/v.

The upper limit of concentration of phosphite ligand in the reaction medium will preferably be in the range of from 0.05-0,5 %w/v or the solubility limit of the phosphite ligand therein, whichever is the lower figure. Usually it will be preferred to operate at phosphite ligand concentrations of less than 1 Ew/v.

The hydroformylation conditions utilized in the process of the present invention involve use of temperatures, preferably being in the range of from 50-70 "C, and involve use of a total pressure of from 4 to 75 bar, and more preferably in the range of from 25-65 bar.

In operating the process of the invention, it is desirable to supply amounts of hydrogen and carbon monoxide in a molar ratio in the range of from 2:1 to 1:2 and more preferably in an approximately 1:1 molar ratio.

The formation of such mixtures of hydrogen and carbon monoxide can be effected by any of the methods known in the art for producing synthesis gas for hydroformylation, e.g. by partial oxidation of a suitable hydrocarbon feedstock such as natural gas, naphta, fuel oil or coal.

It will be appreciated that the mixtures of carbon monoxide and hydrogen to be applied may be diluted with an inert gas, such as nitrogen, argon, carbon dioxide and gaseous hydrocarbons such as methane, ethane and propane.

In operating the process of the invention the total pressure of hydrogen and carbon monoxide in the hydroformylation reactor can range from 20 bar up to 75 bar. The partial pressure of hydrogen may exceed that of carbon monoxide or vice versa, but preferably they are about equal.

At all events it will usually be desirable to operate at a partial pressure of hydrogen and of carbon monoxide of at least about 0.05 bar up to about 30 bar.

One can employ any apolar solvent, which does not interfere to any substantial degree with the desired hydroformylation reaction under the operational conditions.

Illustrative examples of such solvents include the saturated hydrocarbons, such as pentanes, naphtha, kerosene, cyclohexane etc.

as well as the aromatic hydrocarbons. More preferably toluene, benzene or xylene or mixtures thereof will be used.

An additional advantage of the use of such solvents is that they enable a rather simple and efficient extraction with water during recovery of the reaction mixture.

The concentration of the substituted vinyl derivative is mostly not a critical limitation and can vary over an extremely wide range. For example, one could employ ratios of substituted vinyl derivative to rhodium compound between about 1200:1 and about 10:1 as a preferred range.

The process of the present invention may be carried out as batch, continuous or semi continuous process.

A surprising and advantageous effect of the process of the present invention is formed by the high conversion rate as compared to those obtained by prior art processes using as well phosphines as phosphites. E.g. a conversion rate for the hydroformylation of allyl acetate into 3-acetoxy-2-methylpropionaldehyde according to the process of the present invention may amount to 5200 mol/mol rhodium compound.-hour.

Moreover the process of the present invention is characterized by a surprisingly high total selectivity for both aldehydes ( > 95%) and selectivity for the iso aldehyde (about 70%).

It will be appreciated by a person skilled in the art, that the found high conversion rates could certainly not be predicted or even expected and that such high conversion rates enable efficient one pass production of the desired branched aldehyde product at an industrial scale, during which the influence of the deactivation of the catalyst and loss of e.g. triphenylphosphine ligand, as noted previously in the literature, will become much smaller, thus avoiding the need of an increase of the rhodium concentration for compensation for lost activity or the inevitable gasstripping, which necessitates high gas recycle rate and/or distillation.

It will be appreciated, that the process of the present invention will also enable the manufacture of methylmethacrylate more economically by conversion of the obtained branched aldehyde product, via dehydration and/or oxydation, which forms another aspect of the invention therefore.

The residence time can vary from about a couple of minutes to about two hours. As will be appreciated, this variable will preferably be as short as possible and will be influenced to a certain extent by the reaction temperature, the choice of specific reactant, the specific composition of catalyst system, the total synthesis gas pressure and the partial pressure excerted by its components.

The following examples illustrate the invention, however without any restriction of the scope of the present invention.

All experiments were carried out in a 300 ml magnetically stirred Hastelloy C autoclave ("Hastelloy" is a trade mark). The reaction mixtures obtained were analyzed by means of gas-liquid chromatography.

Example 1 The autoclave was charged with allylacetate (20 ml), triphenylphosphite (0.3 mmol) and rhodium di(carbonyl) acetyl acetonate (0.1 mmol) and 50 ml toluene.

The autoclave was flushed with an equimolar mixture of hydrogen and carbon monoxide and then pressurized to 60 bar. The reaction mixture was heated up to 60 "C, whilst maintaining the pressure.

After a total reaction time of 0.5 hours, the mixture was allowed to cool to room temperature. Allyl acetate conversion into autoxy aldehydes was 98*, of which 73% was 3-acetoxy-2-methyl propionaldehyde. The total allylacetate conversion was found 100%.

The average conversion rate was found to be 5130 gmol/gat Rh.hr.

Example 2 In rather the same way as described in example 1, an experiment was carried out, wherein 1 mmol triphenylphosphite was used and wherein the total reaction time was one hour, giving an allylacetate conversion of 99% to acetoxy aldehydes, of which 71% was 3-acetoxy-2-methyl-propionaldehyde, while the average conversion rate was 2400 gmol/gat Rh.hr.

Example 3 In rather the same way as described in example 1, an experiment was carried out, using vinylacetate (20 ml), triphenylphosphite (0.3 mmol) at a temperature of 60 "C and a total reaction time of 2 hours, giving a vinylacetate conversion of 90% into acetoxy aldehydes, of which 93% was 2-acetoxy-propionaldehyde, and an average conversion rate of 1500 gmol/gat Rh.hr.

Comparative Example A In rather the same way as described in example 1, an experiment was carried out using 2.5 mmol triphenylphosphite and a total reaction time of 2 hours, giving a total allylacetate conversion of 100% of which 92% into acetoxy aldehydes, 70% of this was 3-acetoxy -2-methyl-propionaldehyde, and an average conversion rate of only 1260 gmol/gat Rh.hr.

Comparative Example B In rather the same way as described in example 1, an experiment was carried out, using 5 mmol triphenylphosphite, at a temperature of 70 "C and a total reaction time of 2 hours, giving an allylacetate conversion of 90% into acetoxy aldehydes, of which 60% was 3-acetoxy-2-methyl-propionaldehyde and at an average conversion rate of only 1200 gmol/gat Rh.hr.

Comparative Example C In rather the same way as described in example 1, an experiment was carried out, using 0.3 mmol tri(chlorophenyl)phosphite, giving a total allylacetate conversion of 100% but only 82% was converted into acetoxy aldehydes, of which 65% was 3-acetoxy-2methyl-propionaldehyde. The average conversion rate was 5000 gmol/gat Rh.hr.

Comparative Example D In rather the same way as described in example 1, an experiment was carried out using 0.3 mmol tri(n-butyl)phosphite and a total reaction time of 1 hour, giving an allylacetate conversion only 20% into acetoxy aldehydes, of which 70% was 3-acetoxy-2-methylpropionaldehyde, and at an average conversion rate of only 500 gmol/gat Rh.hr.

Comparative Example E In rather the same way as described in example 1, an experiment was carried out, using 50 ml diglyme instead of 50 ml toluene, giving an allylacetate conversion of 95% into acetoxy aldehydes, of which 70% was 3-acetoxy-2-methyl-propionaldehyde and at an average conversion rate of only 1000 gmol/gat Rh.hr.

Comparative Example F In rather the same way as described in example 1, an experiment was carried out, using vinylacetate (20 ml), tri(n-butyl)phosphite (0.3 mmol), at a temperature of 60 "C and a total reaction time of 5 hours, giving a vinyl acetate conversion of 50% into acetoxy aldehydes, of which 93% was 3-acetoxypropionaldehyde and at an average conversion rate of only 300 gmol/gat Rh.hr.

Claims (12)

1. Process for the preparation of branched aldehydes comprising hydroformylation of alkene derivatives of the formula

wherein Z represents a lower alkyl group, optionally substituted by an aryl group, wherein n = 0, 1 or 2, in the presence of a catalyst system comprising a rhodium compound and a triphenyl phosphite ligand, wherein the phenyl groups may bear one or two substituents selected from lower alkyl, lower alkoxy and hydroxy, and wherein the phosphite ligand:Rh molar ratio is in the range of from 2 to 10, in the presence of carbon monoxide and hydrogen, in an apolar solvent, at a temperature of < 80 "C and at a pressure in the range of from 20 to 75 bar, and subsequent recovery of the predominantly formed branched aldehyde from the obtained normal-branched-aldehyde mixture.

2. Process according to claim 1, characterized in that Z represents a lower alkyl residue.

3. Process according to any of the claims 1 and 2, characterized in that Z represents a methyl residue.

4. Process according to any one of the claims 1-3, characterized in that triphenylphosphite is used.

5. Process according to any one of the claims 1-4, characterized in that as apolar solvent toluene, benzene or xylene or mixtures thereof are used.

6. Process according to any one of the claims 1-5, characterized in that the molar ratio between rhodium compound and phosphite ligand is in the range of from 2 to 5.

7. Process according to any one of the claims 1-6, characterized in that the hydroformylation is carried out at a temperature in the arange of from 50-70 "C.

8. Process according to any one of the claims 1-7, characterized in that allylacetate is hydroformylated.

9. Process according to claim 1, substantially as described with reference to the examples.

10. Branched aldehydes, obtained according to the process of claims 1-9.

11. 3-Acetoxy-2-methyl-propionaldehyde, obtained according to the process of claims 1-9.

12. Process for the preparation of methyl methacrylate comprising dehydratation and oxidation of the product obtained according to the process of claims 1-9, applied on allylacetate as starting material.