DE102011107930B3 - Preparing an aldehyde e.g. undecanal comprises hydroformylation of an olefin using formaldehyde and/or p-formaldehyde in the presence of a transition metal catalyst under additional hydrogen pressure - Google Patents

Abstract

Preparation of an aldehyde comprises hydroformylation of an olefin using formaldehyde and/or p-formaldehyde in the presence of a transition metal catalyst under additional hydrogen pressure, where the catalyst is a homogeneous rhodium catalyst with a chelating phosphorus ligand.

Description

The present invention relates to a process for the preparation of aldehydes from olefins using formaldehyde or paraformaldehyde in the presence of a transition metal catalyst.

The hydroformylation, also called oxo synthesis, olefinically unsaturated compounds by means of noble metal catalysts has long been known. Numerous publications have been published in the literature (see, for example, DE 10 2006 015 932 A1 and DE 10 2005 024 281 B4 ).

The conventional reaction of hydroformylation is characterized by the use of elemental hydrogen and carbon monoxide (synthesis gas) at elevated pressure. In addition to the apparatus requirements with regard to the high-pressure technique to be used, the toxicity of the carbon monoxide used above all presents a challenge for a reliable reaction. In order to avoid the risks of the mentioned synthesis gas mixture, the hydroformylation with formaldehyde or paraformaldehyde as reagents is advisable for a safer reaction procedure ,

From the literature, Adv. Synth. Catal. 2010, 352, pp. 299 to 304, it is already known to substitute synthesis gas by formaldehyde or paraformaldehyde.

In this method, a metal precursor such. [RhCl (cod)] ₂ in combination with bidentate phosphine ligands (these are phosphorus ligands with two possible coordination sites) for the hydroformylation of olefins. The ligands used include 2,2'-bis (diphenylphosphino) -1,1'-biphenyl and 4,6-bis (diphenylphosphino) phenoxazine, which can also be combined to increase the proportion of unbranched aldehydes. To date, there are no experimental or theoretical investigations on the mechanism of the reaction, therefore no analogies can be derived for hydroformylation with synthesis gas.

However, the process using formaldehyde or paraformaldehyde has considerable disadvantages. On the one hand, in addition to a large excess of formaldehyde (5 equivalents based on the molar amount of olefin used), a significantly higher proportion of catalyst (1 mol% based on the substrate used, ie 0.01 mol of catalyst for the reaction of 1 mol of olefin) be used to ensure a time-limited and therefore economic reaction. On the other hand, a second, relatively expensive phosphine ligand (4,6-bis (diphenylphosphino) phenoxazine) is required to produce the desired excess of unbranched aldehyde.

From the IN 232 932 A1 discloses a process for the hydroformylation of olefins using formaldehyde catalyzed by the hydrido complex HRh (CO) (PPh ₃ ) ₃ .

The invention has for its object to provide a process for the preparation of aldehydes from olefins by hydroformylation using formaldehyde or paraformaldehyde, which is characterized by a simpler and more economical reaction.

According to the invention the object is achieved by the method features specified in claim 1. Advantageous embodiments of this procedure are the subject of claims 2 to 4.

It has surprisingly been found that the hydroformylation with formaldehyde or paraformaldehyde can be carried out much more efficiently if the reaction takes place on a rhodium-based homogeneous catalyst with a chelating phosphorous ligand and with the introduction of gaseous hydrogen under elevated pressure.

With these measures, the amounts of catalyst or ligands can be reduced and at the same time an increased regioselectivity is achieved with simplification of the ligand system.

The supply of hydrogen is carried out at a pressure of 1 bar above normal pressure up to 50 bar, preferably up to 10 bar.

Depending on the olefins used, the reaction takes place at normal temperature or temperatures up to 150 ° C., preferably up to 120 ° C.

Under these conditions, accelerated conversion of olefins to aldehydes could be achieved. Furthermore, it was found that the amount of synthesis gas substitute (liquid formaldehyde or paraformaldehyde) can be reduced while maintaining the same rate of turnover. The reaction under additional hydrogen pressure also causes an increase in the n-regioselectivity in the hydroformylation products. Thus, an up to five-fold excess could be achieved in the preparation of unbranched aldehydes as the target product.

The hydroformylation can be carried out with toxicologically less questionable formaldehyde or paraformaldehyde. This can be dispensed with the use of highly toxic and costly carbon monoxide.

With appropriate dosage of the amount of gaseous hydrogen also the regioselectivity can be increased in favor of the unbranched aldehyde. To increase the selectivity no additional and expensive organic ligand is needed, as is the case when only formaldehyde or paraformaldehyde are used.

Of great advantage is that the hydroformylation can be carried out at a pressure of less than 10 bar, whereby a reaction in laboratory glassware is possible. Since the reaction takes place without supply of carbon monoxide, the safety requirements are reduced. The required hydrogen can be easily provided in most laboratories and chemical plants.

The reaction of the olefin by the process according to the invention proceeds in two substeps. It starts with the formation of the active catalyst species. For this purpose, the metal precursor with the appropriate ligand, the olefinic compound and an aqueous solution of formaldehyde or paraformaldehyde in a suitable solvent to the appropriate reaction temperature, preferably 90 to 120 ° C, heated. In the ligands used, for example, bidentate trivalent phosphorus compounds, such as. For example, phosphines or phosphites can be used. In order to ensure an advantageous separation of the product from the reagent, an aqueous solution of formaldehyde or paraformaldehyde, nonpolar solvents are suitable for the reaction. The use of aromatic solvents such as toluene additionally guarantees the solubility when using oxygen-insensitive arylphosphines as ligands.

In order to ensure a complete formation of the catalytically active species, depending on the chosen amounts and concentration ratios, a continued stirring of the reaction mixture after reaching the reaction temperature is possible but not mandatory. Subsequently, the addition of hydrogen with increasing the total pressure, preferably between 1 to 10 bar. The hydrogen pressure is kept constant over the reaction time, optionally by regular replenishment. After completion of the reaction, the organic phase can be separated from the aqueous formalin solution and freed by distillation from unreacted starting material and any by-products.

The invention will be explained below with reference to several examples.

example 1

The conversion of 1-decene to undecanal was carried out under the following conditions:
[RhCl (cod) ₂ ] (246.5 mg, 0.5 mmol), rac-BINAP (1.245 g, 2.0 mmol), 1-decene (97%, 72.23 g, 0.5 mol) weighed into a one-liter reactor (Parr) and treated with formaldehyde (30% in H ₂ O, 62.56 g, 0.63 mol) and toluene (274 ml).

The reaction mixture was purged several times with nitrogen and heated to 90 ° C with stirring (1200 min ^-1 ) over a period of 25 minutes. Stirring was continued for 1 hour at this temperature before the pressure in the reactor was increased by 1 bar by addition of hydrogen. The immediately occurring pressure decrease in the reactor was compensated after 15 minutes by adding hydrogen again. The first sampling took place 110 minutes after reaching the reaction temperature. After sampling and the associated pressure drop hydrogen was added again. The subsequent metered addition of hydrogen was carried out in each case after a drop in the total pressure by about 0.4 bar. After 360 minutes, the second sample was taken for gas chromatographic analysis and the reaction was terminated by cooling to room temperature. The results of the gas chromatographic analysis are shown in Table 1 below.

Comparative Example 1

Under analogous conditions (weights and reaction procedure) as in Example 1, the hydroformylation of 1-decene was repeated to Undecanal, only with the difference that the reaction was carried out without the addition of hydrogen.

The results obtained are given in Table 1 below. Table 1 Examples H ₂ [bar] Yield [%] ^{a, b} Selectivity [%] ^{a, c} Regioselectivity (n: iso) ^{a, d} TON ^{a, e} TOF [h ^-1 ] ^{a, f} example 1 1 70 74 2.0 940 157 Comparative example without 40 73 1.4 550 92

Examples 2 to 4:

The reaction of 1-octene to nonanal was carried out under the following conditions:
[RhCl (cod) ₂ ] (4.93 mg, 10.0 μmol), rac-BINAP (98%, 25.4 mg, 40 μmol), 1-octene (1.12 g, 10.0 mmol) Weighed into a twenty-five milliliter (Parr) reactor and added formaldehyde (37% in 1120, 974 mg, 12.0 mmol) and toluene (7.5 mL). The reaction mixture was purged several times with nitrogen and heated with stirring (1000 min ^-1 ) over a period of 25 minutes at 90 ° C, before the pressure in the reactor by addition of hydrogen by 5 bar (10 bar) was increased. After 360 minutes, the reaction was stopped by cooling to room temperature and the reaction mixture was analyzed by gas chromatography.

When Example 3 was carried out, only one other solvent, tetrahydrofuran (THF), was used in comparison with Example 1.

When Example 4 was carried out, in comparison to Example 1, only a higher hydrogen pressure (10 bar) was used.

The results obtained are given in Table 2 below.

Comparative Example 2

Under analogous conditions (weighing and reaction) as in Example 2, the hydroformylation of 1-octene was repeated to nonanal, but with the difference that the reaction was carried out without addition of hydrogen.

The results obtained are given in Table 2 below. Table 2 Examples solvent H ₂ [bar] Yield [%] ^{a, b} Selectivity [%] ^{a, c} Regioselectivity (n: iso) ^{a, d} TON ^{a, e} TOF [h ^-1 ] ^{a, f} Example 2 toluene 5 70 80 4.7 870 145 Example 3 THF 5 58 97 2.0 600 100 Example 4 toluene 10 70 89 3.9 790 132 Comparative Example 2 toluene without 29 85 1.8 340 57

In the tables a to f have the following meaning:
^a The values were determined by gas chromatographic analysis of the reaction mixture.
^b The yield refers to the amount of product formed (n- and iso-aldehyde) based on the maximum possible amount of product. The maximum possible amount of product corresponds to the amount of olefin used.
^c The selectivity denotes the proportion of aldehydes (n and iso) formed relative to the total conversion.
^d Regioselectivity refers to the ratio between the molar amounts of regioisomeric products (n- / iso-aldehyde).
^e The turnover number (TON) refers to the converted amount of starting material (olefin) based on the amount of catalyst used.
^f The turnover frequency (TOF) refers to the converted amount of starting material (olefin) based on the amount of catalyst used in a given time. The above values were averaged over the entire reaction time (6 h).

The proposed procedure under additional hydrogen pressure leads overall to a significant increase in efficiency compared to known reactions using formaldehyde without hydrogen, as the achieved turnover frequencies (TON values) in the tables occupy.

Claims (4)

A process for the preparation of aldehydes by hydroformylation of olefins using formaldehyde and / or paraformaldehyde in the presence of a transition metal catalyst, characterized in that the reaction is carried out under additional hydrogen pressure on a homogeneous rhodium catalyst having a chelating phosphorous ligand. A method according to claim 1, characterized in that the reaction is carried out at a hydrogen pressure of 1 to 25 bar. Method according to one of claims 1 or 2, characterized in that the reaction is carried out at a hydrogen pressure of 1 to 10 bar. Method according to one of claims 1 to 3, characterized in that the hydroformylation is carried out at temperatures between 90 and 120 ° C.