FR2477140A1 - PROCESS FOR THE PREPARATION OF A-CETOXY OR A-PROPIONYLOXY-PROPIONALDEHYDE - Google Patents

Abstract

The invention relates to a process for preparing alpha -acetoxypropionaldehyde or alpha -propionyloxypropionaldehyde. The process comprises the following stages: i) hydroformylation of vinyl acetate or vinyl propionate with a mixture of hydrogen and carbon monoxide in an organic solvent in the presence of an essentially water-insoluble rhodium complex and a trisubstituted phosphine, ii) extraction of the reaction mixture obtained in stage i) by an aqueous medium for separation into an aqueous layer, which contains alpha -acetoxypropionaldehyde or alpha -propionyloxypropionaldehyde, and an organic layer which contains the catalyst components and iii) returning the organic layer obtained in stage ii) to the hydroformylation stage, that is stage i).

Description

dans laquelle R est un radical méthyle ou éthyle.The invention relates to a process for the preparation of a-acetoxy- or a-propionyloxy-propionaldehyde by hydroformylation of vinyl acetate or vinyl propionate using a rhodium complex as the main catalyst element. This reaction is represented by the following equation

in which R is a methyl or ethyl radical.

 Α-acetoxypropionaldehyde and α-propionyloxypropionaldehyde are very useful starting materials in industry for various organic syntheses including the preparation of lactic acid, lactic acid esters and threonine, for example.

It is well known that hydroformylation of vinyl acetate and vinyl propionate using a rhodium complex catalyst provides an α-acetoxypropionaldehyde and an α-propionyloxypropionaldehyde, respectively, with relatively high yields (e.g. Patent No 980 239; Journal of the Chemical Society, (A) 2753 (1970); U.S. Patent No 4,072,709). It is well known that rhodium complexes are very hillside. Therefore, for the production of a-acetoxy- or a-propionyloxy-propionaldehyde on a commercial scale by hydroformylation of vinyl acetate or vinyl propionate, it is particularly important, from a technological point of view, to efficiently separate the product, for example a-acetoxy- or a-propionyloxy-propionaldehyde, which is relatively thermally as well as chemically unstable, from the reaction medium containing the rhodium complex, and to reuse the catalyst by recycling it while retaining the catalytic activity of the rhodium complex. However, no research report can be found aimed at solving these technical problems. In the prior processes, these technical problems have never been resolved. To isolate the α-acetoxy- or the α-propionyloxy-propionaldehyde from the mixture of the hydroformylation reaction, the known prior processes use distillation. Detailed research by the inventors of the present process has shown that the separation of the aldehyde product by distillation presents, inter alia, the following problems: a) -acetoxy- or a-propionyloxy-propionaldehyde undergoes undesirable side reactions, such as that decarboxylation, polycondensation and oxidation reactions, under the distillation conditions and b) a repeated hydroformylation reaction followed by separation by distillation results in a reduction in the catalytic activity of the rhodium complex recycled and reused when the number repetitions increases and, at the same time, high-boiling by-products accumulate. Such separation by distillation cannot therefore be used on an industrial scale.

According to the invention, there is provided a process for the preparation of a-acetoxypropionaldehyde and a-propionyloxypropion-aldehyde according to which
i) vinyl acetate or vinyl propionate is hydroformylated with a mixture of hydrogen and carbon monoxide in an organic solvent, in the presence of a rhodium complex substantially insoluble in water and a phosphine trisubstituted,
ii) the reaction mixture obtained in step i) is subjected to an extraction with an aqueous medium, so as to separate it into an aqueous layer containing α-acetoxypropionaldehyde or α-propionyloxypropionaldehyde and an organic layer containing the elements catalysts, and
iii) the organic layer extraction residue) obtained in step ii) is recycled to the hydroformylation step, that is to say step i).

In this process, a-acetoxy- or a-propionyloxy-propionaldehyde can be efficiently extracted from the reaction mixture into the aqueous layer.

In addition, when the organic layer containing the catalyst elements is recycled to the hydroformylation stage, the catalytic activity can be kept at a satisfactory level, while the loss of rhodium complex and trisubstituted phosphine due to the dissolution in the aqueous layer during the extraction step is very weak. Consequently, the process according to the invention makes it possible to prepare a-acetoxy- or a-propionyloxy-propionaldehyde by hydroformylation of vinyl acetate or of vinyl propionate in an advantageous manner on an industrial scale.

 When we take into consideration the balance between the hydrophilic and hydrophobic parts as we can estimate them from the structural formula of a-acetoxy- or a-propionyloxy-propionaldehyde, it is quite surprising that aldehydes mentioned above can be separated very efficiently by extraction of the hydroformylation reaction mixture with an aqueous medium.

With regard to the extraction step using an aqueous medium, the organic solvent to be used in accordance with the invention is a solvent which is substantially insoluble in water.

Mention may be made of a large number of solvents which may be used. However, in view of the solubilities of the catalyst elements, of the loss of catalyst elements due to their dissolution in the aqueous layer, of the price, of the physical properties also suitable for the subsequent separation step, of the chemical stability. , the result of the hydroformylation reaction, etc., there may be mentioned as desirable compounds, aromatic hydrocarbons optionally substituted by at least one lower alkyl radical such as benzene, toluene, xylene and ethylbenzene, and hydrocarbons saturated, substituted or unsubstituted alicyclics, such as cyclohexane and methylcyclohexane. Benzene, toluene and xylene are particularly preferred.

As the rhodium complex, any rhodium complex which is active as a hydroformylation catalyst under hydroformylation conditions and which is substantially insoluble in the aqueous medium can be used. A large number of such rhodium complexes are known. Most of the known rhodium complexes can be used in the process according to the invention. Mention may be made, by way of examples,
HRh (CO) (PA3) 3 (A = aryl radical), RhCl (PA3) 3, Rh (acac) 3 (acac = acetylacetonate radical), Rh (OAc) 3 (OAc = acetoxy radical), Rh4 (CO) 12 r Rh6 (CO) 16 t CRh (Co) 2 (PA3) 2l2 and Rh203. From the point of view of catalytic activity, solubility, ease of handling, etc., rhodium complexes of the HRh (CO) (PA3) 3 type are preferred. With regard to the way of adding the rhodium complex, a method can be implemented according to which a catalyst solution is prepared in an independent reactor, in the usual manner, and this solution is introduced into the hydroformylation reactor.

The rhodium complex is generally used in an amount ranging from 0.1 to 25 mmol, preferably from 0.1 to 10 mmol per liter of hydroformylation reaction mixture.

If the rhodium complex is used in amounts of less than 0.1 mmol / liter of the reaction mixture, an industrially satisfactory reaction rate cannot be obtained. On the other hand, the use of the rhodium complex in large, unnecessary amounts, greater than 25 mmol / liter of the reaction mixture, is disadvantageous, not only from the economic point of view but also because of the significant losses of rhodium complex due to dissolution in the aqueous layer during the extraction step (i.e. step ii)).

The trisubstituted phosphine to be used in step i) of the process according to the invention is represented by the general formula PR'R "R" ', in which R' and R "are each an aromatic hydrocarbon group and R" 'is a aromatic hydrocarbon group or a saturated aliphatic hydrocarbon group containing not less than 3 carbon atoms. Examples of such trisubstituted phosphines are substituted or unsubstituted triarylphosphines, such as triphenylphosphine, tritolylphosphine and trinaphtylphosphine, and diaryl-alkyl-phosphines such as diphenylpropylphosphine and diphenylhexylphosphine. Among these latter, more particularly preferred are substituted or unsubstituted triarylphosphines. The inventors have determined that the selectivity with respect to α-acetoxy- or α-propionyloxypropionaldehyde, the reaction rate, the lifetime of the catalyst, the loss of rhodium due to dissolution in the aqueous layer and the loss of trisubstituted phosphine due to dissolution in the aqueous layer are highly dependent on the amount of trisubstituted phosphine. Thus, lower amounts of trisubstituted phosphine are favorable with regard to the selectivity, the reaction rate and the loss of trisubstituted phosphine due to the dissolution in the aqueous layer, while larger quantities of trisubstituted phosphine are favorable in as regards the lifetime of the catalyst and the loss of rhodium due to dissolution in the aqueous layer. It is therefore found that the trisubstituted phosphine has contradictory effects depending on the quantities in which it is used. When all of these factors are considered collectively, from an industrial perspective, the appropriate amount of trisubstituted phosphine is generally 5 to 50 moles / atomgram of rhodium. More precisely, it is advantageously used in an amount ranging from 10 to 150 mmol / liter of the hydroformylation reaction medium. Any combination of two or more trisubstituted phosphines can also be used.

The hydroformylation reaction in step i) of the process according to the invention can be carried out under the usual hydroformylation reaction conditions, namely at a reaction temperature of 50-1200C and under a reaction pressure of 0.5-200 kg / cm2 with a partial pressure of carbon monoxide of 0.1-150 kg / cm2. At temperatures below 500C the reaction rate is too low while at temperatures above 1200C undesirable side reactions occur disadvantageously. The lower the partial pressure of carbon monoxide in the hydrogen-monoxide mixture The higher the selectivity for a-acetoxy- or a-propionyloxy-propionaldehyde tends to be high. However, when the partial pressure of carbon monoxide exceeds a certain limit, there is also a tendency towards a decrease. of the reaction speed. In view of this, it is preferred to carry out the process under a partial pressure of carbon monoxide from 4 to approximately
2 50 kg / cm. A hydrogen / carbon monoxide molar ratio as recommended for common hydroformylation reactions can be applied as the hydrogen / carbon monoxide molar ratio in the present process. When the hydroformylation reaction is carried out using a hydrogen mixture / carbon monoxide with a hydrogen / carbon monoxide molar ratio of about 0.5-5, it is desirable that the reaction pressure be maintained at a value not less than about 25 kg / cm2 having regard to the selectivity for lra-acetoxy- or α-propionyloxy-propionaldehyde, reaction rate, catalyst life, etc. The upper limit of the reaction pressure is preferably 150 kg / cm 2. Consequently, under the preferred conditions of the process according to the invention, hydroformylation of vinyl acetate or vinyl propionate is carried out at a reaction temperature of 50-1200C and under a reaction pressure of about 25-150 kg / cm2 with a partial pressure of carbon monoxide from 4 to about 50 kg / cm2 using a trisubstituted phosphine in an amount between about 5 and about 50 moles per gram atom of rhodium, and thus a high reaction rate and a high selectivity can be obtained.

The hydroformylation reaction of the process according to the invention, like the usual hydroformylation reactions of olefins, can be carried out continuously or batchwise in a reactor with an agitator or in a reactor of the bubbling column type, which is known per se.

 To prevent the accumulation of reaction heat, to increase the selectivity for a-acetoxv- or a-propionyloxy-propionaldehyde and to prevent the accumulation of high boiling by-products, it is advantageous to use carry out the reaction while maintaining the vinyl acetate or vinyl propionate concentration in the reaction system within a certain determined range by continuously feeding the vinyl acetate or vinyl propionate. The concentration of a-acetoxy- or a-propionyloxy-propionaldehyde in the reaction medium should preferably be maintained at a value of about 0.5 to about 3 moles / liter of the reaction medium from the point of view of the accumulation of sub -products with high boiling point, of the loss in rhodium complex and in trisubstituted phosphine due to the dissolution in the aqueous layer, of the effi ciency of the extraction of 1 a-acetoxy- or a-propionyloxypropionaldehyde in the aqueous phase, etc.

The reaction medium obtained in the stamp (stage i) of hydroformylation of vinyl acetate or of vinyl propionate is subjected to an extraction with an aqueous medium in stage ii), 1 'a-acetoxy- or a- propionyloxy-propionaldehyde being separated in the aqueous layer. In the process according to the invention, water or an aqueous solution containing a small amount of an organic carboxylic acid derived from vinyl acetate or vinyl propionate is used.

Through extensive research, the inventors have found that the rate of extraction of a-acetoxy- or a-propionyloxy-propionaldehyde in the aqueous layer and the loss of rhodium complex and of trisubstituted phosphine due to the dissolution in the aqueous layer are dependent on factors such as the effectiveness of the contact between the aqueous layer and the layer of the hydroformylation reaction mixture, the extraction temperature, the concentration of α-acetoxy- or α-propionyloxypropionaldehyde in the reaction mixture; the volume ratio of the aqueous medium to the reaction mixture and of the atmosphere at the time of extraction. Thus, the greater the effectiveness of the contact between the aqueous medium and the layer of the hydroformylation reaction medium, the higher the temperature the lower the extraction ratio, the higher the volume ratio of the aqueous medium to the hydroformylation reaction mixture, then the higher the extraction rate of a-acetoxy- or a-propionyloxy-propionaldehyde in the aqueous layer. 'raising and the loss of rhodium complex and tri-substituted phosphine due to dissolution in the aqueous layer tends to decrease. For the extraction step, extraction columns of the stirred reactor type, particularly of the RDC (rotary disk contactor) type are preferred from the point of view of the effectiveness of the contact between the aqueous layer and the reaction medium. 'hydroformylation.

The extraction temperature is chosen in the range of about 5 to about 400C. The volume ratio of the aqueous medium to the medium of the hydroformylation reaction depends on the concentration of α-acetoxy- or α-propionyloxy-propionaldehyde in the reaction medium. However, the ratio should preferably be chosen in the range 0.3-3 when said concentration is from about 0.5 to about 3 moles / liter of the reaction medium. Extraction with the aqueous medium from step ii ) is preferably carried out under an atmosphere of an inert gas substantially free of oxygen, such as nitrogen, helium or argon, or a hydrogen-carbon monoxide mixture having a partial pressure carbon monoxide of at least 0.1 kg / cm2, or a hydrogen-carbon monoxide mixture diluted with the inert gas mentioned above and having a partial pressure of carbon monoxide of at least 2 0.1 kg / cm2. It has been found that by doing so, the rhodium complex can be prevented from dissolving in the aqueous layer. The extraction can be carried out either continuously or discontinuously. However, continuous extraction is more advantageous from an industrial point of view.

The organic layer (extraction residue) containing the catalyst elements obtained in step ii) is recycled during
from step iii) to the step of the hydroformylation reaction during which it is reused. In this case, part of the extraction residue, after having been subjected, if necessary, to a known catalytic activation process, is recycled to the hydroformylation stage.

 The aqueous layer containing α-acetoxy- or α-propionyloxy-propionaldehyde obtained in step ii) can be supplied such as to a reaction system such as an oxidation reaction or Strecker's reaction, for example, in which the a-acetoxy- or a-propionyloxy-propionaldehyde is transformed into other useful compounds, or led to a distillation zone in which the a-acetoxy- or apropionyloxy-propionaldehyde is isolated by fractional distillation. It has been found that, in such fractional distillation, maintaining the temperature of the liquid to be distilled at 900C or below is necessary to obtain a-acetoxy- or a-propionyloxy-propionaldehyde with a high yield and having a purity suitable for the practical use of the aldehyde. When the temperature of the liquid part to be distilled is higher than 900C and reaches about 950C or more, for example, hydrolysis, polycondensation or other reactions take place during distillation , the purity and the yield of 1 t a-acetoxy- or a-propionyloxypropionaldehyde then decreasing. The fractional distillation considered above is generally carried out under a reduced pressure depending on the aldehyde produced, while the temperature of the liquid to be distilled is maintained at 900C or at a lower temperature. Thus, in the case of a-acetoxypropionaldehyde, one operates under a reduced pressure of 10-90 mm Hg and, for a-propionyloxypropionaldehyde, under a reduced pressure of 1-40 mm Hg. During the implementation of the process according to the invention, it is also possible to partially remove traces of rhodium complex and of organophosphorus compound contained in the aqueous layer, before fractional distillation, by subjecting the aqueous layer to an extraction with an organic solvent or to a treatment with an adsorption agent such as activated carbon. As regards the purity of the a-acetoxy- or a-propionyloxypropionaldehyde, it is possible to obtain extremely pure a-acetoxy- or a-propionyloxy-propionaldehyde, substantially free of impurities, if desired. , but it is advantageous to isolate it as a product containing a very small amount of water and / or an organic carboxylic acid derived from vinyl acetate or vinyl propionate.

 The following examples, given without any limitation being implied, illustrate the present invention.

EXAMPLE 1
In 130 ml of toluene is dissolved 276 mg (0.3 mmol) of HRh (CO) llP (C6Hs) 33 and 786 mg (3 mmol) of triphenylphosphine under an atmosphere of a hydrogen-carbon monoxide mixture (molar ratio H2 / CO = 2/1) at room temperature, and the solution is washed by bringing it into contact with 2 portions of 130 ml of distilled water which has been purged with nitrogen for 30 min, while stirring the solution with at 500 rpm. A 300 ml stainless steel autoclave equipped with a magnetic stirrer, a thermometer, a pressure regulator is adequately purged with a hydrogen-carbon monoxide mixture (H2 / CO molar ratio = 2/1). , a valve for regulating the flow of exhaust gas and the inlets for the introduction of the starting materials and charging it with the toluene solution washed above. The autoclave is carried under an internal pressure of 30 kg / cm2 (partial pressure of carbon monoxide 10 kg / cm2) using a hydrogen-carbon monoxide mixture (molar ratio
H2 / CO = 2/1). The autoclave is then immersed in an oil bath and heated to 700C (internal temperature). The stirring is started at the rate of 600 revolutions / minute and, while maintaining the temperature at 700C, 15.5 g (180 mmol) of vinyl acetate are introduced continuously through the vinyl acetate feed inlet and this over a period of one hour.

During the reaction, a hydrogen-carbon nionoxide mixture having the above-mentioned H2 / CO molar ratio mentioned above is introduced from a small gas tank, so as to provide an exhaust gas flow rate of 8.5 liters. / hour. The pressure of the gas mixture is continuously adjusted to 30 kg / cm 2 by passing the mixture through the pressure regulator. The low boiling compounds (vinyl acetate, propionaldehyde, etc.) contained in the gas The exhaust are collected in a trap placed in a dry ice-acetone bath. After completion of the addition of vinyl acetate, stirring is continued under a constant pressure (30 kg / cm2) and at a constant temperature (700C) for 2 hours, so as to allow the reaction to continue . Analysis of the reaction medium by gas chromatography shows that the conversion rate of vinyl acetate 3 hours after the start of the reaction is 88% and that the selectivity for α-acetoxypropionaldehyde is 94 g based on transformed vinyl acetate.

After the reaction, the reaction mixture is cooled to room temperature, then depressurized and transferred, under an atmosphere of hydrogen-carbon monoxide whose molar ratio above has been maintained, in a 300 ml glass extractor equipped with an agitator and connected to the autoclave. 40 ml of distilled water previously purged with nitrogen are added to the extractor, the addition being carried out at 250C under the above atmosphere of hydrogen-carbon monoxide 2 (partial pressure of carbon monoxide = 0.33 kg / cm).

Extraction of the acetoxypropionaldehyde is carried out in the reaction medium with water, with stirring at 500 revolutions / minute for 15 minutes. The toluene solution layer is separated from the aqueous extraction layer, 35 ml of distilled water is added to the toluene layer and the same extraction process is repeated. The volume ratio of the amount of distilled water used for the extraction (75 ml) to the reaction medium is 1/2. By extraction, 962 of the α-acetoxypropionaldehyde which formed was transferred to the aqueous layer. The rhodium concentration of the aqueous extraction layer as measured by atomic absorption spectrometry is 0.05 ppm and the phosphorus concentration, as measured by the colorimetric method, is 2 ppm.

EXAMPLE 2
The reaction residue containing the catalyst elements obtained by extraction in Example 1 is carried out under pressure from the autoclave extractor used in Example 1 which has been purged with the hydrogen-carbon monoxide mixture.

The hydroformylation is carried out by the process of Example 1 by introducing vinyl acetate continuously, for about 55 minutes, until the amount of vinyl acetate in the reaction medium reaches 15.5 g (180 mmol).

The reaction mixture is subjected to the extraction of the resulting α-acetoxypropionaldehyde with water by the same process and under the same conditions as in Example 1. The hydroformylation of vinyl acetate, followed by extraction. The conversion rate of vinyl acetate in the third, sixth and tenth cycles is 89, 91 and 90%, respectively.

No decrease in catalytic activity is thus observed due to the repetition of the reaction and extraction procedure. The concentration of rhodium in the aqueous extract layer, as determined by atomic absorption spectrometry, for the third, sixth and tenth cycles, is 0.04, 0.03 and 0.06 pprn, respectively. extraction medium (organic layer) obtained after the tenth cycle is transferred under a nitrogen atmosphere to a distillation apparatus under reduced pressure and the solvent, the vinyl acetate which has not reacted, and the α-acetoxypropionaldehyde- remaining, are extracted by distillation under reduced pressure at a temperature of the liquid to be distilled of 800 C. No accumulation of by-products with high boiling point is noticed in the distillation residue. Furthermore, 250 ml of the combined aqueous extraction layer are introduced into a distillation apparatus under reduced pressure, previously purged with nitrogen, and a fractional distillation is carried out under reduced pressure for approximately 1 hour, while maintaining the temperature of the liquid part at 650 C. Analysis by gas chromatography shows that the recovery rate of α-acetoxypropionaldehyde based on α-acetoxypropionaldehyde present in the aqueous extraction layer is 98%. No impurities were found in the α-acetoxypropionaldehyde fraction, except for the presence of very small amounts of water and acetic acid.

EXAMPLE 3
Dissolve in 125 ml of toluene, at room temperature and under an atmosphere of a mixture of hydrogen carbon monoxide (molar ratio H2 / CO = 2/1) 207 mg (0.23 mmol} of HRh (CO) [P (C6H5) 3] 3 and 393 mg (1.5 mmol) of triphenylphosphine The solution is washed twice by bringing it into contact with 125 ml of distilled water, purged with nitrogen gas, while stirring at 500 rpm for 30 minutes. Purge the appropriate baleen with a mixture of hydrogen and carbon monoxide (molar ratio H2 / CO 2/1) a 300 ml stainless steel autoclave equipped with a magnetic stirrer, a thermometer, a pressure regulator, a valve for regulating the flow rate of the exhaust gases, and an inlet for supplying a mixture of hydrogen-carbon monoxide, then the washed toluene solution mentioned above and 22 g (256 mmol) of vinyl acetate are introduced therein. The interior of the autoclave is brought to a pressure of 40 kg / cm 2 (partial pressure carbon monoxide = 13.3 kg / cm2) with a hydrogen-carbon monoxide mixture (H2 / CO molar ratio = 2/1). The autoclave is then immersed in an oil bath and heated to 800C (internal temperature) .Stirring is started at the rate of 600 rpm and, while maintaining the temperature at 800C, the hydrogen mixture is introduced. carbon monoxide mentioned above from a small tank, so as to provide an exhaust gas flow rate of 10 liters / hour, the pressure of the gas mixture being adjusted to a constant value of 40 kg / cm2 by passing the mixture through the pressure regulator. By proceeding in this way, the hydroformylation of vinyl acetate is carried out under constant pressure (40 kg / cm2) and at constant temperature (80 C) for 2.5 hours. Analysis of the reaction medium by phase chromatography gas shows that the conversion rate of vinyl acetate after two and a half hours is 92%, the selectivity for acetoxypropionaldehyde based on the transformed vinyl acetate being 93%.

 After the reaction, the reaction mixture is cooled to room temperature, it is depressurized, and 70 ml of the reaction mixture are transferred to a 200 ml extractor, equipped with a stirrer, under an atmosphere of a hydrogen gene-monoxide mixture. carbon (H2 / CO molar ratio = 1/1). Is added to the extractor, at 25 ° C. and under an atmosphere of a hydrogen-carbon monoxide mixture (molar ratio H2 / CO = 1/1; partial pressure of carbon monoxide = 0.5 ks / cm2) 35 ml d distilled water purged with nitrogen gas, the water / reaction mixture volume ratio being 1/2.

The α-acetoxypropionaldehyde is extracted from the reaction medium with water, with stirring at 500 rpm for 30 minutes. By the extraction process, 89% of the -acetoxypropionaldehyde which had formed is extracted into the aqueous layer. The rhodium concentration of the aqueous extraction layer, as measured by atomic absorption spectrometry, is 0.06 ppm.

 The remaining 70 ml of the reaction mixture are transferred, under a nitrogen atmosphere, to a 200 ml extractor equipped with a stirrer, and the extraction of the α-acetoxypropionaldehyde is carried out under a nitrogen atmosphere, using 35 ml (volume ratio to reaction medium = 1/2) of distilled water, under the same conditions as indicated above.

The extraction percentage of the acetoxypropionaldehyde is 88% and the rhodium concentration of the aqueous extraction layer as measured by atomic absorption spectrometry is 0.04 ppm.

EXAMPLE 4
Hydroformation of vinyl propionate is carried out by following the procedure of Example 3, but using 25 g (250 mmol) of vinyl propionate in place of vinyl acetate and 456 mg (1.5 mmol) of tritolylphosphine in place of triphenylphosphine. The vinyl propionate conversion rate is 88% and the selectivity for α-propionyloxypropionaldehyde is 91%, based on the transformed vinyl propionate. The reaction mixture is cooled to room temperature and then extracted twice with 75 ml of distilled water purged with nitrogen, according to the extraction process of Example 1, the volume ratio of the total amount of water used the reaction medium being 1/1. The percentage of extraction of α-propionyloxypropionaldehyde is 90% and the rhodium concentration of the aqueous extraction layer is 0.03 ppm. Then 150 ml of the aqueous extraction layer are introduced into a distillation apparatus under reduced pressure, previously purged with nitrogen, and a fractional distillation is carried out under reduced pressure for approximately 30 minutes, while maintaining the temperature of the liquid to be distilled 750 C. The recovery rate of a-propionyloxypropionaldehyde, as determined by gas chromatography, is 96%, based on the propionyloxypropion-aldehyde present in the aqueous extraction layer. small amounts of water and propionic acid in the α-propionyloxypropionaldehyde fraction but other impurities could not be detected.

EXAMPLE 5
A solution prepared in advance of 18.7 mg (0.025 mmol) of Rh4 (CO) 12 and 524 mg (2 mmol) of triphenylphosphine in 80 is introduced into a 300 ml stainless steel autoclave, equipped with a magnetic stirrer. ml of benzene, and 20 ml of vinyl acetate. The autoclave is appropriately purged with a hydrogen-carbon monoxide mixture (H2 / CO molar ratio = 1/1) then it is put under pressure as an intro.
2 producing the same gas mixture at a pressure of 40 kg / cm, the partial pressure of carbon monoxide being 20 kg /
7 cm-. The autoclave is then immersed in an oil bath and heated to 1000C (internal temperature). When the temperature has reached 100 ° C., agitation is started and the temperature is then maintained at 1000 C. During the reaction, the pressure is maintained at 40 kg / cm 2 by introducing the gas mixture (molar ratio H2 / CO = 1/1) from a small gas tank via a pressure regulator. By operating in this way, hydroformyation of the vinyl acetate is carried out under constant pressure and at constant temperature for 3 hours. Analysis of the product by gas chromatography shows that the conversion rate of vinyl acetate, after 3 hours, is 79%, the yields of α-acetoxypropionaldehyde and propionaldehyde being 151 mmol and 5 mmol respectively .

 The formation of ss-acetoxypropionaldehyde is not confirmed.

After the reaction, the reaction medium is cooled to room temperature, it is depressurized, and it is carefully transferred under an atmosphere of the gaseous mixture (molar ratio
H2 / CO = 1/1) in a 300 ml separation funnel (dropping funnel) equipped with an agitator. Under an atmosphere of the gas mixture (molar ratio H2 / CO = 1/1; partial pressure of carbon monoxide = 0.5 kg / cm2) and at room temperature, 100 ml of distilled water is added (H2O / reaction medium = 1 / l by volume), and the α-acetoxypropionaldehyde is extracted from the reaction medium with water, stirring at 500 rpm for 10 minutes. By this extraction process, 96% of the α-acetoxypropionaldehyde which has formed is extracted in the aqueous layer.

EXAMPLE 6
The extraction residue of Example 5 (benzene solution containing the catalyst elements) is introduced into the autoclave used in example 5 with a sufficient quantity of vinyl acetate so that the quantity of vinyl acetate in the reaction medium, ie 20 ml, and the hydroformylation of vinyl acetate is repeated four times followed by the extraction of α-acetoxypropionaldehyde with water, following the process of the example 5.

 During the first, second, third and fourth cycles, α-acetoxypropionaldehyde was obtained in amounts of 152, 151, 153 and 150 mmol, respectively, no decrease in catalytic activity being observed.

EXAMPLE 7
Hydroformylation of vinyl propionate is carried out and extraction with water following the process of Example 5 but using 20 ml of vinyl propionate in place of vinyl acetate, and toluene to instead of benzene. The conversion rate of vinyl propionate is 76%, the a1 extraction rate of α-propionyloxypropionaldehyde being 889. The rhodium concentration of the aqueous extraction layer is 0.15 ppm. The extraction residue ( organic layer) containing the catalyst elements obtained after the extraction process of the α-propionyloxypropion-aldehyde is transferred under pressure from the extractor to the autoclave, a sufficient quantity of vinyl propionate is added to obtain an amount total vinyl propionate in the reaction medium of 20 ml and the reaction is carried out by the process of Example 5. The reaction medium is subjected to an extraction of α-propionyloxypropionaldehyde with water according to the same process and under the same conditions as in Example 5. The hydroformylation of vinyl propionate followed by extraction is thus repeated five times. During the second, third, fourth and fifth cycles, tau x transformation of vinyl propionate by 78, 79, 79 and 77%, respectively, no reduction in catalytic activity being observed.

COMPARISON EXAMPLE 1
The hydroformylation of the vinyl acetate is carried out according to the process of Example 1, except that the catalytic solution is prepared by dissolving 276 mg (0.3 mmol) of HRh (CO) (CgHg) 313 and 786 mg (3 mmol) of triphenylphosphine in 130 ml of dioctyl phthalate (DOP) at room temperature and under an atmosphere of a hydrogen-carbon monoxide mixture (molar ratio H2 / CO = 2/1).

The vinyl acetate conversion rate is 86% and the selectivity for α-acetoxypropionaldehyde is 92% based on the transformed vinyl acetate.

After the reaction, the reaction mixture is cooled to room temperature, depressurized, then transferred under an atmosphere of hydrogen-carbon monoxide mixture (H2 / CO molar ratio = 2/1) to a distillation apparatus under reduced pressure connected to the autoclave. , and the α-acetoxypropionaldehyde produced is separated by distillation under reduced pressure for about 1 hour, the temperature of the liquid to be distilled being maintained at 900C. At the end of the distillation, 85% of the acetoxypropionaldehyde present in the reaction medium was recovered. The residue obtained after distillation under reduced pressure is brown in color, and a transformation of the catalyst into metallic rhodium is observed. This distillation residue is transferred under pressure to an atmosphere of hydrogen-carbon monoxide mixture (molar ratio
H2 / CO = 2/1) again in the autoclave, and the reaction is repeated under the same conditions as in Example 1 by introducing 15.5 g (180 mmol) of vinyl acetate continuously for 1 hour .

 The hydroformylation of vinyl acetate is repeated in this way, followed by separation of the α-acetoxypropionaldehyde produced by distillation. A significant decrease in catalytic activity is observed as the number of test repeats increases.

COMPARISON EXAMPLE 2
250 ml of the aqueous extract obtained by the same process as in Example 1 are introduced into a distillation apparatus under reduced pressure, previously purged with nitrogen. The aqueous extraction layer is subjected to a fractional distillation under reduced pressure for about 1 hour, while maintaining the temperature of the distilled liquid: at 1000C. The recovery rate of α-acetoxypropionaldehyde, as determined by gas chromatography, is 85% based on the α-acetoxypropionaldehyde present in the aqueous extraction layer. It is noted that a hydrolysis of α-acetoxypropionaldehyde (formation of acetic acid) has partially taken place.

COMPARISON EXAMPLE 3
The reaction is carried out according to the procedure of Example 1, except that 56 mg (0.075 mmol) of Rh4 (CO) 12 is used in place of HRh (CO) [P (C6H5) 33 plus triphenylphosphine. The vinyl acetate conversion rate is 868, the selectivity for α-acetoxypropionaldehyde being 94% based on the transformed vinyl acetate. The rhodium concentration of the aqueous extraction layer is 2.98 ppm.

Claims (8)

1.- Process for the preparation of a-acetoxy- or ct-propionyl-oxy-propionaldehyde, characterized in that  i) vinyl acetate or vinyl propionate is hydroformylated with a mixture of hydrogen and carbon monoxide in an organic solvent, in the presence of a rhodium complex substantially insoluble in water and a trisubstituted phosphine,  ii) the reaction medium obtained in step i) is subjected to an extraction with an aqueous medium, so as to separate it into an aqueous layer containing α-acetoxy- or α-propionyloxypropionaldehyde and an organic layer containing catalyst elements, and iii) the organic layer obtained in step ii) is recycled to the hydroformylation step, that is to say step i).  2.- Method according to claim 1, characterized in that the hydroformylation of vinyl acetate or vinyl propionate in step i) is carried out at a temperature of 50 2 1200C and under a reaction pressure of 0, 5-200 kg / cm2 with  2 a partial pressure of carbon monoxide of 0.1-150 kg / cm2.  3.- Method according to claim 1, characterized in that the hydroformylation of vinyl acetate or vinyl propionate in step i) is carried out at a temperature of 2 50-1200C, under a reaction pressure d about 25-150kg / cm2 with a partial pressure of carbon monoxide from 4 to about 50 kg / cm2, and in the presence of a trisubstituted phosphine in an amount of about 5 to about 50 moles / gram atom of rhodium. 4.- Method according to claim 1, characterized in that, in step i), the rhodium complex is used at a concentration of 0.1-25 mmol / liter of the hydroformylation reaction medium. 5.- Method according to claim 1, characterized in that, in step ii), the extraction process is carried out at a temperature of about 5-400C and under an atmosphere consisting of an inert gas or a hydrogen mixture - carbon monoxide with a partial pressure of carbon monoxide of not less than 0.1 kg / cm2 or a mixture of hydrogen and carbon monoxide diluted with an inert gas and having a pressure  2 partial carbon monoxide not less than 0.1 kg / cm2. 6.- Method according to claim 1, characterized in that, in step ii), the aqueous medium for the extraction is used in an amount of 0.3-3 parts by volume, based on the volume of the medium. the hydroformylation reaction.  7.- The method of claim l, characterized in that the -acetoxy- or a-propionyloxypropionaldehyde is recovered from the aqueous layer obtained in step ii) by fractionating said layer while maintaining the liquid to be distilled at a temperature of 900C or below.  8.- Method according to claim 1, characterized in that a-acetoxypropionaldehyde is prepared from vinyl acetate.