MXPA98000905A - Continuous preparation of 5-formilvaleric esters in its form p - Google Patents

Abstract

The 5-formylvaleric esters are separated, in a yield of not less than 90%, by distillation of a mixture of the formylvaleric ester of 5-formylvaleric ester and either 3- or 4-formylvaleric ester or a mixture of the 3- and 4-formylvaleric esters, wherein The radical esters of the respective formylvaleric esters are identical, wherein the 3- or 4-formylvaleric ester or a mixture of these is separated from the 5-formylvaleric ester in a distillation column at a pressure in the range from 2 to 100 mbar and a temperature not exceeding 150 ° C (measured as the temperature at the bottom of the column (and the esters used are the corresponding methyl or ethyl esters, where the purity of the 5-formylvaleric ester is not less than 98% and as an impurity, the 4-formylvaleric ester is present in a amount not greater than 100p

Description

CONTINUOUS PREPARATION OF 5-FORMILVALERIC ESTERS IN THEIR PURE FORM The present invention relates to a process for preparing 5-formylvaleric esters in a yield of not less than 90 'by distillation of a mixture of ester-lavalier ester of the 5-formylvaleric ester and the 3-formylvaleric ester or 4-α-amylvaleric ester or a mixture of 3-formylvaleric ester and 4-formylvaleric ester, wherein the ester radicals of the respective para-valeric esters are identical. 5-formylvaleric esters ("5-FVE") are important intermediates in the preparation of adipic acid and caprolactam and, therefore, for the preparation of polyamide-6,6 and polycaprolactam. 5-FVE are usually obtained by idroformylation of 4-pentenoic esters in a mixture with isomeric 3- and 4-formylvaleric esters. The 4-pentenoic esters in turn, in general, are obtained by isomerization of 3-pentenoic esters obtained by carbonylation of butadiene. For the preparation of adipic acid and caprolactam from 5-FVE it is essential that the 5-FVE be of high purity. In particular, the corresponding isomeric compounds, particularly the 4-formylvaleric (4-FVE) esters, cause interference during the preparation of caprolactam through the 6-aminocaproic esters, since, according to the previous observations, the properties of caprolactam as UV Index and fiber quality, for example, expressed by the length of the fiber, of the polycaprolactam deteriorates if the 5-FVE does not have sufficient purity. The differences in the boiling points of the isomeric formylvaleric esters at atmospheric pressure are in the range from 2 to 5 ° C, for the C 1 -C 2 alkyl esters. Thus, for example, the difference in boiling point between the corresponding methyl formylvalerate (5-FVE: 221.5 ° C, 4-FVE: 223.6 ° C) is only 2.4 ° C. This makes the separation of the 5-FVE from its isomeric 3- and 4-formylvaleric esters, by distillation at atmospheric pressure, unsuitable for an industrial scale. If the difference in the boiling point of two homologues or isomeric compounds determined at pressure pl is bdl, and the difference in the boiling point of the same compounds or a pressure p2, where p2 < pl, is bd2, then bd2 < bdl (see, R.?. Perry, D. Green, Perry's Chemical Engineers Han book, 6th Ed., 1984, Chap. 13, p. 17, fig. 13-14). Therefore, the distillation under reduced pressure is also inadequate, since the differences in the boiling point also become smaller as the pressure becomes lower.

In the example given in EP-B 295 551, according to b), a mixture of the formylvaleric ester is separated by fractional distillation without any indication of experimental parameters such as pressure and temperature. There is no information about the content of the 4-formylvaleric ester in the 5-FVE fraction, although it can be presumed to be significantly greater than 100 ppm (based on the amount of 5-FVE): in the fractional distillation in step b) of the example given in EP-B 295551 was formed about 3o by weight (10 g) of a residue. This high proportion of the waste can only be explained by the thermal decomposition of formilvaleric esters during distillation. This, in turn, allows us to conclude that the distillation was carried out at relatively high temperatures and finally at atmospheric pressure or only at a slightly reduced pressure. Under these conditions, the formilvaleric esters can, as indicated in the foregoing, separate only with difficulty due to the small difference in boiling point. Therefore, the fraction of 5-FVE contained, with a probability, approaching the certainty, significant quantities, that is, greater than 100 ppm, of the isomeric formilvaleric esters, in particular of the 4-formylvaleric ester, since this in general it is present in larger amounts than the compound substituted in the corresponding 3-position. Another indication of the deficient separation of the isomeric compounds is the composition of the second fraction: it contained 2% by weight of methyl 5-formylvalerate, 70% by weight in methyl 4-formylvalerate and 28% by weight of methyl 3-formylvalerate. Other advantages of the fractional distillation of the formylvaleric esters described in EP-B 295 551 are the loss of the desired product 5-FVE (2% by weight in the second fraction) and the formation of a residue. An object of the present invention is to provide a process for the effective and efficient separation of 5-FVE from a mixture with its isomeric 3- and 4-formylvaleric esters in a purity greater than 98% and a content of 4-formylvaleric ester. not greater than 100 ppm (based on the amount of 5-FVE). In addition, it is also an object of the present invention to provide a process that allows the 5-FVE to be isolated with the purity mentioned above from the reaction mixture obtained in the hydroformylation of the 4-pentenoic ester. In addition, the yield of 5-FVE should be not less than 90%. We have found that this objective is achieved by a process known to prepare the 5-formylvaleric esters in a yield of not less than 90%, by distillation of a mixture of the formylvaleric ester of 5-formylvaleric ester and any of the ester 3- or 4- formilvaler or a mixture of the 3- and 4-formylvaleric esters, wherein the ester radicals of the respective formylvaleric esters are identical; the process comprises the separation of the 3- or 4-formylvaleric ester or a mixture of these, from the 5-formylvaleric ester, in a distillation column at a pressure in the range from 2 to 100 mbar and a temperature not higher than 150 ° C (measured as the temperature at the bottom of the column) and using as esters the corresponding methyl or ethyl ester, wherein the purity of the 5-formylvaleric ester is not less than 98% and, as an impurity, the ester 4 formylvaleric is present in an amount not greater than 100 ppm. In view of the fact that the aforementioned prior art and general technical knowledge not only do not suggest a separation by distillation, particularly under reduced pressure, but rather point away from this process, it was surprising that in the search for a solution to the problem present, it was found that a reduction of the pressure does not decrease, but rather increases, the differences in the boiling point of the isomeric formylvaleric esters, in particular of the C? -C2 alkyl compounds. In addition, a process has been found wherein the mixture of the formylvaleric ester used in the substitution by a mixture obtainable from the product of hydroformylation of the 4-petenoic ester or a mixture of 2-, 3- and / or 4-pentenoic esters , includes: (a) a mixture of the formylvaleric ester, (b) the pentenoic ester (s) used, (c) ester valeric, (d) compounds with high boiling point, and (e) compounds with low boiling point and (1) low boiling compounds, the pentenoic ester (s) and the valeric ester are first removed by distillation through the top in a first distillation column ( column for low-boiling compounds) at a pressure in the range from 10 to 300 mbar and temperatures in the lower part in the range no greater than 150 ° C, (2) the remaining tails or residues are fed to another column of distillation (column of isomers) and the 3- and / or 4-formylvaleric esters are separated through the top at a pressure in the range of 2 to 100 mbar and the temperatures in the lower part in the range no greater than 150 ° C, and (3) the remaining tails or residues are fed to another distillation column (column of purity) and the 5-formylvaleric ester is separated through the upper part at a pressure in the range from 2 to 20 mbar and the temperatures in the lower part in the range not higher than 150 ° C. The mixtures of the formylvaleric esters consist of 5-formylvaleric ester and either 3- or 4-formylvaleric ester or a mixture of 3- and 4-formylvaleric esters, wherein the ester radicals of the respective formylvaleric esters are identical, in general obtained by catalytic hydroformylation of the corresponding 4-pentenoic ester or the corresponding 3-pentenoic ester which is iso-bristle in a first reaction step to form the 2- and 4-pentenoic esters, to give a mixture of esters 2-, 3- and 4-pentenoics, wherein, in a subsequent reaction step, the 4-pentenoic ester is hydroformylated thermally with high regioselectivity. In an alternative mode, the isomerization may also be carried out as a separate process step, prior to hydroformylation, with the isomerization mixture having to be at least enriched by detylation in the 4-petenoic ester which is present in only a low concentration in the balance. The hydroformylation of the pentenoic esters to give the 5-formylvaleric esters in general requires the presence, as a catalyst, of a metal compound of the transition group VIII which is capable of forming carbonyl metal complexes under the conditions of the synthesis. Preference is given to cobalt or rhodium compounds which can be modified by ligands such as "phosphines or phosphites." Depending on the composition of the pentenoic ester isomers, the following preferred processes have been found useful: 1. Cobalt catalysts Cobalt compounds, that is, cobalt carbonyls or precursors that can be converted to cobalt carbonyls under the reaction conditions, are generally capable of converting pentenoic esters, including isomeric mixtures containing the esters. - and '3-pentenoics (PE), in formilvaleric esters with a selectivity around 95% in conversions of < 70%, with the content of n that can be up to 70% according to EP-B 295554. Higher conversions are equally possible, but, according to the previous observations, give rise to the selectivity losses due to the increased formation of the by-products. 2. Rhodium / triphenylphosphine catalysts According to EP-B 125 567, among the isomers of the pentenoic ester only the 4-pentenoic ester can be converted to the 5-formylvaleric ester using these catalysts. Accordingly, in the hydroformylation of the petenoic ester mixtures only the 4-pentenoic esters react; the following steps are carried out: a) the isomerization of the 3-PE to give mixtures of isomeric PE and the enrichment, by distillation, of the isomerization mixture for a content of 4-PE of about 95% (as described in detail in EP-B 125 567), b) selective hydroformylation of 4-PE to give mainly 5-FVE (use is made of the rhodium / P (C0Ha) 3 hydroformylation catalyst, and c) separation, by distillation, of the formilavaléricos esters and the return of the PE to step a). 3. WO 94/26688 discloses water soluble rhodium / phosphine catalysts. Using these catalysts it is very possible to convert, from the isomers of the pentenoic ester, only the 4-pentenoic ester into the 5-formylvaleric ester. Accordingly, in the hydroformylation of the pentenoic ester mixtures, only the 4-pentenoic ester reacts. The process comprises the same three steps that were specified in subsection 2.: a) isomerization of 3-PE to give isomeric PE mixtures; distillation enrichment of 4-PE, b) selective hydroformylation of the 4-PE to give mainly 5-FVE (preference is given to the water-soluble hydroformylation catalyst rhodium / P (m- CbH4SOjNa) j, c) separation by distillation of the formilavaleric esters and the return of the PE to step a). 4. Patent EP-A 556 681 describes the rhodium / chelating phosphite catalysts the hydroformylation of the pentenoic esters to give the 5-formylvaleric esters occurs in a particularly advantageous manner in the presence of Rh / phosphite chelating catalysts. If internal pentenoic esters are used, isomerization of pentenoic esters usually occurs in the same process step before actual hydroformylation. Due to the significantly higher reactivity of the 4-PE compared to the other isomers, this is by far preferentially hydroformylated, so that 5-FVE is selectively obtained. The examples demonstrate the use of 4-, 3- and 2-PE and also a mixture of 3- and -PE. A regioselectivity to the 5-formylvaleric ester of up to 94% is obtained (cis / trans-3-pentenoic ester used). Suitable pentenoic esters are derived from alkanols having from 1 to 12 carbon atoms or cycloalkanols having from 5 to 8 carbon atoms. Particular preference is given to Ci-Ci alkyl pentenoates, in particular C pen-C alkyl pentenoates, for example, methyl pentenoate. Suitable compounds are, for example, 4-pentenoic esters, 3-pentenoic esters and 2-pentenoic esters, individually or as mixtures. Examples that may be mentioned are methyl, ethyl, propyl, isopropyl, butyl, hexyl, nonyl, dodecyl, cyclopentyl or cyclohexyl 2-, 3-, or 4-pentenoic acid esters (particularly preferably methyl and ethyl esters). According to the present invention, a mixture of the formylvaleric ester of the 5-formylvaleric ester and any of 3- or 4-formylvaleric ester or, preferably of a mixture of the 3- and 4-formylvaleric esters, wherein the ester radicals of the The respective formylvaleric esters are identical, distilled, and the 3- or 4-formylvaleric ester or a mixture thereof is separated from the 5-formylvaleric ester in a distillation column at a pressure in the range from 2 to 100 mbar, in particular from 5 to 50 mbar and at a temperature not higher than 150 ° C, preferably in the range from 100 to 130 ° c, (measured as the temperature in the lower part of the column.) In accordance with the present invention, the methyl or ethyl esters. The preferred initial mixture has the following composition: from 60 to 98% by weight, in particular from 80 to 96% by weight, of methyl 5-formylvalerate, from 1 to 20% by weight, in particular from 2 to 10% by weight of methyl 4-formylvalerate, from 1 to 20% by weight, in particular from 2 to 10% by weight, of methyl 3-formylvalerate, and from 0 to 2% by weight, in particular from 0 to 1% by weight, weight, of high-boiling compounds. The 5-FVE remaining in the waste has, according to the present invention, a purity of not less than 98%, preferably not less than 98.5% and contains the 4-formylvaleric ester in an amount of less than 100 ppm, in particular less than 80 ppm, as impurity. The distillation apparatus that is used is usually a distillation column, preferably a packed column having at least 30, in particular from 35 to 50, theoretical plates. In a particularly preferred embodiment, use is made of a packed column in which the packaged material has an ordered structure. These packaging materials are commercially available, for example, Sulzer with the name of DX or DY.

In a particularly preferred embodiment, the mixture of the formylvaleric ester which is used is replaced by a mixture obtained from the product of a hydroformylation of the 4-petenoic ester or a mixture of 2-, 3- and / or 4-penteno-isomeric esters which includes: (a) a mixture of the formylvaleric ester, (b) the pentenoic ester (s) used, (c) valeric ester, (d) high-boiling compounds, and (e) compounds with a point of low boiling and (1) low-boiling compounds, the pentenoic ester (s) and the valeric ester are first removed by distillation through the top in a first distillation column (column for compounds with low boiling point) at a pressure in the range from 10 to 300 mbar, preferably from 20 to 100 mbar (measured as the pressure at the top of the column), and temperatures at the bottom in the range no greater of 150 ° C, in particular in the range from 100 to 130 ° C, (2) the remaining tails or residues are fed to another distillation column (column of isomers) and the 3- and / or 4-formylvaleric esters are separated in the upper part at a pressure in the range of 2 to 100 mbar, in particular from 5 to 50 mbar ( measured as the pressure in the upper part of the column) and the temperatures in the lower part in the range not higher than 150 ° C, in particular in the range from 100 to 130 ° C, and (3) the remaining residues are fed to another distillation column (purity column) and the 5-formylvaleric ester is separated at the top at a pressure in the range from 1 to 20 mbar, in particular from 1 to 10 mbar (measured as the pressure at the top of the column), and temperatures in the lower part in the range not higher than 150 ° C, particularly in the range from 100 to ÍSO ^ C. The term "low boiling compounds" refers to all compounds that have lower boiling points than the formylvaleric ester. Accordingly, the term "high boiling point compounds" comprises all those compounds which have boiling points higher than those of 5-FVE. The preferred process, according to the present invention, provides 5-FVE in a purity of at least 98%, preferably greater than 98.5% and an amount of 4-formylvaleric ester, as an impurity, not greater than 100 ppm, in particular not greater than 80 ppm, based on the amount of 5-FVE. If the mixture of the formylvaleric ester is prepared by means of a homogeneous rhodium catalyst and the catalyst is still present in the reaction mixture after hydroformylation, it is advisable to remove the catalyst before the first distillation step mentioned above, preferably distilling the product of hydroformylation at a temperature preferably not higher than 120 ° C and a pressure, in general, not higher than 30 mbar; the rest of the procedure is then as described in the above. Another preferred embodiment holds that, the process steps described in the above can be carried out in the presence of very little oxygen, preferably with the exclusion of oxygen. For the purpose, it is possible to make use of the distillation apparatuses that are welded at the points of contact in which the individual parts to be connected are in abutting contact with each other. Likewise, . When flange connections are used, the penetration of atmospheric oxygen from the outside into the apparatus can be prevented or reduced by applying blisters of suitable protective gas around the flange. In the practice of the process it is possible to accept a certain proportion of oxygen, as a general rule, the content of 02 / hour depends on the desired degree of decomposition of the 5-FVE and the duration of the distillation. The empirical equation I% decomposition of 5-FVE = (3.96 • 10"1 • a + 1.8) - t I where a is the content of Q¿ in ppm / hyt is the time in h, it can be used as a base for 130 ° C and 0 <; t < 5h If, for example, the decomposition of 5-FVE is not greater than 5% during 2 H hours, a content of 0¿ not greater than 505 ppm / h could be allowed. The process of the present invention has the advantage, over prior art processes, that 5-FVE can be obtained on an industrial scale with a high purity and with a 4-formylvaleric ester content that may be insignificant for another process further, in particular for the preparation of the polycaprolactam fibers.

Examples In all the examples, the expression "ester" always refers to the methyl ester.

Example 1 120 kg of a hydroformylation product whose composition is given in the table below, was treated by distillation. The low-boiling compounds were separated in a packed column (Sulzer CY with 10 theoretical plates) at a pressure at the top of the column of 40 mbar and a temperature at the bottom of 113 ° C; the separation of the isomer is carried out in a packed column (Sulzer DX with 40 theoretical plates) at a pressure at the top of the column of 12 mbar and a temperature at the bottom of 112.5 ° C, and the point compounds High boilers formed were separated from 5-FVE in a thin film evaporator superimposed with a packed column (CY sulzer with 20 theoretical plates) at a pressure at the top of the column of 4 mbar and a temperature in the lower than 130 ° C as residual product. This resulted in a total 5-FVE yield of 94% (67.7 kg), based on the amount of 5-FVE in the feed for the treatment. The purity of 5-FVE was 98.5%. The content of 4-FVE was 80 ppm (based on 5-FVE). The yield of the mixture of the 3- / 4-FVE isomers was 99% (11.8 kg). In the experiment carried out, the decomposition of 5-FVE by oxygen was not greater than 6% (total yield: 94%). According to the equation I determined in empirical form, a maximum concentration of Q¿ of 510 ppm 0¿ / h is obtained for a distillation time t of 3h.

Example 2 Example 1 was repeated, but the pressure at the top of the column separating the isomers was increased to 20 mbar, with a temperature at the bottom of 132 ° C. The total yield of 5-FVE decreased to 92% of the amount of 5-FVE fed. The purity of 5-FVE was 98.5, the content of 4-FVE was 80 ppm (based on 5-FVE).

Comparative Example 1 Example 1 was repeated, but the pressure at the top of the column for the separation of the compounds with high boiling point was increased to 8 mbar. The necessary temperature in the lower part was 158 ° C. The total yield of 5-FVE decreased to 89% of the amount of 5-FVE fed.

Comparative Example 2 100 g of 5-FVE were heated for 3 hours at 130 ° C with 7 mg of oxygen per g of FVE and hour. This resulted in the decomposition of 20% by weight of the 5-FVE used. Comparative Example 2 was repeated at different times of stay and an oxygen content of less than 10 ppm (based on 5-FVE): after 1 hour of dwelling, 1% by weight of 5-FVE had decomposed , after a 3-hour stay, 4% by weight of 5-FVE had decomposed, and after a stay of 7 hours, 8.5% by weight of 5-FVE had decomposed.

Preparation of the hydroformylation product 637 kg of a mixture of 0.2% by weight of methyl cis-2-pentenoate, 71.5% by weight of methyl cis-3-pentenoate, 23.8% by weight of methyl trans-3-pentenoate, 0.85% by weight of methyl trans-2-pentenoate, and 3? > by weight of ß-picolino and about 0.6% by weight of unidentified impurities, were exposed to a gas atmosphere for synthesis (C0 / H2 ratio by volume = 1: 1) in a cascade of two vessels at 100 ° C , a pressure of 4 bar and a residence time of 5 hours, in the presence of a commercial rhodium catalyst (Rh content: 120 ppm, based on the mixture). After cooling and depressurization to ambient pressure, the obtained hydroformylation product was used in the corresponding examples. The composition of the product is given in the following table.

Table: Hydroformylation product composition

Claims (5)

2. A process for preparing 5-formylvaleric esters in a yield of not less than 90%, by distillation of a mixture of the formylvaleric ester of the 5-formylvaleric ester and the 3- or 4-formylvaleric ester or a mixture of the 3- and 4- esters formylvaleric, wherein the ester radicals of the respective formylvaleric esters are identical; the process comprises the separation of the 3- or 4-formylvaleric ester or a mixture of these from the 5-formylvaleric ester in a distillation column at a pressure in the range from 2 to 100 mbar and a temperature not higher than 150 ° C (measured as the temperature at the bottom of the column) and using as esters the corresponding methyl or ethyl ester, wherein the purity of the 5-formylvaleric ester is not less than 98% and, as an impurity, the 4-formylvaleric ester in the present as an amount not greater than 100 ppm. The process according to claim 1, wherein the mixture of the formylvaleric esters that are used is replaced with a mixture obtainable from the product of a hydroformylation of the 4-pentenoic ester or a mixture of the 2-, 3- esters and / or 4-pentenoic, comprising: (a) a mixture of the formylvaleric esters, (b) the pentenoic ester (s) used, (c) valeric ester, (d) compounds of high boiling point, and (e) compounds with boiling point i > garlic and (1) low-boiling compounds, the pentenoic ester (s) and the valeric ester are first removed by distillation through the top in a first distillation column (column for compounds with low boiling point) at a pressure in the range from 10 to 300 mbar and temperatures in the lower part in the range no greater than 150 ° C, (2) the bottoms or residues are fed to another distillation column (column of isomers) and
3. 3- and / or
4. 4-formylvaleric esters are separated through the top at a pressure in the range of 2 to 100 mbar and temperatures in the lower part in the range no greater than 150 ° C, and ( 3) the remaining residues are fed to another distillation column (column of purity) and the
5. 5-formylvaleric ester is separated through the upper part at a pressure -in the range from 2 to 20 mbar and temperatures in the lower part in the range no greater than 150 ° C. The process, according to claim 1 or 2, wherein the steps of the process are carried out in the presence of very little oxygen, preferably with the exclusion of oxygen.