Process for the continuous preparation of pure 5-formyl valeric

Details Process for the continuous preparation of pure 5-formyl valeric Process for the continuous preparation of pure 5-formyl valeric

1998-01-27

2000-02-29

Manoharan, Virginia

Distillation: processes, separatory

Convective distillation with normally gaseous medium, e.g., air

203 73, 203 80, 560177, 560218, B01D 334, C07C 6754, C07C 69716

Patent

active

060305053

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for preparing 5-formylvaleric esters in a yield of not less than 90% by distillation of a formylvaleric ester mixture of 5-formylvaleric ester and either 3- or 4-formylvaleric ester or a mixture of 3- and 4-formylvaleric esters, where the ester radicals of the respective formylvaleric 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 is generally obtained by hydroformylation of 4-pentenoic esters in admixture with the isomeric 3- and 4-formylvaleric esters. 4-Pentenoic esters are in turn generally obtainable by isomerization of 3-pentenoic esters which are themselves obtainable by carbonylation of butadiene. For the preparation of adipic acid and caprolactam from 5-FVE it is essential that the 5-FVE is of high purity. In particular, the corresponding isomeric compounds, particularly 4-formylvaleric esters (4-FVE), cause interference in the preparation of caprolactam via the 6-aminocaproic esters, since, according to previous observations, the properties of the caprolactam such as the UV index and the fiber quality, for example expressed by the fiber length, of polycaprolactam are impaired if the 5-FVEs are not of sufficient purity.
The differences in the boiling points of the isomeric formylvaleric esters at atmospheric pressure are in the range from 2 to 5.degree. C. for the C.sub.1 -C.sub.2 -alkyl esters. Thus, for example, the boiling point difference between the corresponding methyl formyl valerates (5-FVE: 221.2.degree. C.; 4-FVE: 223.6.degree. C.) is only 2.4.degree. C. This makes 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 boiling point difference of two given homologous or isomeric compounds at a pressure p1 is bd1, and the boiling point difference of the same compounds at a pressure p2, where p2<p1, is bd2, then bd2<bd1 (see R. H. Perry, D. Green, Perry's Chemical Engineers Handbook, 6th Ed., 1984, Chapter 13, p. 17, FIG. 13-14). Distillation under reduced pressure is therefore also unsuitable, since the boiling point differences also become smaller as the pressure becomes less.
In the example given in EP-B 295 551, under b), a formylvaleric ester mixture is separated by fractional distillation without any indication of experimental parameters such as pressure and temperature. There is no information about the content of 4-formylvaleric ester in the 5-FVE fraction, although it can be presumed that it was 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 over 3% by weight (10 g) of a residue were formed. Such a high proportion of residue can only be explained by the thermal decomposition of the formylvaleric esters during the distillation. This in turn enables it to be concluded that the distillation was carried out at relatively high temperatures and finally at atmospheric pressure or only slightly reduced pressure. Under such conditions, the formylvaleric esters can, as indicated above, be separated only with difficulty owing to the low boiling point difference. The 5-FVE fraction therefore contained, with a probability verging on certainty, significant amounts, ie. greater than 100 ppm, of the isomeric formylvaleric esters, in particular the 4-formylvaleric ester, since this is generally present in greater amounts than the corresponding compound substituted in the 3 position. A further indication of the poor separation of the isomeric compounds is the composition of the second fraction: this contained 2% by weight of methyl 5-formylvalerate, 70% by weight of methyl 4-formylvalerate and 28% by weight of methyl 3-formylvalerate.
Further disadvantages 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

REFERENCES:
patent: 4931590 (1990-06-01), Kummer et al.
patent: 4950429 (1990-08-01), Vagt et al.
patent: 5003102 (1991-03-01), Bertleff et al.
R. H. Perry,et al., Perry's Chem. Eng. Handbook, 6.sup.th Ed., 1984, Chapter 13, p. 17, Fig. 13-14.

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