Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-06-26
2003-07-01
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S854000
Reexamination Certificate
active
06586641
ABSTRACT:
The present invention relates to the field of industrial organic chemistry. More precisely, the present patent application relates to a process in which polyhydric alcohols prepared by the condensation of formaldehyde with higher aldehydes, followed by hydrogenation, are freed of higher-boiling substances formed in the preparation.
When reacted with formaldehyde in the presence of bases, aldehydes which have at least one acidic hydrogen atom in the &agr;-position to the carbonyl group first form methylolated aldehydes by simple aldol condensation. These methylolated aldehydes then serve as starting substances for the preparation of said polyhydric alcohols by reduction of the aldehyde group to the alcohol group.
Different process variants can be used here, according to how this reduction is carried out.
Firstly, there is the inorganic Cannizzaro process, where formaldehyde is reacted with the higher aldehyde in the presence of stoichiometric amounts of an inorganic base, generally NaOH, Ca(OH)
2
or Ba(OH)
2
. After the condensation, the methylolated aldehyde then reacts with more formaldehyde under the influence of the base in a so-called crossed Cannizzaro reaction to give the polyhydric alcohol and formic acid, in the form of its salt, by disproportionation. The production of this formate is a disadvantage because it cannot be re-used and has to be disposed of. This pollutes the environment; in addition, one mole of formaldehyde is lost per mole of alcohol obtained.
In a widely used variant, the so-called organic Cannizzaro process, the inorganic base is replaced with a tertiary amine, generally a trialkylamine. This amine is also used in stoichiometric amounts. The reaction proceeds in the same way as in the inorganic Cannizzaro process except that the trialkylammonium formate of the amine used is formed instead of an alkali metal or alkaline earth metal formate. This organic Cannizzaro reaction proceeds without the formation of alkali metal salts, thereby simplifying the work-up. Also, it is possible to work up the trialkylammonium formate further and recover the bound amine, which is then re-used in the reaction. Different variants of this work-up of trialkylammonium formates are described in patent applications EP-A-289 921, WO 97/17313 and DE-A-198 48 568.
Finally, it is also known to prepare polyhydric alcohols by the so-called hydrogenation process. Here, the condensation reaction between formaldehyde and higher aldehyde is carried out in such a way that the reaction stops at the methylolated alkanal stage. This is achieved by adding only catalytic amounts of a tertiary amine, which here again is generally a trialkylamine. The methylolated alkanals are reduced by hydrogenation in a manner known per se to give the desired polyhydric alcohol.
Different reaction variants of this hydrogenation process can be found for example in patent applications DE-A-25 07 461, DE-A-27 02 582 and DE-A-28 13 201. A particularly suitable process is disclosed in WO 98/28253. Here, a complete conversion of the educts to methylolated alkanals is achieved by an efficient and comparatively simple process for separation of the reaction mixture initially obtained, and recycling of the resulting fractions. The alkanal obtained is then hydrogenated in a manner known per se. In a first reaction step, the starting aldehyde is reacted with 2 to 8 times the amount of formaldehyde in the presence of approx. 5 to 10 mol % of a trialkylamine, preferably trimethylamine. When the reaction is complete, the mixture obtained is then separated by distillation to give a bottom stream containing the alkanal and a distillate stream containing unreacted educts. Alternatively, the crude reaction mixture can also be separated into an aqueous phase and an organic phase, the latter containing unconverted reaction products. The distillate stream or organic phase is recycled into the first step, so only a small part of the starting compounds is lost. The bottom product obtained after distillation or the aqueous phase obtained after phase separation is then subjected to an appropriate catalytic or thermal treatment in order to effect a complete conversion of by-products (arising due to incomplete reaction or elimination) to the desired alkylolated alkanal. This is followed by another distillation, where a top product is withdrawn and recycled into the first reaction step. The bottom product obtained after this last distillation is then hydrogenated to polyhydric alcohol.
The crude product mixtures obtained by the hydrogenation process have a higher product content than crude mixtures obtained by the Cannizzaro process. The work-up of the mixtures obtained by this process is therefore fundamentally different from that of the mixtures obtained by the hydrogenation process.
The only common feature of the two processes is that the polyhydric alcohol is freed, by distillation, of components which are more volatile than said alcohol (so-called low-boiling components) or less volatile than said alcohol (so-called high-boiling components). Low-boiling components here are especially water, methanol and, when using an amine as catalyst, the free amine and also trialkylammonium formate.
The high-boiling components are often compounds which are derivatives of the polyhydric alcohol prepared and which are formed therefrom by reaction with e.g. formaldehyde, methanol or a further molecule of the alcohol prepared. The following compounds are examples of typical higher-boiling secondary components in the case where the trihydric alcohol trimethylolpropane (TMP), C
2
H
5
C(CH
2
OH)
3
, is synthesized from formaldehyde and n-butyraldehyde in the presence of catalytic amounts of trialkylamine: so-called di-TMP, [C
2
H
5
C(CH
2
OH)
2
CH
2
]
2
O, linear bis-TMP-formal, [C
2
H
5
C(CH
2
OH)
2
CH
2
O]CH
2
, cyclic TMP-formal:
the condensation product of TMP, formaldehyde and methanol (TMP-FA-MeOH), the acetal of dimethylolbutanal with trimethylolpropane (DMB-TMP-acetal) and TMP formates, i.e. formic acid monoesters of trimethylolpropane.
It is obvious that the formation of these high-boiling components containing TMP units is undesirable because they markedly reduce the yield of desired product. However, the formation of these high-boiling components can never be completely suppressed, even when caution is exercised in carrying out the reaction. To increase the yield, it is desirable to decompose these high-boiling components. Various processes with this aim are disclosed in the literature.
Patent DE-P-287 251 describes the decomposition of high-boiling components, especially bis-TMP-formal, in solutions recovered after distillative separation of the TMP obtained in the preparation of TMP by the inorganic Cannizzaro process. The resulting bottom product is then treated with 1 to 10% by weight of a strong or moderately strong acid, for example sulfuric acid or phosphoric acid, and then heated for 6 minutes to 10 hours at temperatures of 80 to 180° C. This treatment cleaves some of the high-boiling components derived from TMP. For example, the addition of 5% by weight of concentrated sulfuric acid to a crude high-boiling mixture and heating at 130° C. for 12 minutes, with subsequent distillation to recover TMP, effects a complete decomposition of bis-TMP-formal and hence increases the yield of TMP, but unwanted cyclic TMP-formal (not previously present) is also formed in appreciable amounts.
In SU 335141, whose disclosure is practically identical to that of the article “The Soviet Chemical Industry”, 1977, 9:8, pages 599 to 600, a process is disclosed in which the low-boiling fraction of TMP obtained by the inorganic Cannizzaro process is worked up by adding 1 to 8% by weight of sulfuric acid and introducing superheated steam at a temperature of 180 to 200° C. into the solution with a bottom temperature of 170 to 180° C. TMP is then distilled from this bottom product. An increase in the overall yield of TMP can thus be achieved by hydrolysis of the cyclic TMP-formal and the TMP formates, the indicated yield of TMP in the d
Dernbach Matthias
Kratz Detlef
Schulz Gerhard
Stammer Achim
BASF - Aktiengesellschaft
Keil & Weinkauf
Shippen Michael L.
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