Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-06-21
2001-02-13
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S457000, C568S464000
Reexamination Certificate
active
06187971
ABSTRACT:
The invention relates to a process for the preparation of geminate polymethylol compounds by condensation of aldehydes with formaldehyde and hydrogenation of the resulting polymethylolalkanals, without the formation of formates by coupling.
PRIOR ART
Processes Involving the Formation of a Coupling Product
Trimethylol propane (TMP) is usually prepared industrially by the so-called inorganic Cannizzaro process. In this case n-butyraldehyde (n-BA) is caused to react with excess formaldehyde (FA) in the presence of stoichiometric amounts of inorganic base such as NaOH or Ca(OH)
2
. Not only TMP is formed by the Cannizzaro reaction but also one equivalent of sodium or calcium formate. The occurrence of an inorganic salt as coupling product has varied drawbacks. Firstly the separation of the salt of TMP is complicated and involves additional expenditure; secondly the inorganic salt—if it is to be utilized to good effect—must be worked up and purified: and thirdly the occurrence of a coupling product signifies a loss of the stoichiometric amounts of sodium hydroxide solution and formaldehyde used. Furthermore, the yields obtained in this inorganic Cannizzaro reaction, including those of the butyraldehyde, are unsatisfactory, since high-boiling components are formed during the reaction which cannot be utilized.
Similar problems to those stated for TMP relate to the preparation of other triols such as trimethylol ethane (from n-propanal and formaldehyde) or trimethylolbutane (from n-pentanal and formaldehyde). Like TMP these triols are prepared by the inorganic Cannizzaro process with formation of an inorganic salt by coupling. The same applies to the preparation of pentaerythritol from acetaldehyde and formaldehyde. Trimethylol propane, trimethylol ethane and trimethylolbutane are polyols which are used in the plastics industry in a variety of ways for the preparation of varnishes, urethanes and polyesters. Pentaerythritol is a frequently used intermediate in the paints and varnishes industry and is also useful for the preparation of explosives (pentaerythritol tetranitrate).
The reaction of n-BA with FA in the presence of a tert-amine in one improved process is described in DE-A 1,952.738. The stoechiometry of N-BA:FA of approximately 1:6 and the use of superstoichiometric amounts of the amine have however the result that not only TMP but also stoichiometric amounts of trialkylammonium formate are produced. Amine and the formic acid formed are removed by distillation as organic salt and must thus be processed and recovered, in order to make the process economical. The amines used were triethylamine and trimethylamine.
One way of avoiding the occurrence of organic salt (trialkylammonium formate) is described in EP-A 0,142,090, EP-A 0,289,921 and in the German patent applications having the file numbers P 19542035.7 and P19542036.5. Said references also describe the use of stoichiometric amounts of a trialkylamine of an inorganic base as base. The trialkylammonium formate formed as coupling product is converted to methyl formate during the process. The advantage of this organic Cannizzaro process over the inorganic variant is the increased yield. But a disadvantage thereof is the fact that here again a coupling product (methyl formate) is formed and thus one equivalent of formaldehyde more than is necessary is consumed in the process.
Thus a process for the preparation of TMP without the formation of any sort of coupling product is desirable from an economic standpoint.
Processes Without the Formation of a Coupling Product
According to the statements made in DE-A 2,507,461 dimethylolbutanal (DMB) can be prepared by the reaction of n-butyraldehyde (n-BA) with formaldehyde (FA) in the presence of catalytic amounts of a tert-amine via the intermediate monomethylolbutanal (MMB) (equation 1). Subsequent hydrogenation gives TMP (equation 2).
The hydrogenation of the dimethylolbutanal (DMB) formed as intermediate from n-BA and FA to form TMP is also described in DE-A 25 07 461. The same specification reveals that the elimination of water from the resulting intermediate monomethylolbutanal (MMB) causes the formation of the by-product ethylacrolein (EA). The possibility of utilizing EA via its reverse reaction in the presence of water (equation 3), is explained in example 5.
The yields of DMB given in the examples are approximately 85%; the TMP yields following hydrogenation are said to be 75% (based on n-BA), whilst yields based on FA are given.
The process of this patent specification has the drawback that use must be made of specific branched-chain tert-amines (eg. dimethylaminoneopentanolamine), which are not available in commercial amounts. Using industrially available amines such as triethylamine worse yields are observed (57% of TMP based on n-BA). The branched-chain amine is not recycled in the said process, which thus keeps the costs of the process high. Neither is unconverted n-BA or FA recycled to the process.
Another variant is described in DE-A 2,702,582, in which use is made of formaldehyde in an excess of at least 8 times over the aldehyde for aldolization in the presence of tert-amines in combination with alkali metal or alkaline earth metal compounds at from −5° to 0° C. The aldol product formed is then hydrogenated to TMP. The bases used are linear tert.-amines. In the majority of the examples inorganic bases are additionally used. The yield obtained when only triethamine is used (example 5, n-BA:FA:NEt
3
=1:10:0.18) is 74.6% of TMP.
This process is based on the use of a large excess of formaldehyde and low temperatures. Large amounts of FA, however, are a contributary factor in the formation of FA adducts of the alcohol components that are present in the reaction mixture (formation of acetals and hemiacetals of FA with DMB and MMB). This in turn leads to an unfavorable yield based on FA used. The use of inorganic reageants for the aldolization gives rise to additional problems when purifying the TMP by distillation. The maintenance of low temperatures (−5° to 0° C.) calls for additional plant requirements. A total of 18 mol % of tert-amine is used which is not recycled to the process.
The processes of DE-A 2,813,201 and DE-A 2,702,582 also both involve a high excess of formaldehyde, and an acceptable yield based on n-butyraldehyde is achieved only at the expense of formaldehyde used, so that these processes are also uneconomical.
DE-A 2,714,516 describes the reaction of ethylacrolein (EA) with formaldehyde (FA) in a ratio of EA:FA of from 1:8 to 1:30 in the presence of basic catalysts. The yield of DMB is stated to be 90% based on EA. However, the yield based on FA is only 12%.
Here again the process is not economical by reason of the large amounts of FA and trialkylamine catalyst used.
It is thus an object of the present invention to provide a process which produces polymethylol compounds, eg trimethylol propane from n-butyraldehyde and formaldehyde, in high yields based on n-butyraldehyde and formaldehyde and without the formation of a coupling product. This process should be equally well suited for the preparation of other polyalcohols from the higher and lower homologous alkanals of n-butyraldehyde.
This object is achieved in a process for the preparation of polymethylol compounds of formula I
in which R denotes another methylol group or an alkyl group containing from 1 to 22 carbon atoms or an aryl or aralkyl group containing from 6 to 22 carbon atoms, by condensation of aldehydes containing from 2 to 24 carbon atoms with formaldehyde using tertiary amines as catalyst to form compounds of formula II
in which R has the meaning specified above and the hydrogenation thereof, characterized in that the condensation is carried out step-wise by
a) causing the aldehydes containing from 2 or more carbon atoms to react, in a first (reaction) stage, with 2 to 8 times the molar amount of formaldehyde in the presence a tertiary amine acting as catalyst,
b) either separating the reaction mixture, in a second (separating) stage) into bottoms predominantly contai
Kratz Detlef
Schulz Gerhard
Stammer Achim
Voit Guido
BASF - Aktiengesellschaft
Keil & Weinkauf
Shippen Michael L.
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