Process for the preparation of malondialdehyde-derivatives

Details Process for the preparation of malondialdehyde-derivatives Process for the preparation of malondialdehyde-derivatives

2000-01-28

2002-03-12

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C554S227000, C549S453000

Reexamination Certificate

active

06355844

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for preparing malondialdehyde-derivatives.
BACKGROUND OF THE INVENTION
Malondialdehyde-derivatives of formula (I):
in which R
1
, R
2
, R
3
and R
4
are the same or different alkyl groups, cycbalkyl group, aralkyl groups, or aryl groups, with up to 12 carbon atoms, can be used as intermediates for the preparation of heterocycles, such as pyrazoles, isoxazoles, pyrimidines, 2-aminopyrimidines or pyrimidones. Additionally, at least in those instances where R
4
=CH
3
, the compounds of formula I can be converted to malondialdehyde tetraalkylacetals (U.S. Pat. No. 2,823,226), which aside from their use as organic intermediates, also serve as hardener components for polyvinylalcohol and polyvinylacetate-films (U.S. Pat. No. 4,655,841).
While malondialdehyde tetraalkylacetals can be obtained by directly reacting orthoesters with alkylvinylethers in the presence of suitable Lewis-acids (EP 0058928), the use of alkylvinylethers, on a commercial scale, has several major drawbacks. Methylvinylether, which is needed as the starting material for the preparation of the economically important 1,1,3,3-tetramethoxypropane, is a highly flammable gas that tends to polymerize and, above all, is relatively high priced. Although the higher alkylvinylethers are liquids at room temperature, they are still very expensive and are available to a lesser extent in comparison to vinylesters.
In the preparation of malondialdehyde tetraalkylacetals by Lewis-acid-catalyzed reaction of vinylesters with orthoformates (U.S. Pat. No. 2,459,076), at least 2 moles of orthoester per mole of vinylester must be used in order to achieve acceptable yields. The reaction cannot be halted on the step of the primary addition product of general formula I, since the acid-catalyzed follow-up reaction (R
5
stands for R
1
, R
2
and R
3
) with the orthoester, which is present in the mixture, proceeds faster than the primary addition reaction.
U.S. Pat. No. 2,823,226 deals with this problem. The inventors of the '226 Patent disclose a process which, starting from vinylacetate and orthoformates, basically gives the compounds of formula I with R
4
=CH
3
without the uneconomical need to use a large excess of orthoester. As suitable catalysts, only mercury-containing catalysts or mixtures of catalysts are mentioned, which have to be used in relatively high concentrations. (For example, the 7.1%, by weight, which is referred to in the '226 Patent is the amount of TMOF used as a starting material.) Because of the high disposal costs of mercury containing residues, the possible contamination of the products with mercury and/or mercury compounds, for regulatory reasons and, most importantly, for ecological reasons, production of the compounds of general formula I according to this process does not make sense.
Thus, a need exists for a process that affords derivatives of malondialdehyde from orthoesters and vinylesters in high yields without the drawback of using mercury-containing catalysts.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a process for preparing malondialdehyde-derivatives of general formula I:
in which R
1
, R
2
, R
3
and R
4
are the same or different alkyl groups, cycloalkyl groups, aralkyl groups or aryl groups, with up to 12 carbon atoms, by reacting vinylesters of general formula II:
with orthoesters of general formula III:
in the presence of a precious metal-catalyst selected from the group consisting of Ru, Rh, Pd, Os, Ir and Pt.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for preparing malondialdehyde-derivatives of general formula I:
in which R
1
, R
2
, R
3
and R
4
are the same or different alkyl groups, cycloalkyl groups, aralkyl groups, or aryl groups, with up to 12 carbon atoms, from vinylesters and orthoesters without the necessity of using mercury-containing catalysts,
It has been found that the foregoing is achieved in a simple manner and that malondialdehyde-derivatives of general formula I are obtained advantageously if a vinylester of general formula II:
in which R
4
, as defined above, is reacted with an orthoester of general formula III:
in the presence of a precious metal-catalyst selected from the group consisting of Ru, Rh, Pd Os, Ir and Pt. The use of Pd- and Pt-containing catalysts turned out to be especially advantageous, and as such are preferred, due to their comparably high selectivities and reactivities.
In a preferred embodiment of the process according to the present invention, R
1
, R
2
and R
3
identical, especially preferred is the compound of formula I in which R
1
, R
2
, R
3
and R
4
represent a methyl group. In this case, trimethyl orthoformate and vinyl acetate can be used as relatively inexpensive and easily available starting materials. Also, due to the relatively low molecular weight of the protective groups, the resulting 1,1,3-trimethoxy-3-acetoxy-propane is especially suited for the preparation of heterocycles.
It has also been found that the formation of the compounds of general formula I is greatly enhanced by the simultaneous presence of acids, especially of Lewis-acids. The addition of suitable Lewis-acids not only leads to an increase in the reaction rate, but also leads to improved selectivities for the compounds of general formula I. Heterogeneous catalyst-components like acidic aluminas, montmorillonites, ion exchange resins or zeolites, as well as at least partially dissolved halides, such a ZnCl
2
, SnCl
4
, AlCl
3
, FeCl
3
, TiCl
4
, SbF
5
or compounds that result from these halides by substitution, for example PhSnCl
3
, can be used an Lewis acids according to a preferred embodiment of the invention. The use of BF
3
or BF
3
-adducts like BF
3
*OEt
2
or BF
3
*MeOH have been found to be especially preferred.
The above described acid-catalyzed follow-up reaction of the compounds of general formula I with the orthoester of general formula III can generally not be totally suppressed under the preferred conditions of the invention, i.e. the presence of one or several Lewis-acids. Also, the presence of the acid leads to at least a partial equilibration of the compounds of general formula I, with the referring malondialdehyde tetraalkyl-acetals of general formula IV and the 1,3-di(alkylcarboxy)-1,3-dialkoxypropanes of general formula V.
If necessary, the compounds of the general formulas IV and V can be separated from the compounds of general formula I by distillation, thereby giving the latter in pure form. Since upon recycling the compounds of general formula IV and V back into the reaction mixture and with sufficient residence times, they again form the equilibrium mixture of the compounds of general formulas I, IV and V, these byproducts can in principle be completely converted to the product of general formula I. However, since the reaction of the compound of general formula I with the orthoesters of general formula III in not desired, under practical conditions, a slight excess of the malondialdehyde tetraalkylacetal of general formula IV is normally formed.
In order to suppress the acid-catalyzed side-reactions as much as possible, and since the orthoester is the more expensive starting material, the process according to the invention is preferably conducted with a molar access of the vinylester of general formula II. While in principle there is no limit to the molar excess that can be used, the simultaneously resulting reduction of the space-time-yield leads to a preferred molar excess between about 5% and about 30%.
As can be seen from the above, the reactivity of the precious metal-catalysts, as well as the ratio of the precious metal catalyst-concentration to the Lewis acid(s)-concentration, is of special significance. In order to achieve high yields of the compounds of general formula I, the catalyst-system consisting of the precious metal-catalyst and the Lewis acid must accelerate the primary coupling reaction as much as possible, while, at the same time, the acid-cataly

Affiliated with

Also associated with

Rating

Process for the preparation of malondialdehyde-derivatives does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for the preparation of malondialdehyde-derivatives, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation of malondialdehyde-derivatives will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2874564