Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-12-01
2003-09-09
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S100000, C560S105000, C560S102000, C560S187000, C560S204000, C422S198000, C422S201000, C422S205000, C422S224000, C562S406000
Reexamination Certificate
active
06617469
ABSTRACT:
The invention relates to a process for preparing malonic diesters by carbonylation of haloacetic esters, in particular alkyl chloroacetates, with carbon monoxide and reaction with monohydric alcohols and bases in the presence of transition metal catalysts using a reactor with one or more internal heat exchanger(s).
It is known that malonic diesters of the formula I
where R
1
and R
2
are each, independently of one another, an unbranched or branched alkyl or alkenyl group, a cycloalkyl group or an aralkyl group having from 1 to 30 carbon atoms, preferably an alkyl group having from 1 to 6 carbon atoms, can be prepared by carbonylation of haloacetic esters of the formula II
where R
1
is as defined above and Hal is a halogen atom, with carbon monoxide and reaction with a monohydric alcohol of the formula R
2
OH, where R
2
is as defined above and preferably corresponds to the radical R
1
in formula II, using a base in the presence of a transition metal catalyst.
In the carbonylation of compounds of the formula II and reaction with monohydric alcohols, considerable heat of reaction is liberated. On an industrial scale, the reaction is therefore customarily carried out in a loop reactor such as a BUSS reactor (DE-A 25 53 931).
The yields of compounds of the formula I achieved are usually above 90% of theory, based on the amount of haloacetic ester used, even when the reaction is carried out on an industrial scale. With a view to minimizing the production costs, it is therefore particularly important to optimize the space-time yields. In principle, these can be improved by increasing the reaction temperature and increasing the starting material concentrations.
An increase in the reaction temperature is desirable not only because of the associated increase in the reaction rate, but also, in view of the highly exothermic nature of the reaction, because of the greater temperature difference between reaction medium and cooling medium.
However, an increase in the reaction temperature is subject to limits for a number of reasons. Thus, reaction temperatures significantly above 100° C. are not possible because the catalyst is then generally no longer stable even in the presence of high carbon monoxide partial pressures.
It is also known that the yield of malonic diesters, based on the amount of haloacetic esters reacted, drops with increasing reaction temperature. Thus, the isolated yields of the particularly important dimethyl malonate are from 2 to 3 percent lower when the reaction is carried out at 90° C. instead of at 50-70° C. under otherwise unchanged conditions. Conversely, reaction temperatures significantly below 90° C. are not acceptable on an industrial scale because of the considerable increases in the reaction times associated therewith (JP 57-183 741).
An increase in the starting material concentration is likewise subject to restrictions. Thus, the halides formed during the reaction are generally obtained as solid salts. The bases used are also frequently crystalline solids under the reaction conditions (for example sodium carbonate). The formation of salt leads, particularly together with the water formed during the reaction, at comparatively high starting material concentrations of, for example, 25% solids in the reaction mixture to this mixture no longer being able to be fully uniformly mixed when carrying out the reaction in a stirred reactor or a loop reactor or BUSS reactor. It has also been found that an increase in the content of, for example, alkyl chloroacetate and/or dialkyl malonate in the reaction mixture to over 3.75 mol/l of reaction volume is associated with a reduction in selectivity in conventional reactors.
Although it is possible to improve the selectivity of the carbonylation reaction by means of additives to the reaction mixture (JP 54 112 818), this can make the work-up of the reaction products more difficult. Contamination caused by additives is also a considerable disadvantage in respect of further utilization of the solvent(s), of the catalyst or of its downstream products and especially of the salt formed.
It is therefore an object of the invention to find a process for preparing malonic diesters of the formula I by carbonylation of haloacetic esters of the formula II with carbon monoxide and reaction with monohydric alcohols which does not have the abovementioned disadvantages and which gives improved space-time yields at simultaneously unimpaired or improved product selectivity.
It has now surprisingly been found that very high space-time yields can be achieved if the carbonylation reaction and reaction with the monohydric alcohol is carried out in a stirred reactor provided with one or more internal heat exchanger(s).
The invention accordingly provides a process for preparing malonic diesters of the formula I,
where R
1
and R
2
are each, independently of one another, an unbranched or branched alkyl or alkenyl group, a cycloalkyl group or an aralkyl group having from 1 to 30 carbon atoms, by carbonylation of haloacetic esters of the formula II,
where R
1
is as defined above and Hal is a halogen atom, using carbon monoxide, a monohydric alcohol of the formula R
2
OH, where R
2
is as defined above, a base and a transition metal catalyst, wherein the reaction is carried out in a stirred reactor with one or more internal heat exchanger(s).
In this way, for example, it was possible to use up to 5.2 mol of methyl chloroacetate per liter of liquid phase of the reaction mixture in the preparation of the industrially particularly important dimethyl malonate without mixing problems occurring. In addition, the yields of isolated target product (assay: >99.7%) achieved in this way were, for example, 92.0% and thus comparable with those obtained under analogous conditions but in greater dilution in the BUSS reactor (91.5%) or a stirred reactor (91.3%).
The components can be combined at ambient temperatures (room temperature). The reaction temperatures are from 40 to 100° C., preferably from 50 to 95° C. However, regardless of the type of reactor used, it has been found to be advantageous in terms of high space-time yields to approach desirable high reaction temperatures of, for example, 90° C. continuously via a defined temperature ramp. It has been found to be particularly advantageous to heat the reaction mixture initially to the temperature required for starting the reaction, for example 50° C., before then increasing the temperature stepwise or preferably continuously to, for example, 90° C. If desired, an afterreaction phase can follow at the same temperature level or a lower temperature level.
To enable good mixing of the carbon monoxide with the suspension comprising the remaining components of the reaction mixture in the case of the stirred reactor and the stirred reactor with one or more internal heat exchanger(s), the use of a sparging stirrer is advantageous. In this way, satisfactory dispersion of the carbon monoxide in the reaction mixture can be achieved even on an industrial scale without external pumps or compressors having to be used.
Surprisingly, it has also been found that deposits of the halide formed during the reaction can be largely avoided if a stirred reactor provided with sparging stirrer and internal heat exchangers as described in EP-A-0 633 060, hereinafter also referred to as a “BIAZZI” reactor, is employed.
With regard to the excellent mixing of the carbon monoxide with the other components of the reaction mixture in a loop reactor or “BUSS” reactor, it has also surprisingly been found when using a “BIAZZI” reactor for the carbonylation of the haloacetic esters and reaction with the monohydric alcohol that the catalyst is subject to a significantly lower decomposition rate at the same carbon monoxide partial pressure and the same temperature. This enables higher reaction temperatures to be achieved and/or a lower than usual amount of transition metal catalyst to be used, as a result of which the costs of recirculating the latter to the process are lower.
The halogen in the haloacetic ester is chlorine, bromine or
Bauer Frank
Latz Wilfried
Prange Uwe
Theis Christoph
Degussa - AG
Reyes Hector M
Rotman Alan L.
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