Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-03-12
2003-05-20
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S451000
Reexamination Certificate
active
06566558
ABSTRACT:
The present invention relates to a method for carrying out hydroformylation reactions. Specifically the present invention relates to the hydroformylation reactions catalysed by heterogeneous catalysts in near-critical or supercritical fluids.
BACKGROUND
The use of carbon monoxide as a reagent for organic synthesis is diverse with a wide number of reactions carried out. One process of industrial importance is hydroformylation (also known as the “oxo process”) which is used for large-scale production of aliphatic aldehydes and alcohols from olefins (alkenes) using cobalt- or rhodium-based homogeneous catalysts.
In general, the hydroformylation reaction involves reaction of an alkene or alkyne with a mixture of carbon monoxide and hydrogen over a catalyst at high pressure to produce a carbonyl compound. Mixtures of hydrogen and carbon monoxide are frequently referred to as synthesis gas or syn gas.
FIG. 1
shows the hydroformylation of an alkene in general terms. The resulting carbonyl compound, which may be the normal (n) or iso product, can then be reduced to give the corresponding alcohol. An alternative route is first to convert the alkene or alkyne to a trialkylborane and then to react this product with carbon monoxide and a reducing agent.
It is well known that reactions of this type are limited by the solubility of the gases in the liquid reagent or solvent (known as Mass Transport Limitations). The use of supercritical fluids in the replacement of conventional solvents for environmental reasons is gradually being adopted. The use of supercritical fluids as reaction media also gives higher solubilities of gases in the system and gives effectively a higher activity of these reagents by overcoming Mass Transport limitations.
Work has previously been carried out on batch systems using homogeneous catalysts in supercritical fluids. The following are examples of known heterogeneous hydroformylation reactions:
1) the Hydroformylation of olefins, Chemtracts: Org. Chem. 1996, 9 (6), 318-321 and Chemtracts: Inorg. Chem. (1995), 7(2), 120-123.
2) The Hydroformylation of Propylene in a batch system using homogeneous catalysis in Supercritical fluids is reported by Akgerman et al (Fourth Italian Conference on Supercritical Fluids and their Applications, September 1997 Proceeding, page 263-269).
3) U.S. Pat. No. 5,198,589 describes a batch or continuous batch process using homogenous catalysis.
However, the use of homogeneous catalysts and batch processes lead to the problems of catalyst separation, long residence time and scale-up hazards. Indeed, it is quite a significant problem with the processes described in these publications that the use of homogeneous catalysts requires a separation step at the end of the process to recover the catalysts, because this necessitates extra processing steps and thus increases costs. Also, separation is particularly difficult in the case of alkenes which have a chain length longer than C7 because separating the catalysts from the products by distillation requires high temperatures which destroy the catalysts. Consequently, these processes involving alkenes having a chain length greater than C7 cannot be carried out in continuous-flow reactors (tubular reactors).
The use of homogeneous catalysts also means that these processes are usually carried out in batch or semi-batch reactors. Such conditions require extensive capital expenditure when scaling up owing to the design requirement for vessels capable of working at high pressure. The use of batch systems also has the disadvantage of increased down time for charging and discharging the reaction vessel. There is also the problem that the product of the reaction may be a mixture of thermodynamic and kinetic products, owing to the large residence time of the reactants in the reactor.
Work has been carried out in the past on heterogeneous catalysis for hydroformylations under conventional (i.e. not near-critical or supercritical conditions). However, these reactions have never proved successful, usually because of low conversion to the products and catalyst deactivation. Heterogeneous catalysed hydroformylation reactions carried out in supercritical media have not previously been reported. As a result, hydroformylation reactions cannot presently be carried out using a heterogenous catalyst on an industrial scale.
There is thus a need for a hydroformylation process in which the catalyst can be easily separated from the product by simple filtration. Ideally, the process should enable separation to be achieved even for hydroformylations of alkenes, alkynes or trialkylboranes having chain lengths greater than C7.
There is also a requirement for a hydroformylation process in which a continuous flow reactor (tubular reactor) can be used. Ideally, the process should allow the operator the ability to control residence time as well as the other reaction parameters independently in order to allow greater control of the reaction. There is also a need for a process which is more efficient and/or more selective than conventional processes.
Surprisingly, we have found that hydroformylation of alkenes, alkynes and trialkylboranes can be effected using a heterogenous catalyst in supercritical media. Thus, by using a combination of a supercritical medium, comprising one or more components, and a heterogeneous catalyst (e.g. the Deloxan HK1 2% rhodium complex catalyst from Degussa) it is possible to carry out hydroformylation reactions with high conversion. It is also possible to perform the reaction with good selectivity for the n or iso products where there is the possibility of forming both the normal and iso products. The present invention thus solves the problems of the prior art by effecting the hydroformylation reaction under conditions close to or above the supercritical point of the reaction medium in the presence of a heterogeneous catalyst in a continuous flow reactor.
According to the present invention, there is provided a process for hydroformylation of a substrate, wherein the substrate is selected from alkenes, alkynes, and trialkylboranes and is reacted with hydrogen and carbon monoxide in the presence of a heterogeneous catalyst, the substrate being a fluid in its supercritical or near-critical state and/or, reaction taking place in the presence of a solvent for the substrate, the solvent being in its supercritical or rear-critical state, and the process being carried out in a continuous flow reactor. The yield and/or selectivity of the reaction may be influenced by controlling one or more of the reaction conditions of temperature, pressure, residence time, flow rate and catalyst.
In an embodiment, the catalyst comprises a support selected from: an organosiloxane-polycondensate, an organosiloxane-copolycondensate, or polymeric secondary and/or tertiary organosiloxanamine combinations; and a metal or metal complex in which the metal is selected from: platinum, nickel, palladium, cobalt, rhodium, iridium, iron, ruthenium, and osmium, and the catalyst optionally includes a promoter. Rhodium is a particularly preferred metal.
Suitable catalysts thus include Deloxan HK1 which is a 2% Rh catalyst on a polyaminosiloxane support obtainable from Degussa.
The hydroformylation reaction of the present invention satisfies the above requirements by providing a process in which the products can be separated from the catalyst after reaction without difficulty. This is true for reactions on alkenes, alkynes or trialkylboranes having a chain length greater than C7. Hence alkenes, alkynes or trialkylboranes having a chain length greater than C7 can be hydroformylated and the products easily separated from the catalyst without the need for distillation or further work-up.
The process also results in yields and selectivities which are better than conventional processes. In particular, the feature of selectivity is an important feature of the invention because the iso product is frequently a by-product of hydroformylation reactions carried out under conventional conditions in cases where the production of both normal and iso-
Meehan Nicola J.
Poliakoff Martyn
Roeder Stefan
Ross Stephen K.
Wieland Stefan
Bromberg & Sunstein LLP
Padmanabhan Sreeni
Thomas Swan & Co. Limited
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