Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Patent
1986-09-02
1988-10-18
Lone, Werren B.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
560265, C07C 4538, C07C 6700
Patent
active
047789239
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the conversion of methanol to methyl formate, more particularly to a process using a platinum group metal catalyst.
Methyl formate is a useful organic chemical and can be used as an intermediate for the preparation of a wide range of other chemicals including formic acid itself and higher carboxylic acids such as acetic acid and propionic acid and their esters.
Methanol is a readily available starting material and can be obtained either from natural gas or from syn gas using existing technology. It is therefore an object of the present invention to provide a process for converting methanol to methyl formate.
The reaction of methanol with cycloheptene using RhH(PPh.sub.3).sub.4, where Ph is phenyl as catalyst, in which the double bond of the cycloheptene is reduced, has previously been described in J Org Chem, 1974, 39, 1622.
In this reaction the methanol acts as a hydrogen donor and the olefin as a hydrogen acceptor. The above cited reference reported, however, that no formaldehyde was detected.
It has now been found that methanol can be converted into methyl formate using a platinum group metal catalyst in the absence of an added hydrogen acceptor.
Accordingly, the present invention provides a process for the preparation of methyl formate from methanol characterised in that methanol is contacted at elevated temperature with a platinum group metal catalyst in the absence of an added hydrogen acceptor.
The present invention represents an improvement over the prior art as it obviates the need to have present an organic hydrogen acceptor which has to be separated from the methyl formate at the end of the process. Since such components are in general separated by distillation the present invention eliminates an expensive, energy-intensive step from the overall process.
By platinum group metal is meant ruthenium, rhodium, palladium, osmium, iridium and platinum. The preferred metal is ruthenium.
The catalyst can be a hydrocarbon complex of a platinum group metal for example the hydrocarbon can be C.sub.5 Me.sub.5 or C.sub.6 Me.sub.6 where Me represents methyl and the C.sub.5 or C.sub.6 moiety is cyclic. Alternatively the catalyst can be a phosphine or phosphite complex and can be formed in situ by reaction of a metal compound and a phosphine or phosphite. In either of the forms described above the catalyst is dissolved in the methanol feedstock to form a homogeneous solution or suspended therein prior to heating to elevated temperature.
As an alternative to using a platinum group metal catalyst which is soluble in the methanol feedstock, a platinum group metal compound supported on an inert solid can be used. Such catalysts, which are insoluble in the reaction medium are easier to separate from the liquid products at the end of the reaction. The inert solid can be inorganic for example a metal oxide, silica, alumina and the like, and is particularly those inorganic solids having terminal hydroxyl groups capable of reacting with the platinum group compound or a precursor thereof. Alternatively the solid can be organic such as a polymer or polymeric resin e.g. polystyrene or poly(styrene/divinylbenzene).
Methods of supporting platinum group metal compounds on such supports will be familiar to the skilled man and include precipitation, impregnation and ion-exchange techniques. A preferred technique is to functionalise the inert solid with a ligand (e.g. a phosphine) and then to coordinate a suitable platinum group metal to the ligand. An example of a phosphine ligand whch can be used to functionalise the inert solid is (EtO).sub.3 SiCH.sub.2 CH.sub.2 PPh.sub.2.
When a supported plantinum group metal catalyst of the type described above is used the methanol may be fed in vapour form over the catalyst in a continuous manner. The methanol vapour can be diluted with an inert gas e.g. nitrogen, helium, argon, etc, if desired.
It is preferred to flush the methanol solution or suspension of the catalyst with either nitrogen or argon, more preferably argon, prior to reaction.
The cat
REFERENCES:
patent: 4149009 (1979-04-01), Yoneoka et al.
Aplin Richard P.
Maitlis Peter M.
Smith Thomas A.
BP Chemicals Limited
Lone Werren B.
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