Preparation of aromatic aldehydes

Details Preparation of aromatic aldehydes Preparation of aromatic aldehydes

1997-02-14

1998-06-09

Geist, Gary

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

Organic compounds

Oxygen containing

502308, 502324, 502325, C07C 4541

Patent

active

057636761

DESCRIPTION:

BRIEF SUMMARY
This is the U.S. National Stage Application of PCT/EP95/03167 filed Aug. 10, 1995 now WO96/05161 published Feb. 22, 1996.
The present invention relates to a process for preparing aromatic aldehydes by reaction of appropriate carboxylic acids or their esters with hydrogen in the gas phase in the presence of zirconium oxide and lanthanide element-containing catalysts.
It is known to convert carboxylic acids such as benzoic acid or cyclohexanecarboxylic acid or their esters into the corresponding aldehydes by hydrogenation in the gas phase.
U.S. Pat. No. 3,935,265 discloses that alkyl esters of aromatic carboxylic acids can be hydrogenated at from 400.degree. to 600.degree. C. on Al.sub.2 O.sub.3 using hydrogen. For example, methyl benzoate is reacted with a selectivity of 37% (conversion: 39%) to give benzaldehyde. Ru/Sn (EP-A-539 274), manganese oxide (EP-A-290,096, U.S. Pat. No. 4,585,899), iron oxide (EP-A-304 853), vanadium oxide and/or titanium dioxide (U.S. Pat. No. 4,950,799, EP-A-414 065), Cu/Y.sub.2 O.sub.3 (U.S. Pat. No. 4,585,900), Cr.sub.2 O.sub.3 /ZrO.sub.2 (EP-A-150 961), or lanthanide oxides/Al.sub.2 O.sub.3 catalysts (U.S. Pat. No. 4,328,373, EP-A-101 111), for example, are furthermore employed for the hydrogenation of aromatic carboxylic acids.
In the known hydrogenation processes, in most cases, partly as a result of very high hydrogenation temperatures, only unsatisfactory yields and selectivities are achieved.
It is an object of the present invention to remedy the above-mentioned disadvantages.
We have now found that this object is achieved by a novel and improved process for preparing aromatic aldehydes of the general formula I ##STR1## where R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are hydrogen, C.sub.1 - to C.sub.6 -alkyl, C.sub.3 - to C.sub.8 -cycloalkyl, aryl, hydroxyl, C.sub.1 - to C.sub.4 -alkoxy, phenoxy, C.sub.7 - to C.sub.12 -alkylphenyl, C.sub.7 - to C.sub.12 -phenylalkyl, amino, methylamino, dimethylamino or halogen and -cycloalkyl, aryl, C.sub.7 - to C.sub.12 -alkylphenyl or C.sub.7 - to C.sub.12 -phenylalkyl, general formula II ##STR2## where R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 have the abovementioned meanings or where from 0.1 to 20 bar in the presence of a catalyst, whose catalytically active mass contains from 80 to 99.9% by weight of zirconium oxide and from 0.1 to 20% by weight of one or more lanthanide elements.
The process according to the invention can be carried out as follows:
The hydrogenation according to the invention of the aromatic carboxylic acids or their esters II with hydrogen in the presence of a catalyst whose catalytically active mass contains from 60 to 99.9, in particular from 80 to 99.9,% by weight of zirconium oxide and from 0.1 to 40, in particular from 0.1 to 20, % by eight of one or more lanthanide elements, is as a rule carried out at from 200.degree. to 450.degree. C., preferably from 250.degree. to 400.degree. C., particularly preferably from 300.degree. to 380.degree. C., and from 0.1 to 20 bar, preferably from 0.7 to 5 bar, particularly preferably atmospheric pressure (normal pressure). The required temperature and the required pressure are dependent on the catalyst activity and the thermal stability of starting material and product.
Suitable catalysts are supported catalysts, but preferably unsupported catalysts of zirconium oxide in cubic, tetragonal or monoclinic phase, preferably in monoclinic phase, which are preferably doped with one or more elements from the lanthanide series. As a rule, the catalytically active mass contains from 80 to 99.9% by weight, preferably from 90 to 99.9% by weight, particularly preferably from 92 to 99% by weight, of zirconium oxide and from 0.1 to 20% by weight of one or more lanthanide elements, preferably from 0.1 to 10% by weight of lanthanum, cerium, praseodymium, neodymium, samarium, europium or mixtures thereof, particularly preferably from 1 to 8% by weight of lanthanum(III) oxide. As a rule, doping is carried out by impregnating the zirconium oxide with salt solutions (aque

REFERENCES:
patent: 4328373 (1982-05-01), Strojny
patent: 4613700 (1986-09-01), Maki et al.

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