Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1999-06-16
2000-06-06
Padmanabhan, Sreeni
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568383, 568449, 568471, 568472, C07C 4529
Patent
active
060720875
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a novel process for the preparation of carbonyl compounds by gas-phase oxidation of alcohols with an oxygen-containing gas in the presence of (copper and/or silver)-containing catalysts and a phosphorus compound which is volatile under the conditions of the reaction and of which one of two portions is added to the gaseous starting mixture whilst the other portion is blended directly with the catalyst bed.
Processes for the preparation of carbonyl compounds by gas-phase oxidation over copper or silver catalysts and in the presence of a volatile phosphorus compound are known in the art.
Thus EP-A 007,570 discloses a process for the preparation of glyoxal by gas-phase oxidation of ethylene glycol with oxygen over a copper-containing oxidation catalyst in the presence of a phosphorus compound that is volatile under the conditions of the reaction, wherein the amount of phosphorus compound used is from 1 to 100 ppm based on ethylene glycol used. These processes produce unsatisfactory yields of glyoxal of not more than 70% molar, based on ethylene glycol used.
According to the processes disclosed in U.S. Pat. No. 4,282,374 and U.S. Pat. No. 4,503,261 relating to the gas-phase oxidation of ethylene glycol over copper catalysts or over a laminated catalyst comprising copper and silver crystals, advantageous results are obtained with regard to the useful life of the catalysts used and the yield of glyoxal when the reaction is carried out in the presence of a volatile phosphorus compound and the amount of phosphorus (calculated as P), based on the weight of ethylene glycol, is from 1 to 100 ppm or from 0.5 to 20 ppm respectively. However, it has been found that when these processes are operated for a lengthy period the yield of glyoxal and the purity of the product both diminish as the test period increases. This drawback is due to the increasing formation of formaldehyde and CO/CO.sub.2.
In EP-B 0,271,812, it is proposed to prepare carbonyl compounds such as glyoxal by gas-phase oxidation of alcohols with an oxygen-containing gas in the presence of (copper or silver)-containing catalysts and a phosphorus compound which is volatile under the conditions of the reaction, wherein the phosphorus compound is added to the gaseous starting mixture in an amount of less than 0.5 ppm, based on the weight of alcohol used and calculated as phosphorus, before said mixture is caused to react over the catalyst. According to the process described in EP-B 0,271,812, glyoxal is obtained in yields of up to 80% molar.
The above processes of the prior art exhibit the drawback of unsatisfactory yields. In the known processes, glyoxal is obtained in the form of an aqueous solution containing glycolaldehyde, formaldehyde and organic acids as impurities. Other undesirable by-products are the resulting combustion products CO, CO.sub.2 and H.sub.2 O. As a result of these by-products the known processes suffer from the additional drawback of unsatisfactory catalyst on-stream times.
A content of formaldehyde in the glyoxal is, in many glyoxal applications, highly undesirable on account of the toxicological properties of formaldehyde and its high reactivity. Since it is only possible to remove formaldehyde from the crude glyoxal by considerably elaborate means and at the expense of yield, for example by treatment with steam or by methods involving chemical conversion, there has been the need to find a process which makes it possible to synthesize glyoxal by the catalytic gas-phase oxidation of ethylene oxide over long on-stream periods and with substantial lack of formation of undesirable by-products.
We have now found a process for the preparation of carbonyl compounds of the formula ##STR4## in which R.sup.1 denotes a hydrogen atom or an alkyl radical containing from 1 to 3 carbon atoms, R.sup.2 denotes a hydrogen atom or a radical of the formula ##STR5## in which R.sup.3 denotes a hydrogen atom or, together with R.sup.4, an oxygen atom, R.sup.4 denotes the radical OR.sup.6 or, together with R.sup.3, an oxygen atom, R.s
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Demuth Dirk
Fetzer Thomas
Menig Helmuth
Resch Peter
Ruppel Wilhelm
BASF - Aktiengesellschaft
Padmanabhan Sreeni
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