Preparation of carbonyl compounds

Details Preparation of carbonyl compounds Preparation of carbonyl compounds

1999-02-01

2001-07-03

Padmanabhan, Sreeni (Department: 1621)

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

Organic compounds

Oxygen containing

C568S471000, C568S402000, C502S208000

Reexamination Certificate

active

06255534

ABSTRACT:

The present invention relates to a novel process for preparing carbonyl compounds by gas-phase oxidation of alcohols by means of an oxygen-containing gas in the presence of a catalyst system comprising at least one phosphorus-containing copper- and/or silver-containing catalyst or a catalyst bed comprising an essentially phosphorus-free and at least one phosphorus-containing copper- and/or silver-containing catalyst.
Processes for preparing carbonyl compounds by gas-phase oxidation over copper and/or silver catalysts in the presence of volatile phosphorus compounds are known from the prior art.
Thus, EP-A 007 570 describes a process for preparing glyoxal by gas-phase oxidation of ethylene glycol by means of oxygen over a copper-containing oxidation catalyst in the presence of phosphorus compounds which are volatile under the reaction conditions, in which from 1 to 100 ppm of phosphorus, based on ethylene glycol used, are introduced with the starting compounds. These processes give unsatisfactory glyoxal yields of up to 70 mol %, based on ethylene glycol reacted.
According to the processes of U.S. Pat. No. 4,282,374 and U.S. Pat. No. 4,503,261, the gas-phase oxidation of ethylene glycol over copper catalysts or over a layer catalyst comprising copper and silver crystals gives advantageous results in respect of the life of the catalysts and the glyoxal yield if the reaction is carried out in the presence of a volatile phosphorus compound, where the amount of phosphorus (calculated as P) is from 1 to 100 ppm or from 0.5 to 20 ppm, based on the weight of ethylene glycol, and the phosphorus is introduced with the starting compounds upstream of the catalyst bed. However, when these processes are operated for a prolonged period it has been found that the glyoxal yield and product purity become increasingly poor as the duration of the experiment increases. This disadvantage is attributable to increased formation of formaldehyde and of CO/CO
2
.
EP-B 0 271 812 proposes, for the preparation of carbonyl compounds such as glyoxal, a gas-phase oxidation of alcohols by means of an oxygen-containing gas in the presence of copper- or silver-containing catalysts and a phosphorus compound which is volatile under the reaction conditions, in which process the phosphorus compound is mixed into the gaseous starting mixture in one portion in an amount of less than 0.5 ppm, based on the weight of alcohol used and calculated as phosphorus, prior to the reaction over the catalyst. According to the process described in EP-B 0 271 812, glyoxal is obtained in yields of up to 80 mol %.
Furthermore, DE-A 19 23 048 discloses a process for preparing carbonyl compounds by gas-phase oxidation of hydroxy compounds over catalyst beds comprising copper-phosphorus catalysts containing from 1 to 5% by weight of phosphorus. This process gives unsatisfactory glyoxal yields.
The abovementioned processes of the prior art have the disadvantage of an unsatisfactory yield. In the known processes, glyoxal is obtained as an aqueous solution contaminated by glycol aldehyde, formaldehyde and organic acids. Further undesirable by-products are the combustion products CO, CO
2
and H
2
O. As a consequence of the by-products, the known processes have the additional disadvantages of unsatisfactory catalyst lives.
In addition, the presence of formaldehyde in the glyoxal is highly undesirable for many applications of glyoxal because of the toxicological properties and the high reactivity of formaldehyde. Since formaldehyde can be removed from the crude glyoxal only at considerable expense and with acceptance of yield losses, for instance by treatment with steam or by chemical reaction, an improved process is needed.
It is an object of the present invention to provide a process which allows glyoxal to be prepared by catalytic gas-phase oxidation of ethylene glycol while largely avoiding the formation of undesirable by-products, even for long operating times.
We have found that this object is achieved, in a process for preparing carbonyl compounds of the formula
where R
1
is a hydrogen atom or an alkyl radical having from 1 to 3 carbon atoms, R
2
is a hydrogen atom, an unsubstituted or C
1
-C
3
-alkyl-monosubstituted to -trisubstituted C
2
-C
4
-alkenyl radical or a radical of the formula
where R
3
is a hydrogen atom or together with R
4
is an oxygen atom, R
4
is the radical OR
6
or together with R
3
is an oxygen atom, R
5
is a hydrogen atom, an unsubstituted or C
1
-C
3
-alkyl-monosubstituted to -trisubstituted C
2
-C
4
-alkenyl radical, an alkyl radical having from 1 to 8 carbon atoms or a cyclohexyl or cyclopentyl radical and R
6
is an alkyl radical having from 1 to 4 carbon atoms, a cyclohexyl or cyclopentyl radical or a radical of the formula —CH
2
—CHO or —CH
2
—CH
2
—O—CH
2
—CHO, by gas-phase oxidation of methanol or alcohols of the formula
where R
1
and R
5
are as defined above and R
7
is a hydrogen atom or a radical OR
8
and R
8
is a hydrogen atom, an alkyl radical having from 1 to 4 carbon atoms, a cyclohexyl or cyclopentyl radical or a radical of the formula —CH
2
—CH
2
—OH or —CH
2
—CH
2
—O—CH
2
—CH
2
—OH, by means of an oxygen-containing gas in the presence of copper- and/or silver-containing catalysts and in the presence or absence of a phosphorus compound which is volatile under the reaction conditions in such an amount that the amount of phosphorus (calculated as P) is up to 20 ppm, based on the total a mount of alcohol used, by the improvement which comprises using a catalyst system comprising at least one phosphorus-containing copper- and/or silver-containing catalyst.
In a further embodiment of the process of the present invention, the catalyst system used is a catalyst bed comprising an essentially phophorus-free and at least one phosphorus-containing copper- and/or silver-containing catalyst. In the novel process, glyoxal is obtained from ethylene glycol in long-term-continuous operation in high yield and purity and with a significantly reduced formaldehyde content. The novel process is also technically simple to implement in large-scale plants.
Reduction of the hot spot temperatures also results in an increased operating life of the catalyst in the reactor.
In the alcohols of the formula III, alkyl radicals are, for example, methyl, ethyl, propyl or butyl radicals. In the process of the present invention, terminal hydroxyl groups are converted into aldehyde groups and secondary hydroxyl groups are converted into keto groups.
Examples of starting compounds of the formula III are:
HO—CH
2
—CH
2
—OH, H
3
COCH
2
—CH
2
OH, CH
3
—CH
2
OH, C
2
H
5
OCH
2
—CH
2
OH, H
3
C—CH(OH)—CH
2
—OH, C
2
H
5
—CH(OH)—CH
2
OH,
 HO—(CH
2
)
2
—O—(CH
2
)
2
—OH,
The gas-phase oxidation of the alcohol by means of the oxygen-containing gas over the copper- and/or silver-containing catalysts is carried out in a manner known per se, e.g. at from 225 to 500° C.
Examples of suitable copper- and/or silver-containing catalysts are metallic copper or silver, copper-containing or silver-containing alloys or compounds with metals or nonmetals which may further comprise phosphorus or, in the case of the phosphorus-containing catalysts, comprise phosphorus, e.g. copper phosphides, copper bronzes or alloys of copper with silver and/or gold, copper ores such as malachite and copper or silver compounds which can be reduced completely or partially to copper or silver during the reaction, e.g. copper(I) oxide, silver(I) oxide, copper(II) oxide, and compounds which are converted into copper oxides on heating, e.g. copper nitrate and copper acetate. Other suitable compounds are copper phosphate and copper antimonate. It is also possible for further metal oxides or nonmetal oxides, e.g. the oxides of zinc, chromium, antimony, tin or bismuth, to be mixed into the copper-containing compounds.
The essentially phosphorus-free copper- and/or silver-containing catalysts employed in the present invention have a phosphorus content of from 0 to 400 ppm, preferably from 150 to 400 ppm, corresponding to from 0.015 to 0.04% by weight, and particular

Affiliated with

Also associated with

Rating

Preparation of carbonyl compounds does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Preparation of carbonyl compounds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation of carbonyl compounds will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2557402