Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1999-06-25
2000-12-12
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
562414, C07C 51215
Patent
active
061601705
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new process for the production of mono- and poly-carboxylic aromatic acids by oxidation with molecular oxygen and/or air of aromatic compounds containing at least one oxidisable substituent group attached directly to the carbon atom of the corresponding aromatic ring.
The term "oxidisable substituent group" is to be understood as meaning any substituent in which a carbon atom is bonded directly to the aromatic ring and which, after oxidation, is converted into the COOH group, still bonded to the aromatic ring.
The methyl, methylene, hydroxymethyl, hydroxymethylene, ketone and aldehyde groups are considered to be among the more interesting oxidisable groups. The aromatic compounds used as starting materials in the present invention are therefore those which possess one or more of the mentioned oxidisable groups. In order better to illustrate the invention, there will be indicated hereinafter, purely by way of non-limiting example, some of the possible oxidations which can be carried out with the present invention: ##STR1##
In particular, where there are two or more oxidisable groups, each of these groups has to be separated from the others by at least one carbon atom of the unsubstituted aromatic ring. With the process of the present invention it is thus not possible to oxidise o-xylene to phthalic acid, or 1,2-dimethylnaphthalene to 1,2-dinaphthoic acid.
According to the prior art, the above-mentioned oxidation processes are carried out with oxygen and/or air in the presence of a catalyst.
The catalysts known from the literature and used industrially in oxidation reactions of the type indicated above normally contain cobalt salts as the main active element, together with other metals, such as, for example, manganese.
These metals are usually used in the form of monocarboxylic aliphatic acid salts, preferably acetates, which are soluble in aqueous acetic acid, which is in fact the preferred solvent for aromatic compounds in this type of reaction.
However, both catalysts based only on the cobalt salt and bimetal catalysts have a disadvantage of not inconsiderable importance; they can oxidise only partially the oxidisable groups of the aromatic compounds in question.
In order to obtain complete oxidation, it is necessary to integrate the catalyst with suitable activators, which clearly involves per se an increase in the operating costs.
The activators of the oxidation catalysts can be of either inganic or organic character and perform the task of activating the oxidation reaction of the catalysts which can in turn be reduced during the oxidation of the aromatic compounds.
The use of activators of the first type, rather than the second, leads to two distinct oxidation processes.
The activator used in the first process is bromine in its various forms, that is to say: molecular bromine, hydrobromic acid, bromides, etc. The activating action of bromine, however, takes place at temperatures higher than 180.degree. C., normally from 200 to 225.degree. C., and at pressures of approximately from 20 to 25 bar. Given the high operating temperatures, the corresponding apparatus has to be constructed with materials having a particular thermal resistance, such as titanium or its alloys, which involves a further increase in costs.
The second process, however, uses acetaldehyde as the oxidation activator. In the course of the reaction, the acetaldehyde is oxidised to acetic acid with a yield of approximately 80%; the remaining acetaldehyde is, however, irretrievably burnt to CO.sub.2 +H.sub.2 O. This oxidation, in addition to involving a substantial waste of acetaldehyde, also has the disadvantage of substantially increasing the thermal charge of the reactor.
The conversion of acetaldehyde into acetic acid is also a rather negative economic phenomenon, given that the cost of acetaldehyde is higher than that of acetic acid and the increase in weight from acetaldehyde to acetic acid is not sufficient to cancel the difference in cost.
U.S. Pat. No. 5,112,592 describes the use of metals of gro
REFERENCES:
patent: 3299125 (1967-01-01), Ichikawa et al.
patent: 3562318 (1971-02-01), Barone et al.
patent: 4992579 (1991-02-01), Schammed
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