Preparation of carbonyl compounds from alcohols

Details Preparation of carbonyl compounds from alcohols Preparation of carbonyl compounds from alcohols

2002-07-23

2004-09-14

O'Sullivan, Peter (Department: 1621)

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

Organic compounds

Oxygen containing

C549S071000, C549S484000, C568S322000, C568S339000, C568S360000, C568S402000, C568S426000, C568S431000

Reexamination Certificate

active

06790997

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a novel process for the preparation of carbonyl compounds by oxidation of alcohols in the presence of catalysts based on osmium compounds.
Aldehydes and ketones are important carbonyl compounds, which find use as chemical intermediates, particularly as fine chemicals, and also as precursors for dyes, medicaments, and active ingredients for agro-chemicals.
Although the literature already discloses a large number of preparative processes for aldehydes and ketones, there is great interest in new environmentally friendly catalytic synthesis methods because of the variety of differing carbonyl compounds of industrial interest. For example, hydroformylation of olefins, the formylation of aromatics, the ozonolysis of olefins, and the oxidation of alcohols are applied industrially to the synthesis of aldehydes. Of the synthetic processes mentioned, the oxidation of alcohols is particularly interesting for fine chemical syntheses. The availability and price of alcohols make them ideal starting materials for aldehyde and ketone syntheses. Oxidations of alcohols to carbonyl compounds succeed in the presence of stoichiometric amounts of chromium compounds using dimethyl sulfoxide/oxalyl chloride, periodate, manganese dioxide or other reagents. From an ecological, but also economic standpoint, processes employing cost-effective oxidizing agents, such as hydrogen peroxide with sodium hypochlorite in the presence of catalysts, are more interesting. However, catalytic processes employing oxygen as the oxidizing agent are even more advantageous. The literature discloses metal-catalyzed oxidations of alcohols using oxygen, which in most cases employ ruthenium and palladium catalysts. In general, only alcohols having allylic or benzoic structure are converted with good yields, although it is disadvantageous that relatively high catalyst concentrations are necessary, long reaction times are required, or cocatalysts must be added. The prior art processes require catalyst quantities that are too high for industrial application. The quantity of the noble metal catalyst that is used dominates the raw material costs of the reactions and makes the corresponding processes uneconomical. Furthermore, it is difficult to separate noble metal traces from the product if >1 mol % of catalyst is used. However, this is a requirement for application of the process in the field of pharmaceutical and agrochemical intermediate production.
Osmium-catalyzed alcohol oxidations have hardly been investigated up to now. The oxidation of predominantly allylic and benzylic primary alcohols in the system OsO
4
(1 mol %)/CuCl (1.5 mol %) in toluene at 100° C. with oxygen and with the addition of molecular sieves has been described; results between 19 and 96% were achieved at high selectivity (cf. K. S. Coleman, M. Coppe, C. Thomas, J. A. Osborn,
Tetrahedron Lett
., 40, 3723 (1999)). The oxidation of 4-methoxybenzalcohol to 4-methoxy-benzaldehyde using oxygen and 1 mol % OsO
4
in toluene at 100° C. in the presence of molecular sieves is also described. However, it is pointed out that leaving out CuCl leads to a reduction in the catalyst activity.
The need therefore exists for a novel, industrially operable process for the preparation of carbonyl compounds that is cost-effective, requires low quantities of metal catalysts, and facilitates a high catalyst productivity.
Surprisingly, a process for the preparation of carbonyl compounds by oxidation of alcohols in the presence of osmium compounds is found to fulfil the above-recited conditions and additionally delivers the carbonyl compounds in high purity and yield.
SUMMARY OF THE INVENTION
The present invention provides a process for the preparation of carbonyl compounds of the formula (I)
where
R and R
1
are independently hydrogen or an alkyl, cycloalkyl, aryl, or heteroaryl radical, each of which is optionally substituted, or
R and R
1
combine with the carbon atom to which they are bonded to form a cycloalkyl radical,
comprising reacting alcohols of the general formula (II)
where R and R
1
are as defined above for formula (I), with an oxidizing agent in the presence of a catalytic quantity of an osmium compound in water or a solvent mixture containing water at a pH of from 7 to 14.
DETAILED DESCRIPTION OF THE INVENTION
When R and R
1
as defined above are alkyl, they generally represent a straight-chain or branched hydrocarbon radical having from 1 to 18 carbon atoms that is optionally substituted by from 1 to 8 identical or different substituents. Alkyl preferably represents a straight-chain or branched hydrocarbon radical having from 1 to 8 carbon atoms, which is optionally substituted by from 1 to 3 identical or different substituents. More preferably, alkyl represents methyl, ethyl, and octyl.
Where R and R
1
as defined above are cycloalkyl, they generally represent a cyclic hydrocarbon radical having from 5 to 18 carbon atoms that is optionally substituted by from 1 to 8 identical or different substituents and in which one or more CH
2
groups of the cycloalkyl radical can be replaced by heteroatoms (preferably N, O, or S). Suitable cycloalkyl radicals R or R
1
in which one or more CH
2
groups of the cycloalkyl radical are replaced by one or more heteroatoms (preferably N, O, or S) are a piperadine or piperazine radical. The cycloalkyl radical preferably contains from 5 to 10 carbon atoms (more preferably cyclohexyl) in which again one or more CH
2
groups of the cycloalkyl radical can be replaced by one or more heteroatoms (preferably N, O, or S).
When R and R
1
as defined above are aryl, they generally represent an aromatic radical having from 6 to 14 carbon atoms (preferably from 6 to 10 carbon atoms) that is optionally substituted by from 1 to 8 identical or different substituents and is optionally fused (particularly phenyl or naphthyl that is optionally substituted by from 1 to 3 identical or different substituents, preferably phenyl, p-methylphenyl, or p-methoxyphenyl).
When R and R
1
as defined above are heteroaryl, they generally represent an aromatic radical having from 4 to 14 carbon atoms (preferably from 5 to 10 carbon atoms, particularly from 5 to 7 carbon atoms) and from 1 to 3 (preferably 1 or 2) heteroatoms selected from the group consisting of N, O, and S that is optionally substituted by from 1 to 8 identical or different substituents and is optionally fused (most preferably furan or thiophene).
Said alkyl, cycloalkyl, aryl, or heteroaryl radicals are each optionally substituted by from 1 to 8 identical or different substituents selected from the group consisting of alkyl, CN, COOH, COO-alkyl, COO-aryl, CO-alkyl, CO-aryl, O-alkyl, O-aryl, O—CO-aryl, O—CO-alkyl, OCOO-alkyl, N(alkyl)
2
, NH-alkyl, N(aryl)
2
, NH-aryl, NO, NO
2
, NOH, aryl, fluorine, chlorine, bromine, iodine, NO
2
, Si(alkyl)
3
, CHO, SO
3
H, SO
3
-alkyl, SO
2
-alkyl, SO-alkyl, CF
3
, NHCO-alkyl, CONH
2
, CONH-alkyl, NHCOH, NHCOO-alkyl, CHCHCO
2
-alkyl, CHCHCO
2
H, PO(aryl)
2
, PO(alkyl)
2
, PO
3
H
2
, and PO(O-alkyl)
2
, where the alkyl and aryl radicals again have the general and preferred meanings given above.
Particularly suitable alcohols of the formula (II) for the preparation of carbonyl compounds of the formula (I) are those in which at least one of the radicals R or R
1
represents an aryl or heteroaryl group as defined above.
The compounds of the formula (II) can be used individually or in any desired mixture.
The process of the invention is carried out in the presence of water as solvent. A two-phase solvent system is generally formed with the alcohol of the formula (II). In principle, additional organic solvent can be added as well as the alcohol of the formula (II). From 1 to 5 l/mol (preferably from 2 to 3 l/mol) of the alcohol of the formula (II) are usually used. Suitable additional solvents include inert organic solvents, such as aliphatic ethers, aromatic or aliphatic hydrocarbons, tertiary alcohols and esters, halogenated hydrocarbons, dipolar aprotic solvents such as dialkyl sulfoxides, N,N-di

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