Process for the preparation of heterocyclic aldehydes

Details Process for the preparation of heterocyclic aldehydes Process for the preparation of heterocyclic aldehydes

1997-02-20

1998-07-21

Owens, Amelia

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

549346, 549483, C07D31500, C07D30702

Patent

active

057837112

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The present invention relates to a process for the preparation of aldehydes of the general formula I ##STR3## in which the variables A and B stand for methyl groups which may carry one or two substituents inert under the conditions of the reaction, and m and n stand for 1 to 5, the sum of m and n being greater than 2.
Aldehydes of the general formula I, in which the formyl group is attached to a saturated ring interrupted by an oxygen atom, are of great significance as intermediates. Thus 4-formyltetrahydropyran is for example a building block for herbicides of the cyclohexenone class (cf EP-A 142,741).
The preparation of aldehydes from carboxylic acids or carboxylic acid esters is usually carried out in industrial plants in two stages in which the starting materials are first of all reduced as far as the alcohol stage, and oxidation is then performed to form the aldehyde. For example, the preparation of 4-formyltetrahydropyran from methyl tetrahydropyran-4-carboxylate has been well examined (cf EP-A 546,396 and DE-A 4,039,918).
EP-A 439,115 discloses the hydrogenation of aliphatic or alicyclic carboxylic acids, eg, cyclohexanoic acid, in the presence of a chromium/zirconium dioxide catalyst to produce the corresponding aldehydes.
EP-A 343,640 describes the hydrogenation of heteroaromatic carboxylic acids to the corresponding aldehydes where the catalyst used must contain at least one zinc or yttrium oxide, an oxide of the Lanthanide Group, or an oxide of a Group IVa element such as zirconium oxide. No reference is made to saturated heterocyclics.
It is the object of the invention to partially hydrogenate the carboxylic acids IIa or the esters IIb by a direct route to form the aldehydes I, ie without detouring through the alcohols and subsequent oxidation to the aldehydes
Accordingly, there has been found a process for the preparation of the heterocyclic aldehydes of formula I, wherein a carboxylic acid of the general formula IIa ##STR4## or one of its esters IIb derived from a C.sub.1 -C.sub.10 alcohol, is hydrogenated at a temperature of from 200.degree.to 450.degree.C. over a catalyst.
The carboxylic acids IIa and esters IIb suitable for the reaction to be carried out in the process of the invention can carry, on the ring, primarily from one to three substituents (R) which are inert under the reaction conditions, in particular C.sub.1 -C.sub.3 alkyl or C.sub.1 -C.sub.3 alkoxy groups.
The preferred end products of the process I are, for example, those derived from carboxylic acids IIa or their esters IIb, in which the ring containing the oxygen atom exhibits from 5 to 7 ring members, ie in which the sum of n and m is from 3 to 5, whilst one or two of the radicals R stand(s) for a C.sub.1 -C.sub.3 alkyl group and the other radicals R stand for hydrogen. Such compounds I are primarily 3-formyl-2-methyltetrahydrofuran, 3-formyl-2,4-dimethyltetrahydrofuran, 2-ethyl-4-formyl-tetrahydrofuran, 3-formyl-5-isopropyltetrahydropyran, and 3-formyl-2,7-dimethyl-oxepane. Those end products I are particularly preferred in which the hetero ring is unsubstituted, as in 3-formyltetrahydrofuran and, in particular, 4-formyltetra-hydropyran.
In the group of esters regarded as being suitable starting materials it is preferred to use those esters IIb which are derived from C.sub.1 -C.sub.10 monoalcohols. Of these, those esters IIb are primarily suitable in which the monoalcohol component exhibits an unsubstituted C.sub.1 -C.sub.10 hydrocarbon radical, as in the case of C.sub.1 -C.sub.10 alkanols such as, primarily, methanol, ethanol, n-propanol, 1-methylethanol, n-butanol, 1-methylpropanol, 2-methylpropanol and 1,1-dimethylethanol and in addition n-pentanol, n-hexanol, n-heptanol, n-octanol, and 2-ethylhexanol, and also such as, primarily, cyclopentanol and cyclohexanol and also 2-methylcyclohexanol, 2,6-dimethyl-cyclohexanol, cycloheptanol, and cyclooctanol, naphthols or such as, primarily, phenylmethanol, 2-phenylethanol and 3-phenylpropan-1-ol and also 1-phenylethanol, 2-phenylpropan-1-ol, and 1-phenylpropan-1-

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