Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1996-01-05
1998-06-09
Geist, Gary
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C07C 4500
Patent
active
057636753
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/GB94/01227, filed Jun. 6, 1994.
This invention relates to a chemical process and more particularly to a method for the preparation of 2-hydroxyarylaldehydes.
A number of 2-hydroxyarylaldehydes are known as useful products in the perfume and agricultural chemical industries and especially as intermediates for the corresponding oximes, for example 5-nonylsalicylaldoxime, which are used as metal extractants.
Our EP-A-0529870 describes a method of preparing 2-hydroxyarylaldehydes by reacting a magnesium bis-hydrocarbyloxide, derived at least in part from a hydroxyaromatic compound having at least one free position ortho to the hydroxyl group, with formaldehyde or a formaldehyde-liberating substance under substantially anhydrous conditions.
In particular, EP-A-0529870 describes reacting a magnesium bis-phenoxide, such as magnesium bis(4-nonylphenoxide), with paraformaldehyde in a substantially anhydrous solvent system at reflux temperature so that the volatile by-products of the reaction, for example methanol, methyl formate and methylal, are distilled from the reaction mixture as they are formed. It is stated that the reaction is preferably carried cut at atmospheric pressure but that higher pressures may be employed if desired.
It has now been found that it can be advantageous to carry out the aforesaid formylation reaction at reduced pressures, that is to say at pressures lower than normal atmospheric pressure. In particular, it has been found that, in addition to facilitating removal of volatile reaction by-products, a significant improvement in the yield of and/or purity of aldehyde and an appreciable reduction in formation of by-products can be observed when the reaction is carried out at reduced pressure (and consequently at a lower temperature) compared with carrying out the same reaction in the same solvent system at atmospheric pressure.
Accordingly, the invention provides a method for the preparation of a 2-hydroxyarylaldehyde which comprises reacting a magnesium bis-hydrocarbyloxide, derived at least in part from a hydroxyaromatic compound having at least one free position ortho to the hydroxyl group, with formaldehyde or a formaldehyde-liberating compound under substantially anhydrous conditions at a pressure of from 50 to 700 mm Hg absolute.
The substantially anhydrous conditions required by the reaction may be conveniently provided by the use of substantially anhydrous reactants together with conventional techniques, for example distillation, for removal of adventitious moisture. It is usually advantageous to perform the reaction in the presence of a substantially anhydrous solvent system. Suitable solvent systems typically comprise an inert non-polar or low polarity organic solvent and/or a polar organic solvent capable of acting as a ligand with respect to magnesium atoms.
Suitable inert non-polar or low polarity organic solvents will be liquids at the reaction temperature and will act as solvents for the magnesium bis-hydrocarbyloxide. Preferably, they will allow removal of one or more of the volatile by-products by distillation during the course of the reaction. Examples of suitable inert solvents include aromatic hydrocarbons, for example toluene, xylene, mesitylene, cumene, cymene, tetralin and chlorinated aromatic hydrocarbons, for example chlorobenzene and o-dichlorobenzene. Mixtures of inert solvents may be used.
Suitable polar solvents will be liquids at the reaction temperature and may be regarded as co-solvents when used in conjunction with non-polar or low polarity solvents. As examples of suitable polar co-solvents, there may be mentioned polar aprotic solvents such as dimethylsulphoxide, sulpholane, dimethylacetamide, N-formylpiperidine, N-methylpyrrolidinone, tetramethylurea and, especially, dimethylformamide, tertiary bases such as triethylamine, tri-octylamine, tetramethylethylenediamine and pyridine, ethers such as diethyl ether, diphenyl ether, tetrahydrofuran, glyme, and other polar solvents such as "Polymeg" 10
Geist Gary
Puttlitz, Jr. Karl J.
Zeneca Limited
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