Process for the preparation of 3-carboxy-4-hydroxybenzaldehides

Details Process for the preparation of 3-carboxy-4-hydroxybenzaldehides Process for the preparation of 3-carboxy-4-hydroxybenzaldehides

1997-01-24

1998-07-21

Geist, Gary

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

Organic compounds

Oxygen containing

568442, 568764, C07C 4500

Patent

active

057837376

DESCRIPTION:

BRIEF SUMMARY
This is the U.S. National Stage Application of PCT/FR 96/00779, filed May 24, 1996, now WO96/37454 published Nov. 28, 1996.
The present invention concerns a process for the preparation of 3-carboxy-4-hydroxybenzaldehydes and derivatives thereof from phenolic compounds carrying formyl and/or hydroxymethyl groups in the 2 and 4 positions.
The invention also concerns the preparation of 4-hydroxybenzaldehydes from 3-carboxy-4-hydroxybenzaldehydes.
More particularly, the invention concerns the preparation of 3-methoxy-4-hydroxybenzaldehyde and 3-ethoxy-4-hydroxybenzaldehyde, respectively known as "vanillin" and "ethylvanillin".
Vanillin is primarily obtained from natural sources such as lignin, but some is prepared chemically.
A number of preparation methods have been described in the literature edition!. A number of these use guaiacol, or 2-methoxyphenol, as a starting material.
Thus, vanillin can be prepared by reacting guaiacol with glyoxylic acid, oxidising the condensate in air then liberating the vanillin from the reaction medium by acidification. The process suffers from the disadvantage that glyoxylic acid is an expensive reactant.
The Reimer-Tiemann reaction can also be used to obtain vanillin by reacting guaiacol and chloroform in the presence of potassium hydroxide. Resin formation is a disadvantage of this preparation method.
In the Gatterman reaction, vanillin is synthesised by reacting hydrogen cyanide with guaiacol in the presence of hydrochloric acid. Apart from using a reactant requiring delicate handling, that process has the disadvantage of being non-selective since vanillin formation is accompanied by isovanillin and o-vanillin formation.
A major difficulty in synthesising vanillin is selectively fixing a formyl group on the guaiacol in the position para to the hydroxy group.
A further problem is to provide a process which is industrially competitive.
The present invention provides a novel process which can overcome the above disadvantages and satisfy the requirements mentioned above.
A first object of the present invention is to provide a process for the preparation of a 3-carboxy-4-hydroxybenzaldehyde characterized in that the group in the 2 position in a phenolic compound carrying formyl and/or hydroxymethyl groups in the 2 and 4 positions is selectively oxidised to a carboxy group, and optionally a hydroxymethyl group in the 4 position is selectively oxidised to a formyl group.
A further object is to provide a preparation for a 4-hydroxybenzaldehyde using a process for the decarboxylation of a 3-carboxy4-hydroxybenzaldehyde.
The process of the invention is suitable for the preparation of vanillin. It can be used for the selective oxidation of 4,6-diformylguaiacol or 4,6-di(hydroxymethyl)guaiacol or 4-formyl-6-hydroxymethylguaiacol or 4-hydroxymethyl-6-formylguaiacol to 5-carboxy-vanillin then the elimination of the carboxy group in the 5-position to produce vanillin.
Similarly, it can be applied to guetol (2-ethoxyphenol) to produce ethylvanillin.
The process is not only selective but is also highly competitive industrially as it uses cheaper reactants.
The starting substrate used in the process of the invention is a phenolic compound carrying formyl and/or hydroxymethyl groups in the 2 and 4 positions.
The term "phenolic compound" denotes any aromatic compound with an aromatic nucleus which carries a hydroxy group.
In the following disclosure of the present invention, the term "aromatic" denotes the conventional idea of aromaticity as defined in the literature, in particular in "Advanced Organic Chemistry" by Jerry MARCH, 4.sup.th edition, John Wiley and Sons, 1992, pp. 40 ff.
The phenolic compound has hydroxymethyl and/or formyl groups in the 2 and 4 positions.
Preferably, the phenolic compounds used in the process of the invention have the following general formula (II): ##STR1## where: Y.sub.1 and Y.sub.2, which may be identical or different, represent one of the following groups: represent a hydrogen atom, an alkyl, alkenyl, alkoxy, hydroxyalkyl, alkoxyalkyl, cycloalkyl or aryl radi

REFERENCES:
patent: 4351962 (1982-09-01), Gradeff et al.
Eugenio et al; Farmaco et al; 46(5): 669-676, 1991.
CA vol. 52; 11776i; Cavina et al; Rend.ist.super.sanita. 18,750-765, 1955.
Jerry March; Advanced Organic Chemistry; Third Edition; p. 507, 1985.

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