Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1996-10-16
1998-05-26
Reamer, James H.
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
562424, 562406, 562475, 562463, C07C 4565
Patent
active
057568537
DESCRIPTION:
BRIEF SUMMARY
The subject of the present invention is a process for the preparation of a 4-hydroxybenzaldehyde carrying at least one substituent in the position ortho to the OH group.
It more particularly relates to the preparation of 3-methoxy-4-hydroxybenzaldehyde and of 3-ethoxy-4-hydroxybenzaldehyde, known respectively as "vanillin" and "ethyl vanillin".
Vanillin is obtained mainly from natural sources such as lignin but a part is prepared chemically. Encyclopedia of Chemical Technology, 23, p. 1710, 3rd edition! and a number of them start from guaiacol or 2-methoxyphenol.
Thus, mention may be made of the preparation of vanillin by reaction of guaiacol and glyoxylic acid, oxidation of the condensate by air and then release of the vanillin from the reaction mixture by acidification. The disadvantage from which this process suffers is that it uses glyoxylic acid, which is an expensive reactant.
Another access route to vanillin according to the Reimer-Tiemann reaction comprises the reaction of guaiacol and chloroform in the presence of potassium hydroxide. The formation of resin is a disadvantage of this method of preparation.
According to the Gatterman reaction, vanillin is synthesized by reaction of hydrocyanic acid with guaiacol, in the presence of hydrochloric acid. In addition to the use of a reactant which is difficult to handle, this process has the disadvantage of not being selective, because the vanillin is accompanied by isovanillin and o-vanillin.
A major difficulty present in the synthesis of vanillin is selectively to attach a formyl group to guaiacol in the position para to the hydroxyl group.
Another problem to be solved is to provide a process which is competitive from an industrial viewpoint.
The present invention provides a new process which makes it possible to overcome the above-mentioned disadvantages while satisfying the requirements mentioned above.
A process for the preparation of a substituted 4-hydroxybenzaldehyde, substituted at least in the 3 position by an alkoxy group, has now been found, which constitutes the subject of the present invention, characterized in that it comprises subjecting a substituted phenol compound, substituted at least in the 2 position by an alkoxy group and in which the 4 and 6 positions are free, to a first stage of carboxylation in the 6 position, then to a stage of hydroxymethylation in the 4 position, followed by a stage of oxidation of the hydroxymethyl group to a formyl group, and finally to a last decarboxylation stage.
The process of the invention is based on the preparation of 2-hydroxybenzoic acids hydroxymethylated in the 5 position and substituted at least in the 3 position by an alkoxy group, which are used as intermediates in the synthesis of substituted 4-hydroxybenzaldehydes, substituted at least in the 3 position by an alkoxy group.
Another subject of the invention is the process for the oxidation of 2-hydroxybenzoic acids hydroxymethylated in the 5 position and substituted, at least in the 3 position by an alkoxy group, to the corresponding formylated 2-hydroxybenzoic acids.
The process of the invention is entirely well suited to the preparation of vanillin. Indeed, it makes it possible to selectively formylate guaiacol in the para position by successively carrying out carboxylation of guaiacol in the 6 position, hydroxymethylation followed by oxidation resulting in the formyl group in the 4 position and finally removal of the carboxyl group situated in the 6 position.
This process is not only selective but also very competitive from an industrial viewpoint because it uses inexpensive reactants.
Although the process of the invention is perfectly well suited to the use of guaiacol and of 2-ethoxyphenol, it is also suitable for other substituted phenol compounds.
"Substituted phenol compound" is understood to mean any aromatic compound in which the aromatic ring carries a hydroxyl group, an alkoxy group in the 2 position and other possible substituents and in which the 4 and 6 positions are free.
In the account which follows of the present invention,
REFERENCES:
patent: 4036873 (1977-07-01), Huffman
patent: 4996354 (1991-02-01), Neumann et al.
Arch. Microbiol. (amiccw, 03028933); 79; vol.121 (1); pp. 23-28, Kyoto Univ.; Wood Res. Inst.; Uji; Japan, XP002003065 Ohta M et al; "Microbial degradation of dehydrodiconiferyl alcolol, a lignin substructure model" see page 26.
Jouve Isabelle
Maliverney Christian
Metivier Pascal
Carleton Katherine L.
Reamer James H.
Rhone-Poulenc Chimie
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