Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-05-13
2001-02-06
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S433000, C568S442000, C568S764000, C562S475000
Reexamination Certificate
active
06184421
ABSTRACT:
The present invention concerns a process for the preparation of a 4-hydroxybenzaldehyde and its derivatives.
More particularly, the invention concerns the preparation of 3-methoxy-4-hydroxybenzaldehyde and 3-ethoxy-4-hydroxybenzaldehyde, respectively known as vanillin and ethylvanillin.
In French patent application n
o
95/06186, a process is described for the preparation of 4-hydroxybenzaldehydes, more particularly vanillin and ethylvanillin.
The process described consists of preparing a 3-carboxy-4-hydroxybenzaldehyde then decarboxylating that compound to produce the 4-hydroxybenzaldehyde.
According to FR n
o
95/06186, the 3-carboxy-4-hydroxybenzaldehyde is prepared from one of the compounds given below and mixtures thereof, more particularly with the following formulae (IIa), (IIb), (IIc) and (IId) given below:
where:
M represents a hydrogen atom and/or a metallic cation from group (Ia) or (IIa), or an ammonium cation;
Z
1
, Z
2
and Z
3
, which may be identical or different, represent a hydrogen atom, an alkyl, alkenyl, alkoxy, hydroxyalkyl, alkoxyalkyl, cycloalkyl or aryl radical, a hydroxyl group, a nitro group, a halogen atom, or a trifluoroethyl group.
In that patented process, the starting compound is a bifunctional phenolic compound carrying two functional groups on the aromatic ring in the ortho and para positions which can be a —CHO group and/or a —CH
2
OH group.
Firstly, the ortho group is selectively oxidised to a carboxylic group; the group in the para position is at most oxidised to a formyl group. After eliminating the carboxy group in the ortho position, a 4-hydroxybenzaldehyde is obtained.
Thus vanillin and ethylvanillin can advantageously be prepared using a process which is selective and also highly competitive from an industrial viewpoint as it uses inexpensive reactants.
However, in that process it is difficult to obtain a reaction yield (expressed with respect to the starting phenol) of more than 70% as obtaining a high yield of a bifunctional phenolic compound is accompanied by that of a by-product, namely a bis-arylmethane.
During our research, we discovered in French application no96/12479 that a 4-hydroxybenzaldehyde can be prepared from a mixture of monosubstituted phenolic compounds, one (A) carrying a formyl or hydroxymethyl group in the 2 position, and the other (B) carrying a formyl or hydroxymethyl group in the 4 position, and selectively oxidising the formyl or hydroxymethyl group in the 2 position of compound (A) to a carboxy group, and possibly a hydroxymethyl group in the 4 position of compound (B) to a formyl group, thus producing a mixture of a 2-hydroxybenzoic acid and a 4-hydroxybenzaldehyde from which the latter is separated.
More particularly, that mixture of phenolic compounds used has general formula (II):
where, in formulae (IIA) and (IIB):
Y
1
and Y
2
, which may be identical or different, represent one of the following groups:
a —CHO group;
a CH
2
OH group;
Z
1
, Z
2
and Z
3
, which may be identical or different, represent a hydrogen atom, an alkyl, alkenyl, alkoxy, hydroxyalkyl, alkoxyalkyl, cycloalkyl or aryl radical, a hydroxyl group, a nitro group, a halogen atom, or a trifluoroethyl group.
The disadvantage of that process is that to obtain compounds with formula (IIA) or (IIB), by hydroxymethylation of a phenol, it is essential to work with a low degree of conversion of the starting phenol which results in low productivity.
Thus the existing processes must be improved in order to have available a process which is of great economic interest which minimises the by-products and can produce a high operating productivity.
We have discovered, and this constitutes one aspect of the present invention, a process for the preparation of a 4-hydroxybenzaldehyde and its derivatives, characterized in that it consists of selectively oxidising, to a carboxy group, the group in the 2 position with respect to the hydroxyl group, present in the phenolic compounds in a mixture comprising at least:
a phenolic compound (A) carrying formyl and/or hydroxymethyl groups in the 2 and 4 position;
a phenolic compound (B) carrying a formyl or hydroxymethyl group in the 4 position;
a phenolic compound (C) carrying a formyl or hydroxymethyl group in the 2 position;
resulting in a mixture comprising a 3-carboxy-4-hydroxybenzaldehyde, a 4-hydroxybenzaldehyde and a 2-hydroxybenzoic acid, which then undergoes a decarboxylation operation to produce the 4-hydroxybenzaldehyde and a phenol which can optionally be recycled.
In a further aspect, the invention provides a starting mixture of phenolic compounds claimed as the mixture itself, and the mixture obtained after oxidation.
Finally, processes for preparing these mixtures constitute further aspects of the invention.
In the process of the invention, we have discovered that by starting from a mixture of starting compounds as defined above, it is possible to carry out simultaneous intramolecular oxidation (A) and intermolecular oxidation (B+C) since oxidation of the carboxy group takes place preferentially on the hydroxymethyl or formyl group in the ortho position.
The process of the invention thus comprises an oxidation step and a decarboxylation step for a 3-carboxy-4-hydroxybenzaldehyde to a 4-hydroxybenzaldehyde and a 2-hydroxybenzoic acid which can produce the phenolic starting compound which can then be recycled; the 4-hydroxybenzaldehyde is then recovered conventionally.
The starting substrates used in the process of the invention are mixtures of phenolic compounds, one (A) carrying formyl and/or hydroxymethyl groups in the 2 and 4 positions, the second (B) carrying a formyl or a hydroxymethyl group in the 4 position and the last, (C), in the 2 position.
The term “phenolic compound” means any aromatic compound with an aromatic nucleus which carries a hydroxy group.
In the following disclosure of the present invention, the term “aromatic” means the conventional idea of aromaticity as defined in the literature, in particular in “Advanced Organic Chemistry” by Jerry MARCH, 4
th
edition, John Wiley and Sons, 1992, pp. 40 ff.
Thus a mixture (II) of phenolic compounds is used which, more particularly, have the following formulae:
In formulae (IIA) to (IIC):
Y
1
and Y
2
, which may be identical or different, represent one of the following groups:
a —CHO group;
a —CH
2
OH group;
Z
1
, Z
2
and Z
3
, which may be identical or different, represent a hydrogen atom, an alkyl, alkenyl, alkoxy, hydroxyalkyl, alkoxyalkyl, cycloalkyl or aryl radical, a hydroxy group, a nitro group, a halogen atom, or a trifluoromethyl group.
Particularly suitable compounds for use in the process of the invention have formulae (IIA) to (IIC) where Z
1
, Z
2
and Z
3
, which may be identical or different, represent one of the following groups:
a hydrogen atom;
a linear or branched alkyl radical containing 1 to 12 carbon atoms, preferably 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl;
a linear or branched alkenyl radical containing 2 to 12 carbon atoms, preferably 2 to 4 carbon atoms, such as vinyl or allyl;
a linear or branched alkoxy radical containing 1 to 12 carbon atoms, preferably 1 to 4 carbon atoms, such as a methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy or tert-butoxy radical;
a phenyl radical;
a halogen atom, preferably a fluorine, chlorine or bromine atom.
The present invention does not exclude the presence of substituents of different natures on the aromatic ring, provided that they do not interfere with the reactions taking place in the process of the invention.
The present invention is preferably applicable to compounds with formula (IIA) to (IIC) where Z
1
represents a hydrogen atom or a linear or branched alkyl or alkoxy radical containing 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms; Z
2
and Z
3
represent a hydrogen atom; and Y
1
and Y
2
are identical and represent a formyl group or a hydroxymethyl group.
Preferred examples of mixtures of phenolic compounds for use in the process of the invention are:
o-hydroxymethylguaia
Padmanabhan Sreeni
Rhodia Chimie
Seugnet Jean-Louis
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