Improvements in the Manufacture of Vanillin from Protocatechuic Aldehyde.
Year: 1895

page_text: Date of Application, 17th Sept., 1895-Accepted, 26th Oct., 1895
[Communicated from abroad by LA SOCIÉTÉ CHIMIQUE DES USINES DU RHÔNE,
ANCT. GILLIARD P. MONNET & CARTIER, 8 Rue de Rotz, à Lyon (Rhône),
France.]
Improvements in the Manufacture of Vanillin from Protocatechuic
Aldehyde.
I, JOHN IMRAY, of No. 28 Southampton Buildings, Chancery Lane, in the
County of London, Consulting Engineer and Chartered Patent Agent, do hereby
declare the nature of this invention and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
Direct methylation of protocatechuic aldehyde produces only traces of vanillin
the product consisting principally of isovanillin with more or less methyl-vanillin.
It has been frequently attempted to protect from methylation the hydrogen of
the hydroxyl group standing in the para position to the CHO group of proto-
catechuic aldehyde, and thus prevent the formation of isovanillin, by previously
substituting an indifferent group, which after the methylation of the second
hydroxyl group of protocatechuic aldehyde, standing in the meta position to
the CHO group, can be removed by one of the ordinary processes of splitting.
For this purpose indifferent groups of the types of benzyl, and benzene-sulpho
or toluene-sulpho groups have hitherto been employed, but it has been found that
in the process of substitution these groups replace the hydrogen of the meta as well
as para-hydroxyl, and that consequently both meta- and para-, as well as di-,
substitution products of protocatechuic aldehyde are formed.
It has therefore been necessary to use a special method of purification of the
para substitution product, especially to remove the meta substitution product
before methylation, otherwise when it is subsequently methylated and submitted to
a splitting operation, a mixture of vanillin with isovanillin and methyl-vanillin is
nevertheless obtained.
According to the present invention, the formation of a meta substitution product
is completely avoided by the employment of a substituting group of a new type,
namely, nitro-para-toluenesulpho chloride, which possesses the formula
It was first prepared by my foreign correspondents by the direct nitration of
para-toluene-sulphochloride. It melts at 36° C., boils at 175°-180° C. under a
0 reduced pressure of 7 m.m., and with ammonia yields an amide that melts at
143° 144° C.
Under suitable conditions the above described nitro-para-toluenesulphochloride
condenses with proto-catechuic aldehyde in such a manner that only the hydrogen

page_text: of the hydroxyl in the para position is replaced. For methylation of the para-
nitrotoluenesulpho-proto-catechuic aldehyde thus obtained the usual methods at
elevated temperatures are uot applicable, as the heat would cause decomposition of
the molecule.
The product can, however, be easily converted into nitro-toluene sulpho vanillin
by treatment with dimethyl sulphate in presence of one molecule of alkali at
ordinary temperatures.
The saponification of the nitro-para-toluene-sulphovanillin is effected by treat-
ment with two molecules of potassium hydroxide in alcoholic solution at the
temperature of the water bath.
The crude vanillin forined is isolated and purified by the usual methods.
For example. In a vessel, provided with suitable stirring apparatus, a solution
of 6 kilos. protocatechuic aldehyde in 150 kilos. water at ordinary temperature is
mixed with a solution of 10 kilos. nitroparatoluene sulpho chloride in 75 kilos.
toluene. Under continuous stirring 13 kilos. aqueous 13.3 per cent. caustic soda
solution, diluted with 75 kilos. water, is allowed to flow in quite gradually. The
condensation is completed with only a slight rise in temperature, whereupon &
further 13 kilos. aqueous 13.3 per cent. caustic soda solution is added at once.
After thoroughly stirring for half an hour and allowing the mixture to stand, the
alkaline aqueous layer is run off from the toluene and the nitroparatoluene sulpho-
protocatechuic aldehyde is precipitated from it by addition of dilute sulphuric
acid.
The product thus obtained, after being washed, with cold water, is dissolved in
50 kilos. alcohol, and 11 kilos. 19.5 per cent. alcoholic potash solution as well as
5 kilos. dimethyl sulphate are added, the whole operation being conducted at
ordinary temperature. After a few minutes, methylation is complete and the
whole solidifies to a crystalline mass.
It is washed with cold water to remove the
bye product, potassium methyl sulphate, and the undissolved methylated product is
dissolved in 40 kilos. alcohol and the solution treated at water bath temperature
with 21 kilos. of 19.5 per cent. alcoholic potash solution.
Finally the alcohol is distilled off and the residue taken up with water, from
which solution the crude vanillin is precipitated in the cold by the addition of
dilute sulphuric acid. The purification of the precipitated vanillin is carried out
in the usual way.
Having now particularly described and ascertained the nature of this inven-
tion and in. what manner the same is to be performed, I declare that what I
claim is :-
1. The herein described preparation of paranitrotoluene sulpho protocatechuic
aldehyde by the action of nitroparatoluene-sulpho-chloride dissolved in toluene
upon an aqueous solution of protocatechuic aldehyde in presence of a molecule of
caustic soda or potassa.
2. The herein described preparation of nitrotoluene sulpho vanillin by the action
of dimethyl sulphate on paranitrotoluene sulpho protocatechuic aldehyde in presence
of a molecule of alkali at ordinary temperature.
3. The herein described transformation of nitrotoluene sulpho vanillin into
vanillin by saponification on the water bath with two molecules of potassic
hydrate.
4. Paranitrotoluene sulpho catechuic aldehyde manufactured as set forth in
Claim 1.
5. Nitrotoluene sulpho vanillin manufactured as set forth in Claim 2.
בז
ABEL & IMRAY,
Agents for the Applicant.