Process for the Separation of Metacresol and Paracresol.
Year: 1899

page_text: Date of Application, 11th Sept., 1899-Accepted, 11th Nov., 1899
COMPLETE SPECIFICATION.
Process for the Separation of Metacresol and Paracresol.
1. Dr. FRITZ RASCHIG, Manufacturing Chemist, of Ludwigshafen-on-the-Rhine,
Germany, 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:.
Coal-tar, and consequently also the mixture of phenols produced from it,
contains, as is well known, all three cresols, viz.:-ortho-, meta, and paracresol.
Hitherto the industrial use of cresols depended chiefly on their disinfecting
properties, which are shared by all three isomers, in consequence of which no
value was attributed to the separation of the constituents.
Recently, however, cresol has been used for the manufacture of other chemical
products; and in order to obtain these in a pure condition, it is desirable, that
the raw materials should also be pure. For instance, trinitro-cresol, which is
obtained by sulphonating the mixture of cresols and then treating it with nitric
acid, in a manner analogous to the production of picric acid from phenol, has
found application during the last few years as a substitute for pieric acid. This
trinitro-cresol is exclusively a derivative of the meta-cresol; the whole of the
ortho- and paracresol contained in the mixture of cresols, disappears in the
process of nitration, by being completely oxidised.
This oxidation naturally uses up large quantities of nitric acid, and as the
mixture of the three cresols resulting from coal-tar generally consists of 35
per cent. of metacresol, 25 per cent. of paracresol and 40 per cent. of ortho-cresol,
its nitration consumes about three times the quantity of nitric acid, which would
be necessary for only converting its contents of metacresol into trinitro-metacresol.
The first step that suggested itself for the purpose of saving nitric acid, was to
attempt the isolation of the pure metacresol from the mixture of cresols. By
frequently repeated fractional distillation, the ortho-cresol, which distils at 188°
Cent., may indeed be separated from the metacresol and paracresol, which distil
at 2000, whereby a cresol mixture is obtained consisting of about 60 per cent. of
metacresol and 40 per cent. of paracresol, and which on nitration consumes only
about twice the quantity of nitric acid which would be necessary for the 60 per cent.
of metacresol. But up to the present a process for removing also the paracresol
has not been known.
The process hereafter described has this object and is based on the easy
olubility of the metacresol sulphonic acid in sulphuric acid, while the paracresol
ulphonic acid, as well as its sodium salt, is sparingly soluble in it.
The commercial mixture of metacresol and paracresol is heated with a larger
uantity of concentrated sulphuric acid than that necessary for converting the
resols into their sulphonic acids, until the sulphonic acids have been formed.
ubsequently the product of the reaction is allowed to stand until the paracresol-
ulpho-acid has crystallised out and the crystals are separated from the mother
quor. As the sodium salt of the paracresol-sulpho-acid is also insoluble in
ulphuric acid, as mentioned above, it is possible to convert the paracresol-
alpho-acid into its sodium salt by adding sodium sulphate, or other easily soluble

page_text: sodium compounds, such as the acetate, the carbonate, or the chloride, after the
two cresols have been converted into their sulphonic acid, and the sodium salt
thus produced will also crystallise out. The cresols are recovered from their
sulphonic acids in the known manner, by splitting off the sulpho-groups by means
of superheated steam.
EXAMPLE No. 1.
10 kilos. of a commercial mixture of about 60 per cent. of metacresol and
40 per cent. of paracresol are dissolved in 40 kilos. of concentrated sulphuric acid,
the solution is heated to about 100° Cent. for an hour, and then allowed to
stand for about a week at ordinary atmospheric temperature.
During this time the solution forms a pasty mass consisting of crystals of
paracresol-sulphonic acid, and a mother liquor composed of metacresol-sulphonic-
acid and any excess of sulphuric acid. The crystals are separated from the liquid
by filtration, pressure or centrifugal action.
The crystals, as well as the liquid, may then be treated with superheated steam
by the usual method, for splitting off the sulphuric acid and obtaining pure para-
cresol and metacresol. If, however, it is the question of producing trinitro-
metacresol, this operation is, of course, dispensed with and the mother liquid
nitrated directly.
The great commercial progress which is embodied in this method of working,
will appear from the following figures:-
10 kilos. of the mixture of metacresol and paracresol mentioned above require
for their complete nitration 100 kilos. of nitric acid of 1.38 specific gravity (40° Bé.)
and yield 10 kilos. of trinitro-cresol.
If, however, the paracresol has been separated out in the shape of its sulphonic
acid according to the above prescription, only 50 kilos. of nitric acid are necessary
for complete nitration, and the yield is 95 kilos. of trinitro-metacresol. The
actual yield is slightly less, because a small quantity of the metacresol-sulphonic
acid adheres to the crystals of the para-acid and is consequently not subjected
to nitration, but the deficiency in the yield of nitro-product amounting to about
half a kilo. will not cost one tenth as much as the 50 kilos. of nitric acid which
are saved.
EXAMPLE No. 2.
10 kilos. of the same mixture of metacresol and paracresol are dissolved in
25 kilos. of concentrated sulphuric acid and heated to 100° C. for about an hour.
Subsequently a hot solution of 4 kilos. of anhydrous sodium sulphate in 20 kilos.
of water is added, and the mixture is allowed to stand until it has completely
cooled. The result is a crystalline mass consisting of crystals of para-cresol-
sulphonate of soda and a liquor of metacresol-sulphonic acid, sulphuric acid and
minute quantities of sodium sulphate representing the excess. This pasty mass
is divided into a solid and a liquid portion, as described above. As in the
previous example, the liquid may be directly nitrated, or worked up into meta-
cresol by means of steam. The sodium sulphate may, of course, be replaced by
other easily soluble sodium compounds, such as the acetate, carbonate or chloride.
The proportions of materials stated in these two examples have been found
most advantageous, but may be slightly varied without materially affecting the
result. For instance in the first example the quantity of sulphuric acid may he
reduced, especially when working below the normal temperature, as would be
the case in the winter.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to he performed, I declare that what
I claim is
1. The process for separating metacresol and paracresol, which consists in
converting them into sulpho acids, separating the solid para-acid from the liquid

page_text: meta-acid, and regenerating the cresols from the sulpho acids by means of steam,
substantially as described.
2. The process for separating metacresol and paracresol, which consists in con-
verting them into sulphonic acids, adding a solution of a sodium salt in quantity
sufficient at least for the conversion of the para-acid into its sodium-salt, separat-
ing the solid paracresol-sulphonate of soda from the liquid metacresol-sulphonic
acid, and regenerating the cresols from the sulphonic acids by means of steam,
substantially as described.
3. The method described above for separating metacresol from paracresol by
utilizing the different solubilities of their sulphonic acids in sulphuric acid.
Dated this 11th day of September 1899.
FAIRFAX & WETTER,
Agents, 37 and 39, Essex Street, Strand, London.