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

page_text: PROVISIONAL SPECIFICATION.
Process for the Separation of Metacresol and Paracresol.
I, Dr. FRITZ RASCHIG, Manufacturing Chemist, of Mündenheimer Landstrasse,
Ludwigshafen on the Rhine, Germany, do hereby declare the nature of this inven-
tion to be as follows:-
Coal tar and consequently also the commercial cresol obtained from the same
contains the three isomeric varieties of cresol, viz., ortho-, meta-, and paracresol.
From this mixture of cresols the ortho cresol which distils at 180° C. may be
separated by fractional distillation, so as to leave a mixture consisting of about
60 per cent. of metacresol and 40 per cent. of paracresol.
Both cresols boil at 200° and cannot be separated from each other by fractional
distillation.
Their separation is, however, very desirable from a commercial point of view,
because, for instance, the trinitro cresol recently used as a substitute for picric
acid is exclusively a derivative of the meta-cresol.
In nitrating the mixture containing the three isomers, or the mixture of meta-
and para-cresol left after the removal of the ortho cresol, only the metacresol is
nitrated, while the ortho-cresol and the paracresol are completely oxidised, thereby
increasing the consumption of nitric acid, and consequently the cost of production
of the metacresol.
The new process for separating the metacresol from the paracresol is based on
the fact, that the sulpho-acids obtained by sulphonating the mixture of both
cresols behave differently when treated with superheated steam, that is to say,
they are split up into cresol and sulphuric acid at different temperatures. The
metacresol-sulphonic acid splits already at a temperature between 120° and
130° C., while the paracresol-sulphonic acid remains intact at this temperature,
and is only decomposed at about 1400-1600, by giving off paracresol.
In carrying out this process, the commercial mixture of metacresol and para-
cresol, which contains about 60 per cent. of the former and about 40 per cent. of
the latter, is treated with fuming sulphuric acid, preferably by dissolving
100 kilos of the cresol mixture in about 400 kilos of concentrated, or about
300 kilos of fuming sulphuric acid, containing 20 per cent. of SO. If con-
centrated acid is used, I heat to 100° for about an hour, but if fuming acid is
used for sulphurizing, the reaction causes considérable increase of heat, without
requiring any external heating. The ratios between the quantity of cresol
mixture and that of acid may differ from those stated above, but the latter have
been found specially suitable.
The mixture resulting from the reaction is now treated with superheated steam
at a temperature ranging between (approximately) 120 and 130° C., care being
taken that the latter temperature will not be exceeded. This limit of tempera-
ture may be regulated or maintained in a simple manner by adding to the product
of the reaction so much water, that the boiling point of the mixture will be
between 125 and 130° C. When steam is admitted, the decomposition of the

page_text: meta-cresol sulphonic acid takes place smoothly, as soon as the said temperature
has been reached, the result being sulphuric acid and metacresol, which distils
off, while the paracresol sulphonic acid remains behind undecomposed. After
the metacresol has been distilled off, the paracresol sulphonic acid may also be
split up by superheated steam, but at a higher temperature.
Dated this 20th day of December 1899
* Focess for the separation of Metacresol and Paracresol.
I, Dr. FRITZ RASCHIG, Manufacturing Chemist, of Mündenheimer Landstrasse,
Ludwigshafen on the Rhine, Germany, do hereby declare the nature of this inven-
tion 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 commercial cresol obtained from the same,
contains the three isomeric varieties of cresol, viz., ortho-, meta-, and paracresol.
From this mixture of cresols the ortho cresol which distils at 180° C. may be
separated by fractional distillation, so as to leave a mixture consisting of about
60 per cent. of metacresol and 40 per cent. of paracresol.
Both cresols boil at 200° and cannot be separated from each other by fractional
distillation.
Their separation is, however, very desirable from a commercial point of view,
because, for instance, the trinitro cresol recently used as a substitute for picric
acid, is exclusively a derivative of the meta-cresol.
In nitrating the mixture containing the three isomers or the mixture of meta-
and para-cresol left after the removal of the ortho-cresol, only the metacresol is
nitrated, while the orthocresol and the paracresol are completely oxidised, thereby
increasing the consumption of nitric acid, and consequently the cost of production
of the metacresol.
The new process for separating the metacresol from the paracresol is based on
the fact, that the sulpho-acids obtained by sulphonating the mixture of both
cresols behave differently when treated with superheated steam, that is to say,
they are split up into cresol and sulphuric acid at different temperatures. The
metacresol sulphonic acid splits already at a temperature between 120
130° C., while the paracresol sulphonic acid remains intact at this temperature,
and is only decomposed at about 140-160°, by giving off paracresol.
and
In carrying out this process the commercial mixture of metacresol and para-
cresol, which contains about 60 per cent. of the former and about 40 per cent. of
the latter, is treated with concentrated or fuming sulphuric acid, preferably by
dissolving 100 kilos of the cresol mixture in about 400 kilos of concentrated, or
about 300 kilos of fuming sulphuric acid containing 20 per cent. of SO. If con-
centrated acid is used I heat to 100° for about an hour, but if fuming acid is
used for sulphurizing, the reaction causes considerable increase of heat, without
requiring any external heating. The ratios between the quantity of cresol
mixture and that of acid may differ from those stated above, but the latter have
been found specially suitable.
The mixture resulting from the reaction is now treated with superheated steam
at a temperature ranging between (approximately) 120 and 130° C., care being
taken, that the latter temperature will not be exceeded. This limit of tempera-
ture may be regulated or maintained in a simple manner by adding to the product

page_text: of the reaction so much water, that the boiling point of the mixture will be
between 125 and 130° C. When steam is admitted, the decomposition of the
meta-cresol sulphonic acid takes place smoothly, as soon as the said temperature
has been reached, the result being sulphuric acid and metacresol, which distils
off, while the paracresol sulphonic acid remains behind undecomposed. After
the metacresol has been distilled off, the paracresol sulphonic acid may also be
split up by superheated steam, but at a higher temperature.
Having now particularly described and ascertained the nature of the said
invention and what manner the same is to be performed, I declare that what I
claim is:-
1. The process for separating metacresol from paracresol, which consists in
sulphonating a mixture of the two cresols and treating the mixture of sulpho-
acids thus obtained with steam at a temperature which causes the decomposition
of the metacresol sulphonic acid, but leaves the paracresol sulphonic acid intact,
substantially as described.
2. The process for separating metacresol from a mixture of metacresol sulphonic
acid and paracresol sulphonic acid, which consists in subjecting the said mixture
to superheated steam at a temperature ranging approximately between 120
and 130° C., thereby splitting up the metacresol sulphonic acid into metacresol
which distils off, and sulphuric acid which remains with the undecomposed para-
cresol sulphonic acid, substantially as described.
Dated this 1st day of September 1900.
FAIRFAX & WETTER,
Agents, 37 and 39, Essex Street, Strand, London.