Improved Process for the Purification of Anthracene.
Year: 1899

page_text: Date of Application, 14th Apr., 1899-Accepted, 8th July, 1899
Improved Process for the Purification of Anthracene.
We, AKTIEN-GESELLSCHAFT FÜR THEER-UND ERDÖL-INDUSTRIE, Manufacturers,
of Berlin, Flottwellstrasse No. 7, and Dr. GUSTAV KRAEMER, Chemist, of Flottwell-
strasse No. 7, Berlin, 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:
-
Attempts have been made in various ways to purify the crude anthracene
which is obtained directly by crystallisation from the high boiling fraction of
coal tar (anthracene oil) and has as a rule a degree of purity of hardly more than
30 per cent. By one recrystallisation from benzene the phenanthrene is virtually
the sole impurity removed and the degree of purity is raised only to from 50
to 60 per cent.
By recrystallisation from pyridine (English Patent Specification No. 5785 of
1887) a material containing some 80 per cent. of anthracene is obtained. Liquid
sulphur dioxide and acetone are less favourable in their action than pyridine;
the use of both has been patented. and their applicability resides in the solubility
of carbazole in the solvent, so that on allowing the solution to crystallise the
greater part of the carbazole, amounting to some 30 per cent. of the anthracene
remains in the mother liquor with the phenanthrene.
According to the present invention crude anthracene is treated in the follow-
ing manner for the purpose of purifying it.
The crude anthracene is melted and allowed to cool partially. Those com-
ponents of the raw material which have melting points higher than those of the
other components, namely carbazole and anthracene, crystallise first together with
a certain quantity of phenanthrene, the rest of which, however, together with a
little anthracene, remains liquid and is drained away from the crystals. The
crystals are then freed from carbazole by fusion with caustic potash and the
anthracene is treated with benzene whereby the phenanthrene which it still con-
tains is dissolved.
The following example illustrates the process:
The fused crude anthracene is placed in a weil insulated metal kettle capable
of holding 2000 kilos. or more, and is allowed to cool gradually. After some
50 per cent. of the mass has crystallised the efflux pipe at the bottom of the vessel
is opened and the liquid portion is allowed to flow into a similarly mounted
vessel in which a large portion of the anthracene still in solution may be recovered
by further partial cooling and crystallisation. The crystals obtained in this
second cooling process, which are of lower anthracene content than are those
obtained in the first process, may be raised to the value of the first crystals (some
45 to 50 per cent.) by another fusion.
The first crystals are transferred to a cast iron vessel provided with a stirrer
and are melted anew.
The stirrer is then put in motion and a hot solution of caustic potash of 50 per
cent. strength is gradually introduced into the mass heated to a temperature only
little above its melting point; the quantity of potash used is that estimated as

page_text: sufficient to react with the carbazole present. The mixture is further heated, care
being taken that the temperature does not materially exceed 260° C., that is,
that the temperature of decomposition of potassium carbazole is not reached.
After the reaction is over the stirrer is stopped.
The melted mass separates into two layers, the lower of which is a layer of
mobile fused potassium carbazole; this is drawn off through the cock and the
upper anthracene layer is run into about its own volume of benzene, preferably
the so-called 90 per cent. benzole of commerce, although any kind of benzole
fraction, even heavy benzole, also called solvent naphtha, will serve. The benzole
holds the phenanthrene left in the anthracene, in solution while the anthracene
remains undissolved; it is pressed or centrifuged from the benzole and washed
with some, more of the same solvent, whereupon it is obtained in the form of a
fine pale brown powder containing upwards of 90 per cent. of anthracene accord-
ing to the duration of the final washing.
Having now particularly described and ascertained the nature of this
invention and in what manner the same is to be performed, we declare that what
we claim is:-
Process for obtaining a compound containing a high percentage of anthracene
from crude anthracene, which consists in first enriching the crude anthracene by
melting and partial separation by crystallisation, then removing the carbazole from
the crystalline product obtained, and then treating the anthracene freed from
carbazole with benzole hydrocarbons and in particular with ordinary commercial
benzene substantially as described.