Improvements in Purifying Saccharine.
Year: 1893

page_text: Date of Application, 1st June, 1893-Accepted, 22nd July, 1893
COMPLETE SPECIFICATION.
Improvements in Purifying Saccharine.
I JAMES YATE JOHNSON of 47 Lincoln's Inn Fields in the County of
Middlesex Gentleman do hereby declare the nature of this invention which has
been communicated to me from abroad by Dr. F. Von Heyden Nachfolger of
Radebeul near Dresden in the Empire of Germany and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement :-
Crude saccharin consists of a mixture of para sulphamin benzoic acid and ortho
benzoic sulphonimid. The present invention relating to the separation of these
substances is based upon the difference in the solubility of their salts. My foreign
correspondents have discovered that the para sulphamin benzoic acid salt of sodium
alone crystallizes out of a suitably concentrated solution of crude saccharin
neutralized with soda whilst the sodium combination of the saccharin remains in
solution and by drawing off and precipitating with acid can be caused to yield pure
saccharin.
The solution of para sulphamin benzoic acid salt and saccharin salt obtained in
the manufacture of saccharin may be directly subjected to this purifying process by
evaporating it to a suitable degree of concentration so that on cooling the salt of
the para sulphamin benzoic acid alone crystallizes out. The point at which the
required degree of concentration is reached can be ascertained by testing a sample
of the mixture. It is preferable however to convert the solution obtained in the
manufacture of saccharin into crude or solid saccharin in the first place and
afterwards to subject this crude saccharin to the purifying process. In this case it
is unnecessary to prepare a solution of diluted saccharin in the first place and
afterwards to concentrate the same but a hot solution of the required degree of
concentration is produced in the first instance as explained in the following examples
which are given in order to illustrate the working of the invention in practice
without limiting myself to the details
100 parts of 60 per cent. saccharin (containing about 40 per cent. of para sulphamin
benzoic acid being the ordinary saccharin of commerce) are heated with 160 parts
of a solution of soda (containing 30 parts of soda) until carbonic acid ceases to be
generated. The resulting solution containing chiefly undissolved sodium salt of
para sulphamin benzoic acid solidifies on cooling into a crystalline paste which is
thoroughly separated from the liquid part by centrifugal action or otherwise.
The mother lye is diluted with water and on precipitation with mineral acid
yields about sixty parts of purified saccharin. The remaining crystalline mass
consisting of para sulphamin benzoic acid salt of sodium is dissolved in a large
quantity of water and precipitated with mineral acid. About 40 parts of para
sulphamin benzoic acid are thereby obtained. It is advantageous to separate or
remove the small quantity of the solution of saccharin salt adhering to the para salt
by the application of a small quantity of water before the said para salt is
decomposed with the acid. In place of the sodium salt the more difficultly soluble
potassium salt may be employed in the separating process if preferred.

page_text: ceases to be generated and the materials are dissolved. On cooling the potassium
salt of para sulphamin benzoic acid crystallizes out the potassium combination of
saccharin remaining in solution. The products are then treated as hereinbefore
described in the first example.
In place of the sodium or potassium salts the ammonium, calcium, barium,
strontium or magnesium salts of para sulphamin benzoic acid may be employed for
the separation of the latter these salts being likewise considerably less readily
soluble than the corresponding salts of the ortho benzoic sulphonimid.
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 :-
In purifying saccharin the separation of para sulphamin benzoic acid from
mixtures thereof with ortho benzoic sulphonimid by the partial crystallization of
solutions of the sodium, potassium, ammonium, calcium, barium, strontium or
magnesium salts of such mixtures the para sulphamin benzoic acid salt being
crystallized out of the solution whilst the whole or the greater part of the ortho
benzoic sulphonimid salt remains in solution substantially as herein before described.
Dated this 1st June 1893.
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C.