Aniline Colors - Who is the Inventor of Aniline Red?

Scientific American 19, 9.5.1863

It is generally conceded that Prof. Hofmann, of London, England, is the original and first inventor of the red color derived from aniline. Some doubts have been raised, however, in the minds of many inventors and manufacturers in this country, in regard to this fact, since Joseph Renard, of Lyons, France, has obtained patents in France and in the United States, in which he claims, as his invention, the red coloring matter obtained by treating aniline with a metallic salt, or its equivalent. To clear up these doubts we publish the following data: -

The process of Prof. Hofmann, in London, has been published in Les Comptes Rendus de l'Academie des Sciences, Vol. XLVII., page 492, in the number for October, 1858, under the head of "Action of Bichloride of Carbon on Aniline."

At the usual temperature of bichloride of carbon and aniline have no reaction on each other; at the temperature of boiling water the mixture begins to change, but even after a digestion of several days, the reaction is not at all complete. By sumbitting a mixture of one part of bichloride of carbon and three parts of aniline, both perfectly anhydrous, during a period of about thirty hours, to a temperature of 170 to 180 degrees Centigrade, that is, to the boiling temperature of the aniline, the liquid is transformed in to a blackish mass, either soft and sticky or hard and brittle, according to time and temperature. This black mass, which adheres with great tenacity to the retorts in which the reaction has been effected, is composed of several different materials. By washing it well in water a portion of it is dissolved, and the rest remains insoluble in a resinous state of more or less solidity. The aqueous solution produces with potash an oily precipitate which contains a considerable proportion of unchanged aniline. By boiling this precipitate in a retort with diluted potash, the aniline passes over by distillation until a sticky oil remains, which solidifies with a crystalline strukture. By washing with alcohol and by one or two crystallizations in boiling alcohol, the mass is rendered perfectly white and pure, and a very soluble substance, - a beautiful crimson - remains in solution. That portion of the black mass which remains insoluble in the water dissolves readily in hydro-chloric acid; from this solution it is again precipitated by alkalies in the state of an amorphous powder of a dirty red soluble in alcohol, to which it imparts a rich crimson color. The greatest part of this substance is the sama coloring matter which accompanie the fatty crystalline substance.

We now give a verbal translation of the original specification of Joseph Renard's patent on the preparation and use of "fuchsine" (a new red coloring matter), taken out in France, and dated April 9, 1859:-

We have given the name of "fuchsine" to this matter on account of the resemblance of its color to that of the flower "fuchsia." To obtain it we heat to ebullition a mixture of aniline and of anhydrous bichloride of tin, the ebullition being continued for 15 to 20 minutes. At the beginning the mixture turns yellow, it darkens, becomes reddis, until at the end it turns out to be a beautiful red, when it appears in small layers of a black color. At this moment, and while it is still liquid, it is poured in water, and the whole heated to ebullition; the fire is withdrawn, the moisture is left standing for an instant, to allow the insoluble parts to settle down, it is then filtered while hot, and the residuum is further extracted by repeated ebullitions with water. The filtered liquor contains the coloring matter in solution. In order to separate it, its property, to be insoluble in saline solutions, is made use of by adding to the liquor certain soluble salts in the solid state, for instance, chloride of soda, neutral tartrate of potash, neutral tartrate of soda and many others; the salt dissolves and the coloring matter precipitates in the solid state; it is separated by decantation or filtration. To use it, it is dissolved in water, and with this bath the dyeing is effected without mordants or by using the ordinary mordants, acids or salts, with the exception of mineral acids, which alter the color. In the same manner a red color is obtained by the reaction of other anhydrous metallic chlorides on aniline, amongst others, those of bichloride of mercury, perchloride of iron and protochloride of copper.

By the foregoing description we desire to reserve for ourselves the sole property in the following things: - 1st, The production of that new coloring matter obtained by the reaction on aniline of certain anhydrous metallic chlorides, and partcularly on the bichloride of tin. 2d. The application of this coloring matter for dyeing or printing textile fabrics, silk, wool, cotton and thread, and also hides and feathers.

By comparing the two descriptions the following result is arrived at: -

... Hofmann. / Renard.
Organic base used... Aniline / Aniline
State of this base... Anhydrous / Andhydrous
Variable agent... Bichlo. or car., / Bichlo. of tin,
State of this agent... Anhydrous / Anhydrous
Temperature.. Ebullition of the aniline / Ebullition of the aniline
Coloring matter obtained... A magnificent crimson / A beautiful red
Nature of this matter... A resin / A resin
Mode of extraction... By dissolution in water  / By dissolution in water

It is unnecessary to continue the parallel any further; by looking at the dates of the two descriptions it will be seen that Hofmann obtained the same color by nearly the same process (the only difference being that one uses bichloride of carbon and the other bichloride of tin) which Renard claimed as his invention about six months after publication of Hofmann's process in Les Comptes Rendus.