The chemical reactions taking place in the preparation of
Neradol D may be expressed thus:-
OH OH OH OH
H ^ H___O_____H ^ H H ^ H__CH_2__H ^ H
| | || | | = | | | | + H_2O
| | CH_2 | | | | | |
H v CH_3 CH_3 v H v CH_3 CH_3 v H
HSO_3 HSO_3 HSO_3 HSO_3
1. Neradol D Reactions
1. The quantitative determination of phenols introduced by Bader, [Footnote: Bull. soc. scient., Bucarexi, 1899, 8, 51.] which consists in precipitating them as oxyazo compounds, has been modified by Appelius and Schmidt [FootNote: Collegium, 1914, 597.] for the purpose of detecting Neradol D:—To 50 c.c. of the tannin solution (analytical strength) 15 c.c. of diazo solution are added, the mixture filtered, if necessary, and the filtrate made alkaline with caustic soda; in the presence of Neradol D in sufficient quantity, a blood-red coloration results. If but little Neradol D be present, the procedure is altered as follows:—The tannin solution, to which the diazo solution has been added, is filtered, and the filtrate poured on a piece of filter paper which is then dried; a solution of caustic soda is spotted on the paper, when, if Neradol D be present, a red-edged spot will appear.
According to Tschirch and Edner, [Footnote: Archiv. d. Pharm., 1907, 150.] the diazo solution is prepared as follows:—5 gm.p-nitraniline are introduced into a 500 c.c. measuring flask, 25 c.c. of water and 6 c.c. concentrated sulphuric acid added, the mixture shaken and a solution of 3 gm. of sodium nitrite in 25 c.c. of water plus 100 c.c. of water added, and the whole then filled up to 500 c.c. The solution should be stocked in the dark.
2. A less sensitive reaction for Neradol and wood pulp extract constitutes that of Appelius and Schmidt employing cinchonine, [Footnote: Collegium 1914, 597.] while the presence of the substances in question yields characteristic precipitates.
3. Seel and Sander [Footnote: Zeits. f. ang. Chem., 1916, 333.] recommend the following method of detecting Neradol D:—
(a) Oxyazo Reaction.—About 5 c.c. of the tannin solution are rendered alkaline with caustic soda; after cooling with ice, about half the volume of alcohol is added. 3-4 drops of diazo solution are then added. Frequently, this results in the solution assuming a blue coloration. If not, the solution is acidified with hydrochloric acid, ether added, and the mixture well shaken. The water is now separated from the mixture, fresh water added, together with some caustic soda solution, when, if Neradol D be present, the salt of the colour acid formed dissolves in the water with a beautiful green or bluish-green colour. At the place of contact of the water and the ether a bluish-green ring appears.
The diazo solution is prepared by dissolving p-aminophenol or its hydrochloric in a little dilute hydrochloric acid, cooling in ice and carefully diazotising in the cold till a slight excess of nitrous acid is present. It is essential that this solution should be tested before use, and this is carried out by coupling it with an alkaline phenol solution; if a dark blue oxyazo colour is formed, the solution may be used. It must be kept cool by surrounding it with ice.
(b) Indophenol Reaction.—To 5 c.c. of the solution to be tested, a drop of a solution of dimethyl-p-phenylenediamine is added, the solution rendered alkaline with caustic soda and 1-2 drops of a 5 per cent. solution of potassium ferricyanide added. If Neradol D be present, a blue colour appears, either immediately or after some time. The reaction is rendered more sensitive if alcohol is carefully poured on the solution after it has been rendered alkaline, and potassium ferricyanide is then added. At the place of contact a blue layer is formed, which ultimately diffuses into the alcohol.