Acid, hypophosphorous nitrous

Make a thin paste of 21 5 g. of finely-powdered o-tolidine (a commercial product) with 300 ml. of water in a 1-litre beaker, add 25 g. (21 ml.) of concentrated hydrochloric acid, and warm until dissolved. Cool the solution to 10° with ice, stir mechanically, and add a further 25 g. (21 ml.) of concentrated hydrochloric acid (1) partial separation of o tolidine dihydrochloride will occur. Add a solution of 15 g, of sodium nitrite in 30 ml. of water as rapidly as possible, but keep the temperature below 15° a slight excess of nitrous acid is not harmful in this preparation. Add the clear, orange tetrazonium solution to 175 ml. of 30 per cent, hypophosphorous acid (2), and allow the mixture to stand, loosely stoppered, at room temperature for 16-18 hours. Transfer to a separatory funnel, and remove the upper red oily layer. Extract the aqueous layer with 50 ml, of benzene. Dry the combined upper layer and benzene extract with anhydrous magnesium sulphate, and remove the benzene by distillation (compare Fig. II, 13, 4) from a Widmer or similar flask (Figs. II, 24, 3-5) heat in an oil bath to 150° to ensure the removal of the last traces of benzene. Distil the residue at ca. 3 mm. pressure and a temperature of 155°. Collect the 3 3 -dimethyldiphenyl as a pale yellow liquid at 114-115°/3 mm. raise the bath temperature to about 170° when the temperature of the thermometer in the flask commences to fall. The yield is 14 g. 

Phosphoric, Vanadic, Arsenic, and Antimonic Acids —Nitrous, Phosphorous, Arsenious Acids—Phos-phatic Acid—Iiyponitrous and Hypophosphorous Acids, and their Saits. 

An isothiazolo[5,4-6]triazole prepared from a 4,5-diaminoiso-thiazole and nitrous acid suffered reductive cleavage on treatment with hypophosphorous acid (Scheme 41).147... 

N-Amino groups are replaced by hydrogen on treatment with phosphorus trichloride (l,2,4-triazole-4-acylimines are converted into triazoles) or with nitrous acid (e.g., 824 825). 4-Amino-3,5-diaryl-l,2,4-triazoles are deaminated efficiently by reduction of the diazonium salt with aqueous hypophosphorous acid <2002JHC93>. AAAlkylaminoazoles form stable N-nitroso compounds, normally existing as a mixture of E- and Z-rotamers. 

If an aromatic and an aliphatic amino group are both contained in the molecule, as in 4-aminobenzylamine, the aromatic amino group can be replaced without affecting the primary aliphatic group for this purpose an aqueous solution of sodium nitrite is dropped into a solution of the amine in hypophosphorous acid, primary aliphatic amines being indifferent to nitrous acid below pH 3.547... 

Hyponitrous acid anhydride. See Nitrous oxide Hypophosphorous acid... 

Aniline reacts with nitrous acid to give benzenediazonium salts, which react with a variety of reagents via a substitution reaction. These reagents include cuprous salts, aqueous acid, iodide, hypophosphorous acid, and activated benzene derivatives. Nucleophilic substitution at the sp carbon of a halo-benzene derivative does not occur unless high heat and pressure are used. Electron-withdrawing substituents on the benzene ring significantly lower the temperature required for the reaction. Nucleophiles for this nucleophilic aromatic substitution reaction include water, hydroxide, alkoxide, and amines. 

Reaction of aryl diazonium ions with hypophosphorous acid (H3PO2) replaces the diazonium group with an H atom so that the reaction sequence of reacting an aniline with nitrous acid followed by hypophosphorous acid will remove the aryl NH2 group. 

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