Hydrazine

HYDRAZINE. This compound of hydrogen and nitrogen is a colourless liquid boiling at 113.5° C and solidifying at about o° C to colourless crystals (m.p. 1.4° C) ; it is somewhat heavier than water (sp.gr. 1.014/15° C) in which it dissolves with rise of temperature. Hydrazine, or was first prepared by Th. Curtius in 1887 during the study of the reactions of ethyl diazoacetate, : an ester obtained by the action of potassium nitrite on the hydrochloride of ethyl aminoacetate. On heating with concentrated aqueous caustic potash, ethyl diazo acetate is converted into bisdiazoacetic acid, C2H2N4(CO2H)2, which on digestion with warm dilute sulphuric acid yields oxalic acid and hydrazine sulphate. Another preparation of hydrazine, also due to Curtius consists in boiling aminoguanidine with dilute acids or alkalis (see GUANIDINE). It can also be produced by reducing potassium dinitrososulphonate in cold water with sodium amalgam. F. Raschig (1908) obtained good yields of hydrazine by oxidising ammonia with sodium hypochloride in aqueous solutions rendered viscous with 0.2% of joiner's glue, and this method is employed on a commercial scale. By fractional dis tillation of the aqueous solution, hydrazine hydrate, is obtained as a colourless fuming liquid with strongly alkaline and caustic properties, corroding glass like the caustic alkalis and destroying cork and indiarubber. It boils at 119° C and has specific gravity 1.03 at 25° C. It remains liquid at —40° C.

On distilling hydrazine hydrate with an alkaline dehydrating agent such as barium oxide or solid caustic potash, anhydrous hydrazine is obtained (see above) . Hydrazine forms a sparingly soluble sulphate, employed in its commercial prep aration, and mono- and di-hydrochlorides, and In aqueous solution hydrazine is a powerful reducing agent eliminating copper and silver from their salts ; it is very poisonous, even through the skin.

Organic Hydrazines.

These properties persist in the organic derivatives of hydrazine of which phenylhydrazine, is the most important. This useful reagent was discovered by E. Fischer in 1877 and employed by him in his classical researches on the sugars. It is best prepared by reducing benzenediazonium chloride, with stannous chloride in hydrochloric acid solution, when phenylhydrazine is liberated by caustic soda from its precipitated hydrochloride. It is a colourless, oily liquid rapidly turning brown on exposure ; it boils at 241° C and solidifies to tabular crystals melting at 23° C. Phenylhydrazine is a basic compound slightly soluble in water and forming well defined salts with the strong acids. It serves to detect organic sub stances containing carbonyl groups (see ALDEHYDES, CARBOHY DRATES and KETONES) since it condenses with them to form hydra zones, with elimination of water. The hydrazones and ortho dihydrazones (osazones) are generally well-characterised crystal line derivatives.

Phenylhydrazine, moreover, is an important synthetic reagent (see ANTIPYRINE) and its sulphonic acid is employed in the pro duction of pyrazolone colours and tartrazine (see DYES, SYN