The free base is a clear liquid, with a semen-like odour, boiling-point 135°. It is a common base in putrefying animal substances, and also occurs in the urine in cases of cystinuria. It can be obtained synthetically by reducing ethylene cyanide by the action of sodium in absolute alcohol.
The best method of separating putrescine is the benzoyl chloride method already given.
Putrescine forms crystalline salts, of which the following are the most important:—
Putrescine hydrochloride, C4H12N22HCl, forms long colourless needles, insoluble in absolute alcohol, easily soluble in water.
The platinochloride, C4H12N22HCl.PtCl4 (Pt = 39·2 per cent.), is with difficulty soluble in cold water. When pure, the salt is in the form of six-sided plates.
The aurochloride, C4H12N22HCl.2AuCl3 + 2H2O (Au = 51·3 per cent.), is insoluble in cold water, in contradistinction to cadaverine aurochloride, which easily dissolves.
The picrate, C4H12N22C6H2(NO2)3OH, is a salt of difficult solubility. It crystallises in yellow plates. It browns at 230°, and melts with evolution of gas at 250°.
Dibenzoylputrescine, C4H8(NHCOC6H5)2, forms silky plates or long needles, melting-point 175°-176°. By boiling it for twelve hours with alcohol and strong hydrochloric acid the compound may be broken up into hydrochloride of putrescine and free benzoic acid. As stated before, it is less soluble in alcohol than the corresponding compound of cadaverine.
Putrescine is not poisonous. On the other hand, by repeated treatment with methyl iodide, it takes up four methyl radicals, and the tetramethyl compound, C4H8(CH3)4N2, produces symptoms similar to those of muscarine poisoning.