guanidine

Colorless crystals. Soluble inwater and alcohol. Combustible. Guanidine is a strong monobasic Bronsted base, which absorbs water and carbon dioxide from the air and forms strongly alkaline solutions with water and alcohols; the pH of a 20 wt % aqueous solution is ca. 13.5 (25 ℃). In aqueous solution at elevated temperature guanidine is hydrolyzed to urea; airtight alcohol solutions are stable. Guanidine is infinitely soluble in water, ethanol, methanol, and dimethylformamide.

Guanidine is an intermediate in synthesizing N-Formylguanidine (F700505), which is used in the preparation of Amiloride (A578700), a sodium channel blocker used as a diuretic drug.

Guanidine is formed (1) by heating ammonium thiocyanate to 180 °C, (2) by ammonolysis of orthocarbonates, C(OC2H5)4 + 3NH3 → (NH2)2C=NH + 4C2H5OH, (3) by ammonolysis of chloropicrin, Cl3CNO2 + 7NH3 → NH2)2 C=NH + 3NH4Cl + N2 + 3H2O, (4) by ammonolysis of cyanogen chloride, ClCN + NH3 → ClC(NH2)=NH → HN=C=NH → (NH2)2 C=NH.
Guanidine forms salts with acids, e.g., guanidine nitrate, HNC(NH2)2 · HNO3. By heating at 120 °C for several hours, a mixture of ammonium thiocyanate and dicyanodiamide, guanidine thiocyanate solution is obtained by extracting with water. Treating guanidine with a mixture of nitric and sulfuric acids forms nitroguanidine which is reduced by zinc and acetic acid to aminoguanidine.
By treating aminoguanidine (1) with dilute acid or alkali, there is obtained, first, semicarbazide, finally hydrazine; (2) with nitrous acid, diazoguanidine which is decomposed by alkali into alkali azide (e.g., NaN3) plus cyanamide (H2N·CN) plus water.

Carbamidine is another name for guanidine. It is a crystalline basic compound related to urea. It forms a number of salts which are used as fertilizers. Guanidine phosphate is an example.

Crystallise it from water/EtOH under nitrogen. It is very deliquescent and absorbs CO2 from the air readily. [Jones Trans Faraday Soc 55 524 1959, Beilstein 3 H 82, 3 I 39, 3 II 69, 3 III 154, 3 IV 148.]