Cationic surface-active agents of the aminoalkylene monoamide type are obtained by a process which includes the step of contacting with carbon dioxide a liquid medium containing an amino alkylene monoamide and an alkylene diamide or an amine polyalkylene polyamide so as to precipitate a carbon dioxide addition compound of the said monoamide and separating this addition compound from the residual liquid. The mixture may be dissolved in an organic solvent prior to the CO2 treatment and any unreacted alkylene polyamine which has been used in the production of the amide mixture to be treated may be separated prior to the CO2 treatment. The addition compound can be split into the desired amino alkylene monoamide and carbon dioxide by treating it with a mineral acid such as hydrochloric acid, or by heating. The treated amide mixture may be obtained by reacting an organic acid or its esters with short-chain alcohols of 1 to 3 carbon atoms with an alkylene polyamine. Specified alkylene polyamines are ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, di-(hexamethylene) triamine, propylene diamine, dipropylene triamine, and butylene diamine. The organic acids which may be employed include aliphatic acids and acids containing carbocyclic or heterocyclic ring systems such as benzoic acid, naphthenic acid and pyridine 2-carboxylic acid. The acids may be saturated or unsaturated and both the acids and the alcohols used to form the esters that may be used instead of the acids may contain substituents such as halogen atoms or hydroxyl groups. It is preferred to use fatty acids of 6 to 24 carbon atoms. Specified aliphatic acids are caprylic, isocaprylic, nonylic, capric, caproic, undecylenic, lauric, myristic, palmitic, stearic, hydroxystearic, oleic, ricinoleic, alpha amino capric, undecylenic, linoleic, linolenic, and erucic acids and various mixtures of these acids. Coconut oil fatty acids containing from 12 to 16 carbon atoms and mixed tallow fatty acids are also suitable. Instead of the acids the glycol (or polyglycol) mono- or diesters, the glycerol mono-, di- or tri-esters and the methyl, ethyl or propyl esters may be used. In the production of the amide mixture it is preferred to use an excess of the alkylene polyamine and temperatures of 100 DEG to 250 DEG C. may be employed, the reaction temperature being preferably at or approaching the boiling-point of the lowest boiling component of the reaction mixture under the prevailing pressure which may be atmospheric, subatmospheric or superatmospheric pressure. The treatment with CO2 to form the addition compound may also be carried out over a wide range of pressure and the CO2 should be used in substantial stoichiometric excess. The CO2 in gaseous form may be bubbled through the mixture dissolved in a suitable solvent, or the mixture dissolved in a solvent with or without agitation may be contacted with CO2 in liquid or solid form. Specified solvents are methanol, acetone, dioxane, ethanol, diethyl ether, benzene and butanol. Mixtures of solvents may be employed, e.g. a 1 : 1 mixture of methanol with benzene or ether may be used. If desired, a portion of the diamide may first be separated from the mixture to be treated by taking up the residue after distillation in warm or hot solvent and then cooling to precipitate the diamide and separating the latter by filtration. In examples: (1) to (4) the amide mixture obtained by reacting diethylene triamine with (1) the methyl esters of coconut oil fatty acids; (2) glacial acetic acid; (3) the mixed methyl esters of tallow fatty acid; and (4) coconut fatty acids, is dissolved in methanol (examples 1, 3 and 4) or chloroform (example 2) and the solution then saturated with carbon dioxide to form the addition compound. In (1) the addition product is dissolved in dilute hydrochloric acid to pH 7 and the resulting solution is stated to have excellent deterging and foaming properties, also on heating the addition product in air the product loses CO2 to form a material which dissolves in dilute hydrochloric acid to pH 7 to give a solution with good deterging and foaming properties; (5) triethylene tetramine is heated with methyl stearate and the excess amine removed by vacuum evaporation. The residual mixture is dissolved in warm methanol and cooled to deposit some of the diamide which is filtered off. The filtrate is then saturated with carbon dioxide to form the addition which yields the free monoamide on heating; (6) to (8) ethylene diamine is heated with the mixed methyl esters of coconut fatty acids, coconut oil, and methyl laurate, respectively, and the mixture formed is treated with carbon dioxide as in (5). In (8) the free amide is obtained by heating to remove the carbon dioxide. U.S.A. Specifications 1,947,951 and 2,387,201 are referred to.