In this paper, we mainly focus on protic ionic liquids (PILs) based on alkylammonium cations with the general formula R4NH4-n (n = 1–3, R = Me, Et, Pr, Bu). Protic ionic liquids, as other ILs, have a lot of useful properties, such as good thermal and electrochemical stability, a wide temperature range of liquid state, low flammability, and a simple synthesis procedure, which make them very attractive for a wide range of practical applications. We report the experimental data such as thermal properties (decomposition, melting, and glass transition temperatures), electric conductivity, viscosity of a series of alkylammonium-based PILs and consider their structural features associated with hydrogen bond formation. The effect of the structure/nature of cations and anions of 13 different acids on the above-mentioned properties and the structure of these PILs are discussed. Among the PILs considered, the best studied ones are the salts composed of anions of sulfuric, trifluoromethanesulfonic, and formic acids, and ethylammonium and triethylammonium cations. In this work, we analyze the properties of alkylammonium salts including both the ones investigated in our laboratory (the new data and results published earlier) and those presented in the literature.
