Among the many acid-base concepts, the theory of Usanovich is one of the least known despite the most general scope including almost all chemical reaction types and even redox chemistry. Published 1939 in a Soviet journal in Russian language, it gained little immediate attention, and was later criticized mainly as being too broad in scope. Although several articles recently remembered Usanovich and his acid–base theory, one major inconsistency again was overseen: the electron is put in a row along with anions. Chemical history probably correctly puts this concept aside, also because it added little explanation capabilities beyond the elaborated considerations of the simultaneously published acid–base theory of Gilbert N. Lewis which was later refined by Pearson (hard and soft acids and bases, “HSAB”). A modified version of the core of Usanovich' concept is finally discussed. It combines the classic protic and aprotic acid–base concepts on the foundations of Lewis’ and Pearsons ideas.

This contribution considers the little-known universal acid-base concept of Usanovich. It is quite interesting and useful to see how one can get from the proton-based and quantitative Brönsted-Lowry theory and the electron-based Lewis approach to a comprehensive and unified acid-base concept that includes exchange of all kinds of ions and even electrons. When the consideration of electron exchange touches even redox reactions, however, the Usanovich concept appears to most chemists as too far of a stretch. Publishing the original idea in a Soviet journal in Russian language did not help either in promoting it. Later articles were published in German, and even some English chemistry text books considered the contribution of Usanovich. These chapters, however, would disappear in later editions, and so, what remains today is the fascinating history of acid base concepts that can teach us on how competing ideas contribute to the progress of science in chemistry.