Self-consistent acidity and basicity scales in nonaqueous solvents/Kooskolalised happelisuse ja aluselisuse skaalad mittevesikeskkondades

• Published in: Proceedings of the Estonian Academy of Sciences. Chemistry Vol. 54; no. 2; p. 94
• Main Authors: Leito, Ivo, Kaljurand, Ivari, Rodima, Toomas, Kutt, Agnes, Pihl, Aino, Room, Eva-Ingrid, Soovali, Lilli, Maemets, Vahur, Pihl, Viljar, Koppel, Ilmar A
• Format: Journal Article
• Language: English
• Published: Estonian Academy Publishers 01.06.2005
• ISSN: 1406-0124

A method for creating self-consistent acidity and basicity scales in nonaqueous solvents is presented and the current progress in applying such scales to different solvents is reviewed. The method is based on UV--Vis spectrophotometric titration of a mixture of two acids (or two bases) with a non-absorbing base (acid). From the titration data the relative acidity (relative basicity) of the two compounds--the difference of their [pK.sub.a] values (Δ[pK.sub.a])--is obtained. When a large set of compounds that have different acid (base) strengths is available and Δ[pK.sub.a] measurements are carried out in such a way that each compound is measured against several other compounds, a self-consistent acidity (basicity) scale can be built. The relative acidities (basicities) of the compounds included in the scale can be determined at very high accuracy: many of the error sources, most importantly moisture and impurities in the solvent and in the compounds, influence both compounds in a similar way and at least partially cancel out. Using this method, self-consistent acidity scales have been created in heptane and acetonitrile and self-consistent basicity scales have been developed in acetonitrile and THF. These scales are discussed and future plans are outlined. Key words: acidity scales, basicity scales, [pK.sub.a] values, dissociation constants, nonaqueous solvents. On antud ulevaade mittevesikeskkondades kooskolaliste happelisuse ja aluselisuse skaalade koostamise meetodist ning hetkeseisust selle meetodi rakendamisel erinevates keskkondades. Konealune meetod kujutab endast kahe happe (kahe aluse) segu UV-Vis-spektrofotomeetrilist tiitrimist mitteneelava aluse (happe) lahusega. Tiitrimise andmetest on voimalik leida nende kahe happe (aluse) suhteline happelisus (suhteline aluselisus)--nende ainete pKa-vaartuste erinevus (Δ[pK.sub.a]). Kui kasutada suurt erinevate [pK.sub.a]-vaartustega hapete (aluste) valimit ja moota iga happe (aluse) suhtelist happelisust mitme teise suhtes, siis on voimalik koostada kooskolaline happelisuse (aluselisuse) skaala. Δ[pK.sub.a]-vaartusi on voimalik maarata vaga korge tapsusega, sest paljud olulised veaallikad (esmajarjekorras lisandid lahustis ja ainetes endis) mojutavad kummagi aine [pK.sub.a]-vaartust sarnaselt ning taanduvad (vahemalt osaliselt) valja. Kirjeldatud meetodi abil on loodud kooskolalised happelisuse skaalad heptaanis ning atsetonitriilis ja kooskolalised aluselisuse skaalad atsetonitriilis ja tetrahudrofuraanis. Artiklis on kasitletud senikoostatud skaalasid ja kirjeldatud luhidalt tulevikuplaane.