Basicity of some nitrogen, phosphorus and carbon bases in acetonitrile
Date
2018-07-05
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Abstract
Happelisus ja aluselisus on keemiliste ühendite ühed olulisemad omadused. Hape-alus tasakaalud toimuvad suuremal või vähemal määral peaaegu kõigis keemilistes protsessides ja tihti mõjutavad nende käike oluliselt. Happelisuse ja aluselisuse uuringuid vesikeskkonnas on läbiviidud juba pikka aega ja hapete ning aluste käitumine selles on hästi teada. Paljud protsessid, kus ained käituvad hapete või alustena toimuvad mittevesikeskkondades. Sellistes keskkondades avaldub ainete happelisus või aluselisus oluliselt erinevalt. Mittevesikeskondade eeliseks on see, et neis saab läbi viia väga tugevate või nõrkade hapete ning aluste pKa uuringuid.
Käesoleva doktoritöö eesmärgiks oli erinevate aineperekondade esindajate aluselisuse väärtused atsetonitriili keskkonnas. Nendeks aineperekondadeks olid triarüülfosfaanid, arüülhüdrasoonid, pentafulveenid ja lämmastikheterotsüklid. Atsetonitriil on solvent, mida kasutakse laialdaselt erinevates keemia valdkondades. Uuritud ainetest on lämmastikheterotsüklid, mis on kõige levinumad. Neid esineb looduses, ravimites, pestitsiidies ja nad leiavad rakendust ka paljudes muudes vadkondades. Kui võrrelda doktortöö raames määratud heterotsüklite pKa väärtusi atsetonitriili keskkonnas arvutatud gaasifaasi aluselisuse väärtustega ja kirjandusest leitud pKa väärtustega vees on võimalik teha järeldusi erinevate struktuuriefektide kohta, mis mõjutavad lämmastikeheterotsüklite aluselisust. Nendeks struktuurseteks tunnusteks on peri vesiniku olemasolu, sisemolekulaarne vesinikside, täiendavalt liidetud aromaatne tuum, lämmastike suhteline asukoht tsüklis ja tsükli suurus. Selle tulemusena leiti, et need efektid toimivad kõigis kolmes keskkonnas, aga erineval määral. Leiti, et pKa väärtused vees ja atsetonitriilis korrelleeruvad hästi lämmastikheterotsüklite puhul. Näidati, et arüülhüdrasoonide ja pentafulveenide pKa väärtused korrelleeruvad hästi Hammetti substituendi konstantidega. Töös esitatud korrelatsioonid ja struktuuri mõjutuste uuringut aluselisusele saab edaspidi kasutada sarnaste ühendite pKa väärtuste ennustamiseks.
The acidity and basicity are among the most important properties of chemical compounds. The acid-base equilibria take place at least to some extent in almost all chemical processes and often decisively influences the course of these processes. Acidity and basicity studies in water has a long history and the behaviour of acids and bases in this medium is well known. Many processes where compounds behave as acids or bases take place in non-aqueous media. In non-aqueous media molecules display acidity and basicity often quite differently. The benefit of non-aqueous solvents in the acid-base equilibria studies is that very strong or weak acids and bases and water sensitive compounds can be studied. The aim of this thesis was to determine the basicities of members of different compound families – triarylphosphanes, arylhydrazones, pentafulvenes and nitrogen heterocycles - in acetonitrile. A solvent that is widely used in many different fields of chemistry. Of the studied compounds nitrogen heterocycles are the most widespread figuring in nature, medicine, pesticides and finding use in many other fields. The determined pKa values in acetonitrile combined with computed gas phase basicities and pKa values in water from literature made it possible to rationalize structure effects influencing the basicity of these compounds. These structural features were the presence of the peri hydrogen, intramolecular hydrogen bond, fusion of additional benzene ring, relative position of nitrogen atoms in the ring and the ring size. It was found that these effects are present in all studied media but to a different extent. It was shown that the pKa values of nitrogen heterocycles correlate well in water and acetonitrile. The pKa values of substituted penatafulvenes and arylhydrazones correlate well with the Hammett substituent parameters. The obtained correlations, as well as rationalization of structure-basicity relationships can be used for pKa estimations of similar compounds.
The acidity and basicity are among the most important properties of chemical compounds. The acid-base equilibria take place at least to some extent in almost all chemical processes and often decisively influences the course of these processes. Acidity and basicity studies in water has a long history and the behaviour of acids and bases in this medium is well known. Many processes where compounds behave as acids or bases take place in non-aqueous media. In non-aqueous media molecules display acidity and basicity often quite differently. The benefit of non-aqueous solvents in the acid-base equilibria studies is that very strong or weak acids and bases and water sensitive compounds can be studied. The aim of this thesis was to determine the basicities of members of different compound families – triarylphosphanes, arylhydrazones, pentafulvenes and nitrogen heterocycles - in acetonitrile. A solvent that is widely used in many different fields of chemistry. Of the studied compounds nitrogen heterocycles are the most widespread figuring in nature, medicine, pesticides and finding use in many other fields. The determined pKa values in acetonitrile combined with computed gas phase basicities and pKa values in water from literature made it possible to rationalize structure effects influencing the basicity of these compounds. These structural features were the presence of the peri hydrogen, intramolecular hydrogen bond, fusion of additional benzene ring, relative position of nitrogen atoms in the ring and the ring size. It was found that these effects are present in all studied media but to a different extent. It was shown that the pKa values of nitrogen heterocycles correlate well in water and acetonitrile. The pKa values of substituted penatafulvenes and arylhydrazones correlate well with the Hammett substituent parameters. The obtained correlations, as well as rationalization of structure-basicity relationships can be used for pKa estimations of similar compounds.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
alkalis, phosphates, nitrogen, heterocyclic compounds, alkalinity, nitriles