Synthesis and surface properties of fluorinated surfactants based on heterocyclic compounds

摘要

Abstract:This thesis has as its aim the study of polyfluoroalkyl-substituted five-membered ring heterocycles as potential fluorous surfactants.The first part concerns the preparation of a selected number of new and previously reported polyfluoroalkylated pyrazoles (1,2-diazoles), 1,2,3-triazoles, and tetrazoles with systematic variations in their substituents. The 1,2,3-triazoles were synthesized from partner azides and alkynes using dipolar cycloaddition reactions with good regioselectivity. The tetrazoles were synthesized from azides and nitriles in a similar dipolar cycloaddition, but the reaction was less facile. Alkylation under Mitsunobu conditions gave improved yields and regioselectivity. A preliminary series of pyrazoles was also synthesized through a regioselective cyclocondensation of hydrazines and polyfluorinated 1,3-diketones. The synthesis unexpectedly also provided a number of intermediate amino alcohols. Unfortunately, the regioisomers could not be separated, so the isomers could not be assessed for their surface active properties.The surfactant character of the polyfluoroalkylated 1,2,3-triazoles and tetrazoles was investigated by measuring their effect on surface tension of the samples in m-xylene solution. Triazoles, which contained polyfluoroalkyl chains C6F13CH2CH2 and C7F15CH2 in position-1 revealed quite different behaviour from other types of triazoles and tetrazoles. The triazoles that contained single polyfluoroalkyl ether substituents and the triethyleneglycol substituents in position-4 had highly consistent surfactant behaviour. 2,5-Disubstituted tetrazoles that contained C6F13CH2CH2 and C7F15CH2 substituents at position-1 showed similar results as those of the triazoles. The number of methylene spacer groups between the perfluoroalkyl chain and the heterocycle had a major influence on the surfactant properties. Decreasing the number of spacer groups from two to one (or increasing the fluorine content) gave higher surface activity. The attachment of a hydrophilic group gave better surface activity than the attachment of a lipophilic group, and use of a tetrazole heterocycle in preference to a 1,2,3-triazole core also gave significant improvements.Finally, a preliminary synthetic study demonstrated the potential towards the design of polynuclear heterocyclic fluorous surfactants.