Synthesis and surface properties of fluorinated surfactants based on heterocyclic compounds

Abstract

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.