N,N-dialkyl perfluoroalkanesulfonamides: Synthesis, characterization and properties

Abstract

Twenty derivatives of N,N-dialkyl perfluoroalkanesulfonamides, n-CmF2m+1SO2NRR′ (m=1, 2, 4, 6, 8; R, R′=CH3, CH2CH3 or CH2CH2OCH3), have been prepared and characterized. Their fundamental physicochemical properties, including melting point, density, viscosity and dielectric constant, are determined. The influences of structural variations in both the perfluoroalkyl and alkyl chains on the above properties are extensively studied. Among these N,N-dialkyl perfluoroalkanesulfonamides, 14 compounds are liquid at room temperature, and some of them exhibit low melting points, even lower than −40°C. The empirical solvent polarity scales for these liquid perfluoroalkanesulfonamides, such as ‘energy of transition’ET(30) values and Kamlet–Taft solvent parameters (π*, α, β), are also determined by solvatochromic measurements, and show good linear temperature dependence. The ET(30) values are in the range of 45.36–55.19kcalmol−1 at 25°C, comparable to those of short chain alcohols. The π* parameters for the compounds containing alkyl chain are in the range of 0.550–0.651 at 25°C, being a little higher than those of short chain alcohols. All these prepared compounds show strong hydrogen-bond donating ability (α values ranging from 0.865 to 1.204 at 25°C), comparable to that of short chain alcohols. Meanwhile, those containing alkoxyalkyl chain display strong hydrogen-bond accepting ability (β values ranging from 0.71 to 0.82 at 25°C), comparable to that of short chain alcohols.