A Journey toward Sulfolane Microemulsions Suggested as Inert, Nonaqueous Reaction Media

Abstract

Recently, it turned out that nanostructured reaction media containing highly inert solvents as tetrahydrothiophen-1,1-dioxide (sulfolane) are beneficial for strongly oxidizing or reductive reactions. Because of their ability of solubilizing polar and nonpolar solvents with a large nanostructured interface in particular microemulsions provide such interesting reaction media. Starting from the pseudoternary microemulsion H2O-n-octane-C12E4/C12E5 (polyoxyethylene n-alkyl ether), water was successively replaced by the highly inert tetrahydrothiophen-1,1-dioxide (sulfolane). We found that an increasing sulfolane content drives the system beyond the tricritical point. Replacing the already long chain surfactants C12E4 and C12E5 by a mixture of the even longer chain surfactants C18E6 and C18E8, we were able to prepare nonaqueous sulfolane microemulsions for the first time. We also teach how in a second step the phase behavior of the hydrophilic sulfolane-n-octane-C18E8 system can be tuned at constant temperature (as required by the reaction conditions) by addition of the hydrophobic cosurfactant 1-octanol (C8E0). The change in curvature that occurs by adding 1-octanol is demonstrated measuring the size of reverse micelles by DLS. We found that the radius varies from at least 8 to 16 nm, a suitable sizes for inverse nanoreaction vessels.

Sulfolane: Magic Extractor or Bad Actor? Pilot-Scale Study on Solvent Corrosion Potential

“…Formally, sulfolane is a cyclic sulfone, containing a four-membered carbon ring and sulfonyl functional group (R2SO2) with a sulfur atom double-bonded to two oxygen atoms with a quite large dipole moment (μ=4.7 debye), dielectric constant (ευ=43.4) and low vapor pressure [12,13]. The structure of sulfolane with its zwitterionic and dritterionic resonance structures is illustrated in [14,15].…”

“…Dichotomic (lipo/hydro-philic) nature of sulfolane, directly related to its chemical structure where the five-membered ring allows the sulfonyl moiety to be exposed at the interface (see Figure 1a), makes it broadly used industrially, due to its advantageous combination of physicochemical properties [13]. In fact, a strong solvation of cations by the oxygen atoms in the sulfone group, possibly increases nucleophilicity of the corresponding, less solvated anions.…”