On-Line Cd Detection In Chiral Separation Of Spiro-Lambda(4)-Sulfanes

Enantiomers of chiral spiro-lambda(4)-sulfanes with equatorial diaryl and axial bis(acyloxy), (alkoxy)-(acyloxy) or (acylamino)-(acyloxy) S-substituents were separated on a Kromasil-based chiral sorbent, namely on O,O'-bis(3,5-dimethylbentoyl)-N,N'-diallyl-L-tartardiamide silica CSP, by using n-hexane (or n-heptane)-dioxane (or 2-propanol) isocratically mixed mobile phases, Direct chiral separation was monitored by a homemade HPLC-CD system consisting of a circular dichroism (CD) spectrophotometer (Jobin-Yvon Model III Dicrograph) and a high performance liquid chromatograph. The system was used in conjunction with HPLC-UV to study the chemical and stereochemical purity of the samples. By the stopped-flow technique CD spectra were measured in the 350-230 nm spectral range. Monitoring at a selected wavelength enabled high-sensitivity detection. Racemic spiro-lambda(4)-sulfanes were also separated into pure enantiomers on preparative scale. Regardless of the structural type of diaryl-spiro-lambda(4)-sulfanes, the first-eluted enantiomer was always found to show a CD spectrum marked by an intense positive band near 240 nm and a negative one at approximate to 210 nm (positive couplet) that allows prediction of absolute configuration.