Advancing Quantitative ³¹P NMR Spectroscopy for Reliable Thiol Group Analysis

Accurate thiol quantification is essential for advancing thiol-X-ligation strategies in polymer and materials synthesis. Conventional assays, most notably Ellman's test, are limited in scope, particularly for hydrophobic or multifunctional thiols. Here, we introduce a straightforward and broadly applicable ³¹P NMR spectroscopy method for thiol quantification, using 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (TMDP) as a phosphitylation reagent. The approach extends established ³¹P NMR protocols for hydroxyl and carboxyl group analysis to thiols, offering high specificity and stability in readout. The method demonstrates applicability across a wide range of substrates, from small organic molecules to polymeric multi thiols with M_n up to 8000 g·mol^-1. Comparative validation against Ellman's assay and ¹H NMR spectroscopy reveals superior selectivity and resolution of the TMDP-based ³¹P NMR protocol, particularly for technical-grade thiols, where conventional methods fail to distinguish degradation products. This study establishes the TMDP-enabled ³¹P NMR as a reliable, information-rich tool for thiol quantification, giving simultaneously insights on hydroxy and carboxyl functionality patterns.