ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Determination of pK_a of N-alkyl-N,N-dimethylamine-N-oxides using ¹H NMR and ¹³C NMR spectroscopy

Alexander Búcsi, Janka Karlovská, Michal Chovan, Ferdinand Devínsky, and Daniela Uhríková

Department of Physical Chemistry of Drugs, Comenius University, Odbojárov 10, 832 32, Bratislava, Slovakia

E-mail: bucsi@fpharm.uniba.sk

Abstract: The pK_a values of N-alkyl-N,N-dimethylamine-N-oxides were determined from the pH dependences of chemical shifts in ¹H NMR and ¹³C NMR spectra. The dependences were measured at concentrations below and above the critical micelle concentration of the amine oxides. Above the critical micelle concentration, the plots of the peak positions vs. pH were either sigmoid (the groups close to the nitrogen) or “peak type” (farther groups). The sigmoidal behaviour was a direct result of the acid-base reaction; on the other hand, the “peak type” behaviour was probably an indirect consequence of the pH variation, mediated with the change in micelle size.

Keywords: N-alkyl-N,N-dimethylamine-N-oxide – micelle – pKa – NMR

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-013-0517-3

Chemical Papers 68 (6) 842–846 (2014)