Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.0 degrees C. The rates of chlorine dioxide decay are first order in both ClO2 and CSH concentrations and increase rapidly as the pH increases. The proposed mechanism is an electron transfer from CS- to ClO2 (1.03 x 10(8) M(-1) s(-1)) with a subsequent rapid reaction of the CS* radical and a second ClO2 to form a cysteinyl-ClO2 adduct (CSOClO). This highly reactive adduct decays via two pathways. In acidic solutions, it hydrolyzes to give CSO(2)H (sulfinic acid) and HOCl, which in turn rapidly react to form CSO3H (cysteic acid) and Cl-. As the pH increases, the (CSOClO) adduct reacts with CS- by a second pathway to form cystine (CSSC) and chlorite ion (ClO2-). The reaction stoichiometry changes from 6 ClO2:5 CSH at low pH to 2 ClO2:10 CSH at high pH. The ClO2 oxidation of glutathione anion (GS-) is also rapid with a second-order rate constant of 1.40 x 10(8) M(-1) s(-1). The reaction of ClO2 with CSSC is 7 orders of magnitude slower than the corresponding reaction with cysteinyl anion (CS-) at pH 6.7. Chlorite ion reacts with CSH; however, at p[H+] 6.7, the observed rate of this reaction is slower than the ClO2/CSH reaction by 6 orders of magnitude. Chlorite ion oxidizes CSH while being reduced to HOCl, which in turn reacts rapidly with CSH to form Cl-. The reaction products are CSSC and CSO3H with a pH-dependent distribution similar to the ClO2/CSH system.

A multistep experiment for an advanced synthesis lab course that incorporates topics in organic−inorganic synthesis and catalysis and highlights green chemistry principles was developed. Students synthesized two N-heterocyclic carbene ligands, used them to prepare two well-defined copper(I) complexes and subsequently utilized the complexes as catalysts in the Huisgen 1-3 dipolar cycloaddition of benzyl azide and phenylacetylene. The catalytic reaction exhibits high atom economy, is performed without a solvent at room temperature, and is high yielding. Thus, students were able to practice and apply concepts of green chemistry through catalysis. In the process of preparing ligands and complexes, several techniques were utilized that were aimed at performing reactions more efficiently (microwave experiments) or performing reactions in benign solvents (H 2 O). Another major component of this experiment is emphasis on technical writing through student preparation of formal communications and full paper using the formal ACS format.

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An effective way of teaching undergraduates a full complement of research skills is through a multiweek advanced laboratory experiment. Here we outline a comprehensive set of experiments adapted from current primary literature focusing on organic and inorganic synthesis, catalysis, reactivity, and reaction kinetics. The catalyst, bis(2-(2′-hydroxyphenyl)-2-oxazoline)oxorhenium(V) tetrapentafluorophenylborate ( 1) is isolated through a multistep reaction starting with the formation of the ligand, 2-(2′hydroxyphenyl)-2-oxazoline (2), followed by complexation of a Re−oxo precursor to form chlorobis(2-(2′-hydroxyphenyl)-2-oxazoline)oxorhenium(V) (3). Both Re(V)−oxo complexes are diamagnetic and allow for NMR analysis. Complex 1 is an air-stable and highly active catalyst for two reactions: (1) hydrosilylation of carbonyls and (2) hydrolysis of Et 3 SiH to form Et 3 SiOH and H 2 gas. Students monitor the evolution of hydrogen gas in the second reaction and use the data to investigate the reaction kinetics in order to obtain the complete rate law and the second-order rate constant for the catalytic reaction. The complete project provides a wealth of opportunities to focus on experimental skills, fundamental concepts in inorganic and organic chemistry, catalysis, reactivity, and experimental kinetics.