A Europium-Ion-Based Luminescent Sensing Probe for Hydrogen Peroxide

✍ Scribed by Otto S. Wolfbeis; Axel Dürkop; Meng Wu; Zhihong Lin

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 115 KB
• Volume: 41
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/1521-3773(20021202)41:23<4495::aid-anie4495>3.0.co;2-i

✦ Synopsis

the diarylmethyl cation 1 þ . The carbocation, which was formed with a rate constant (k i ) of 5 î 10 2 s À1 was consumed with a rate constant (k TFE ) of 10.4 s À1 under these conditions (Table 2, entry 15). Analogously, formation and consumption of 1 þ was observable in other TFE/CH 3 CN mixtures containing alkali metal perchlorates [14] (Table 2, entries 12 and14).

The direct observation of the carbocationic intermediate demonstrated in this experiment is certainly not a singular case. Increasing stabilization of the carbocation and decreasing solvent nucleophilicity transform the generally accepted energy profiles of S N 1 reactions with carbocations as shortlived intermediates (Figure 3, upper graph) into energy profiles which imply the buildup of significant concentrations of the intermediate carbocations (Figure 3, lower graph).

The occurrence of such scenarios can easily be predicted from available ionization and combination rate constants as demonstrated herein. Since ionization and nucleophile addition must be uncoupled when the intermediate is observable, the investigation of such reaction cascades may open a new era in the study of solvolytic displacement reactions. As salt and solvent effects on the two steps of the reaction can now be studied separately, many ambiguities in the earlier interpretations of the mechanisms of solvolytic displacement reactions can be resolved.