Kinetics and mechanism of the protonation of 6-(triphenylphosphonio-3′-cyclopentadienyl)-2,3,5-trihalocyclohexa-2,5-diene-1,4-dione by trifluoroacetic acid in aprotic media

✍ Scribed by F. F. Pérez-Pla; Saad Housseini; J. Palou; C. D. Hall

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 234 KB
• Volume: 29
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/(sici)1097-4601(1997)29:8<561::aid-kin1>3.0.co;2-s

✦ Synopsis

6-(Triphenylphosphonio-3Ј-cyclopentadienyl)-2,3,5-trihalocyclohexa-2,5-diene-1,4-diones (2) are a new class of phosphorus containing dyes that behave as weak bases. Mono-protonation occurs at the cyclopentadiene ring leading to three isomers as assessed by NMR. The kinetics of the protonation were studied by the stopped-flow technique in aprotic media. The activation energies and deuterium isotope effects suggest that the rate-limiting step is the addition of trifluoroacetic acid to the quinone ring rather than direct protonation of the cyclopentadiene ring.