Anodic oxidation of methylbenzenes. Synthetic routes to certain cyclohexa-1,4-dienes

Comment: Electron-transfer reactions in the 9-mesityl-10-methylacridinium ion: impurities, triplet states and infinitely long-lived charge-shift states?

“…This same species phosphoresces in a glassy matrix at 77 K. These features are highly characteristic of a local triplet state. Furthermore, there are marked similarities between mes-acr + and nap-acr + , as studied by Jones et al 13 Partial decomposition of the CSS in the case of mes-acr + arises because of chemical breakdown of the mesityl cation [18][19][20][21][22][23][24] and promotes reactions with added substrates. 6 Overall the photophysics and photochemistry of mes-acr + follow quite usual pathways known for many related dyads and certainly do not require the involvement of any excited state with unusual properties.…”

“…Under rapid mixing conditions, electron paramagnetic resonance (EPR) spectroscopy shows that chemical oxidation forms the mesitylene dimer radical cation while the monomeric radical cation could not be detected. 20 Furthermore, oxidation is known to be followed by rapid proton loss, 21 even in acidic solution, 22 while the radical cation is highly susceptible to attack by nucleophiles 23 and radicaloid species. 24 By themselves, these secondary reactions will limit the lifetime of the CSS to the microsecond region.…”

Oxidação eletroquímica de compostos aromáticos 1,2-dimetoxilados-4-substituídos

“…Se o mecanismo EECrC p estivesse operando, a formação do cátion ocorreria numa etapa química (C r ) e a superfície do eletrodo não influenciaria a distribuição isomérica 203 • Além do 1,2,4-trimetil-benzeno, Barba e co1. 204 estudaram a metoxilação anódica dos outros trimetil-benzenos, do pentametil-e do hexametil-benzeno.…”

“…Para o conjunto de processos estudados: oxidação dos trimetil-benzenos e pentametil-benzeno Barba e co1. 204 formulam o mesmo mecanismo ECEC, que explicaria também as razões trans/cis observadas nos produtos de metoxilação nuclear (mesma análise feita para o 1,2,4-trimetil-benzeno).…”

“…Somente no caso do hexametil-benzeno haveria, segundo os autores 204 , participação do mecanismo EECrC p que justificaria a alteração das razões trans/cis observada neste caso, pois com a formação do cátion intermediário no seio da solução (etapa C r ), os isômeros cis e trans seriam formados em mesma extensão.…”