Quantum yield determinations in SRN1 type reactions. Photoinduced nucleophilic substitution of aromatic amines.

NATALIA TORRES, LILIANA JIMENEZ, ADRIANA PIERINI

La Serena, Chile

Congreso; X Encuentro Latinoamericano de Fotoquímica y Fotobiología (XELAFOT); 2010

Universidad de Santiago de Chile

Nucleophilic substitution reactions by electron transfer (eT) have been apowerful synthetic tool to obtain new organic compounds from substrates andnucleophiles that do not react or react slowly through SN2 or SN1 mechanisms. This typeof reactions (SRN1) involves electron transfer steps, generating a chain process, withradicals and radical anions as intermediates. A widely used method to initiate them is byphotoestimulation. Information about global quantum yields in these photoinduced eTreactions, which include initiation and propagation steps, provides us a betterunderstanding of the system efficiency, involving in this context different nucleophileand substrate chemical features.Our work is based in the measurement and comparison of quantum yield valuesfor the SRN1 mechanism involved in the reaction of an aromatic amine set, asnucleophiles, with haloaromatic substrates. It was used abenzophenone/benzhydrol system as actinometer, which permits long irradiation times(30 min ca.).Results show that the anions of 2-pyrimidinamine and 2,6-diethylaniline arepoor electron donors leading itself to a low quantum yield for the initiation step whichcan be increased adding more equivalents of the base t-BuOK. The propagationquantum yields are moderate with all studied substrates, resulting in short chain lengths,around 7-8. The anion of 2-naphthalenamine presents a better initiation and also ahigher propagation cycle.