JIMENEZ LILIANA BEATRIZ
Congresos y reuniones científicas
Título:
Quantum yield determinations in SRN1 type reactions. Photoinduced nucleophilic substitution of aromatic amines.
Autor/es:
NATALIA TORRES, LILIANA JIMENEZ, ADRIANA PIERINI
Lugar:
La Serena, Chile
Reunión:
Congreso; X Encuentro Latinoamericano de Fotoquímica y Fotobiología (XELAFOT); 2010
Institución organizadora:
Universidad de Santiago de Chile
Resumen:
Nucleophilic substitution reactions by electron transfer (eT) have been a
powerful synthetic tool to obtain new organic compounds from substrates and
nucleophiles that do not react or react slowly through SN2 or SN1 mechanisms. This type
of reactions (SRN1) involves electron transfer steps, generating a chain process, with
radicals and radical anions as intermediates. A widely used method to initiate them is by
photoestimulation. Information about global quantum yields in these photoinduced eT
reactions, which include initiation and propagation steps, provides us a better
understanding of the system efficiency, involving in this context different nucleophile
and substrate chemical features.
Our work is based in the measurement and comparison of quantum yield values
for the SRN1 mechanism involved in the reaction of an aromatic amine set, as
nucleophiles, with haloaromatic substrates. It was used a
benzophenone/benzhydrol system as actinometer, which permits long irradiation times
(30 min ca.).
Results show that the anions of 2-pyrimidinamine and 2,6-diethylaniline are
poor electron donors leading itself to a low quantum yield for the initiation step which
can be increased adding more equivalents of the base t-BuOK. The propagation
quantum 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 a
higher propagation cycle.
powerful synthetic tool to obtain new organic compounds from substrates and
nucleophiles that do not react or react slowly through SN2 or SN1 mechanisms. This type
of reactions (SRN1) involves electron transfer steps, generating a chain process, with
radicals and radical anions as intermediates. A widely used method to initiate them is by
photoestimulation. Information about global quantum yields in these photoinduced eT
reactions, which include initiation and propagation steps, provides us a better
understanding of the system efficiency, involving in this context different nucleophile
and substrate chemical features.
Our work is based in the measurement and comparison of quantum yield values
for the SRN1 mechanism involved in the reaction of an aromatic amine set, as
nucleophiles, with haloaromatic substrates. It was used a
benzophenone/benzhydrol system as actinometer, which permits long irradiation times
(30 min ca.).
Results show that the anions of 2-pyrimidinamine and 2,6-diethylaniline are
poor electron donors leading itself to a low quantum yield for the initiation step which
can be increased adding more equivalents of the base t-BuOK. The propagation
quantum 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 a
higher propagation cycle.
