Doctoral dissertation
Activation of nitric acid in fluorinated alcohol for aromatic nitration and oxidation of alcohols
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Abstract
The objective of this thesis was to find an alternative way of activating nitric acid and its
lower valent analogues to use them as reagents or as catalysts. The research was split into
three sections. The first section describes the use of the nitric acid activated by fluorianted
solvents (2,2,2-trifluoroethanol-TFE, 1,1,1,3,3,3-hexafluoroisopropanol-HFIP, trifluoroacetic
acid-TFA) as a reagent for aromatic nitration. The results obtained with such
a method were compared with classic nitration with a mixed acid system. It was found
that the activation of HNO3 with HFIP was of similar strength as in conc. H2SO4. For
the effective nitration of various aromatic molecules in HFIP 1 equiv. of HNO3 was used
without the addition of external acids. In reactions with 1,3-dimethoxybenzene derivatives
new products, i.e., bisphenylnitrosonium nitrates, were identified. Therefore, two mechanistic
studies were carried out. In the first mechanism we identified intermediates for the
formation of bisphenylnitrosonium nitrates. The reaction path was further explained by
DFT calculations. In the second mechanism we explained the nitration of arenes in fluorinated
alcohols. In the end we compared our method of nitration of aromatic compounds
with HNO3 in HFIP with other literature methods in terms of the environmental potential
by calculating green metrics (atom economy, E factor, etc.). In the second section, the
activation of nitric acid for reactions of oxidation was studied. Nitric acid was used as the
sole catalyst for the aerobic oxidation of various benzyl alcohols and complete conversion
into the corresponding benzaldehydes was obtained. For less reactive aliphatic alcohols
an additional iron co-catalyst was used to selectively oxidise the secondary alcohol group.
The last section describes the study of aerobic oxidative halogenation in conjunction with
an iridium catalyst. This was performed as collaboration with the Martín-Matute group,
Stockholm University. We successfully coupled the 1,3-hydride shift in allylic alcohols
catalysed by an iridium catalyst with aerobic oxidative iodination. The iodine(I) reagent
was generated in situ by the aerobic oxidation of iodine using NOx as a catalyst. The
developed method was used for the regioselective synthesis of
-iodoketones from allylic alcohols.