1,657 research outputs found
The 'belle époque' of photochemistry
No full textIn 1908 the pioneer of photochemistry, Giacomo Ciamician, presented a comprehensive account on his
ongoing work in molecular photochemistry. He reported a number of reactions caused by light and
ascertained that these were caused by light alone, not heat. These included geometrical isomerization of
C=C, C=N andN=N bonds, 2 + 2 cycloaddition involving olefins as well as a,b-unsaturated ketones
and esters, reactions of ketones such as a-cleavage and intermolecular hydrogen abstraction from
alcohols leading to reduction or coupling, inter- and intramolecular reactions of nitro compounds,
photooxygenation reactions: in fact a large fraction of the presently known reaction types. The rich
perspective that photochemistry offered to synthesis was revealed by this talk. Actually, Ciamician
thought that this would become a serious alternative to thermal methods and provide a less polluting
way for synthesis, imitating the mild conditions of biochemical reactions. This hope did not materialize,
however, and the actual development of molecular photochemistry had to wait for several decades
Green chemistry: State of the art through an analysis of the literature
No full textThe literature of green chemistry has undergone a dramatic increase in the new millennium. Besides that, in ad
hoc journals, papers of this type are published in journals of general, organic, and catalytic chemistry. The high
proportion of communications within this area indicates that this is a hot topic. These reports mainly concern
more environment-friendly synthetic methods, based on better catalytic systems, less harmful solvents and, more
rarely, ‘‘alternative’’ physical techniques. Although the compliance with the green chemistry postulates is still
partial, a trend in this direction is recognizable. For example, the number of preparative papers that introduce an
environmental assessment is rapidly increasing
Photochemistry of transition metal complexes (2017–2018)
No full textThis chapter reviews the major advances in the field of photochemistry and photocatalysis by transition metal compounds published in 2017–2018. Particular attention has been given to (i) photocatalysis in synthesis (ii) photoreactivity; (iii) biomedical applications of photoactive transition metal complexes, e.g. as photo-CORMs and PDT (photodynamic therapy) agents
Convenient synthesis of electron-donating substituted benzonitriles by photolysis of phenyl halides and esters
No full textIrradiation of electron-donating substituted phenyl halides
(fluorides and chlorides) or esters (mesylates, triflates and
phosphates) in aqueous MeCN in the presence of KCN gives
the corresponding benzonitriles in 48 to 100% yield through an
ArSN1 reaction with the intermediacy of a triplet phenyl cation
Engineering amino acid and peptide supramolecular architectures through fluorination
No full textFluorinated non-natural amino acids are attracting considerable research interest, especially in the biomedical field and in materials science, thanks to their ability to self-assemble into peculiar supramolecular structures. The conformational changes induced by the presence of fluorine atoms obviously affect their functions, as well as the biological activity of the deriving peptides and proteins. Here, we will briefly describe the main effects of fluorination on the aggregation behavior of such building blocks, focusing in particular on their improved tendency to form fibrils, and gels therefrom. Our aim is to underline the promising potential of fluorination as a tool to affect the self-assembly features of amino acids, both when used alone and when inserted into polypeptide sequences. The ability of fluorine to influence physical, chemical, and structural properties of these substrates offers the possibility to engineer bioinspired materials with specific and tunable functions
Solarylations via 4-aminophenyl cations
No full textThe application of the photo-SN1 reaction on some 4-chloroanilines was explored under solar
irradiation in view of obtaining a convenient metal-free arylation method. Several reactions
previously carried out by UV irradiation, as well as some new ones, where either a new trap
(R-methylstyrene) or a new halide (N,N-dimethyl-4-fluoroaniline) were adopted, were studied under
these conditions and found to occur conveniently. Furthermore, at least in some cases the halide
starting concentration could be raised up to 0.2 M, the excess trapping agent reduced from 20:1 to
2.5:1, and the solvent replaced by more environmentally friendly (co)solvents including water. Under
these improved conditions, the photoarylation was carried out in a gram scale by merely exposing the
solution to solar irradiation. This process has a low impact on the environment and can be considered
a serious competitor of metal-catalyzed arylations
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