Large amounts of chemicals are emitted into the troposphere as a result of anthropogenic and biogenic processes, that give rise to a very complex scenario which includes a variety of chemical ...transformations. During the past decades, it has become well recognized that oxygen-, nitrogen-, and carbon-centered free radicals play a key role in the chemistry of the troposphere. More recently, increasing attention has been devoted to the relevance that free radical chemistry may have in influencing the indoor air quality. Since modern populations typically spend most of their time indoors, indoor air quality is recognized as an important environmental and health problem. Reactive radicals in indoor air may be the result of indoor penetration of outdoor air or of indoor generation from specific sources. There is a great lack of knowledge about the presence and the concentrations of chemically reactive radicals in indoor air, that, in analogy to the processes occurring in the troposphere, may be formed indoors as well. In the present paper, some of the key aspects of outdoor and indoor free radical chemistry are discussed together with the experimental evidences so far obtained for the occurrence of radicals and radical-chain reactions in such environments.
The study of the electrochemical behavior (CV) of 9-anthrylmethylcyclopentadienyl (AnCH2C5H4) derivatives of rhodium(I) and iridium(I) of formula M(η5-AnCH2C5H4)L2 (M = Rh or Ir; L = η2-C2H4, η1-CO, ...η2-C8H14, PPh3; L2 = η4-C8H12), 1−8, in strictly aprotic conditions, allows a satisfactory interpretation of the observed electrode processes and gives information about the location of the redox sites along with the thermodynamic characterization of the corresponding redox processes. These data show that the occurrence of an intramolecular charge-transfer process between the photoexcited 9-anthryl group and the cyclopentadienylmetal unit is a possible route for the observed anthracenic fluorescence quenching in the compounds 1−8. Moreover, a study was carried out on the redox behavior of these complexes under chemical activation. The one-electron oxidation of compounds 1−8 by thallium(III) trifluoroacetate leads to the formation of the corresponding cation radicals, whose highly resolved X-band EPR spectra were fully interpreted by computer simulation as well as by semiempirical and DFT calculations of spin density distribution.
Pd(hfacac)
2 and Cu(hfacac)
2(H
2O)
2 (hfacac=1,1,1,5,5,5-hexafluoropentane-2,4-dionate) catalyse the oxidation of methane by H
2O
2 in trifluoroacetic anhydride to the methyl trifluoroacetate, under ...mild conditions, CO
2 being the main by-product. Under the same conditions, ethane and propane are both more easily oxidized than methane to the corresponding trifluoroacetates.
Both Pd(hfacac)
2
2 and Cu(hfacac)
2(H
2O)
2
3 (hfacac=1,1,1,5,5,5-hexafluoropentane-2,4-dionate) catalyse the oxidation of methane to methyl trifluoroacetate
1 by H
2O
2 in trifluoroacetic anhydride (TFAA), at temperatures as low as 50
°C, under 25–30
atm methane partial pressure, the main by-product being CO
2. Under the same conditions, ethane and propane are oxidized to the corresponding trifluoroacetates. The
iso-to-
normal propyl esters ratio varies markedly (7.2 versus 34) on passing from
2 to
3.
9-Anthroylacetone and its photodimer Cicogna, Francesca; Ingrosso, Giovanni; Lodato, Fabio ...
Tetrahedron,
12/2004, Volume:
60, Issue:
51
Journal Article
Peer reviewed
9-Anthroylacetone undergoes a head-to-tail 4π+4π photo-dimerisation reaction that leads to the formation of 5,11-bis(1,3-diketobutyl)-5,6,11,12-tetrahydro-5,12,6,11-di-
o-benzeno-dibenzo
a,
...ecyclooctene both in solution and in the solid state when irradiated with different sources (sunlight, tungsten lamp, xenon lamp, UV laser beam 351–364
nm), the reaction being accompanied by a colour variation from bright yellow to colourless. Quantum yields >0.023
mol/Einstein are evaluated for the solid state reaction. Interestingly, the dimer dissociates to give 9-anthroylacetone, both thermally (
T>130
°C) and photochemically, by short UV wavelength irradiation. The single-crystal X-ray structure of 9-anthroylacetone and its dimer are reported.
9-Anthroylacetone undergoes a head-to-tail 4π+4π photo-dimerisation reaction both in solution and in the solid state when irradiated with different sources; the dimer reversibly dissociates into 9-anthroylacetone, both thermally and photochemically.
A variety of phenolic derivatives
4
, carrying the guaiazulene moiety, were prepared starting from guaiazulene. Compounds
4
react with oxygen-centred radicals exhibiting chromotropic behaviour. The ...radical scavenging power of these compounds was evaluated by different methods. Compounds
4
are less efficient than some of the most common radical scavengers but show quite selective behaviour towards different oxygen-centred radicals. A correlation is found between the antioxidant activity of the compounds
4
and the corresponding phenolic O–H bond dissociation energy. Some aspects of the reaction of the compounds
4
with oxygen-centred radicals were elucidated by EPR and DFT studies.
Graphic
The ambient temperature reaction of Ir(η5‐C5Me5)(CO)2 with Hg(CF3CO2)2 yields a mixed‐metal cluster of iridium and mercury (see picture) which contains the novel Ir6Hg6 twelve‐membered ring ...comprising six Ir(η5‐C5Me5)(CO) fragments connected to each other through mercury centers; additional mercury centers and metal–metal bonds give rise to a network within the ring.
Aziridinyllithiums
4a and
4b, which are stable at low temperature, can be generated by deprotonation of
3a and
3b. Oxazolinyl aziridines
5a-j and
6a-b have been prepared by the reaction of oxazolinyl ...aziridinyllithiums
4a and
4b with electrophiles. Aziridines
6c and
6d were, instead, synthesized by a Darzens-like reaction from 2-(1-chloroethyl)-2-oxazoline
1b.
Graphic
PDF
![[{Ir(η5-C5Me5)(CO)}6Hg8][CF...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1433-7851/small "[{Ir(η5-C5Me5)(CO)}6Hg8][CF3CO2]6, a Mixed-Metal Cluster with an Ir6Hg6 Twelve-Membered Ring and Additional Hg Centers and Metal-Metal Bonds")
