Coronene oxidation

Low-temperature protonations of benzo[<3]coronene 90 and benzo[ /z/]perylene 91 were studied in FSO3H/SO2CIF and CF3SO3H/SO2CIF superacids (Fig. 31). For 90, rapid competing oxidation to the RC prevented the observation of 90H by NMR spectroscopy the RC was probed by ESR spectroscopy. For 91, competing oxidation was less problematic and a persistent arenium ion 91H could be seen by NMR which was line-broadened due to the presence of the RC. Protonation of a mixture of 90 and 4,5-dihydropyrene 1 produced the C-3 protonated IH and 90H. Addition of 1 to the superacid solution containing 91H and 91 led to the detection of the C-3 protonated IH and the disappearance of 91H (by NMR). 

Arenium ion energies (AAH ion - neutral) and changes in carbon charges [Aq = (ion) - q (neutral)] for protonation of 90 and 91 were probed by the AMI method. The singlet oxidation dication of 90 was also calculated. The charge delocalization modes in the PAH arenium ions were discussed and compared. The AMI studies indicated that benzo[<3]coronene cations were less delocalized than benzo[g/z/]perylene ions. Benzannelation (91 92) severely limited the conjugation path in the carboca-tions despite the fact that coronene 92 was still planar. Further benzannelation (92 90) had a minimal effect on the charge delocalization mode. 

The synthetically most valuable intermediate in heterofullerene chemistry so far has been the aza[60]fulleronium ion C59N (28). It can be generated in situ by the thermally induced homolytic cleavage of 2 and subsequent oxidation, for example, with O2 or chloranil [20-24]. The reaction intermediate 28 can subsequently be trapped with various nucleophiles such as electron-rich aromatics, enolizable carbonyl compounds, alkenes and alcohols to form functionalized heterofullerenes 29 (Scheme 12.8). Treatment of 2 with electron-rich aromatics as nucleophilic reagent NuH in the presence of air and excess of p-TsOH leads to arylated aza[60]fullerene derivatives 30 in yields up to 90% (Scheme 12.9). A large variety of arylated derivatives 30 have been synthesized, including those containing cor-annulene, coronene and pyrene addends [20, 22-25]. 

SAMFETs have also been used in chemical sensing. The a-substituted quincpiethiophene SAMFETs were covered with a 10-nm pinhole-riddled iron tetraphenylporphyrin chloride layer, that acts as a receptor to nitric oxide (NO), an important biomarker [74]. The threshold voltage, measured by the FET transfer characteristics with the porphyrin receptor shifts upon increased exposure to NO. Annealing the monolayer FET in vacuum restores the initial FET behavior. Also, in the single monolayer HBC assembled FETs between metallic SWCNT source and drain electrodes increased current levels were measured in /d-Fds and Aj-Fg characteristics (Fig. 9) upon exposure to solutions of the electron acceptor TCNQ [68]. While the mechanism of response is not known, TCNQ has an affinity for coronene, and likely gives rise to charge transfer between electron-deficient TCNQ... 

Bernstein et al. have used IR spectroscopy and mass spectrometry to study the products formed from photochemical transformation of naphthalene, anthracene, chrysene, phenanthrene, pyrene, tetracene, pentacene, perylene, benzo(e)pyrene, benzo(ghi)perylene, and coronene in water ices using ultraviolet radiation under astrophysical conditions [27]. The results of their investigation have revealed that peripheral carbon atoms can be oxidized to produce aromatic alcohols, ketones, ethers (when bay region is present,... 

UV radiation of coronene in D20 ice in a ratio of less than 1 part in 500 induces rapid exchange of its hydrogen atoms with deuterium by three different chemical processes which include D atom addition, D atom exchange at the aromatic edge site shown in Scheme 4 below and D atom exchange at the oxidized edge site shown in Scheme 5 [28]. 

The high-molecular-weight PAHs perylene, indeno[l,2,3-c /]pyrene, dibenz[a/ ]anthracene, benzo[g/i ]perylene and coronene are also oxidized by some fungi (Gramss et al., 1999 Zheng Obbard, 2002 Fau et al, 2003 Steffen et al., 2003 Verdin et al., 2005). Although minor amounts of... 

The CaO from CaCOs decomposition, the other new specie involved in the combustion mechanisms at LCL runs, is a solid porous material, which behaves like a fluid at the fluidised bed. That means that its interactions with radicals from coal are not limited and the radicals could be adsorbed [9] into its porous structure, hindering their total oxidation and, in consequence, promoting their interaction. This fact is corroborated by the Coronene formation in LCL experiments. Coronene (Co) is the most stable of the PAH studied and the radicals trend in their stabilization will be towards Co formation. Besides, as result of the fluidisation movement and the high temperature, CaO can be fragmented into smaller particles, elutriation and attrition phenomena, the smaller particles formed undergoing entrainment by the airflow. 

It could be also concluded that the porous character of the limestone facilitates the radical interactions, pyrosynthesis reactions, by hindering the oxidation process. That is corroborated by the Coronene emissions detected when limestone-coal blend is fed into the fluidised bed to control SO emissions. Coronene formation, the most stable PAH studied... 

Coronene and other polycyclic hydrocarbons are electron enddized by CgF sFg, and weaker oxidizers such as ASF5, to yield highly conducting salts (e.g., C24H,2 AsF6"). Richardson, T. J. Tanzella, F. L. Bartlett, N., to be published. 

If such oxidative couplings occur vithin the same molecule, cycliza-tions, usually to six-membered rings, take place. Anhydrous aluminum chloride proves useful in such intramolecular dehydrogenations. At 120 °C, it cyclizes benzil to 9,10-phenanthrenequinone [407] and bridges benzene rings in the synthesis of coronene [408], At the same time, partial aromatization takes place (equations 46 and 47). 

Figure 2.70 Immobilization of Cso on surfaces, (a) Covalent linking to gold or to indium-tin oxide and noncovalent attachment to gold modified with coronene ( RSC 2005) ...

The extent of oxidation and thus the observed stoichiometry vary widely in the materials prepared by the oxidation of coronene. The X-ray diffraction patterns of these solids are characteristic of the particular stoichiometries ... 

The monocation dimer of coronene (Willigen et al., 1968) and pyrene (Cooper and Forbes, 1968) have been detected by esr spectroscopy in S03-BF3 solution at low temperatures. Broad bands in the region of 500- 600 nm in spectra of p-dihydroxy- and p-dialkoxybenzenes (e.g. hydroquinone, 1,4-dimethoxybenzene) in sulfuric acid at 77°K have been attributed to the presence of Mj4" by Yamada and Kimura (1969), while Carter and Vincow (1967a) observed by esr (benzene)i+ in irradiated solutions of benzene in sulfuric acid at —103°. Using a flow-system, it was found by esr spectroscopy that the oxidation of mcsitylene by cobalt(III) tri-fluoroacetate in TFA solution led to Mj+ rather than M + signals (Shih and Dessau, 1971). 

When coronene, C24H12, (C) is treated with thallium(III) trifluoroacetate as oxidant under dried nitrogen atmosphere in l,l,l,3,3,3-hexafluoropropane-2-ol solvent coronene radical species are formed. Depending on the sample preparation the ESR spectra are dominated by the monomeric ion (C)", or are superpositions of spectra due to ( ) and the dimeric ion (C2) or even the trimeric ion (Cs). A stick-plot analysis of the spectrum of the nearly pure monomer is part of Exercise E3.5. It is also possible to accurately measure the hyperfine coupling constant (0.0766 mT for 24 H) and the corresponding peak-peak line-width (AHpp = 0.009 mT) for the ( 2) species in Eig. 3.7(b), since the lines are quite sharp, compared to those from the monomer. The line shape of ( 2)" can therefore be obtained by simulation, that of ( ) from experiment The component spectra are then superimposed in a ratio appropriate for the experimental spectrum. This ratio is usually obtained by manual adjustment for best visual agreement with the experimental line shape in the present... 

The termination of the experiment afl r 15 minutes residence time may result in misleading conclusions. Fig. 3-31 shows the isothermal oxidation of coronene at a constant temperature of 350 °C. Up to approximately 30 minutes residence time the curve seems to exhibit an asymptotic rise, but after 35 minutes the characteristic of the curve changes to an exponential rise, which is typical for autocatalytic ractions. After a residence lime of 75... 

As both symmetrical and unsymmetrical stilbenes can be readily synthesized by employing Wittig [126], Heck [127], or McMurry [128] reactions, various graphene-type molecules have been prepared via photolytic cyclodehydrogenation, some of which will be discussed at this point A typical example of photocyclization is the irradiation of the [2.2.2]paracydo-phane 96 in the presence of an oxidant, such as iodine, leading to the corresponding coronene derivatives 97 in high yield. This offers a versatile method for the preparation of new coronene derivatives with different functionality and substitutional symmetry (Scheme 13.26) [129]. 

The extension of PAHs using maleic anhydride in the presence of an oxidizing agent was also explored by Clar and Zander. The decarbonylation took place with soda-lime tuider vacuum sublimation. Coronene 16 and ovalene were synthesized by this method (Scheme 5) [22, 24]. 

Chromophores (NLO) phosphine oxides, LC siloxanes rare earths sulfonimides thiophenes coronenes POSS, etc. 

The so-called superbenzene, coronene, was used as a substrate by Pozniak and Dunbar (1997) in an FTICR-MS study of the formation kinetics of monomer and dimer association complexes with Sc and Y, together with several other main-group and transition metal cations. The formation of coronene adducts was also observed for RO" " and R(OH)2 ions, for both Sc and Y, with rates similar to the attachment rates for the corresponding bare metal ions the same ions were produced by the reaction of R(coronene) with background oxygen/water. In a different approach, Duncan and coworkers used covaporization of Nd oxide and pyrene in a laser plasma source with time-of-flight mass spectrometry (TOF-MS) detection to produce NdO(pyrene) " ions, with =1, 2 (Ayers et al., 2004). 

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