Fluorenones formation

Although the exact mechanism of the fluorenone formation is not known, it is believed that the monoalkylated fluorene moieties, present as impurities in poly(dialkylfluorenes), are the sites most sensitive to oxidation. The deprotonation of rather acidic C(9)—H protons by residue on Ni(0) catalyst, routinely used in polymerization or by metal (e.g., calcium) cathode in LED devices form a very reactive anion, which can easily react with oxygen to form peroxides (Scheme 2.26) [293], The latter are unstable species and can decompose to give the fluorenone moiety. It should also be noted that the interaction of low work-function metals with films of conjugated polymers in PLED is a more complex phenomenon and the mechanisms of the quenching of PF luminescence by a calcium cathode was studied by Stoessel et al. [300],... 

One of the best tests of purity of dioxane is the formation of the purple disodium benzophenone complex during reflux and its persistence on cooling. (Benzophenone is better than fluorenone for this purpose, and for the storing of the solvent.) [Carter, McClelland and Warhurst Trans Faraday Soc 56 343 I 960], TOXIC. 

Tough, transparent, heat and flame resistant, multiblock (bisphenol fluorenone carbonate) (BPF)-dimethylsiloxane copolymers have been synthesized by interfacial polycondensation of phosgene with various mixtures of BPF end-capped siloxane oligomers and free BPF or its monosodium salt 232). Siloxane content of the copolymers were varied between 7 and 27%. Presence of two Tg s, one below —100 °C and the other as high as 275 °C, showed the formation of two-phase morphologies. 

The principles needed to design a polymer of low flammability are reasonably well understood and have been systematized by Van Krevelen (5). A number of methods have been found for modifying the structure of an inherently flammable polymer to make it respond better to conventional flame retardant systems. For example, extensive work by Pearce et al. at Polytechnic (38, 39) has demonstrated that incorporation of certain ring systems such as phthalide or fluorenone structures into a polymer can greatly increase char and thus flame resistance. Pearce, et al. also showed that increased char formation from polystyrene could be achieved by the introduction of chloromethyl groups on the aromatic rings, along with the addition of antimony oxide or zinc oxide to provide a latent Friedel-Crafts catalyst. 

The Problem of Pure Blue Emission in Polyfluorenes Excimer and Aggregate Formation or Fluorenone Defects ... 

A lifetime of 27 ns at room temperature (in the absence of quencher, but in the presence of 0.025 M OH ) has been calculated from a linear Stem-Volraer plot using 9-fluorenone as quencher i >. In general, lifetimes of excited substrates are dependent on the nucleophile concentration. Quenching of the excited state by the nucleophile probably takes place by either formation of a a-complex or simply return to ground state starting material. 

Closely related to the already mentioned electrocyclizations of N-acyl thione S-imide (see Section 4.14.9.2) are some intermolecular cycloadditions involving this unusual class of 1,3-dipoles. Thus, the thione-S-imide intermediate (233) is probably involved in the formation of spirodithiazoline derivative (234) from the thione (235) and aryl azides <93HCA2147>. Also fluorenone-S-/ -tosylimide affords with carbonyl or thiocarbonyl compounds (R H) the corresponding oxathia- or dithia-zolidine derivatives (236) (Y = O or S) <80BCJ1023> (Scheme 44) (see also Section 4.14.6.1). 

Background and Possible Intermediates. Accepting the premise of carbanion formation in the basic media, the mode of reaction with molecular oxygen can now be considered. Sprinzak (8) reported that the autoxidation of fluorene in basic media proceeds by direct reaction of the fluorenyl carbanion with oxygen to form initially the hydroperoxide, which decomposes to yield 9-fluorenone, as depicted below. 

The quantum yield for the formation of 19 reaches a maximum (ca. 0.7) at 0.02A/ 18, but decreases sharply as the solution becomes more concentrated. The decrease in quantum yield at high ketenimine concentrations is explained by quenching of the fluorenone singlet. Consistent with this, the fluorescence of fluorenone is also quenched by ketenimine. 

The conditions for the photocycloaddition (discussed in detail in a later section of this review) can be relatively mild. There is usually a small probability of the oxetane being destroyed in dark reactions which would probably preclude isolation after preparation by any method. One mode of decomposition of oxetanes is fragmentation, either back to the starting materials or to the other possible carbonyl compound and olefin. For example, the oxetane from 4,4 -dimethoxybenzophenone and isobutylene forms readily and is easily detected and characterized by infrared and NMR spectroscopy. All efforts to purify it, however, have led to its decomposition into formaldehyde and the diarylethy-lene.17 37 In some cases, as with fluorenone and isobutylene37 or 2-methyl-2-butene,25b the oxetane is apparently too unstable for detection, but the presence of the olefin 96 attests to its formation. 

Fig. 7. Dependency of the reciprocal of the quantum yield for adduct formation on ketenimine concentration in the fluorenone-dimethyl-iV-(cyclohexyl)ketenimine reaction. Slope = 0.006M intercept = 1.08. (From Singer and Davis220 with permission of the American Chemical Society.)...

Similar surface-supported amides have been derived from the Sm" amide Sm N-(SiHMe)2 2(thf)x by grafting on MCM-41, MCM-48 or AS-200 further elaboration led to the formation of the corresponding Sm-fluorenone ketyl, which was shown to contain surface-confined ketyl radicals.Treatment of Sm N(SiHMe2)2 (thf)x MCM-41 with MeOH, AlHBu 2 or Si(H)Me2-substituted indene gave surface-supported catalysts for methyl methacrylate polymerisation. 

Concerning electrophilic side reactions, intramolecular Friedel-Crafts condensations have been reported for example, fluorenone is formed from 2-benzoylbenzenediazonium tetrafluorobo-rate.241 The strong Lewis acid boron trifluoride can also be responsible for side reactions, such as the extensive formation of tars from nitro-substituted arenediazonium tetrafluorobor-ates or the acidic hydrolysis of ester substituents, especially in the case of 2-(ethoxycar-bonyl)benzenediazonium tetrafluoroborate.105,242... 

The quadrupole mass spectrometer which was used for these initial studies could provide only limited insight into the formation or structures of these unusual ions from fluorene and amino PAH. Experiments using substituted fluorenes, such as 1-, 2-, and 9-methylfluorene, 9-phenylfluorene, and carbazole, revealed that the (M + 14) ion did not form if the C-9 position was blocked. Knowing that the (M + 14) ion was formed by a reaction at the C-9 carbon, two possible structures could be drawn for this anion. One possibility would be 9-methylfluorene (structure I), which could arise from the addition of CH2 to fluorene. Similar formation of adducts from methane buffer gas under NICI conditions has been reported (7, 8). Alternatively, fluorene could lose the two hydrogens at the 9-position and add oxygen to form 9-fluorenone (structure II)... 

This corresponds to results reported by Peters [35] who observed the fluorenone radical anion in the presence of diazabicyclo[2.2.2]octane (DABCO) with a halflife of ca. 60 ps. The unusually long lifetime of the transients observed by us can be explained with the formation of radical ion pairs in the triplet state. 

The formation of a phenanthridine lactone by the persulfate oxidation of 2 -cyanobiphenyl-2-carboxylic acid is interesting in that little is known of the addition of radicals to the C=N system. The mechanism proposed below (Scheme 1) also accounts for the occurrence of fluorenone as a by-product.64... 

The pyrolysate contained an appreciable amount of product of molecular weight 196, which could be either xanthone or the lactone 30. Directly coupled gas chromatography-mass spectrometry identified it as 30. The retention time and mass spectrum of this product agreed closely with those of an authentic sample of 30, synthesized by the method of Graebe and Schestakow (1895), which was clearly distinguishable from xanthone on both counts. The formation of 30 parallels that of fluorenone from phthalic anhydride and benzene, observed by Fields and Meyerson (1965). 

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