Azulene oxidation

The generic term azulene was first applied to the blue oils obtained by distillation, oxidation, or acid-treatment of many essential oils. These blue colours are usually due to the presence of either guaiazulene or velivazulene. The parent hydrocarbon is synthesized by dehydrogenation of a cyclopentanocycloheptanol or the condensation of cyclopentadiene with glutacondialdehyde anil. 

Oxidation of thiophene with peracid under carefully controlled conditions gives a mixture of thiophene sulfoxide and 2-hydroxythiophene sulfoxide. These compounds are trapped by addition to benzoquinone to give ultimately naphthoquinone (225) and its 5-hydroxy derivative (226) (76ACS(B)353). The further oxidation of the sulfoxide yields the sulfone, which may function as a diene or dienophile in the Diels-Alder reaction (Scheme 88). An azulene synthesis involves the addition of 6-(A,A-dimethylamino)fulvene (227) to a thiophene sulfone (77TL639, 77JA4199). 

Additions of sulfinic acids to polyenes ( hydrosulfonylation ), however, proceed with very strong acids80 or under catalysis of Pd complexes81 (equation 17). With copper(II) arenesulfinates, azulene has been oxidatively sulfonylated in the 1- and 2-positions of the five-membered ring82 (equation 18). The sulfonylmercuration has also been applied with success to conjugated dienes83 (equation 19). 

Polycyclic aromatic hydrocarbons, indole and quinoline derivatives, naphthylamines, azulenes Silica gel G Formation of oxidation products via the initially formed iodine complexes [15]... 

On adding one drop of nitrobenzene to an equimolar, ten millimolar, mixture of the other two solids a violent reaction produced gas and carbonaceous material. This was initially attributed to the oxidative powers of the nitrobenzene [1], However, diphenylacetylene is a high energy molecule, AH°f +315 kJ/mole. At least 98% of the potential chemical energy present will have been the diphenylacetylene. It is probable that the nitrobenzene merely provided a liquid phase in which the aluminium chloride could interact with the acetylene, catalysing reaction beyond the intended azulene dimerisation product[2]. 

Hemoglobin is another heme-containing protein, which has been shown to be active towards PAH, oxidation in presence of peroxide [420], This protein was also modified via PEG and methyl esterification to obtain a more hydrophobic protein with altered activity and substrate specificity. The modified protein had four times the catalytic efficiency than that of the unmodified protein for pyrene oxidation. Several PAHs were also oxidized including acenaphthene, anthracene, azulene, benzo(a)pyrene, fluoranthene, fluorene, and phenanthrene however, no reaction was observed with chrysene and biphenyl. Modification of hemoglobin with p-nitrophenol and p-aminophenol has also been reported [425], The modification was reported to enhance the substrate affinity up to 30 times. Additionally, the solvent concentration at which the enzyme showed maximum activity was also higher. Both the effects were attributed to the increase in hydrophobicity of the active site. 

The electrochemical reduction of azulene with carbon, platinum, lead or zinc cathode does not give any product, whereas that with magnesium electrode yields a dimeric compound as the only reduction product, though the dimeric compound is easily transformed to the corresponding monomeric compound by a mild oxidation as shown in equation 2825. 

Determination of electrochemical oxidation potentials and electrochemical reduction of 13 p-phosphorylated acyclic nitrones shows that phosphorylated compounds have a clear anodic shift of potentials of both, oxidation (Ep 1.40 to 2.00 V versus SCE in CH3CN) and reduction (Ep—0.94 to —2.06 V). This is caused by a strong electron-acceptor influence of the diethoxyphosphoryl group (430). In contrast, a reversible one-electron oxidation of azulene nitrones (233) (Scheme 2.80) occurs 0.6 V below the Ep potential of PBN, that is at the value one observes the oxidation of AH -imidazole-1,3-dioxides (219) (428, 429). In other words, the corresponding RC (234) is 14 kcal more stable than the RC of PBN. Although the EPR spectrum of RC (234) was not recorded, RC (236) from dinitrone (235) turned out to be rather stable and gave an EPR spectrum (170). 

Table I summarizes the pKR+ values and redox potentials for the tri(l-azulenyl)methyl cations. The oxidation exhibited a barely separate two-step, two-electron oxidation wave. This wave is ascribed to the oxidation of two azulene rings to generate a tricationic species. The reduction showed a one-electron wave, which is ascribed to the formation of a neutral radical.

We have established the conversion between the two colored species by electrochemical reaction utilizing the concept of a Wurster type violene-cyanine hybrid. Dications 222+ and 232+ showed significant changes in their absorption spectra in different oxidation states. Therefore, dications 222+ and 232+ could function as new violene-cyanine hybrids, in which the four end groups (X and Y) in the general structure are azulenes (Figure 4). 

Nitration with tetranitromethane proceeds along the ion-radical ronte. Tetranitromethane is a smooth nitrating agent and mild oxidizer. It is convenient for nitration of highly activated snbstrates snch as phenols, azulene, and heterocycles in the presence of pyridine, N,iV-dialkylaniline, etc. As shown (Morkovnik 1988), these reactions inclnde one-electron transfer ... 

It has also been shown by X-ray diffraction that the major diastereomer of 9-phenyl-4,8,10-trithiadibenzo[t , y]-azulene 8-oxide (cf. Section 13.11.6.5) is the trans-isomer with the phenyl group and the sulfinyl-oxygen atom occupying the equatorial positions (R.s,Sc and Ss,Rc configurations) <1996CL655>. 

Dibenzo-fused dithiepins undergo photochemically induced ring contractions. Thus, irradiation of 2-phenyldibenzo-[df [l,3]dithiepin 1-oxide 72 <1999T5027> and 9-phenyl-4,8,9-trithiadibenzo[i2/,9]azulene 8-oxide 70 <1996CL655> using a high-pressure mercury lamp (400 W) gave disulfides 99 and 100 (Scheme 22). 

The reaction of arenes with aryllead tricarboxylates performed in trifluoroacetic acid, affording biarenes, takes place via a cationic 7t-complex.162 Since azulenes form 7r-donor/acceptor complexes with various 7r-acids, the arylation of 4,6,8-trimethylazulene 108 was attempted with />-methoxyphenyllead triacetate 1 (Equation (135)).163 Only one isomer of 1-arylazulene 109 was formed although in a modest 27% isolated yield. Based on recovered unreacted azulene, the effective yield was 43%. A dimer 110, 3,3 -dianisyl-l,l -biazulene (4% yield), was suggested to result from the one-electron oxidation of the intermediate 4-methoxyphenyl cation in the 7t-complex. 

Photolysis of 4,8,10-trithiadibenzo[rif, ]azulene 8-oxides 28 under irradiation with high-pressure Hg lamp (500W, A = 313nm) afforded an unstable, acid-sensitive 1,2,4-oxadithiocine ring system 29, which was characterized by H NMR and mass spectrometry (Scheme 3, Section 14.08.5.1 <1996CL655>). 

The electrochemical oxidation of a wide range of conjugated monomers results in the deposition of an electrically conductive film on the working electrode (Waltman and Bargon, 1986). This method has mostly been used for the polymerisation of heteroatom-containing monomers, e.g. pyrrole, thiophenef aniline, indole, etc., and polycyclic monomers, e.g. azulene, fluorene, pyrene , etc. The example of pyrrole is illustrative of the inherent advantages and problems of electrochemical polymerisation. 

Figure 4 Carajurone (R=CHs) and the related carajuretin (R=H) result by the very rapid enzymatic aerial oxidation of flavans present in the leaves of Arrabidaea chica. The plant is one of the most used Amazonian medicinal plants and the anti-microbial and other activities may be related to the presence of these red pigment. Some indigenous tribes use them as face paints and carajurone has been commercialised in the past as chica red. Genipa americana fruit juice, by the action of an endogenous glucosidase followed by aerial oxidation, provides another pigment. The juice has multiple medicinal uses probably associated with its antimicrobial action. Here the dye is blue-black and is believed to be an ethylene-bis- -aza-azulene , derived by condensation of the genipin monomer with primary amines. ...

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