9.10- Dihydroanthracene dehydrogenation

Moro-Oka et al. (1976) have reported that the oxidation of 9,10-dihydroanthracene by K02 solubilized in DMSO by 18-crown-6 gives mainly the dehydrogenated product, anthracene. Under the same conditions, 1,4-hexadiene is dehydrogenated to benzene. The authors proposed a mechanism in which the superoxide ion acts as a hydrogen-abstracting agent only. The oxidations of anthrone (to anthraquinone), fluorene (to fluorenone), xanthene (to xanthone) and diphenylmethane (to benzophenone) are also initiated by hydrogen abstraction. 

Benzophenones are produced by the oxidation of diarylmethanes under basic conditions [6-9], The initial step requires a strongly basic medium to ionize the methane and the more lipophilic quaternary ammonium catalysts are preferred (Aliquat and tetra-n-octylammonium bromide are better catalysts than tetra-n-butyl-ammonium bromide). The oxidation and oxidative dehydrogenation of partially reduced arenes to oxo derivatives in a manner similar to that used for the oxidation of diarylmethanes has been reported, e.g. fluorene is converted into fluorenone (100%), and 9,10-dihydroanthracene and l,4,4a,9a-tetrahydroanthraquinone into anthraquinone (75% and 100%, respectively) [6]. 

Some 10-X-3 species behave as oxidizing agents. Chloroiodinane (21) oxidizes aqueous potassium iodide to iodine. Brominane (35) oxidizes I, Br- and aniline to I2, Br2 and azobenzene, respectively. 9,10-Dihydroanthracene is dehydrogenated by (35) to give anthracene in quantitative yield (80JA7382). 

Wolthuis employed chloranil in refluxing xylene to effect nearly quantitative dehydrogenation of 1,4-dihydroanthracene derivatives such as (11) obtained by a synthesis starting with (9), the adduct of benzyne with furane. Functioning as an... 

Dehydrogenation. The perchlorate is an eifective reagent for the aromatization of hydroaromatic compounds. It converts 9,10-dihydroanthracene into anthracene in quantitative yield. It provides the best means available for the conversion of perinaphthanones into perinaphthenones and for the dehydrogenation of chrom-anones to chromones. ... 

Two high-yield three-step syntheses of (195) from anthraquinone have been developed via the bis-epoxide (194) (67% and 89% overall). Compound (195) was obtained from (194) either by conversion into lO-hydroxymethyl-9-anthraldehyde with LiBr, followed by oxidation, or by conversion into 9,10-dihydroanthracene-9,10-dicarboxaldehyde with BF3, followed by dehydrogenation. 

A diverse range of carbocycles and heterocycles has been aromatized by aerobic dehydrogenation under AC catalysis [80]. Substrates include 9,10-dihydroanthracenes [81], a l,8-diaza-9,10-dihydroanthracene [82], Hantzsch 1,4-dihydropyridines [83], pyrazolines [83], 2-arylimidazolines [84, 85], indolines [86], 3,4-dihydropyrimidin-2(l//)-ones [87, 88], and various... 

Table 7.3 Oxidative dehydrogenation of 9,10-dihydroanthracene ito anthracene in the liquid phase over carbon-based catalysts.

In this experiment the metal-free carbon nanotubes acted directly as a support and active phase for the liquid-phase ODH of dihydroanthracene to anthracene at low temperature. The results are compared with those obtained on other catalysts. Oxidative dehydrogenation of dihydroanthracene in the liquid-phase was carried out over different CNT-based materials. The results are presented in Table 7.3. The test was also performed on an exfoliated graphite material for comparison. The results clearly showed that the reaction was chemically selective whatever... 

Fig. 7.17 Tentative mechanism of the oxidative dehydrogenation of dihydroanthracene to anthracene over heat-treated carbon nanotubes.

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