Anthraquinone from benzophenone

Umemoto [36] used external generation, followed by stopped-flow detection, to study the protonation of anthracene, anthraquinone, and benzophenone anions in dimethylformamide-water solutions using an apparatus similar to Figure 29.20c. The measured half-lives were about 1.5 min or more. In the case of anthracene, the decomposition rates agreed with those obtained from polaro-graphic measurements and the following scheme was proposed. 

Oxidative cleavage of ring B of anthraquinones yields benzophenone derivatives which are transformed to xanthones. Both hydroxyl groups of the symmetrically substituted benzene nucleus of the benzophenone carboxyhc acid intermediate can participate in the closure of the xanthone ring. From the xanthones dimeric products are formed probably via phenol oxidase or peroxidase-derived radicals (C 2.3.1 and C 2.4.1). 

Apart from benzophenones, thioxanthone, anthraquinones, ketocou-marins, and some 1,2-diketones are used in conjunction with coinitiators for initiating vinyl polymerizations. As explained earlier, both electron and hydrogen transfer can bring about radical formation in the case of Type II photoinitiators. In many systems, both processes occur. 

Xanthones in higher plants are also formed by this mixed pathway, though the polyketide chain originates from a benzoic acid instead of the usual cinnamic acid. Cyclization now affords a benzophenone (691), rather than a chalcone, which subsequently cyclizes to the xanthone, a route used with considerable success in the laboratory (Scheme 280). Other xanthones are derived only from acetate, through ring opening, decarboxylation and cyclization of an anthraquinone precursor. 

Aliphatic aldehydes and ketones and also aliphatic-aromatic ketones can be converted into the corresponding hydrocarbons alkyl-phenols can be obtained from phenolic-aldehydes and -ketones p-hydroxy-benzophenone yields p-benzylphenol benzoin and benzil yield dibenzyl anthraquinone yields anthracene dihydride. 

The use of i3C2-acetate labelling to detect the involvement of symmetrical intermediates has found extensive use in biosynthetic studies. Thus, as shown in Scheme 4, incorporation of [1, 2- 2] acetate into ravenelin (7) in cultures of Helminthosporium ravenelii resulted in the observation of a randomisation of labelling in ring-C which confirmed the predicted involvement of a symmetrical benzophenone intermediate (6), itself derived from cleavage of an octaketide-derived anthraquinone, presumably helminthosporin (5) [12]. 

Photosensitized crosslinking of polymers has been the subject of numerous publications [l - 30], concerned mainly with poly(ethylene), poly(vinyl alcohol), various vinyl copolymers, copolymers of maleic anhydride and/or phtalic anhydride with styrene and some polymers derivated from cinnamic acid. The following compounds were used as sensitizers benzophenone, 4-chloro- and 4,4-dimethylbenzophenone [l, 3-6, 8, 9l, oC -and -derivatives of anthraquinone [3, 23] acetophenone, hydroquinone, triphenylmethane and pyridine li.] chlorobenzene and no less than trichlorinated n-paraffins [6], a complex of zink chloride with o-dia-nizidine fill potassium bichromate [l2j, anthracene fl3, 14] 2,5-methoxy-4-amino-trans-stilbene [l5], benzyl ideneacetophenone fl6-l8] -thiophenylacetophenone,... 

In photo-oxidized polymers, HAS may meet excited chromophores (Ch ) such as residues of polymerization catalysts or carbonyls arising in oxidized PO. Attempts were made to obtain information on the ability of HAS or derived NO to quench Ch [213, 214], The phosphorescence emissions from sensitizers anthraquinone, benzophenone or benzhydrol were not affected by HAS. These data indicate that quenching ability is lacking in the HAS mechanism [214],... 

Under benzophenone-sensitization the quantum yields and the photostationary state are practically independent of the stilbene concentration [25,196], Similar results were obtained with azastilbene sensitized by biacetyl [132] or anthraquinone [206] except for rather low concentrations [120,128], Energy transfer from biacetyl to StPs has also been studied by monitoring the biacetyl phosphorescence [221], With azastilbenes systematic studies have been made concerning the influence of structure on the sensitized isomerization [128, 130, 132, 206]. The results are, however, not easily understood. Relatively low d> -, values were found, the sums of d> c and d>sc, are considerably less than unity and ([e]/[t])scns does not equal Wi-c/Vc. ... 

The 9,10-anthraquinone system is a classic example of an EE mechanism, which includes a synproportionation process. Absorbance versus distance profiles were measured for this reaction and the homogeneous and heterogeneous rate constants were in agreement with those derived from cychc voltammetry [169]. Protonation of the benzophenone anion radical by benzoic add and o-cresol was studied using this technique [170]. A variety of electrode geometries were explored in determining the heterogeneous... 

The same applies to the American Cyanamid process, in which anthraquinone is produced in 90% yield from benzene by way of benzophenone by pressure car-bonylation at 40 bar with CuC /PdCb as catalyst, at 220 to 250 °C. 

The research group of Abelt has been seeking to construct photochemically active derivatives of p-cyclodextrin by capping the molecule with sulfonate derivatives of benzophenone and anthraquinone [27,28]. Under certain reaction conditions (irradiation in water or acetonitrile) the cyclodextrin itself is photo-oxidized to the aldehyde at one of the primary hydroxyls. Abelt and coworkers have used MMX [29] calculations to demonstrate the feasibility of, and perhaps even some selectivity in, the intramolecular hydrogen abstraction from this position by the covalently bound, photochemically induced radical. 

The carbonyls on naphthoquinones and anthraquinones also can abstract hydrogens from ortho substituents. One such example is a 1,2-di-r-butylanthraquinone, which undergoes the same photocy-chzation as the similarly substituted benzophenones and acetophenones as well as some butyl rearrangement. Interestingly, the ratio of cyclization to rearrangement and disproportionation is 2 1, with neither reaction of the biradical intermediate dominating, unhke the simple monoketone cases. 

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