Anthracene reduction

Fig. 46. (a) Transmission spectrum of anthracene, KBr pellet, (b) SNIFTIRS difference spectrum for anthracene reduction to the anion radical. Platinum electrode in 0.1 M TBAF in acetonitrile. Modulation potential —1.50 to —2.50 V vs. Ag/Ag+ reference. 

The first tris(arene) niobium complex, [Nb(l-4-jj -anthracene)3], prepared by the Na or K anthracene reduction of NbCl4(THF)2, undergoes facile anthracene displacement in the presence of CO to afford [K(18-crown-6)(THF)2][Nb(CO)6]. Reduction of TaCls by sodium naphthalene provides [Na(THF)][Ta(jj -naphthalene)3], the first homoleptic naphthalene complex of a third row transition metal. This complex reacts with CO and anthracene to give [Ta(CO)e] and [Ta(l-4-jj -anthracene)3], respectively. The latter product reacts with cyclooctatetraene (COT) to give [Ta(COT)3]-.==i= ... 

By comparison, the radical species AH aheady exists in a non-aromatic 13 re form the resonance structure of two separated 6jre systems (Fig. 7.12) and a localised radical on an sp carbon is also relatively stabilised and therefore should predominate. The addition of a further electron to this relatively localised orbital does not significantly alter the aromaticity of the molecule or the general geometry and is therefore much less thermodynamically disfavoured than anthracene reduction, such that its formal potential is more positive. 

Anthracene and Related Compounds. The formation of anthracene by elimination of hydride from 9,10-dihydroanthracene has been reported in the preceding section. An improved high-yield synthesis of 7,12-dimethylbenz-[ajanthracene (336), a compound of biological interest, utilizes the reaction of 7,12-benz[a]anthraquinone with MeLi. Subsequent reaction with dry HCl in ethyl acetate produces 7-(chloromethyl)-12-methylbenz[a]anthracene, reduction of which gives (336). 

Reduction of anthraquinone gives dianthryl, anthrone and finally anthracene. 

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Only the reduction products involving the keto groups are of any academic or industrial importance. Complete reduction of the keto groups by ammonia and zinc (von Perger method) gives rise to anthracene in good yields and quaUty (10). This method is of importance since substituted anthracenes can be prepared from the corresponding anthraquinones. Industrially, an important dyestuff intermediate, 3-chloroanthracene-2-carboxyhc acid, (2) is prepared by this method (11) from 3-chloroanthraquinone-2-carboxyhc acid [84-32-2]... 

The synthetic procedure described is based on that reported earlier for the synthesis on a smaller scale of anthracene, benz[a]anthracene, chrysene, dibenz[a,c]anthracene, and phenanthrene in excellent yields from the corresponding quinones. Although reduction of quinones with HI and phosphorus was described in the older literature, relatively drastic conditions were employed and mixtures of polyhydrogenated derivatives were the principal products. The relatively milder experimental procedure employed herein appears generally applicable to the reduction of both ortho- and para-quinones directly to the fully aromatic polycyclic arenes. The method is apparently inapplicable to quinones having an olefinic bond, such as o-naphthoquinone, since an analogous reaction of the latter provides a product of undetermined structure (unpublished result). As shown previously, phenols and hydro-quinones, implicated as intermediates in the reduction of quinones by HI, can also be smoothly deoxygenated to fully aromatic polycyclic arenes under conditions similar to those described herein. 

To demonstrate the effect in more detail a series of experiments was carried out similar to that of volume overload, but in this case, the sample mass was increased in small increments. The retention distance of the front and the back of each peak was measured at the nominal points of inflection (0.6065 of the peak height) and the curves relating the retention data produced to the mass of sample added are shown in Figure 7. In Figure 7 the change in retention time with sample load is more obvious the maximum effect was to reduce the retention time of anthracene and the minimum effect was to the overloaded solute itself, benzene. Despite the reduction in retention time, the band width of anthracene is still little effected by the overloaded benzene. There is, however, a significant increase in the width of the naphthalene peak which... 

Thus, 9,10-diphenylanthracene ( p = — 1.83 V vs. SCE) is reduced at too positive a potential and hence its rate of reaction with the sulphonyl moieties is too low. On the other hand, pyrene (Ep = — 2.04 V) has a too negative reduction potential and exchanges electrons rapidly both with allylic and unactivated benzenesulphonyl moieties. Finally, anthracene Ev = —1.92 V) appears to be a suitable choice, as illustrated in Figure 3 (curves a-d). Using increasing concentrations of the disulphone 17b, the second reduction peak of XRY behaves normally and gives no indication of a fast electron transfer from A. 

The correct potential for a preparative electrolysis is normally chosen by inspection of a steady state current-potential (i-F) curve. Figure 1 shows a typical i-E curve for the reduction of anthracene at a mercury cathode in dimethylformamide (Peover et al., 1963) the curve shows two reduction waves. In the potential range where the current rises with variation of the potential, the rate of an electron transfer process is increasing while in the plateau regions the rate of the electron transfer... 

Fig. 1. i-E curve for the reduction of anthracene at a dropping mercury electrode in acetonitrile containing 01m tetraethylammonium perchlorate. 

Figure 17.7 Electrocatalysis of O2 reduction by Pycnoporus cinnabarinus laccase on a 2-aminoanthracene-modified pyrolytic graphite edge (PGE) electrode and an unmodified PGE electrode at 25 °C in sodium citrate buffer (200 mM, pH 4). Red curves were recorded immediately after spotting laccase solution onto the electrode, while black curves were recorded after exchanging the electrochemical cell solution for enzyme-fiiee buffer solution. Insets show the long-term percentage change in limiting current (at 0.44 V vs. SHE) for electrocatalytic O2 reduction by laccase on an unmodified PGE electrode ( ) or a 2-aminoanthracene modified electrode ( ) after storage at 4 °C, and a cartoon representation of the probable route for electron transfer through the anthracene (shown in blue) to the blue Cu center of laccase. Reproduced by permission of The Royal Society of Chemistry fi om Blanford et al., 2007. (See color insert.)...

Ni CL, Abdalmuhdi I, Chang CK, Anson FC. 1987. Behavior of four anthracene-linked dimeric metalloporphyrins as electrocatalysts for the reduction of dioxygen. J Phys Chem 91 1158. 

The same nonpolar conformation can be achieved by conversion to bicyclic structures. 1,4-Cyclo-addition of ethylene to anthracene-9-carboxylic acid gives acid 68. Successive conversion to the N-methylamide, via the acid chloride, followed by reduction with lithium aluminum hydride produced... 

Lengthening the side chain produces the antidepressant maprotiline (73), which has a topological relationship to the clinically useful tricyclic antidepressants. The requisite acid is constructed by conjugate addition of the carbanion of anthrone (64) to acrylonitrile, followed by hydrolysis to give 70. Reduction of the carbonyl group with zinc and ammonia gives anthracene 71 by dehydration of the intermediate... 

The HO—LU interaction came early to the notice of theoreticians. Hiickel 74> pointed out the role of LU in the alkaline reduction of naphthalene and anthracene. Moffitt 75> characterized the formation of S03, SO2CI2, etc. by the reactions of SO2 as an electron donor with the S-atom-localiz-ing character of HO MO. Walsh 76) considered that the empirical result of producing nitro compounds in the reaction of the nitrite anion with the carbonium ion should be attributed to the HO of the NO2 anion which is localized at the nitrogen atom. 

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