Reduction of Anthracene in DMF

The reduction of anthracene (abbreviated A, C14H10, Fig. 7.9) in the aprotic solvent dimethylformamide (DMF) has been studied by B.S. Jensen etal [J.Am. Chem. Soc. 97 (1975) 5211]. The comparative voltammetry in the presence of differing concentrations of phenol has been discussed by J.-M. Saveant in Elements of Molecular and Biomolecular Electrochemistry [(2006) John Wiley and Sons]. Exemplar voltammetry is given in Fig. 7.10. 

The addition of phenol provides a source of protons and therefore disrupts the EE mechanism by introducing possible irreversible follow-up kinetics. In particular, the anthracene radical anion is prone to protonation  

The resulting AH radical is more easily reduced than anthracene, and therefore is rapidly reduced and protonated again to yield AH2. The initial protonation is rate-determining for the overall two-electron transfer, and so both electron transfers are observed in a single voltanmietric wave, which may be shifted to more positive potentials by accelerating the protonation process, e.g. by elevating the concentration of phenol. 

Because the product AH2 (Fig. 7.11) is neither acidic nor electroactive in the potential range studied, its formation is electrochemically irreversible. In the presence of phenol, no peaks are observed in the reverse sweep of the voltammogram, indicating that electroactive product materials such as A are fully depleted by the coupled homogeneous chemistry. 

As discussed in Problem 7.7, conventional voltammetry cannot distinguish this reaction from the case where AH reacts heterogeneously to gain an electron at the electrode surface, followed by further protonation to form AH2. The disproportionation is thermodynamically favoured if 

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Fig. 2 Reduction of /-BuBr in DMF. Left electrochemical reduction. Right reduction by anthracene anion radical. O experimental data, oblique lines theoretical predictions.

To demonstrate the utility of SECM measurements, the reduction of anthracene (AC) in DMF in the presence of phenol (PhOH) was studied, as an example of a DISP1 process, yielding 9,10-dihydroanthracene (ACH2) (40,41) ... 

FIGURE 2.34. a Reductive cyclic voltammetry of an aromatic hydrocarbon (e.g., anthracene) in an aprotic solvent (e.g., DMF) upon successive additions of a weak acid (e.g., phenol), b Thermodynamics of the combined addition of two electrons and two protons. 

It is clear that deuterium as a substituent has the electron-donating effect. In other words, it can decrease electron affinity of the whole molecule. Potentials of reversible one-electron reduction for naphthalene, anthracene, pyrene, perylene, and their perdeuteriated counterparts indicate that the counterparts exhibit slightly more negative potentials (Goodnow and Kaifer 1990, Morris and Smith 1991). For example, the measurable differences in the reduction potentials are equal to -13 mV for the pair of naphthalene-naphthalene-dj or -12 mV for the pair of anthracene-anthracene-djo. The possible experimental error does not exceed 2 mV (Morris and Smith 1991). In another example, in DMF with 0.1 M n-Bu4NPFg, the deuterated pyrenes were invariably found to be more difficult to reduce than pyrene itself. The largest difference observed, 12.4 mV, was between perdeuteriated pyrene and pyrene bearing no deuterium at all with standard deviations between 0.2 and 0.4 mV (Hammerich et al. 1996). 

Fig. 5 Typical normalized voltammetric curves for homogeneous redox catalysis. The figure shows experimental data for the catalytic of reduction of DTBP by anthracene (ImM in DMF/O.IM TEAP at 25°C). The voltammetric curves were obtained, from left to right, at scan rates of 0.02, 0.05, 0.1 and 0.2 Vs . respectively. The concentrations of DTBP are, from bottom to top (a) = 0. (b)==1.0, and (c) = 2.0mM. All currents are normalized to...

In several examples the reductive halide-hydrogen exchange has been studied on a preparative scale. For example, the indirect electroreduction of 2-chloropyridine in DMF using anthracene as mediator gives pyridine in 83-86 % yield 2 . For the dehalogenation of 1-chlorohexane (80% yield), naphthalene is applied as redox catalyst. Similarly, 6-chloro-hexene yields 1-hexene (60%) and methylcyclopentane (25%), which is the product of the radical cyclization . The indirect electrochemical reduction of p- and y-bromocarboxylic esters forms coupling and elimination products besides the dehalogenated products... 

Reductive acylation. Treatment of anthracene and a dicarboxylic acid chloride with magnesium in DMF leads to the dibenzo bridged diketone product. ... 

The indirect reduction of tosyl esters can be performed7 in non-aqueous solutions. Thus, for example, the anthracene anion radical formed by cathodic reduction in DMF/TBAB (tetrabutylammonium bromide) electrolyte may reduce tosylates in solution. Similarly, the pyrene anion radical was shown8 (Figure 1) to react also with ethyl tosylate. The redox catalysis general scheme (indirect reduction by a redox P/Q couple) where P is a reducible species and Q its stable reduced form can be written as below ... 

The first example has been reported of the photofixation of COg in a non-biological system this involves the formation of 9,10-dihydrophenanthrene-9-carboxylic acid from irradiation of the phenanthrene-amine-COa system in DMSO or DMF.71 Both aliphatic and aromatic amines are effective, but the polarity of the solvent is important and the reaction does not occur in THF, dioxan, or n-hexane. Yields of carboxylic acids (up to 46%) have been reported and seemingly anthracene, pyrene, naphthalene, and biphenyl also undergo this reductive carboxylation. 

The diminution of electrode fouling in oxido-reductive mode is shown in Fig. 22. Other ECL systems were also examined and sonoelectrochemical enhancement was observed for luminol (3-aminophthalhydrazide). This system has been thoroughly studied for the detection of low concentrations of residual hydrogen peroxide in contact-lens cleaning solutions. The ECL intensity of 9,10-diphenyl-anthracene in sonicated DMF solutions was increased by factors of 20-30 depending on the concentration of the solutions, ultrasound power, and fre-quencyT Similar effects were observed from l,5-diphenyl-3-styrylpyrazoline, rubrene, 9,10-dimethyl-anthracene, and perylene. ... 

Highly reactive calcium can be readily prepared by the reduction of calcium halides in tetrahydrofuran (THF) solution with preformed lithium biphenylide under an argon atmosphere at room temperature [2]. This colored calcium species seems to be reasonably soluble in THF. However, the reactive calcium complex prepared from preformed lithium naphthalenide was insoluble in THF solution and precipitated out of solution to give a highly reactive black solid. As this lithium naphthalenide generated calcium species was insoluble in most deuterated solvents and reacted with deuterated DMSO and DMF, the exact nature of this black calcium complex has not been determined. Acid hydrolysis of the black material releases naphthalene as well as THF. Accordingly, the most likely structure of the black material is a Ca-naphtha-lene-THF complex similar in nature to the soluble magnesium-anthracene complex reported [3]. 

The cis- 1,2-glycols, obtainable from the parent aromatic hydrocarbon by osmium tetroxide hydroxylation, can be converted to the corresponding trans-1,2-glycols by oxidation-reduction, using a mixture of dimethyl sulfoxide, sulfur trioxide, and pyridine, followed by lithium aluminum hydride reduction. The trans- 1,2-glycols can be dehydrated to arene oxides using DMF-DMA as mentioned above. Benzo[a]pyrene 4,5-oxide (28) and 7,12-dimethylbenz[a]anthracene 5,6-oxide (30) have been prepared by this method in 68 and 80% yields, respectively.18... 

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