Naphthalene homogeneous catalysis

Homogeneous catalysis by gold is not new [13,19], however, and even before 2004 there were about a hundred published papers on this topic, the first being the chlorination of naphthalene to octachloronaphthalene using AuCl or AuClj, in 1935 [2]. The gold compounds were among the most active catalysts (but it is now known that other Lewis acid catalysts, such as ferric chloride, are superior for this reaction). 

Figure 2. (A) Dependence on A of the logarithm of the rate constants of reoxidation of the following radical anions (with increasing A ) biphenyl, 1-methylnaphthalene, naphthalene, 2-methylphenanthrene, phenanthrene, / -etrphenyl, and benzonitrile in the presence of chlorobenzene. From Ref. [7]. (B) Rate constants of the homogeneous electron exchange between chlorobenzene and redox catalysis as functions of the half-wave potential difference and of the standard potential difference (at room temperature in the considered solvent =). With increasing AE biphenyl, naphthalene, dibenzothiophene, phenanthrene, / -toluonitrile, m-toluonitrile, /7-terphenyl, and benzonitrile. From Refs 1 and 2.

Indirect reductions are also permitted because species (radical anions and/or dianions) formed after homogeneous electron transfer are so basic that they are rapidly protonated by solvent or any acidic impurities. Thus, dienes and trienes like allocimene and dimethyl 2,3-butadiene may afford a redox catalysis processes [42] in dimethylforma-mide (DMF) in the presence of naphthalene as a mediator. 

The catalytic properties of V-HMS were investigated in detail by Reddy et al. [44], Naphthalene and 2-methylnaphthalene were oxidized at the 1,4-positions to afford the related 1,4-naphthoquinones. Under analogous conditions, 2,6-DTBP (83 % conv.) led to the corresponding p-quinone (87 %) and p-diphenoqui-none (4 %). The relative role of homogeneous and heterogeneous pathways in catalysis remained uncertain, because different amounts of V ions were released into the liquid phase under different conditions. 

It should also be mentioned that SUP catalysis has not only been successfully applied for the immobilisation of homogeneously dissolved transition metal conplexes but also for acidic catalysis. The first example of an immobilised acidic chloroaluminate(III) on a support was reported, as early as 2000, by Holderich and co-workers for the allqrlation of different aromatics (benzene, toluene, naphthalene and phenol) [85]. The acidic ionic liquid... 

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