Reduction of naphthalene

As previously described, a mixture of and J -octalins can be prepared by the reduction of naphthalene or Tetralin. Another route to this mixture is the dehydration of a mixture of 2-decalol isomers. This latter route has certain advantages in that one can avoid the handling of lithium metal and low-boiling amines. Moreover, 2-decalol is available commercially or can be prepared by the hydrogenation of 2-naphthol (5). In either case a comparable mixture of octalins is obtained, which can be purified by selective hydroboration to give the pure J -octalin (Chapter 4, Section III). 

Many expensive reductions such as the Birch reduction of naphthalene to isotetralin, benzene to cyclohexene, with metallic sodium and liquid ammonia, or reduction with LiAlHa, can generally be carried out electrochemically at much lower cost and under safe conditions. Electrochemical processes allow fluorinations to be carried out without using fluorine gas. Conducting polymers have been made by electrochemical processes which operate under ambient conditions, and the polymer can be synthesized, doped and shaped in film form in a single step. 

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. 

Compounds of this type may only be isolated in the presence of suitable donor molecules, among those, diglyme has been used frequently, but other examples include TMEDA or 2,2,1-crypt for sodium.150 The reduction of naphthalene or anthracene with sodium in diglyme affords separated ions with the radical anion [Na(diglyme)2][naphthalene/anthracene] 139, 140.151... 

In all the above sequences, single isomers are produced by careful control of the reaction conditions combined with purification by selective isolation at various points in the synthesis. Occasionally two isomers are produced which give dyestuffs that have very similar properties in these cases it is often quite acceptable and economically beneficial not to separate the individual components but to use the total mixture in dye preparation. An example is the mixture of l-naphthylamine-6- and 7-sulphonic acids (4.46 mixed Cleve s acids), which arises by nitration and reduction of naphthalene-2 Sulphonic acid (Scheme 4.30). 

The procedure described for the Birch reduction of naphthalene is a modification of the methods previously developed by Birch,5 Hiickel,2 and Grob.6 Apart from this reduction, no other practical approaches to isotetralin have become known. The scale employed in the present procedure is not mandatory to achieve optimum yields. Equally good yields were realized when the runs were halved or enlarged up to fourfold. In the latter case, however, the apparatus already reaches pilot plant dimensions. 

Under nominally aprotic conditions, 1,2-protonation dominates in naphthalene. Reduction of naphthalene in anhydrous acetonitrile containing tetraethylammo-nium p-toluenesulfonate yields 1,2-di-hydronaphthalene, which is subsequently... 

The well-known instability of the disulhde anion-radicals, (R SSR ), is apparently explained by the antibonding electron population, presumably in the framework of the disulfide bond. In some cases, these anion-radicals turned out to be more or less stable (Breitzer et al. 2001). Two examples are shown in Schemes 3.25 and 3.26 that needs to be distinguished. First, one-electron reduction of naphthalene-l,8-disulhde generates the corresponding anion-radical (Scheme 3.25). 

Many reductions with sodium are carried out in boiling alcohols in methanol (b.p. 64°), ethanol (b.p. 78°), butanol (b.p. 117-118°), and isoamyl alcohol (b.p. 132°). More intensive reductions are achieved at higher temperatures. For example reduction of naphthalene with sodium in ethanol gives 1,4-dihydronaphthalene whereas in boiling isoamyl alcohol tetralin is formed. 

Radical ion pairs also react by proton, atom, or group transfer. We illustrate proton transfer in reactions of aromatic hydrocarbons with tertiary amines. These reactions cause reduction or reductive coupling. In the reduction of naphthalene, the initial ET is followed by H" transfer from cation to anion, forming 67 paired with an aminoalkyl radical the pair combines to generate... 

Notably, Zn2+ ions are more easily reduced than naphthalene. This indicates that the electroreduction of the latter is very likely achieved on a recovered electrolytic zinc cathode. What happens under these conditions So far, no data allow us to answer this question. The only information is the experimental observation of a characteristic transient color of the naphthalene anion radical indicating the reduction of this hydrocarbon, simultaneously with the reduction of Zn2+, owing likely to a too high current density set at the cathode11. Moreover, the presence of an alkyl halide under such conditions would lead to its reduction on the zinc deposit, and this reduction would occur more easily than the reduction of naphthalene according to complex processes (equation 25). 

This reaction principle was also extended to a number of substituted benzene derivatives 386.39°-39i) xhus, the reduction of p-xylene (Hg cathode, N-methylpyrroli-done-H20—Bu4NBr electrolyte) yields 1,4-dimethylcyclohexadiene with a current efficiency of about 80% 393). A number of papers have also been published on the reduction of naphthalene 394 397> ... 

The cathodic reduction of naphthalene (40) has been the topic of numerous studies 58 60). However, most were concerned with the mechanism of the initial electron-proton transfers. For example, in 0.5 M (C4Hg)4NBF4 in DMF — 1.8% HzO naphthalene exhibited 61) one polarographic wave, Ei/Z = —2.56 V(SCE). 

The reduction of naphthalene was also performed in acetonitrile-water with... 

Reduction of naphthalene under conditions suitable for reduction of isolated benzene rings resulted, as expected, in the formation of some 1,4,5,9-tetrahydronaphthalene (44). It was carried out12) in 15% aqueous (C4H9)4NOH at 80 °C and the yield of the products and the low current efficiency (17% naphthalene remained unreacted in spite of the transfer of large excess charge) were caused by anodic side reactions, as the experiment was conducted in an undivided cell. 

Vlieger JJ, Kieboom PG, van Bekkum H. Metal-ammonia reduction of naphthalene at -33°C formation of oligomeric compounds. J Org Chem 1986 51 1389. 

I With THF as the solvent similar results were obtained. Acidic proton donors, such as phenol, did not sustain reduction of naphthalene. 

Lithium dissolved in amines of low molecular weight constitutes a useful and convenient reagent for reducing aromatic hydrocarbons to monoolefins.6 Although mixtures of isomeric olefins are usually obtained with primary amine solvents, the use of secondary amines as cosolvents dramatically increases the selectivity of these reductions so that the more thermodynamically stable olefin usually becomes the predominant product. Thus, in the reduction of naphthalene, the amount of A9,10-octalin increases from 52% when pure ethylamine is the solvent to 80-82% when the solvent is an ethylamine-dimethylamine mixture. As another example, the reduction of f-butylbenzene with lithium in pure ethylenediamine produces a product containing 70% of 1-f-butylcyclohexene.7 When a mixture of ethylenediamine and morpholine is used as the reaction solvent, the product contains 84% of 1-f-butyleyclohexene.8... 

Naphthalene is readily hydrogenated to tetrahydronaphthalene, which is used as a paint solvent, but further reduction to produce decahydro-naphthalene (decalin) requires forcing conditions (Raney nickel catalyst at 200 °C). The first step in the reduction of naphthalene can be achieved by reaction with sodium in boiling ethanol, which produces 1,4-dihy-dronaphthalene. The tetrahydro compound is formed in the higher-boiling 3-methylbutanol (isopentyl alcohol) (Scheme 12.4). 

Dehydrogenatioa, Vogel ei al. present procedures for the synthesis of tricyclo-[4.4.1.0 ]undeca-3,8-diene (C) by reduction of naphthalene to isotetralin (A), addition of dichlorocarbene (B), and dechlorination (C). Dehydrogenation with DDQ in... 

The high electron-donating ability of McjSiNa causes reduction of naphthalene [Eq. (22)] (30a). 

The activating influence of the trimethylsilyl function is also apparent in the reduction of naphthalene derivatives (Scheme 40). The 1,4-disilyl derivative (201) is reduced exclusively in the substituted ring to give (202), while 2-trimethylsilylnaphthalene (203) affords a 4 1 mixture of (204) and (205), respectively. " As would be expected, the reduction of C-silylbenzoic acids and their esters is controlled by the carboxy function."... 

Direct reduction of naphthalene 1,4-quinone with diisobutylaluminum hydride produces the free cis-1,4-dihydrodiol. C -naphthalene dioxide 153 and compound 158 have been obtained by the photooxidation of l,6-imino[10]annulene, followed by thermal isomerization and reaction with nitrosylchloride. An inter-... 

Under nominally aprotic conditions, 1,2-protonation dominates in naphthalene. Reduction of naphthalene in anhydrous acetonitrile containing tetraethyl ammonium p-toluenesulfonate yields 1,2-dihydronaphthalene, which is subsequently reduced to tetralin [169]. Similarly, reduction of I in anhydrous DMF gives 1,3,5-cyclooctatriene almost exclusively [53]. The formation of the thermodynamically more stable products is most probably due to base-catalyzed isomerization. 

Reductive coupling, in aprotic solvents, of aromatic hydrocarbons with CO2 has long been known. Reduction of naphthalene in DMF in the presence of COo leads to 1,4-dicarboxy-1,4-dihydronaphthalene ( 50%) [246]. Under similar conditions, phenanthrene gives fra725-9,10-dicarboxy-9,10-dihydrophenanthrene ( 30%) [246]. Carboxylation of aromatic halides can be achieved in aprotic solvents either by using transition metal catalysts or by direct reduction using sacrificial anodes in undivided cells (cf. Chapter 8). 

Reduction of naphthalene by Li metal in C2HSNH2 gives a 52% yield of 1,2,3,4,5,6,7,8-octahydronaphthalene. (a) What will this compouhd yield upon ozono-lysis ... 

Dauben and Bertelli synthesized heptalene (9) starting with reduction of naphthalene-1,5-dicarboxylic acid (4) with sodium and ethanol in liquid ammonia to the... 

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