Decalins, from naphthalene

The dehydrogenation of decalin to naphthalene has been investigated on Pt/C, Pt/A1(0H)0 and Pt/Al203 catalysts. The maximum conversion of decalin on 3.9% Pt/C, which did not repel decalin, was observed at 483 K under the conditions of 0.3 g of the catalyst and 1ml of decalin, which was corresponded to the liquid film state under reactive distillation conditions. However such a maximum was not observed on Pt/Al(OH)0 and Pt/Al203, which repelled decalin. Furthermore it was found that the reaction temperature, at which the maximum hydrogen evolution was observed on Pt/C, was shifted from the boiling point of decalin to that of naphthalene with increasing the amormt of naphthalene in the reaction solution. 

The catalysis pair of decalin dehydrogenation/naphthalene hydrogenation is usable as a hydrogen storage medium loaded in hydrogen vehicles. Here, the power density obtainable from decalin is the most significant factor for the onboard application. 

Usually o.v-dccalin is formed more selectively from tetralin than from naphthalene. Baker and Schuetz obtained a mixture of 77% cis- and 23% frans-decalin in the hydrogenation of naphthalene over Adams platinum oxide in acetic acid-ether at 25°C and 12.8 MPa H2, while cA-decalin was obtained exclusively in the hydrogenation of tetralin in acetic acid under similar conditions.23... 

Naphthalene is reduced to 1,4-dihydronaphthalene by sodium and alcohol. Isomerization of this product to 3,4-dihydronaphthalene occurs with sodamide in liquid ammonia. Tetrahydronaphthalene (tetralin) is formed from naphthalene by sodium in amyl alcohol or by reduction with nickel-aluminum alloy and aqueous alkali. Catalytic hydrogenation of naphthalene can be stopped at the tetralin stage over copper chromite, Raney nickel, or alkali metal catalysts. cis-Decahydronaphthalene is produced by high-pressure hydrogenation of tetralin over Adams catalyst, whereas a mixture of cis- and trans-decalins is obtained from naphthalene under the same conditions. ... 

Further evidence for cw-hydrogenation with this catalyst is that all cw-cyclo-hexane-dj (I) is obtained from CeD and only cw-decalin (II) is obtained from naphthalene. ... 

Sen and coworkers have examined systems based on Pd(OAc)2 in triflic acid (TfOH) at 80 °C (equation 5). Na2Cr207/Pd(0Ac)2/Tf0H aromatizes cyclohexanes for example, decalin gives naphthalene (9%) and a-tetralone (4%). Normally the functionalization product of an alkane is more reactive than the alkane itself and so only the low conversion prevents the initial product from being oxidized further. Shilov and Sen s use of triflic acid in this context means that the initial functionalization product at the alcohol oxidation level is protected as the triflate ester, which is relatively insensitive to oxidation. 1,4-Dimethylbenzene is oxidized to triflates with a 50 1 preference for oxidation at the ring rather than of the side chain, unlike the selectivity expected in a radical process. A kinetic isotope effect of 5 was measured. In certain cases the reaction can be... 

The formation of the naphthalene (73) from the bis-ylide (72) and diethyl ketomalonate involves an unusual olefin synthesis on the carbonyl of an ester group. The methylene-pyrans (75) were formed when the diethyl malonates (74) were refluxed with j3-keto-ylides in xylene or decalin. Possible intermediates are the ketens (76) and the allenes (77). Addition of ylide to the allenes gives the betaines (78) which form methylene-pyrans either directly or via acetylenes as shown. 

Naphthalene itself is solid at ambient temperatures (m.p. 80.5°C) but is dissolved easily in aromatic compounds such as toluene (refer Table 13.1) [10,12], so that the oily mixture can be handled as a "naphthalene oil." The naphthalene oil is catalytically hydrogenated to decalin and methylcyclohexane simultaneously. Decalin and methylcyclohexane are converted into hydrogen and naphthalene oil again by dehydrogenation catalysis. From the handling viewpoint, the naphthalene oil may be deemed as a preferential and practical material for hydrogen storage and transportation. 

Because the cis-decalin molecule extends its two methine carbon-hydrogen bonds on the same side in contrast to frans-decalin, the carbon-hydrogen bond dissociation of adsorbed decalin would be advantageous to the cis-isomer on the catalyst surface (Figure 13.17). A possible reaction path by octalin to naphthalene in dehydrogeno-aromatization of decalin will be favored to the cis-isomer, since its alkyl intermediate provides the second hydrogen atom from the methine group to the surface active site easily. 

In the present estimation, a continuous dehydrogenation reactor in which decalin is supplied to the catalyst at various feed rates without internal refluxing is assumed. Here all the condensable products and unconverted decalin were removed from the reactor to the condensation part (see Figure 13.22). Now, the stationary rates of hydrogen generation (VH), naphthalene formation (VN), and evaporation of unconverted decalin (VD) are defined as the magnitudes per area of the catalyst layer (mol/m2h). All these rates are expressed from mass balance as follows . 

Cyclization to five-membered rings forms the alkylindans and indenes cyclization to six-membered rings gives tetralins and naphthalenes. Tetralins and decalins, however, were not observed in any of the experiments, because of unfavorable equilibrium. For example, less than 0.02-0.1% tetralin and less than 0.001% decalins would be expected if they were in equilibrium with the naphthalene formed in the n-butylbenzene experiments. [Equilibrium conversions calculated from the data of Egan (15), Allam and Vlugter (16), and Frye and Weitkamp (17)]... 

The molecules only contain kata-condensed molecules, i.e. molecules with the rings fused together in the same way as in naphthalene, anthracene, phenanthrene and the corresponding saturated compounds such as decalin. The consequences of deviations from these assumptions will be discussed later. 

The results described above illustrate the problem of separating effects due to catalysis provided by pyrrhotite from those due to the chemistry of the reduction of pyrite. It must also be borne in mind that reduction of pyrite produces a nearly equivalent amount of l S, which remains available to enter subsequent reactions by mechanisms now only poorly understood. In order to remove these complications, pyrrhotite was prepared by the reduction of pyrite with tetralin, isolated from the reaction residue, and then heated with fresh tetralin. Figures 4 and 5 contain the yields of naphthalene and 1-methylindan, and the ratios of trans- to cis-decalin as a function of concentration. In this case, the pyrite was a hand-picked sample of micro-crystals taken from a coal nodule. As may be seen, the yields of naphthalene and 1-methylindan, and the ratio of trans- to cis-decalin all increase with pyrite concentration. The slope of the line for naphthalene yield is 0.91. A slope of 0.53 is calculated for stoichiometric reduction of FeS to FeS by tetralin to yield naphthalene. Thus, roughly half of the naphthalene produced can be accounted for by the demand for hydrogen in the reduction of pyrite. 

The stereochemistry of hydrogenating naphthalene is described in Weitkamp s review. Mainly cis-decalin is formed when the hydrogenation is catalyzed by platinum metals under relatively mild conditions ruthenium is the most stereoselective (95-98% cis) while palladium is the least. The t/ans-decalin which is formed appears to result from the reduction of octalin intermediates via a mechanism similar to that which accounts for the formation of frans-dialkylcyclohexanes from dialkylbenzenes. 

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