Octalin, from naphthalene

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. 

Use of a co-amine is embodied in an improved procedure for the preparation of A -octalin. A mixture of 0.2 mole of naphthalene and 250 ml. each of ethylamine and dimethylamine is placed in a flask fitted with a dry ice condenser, 1.65 g.-atoms of lithium wire cut in half-centimeter pieces is added all at once, and the mixture is stirred magnetically for 14 hrs. The solvent mixture is allowed to evaporate and the grayish white residue (containing excess lithium) is decomposed by cautious addition of about 100 ml. of water with cooling. The precipitated product is collected and the filtrate extracted with ether distillation affords 19-20 g. of hydrocarbon found by VPC analysis to contEiin 80% of A "-octalin and 20% of A -octalin. Isolation of the major product in pure form is accomplished by reaction of the mixture with bis-3-methyl-2-butylborane, which adds selectively to the less hindered A -isomer. Oxidation of the product with hydrogen peroxide to convert the adduct into an easily separated alcohol, followed by distillation, affords A" " -octalin of 99% purity in yield from naphthalene of 50-54%,... 

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... 

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. 

But we have noticed, in several instances, that small amounts of naphthalene arc found in the products of acid-catalyzed conversion of terpenes (unpublished results), a fact nicely explained by hydrogen tran.sfer from the octalin. 

Among the preparative routes to the octaliii mixtures, the acid-catalyzed dehydration of 2-decaloP and the metal-amine reduction of naphthalene appear most satisfactory. Apart from the purification method described in this preparation, pure A -io-octalin has also been obtained by reaction of the octalin mixture with nitrosyl chloride. After separation of the adducts by fractional crystallization, the pure A - -octalin has been regenerated from its nitrosyl chloride adduct. ... 

Naphthalene, obtained from a petroleum reformate, was chromato-graphically pure after recrystallization. The two monomethylnaph-thalenes were obtained by distillation from the same reformate. The 1-methylnaphthalene was a heart cut of 99-f% purity from a precise fractional distillation. 2-Methylnaphthalene from the same distillation was recrystallized to high purity. 1,3-Dimethylnaphthalene, 1,7-dimethylnaphthalene, and 1,8-dimethylnaphthalene were synthetic samples that were kindly donated by Dr. G. D. Johnson of Kansas State University and Dr. L. Friedman of Case Institute. The remaining isomers were obtained from commercial sources. They were treated with Raney nickel in methanol under reflux to destroy catalyst poisons such as sulfur compounds. The liquid isomers were further purified by preparative-scale gas chromatography. Octalins were prepared by reducing pure naphthalene with lithium in ethylamine (29). 

Distribution of Octalin Isomers from Random Addition of Hydrogen to Naphthalene or Tetralin... 

Table X. Analysis of the octalins (Table VIII) from the partial saturation of naphthalene on a ruthenium catalyst showed that the ratio of A > -octalin to A i -octalin closely approximated the random 4/1 and was perhaps 30 times the equilibrium ratio. Similarly, the ratio of cis-Ai> -octalin to cis-A. s-octalin was close to the random 2 to 1. However, the ratios of octalins with external double bonds (Ai>2- and A > -) to those with internal double bonds (Ai - and A i -) were lower than random. The rates of saturation of the octalins with more-exposed double bonds...

There is much evidence from early work summarised by H.A. Smith, and amply confirmed by later careful work, that naphthalene can be hydrogenated to tetralin, i.e. one of the rings could be saturated, with a high degree of selectivity on nickel and the noble metals (Table 10.5), although in some cases it declined somewhat at higher temperatures. In further hydrogenation, yields of octalin were... 

Thermodynamic reaction equilibrium for the naphthalene and tetralin hydrogenation to decalins was calculated according to Gibb s free energy change by the FLOWBAT program [12]. The results predict full conversion of both n hthalene and tetralin to decalins under the conditions studied. Moreover, thermodynamics favours the formation of trans-decalin, 93.5-96.6% in the temperature range 85-160°C [12]. The thermodynamic equilibrium of and A -octalin was not calculated since the required thermodynamic properties were not available. Weitkamp [7] has reported that the equilibrium ratio of the octalins varies from 15 to 3.5 at 0-200 C (5.9 and 3.6 at 100 and 177°C, respectively), with A -octalin the major component. 

Equation 4 was discretised by a 5-point central difference formula and thereafter first-order differential equations 1, 2, 4 and 6 were solved by a backward difference method. Apparent reaction rate was solved by summing the average rates of each discretisation piece of equation 4. The reactor model was integrated in a FLOWBAT flowsheet simulator [12], which included a databank of thermodynamic properties as well as VLE calculation procedures and mathematical solvers. The parameter estimation was performed by minimising the sum of squares for errors in the mole fractions of naphthalene, tetralin and the sum of decalins. Octalins were excluded from the estimation because their content was low (<0.15 mol-%). Optimisation was done by the method of Levenberg-Marquard. 

---