Naphthalene, preparation from tetralin

The reactions of tetralin in the presence of coal were investigated to determine the extent of conversion along various pathways in the absence of further added catalysts. As may be seen from Figure 1, the yield of products generated under typical liquefaction conditions (450°C, 30 minutes) increases with the amount of coal added. Three products arise from tetralin naphthalene, n-butylbenzene, and 1-methylindan. Positive identification of the latter isomer was made by comparison of gas chromatographic retention times with those of authentic samples of 1- and 2-methylindan prepared by independent synthesis. 

Commercial tetralin contains naphthalene as the principal impurity and this interferes with the preparation of tetralin-1-hydroperoxide or with use of the hydrocarbon as hydrogen donor in hydrogen-transfer reactions. An early purification procedure is uninviting fractionation extraction in turn with mercury (to remove sulfur impurities), with mercuric acetate solution (to remove olefins), and with sulfuric acid fractionation. More recently Bass sulfonated the crude hydrocarbon with coned, sulfuric acid and added ammonium chloride to precipitate ammonium tetralin-6-sulfonate. The salt was crystallized until pure and hydrolyzed by steam distillation from sulfuric acid solution. Distillation from sodium gave material showing no ultraviolet bands characteristic of naphthalene. 

The structural elucidation of dihydroxyserrulatic acid (120) required evidence for the tetralin ring and the relative arrangement of the substituents around it. To this end, the dimethoxy derivative was deoxygenated at Cl6 and the resulting compound was dehydrogenated with DDQ to provide a naphthalene (121). The orientation of substituents on the aromatic ring and the stereochemistry of the side chain double bond was inferred from spectroscopic analysis. Confirmation of the structure and the relative stereochemistry of the three asymmetric carbons was obtained by an X-ray diffraction study of 120. The absolute stereochemistry was determined by conversion of the methoxy naphthalene (121) to 5-(-)-4-(l, 5 -dimethylhexyl)-l,6-dimethylnaphthalene (122) which proved identical to, except for the sign of optical rotation, a synthetic sample of the / -enantiomer (123) prepared from / -citronellal (Scheme 29) (102). 

Autoxidation may in some cases be of preparative use thus reference has already been made to the large-scale production of phenol+ acetone by the acid-catalysed rearrangement of the hydroperoxide from 2-phenylpropane (cumene, p. 128). Another example involves the hydroperoxide (94) obtained by the air oxidation at 70° of tetrahydro-naphthalene (tetralin) the action of base then yields the ketone (a-tetralone, 95), and reductive fission of the 0—0 linkage the alcohol (a-tetralol, 96) ... 

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. 

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