Phenanthrene, purification

In Europe, where an abundant supply of anthracene has usually been available, the preferred method for the manufacture of anthraquinone has been, and stiU is, the catalytic oxidation of anthracene. The main problem has been that of obtaining anthracene, C H q, practically free of such contaminants as carbazole and phenanthrene. Many processes have been developed for the purification of anthracene. Generally these foUow the scheme of taking the cmde anthracene oil, redistilling, and recrystaUizing it from a variety of solvents, such as pyridine (22). The purest anthracene may be obtained by azeotropic distillation with ethylene glycol (23). 

Cohare and co-workers reported that aristolactam BU (22) was prepared, following Kupchen s method, by Perkin condensation of 6-bromo-3,4-di-methoxy phenyl acetic acid (119) and o-nitrobenzaldehyde (120) (Scheme 14). The 2-bromo-4,5-dimethoxy-2 -nitro-ds-stilbene-a-carboxylic acid (121) was obtained. The nitro group of 121 was reduced with ferrous sulfate and ammonium hydroxide, and the resulting 2-bromo-4,5-dimethoxy-2 -amino-cw-stilbene-a-carboxylic acid (122) without purification was submitted to the Pschorr phenanthrene synthesis to yield l-bromo-3,4-dimethoxyphen-anthrene-lO-carboxylic acid (123). The phenanthrylamine 124 was prepared from 123 via a Schmidt reaction, and, by treatment with n-butyllithium and CO2, 124, afforded 22 (42). 

A. Purification of phenanthrene. 1. By azeotropic distillation.2 A mixture of 300 g. of commercial phenanthrene (Note 1), 90 g. of maleic anhydride, and 600 ml. of xylene, contained in a 2-1. round-bottomed flask, is heated under reflux for 20 hours (Note 2). The initially yellow solution rapidly turns to a dark brown on heating. This solution is cooled to room temperature and filtered by suction to remove any insoluble adduct. The filtrate is then extracted with two 100-ml. portions of dilute sodium hydroxide, and the basic extracts are discarded. The organic phase is next washed with water and saturated sodium chloride solution, and finally is filtered through a layer of anhydrous magnesium sulfate. The excess xylene is removed by distillation, first at atmospheric pressure then the final portions are removed at reduced pressure. The residue, while still hot, is poured into a large mortar and, after solidification, is powdered to a convenient size. The yield of crude phenanthrene is 230-240 g. 

Almost no 9,10-diaIkoxyphenanthrenes are known, and the quantities of those few made by other methods are either small or unstated. The best alternative procedure gave 9,10-dimethoxyphenanthrene when 9,10-phenanthrenequinone was combined first with sodium in diglyme and then with dimethyl sulfate, but the yield after two chromatographic purifications was 51 %. The only other reported alkylations of phenanthrene-9,10-diol are by 1-chloro-2-diethylaminoethane in 10% yield, f and by l,2-di(bromomethyl)benzene in 22% yield. s Unlike the procedure recorded here, none of these employ two-phase alkylations catalyzed by phase transfer agents." ... 

Together with benzene and naphthalene two other hydrocarbons are obtained from coal tar though in much smaller amounts. They are anthracene and phenanthrene, both of which have the formula CuHjo. Anthracene together with phenanthrene is present in the coal tar distillate which boils above 270°. The yield of anthracene is about 0.25 to 0.45 per cent of the tar. The crude distillate is purified by a second distillation and separated into two fractions (i) A product known as 50 per cent anthracene which is crystalline and still contains phenanthrene. (2) A less volatile non-crystalline oil known as anthracene oil. The 50 per cent anthracene is largely used, just as it is without further purification, in the preparation of alizarin, itsmost important derivative. To obtain pure anthracene from the crude 50 per cent product it is first redistilled after addition of potassium carbonate which forms a non-volatile compound with a constituent known as carbazole. 

The procedure for the purification of technical phenanthrene is that of W. E. Bachmann with slight modification. 

Chemicals used in this study are listed in Table I. All chemicals were used without further purification. The purity of the naphthalene and phenanthrene were verified by measuring the melting point range of each at atmospheric pressure. 

Purification. Yields reported are not strictly comparable because of variations in the purity of the phenanthrene used, particularly with respect to the content of anthracene. Crude phenanthrenequinone can be separated easily from anthra-quinone and >thcr impurities through the water-soluble bisullile addition compound. - Thus a simple mule to pure qtiinonc at moderate cost is by bisullile piirillcalion of the 80% technical malcriiil. 

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