Naphthalene product purification

Since the presence of even 5-10% of unchanged 1-bromo-naphthalene makes purification of the naphthalene difficult, it is important that the reduction be complete before the product is isolated. With reaction conditions described in this preparation [0.100 mole of ethylenediamine, 0.0080 mole of 1-bromonaphthalono, 60 ml. (0.031 mole) of aqueous 0.5193/... 

Ortho-xylene may be oxidized directly by air in vapor phase over vanadium pentoxide catalysts under conditions resembling those used in oxidation of naphthalene to phthalic anhydride. The stability of the cyclic anhydride structure of phthalic anhydride at the temperatures required and in the presence of oxidizing conditions is, of course, the distinctive feature. Since the oxidation of o-xylene to phthalic anhydride requires the theoretical interaction of only six atoms of oxygen relative to the nine required by naphthalene, the amount of heat generated per unit of product is less, and the volume of diluent gases in the product stream may be lower. Because of decreased formation of quinones and color bodies, product purification should be easier. Very little is available by way of information relative to commercial operating conditions. Some laboratory results of early work showed a maximum conversion to total acids of 18.2 per cent when commercial xylene was oxidized in vapor phase over unfused vanadium oxide catalyst. Recent work with o-xylene showed a conversion of 42.7 per cent to phthalic anhydride over unfused vanadium oxide catalyst and conversions up to 61.7 per cent to phthalic anhydride plus fi.6 per cent to maleic... 

Figure 22-8 shows the features of a horizontal center-fed column [Brodie, Au.st. Mech. Chem. Eng. Tran.s., 37 (May 1979)] which has been commercialized for continuous purification of naphthalene and p-dichlorobenzene. Liquid feed enters the column between the hot purifying section and the cold freezing or recovery zone. Ciystals are formed internally by indirect cooling of the melt through the walls of the refining and recovery zones. Residue liquid that has been depleted or product exits from the coldest section of the column. A spiral conveyor controls the transport of solids through the unit. 

Under N2, clean Li metal (0.17 g, 25 mmol) was placed in a round-bottom flask with a solvent mixture of MeOH (3 mL) and pcntan-t-ol (17 mL). The mixture was heated under N, until the reaction with Li was complete. Then, naphthalene-2,3-dicarbonitrilc (2 g, 11 mmol) was added to the mixture which turned green-brown the mixture was refluxed for 3h. The brown powder, obtained after cooling and removal of the solvent under reduced pressure, was dissolved in anhyd acetone (20 mL) and then hexane (70 mL) was added. The green precipitate was separated from the brown solution by filtration. This purification by precipitation was repeated twice. The green precipitate was placed in a Soxhlet extractor and extracted for 3 h with acetone (200 mL) in order to separate the product from the insoluble metal-free species and LiOH. The acetone solution was evaporated down to a volume of 20 mL. The product precipitated after the addition of hexane (70 mL). This latter purification step was performed several times yield 1.29 g (64%). 

At the end of the extraction cycle, essentially all the naphthalene is in the separator and the insoluble material is left in the extractor. The process can be considered as a naphthalene extraction or as an "insolubles" purification depending upon which is the desired product. 

Technical Observations. The process described above is the best and least expensive. There is, however, another method which is analftgous to the preparation of -naphthol. Sodium naphthalene-a-sulfonate is fused with caustic soda at 290° (not to exceed 300°). The sulfonation is carried out at 80-90°, and the product is salted out in as concentrated a solution as possible. The sulfonate can also be isolated by removing the excess acid with lime or chalk, treating with soda, and evaporating to obtain the product. The sulfonate, thus obtained, can be used in the fusion without further purification, but the resulting a-naphthol is impure. 

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. 

In several preparations in Table 2, a catalytic amount of naphthalene is added to the reaction, and in many a stoichiometric aromatic radical anion is employed. The aromatic compounds, via their radical anions, serve as transfer agents for Li, permitting the reactions to be run at lower T. Such procedures also allow use of a stoichiometric amount of Li metal, preventing overreduction in the case of bifunctional substrates, The presence of the aromatic compound in the product mixture can lead to purification problems however, use of an acid-soluble aromatic, such as 1-dimethylaminonaphthalene, simplifies purification. 

The purification of Buckminster fuUerene (Qo) is a typical example of a production rate controlled by the capacity of the mobile phase. In a solvent that gives a retention factor near unity, the solubility is only 800 ppm [69]. In 1-methyl naphthalene, the solubility is close to 5%. To use this solvent, an adsorbent that retains strongly the fuUerenes is needed [70]. A sUica-bonded tetraphenyl-porphyrin gave satisfactory results [70,71]. 

Distillation of the crude tar yields two groups of products (1) Complex mixtures resulting from fractional distillation and being sold under the names of solvent naphtha, light oil, dead oil, creosote oil, and anthracene oil (2) coal-tar crudes such as benzene, toluene, naphthalene, anthracene, and the less important cumene, carbazole, cresols, and pyridine. Coal-tar intennediates are prepared by purification of these crude products and are used in the manufacture of dyes and other products. 

Examples presented describe the separation and purification of naphthalene from its associated impurities, alkylated mono- and dicyclic aromatics. Supercritical pentane at 42 atm and 215 °C and a chromatography adsorbent of baked brick impregnated with polyethylene glycol (6000 molecular weight) are used to separate a 95% naphthalene-5 % alkylated aromatics mixture into a 99.5% naphthalene fraction of 70% yield and a concentrated impurities fraction of 10% of the feed. Approximately 20% of the product is recycled. 

Because of its more extended aromatic system naphthalene is expected to be more acidic than benzene, but the difference is hardly observed in synthetic experiments. Treatment of naphthalene with BuLi TMEDA in hexane results in the formation of comparable amounts of the 1- and 2-lithio compounds and a dilithio derivative (possibly 1,8-) so that this method is not interesting from a synthetic point of view. If the metallation is carried out with the ternary mixture BuLi f-BuOK, TMEDA in hexane at temperatures in the region of — 20 °C, subsequent addition of dimethyl disulfide affords a mixture of 1-methylthio-, 2-methylthio- and l,8-bis(methyl-thio)naphthalene. The mono- and disubstitution products can be separated by distillation. The favourable ratio of about 15 85, together with the fact that the 2-isomer is solid at room temperature (whereas the 1-isomer is a liquid), permits an easy purification of the predominant product by crystallization. For practical reasons (difficult separation from the products) the use of an excess of naphthalene is avoided (compare the metallation of benzene, Exp. 3), and consequently yields (based on BuLi) are not optimal, since part of the base may react with TMEDA. 

Naphthalenesulfonic acid 106e 145 Naphthalene (100 g) is melted in a flask fitted with a thermometer, dropping funnel, and stirrer, and to it is added concentrated sulfuric acid (160 g) dropwise during 15 min, the temperature being kept at 160°. Stirring is continued for a further 5 min at that temperature, then the solution is poured into cold water (120 ml), and the crystals that separate are collected and pressed on porous plate. For purification, portions (10 g) of the crude product are dissolved in water (5 ml), filtered hot, and treated hot (above 70°) with concentrated hydrochloric acid (about 2 ml). These processes yield about 160 g of the sulfonic acid trihydrate it may be dried on porous plate or placed in a desiccator above sodium hydroxide. 

Basically the same idea was used by Brodie (1971) to create the Brodie Purifier of Union Carbide Corp. (GB-PS 1968), which features a horizontally scraped surface crystallizer with a vertical purification section. The performance of the apparatus depends strongly on the size of the crystals entering the purification section. Walas (1988) reports that as much as 24h residence time is needed to create the correct crystal size. He also presents data about p-dichlorobenzene purification. Mullin (1988) reports that in addition to the p-dichlorobenzene, large-scale production has also been installed for naphthalene. Figure 7.20 shows a diagram of the Purifier. 

Anthracene—CmHid—178—exists as a constituent of coal-tar, and is obtained by expression from the substance remaining in. the still after the distillation of naphthalene, etc. The commercial product thus obtained is a yellowish mass containing 50-80-per cent, of anthracene, the purification of which is a matter of considerable difficulty. It has also been obtained synthetically, by the action of the heat on benzyl toluene, and in other ways. 

Peroxide-free tetrahydrofuran (THF) is distilled under nitrogen from lithium tetrahydroaluminate. Pentane is distilled under nitrogen from P4O10. Iron pen-tacarbonyl [Pressure Chemical] is freshly distilled prior to each use. Commercial triiron dodecacarbonyl [Alfa Products] is obtained wet with methanol, which is removed by subjecting the sample to vacuum (0.1 torr) overnight. Commercial naphthalene (recrystallized quality) is used without further purification. All manipulations are carried out in a nitrogen-flushed dry box or in standard Schlenk apparatus under a nitrogen atmosphere. 

In order to probe the tolerance of the molybdenum(O) aromatic complexes to electrophilic/acidic environments, a tandem addition sequence was attempted for the complex TpMo(NO)(MeIm)(q -naphthalene) (114) (Fig.25) [17]. In a strategy similar to that used with the TpRe(CO)(MeIm)(q -naphthalene) analog,(see below) an acetonitrile solution (-35 °C) of 114 was exposed sequentially to triflic acid, l-methoxy-2-methyl-l-trimethylsiloxypropene, and an amine base. The 1,2-dihydronaphthalene complex 116 was isolated in virtually quantitative yield. No evidence of free naphthalene or 1,4-addition product was observed. Stirring the reaction mixture with exposure to air resulted in an 80% overall yield of 2-(l,2-dihydro-naphthalen-2-yl)-2-methyl-propinoic acid methyl ester (117) following TLC purification [17]. 

Production of Pure Naphthalene without Residues—Replacement of Chemical Purification by Optimized Multiple Crystallization (Example from VFT)... 

Under argon, 269 mg 3-benzyloxy-l,6,8-trimethoxy-naphthalene-2-carboxylic acid 3-bromo-4,5,7-trimethoxy-naphthalen-2-yl methyl ester was dissolved in 1.59 mL THF (0.25 M), from which residual water had been removed with n-butyllithium and o-phenanthroline), and cooled to 5 to -55°C. w-Butyllithium (203 fiL, 0.437 mmol) was then added dropwise. After the solution was stirred for 2 h, the reaction mixture was quenched by the addition of saturated aqueous NH4CI, allowed to warm to ambient temperature, and diluted with EtOAc. After the usual workup, the cmde product was purified by radial thin-layer chromatography (hexane/EtOAc, 9 1, 8 2, 7 3, and then 5 5) to give 130 mg l-(3-benzyloxy-l,6,8-trimethoxy-naphthalen-2-yl)-l-(3-hydroxymethyl-l,6,8-trimethoxy-naphthalen-2-yl)-methanone as a white solid, in a yield of 55%. Further purification was executed by crystallization from cyclohexane-dichloromethane, m.p., 220-224°C. 

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