Benzene, purification

A range of the title compounds were prepared by treating the amines with sulfinyl chloride in benzene. Purification by vacuum distillation led to violent explosions of some of those with 5 membered rings containing two or more heteroatoms on a number of occasions. It is essential to keep the distillation temperature below... 

The procedures used for styrene and benzene purification are given elsewhere (15) as is the technique used to study the association states U The viscometric method relies on the fact... 

Complete issudlatioss pretreatmem, fractionation, hydrogen and benzene purification induded. 

As solvent is removed under vacuum, the product precipitates from solution 6.2 g (100 %) of crude product is isolated by filtration and washed several times with small portions of anhydrous benzene. Purification may be effected by sublimation at 75° (lO" torr) or by recrystallization from hot xylene. Anal. Calcd. for CgHivOsNSn C, 32.69 H, 5.83 N, 4.77 mol. wt. 293.9. 

Octadecylmethyl sulfoxide (OMS) was prepared in the following manner 15 g of octadecyl bromide and 3.5 g of thiourea were dissolved in 150 cm3 of ethanol. The mixture was refluxed for 1 hr after which 100 cm3 of ethanol were removed by distillation. The residue, after cooling, was made alkaline by an ethanol/sodium hydroxide solution (5 g sodium hydroxide in a minimum volume of ethanol). Methyl iodide, 3.7 g, was then added, and the mixture was left to stand overnight. The resulting thioether was recovered by filtration and washed with cold ethanol. The thioether was dissolved in glacial acetic acid then small quantities of 20 vol % hydrogen peroxide, constituting the stoichiometric amount, were added over several hours. The product was precipitated with water, and the precipitate was collected by filtration. The crude product was washed successively with water, ice-cold ethanol, and a small quantity of diethyl ether it was finally dried at 70°C. OMS was purified by successive recrystallization from benzene purification was... 

In the first column, the equipment numbers on the toluene hydrodeallg lation PFD (Figure 1.51 are given. It should be noted that there is not a one-to-one correspondence between the actual equipment and the simulation modules. For example, three splitters and six mixers are required in the simulation, but these are not identified in the PFD. In addition, several pieces of equipment associated with the benzene purification tower are simulated by a single simulation unit. The numbering of the streams in Figure 13.6... 

Consider the benzene purification column, T-101, in Figure 1.5 for the toluene hydrodeallgdation process. The column feed contains noncondensables, mainly methane and a small amount of hydrogen, that must be vented from the system The vent is taken off the top of the reflux drum, V-104. Sketch a control system in which the valve on this vent line is used to control the pressure of the column. 

Example 13.2-1 Benzene purification We wish to produce 99.99% benzene from a feed containing 99% benzene and 1 % toluene. We plan to use a staged column operated with a total condenser. Over this concentration range, the equilibrium line is approximately... 

Purification of anthracene. Dissolve 0-3 g. of crude anthracene (usually yellowish in colour) in 160-200 ml. of hexane, and pass the solution through a column of activated alumina (1 5-2 X 8-10 cm.). Develop the chromatogram with 100 ml. of hexane. Examine the column in the hght of an ultra-violet lamp. A narrow, deep blue fluorescent zone (due to carbazole, m.p. 238°) will be seen near the top of the column. Immediately below this there is a yellow, non-fluorescent zone, due to naphthacene (m.p. 337°). The anthracene forms a broad, blue-violet fluorescent zone in the lower part of the column. Continue the development with hexane until fluorescent material commences to pass into the filtrate. Reject the first runnings which contain soluble impurities and yield a paraffin-hke substance upon evaporation. Now elute the column with hexane-benzene (1 1) until the yellow zone reaches the bottom region of the column. Upon concentration of the filtrate, pure anthracene, m.p. 215-216°, which is fluorescent in dayhght, is obtained. The experiment may be repeated several times in order to obtain a moderate quantity of material. 

Another mode of preparation includes the dismutation of cumene (qv) in DIPB and benzene in presence of an HZSM-12 catalyst at 200°C (6). The ratio p/m increases with the temperature. Finally, but with purification difficulties, DIPB can be coproduced with cumene (7). 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

The solvent is then evaporated, and the unconverted sterol is recovered by precipitation from an appropriate solvent, eg, alcohol. The recovered sterol is reused in subsequent irradiations. The solvent is then evaporated to yield vitamin D resin. The resin is a pale yeUow-to-amber oil that flows freely when hot and becomes a brittie glass when cold the activity of commercial resin is 20 30 x 10 lU/g. The resin is formulated without further purification for use in animal feeds. Vitamin D can be crystallized to give the USP product from a mixture of hydrocarbon solvent and ahphatic nitrile, eg, benzene and acetonitrile, or from methyl formate (100,101). Chemical complexation has also been used for purification. 

Although all four tocopherols have been synthesized as their all-rac forms, the commercially significant form of tocopherol is i7//-n7i a-tocopheryl acetate. The commercial processes ia use are based on the work reported by several groups ia 1938 (15—17). These processes utilize a Friedel-Crafts-type condensation of 2,3,5-trimethylhydroquinone with either phytol (16), a phytyl haUde (7,16,17), or phytadiene (7). The principal synthesis (Fig. 3) ia current commercial use iavolves condensation of 2,3,5-trimethylhydroquiQone (13) with synthetic isophytol (14) ia an iaert solvent, such as benzene or hexane, with an acid catalyst, such as ziac chloride, boron trifluoride, or orthoboric acid/oxaUc acid (7,8,18) to give the all-rac-acetate ester (15b) by reaction with acetic anhydride. Purification of tocopheryl acetate is readily accompHshed by high vacuum molecular distillation and rectification (<1 mm Hg) to achieve the required USP standard. 

Thiophene, which is more stable to acid, is readily sulfonated by shaking with concentrated sulfuric acid at room temperature. Benzene is not reactive under these conditions and this is the basis for the purification of benzene from thiophene contamination. With all three heterocycles, if the a-positions are blocked, then sulfonation occurs at the /3-position. 

Purification as their N-acetyl derivatives is satisfactory for primary, and to a limited extent secondary, amines. The base is refluxed with slightly more than one equivalent of acetic anhydride for half to one hour, cooled and poured into ice-cold water. The insoluble derivative is filtered off, dried, and recrystallised from water, ethanol, aqueous ethanol or benzene (CAUTION toxic ). The derivative can be hydrolysed to the parent amine by refluxing with 70% sulfuric acid for a half to one hour. The solution is cooled, poured onto ice, and made alkaline. The amine is steam distilled or extracted as above. Alkaline hydrolysis is very slow. 

The impurities present in aromatic nitro compounds depend on the aromatic portion of the molecule. Thus, benzene, phenols or anilines are probable impurities in nitrobenzene, nitrophenols and nitroanilines, respectively. Purification should be carried out accordingly. Isomeric compounds are likely to remain as impurities after the preliminary purifications to remove basic and acidic contaminants. For example, o-nitrophenol may be found in samples ofp-nitrophenol. Usually, the ri-nitro compounds are more steam volatile than the p-nitro isomers, and can be separated in this way. Polynitro impurities in mononitro compounds can be readily removed because of their relatively lower solubilities in solvents. With acidic or basic nitro compounds which cannot be separated in the above manner, advantage may be taken of their differences in pK values (see Chapter 1). The compounds can thus be purified by preliminary extractions with several sets of aqueous buffers... 

Benzene, which has been used as a solvent successfully and extensively in the past for reactions and purification by chromatography and crystallisation is now considered a very dangerous substance so it hasto be used with extreme care. We emphasise that an alternative solvent system to benzene (e.g. toluene, toluene-petroleum ether, or a petroleum ether to name a few) should be used first. However, if no other solvent system can be found then all operations involving benzene have to be performed in an efficient fumehood and precautions must be taken to avoid inhalation and contact with skin and eyes. Whenever benzene is mentioned in the text an asterisk e.g. C Hg or benzene, is inserted to remind the user that special precaution should be adopted. 

Has been purified by co-distillation with ethylene glycol (boils at 197.5°), from which it can be recovered by additn of water, followed by crysm from 95% EtOH, benzene, toluene, a mixture of benzene/xylene (4 1), or EtjO. It has also been chromatographed on alumina with pet ether in a dark room (to avoid photo-oxidation of adsorbed anthracene to anthraquinone). Other purification methods include sublimation in a N2 atmosphere (in some cases after refluxing with sodium), and recrystd from toluene [Gorman et al. J Am Chem Soc 107 4404 1985]. 

Benz[a]anthracene [56-55-3] M 228.3, m 159-160". Crystd from MeOH, EtOH or benzene (charcoal), then chromatographed on alumina from sodium-dried benzene (twice), using vacuum distn to remove benzene. Final purification was by vacuum sublimation. 

Rapid purification To dry benzene, alumina, CaH2 or 4A molecular sieves (3% w/v) may be used (dry for 6h). Then benzene is distd, discarding the first 5% of distillate, and stored over molecular sieves (3A, 4A) or Na wire. 

Crystd from hot H2O or pet ether (b 60-70°), pet ether containing a little benzene, from CCI4, or EtOH (ImL/g). An additional purification step is passage of a benzene soln through an activated alumina column. Sublimes in a vacuum. Also crystd three times from MeOH/H20 [Naguib J Am Chem Soc 108 128 79[Pg.121]

Chloroacetic acid [79-11-8] M 94.5, m 62.8 , b 189 , pK 2.87. Crystd from CHCI3, CCI4, benzene or water. Dried over P2O5 or cone H2SO4 in a vacuum desiccator. Further purification by distn from MgS04, and by fractional crystn from the melt. Stored under vac or under dry N2. [Bemasconi et al. J Am Chem Soc 107 3621 1985.]... 

Other purification procedures include the formation of the picrate, prepared in benzene soln and crystd to constant melting point, then decomposed with warm 10% NaOH and extracted into ether the extract was washed with water, and distd under reduced pressure. The oxalate has also been used. The base has been fractionally crystd by partial freezing and also from aq 80% EtOH then from absolute EtOH. It has been distd from zinc dust, under nitrogen. 

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