Of aromatic hydrocarbons

Edeleanu process An extraction process utilizing liquid sulphur dioxide for the removal of aromatic hydrocarbons and polar molecules from petroleum fractions. 

Burdett, R.A., L.W. Taylor and L.C. Jones Jr (1955), Determination of aromatic hydrocarbons in lubricating oil fractions by far UV absorption spectroscopy , p. 30. In Molecular Spectroscopy Report Conf. Institute of Petroleum, London. 

Identification of Aromatic Hydrocarbons. Picric acid combines with many aromatic hydrocarbons, giving addition products of definite m.p. Thus with naphthalene it gives yellow naphthalene picrate, C oHg,(N08)jCeHiOH, m.p. 152°, and with anthracene it gives red anthracene picrate, C 4Hio,(NOj)jCeHjOH, m.p. 138 . For practical details, see p. 394. 

Two methods may conveniently be used to ascend the homologous series of aromatic hydrocarbons ... 

Two interesting appbcations of the Friedel and Crafts reaction to the preparation of aromatic hydrocarbons will bo described, iriz. —... 

Unlike aliphatic hydrocarbons, aromatic hydrocarbons can be sul-phonated and nitrated they also form characteristic molecular compounds with picric acid, styphnic acid and 1 3 5-trinitrobenzene. Many of the reactions of aromatic hydrocarbons will be evident from the following discussion of crystalline derivatives suitable for their characterisation. 

NITRATION OF AROMATIC HYDROCARBONS Aromatic hydrocarbons may be nitrated, i.e., the hydrogen atoms replaced by nitro (NOj) groups, with concentrated nitric acid in the presence of concentrated sulpliuric acid, for example ... 

SULPHONATION OF AROMATIC HYDROCARBONS Aromatic hydrocarbons may be mono-sulphonated by heating with a slight excess of concentrated sulphuric acid for benzene, oleum (7-8 per cent. SOj) gives somewhat better results. The reaction is usually complete when all the hydrocarbon has dissolved. Examples are ... 

An additional useful test is to distil the acid or its sodium salt with soda lime. Heat 0.5 g. of the acid or its sodium salt with 0 2 g. of soda lime in an ignition tube to make certain that there is no explosion. Then grind together 0-5 g. of the acid with 3 g. of soda hme, place the mixture in a Pyrex test-tube and cover it with an equal bulk of soda hme. Fit a wide dehvery tube dipping into an empty test-tube. Clamp the tube near the mouth. Heat the soda lime first and then the mixture gradually to a dull-red heat. Examine the product this may consist of aromatic hydrocarbons or derivatives, e.g., phenol from sahcyUc acid, anisole from anisic acid, toluene from toluic acid, etc. 

The compound is employed for the characterisation of aromatic hydrocarbons (compare Section IV,9), ethers and amines. 

Cations like that present in (iv) exist in solutions of aromatic hydrocarbons in trifluoroacetic acid containing boron trifluoride, and in liquid hydrogen fluoride containing boron trifluoride. Sulphuric acid is able to protonate anthracene at a mero-position to give a similar cation. ... 

The relative basicities of aromatic hydrocarbons, as represented by the equilibrium constants for their protonation in mixtures of hydrogen fluoride and boron trifluoride, have been measured. The effects of substituents upon these basicities resemble their effects upon the rates of electrophilic substitutions a linear relationship exists between the logarithms of the relative basicities and the logarithms of the relative rate constants for various substitutions, such as chlorination and... 

The solubility of hydrogen chloride in solutions of aromatic hydrocarbons in toluene and in w-heptane at —78-51 °C has been measured, and equilibrium constants for Tr-complex formation evaluated. Substituent effects follow the pattern outlined above (table 6.2). In contrast to (T-complexes, these 7r-complexes are colourless and non-conducting, and do not take part in hydrogen exchange. 

The ultraviolet spectra of these compounds are similar to those of trans stilbene or of 2- and 4-stilbazole. The effect on the ultraviolet spectrum of various substituents have been found to parallel in many respects the efiects produced by the corresponding group in derivatives of aromatic hydrocarbons (142). 

An important property of aromatic hydrocarbons is that they are much more stable and less reactive than other unsaturated compounds Ben zene for example does not react with many of the reagents that react rapidly with alkenes When reaction does take place substitution rather than addition is observed The Kekule formulas for benzene seem mcon sistent with its low reactivity and with the fact that all of the C—C bonds m benzene are the same length (140 pm)... 

Oxidative Fluorination of Aromatic Hydrocarbons. The economically attractive oxidative fluorination of side chains in aromatic hydrocarbons with lead dioxide or nickel dioxide in Hquid HF stops at the ben2al fluoride stage (67% yield) (124). 

Amides result from the reaction of aromatic hydrocarbons with isocyanates, such as phenyl isocyanate [103-71-9], ia the presence of aluminum chloride. Phenyl isothiocyanate [103-72-0] similarly gives thioanilides (136). 

Sulfonation of aromatic hydrocarbons with sulfuric acid is cataly2ed by hydrogen fluoride or, at lower temperatures, by boron trifluoride (144). The products obtained are more uniform and considerably less sulfuric acid is needed, probably because BF forms complexes with the water formed ia the reaction, and thus prevents dilution of the sulfuric acid. 

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

There are two approaches to estimation of AG fThe first is an empirical approach (36) based on dynamics of fluorescence quenching of aromatic hydrocarbons ia acetonitrile solution. Accordingly,... 

Silver sulfate has been described as a catalyst for the reduction of aromatic hydrocarbons to cyclohexane derivatives (69). It is also a catalyst for oxidation reactions, and as such has long been recommended for the oxidation of organic materials during the deterrnination of the COD of wastewater samples (70,71) (see WASTES, INDUSTRIAL WATER, INDUSTRIAL WATERTTEATI NT). 

Sulfur dioxide acts as a dienophile ia the Diels-Alder reaction with many dienes (253,254) and this reaction is conducted on a commercial scale with butadiene. The initial adduct, sulfolene [77-79-2] is hydrogenated to a solvent, sulfolane [126-33-0] which is useful for selective extraction of aromatic hydrocarbons from... 

Low temperature tars contain 30—35 wt % non aromatic hydrocarbons, ca 30% of caustic-extractable phenols in the distillate oils, and 40—50% of aromatic hydrocarbons. The latter usually contain one or more alkyl substituent groups. On atmospheric distillation, coke-oven tars yield 55—60% pitch, whereas CVR tars give 40—50% pitch. The pitch yield from low temperature tars is in the 26—30% range. 

The bromination of aromatic hydrocarbons can occur either in a side chain or on the ring, depending on conditions. In the presence of sunlight aLkylben2enes are brominated predominately in the side chain (24). 

Impurities can sometimes be removed by conversion to derivatives under conditions where the major component does not react or reacts much more slowly. For example, normal (straight-chain) paraffins can be freed from unsaturated and branched-chain components by taking advantage of the greater reactivity of the latter with chlorosulfonic acid or bromine. Similarly, the preferential nitration of aromatic hydrocarbons can be used to remove e.g. benzene or toluene from cyclohexane by shaking for several hours with a mixture of concentrated nitric acid (25%), sulfuric acid (58%), and water (17%). 

Flexible tubing for high pressure service, equipped with stainless steel overbraid plus tube adapter end connections, is commonly available with a carbon black-loaded PTFE core tube to dissipate static. Numerous other designs of conductive and antistatic tubing are available for low pressure applications. The utility of conductive tubing in preventing fires during transfer of aromatic hydrocarbon liquids is described in [165]. 

Plants have now been installed by some manufacturers to produce ethylbenzene via catalytic reforming processes. The reforming process is one which converts aliphatic hydrocarbons into a mixture of aromatic hydrocarbons. This may be subsequently fractionated to give benzene, toluene and a xylene fraction from which ethylbenzene may be obtained. 

The dehydrogenation reaction produces crude styrene which consists of approximately 37.0% styrene, 61% ethylbenzene and about 2% of aromatic hydrocarbon such as benzene and toluene with some tarry matter. The purification of the styrene is made rather difficult by the fact that the boiling point of styrene (145.2°C) is only 9°C higher than that of ethylbenzene and because of the strong tendency of styrene to polymerise at elevated temperatures. To achieve a successful distillation it is therefore necessary to provide suitable inhibitors for the styrene, to distil under a partial vacuum and to make use of specially designed distillation columns. 

In the presence of a proton source, the radical anion is protonated and further reduction occurs (the Birch reduction Part B, Section 5.5.1). In general, when no proton source is present, it is relatively difficult to add a second electron. Solutions of the radical anions of aromatic hydrocarbons can be maintained for relatively long periods in the absence of oxygen or protons. 

---