Aromatic hydrocarbons methylbenzene

If the assumption that the entropy of the reaction according to equation (5) is independent of the aromatic substance applies, the entropy contribution TAS must assume a constant value. Mackor et al. (1958b) were able to demonstrate the correctness of this assumption by determining the thermodynamic data for some methylbenzenes and condensed aromatic hydrocarbons. Whereas AH and AO change considerably, the entropy term TAS remains largely unaltered (Table 21). 

There are many other aromatic hydrocarbons, i.e. compounds like benzene, which contain rings of six carbon atoms stabilised by electron delocalisation. For example, if one of the hydrogen atoms in benzene is replaced by a methyl group, then a hydrocarbon called methylbenzene (or toluene) is formed. It has the structural formulae shown. Methylbenzene can be regarded as a substituted alkane. One of the hydrogen atoms in methane has been substituted by a or —group, which is known as a phenyl group. So an alternative name for methylbenzene is phenylmethane. Other examples of aromatic hydrocarbons include naphthalene and anthracene. 

Toluene is a clear, flammable, aromatic hydrocarbon liquid with a smell similar to benzene. It is also called methylbenzene, indicating that a methyl group has been added to one of benzenes carbon atoms. Toluene was first isolated by Pierre-Joseph Pelletier (1788—1842) and Philippe Walter (1810—1847) in 1837. The name toluene comes from the South American tree Toluifera balsamum. Henri-Etienne Sainte-Claire Deville (1818—1881) isolated toluene from the tree s gum, Tolu balsam, in 1841. 

Benzene and many of its derivatives are manufactured on a large scale for use in high-octane gasolines and in the production of polymers, insecticides, detergents, dyes, and many miscellaneous chemicals. Prior to World War II, coal was the only important source of aromatic hydrocarbons, but during the war and thereafter, the demand for benzene, methylbenzene, and the dimethyl-benzenes rose so sharply that other sources had to be found. Today, most of tbe benzene and almost all of the methylbenzene and the dimethylbenzenes produced in the United States are derived from petroleum. 

Large discrepancies were found in applying the treatment to the Friedel-Crafts benzoylation of the methylbenzenes in nitrobenzene solution (Brown et al., 1958a). It was suggested that these difficulties arose from the formation of ternary complexes of aluminum chloride, the aromatic hydrocarbon, and the solvent nitrobenzene. This notion was tested by a study of the total and positional rates of acetylation... 

Colpa et al. (1963) calculated p/if(S1 )-values for a series of aromatic hydrocarbons, but could not detect fluorescence changes in the regions of acidity indicated by the Forster cycle, although fluorescence spectra attributed to proton complexes of 3,4-benzopyrene and 1,2-benzanthracene were observed in some solutions containing only the neutral molecule in the ground state. Flurry and co-workers (1963, 1966, 1967) have carried out theoretical and Forster cycle calculation on the excited state basicities of poly-methylbenzenes and Kuz min et al. (1967) have also calculated p/ (Sj)- and p/ (Tj)-values for polycyclic aromatic hydrocarbons increases in base strength of from 7 to 30 powers of ten were derived for Sj. 

Synonyms Methylbenzene Phenylmethane Toluol (DOT) Antisal la Methacide Methylbenzol NCI C07272 Tolueen (Dutch) Toluen (Czech) Tolueno (Spanish) Toluolo (Italian) Tolu-sol Chemical/Pharmaceutical/Other Ceass Aromatic hydrocarbon... 

The energy for the formation of a charge transfer complex is related to the VIP and VEa of the donor. To examine this relationship for the aromatic hydrocarbons with the measured electron affinities, the energies of complexes of methylbenzenes as the donors and aromatic hydrocarbons as the acceptors were determined. The charge transfer bands for these complexes were not observed [29]. Therefore, only the relation between the energy for complex formation and the VIP and VEa could be examined. The equation is... 

Figure 4.13 is a plot of the experimental data for a series of methylbenzenes with n = 1 to 6 with the aromatic hydrocarbons anthracene, A pyrene, Py phenan-threne, P chrysene, C and triphenylene, T versus 0.1/(IP — Ea — C2) with the least-squares value of C2 = 2.90 0.10 eV. If we consider the narrow range of values for these complexes, the correlation is quite good. 

Write equations to illustrate the oxidation of the following aromatic hydrocarbons by potassium permanganate in basic solution (a) toluene (b) ethylbenzene (c) 1,2-di-methylbenzene. 

Recent publications calculate the basicity of aromatic compounds and the electronic structure of the respective arenium ions by quantum chemical methods in different approximations — by semi-empirical methods MO LCAO (methylbenzenes " ), CNDO, CNDO/2 and CNDO/2FK (benzene " , toluene and other monoalkylbenzenes " , anisole , a series of monosubstituted benzoles , poly-methylbenzenes , monomethylnaphthalenes and polycyclic aromatic hydrocarbons ) INDO (benzene , cresols ) MINDO-2 and MINDO-3 (benzene , toluene ) by nonempirical (ab initio) methods using the basis... 

Synonyms Benzene, 1-methyl-4-(1-methylethyl)- Cymene Cymol Dolcymene 1-lsopropyl-4-methylbenzene 4-lsopropyl-1-methylben-zene 4-lsopropyltoluene p-lsopropyltoluene p-Methylcumene 1-Methyl-4-isopropylbenzene p-Methylisopropyl benzene 1-Methyl-4-(1-methylethyl) benzene Paracymene Paracymol Classificalion Aromatic hydrocarbon DeErnition Obtained chiefly from the wash water of sulflte paper Empirical C H ... 

Petroleum (Otto fuels) and aromatic hydrocarbons 40 % by volume 2,2,4-trimethylpentane (isooctane) 30 % by volume methylbenzene (toluene) 20 % by volume dimethyl- benzene (xylene) 10 %by volume methylnaphthalene... 

Scheme 8.25. A path for hydrogenolysis of a phenol to an aromatic hydrocarbon. The para-methylphenol first reacts (via addition-elimination) with l-phenyl-5-chlorotetrazole to produce a dehydrohalogenated adduct. Catalytic reduction with hydrogen (H2) and palladinm on carbon powder (Pd-C) as the catalyst then produces methylbenzene (toluene) and hydroxytetrazole (which can be recycled to chlorotetrazole by treatment with phosphoryl chloride or thionyl chloride) (see Musliner.W. J. Gates, J.W. Jr. Org. Chem. Bm//., 1967,59,1).

Monocyclic monoterpenic hydrocarbons are derived predominantly from the optically active hydrocarbon 4-isopropyl-1-methylcyclohexane, known as p-menthane (8-2). An exception isp-cymene also known as cymene (l-isopropyl-4-methylbenzene, 8-3), which is an aromatic hydrocarbon. Cymene is a common component of many essential oils, especially the essential oils of cumin (the seed of the herb Cuminum cyminum of the parsley family Apiaceae) and common thyme Thymus vulgaris, from the mint family Lamiaceae) Hsted in Table 8.32 (see later). 

Aromatic hydrocarbons are relatively rare natural components of foods. An important natural component of essential oils of many spices and vegetables is p-cymene (l-isopropyl-4-methylbenzene, 8-3). Together with the related hydrocarbon a,p-dimethylstyrene (8-10), p-cymene is also formed by degradation of citral. Various alkyl benzenes and alkyl xylenes (8-10) are found in small... 

Synonyms Methylbenzene Methylbenzol Phenylmethane Toluol Classification Aromatic hydrocarbon Empirical C Hj Formula CgHjCHj... 

An indication of the nature of the transition state in aromatic substitution is provided by the existence of some extrathermodynamic relationships among rate and acid-base equilibrium constants. Thus a simple linear relationship exists between the logarithms of the relative rates of halogenation of the methylbenzenes and the logarithms of the relative basicities of the hydrocarbons toward HF-BFS (or-complex equilibrium).288 270 A similar relationship with the basicities toward HC1 ( -complex equilibrium) is much less precise. The jr-complex is therefore a poorer model for the substitution transition state than is the [Pg.150]

Experimental work using a pulse-quench catalytic reactor650 to probe transition between induction reactions and hydrocarbon synthesis on a working H-ZSM-5 catalyst has resulted in the suggestion that stable cyclopentenyl cations are formed during the induction period from small amounts of olefins formed in an induction reaction 647 One study reports a surprising observation, namely, enhanced aromatic formation over the physical mixture of Ga203 and H-ZSM-5 (1 1) (18.2% of benzene and methylbenzenes).651... 

Much of the aromatic product obtained by catalytic re-forming is blended with other fractions from petroleum refining to give high-octane gasoline. The rest is separated into its component hydrocarbons, which then are utilized by the chemical industry for the production of chemicals derived from benzene, methylbenzene, and the dimethylbenzenes, as summarized in Figures 22-9 and 22-10,... 

As expected, the aptitude for disproportionation of the aromatic compound depends upon the nature of the alkyl group, and the order of reactivity is isopropyl > ethyl > methyl. Due to their higher nucleophilicity, polyalkylbenzenes react faster than monoalkylbenzenes. This effect is pronounced in the case of methylbenzenes. Toluene itself shows little reactivity over Nafion-H at 193°C. Diethylbenzenes react much faster than dimethylbenzenes. The rate of conversion of diethylbenzenes over Nafion-H at 193°C is 5 10-5 mol min 1 g-1 of catalyst.269 This is a low rate when compared with that using AICI3 HC1 in the liquid phase at room temperature (10-4 mol min-1 g-1 of catalyst).272 However, one should bear in mind that Nafion-H is a truly insoluble heterogeneous catalyst, whereas in the case of AICI3—HC1 a soluble complex is formed with the hydrocarbon and therefore the rates are not directly comparable. The equilibrium composition of the acid-catalyzed disproportionation of diethylbenzenes depends upon the nature of the catalyst. 

On the basis of the evaluation of the proton affinity (860.6 kJmoP for hexa-methylbenzene and 845.6 kJmoP for tetramethylbenzene 148)), the possibility of obtaining hexamethylbenzene and tetramethylbenzene as carbocations in the pores of a zeolite had been excluded. However, Haw and co-workers 146) recently demonstrated by means of NMR spectroscopy that H-heptamethylbenzene may be formed in the cavities of a H(3 zeolite. H-hexamethylbenzene and H-tetramethyl-benzene ions have been observed in zeolite H(3 by a combination of IR and UV-visible spectroscopies 149,150). DRS UV-Vis- and FTIR spectroscopy proved to be techniques well suited to verify, under reaction conditions, the existence of stable H-hexamethylbenzene and H-tetramethylbenzene in the zeolite. Owing to the symmetry properties of H-hexamethylbenzene and H-tetramethylbenzene, characteristic changes of their vibrational features were observed when the aromatic system was perturbed upon protonation. In the same study it was found that the lower polymethylbenzene homologues, such as 1,3,5-trimethylbenzene (PA = 836.2 kJmol ), did not undergo appreciable protonation in H(3 zeolite. On the basis of these results, a proton affinity limit for hydrocarbons that form stable... 

Tapp et al. ° used SAPO-5 and CoAPO-5 to convert methanol to hydrocarbons. The catalytic experiments were carried out at 360 C, 1 bar total pressure, and LHSV=2. The typical hydrocarbon fraction contained 45 wt% of light olefins, 15 wt% of higher aliphatics, 40 wt% of aromatics, and less than 1% of methane. The main aromatics were penta- and hexa-methylbenzene. SAPO-5 remained active for approximately 300 g methanol/g catalyst, while CoAPO-5 remained active for only 30 g methanol/g catalyst. The lower stability of CoAPO-5 with respect to SAPO-5 is in agreement with that observed in small-pore SAPO and MeAPO molecular sieves. The methanol transformation on AIPO4-5 mainly yielded dimethylether and water. 

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