Para-Benzylated toluene

Continuous chlorination of benzene at 30—50°C in the presence of a Lewis acid typically yields 85% monochlorobenzene. Temperatures in the range of 150—190°C favor production of the dichlorobenzene products. The para isomer is produced in a ratio of 2—3 to 1 of the ortho isomer. Other methods of aromatic ring chlorination include use of a mixture of hydrogen chloride and air in the presence of a copper—salt catalyst, or sulfuryl chloride in the presence of aluminum chloride at ambient temperatures. Free-radical chlorination of toluene successively yields benzyl chloride, benzal chloride, and benzotrichloride. Related chlorination agents include sulfuryl chloride, tert-huty hypochlorite, and /V-ch1orosuccinimide which yield benzyl chloride under the influence of light, heat, or radical initiators. 

Fig. 7 Reactions of toluene with HO radical. HO can abstract a benzylic hydrogen atom (a) or add to the aromatic ring at the ipso (b), ortho (c), meta (d), and para (e) positions relative to the methyl group. Each resultant radical can decompose by various pathways, depending on temperature and pressure.

Oxidation of ortho-xylene. The spectra of the adsorbed species arising from interaction of ortho-xylene with the surface of the vanadia-titania catalyst in the presence of oxygen are shown in Figure 4. The spectra show some parallel features with respect to those discussed above concerning the oxidation of toluene and meta- and para-xylene. Also in this case the o-methyl-benzyl species begins to transform above 373 K, with production of adsorbed o-tolualdehyde (band at 1635 cm 0 and of a quinone derivative (band at 1670 cm. Successively bands likely due to o-toluate species (1530,1420 cm 0 grow first and decrease later with production of CO2 gas. 

Fluorination of toluene gives a mixture of ortho- and para- uorotoluene, as expected for an electrophilic process (B), but the partial rate factors (Table 4) [139] show a very high ortho para ratio indicating that radical processes (A) must also be involved. Furthermore, fluorination of the methyl group, giving benzyl fluoride, also occurs in increasing yield as the reaction temperature is raised. 

Toluene is oxidized to cresols (ortho meta para ratio = 5 1 4) and not to the benzyl derivatives, despite the low dissociation energy of the benzylic C—H bond. p-Xylene undergoes oxidation to 2,5-dimethylphenol. 

Protodedeuteration reaction has, however, some limitations. It cannot be used to study compounds subject to secondary condensation in acidic medium, such as certain benzyl alcohol and benzyl ether derivatives. Moreover, the partial rate factors depend greatly on the medium used because different acids show different degrees of selectivity. For instance, the reported partial rate factors for the para position of toluene (/PMe) range from 170 (in sulfuric acid at 6S°C.) (13) to 4000 (in hydrogen bromide) 22). 

Sarca and Laali199 have used triflic acid in butylmethylimidazolium hexafluor-ophosphate BMIM][PF6 ionic liquid for the benzylation of various arenes with benzyl alcohol [Eq. (5.76)]. When compared with Yb(OTf)3, triflic acid proved to be a better catalyst showing higher selectivity (less dibenzyl ether byproduct) by exhibiting similar activity (typically complete conversion). Of the isomeric products, para isomers dominate. Experimental observations indicate that dibenzyl ether originates from less complete protonation of benzyl alcohol and, consequently, serves as a competing nucleophile. Both substrate selectivity (kT/kB) and positional selectivity (ortho/para ratio) found in competitive benzylation with a benzene-toluene mixture (1 1 molar ratio) are similar to those determined in earlier studies, indicating that the nature of the electrophile is not affected in the ionic liquid. 

Friedel-Crafts alkylation of benzene,220 221 toluene,222para-xylene,220 and naphthalene223 with benzyl alcohols have been studied over Nafion-silica nano-composite catalysts, including the kinetics of alkylation.221,223 In most cases, 13% Nafion-silica showed the highest activity, testifying again to the much higher accessibility of the active sites. Complete conversion of para-xylene was found in the presence of triflic acid, and it was the only reaction when ether formation as side reaction did not occur. 

Fujiwara et al.227 tested a nanocomposite material having Nafion immobilized in MCM-41 mesoporous silica in Friedel-Crafts alkylations with benzyl alcohol. Whereas Nafion-MCM-41 showed lower activity in the alkylation of toluene than 13% Nafion SAC-13 under identical conditions, it exhibited increased activity when used in the alkylation of para-xylene. 

The nomenclature of benzene derivatives is described in Sec. 4.6. Common names and structures to be memorized include those of toluene, styrene, phenol, aniline, and xylene. Monosubstituted benzenes are named as benzene derivatives (bromobenzene, nitrobenzene, and so on). Disubstituted benzenes are named as ortho- (1,2-), meta- (1,3-), or para- (1,4-), depending on the relative positions of the substituents on the ring. Two important groups are phenyl (C6H5-) and benzyl (C6H5CH2-). 

Know the meaning of ortho, meta, para, phenyl group (C6H5- or Ph-), benzyl group (C6H5CH2-), aryl group (Ar-), benzene, toluene, styrene, phenol, aniline, xylene, arene, fullerene. 

In a 30-liter reactor, reflux 12.5 kg of (2S,3aS,7aS)-2-carboxyperhydroindole, 50 kg of para-toluenesulfonic acid and 14.2 kg of benzyl alcohol and 38.4 kg of toluene, removing the water formed with the aid of a continuous separator. When no more water separates out, cool, filter off the precipitate of para-toluenesulfonate of the benzyl ester of (2S,3aS,7aS)-2-carboxyoctahydroindole formed, and dry. Yield 91.3%. 

The reason for both trends is the same the benzyl cations that attack the toluene or the benzene have different stabilities depending on the nature of their para substituent X. When X is the electron acceptor NOz, we have the most electron-deficient cation, whereas when X is the electron donor MeO, we have the most electron-rich cation. The formation of Wheland complexes from p-02N—C6H4—CHj should therefore be exothermic and exergonic. Conversely, the formation of Wheland complexes... 

When alkylbenzene derivatives are submitted to metallation, the metal may displace either a benzylic (a) or a ring hydrogen atom (preferably at the sterically unhindered meta or para positions). To avoid contamination by the ring-metallated derivative, a-deprotonation of toluene needs to be done with Schlosser s base18 191,192 while, for example, TMEDA-activated butyllithium gives rise to some contamination by ring-metallated products.193,194 Examples of mono- and dimetallation of alkylbenzenes are reported in Table 8. 

Ti-MOR promoted the ring hydroxylation of toluene, ethylbenzene and xylenes with negligible oxidation of the ethyl side chain [59]. In the same study, however, and in contrast to earlier ones, a similar result was also reported for TS-1. No oxidation of benzylic methyls was observed. Cumene yielded mainly the decomposition products of cumyl hydroperoxide. The oxidation of t-butylbenzene was negligibly low. The reachvity order, toluene > benzene > ethylbenzene > cumene, reflects the reduced steric constraints in the large pores of mordenite. Accordingly, the rate of hydroxylation ofxylene isomers increased in the order para < ortho < meta, in contrast to the sterically controlled one, ortho < meta para, shown on TS-1. It is worth menhoning that the least hindered p-xylene exhibited the same reactivity on either catalyst. 

Fhiorination of aromatics. The reagent reacts with toluene to form benzyl fluoride as the major product ( 65% yield). It is also useful for fhiorination of phenols and of alkyl ethers of phenols the ortho-isomer is formed as the major product. Reactions with this reagent thus differ from those with xenon difluoride, which generally favors formation of para-isomers. 

Norrish Type I cleavage of benzylketones occurs very readily to yield benzyl and acyl radicals. In competition with other processes, these can couple by attack of the acyl radical upon the aromatic nucleus of the benzyl radical to give as a product an acyl toluene derivative. Turro has examined the photochemical properties of the 2-phenylalkanones (326) in solution and complexed with cyclodextrins. In solution the major fate of the Type I biradicals formed is intr2unolecular recombination by attack of the acyl radical at the para position of the benzyl radical to generate (327). However, complexatlon of (326) within the cyclodextrin cavity inhibits formation of (327) and promotes disproportionation of the blradicals to give (328). Turro has also examined the photochemistry of dlbenzylketone Included in zeolites.Recombination of the Type I radicals in this case can produce a mixture of (2-methyl-phenyl) benzylketone and (4-methylphenyl)benzylketone decarbonylation of the acyl radical competes and leads to the isolation of 1,2-dlphenylethane. It is found that the relative yields of the products... 

PCT = para-chlorotoluene OCT = ortho-chlorotoluene BC = benzyl chloride others = polychlorinated toluenes (di-, tri- and tetrachlorotoluenes). 

The equilibration of the ring anions to the benzyl anion is the probable explanation, especially considering the recent work of Gau and our observation of an equilibration between m-xylene and toluene in the presence of (benzyllithium)2 TMEDA (20). (In fact, this type of system might be the basis of another route for a hydrocarbon acidity scale.) The more rapid disappearance of the ortho isomer, compared with the meta, may be the result of a possible intramolecular route for conversion to the benzyl anion. The meta and para isomers probably change to the benzyl anion by an intermolecular route that would be slower and agree with what was observed. Although complete resolution by GLC of the para and meta isomers was not done in this study, the para disappeared faster than the meta, but much slower than the ortho. In other time studies on the disappearance of the meta isomer at room temperature, about half the initial amount of this isomer was gone in three days and all of it in two to three months. 

Salmon et al. used a natural montmorillonite to catalyse the intermolecular condensation of toluene in the presence of bromine to produce ortho- and para-phenyltolylmethanes.31 The reaction was carried out at reflux using carbon disulfide as a solvent. The first stage of the reaction is believed to be the generation of benzyl bromide. A bromide ion is abstracted from benzyl bromide by a Lewis acid site on the clay surface. The resulting electrophilic benzyl cation then attacks toluene. 

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