Toluene electrophilic aromatic substitution, product

No electrophilic aromatic substitution reactions of toluene, ethylbenzene, and cumene occur with BBrj in the dark the electrophile is too weak for these reactions. The photochemical reactions followed by hydrolysis give the p-isomers of the corresponding boronic acids as the major products (delocalization band in Scheme 9) [44]. 

Furosemide can also be synthesized starting with 2,4-dichlorobenzoic acid (formed by chlorination and oxidation of toluene). Reaction with chlorosulfonic acid is an electrophilic aromatic substitution via the species -S02C1 attacking ortho and para to the chlorines and meta to the carboxy-late. Ammonolysis to the sulfonamide is followed by nucleophilic aromatic substitution of the less hindered chlorine by furfurylamine (obtained from furfural—a product obtained by the hydrolysis of carbohydrates). 

Unlike most other electrophilic aromatic substitutions, sulfonation is often reversible (see Section 17-4). When one sample of toluene is sulfonated at 0 °C and another sample is sulfonated at 100 °C, the following ratios of substitution products result ... 

Like benzene, toluene undergoes electrophilic aromatic substitution sulfona-tion, for example. Although there are three possible monosulfonation products, this reaction actually yields appreciable amounts of only two of them the 0- and /7-isomers. 

Unusual orientation has been observed by Yamaguchi in electrophilic aromatic substitution using gallium trichloride. The reaction of toluene and bis-silylated 1,3-butadiyne gives an o-substituted product exclusively (Scheme 7.4), and even isopropylbenzene reacts at the o-position predominantly [15]. The tendency of the reaction to occur at the vicinity of the alkyl substituent is, however, restricted to the diyne-based electrophile for other related electrophiles derived from silylethyne, si-lylallene, or bissilylated 1,5,5,7-octatetrayne normal o/p orientation is observed. 

Regarding the possible mechanism, notably, toluene, ethylbenzene and terf-butylbenzene are less reactive than benzene, which is not consistent with the expected order for an electrophilic aromatic substitutions, such as that found with the classic Fenton reagent. There are also other differences with respect to the Fenton chemistry. In particular, under biphase conditions the reaction is definitely more selective although comparisons are difficult due to the huge amount of data, sometimes inconsistent, on the Fenton system (for which most of the data have been obtained with the iron used in stoichiometric amounts) it seems that selectivities dose to those observed under biphase conditions are only attained at a conversion around of 1%. Furthermore, in the biphase system, only a negligible amount (<1%) of biphenyl was detected among secondary products, whereas in the classic Fenton oxidation this compound is formed by radical dimerization of hydroxycydohexadienyl radicals in typical yields ranging from 8 to 39%. 

R - C = 0. Once formed, the acylium ion undergoes an electrophilic aromatic substitution reaction with the aromatic compound. The product of this acylation reaction is an aromatic ketone. Toluene is acylated by propanoyl chloride to give both ortho and para substituted products. 

At the low-temperature (0°) addition, rate-control is being observed. The o- and p-xylenes are formed faster. At the high-temperature (80°) addition, equilibrium-control is shown m-xylene is the most stable product. The methyl group of toluene activates the ring for electrophilic aromatic substitution and directs substituents to the ortho and para positions. Just as the methyl group favors alkylation at the ortho and para positions, it also favors dealkylation - via electrophilic attack by a proton - at these same positions. This means that while the ortho and para isomers are formed more rapidly, they are also dealkylated more rapidly as shown ... 

Thermal treatment of the dimer with anisole, toluene, and 1-chloronaphtha-lene in the presence of a large excess of pTsOH and air leads to the formation of mono-arylated azafullerenes in 78-90% isolated yields [68]. The reaction with anisole and toluene yield para-substitution products 35 and 39, while 1-chloro-naphthalene is substituted at various positions (Fig. 21). The reaction does not take place in the absence of air or pTsOH. The reaction is presumed to proceed through electrophilic aromatic substitution by C59N, which was proposed as being formed via thermal homolysis of the dimer, followed by oxidation with O2. 

In keeping with the seminal work of Kita, we proposed that the I(III)-mediated amination involved a radical cation intermediate that was generated by single electron transfer from the arene to the I(III) oxidant. The consequent radical cation should be highly reactive, and the attack of a phthalimide nucleophile would lead to a mixture of regiomeric products, like the 5 6 3 mixture that was observed for our toluene reaction (Scheme 10). This hypothesis contrasts with the mechanisms proposed by Chang and Antonchick, as electrophilic aromatic substitution, even with a reactive R2N species, should favor the para product. 

Bromination of Alkylaromatics in SC-CO2. Product Yields. The bromination of toluene in SC-CO2 proceeded smoothly as indicated in equation 6. The major reaction product, formed in >70% yield, was benzyl bromide accompanied by a small amount (10 - 20%) of / -bromotoluene (resulting from a competing electrophilic aromatic substitution process). 

One of the most important reactions in the production of industrial aromatics is electrophilic aromatic substitution another prominent type of reaction is nucleophilic substitution, which is favored for aromatics with electron-withdrawing groups. Free radical reactions, which occur especially in thermal pyrolysis processes and in side-chain oxidation and chlorination reactions, are even more important, in quantitative terms, than electrophilic and nucleophilic substitution reactions. Typical examples are thermal cracking of naphtha and gas-oil fractions, the oxidation of naphthalene to phthalic anhydride, and the side-chain chlorination of toluene. Rearrangement reactions are less significant. 

Whereas the nitro derivatives of benzene are produced by electrophilic aromatic substitution, further important derivatives of toluene are predominantly obtained through reactions of the methyl group they include the production of oxidation products such as benzoic acid and the side-chain chlorinated toluene compounds. 

As another example of the importance of the order in electrophilic aromatic substitutions, consider the conversion of toluene to p-nitrobenzoic acid. The nitro group can be introduced with a nitrating mixture of nitric and sulfuric acids. The carboxyl group can be produced by oxidation of the methyl group of toluene (Section 21.5A). Nitration of toluene yields a product with the two substituents in the desired para relationship. Nitration of benzoic acid, on the other hand, yields a product with the substituents meta to each other. 

PROBLEM 14.9 The synthesis of toluene by the aluminum chloride-catalyzed Friedel-Crafts alkylation of benzene with methyl chloride is badly complicated by the formation of di-, tri-, and polymethylated benzenes. It appears that the initial product of the reaction, toluene, is more reactive in the Friedel-Crafts reaction than is benzene. Analyze the mechanism of electrophilic aromatic substitution to see why toluene is more reactive than benzene. Hint. Look carefully at substitution in the position directly across the ring from the methyl group (the para position) for toluene, and look for differences from the reaction with benzene. 

The reaction of toluene-2,4-diisocyanate with chlorine to l-chloromethyl-2,4-diisocyanatobenzene was carried out in a falling-film microstructured reactor with a transparent window for irradiation [264]. There are two modes of reaction. The desired radical process proceeds with the photoinduced homolytic cleavage of the chlorine molecules, and the chlorine radical reacts with the side chain of the aromatic compound. At very high chlorine concentrations radical recombination becomes dominant and consecutive processes such as dichlorination of the side chain may occur as well. Another undesired pathway is the electrophilic ring substitution to toluene-5-chloro-2,4-diisocyanate, promoted by Lewis acidic catalysts in polar solvents at low temperature. Even small metallic impurities probably from corrosion of the reactor material can enhance the formation of electrophilic by-products. 

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