Methylbenzene, substituted

Neither benzenepentacarboxylic acid nor mellitic acid are manufactured commercially, but synthetic mellitic acid can be purchased as a laboratory chemical (99). Both can be synthesized by oxidizing the corresponding methylbenzenes or other substituted benzenes, and both are present in trace amounts after oxidation of coal or coal-like substances. 

The bold number shows the position on the patent (poly)methylbenzene where the incoming group will substitute. 

Iron pentacarbonyl and l-methoxy-l,4-cyclohexadiene react as shown by Birch and oo-workera, but in dibutyl ether this solvent has been found superior. The tricarbonyl(methoxy-l,3-cyclohexadiene)iron isomers undergo hydride abstraction with triphenylmethyl tetrafluoro-borate to form the dienyl salt mixture of which the 1-methoxy isomer is hydrolyzed by water to the cyclohexadienone complex. The 2-methoxy isomer can be recovered by precipitation as the hexafluoro-phosphate salt. By this method the 3-methyl-substituted dienone complex has also been prepared from l-methoxy-3-methylbenzene. The use of the conjugated 1-methoxy-1,3-cyclohexadiene in Part B led to no increase in yield or rate and resulted chiefly in another product of higher molecular weight. An alternative procedure for the dienone is to react tricarbonyl(l,4-dimethoxycyclohexadiene)iron with sulfuric acid. ... 

Toluene (methylbenzene) is similar to benzene as a mononuclear aromatic, but it is more active due to presence of tbe electron-donating metbyl group. However, toluene is much less useful than benzene because it produces more polysubstituted products. Most of tbe toluene extracted for cbemical use is converted to benzene via dealkylation or disproportionation. Tbe rest is used to produce a limited number of petro-cbemicals. Tbe main reactions related to tbe cbemical use of toluene (other than conversion to benzene) are the oxidation of the methyl substituent and the hydrogenation of the phenyl group. Electrophilic substitution is limited to the nitration of toluene for producing mono-nitrotoluene and dinitrotoluenes. These compounds are important synthetic intermediates. 

Alkylbenzenes such as toluene (methylbenzene) react with NBS to give products in which bromine substitution has occurred at the position next to the aromatic ring (the benzyiic position). Explain, based on the bond dissociation energies in Table 5.3 on page 156. 

Arylisoxazol-5(4//)-oncs 21 react with benzene-1,2-diamines to yield 4-aryl-l,5-benzodiaze-pinones 22 by elimination of hydroxylamine from the intermediate oximes. Unsymmetrically substituted benzene-1,2-diamines are attacked at the more nucleophilic amino group. Thus, 4-methylbenzene-1,2-diamine gives 7-methylbenzodiazepinones 22f-h, whereas 4-nitrobenzene-1,2-diamine gives 8-nitro compounds 22k-n. The benzodiazepinones are accompanied by minor amounts of 2-methylbenzimidazoles 23. Selected examples are given.275... 

The present method of preparation of 4,4 -dimethyl-l,l -biphenyl is that described by McKillop, Elsom, and Taylor 15 It has the particular advantages of high yield and manipulative simplicity and is, moreover, applicable to the synthesis of a variety of symmetrically substituted biaryls 3,3 - and 4,4 -Disubstituted and 3,3, 4,4 -tetrasubstituted 1,1 -biphenyls are readily piepared, but the reaction fails when applied to the synthesis of 2,2 -disubstituted-l,T biphenyls The submitters have effected the following conversions by the above procedure (starting aromatic bromide, product biphenyl, % yield) bromobenzene, biphenyl, 85,1 -bromo-4-methoxybenzene, 4,4 -dimethoxy-l, 1 -biphenyl, 99, 1 bromo 3 methylbenzene, 3,3 dimethyl-1,l -biphenyl, 85 4-bromo-l,2-dimethylbenzene, 3,3, 4,4 -tetramethyl-l,l -biphenyl, 76, l-bromo-4-chlorobenzene, 4,4 -dichloro-l,l -biphenyl, 73, l-bromo-4-fluorobenzene, 4,4 -difluoro-l,l -biphenyl, 73... 

Radical attack on methylbenzene (toluene, 60) results in preferential hydrogen abstraction by Cl leading to overall substitution in the CH3 group, rather than addition to the nucleus. This reflects the greater stability of the first formed (delocalised) benzyl radical, PhCH2 (61), rather than the hexadienyl radical (62), in which the aromatic stabilisation of the starting material has been lost ... 

Methylbenzenes were oxidized, and substituted benzaldehydes were... 

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]

When the parent molecules connected by the azo group are different, azo is placed between the complete names of the parent molecules, substituted or unsubstituted. Locants are placed between the affix azo and the names of the molecules to which each refers. Preference is given to the more complex parent molecule for citation as the first component, e.g., 2-aminonaphthalene-l-azo-(4 -chloro-2 -methylbenzene). 

Although anthraquinone is the starting point for the preparation of many derivatives, involving substitution and replacement reactions, certain compounds are obtained directly by varying the components in the above synthesis. Thus, for example, replacement of benzene with methylbenzene (toluene) leads to the formation of 2-methylanthraquinone. A particularly important variation on the phthalic anhydride route is the synthesis of 1,4-dihydroxyanthraquinone (6.6 quinizarin) using 4-chlorophenol with sulphuric acid and boric acid as catalyst (Scheme 6.3). The absence of aluminium chloride permits hydrolysis of the chloro substituent to take place. 

Table 15 summarizes the values obtained for all methylbenzenes by various methods. Asr has already been repeatedly mentioned, the basicity increases with the number of methyl groups. The differing increase in basicity obtained by different methods is particularly clear if one compares the values for hexamethylbenzene, which vary between 4 and 140. The best agreement between the various methods is found for the first members of this series, including the trimethyl-substituted benzene derivatives. 

Similarly to the methylbenzenes, the condensed aromatics also show a clear increase in basicity with methyl substitution, as may be seen for... 

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. 

Friedel-Crafts-type polyalkylations of alkyl-substituted benzenes with Ic become less difficult as the number of electron-donating methyl groups on the benzene ring increases. This is consistent with the fact that the alkylation occurs via an electrophilic substitution. The tendency of starting methylbenzenes to form rearranged products also increases in the same order from toluene to mesitylene. 

The a-substitution product from oxidation of methylbenzenes in acetic acid can be eliminated by electrochemical hydrogenolysis at the cathode. An undivided cell is used and a palladium on carbon catalyst is suspended in the medium. The necessary hydrogen is generated by reduction of protons at the cathode. In this way, the... 

The reaction from an enamine is initiated by the addition of a trace of a strong acid, e.g. /7-toluenesulfonic acid (TsOH, 4-methylbenzene-sulfonic acid), to the ketone and pyrrolidine in a solvent such as toluene. When the mixture is at reflux in a Dean-Stark apparatus, water is liberated and is removed through azeotropic distillation, leaving the enamine in the reaction vessel. After a follow-up reaction between the enamine and a suitable electrophile, an iminium salt is produced that liberates both the a-substituted ketone and pyrrolidine when it is treated with aqueous acid (Scheme 6.20). 

Fluorescence was observed for the TMB family such as 3,5-dimethoxyphenol, l,3-dihydroxy-5-methoxybenzene (5-methoxyresorcinol), l-acetoxy-3,5-dimethoxyben-zene, and l,3,5-trimethoxy-2-methylbenzene. These results indicated that complete symmetry of the substitution on O atoms is not necessary to observe fluorescence from the TMB family, and that the variation of parent molecules of fluorescent radical cation is possibly performed [153]. Fluorescence was also detected from hexamethxybenzene as an example of pseudo-Dgh molecules. The discussion of the symmetry has been described here on the fluorescence from fluorobenzenes in the vapor-phase or noble gas matrices. 

A new reagent, AMiydroxyphthalimide combined with Co(acac)n (n = 2,3), transforms alkylbenzenes to ketones, whereas methylbenzenes give the corresponding carboxylic acids.1121 Phthalimide N-oxyl was found to be the key intermediate. Novel oxoperoxo Mo(VI) complexes mediate the cost-effective and environmentally benign oxidation of methylbenzenes to carboxylic acids.1384 Similar green oxidation of p-xylene to terephthalic acid was reported by using a Ru-substituted heteropolyanion.1385... 

Similarly, if we look at the H-C bond-dissociation energies of the hydrocarbons shown in Table 4-6, we would infer that Cl- would remove a hydrogen most rapidly from the carbon forming the weakest C-H bond and, again, this is very much in accord with experience. For example, the chlorination of methylbenzene (toluene) in sunlight leads to the substitution of a methyl hydro-... 

Also the mononitration of methylbenzene does not lead to equal amounts of the three possible products. The methyl substituent apparently orients the entering substituent preferentially to the 2 and 4 positions. This aspect of aromatic substitution will be discussed in Section 22-5 in conjunction with the effect of substituents on the reactivity of aromatic compounds. 

Explain why the distribution varies with the nature of the substituting agent. Predict the product distribution of isomeric ions if Br were to add to methylbenzene in the gas phase. 

The orientation and reactivity effects of substituents discussed for the substitution of monosubstituted benzenes also hold for disubstituted benzenes, except that the directing influences now come from two groups. Qualitatively, the effects of the two substituents are additive on the reactivity. We therefore would expect 4-nitromethylbenzene to be less reactive than methylbenzene... 

Table 7.16 Relative Rates of Aromatic Substitutions and Relative a and 7r Complex Stabilities of Methylbenzenes...

Substituted aromatic compounds are named using the suffix -benzene. Thus, C6H5Br is bromobenzene, C6H5CH3 is methylbenzene (also called toluene), C6H5N02 is nitrobenzene, and so on. Disubstituted aromatic compounds are named using one of the prefixes ortho-, meta-, or para-. An ortho- or o-disubstituted benzene has its two substituents in a 1,2 relationship on the ring a meta- or m-disubstituted benzene has its two substituents in a 1,3 relationship and a para- or p-disubstituted benzene has its substituents in a 1,4 relationship. When the benzene ring itself is a substituent, the name phenyl (pronounced fen-nil) is used. 

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