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Electrophilic aromatic sulphonation

The nitration, sulphonation and Friedel-Crafts acylation of aromatic compounds (e.g. benzene) are typical examples of electrophilic aromatic substitution. [Pg.155]

A surprising exception has been reported with evidence for a cleavage reaction in the case of divinyl sulphone. In non-aqueous and slightly acidic media, the behaviour of a., ji-unsaturated aromatic sulphones is also complex (see Table 7) since the cleavage and the saturation may compete. Strongly electrophilic double bonds undergo Michael additions in aprotic solvents by slowly protonated anions. Transfer of labile hydrogen may also lead to unactivated bases. It is noteworthy that in numerous cases (Table 6) the saturation is the preferred route. [Pg.1021]

Electrophilic aromatic substitution is a reaction where a hydrogen atom in an aromatic system, e.g. benzene, is replaced by an electrophile. Some of the important electrophilic substitution reactions are Friedel-Crafts alkylation and acylation, nitration, halogenation and sulphonation of benzene. [Pg.254]

The mec/tanism of aromatic sulphonation may be similar to that previously described for nitration and halogenation, involving attack of the electrophilic +... [Pg.548]

The mechanism of aromatic sulphonation is broadly analogous to that previously described for aromatic nitration and halogenation and may be represented in the following way, the neutral sulphur trioxide molecule functioning as the electrophilic species. Sulphonation differs from nitration and halogenation, however, in that the overall reaction is reversible. [Pg.873]

Some aromatic compounds have been shown to be substituted in the ring by sulphonyl peroxides421,422 to give 50-70% yields of the sulphonate ester, as shown in equation 96. The experimental evidence from this reaction is apparently consistent with an electrophilic aromatic substitution reaction. [Pg.372]

For these and several other reactions in strongly acidic media, protonation of the substrate is probably unimportant, e.g. solvolysis of benzenesulphonyl bromide (PhS02Br) even in 99.98% sulphuric acid132. Rates of SN2 reactions are probably more dependent on solvent nucleophilicity10. Also, electrophilic aromatic substitutions on protonated substrates are expected to be disfavoured, e.g. methanesulphonanilide (39) is half protonated in 84% sulphuric acid, but sulphonation reactions in 80-99.8% sulphuric acid are explained (see below) without postulating protonation of the substrate133. [Pg.686]

Much of the data available on electrophilic aromatic substitution comes from detailed studies of sulphonation over many years134. Remarkably precise product yields (e.g. 0.3%, usually determined by NMR analysis of mixtures) are sometimes reported, and it would be interesting to compare these results with those now available independently... [Pg.686]

Substituted benzyl alcohols can be prepared by o-lithiation of the corresponding benzyl alcohol with 2 moles of Bu Li in TMEDA-pentane followed by reaction with an electrophile. Similarly, the sulphonates (16) are further lithi-ated to (17, X = Li), and (17, X = E) are obtained with electrophiles (E ). Subsequent desulphonation thus leads to a new methodology for electrophilic aromatic substitution. [Pg.226]

In Volume 13 reactions of aromatic compounds, excluding homolytic processes due to attack of atoms and radicals (treated in a later volume), are covered. The first chapter on electrophilic substitution (nitration, sulphonation, halogenation, hydrogen exchange, etc.) constitutes the bulk of the text, and in the other two chapters nucleophilic substitution and rearrangement reactions are considered. [Pg.516]

In conclusion, it should be mentioned that though the great majority of aromatic electrophilic substitution reactions involve displacement of hydrogen, other atoms or groups can be involved. Thus we have already seen the displacement of S03H in the reversal of sulphonation (p. 140), of alkyl in dealkylation (p. 143), and a further, less common, displacement is that of SiR3 in protodesilylation (cf. also p. 161) ... [Pg.149]

Sulphones and sulphonamides—the S -b O class —are similarly powerful directors , and do not suffer electrophilic attack at sulphur (though they occasionally suffer nucleophilic attack on the aromatic ring) but are less useful because of their more limited synthetic applications -. Aryl f-butylsulphoxides are also powerful ortljo-directors , but less hindered diaryl sulphoxides are susceptible to attack by organolithiums at sulphur. ... [Pg.503]

The sulphonation of toluene (Expt 6.37) with concentrated sulphuric acid at 100-120°C results in the formation of toluene-p-sulphonic acid as the chief product, accompanied by small amounts of the ortho and meta isomers these are easily removed by crystallisation of the sodium salt of the para isomer in the presence of sodium chloride. Sulphonation of naphthalene at about 160°C yields largely the 2-sulphonic acid (the product of thermodynamic control) (Expt 6.38) at lower temperatures (0-60 °C) the 1-sulphonic acid (the product of kinetic control) is produced almost exclusively. In both cases the product is isolated as its sodium salt. In anthraquinone the carbonyl groups deactivate the aromatic nucleus towards electrophilic attack and vigorous conditions of sulphonation are required, i.e. oleum at about 160 °C. The product is largely sodium anthraquinone-2-sulphonate (Expt 6.39). [Pg.874]

Most reactions such as halogenation, nitration, sulphonation etc. are reactions with a positive ion, with an electrophilic reagent therefore, in which the aromatic molecule reacts nu-cleophilically. In hydrolysis, alcoholysis and aminolysis of aryl halides the reagents are nucleophilic. Radical reactions are also possible, especially in the gas phase at higher temperatures. [Pg.258]

The presence of a second tertiary amine group can result in further complications owing to competition with the neighbouring enamine function for the electrophilic sulphene (Scheme 88). Aromatic sulphonyl chlorides cannot form sulphenes and hence give the acyclic sulphone (Scheme 89). [Pg.784]

Attempts have been repeated to reveal, by physical methods or by separating as salts of aromatic compounds, the formation of arenium ions from electrophilic reagents for nitration, sulphonation, acylation etc. [Pg.12]


See other pages where Electrophilic aromatic sulphonation is mentioned: [Pg.1021]    [Pg.172]    [Pg.198]    [Pg.172]    [Pg.92]    [Pg.156]    [Pg.92]    [Pg.12]    [Pg.51]    [Pg.59]    [Pg.76]    [Pg.77]    [Pg.975]    [Pg.110]    [Pg.145]    [Pg.975]    [Pg.344]    [Pg.356]    [Pg.807]    [Pg.84]    [Pg.234]    [Pg.235]    [Pg.181]   
See also in sourсe #XX -- [ Pg.267 , Pg.268 ]

See also in sourсe #XX -- [ Pg.267 , Pg.268 ]

See also in sourсe #XX -- [ Pg.267 , Pg.268 ]




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