Substitution of sulphonic groups

Sulphonation of compounds followed by substituting the sulpho group by a nitro group is the method of great practical importance. This method is widely used for the nitration of phenols. The reaction occurs as follows  

Owing to this course of the reaction the oxidation of phenols and the formation of side-products can be largely avoided. This is discussed in more detail in the chapter on the nitration of phenols (p. 502). 

Another method, of great importance in laboratory practice, is the substitution of a halogen by a nitro group. 

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The mechanism of the substitution of sulphonic groups in phenol by nitro groups was extensively studied by Lesniak and T. Urbartski [130 and to this purpose the chromato-polarographic method introduced by Kemula and associates 11311 was used. The trend of the nitration of o and p-phenolsulphonic acids with nitric acid can be depicted by diagram (16a) ... 

Just as chlorosulphonic add may be regarded as derived from hydrochloric acid by the substitution of the group —SOa.OH in place of the hydrogen atom, so also many other compounds are known which likewise may be considered as produced by the introduction of the sulphonic acid group in place of hydrogen. 

There is also a possibility that the reaction may go forward in two steps, the first step being the sulpho-nation of the toluene, and the second step the substitution of nitro-groups for the sulphonic groups ... 

Bourns (1963) investigated the bromination of anisole-4-sulphonic-2,6- 2 acid. In the presence of 0 0 to 2-Om bromide ions the ratio kgjkjy increases from 1-00 to 1-31. As a competitive reaction bromode-sulphonation takes place, bromine substituting the sulphonic group in the 4-position. Using anisole-4-sulphonic acid containing the natural abundance of the sulphur isotopes. Bourns measured sulphur isotope effects k jk is 1-003, 1-013 and 1-017 for initial bromide ion concentrations of 0-0, 0-05 and 0-50m respectively. This confirms, that bromodesulphonation also follows mechanism (6-2). 

The imides, primaiy and secondary nitro compounds, oximes and sulphon amides of Solubility Group III are weakly acidic nitrogen compounds they cannot be titrated satisfactorily with a standard alkaU nor do they exhibit the reactions characteristic of phenols. The neutral nitrogen compounds of Solubility Group VII include tertiary nitro compounds amides (simple and substituted) derivatives of aldehydes and ketones (hydrazones, semlcarb-azones, ete.) nitriles nitroso, azo, hydrazo and other Intermediate reduction products of aromatic nitro compounds. All the above nitrogen compounds, and also the sulphonamides of Solubility Group VII, respond, with few exceptions, to the same classification reactions (reduction and hydrolysis) and hence will be considered together. 

The sodium salt of the cymene sulphonic acid is then fused with sodium hydroxide in the usual manner, and the hydroxyl group substituted for the sulphonic group. This gives l-methyl-3-hydroxy-4-isopropyl-benzene or thymol. 

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) ... 

The neomycin molecule contains both free amino and free hydroxy groups. Many workers have exploited the possibility of chemical de-rivatisation at these positions in attempts to reduce the toxicity of the parent antibiotic. Substitution of methane sulphonate groups at the amino nitrogen has been reported by Umezawa et al83,84 and by Boissier et al . Both groups of workers described the derivative to be less toxic... 

The hydroxy-nitro dye Naphthol Yellow S (6.233 Cl Acid Yellow 1) was discovered in 1879 by Caro and is still manufactured. It is produced by sulphonation of 1-naphthol to give l-naphthol-2,4,7-trisulphonic acid, followed by replacement of the 2- and 4-sulpho groups in nitric acid medium. Nucleophilic substitution of l-chloro-2,4-dinitrobenzene with 4-aminodiphenylamine-2-sulphonic acid gives Cl Acid Orange 3 (6.234). 

Alcohols may be prepared (1) by hydration of alkenes (1) in presence of an acid and (11) by hydroboratlon-oxidatlon reaction (2) from carbonyl compounds by (1) catalytic reduction and (11) the action of Grignard reagents. Phenols may be prepared by (1) substitution of (1) halogen atom In haloarenes and (11) sulphonic acid group In aiyl sulphonic acids, by -OH group (2) by hydrolysis of diazonium salts and (3) industrially from cumene. 

By the action of alkali hydrogen sulphites on alkali nitrites, compounds are obtained the structure of which may be derived from that of ortho-nitrous acid, N(OH)a, by substituting the sulphonic acid group, — S02-0H, for one or more hydroxyl groups. 

Reaction CXLVI. Action of Concentrated Sulphuric Acid on Hydrocarbons or Substituted Hydrocarbons.—When cone, sulphuric acid acts on an aromatic hydrocarbon or substituted hydrocarbon, one or more of the H atoms in the nucleus is replaced by the sulphonic group (S02.0H). 

Reaction CXLVII. Action of Fuming Sulphuric Add (oleum) on Hydrocarbons or Substituted Hydrocarbons.—It is sometimes difficult to introduce a sulphonic group by means of cone, sulphuric acid, and it is then necessary to use fuming acid (i.e., acid containing up to 70% free S03). The same factors as before have an important influence on the reaction. Usually a high temperature is necessary where more than one SOaH has to be introduced. In some cases oleum is used in preference to sulphuric acid, in order to reduce the time and the temperature of sulphonation. 

A series of acids can he derived from orthonitrous acid by the substitution of sulphinic, HSO 2> or sulphonic, HS0 3, radicles in place of the hydroxyl-groups. The result with the sulphonic radicles is ... 

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