Sulfonation of aniline

Fig. 5.18. Sulfonation of aniline. Anilinium hydrogen sulfate, which is initially formed from the substrate and concentrated sulfuric acid, reacts via the minimal equilibrium amount of free aniline its amino groups directs the electrophile to the para-position.

These diazonium salts are good electrophiles for activated aromatic rings, such as amines and phenols, and this is how azo dyes are prepared. Diazotization of the salt of sulfanilic acid, which we have just made by sulfonation of aniline, gives an inner salt that combines with N,N-dimethylaniline to form the water-soluble dye, methyl orange. 

Fig. 13.60. Direct sulfonation of aniline (upper) versus the baking reaction (lower).

Several other functional groups may be present on the aromatic nucleus during the sulfonation reaction, including halo, hydroxyl, phen-oxyl, carboxyl, and amino " groups. Sulfonations of aniline and of dimethylaniline take place by different mechanisms. ... 

Simple meta-substituted phenylsulfamates (91) are sweet, but not the corresponding ortho-isomers or para-isomers. The free arylsulfamic acids (92) were first prepared by Kanetani (1980) by acidification of the corresponding ammonium salts (Figure 4).7 Phenylsulfamic acid (92) (Ar = Ph) was obtained by this procedure this compound has for long been postulated as an intermediate in the baking process for the sulfonation of aniline to sulfanilic acid (see Chapter 7, p. 99). 

Figure 2.18 Proposed mechanism for the electrochemical polymerization and in situ sulfonation of aniline. (Reprinted from Synthetic Metals, 129, Y. Sahin, K. Pekmez, A. Yildiz, 107. Copyright (2002), with permission from Elsevier.)...

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

The older methods have been replaced by methods which require less, if any, excess sulfuric acid. For example, sulfonation of naphthalene can be carried out in tetrachloroethane solution with the stoichiometric amount of sulfur trioxide at no greater than 30°C, followed by separation of the precipitated l-naphthalenesulfonic acid the filtrate can be reused as the solvent for the next batch (14). The purification of 1-naphthalenesulfonic acid by extraction or washing the cake with 2,6-dimethyl-4-heptanone (diisobutyl ketone) or a C-1—4 alcohol has been described (15,16). The selective insoluble salt formation of 1-naphthalenesulfonic acid in the sulfonation mixture with 2,3-dimethyl aniline has been patented (17). 

Important analogs of aniline include the toluidines, xyUdines, anisidines, phenetidines, and its chloro-, nitro-. A/-acetyl. A/-alkyl. A/-aryl. A/-acyl, and sulfonic acid derivatives. 

Most derivatives of aniline are not obtained from aniline itself, but ate prepared by hydrogenation of their nitroaromatic precursors. The exceptions, for example, /V-a1ky1ani1ines, /V-ary1ani1ines, sulfonated anilines, or the A/-acyl derivatives, can be prepared from aniline and have been discussed. Nitroanilines are usually prepared by ammonolysis of the corresponding chloronitroben2ene. Special isolation methods may be requited for some derivatives if the boiling points are close and separation by distillation is not feasible. Table 6 Hsts some of the derivatives of aniline that are produced commercially. 

Tetryl. In the manufacture of Tetryl, it is usual not to nitrate dime thy laniline directly, but to dissolve it first in coned sulfuric acid and then to nitrate the dimethylaniline sulfate so obtained. Direct nitration of dimethylaniline proceeds so violently that it can be carried out only under specialized conditions. Many years experience of Tetryl manufacture has shown that the ratio of sulfuric acid to dimethylaniline should not be lower than 3 1, since a smaller amount of sulfuric acid may be detrimental to the nitration process. However, the ratio of sulfuric acid to dimethylaniline must not be too high, otherwise Tetryl yield is decreased. Temp must be maintained between 20-45° to avoid sulfonation of the benzene ring. Care must be exercised not to leave any unreacted dimethylaniline prior to introduction of nitric acid, because of the potential violence of the dimethyl-aniline-nitric acid reaction. Consequently, continuous methods of prepn are to be preferred as they inherently minimize accumulation of unreacted dimethylaniline... 

Aromatic aminosulfonic acids are synthesized by a sequence of important industrial processes, including sulfonation of benzene. This is followed, wherever necessary, by chlorination, nitration, and reduction, or by aniline sulfonation, possibly involving subsequent baking [7,8]. 

Recent work reports the incorporation of aniline sulfonic acid derivatives, o- and m-aminobenzenesulfonic denoted as 1 and 11, respectively, 3-amino-4-methoxybenzenesulfonic (HI), 3-aniline-1-propane sulfonic acid (IV), and... 

The bishydrazones of the 1,2-diketones from inositols have also been converted into triazoles.222,223 The conversion of arylosazones into the corresponding osotriazoles requires the presence of an oxidant, and it is obvious that simple removal of aniline from the osazone, as suggested by the equation, is not involved. In addition to copper(II) sulfate, the reagent most commonly used, other oxidizing heavy-metal salts, such as ferric sulfate and chloride,224 and mercuric acetate,223 have been used, as well as halogens225 and nitro-sulfonates.226 The osazone acetates are converted into osotriazoles by nitrous acid,227 which decomposes the unacetylated osazones to the aldosuloses228 and the osazone formazans are cyclized with warm... 

In this method, an ale soln of benzene-sulfonic acid(previously standardized with phosgene by weighing the pptd diphenyl-carbamide) is added from a burette to a sample of aniline(or its nitrated compd not jiighvr thsji tctrsnitro-) until the 3ppcufuptcc of a dirty-bluish coloration, when a drop of the reaction mist is placed on a filter paper previously impregnated with amino-/3-naphthol indicator(spot test). This method is not applicable for analysis of penta-nitroani ine(Ref 15)... 

Lee s group has published extensive results on aminolysis of sulfonates.278 281 Thus the reactions of anilines witii 2-cyano-2-propyl and 1-cyanocyclooctylarenesulfonates in acetonidile have been stiidied.278 A dissociative, S k2 mechanism with a loose TS is supported from die usual LFERs. An 5k2 mechanism is also found for the reaction in acetone of (Z)-benzyl (X)-benzenesulfonates witii (Y)-pyridines.279 Nucleophilic substiditions witii die cycloalkyhnetiiylsulfonates (306) and anilines in MeOH were also sfridied.280 Finally die reaction of tiiiopheneethyl arenesulfonates (307) with anilines and AvA -dimethylanilines in MeCN has been reported on.281 Frontside-atiack in an 5n2 mechanism witii a four-centre TS is supported. 

The replacement of a nuclear substituent such as hydroxyl (-OH), chloro, (-C1), or sulfonic acid (-S03H) with amino (-NH2) by the use of ammonia (ammonolysis) has been practiced for some time with feedstocks that have reaction-inducing groups present thereby making replacement easier. For example, l,4-dichloro-2-nitrobenzene can be changed readily to 4-chloro-2-nitroaniline by treatment with aqueous ammonia. Other molecules offer more processing difficulty, and pressure vessels are required for the production of aniline from chlorobenzene or from phenol (Fig. 3). 

Sulfonation. The direct sulfonation of alkylaminotriphenylmethane dyes gives mixtures of substituted products. Although dyes containing anilino or benzylamino groups give more selective substitution, a sulfonated intermediate such as 3[(N-ethyl-N-phenylamino)methyl]benzenesulfonic acid (ethylbenzylanilinesulfonic acid) is the preferred starting material. However, Patent Blue V [354649-0], Cl Acid Blue 3, was made from 3-hydroxybenzaldehyde and two moles of diethyl aniline, followed by sulfonation of the leuco base and oxidation to the dye. FD C Green 2 [5141 -20-8/,... 

The oxidation of a wide range of phenol and other biorefractory organic compounds (e.g., ethanol, aliphatic acids, naphthalene and anthraquinone sulfonic acids, aniline, nitrobenzene, etc.) on platinized titanium was also studied by Kotz et al. (Kotz et al. 1991 Stucki et al. 1991). The elimination of TOC was rather ineffective due to the leakage current for oxygen evolution, and the average EOI was about 0.05. 

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