Para-toluidine method

Examjdes.—Aniline is rapidly tribrominated at room temperature, the end point is very sharp, and this estimation of aniline is preferable to the nitrous acid method. At ordinary temperature ortho- and para-toluidines are dibrominated and meta-toluidine is tribrominated. Dimethylaniline is monobrominated at 0°—5°, dibrominated at 40°—50° and tribrominated at 60°—70°, an interesting example of the effect of temperature. Sulphanilic acid at 60°—70° yields tribromoaniline, and at this temperature p-nitroaniline reacts quantitatively. Phenol at about 22° yields tribromophenol. For reference to the estimation of m-diamines, m-dihydroxy compounds, R salt, cresols, p nitroaniline, diphenylamine, p-nitrophenol, and other notes, see J. S. C. I., 41, 161. 

Muspratt and Hofmann reduced nitrobenzene to aniline by Zinin s method, and nitrotoluene to toluidine, mentioning that aniline cannot be nitrated but nitraniline can be obtained by reducing dinitrobenzene, a reaction later described in detail. Hofmann s paper on the chloro- and bromo-derivatives of aniline has a note by Liebig certifying the accuracy of the work. Hofmann and Muspratt s toluidine was a mixture of ortho- and para-toluidine. Pure orthotoluidine was first obtained by A. Rosenstiehl, metatoluidine by Beilstein and A. Kuhlberg, and paratoluidine by Hofmann. ... 

ASTM Method D 4224-89 Standard Test Method for Anionic Determination by Para-toluidine Hydrochloride. American Society for Testing and Materials, Philadelphia, USA. 

Equivalent weight of sulfated and sulfonated anionics can be determined directly by titration with base or by titration with a cationic surfactant. This requires that the active agent be isolated in relatively pure condition. A more general procedure is the para-toluidine hydrochloride method, which includes pimification of the anionic by extraction to eliminate interferences commonly found in detergents. These procedures are described in Chapter 16. 

In the direct nitration of o-cresol a mixture of the p- and o- derivatives is formed, from which relatively little of the para- isomer can be isolated.1 Better methods for the preparation of the />ara-compound are by diazotization of 5-nitro-o-toluidine and replacement of the diazo group by hydroxyl, or by simply boiling the nitrotoluidme with strong aqueous alkali.1... 

The reduction of the mononitrotoluenes to toluidins by the use of iron and hydrochloric acid forms the basis for a method of estimation of the para isomer in crude nitrotoluene. (3) A weighed amount of the mixed toluidins is dissolved in ether, and then ethereal oxalic acid is added. The toluidins all form compounds with oxalic acid, and all but the para compound are soluble in ether. The solution is then filtered, the residue washed with ether, then dissolved in water and titrated with N/10 sodium hydroxide, using phenolphthalein as the indicator. 

Homologous Amines. Toluidines.—The amino derivatives of the homologues of benzene are formed by the same kind of reactions as those for preparing aniline, viz., the reduction of the homologous mono-nitro compounds. The- amino toluenes in which the amino group is substituted in the benzene ring are known as toluidines, and there are, of course, three isomeric compounds, orthoj meta and para. In the ordinary nitration of toluene the ortho and para compounds are formed. By indirect methods (p. 532) the meta-nitro toluene may also be prepared. These nitro compounds by reduction yield the corresponding toluidines. 

Rosaniline then is another dye compound related to para-rosaniline. It is not isomeric but differs in composition by CH2. This at once suggests that it is a homologue and such has been found to be the case. Its constitution has been established by its synthesis from pure compounds. When, instead of using two molecules of aniline and one molecule of />-toluidine as in the synthetic preparation of para-rosaniline, we use one molectde each of aniline, p-toluidine and ortho-toluidine then we obtain the leuco base of rosaniline alone. From the leuco base the dye salt is obtained by the usual methods. The reactions analogous to the ones for para-rosaniline are ... 

In an I.G. Farben patent [180] the use of disulfur dichloride is described in place of sulfur (method BJ. Possibly the intermediates here are 1,3,2-benzothiazathiolium chlorides (CV) which react with carbon disulfide to give benzothiazoline-2-thiones (CIII). In some instances, the cycUzations are carried out in the presence of sodium hydrosulfite or sodium sulfide. A peculiarity of this reaction is that, simultaneously with the cyclization, chlorination of the arylene ring occurs. Thi.s is not a general rule though. It happens with aniline, o-toluidine, o-anisidine and oc-naphthylamine but not with /)-phenetidine, )S-naphthylamine or benzidine. It seems quite clear therefore that the para position of the aniline must be free if chlorination is to take place, since it is in this position that the chlorine atom is brought in. With anthranilic acid there is formed 4-carbox -6-phenylaminobenzothiazoline-2-thione which shows that the chlorine atom, which is substituted during the reaction, is replaced by a second molecule of anthranilic acid and that decarboxylation occurs at the same time. 

Conversion of Phenols to Amines. Aniline and some diphenylamine are formed when phenol and NHs solution are heated under pressure in the presence of FeCh, Al(OH)s, or Fe(OH)j. When NH and phenol or ortho-or para-cresols are reacted in the vapor phase over an AljO catalyst, yields of up to 88 per cent of the corresponding amines are obtained. However, these amines are customarily obtained by reducing the parent nitro compound, except in cases where it is difficult to obtain the required nitro isomer. For example, it is considered that the amination of symr xylenol is the best method of preparing sym-xylidine (l-amino-3,5-di-methylbenzene). When sym-xylenol is heated under pressure to 320 C with ammonium chloride, about equal amounts of sj/m-xylidine and sym-dixylylamine (5-imino-bis-l,3-dimethylbenzene) are formed. The ortho-and para-nitrophenols and nitrocresols can be aminat more readily. 2-Nitro-p-cresol [OH(l), N02(2), CHj(4)] and o-nitrophenol have been aminated in aqueous ammonia containing ammonium salts of weak acids to inhibit decomposition. Phosphoric, boric, carbonic, and formic acids were used. In one case it is claimed that 55-65 per cent yields of 2-nitro-p-toluidine (MNPT of commerce) were obtained when 2-nitro-p-cresol, 28 per cent aqueous NHj, and monoammonium phosphate, 1 11.5 0.2 molar ratio, were heated under pressure for 10 hr at 140-150°C and then 5 hr at about 160 C. Earlier workers, employing somewhat similar conditions, claimed excellent yields of MNPT when 1 mole of ammonium formate was used per mole of 2-nitro-p-cresol. ... 

Even before Kekule published this speculation, another approach was tried not a method for absolute determinations of ring positions, but rather for relative determinations. Let us say that one of the three isomers of toluidine (methyl aniline) is shown to convert into a particular isomer of nitrobenzoic acid when it is vigorously oxidized, and that this nitrobenzoic acid can be shown to reduce to a particular one of the three isomers of aminobenzoic acid. Since all three of these isomers are mutually interconvertible, one can infer that all three molecules have the same relative positions of their two substituents, even though the absolute identity of that positional assignment remains unknown they are all, say, "ortho" compounds (where in this case "ortho" is intended arbitrarily to express only relative and not absolute positions). Such "genetic" chains of interconversions were rapidly developed after January 1865, so that one could make a table of three different series, the compounds in each series being theoretically or actually all mutually interconvertible. These acquired the then-arbitrary names "ortho," "meta," and "para" families of aromatic isomers. At first no one at-... 

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