Benzene from aniline

Although practically important in other cases, the replacement of an NH2-group by hydrogen via the diazo-compound naturally has none in the example here given. Thus m-nitrotoluene (and from it m-toluidine) is obtained from p-toluidine by nitration of the acetylated base and replacement of the NH2-group (after elimination of the acetyl) by H, as shown above. 

The course of the reaction is very remarkable. We must suppose that the diazotate is reduced to the unstable phenyldiimine which decomposes into benzene and nitrogen. 

Instead of by alkali stannite the diazo-group can be exchanged for hydrogen by prolonged boiling of the diazonium salt in alcohol, which is thereby oxidised to aldehyde. 

A secondary reaction yields at the same time phenol ether by the replacement of the diazonium group by alkoxyl. This is clearly analogous to the conversion of diazonium salts to phenols. 

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The isosteric relationship of benzene and thiophene has often led medicinal chemists to substitute the sulfur containing heterocycle for benzene drugs in biologically active molecules. That this relationship has some foundation in fact is attested by the observation that the resulting analogs often possess full biologic activity. Alkylation of the diamine, 71 (obtained from aniline and the chloroethylamine), with 2-chloromethylthiophene affords the antihistamine methaphenylene (72) The correspond-... 

Hydro-de-diazoniation seems to be an unnecessary reaction from the synthetic standpoint, as arenediazonium salts are obtained from the respective amines, reagents that are normally synthesized from the hydrocarbon. Some aromatic compounds, however, cannot be synthesized by straightforward electrophilic aromatic substitution examples of these are the 1,3,5-trichloro- and -tribromobenzenes (see below). These simple benzene derivatives are synthesized from aniline via halogenation, diazotization and hydro-de-diazoniation. Furthermore hydro-de-diazoniation is useful for the introduction of a hydrogen isotope in specific positions. 

The diaminobenzenes are made from benzene by a combination chlorination-nitration route although para-phenylene diamine is also made directly from aniline. orr/to-Phenylene diamine is widely used for the preparation of biologically active compounds such as fungicides and veterinarian medicines. The mera-diamine is used in fire-retardant textile fibers ( Nomex ) while the / ara-diamine finds use in high-strength textile fibers used for bullet-proof vests, sails, army helmets, and other types of fiber-reinforced plastics ( Kevlar ). 

Method of Preparation Dissolve 1 mL of benzoyl chloride in 5 mL of pure benzene and treat slowly with 1 mL of aniline dissolved in benzene until the odour of the benzoyl chloride was no longer detectable. After vigorous stirring, treat the mixture with dilute HC1. Evaporate to remove excess of amine and the benzene from the solution and recrystallise the product in aqueous alcohol. 

Thioxo-2,3-dihydro[l, 2,4]triazino[6,5-c]isoquinolin-6-one 189 was obtained (75ZOR2407) by the cyclization of the 3-thiosemicarbazone 188 with alkali. Compound 188 was prepared by the reaction of 3-anilino-1,4-dihydro- 1,4-isoquinolinedione 187 or the ether 186 with thiosemicarbazide. Compound 187 was obtained by reaction of the ether 186 in benzene with aniline. The ether 186 was obtained from the alkylation of 179 (R = H) via its silver salt 185. 

Materials. Methylene 4,4 -diphenyldiisocyanate (MDI, Mobay) was recrystallized from cyclohexane. Toluenediisocyanate (TDI— represents mixture of 2,4- and 2,6-isomers in 80/20 ratio), p-toluidine (Aldrich) and aniline (Aldrich) were purified by vacuum distillation before use. Diphenylmethane, tert-butyl peroxide (TBP), 4-bromoaniline, butyl lithium in hexane, and ethyl chloroformate, were obtained from Aldrich and used as received. Spectrograde tetrahydrofuran (THF) and benzene from Burdick and Jackson were used as received. Poly(tetramethylene ether glycol) with MW 1000 was obtained from polysciences and dehydrated under a rough vacuum at 50 °C for 24 h. 

FIGURE 6. Correlation diagram for the occupied and vacant n MOs of benzene and aniline. Values from References 21 and 78... 

Bull(Fr) [33 33, 1175 St 11790905) 2,4-Dinitrodiphenylamine, (02N)2C6H3.NH.C6Hb red ndls (from benz), mp 157° sol in acet, chlf St hot ale can be prepd by interaction of 4-chloro-l,3 dinitro-benzene and aniline or by other methods (Refs 1-4)... 

N,N -Diphenyl-p-phenylenediamine [39529-22-1 ] M 260.3, m 148-149°. Crystd from chlorobenzene/pet ether or benzene. Has also been crystd from aniline, then extracted three times with absolute EtOH. 

Table I. Yield of Aniline and Benzene from Chlorobenzene and Ammonia at 395°C...

It was first prepd in 1923 by Turek on treating 2,4,6-trichloro-l,3,5-trinitrobenzene with an alkali azide in ale, acet or w soln. It can be obtained also from aniline by chlorination to sym-trichloro-aniline, followed by diazotization, treatment with ale to give sym-trichlorobenzene, nitration with mixed nitric-sulfuric acid to trinitrotrichloro-benzene and finally treatment with an ale soln of Na azide(Refs 3,5,6a 8)... 

If either the o- or -position is occupied, only one isomer is obtained transformation to the mefo-position does not occur. This is a standard method of preparation of acyl-amino-ketones, or by a further hydrolysis of amino-ketones. The tendency, illustrated in this reaction, of groups to wander from the amino group to the nucleus, is also shown in previous reactions and in the preparation of aminoazobenzene from diazoamino-benzene (Preparation 456), of sulphanilic acid from aniline sulphate (Preparation 292), of o- and p-chloroacetanilides from acetochloranilide (Preparation 328), of o- and p-toluidine from methylaniline hydrochloride, and of 1 2 4-aminodimethylbenzene (2 4-xylidine) from dimethylaniline hydrochloride. 

Fluorobenzene is prepared from aniline by the Schiemann reaction, shown in Section 22.18. Aniline is, of course, prepared from benzene via nitrobenzene. Friedel-Crafts acylation of fluorobenzene has been carried out with the results shown and gives the required ethyl p-fluorophenyl ketone as the major product. 

Gomberg and Pemert4 recommended the use of the sodium diazotates for the preparation of biaryls from aniline and from p-toluidine and the normal diazo method for negatively substituted amines such as the bromo- and nitro-anilines. Grieve and Hey 7 found little difference in the yields of biaryls obtained by the two procedures when they coupled diazotized aniline with six different components benzene, toluene, m-xylene, chlorobenzene, nitrobenzene, and ethyl benzoate. Where it is applicable, this modification offers the advantage that the dropwise addition of alkali is eliminated. 

Careful studies of the action of absolute ethyl alcohol on various diazonium salts obtained from aniline have proved that phenetole is the main product, along with a very small quantity of benzene.10 The decomposition of benzenediazonium chloride, for example, results in a 61% yield of phenetole and a 5% yield of benzene.11 The remainder of... 

Few sodium stannite deaminations are to be found in the literature, and of these a substantial fraction concerns unsubstituted amines and their homologs. Thus, benzene is obtained from aniline in 60% yield,102 18 and the hydrocarbons derived from 2,3-dimethylaniline and 2,4,5-trimethylaniline are produced in satisfactory yields and in a high state of purity.108... 

The resonance energy of the pseudobase has been approximated by that of the nearest aromatic molecule from which it can be considered to be derived. Thus, benzene is used as the reference molecule for 1,2-dihydro-2-hydroxy-l-methylquinoline, etc. Small differences in the resonance energies of benzene and aniline (1.6 kcal mol- J140 and benzene and styrene etc. have been ignored. 

The concentration of the weak acid or of the weak base can be determined by distribution between water and another solvent, such as benzene or chloroform the partition coefficient of the acid or base between the water and the other solvent must, of course, be known. The degree of hydrolysis may then be calculated from the concentration of the salt and the determined concentration of the weak acid or base. An example of such a salt is aniline hydrochloride. This is partially hydrolysed into aniline and hydrogen chloride. On shaking the aqueous solution with benzene the aniline will distribute itself between the water and benzene in the ratio of the distribution coefficient. The initial concentration of aniline hydrochloride is known, the concentration of the free aniline in the aqueous solution can be computed from that found in the benzene solution, and from this the total concentration of aniline, produced by hydrolysis, is deduced. Sufficient data are then available for the calculation of the degree of hydrolysis. 

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