Anilines bromination

Aniline Bromine Nitric acid, hydrogen peroxide Ammonia, acetylene, butadiene, butane or other petroleum gases, sodium carbide, turpentine, benzene, or finely-divided metals... 

The second point is somewhat less obvious but is readily illustrated by the synthesis of 1,3,5-tribromobenzene. This particular substitution pattern cannot be obtained by direct bromination of benzene because bromine is an ortho, para director. Instead, advantage is taken of the powerful activating and ortho, para-directing effects of the amino group in aniline. Bromination of aniline yields 2,4,6-tribromoanihne in quantitative yield. Diazotization of the resulting 2,4,6-tribromoaniline and reduction of the diazonium salt gives the desired 1,3,5-tribromobenzene. 

According to both the NFPA Guide and Bretherick (Refs 5 13), sulfuric acid causes explosions and/or fires when in intimate contact with a large number (over 70) of materials including acetic anhydride, acet and nitric acid, acrolein, alcohols, alcohols and hydrogen peroxide, anun hydroxide, aniline, bromine and metals, carbides, chlorates, cyclopentadiene, ethylene glycol, various hydrocarbons, hydrochloric acid, iron, mercuric nitride, powdered metals, perchlorates, picrates, pyridine, Na carbonate, steel, sucrose, vinyl acetate, and w. Illustrative... 

Scheme 1-77. A -BOC-Protected 3-methyleneindolines by ort/zo-metalation of A -BOC-anilines, bromination, A -propargylation, and radical cylization.

Aniline is readily halogenated, treatment with bromine water giving an instant precipitate of 2,4,6-tribromoaniline. 

Benzene content Aniline point Bromine number... 

Since, however, some compounds, such as aniline (p. 164), react very rapidly with bromine by substitution, the bromine test should whenever possible be confirmed by the alkaline permanganate test. 

It is also to he noted that ortho and para substitution often occur together in the same molecule, so that the group R enters the para and also both the ortho positions thus both aniline and phenol on bromination readily give symmetric (2,4,6) tribromo-compounds (p. 165), while both toluene and phenol on nitration readily give the symmetric trinitro-derivatives (p. 170). 

Aniline undergoes very ready nuclear substitution by bromine even in the cold, the bromine atoms entering the two ortho positions and the para position with the formation of symmetric or 2,4.6-tribromoaniline. The presence... 

Mono-substitution products of primary amines cannot easUy be prepared by direct action of the appropriate reagent for example, bromination of aniline yields largely the 2 4 6-tribomo derivative and nitration results in much oxidation. If, however, the amino group is protected as in acetanilide, smooth substitution occurs. Thus with bromine, />-bromoacetanilide is the main product the small quantity of the ortlio isomeride simultaneously formed can be easily eliminated by crystallisation. Hydrolysis of p-bromoacetanilide gives/ -bromoaniline ... 

Halogenation. The presence of the amino group activates the ortho and para positions of the aromatic ring and, as a result, aniline reacts readily with bromine or chlorine. Under mild conditions, bromination yields 2,4,6-trihromoaniline [147-82-0]. 

Phenols and phenol ethers readily undergo mono-, di-, or trihromination in inert solvents depending on the amount of bromine used. In water the main product is the 2,4,6-tribromophenol [118-79-6] C H Br O (23). In water or acetic acid anilines also give the tribrorninated product (25). 

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