This is exactly like the reaction which happens with phenol. 2. That's what happens in phenylamine. Bromination of acetanilide gives para brominated acetanilide mainly, because amino group of acetanilide is protected by acetyl group. In the case of the nitrogen and oxygen activating groups displayed in the top row of the previous diagram, electron donation by resonance dominates the inductive effect and these compounds show exceptional reactivity in electrophilic substitution reactions. Substitution
An early method of preparing phenol (the Dow process) involved the reaction of chlorobenzene with a concentrated sodium hydroxide solution at temperatures above 350 ºC. The exact influence of a given substituent is best seen by looking at its interactions with the delocalized positive charge on the benzenonium intermediates generated by bonding to the electrophile at each of the three substitution sites. In examples 4 through 6, oppositely directing groups have an ortho or para-relationship. The strongly activating hydroxyl (–OH) and amino (–NH2) substituents favor dihalogenation in examples 5 and six. In the case of alkyl substituents, charge stabilization is greatest when the alkyl group is bonded to one of the positively charged carbons of the benzenonium intermediate. This page looks at the reaction of the benzene ring in phenylamine (aniline) with bromine water. The synthesized 2,4,6-tribromoaniline was obtained as colourless crystals, Mann F. G., Saunders B. C., Practical Organic Chemistry, 4. As noted on the opening illustration, the product-determining step in the substitution mechanism is the first step, which is also the slow or rate determining step. The product is a. o-bromoaniline b. The steric bulk of the methoxy group and the ability of its ether oxygen to stabilize an adjacent anion result in a substantial bias in the addition of amide anion or ammonia. When bromination of aniline is carried out by protecting -NH2. That means that incoming groups will tend to go into the 2- position (next door to the -NH2 group) or the 4- position (opposite the -NH2 group). Principle: p-bromoacetanilide is prepared by bromination process.Mono substituted products of primary amine cannot prepared easily by direct action of a reagent. These compounds are easily reduced to their dihydroxybenzene analogs, and it is from these compounds that quinones are best prepared. For example, reaction of excess benzene with 1-chloropropane and aluminum chloride gives a good yield of isopropylbenzene (cumene). Substitution of the Hydroxyl Hydrogen
As with the alcohols, the phenolic hydroxyl hydrogen is rather easily replaced by other substituents. Only the 2- and 4-chloropyridine isomers undergo rapid substitution, the 3-chloro isomer is relatively unreactive. Since there are six equivalent carbons in benzene, the total rate would be 6.0. The zinc used in ketone reductions, such as 5, is usually activated by alloying with mercury (a process known as amalgamation). From heats of hydrogenation or combustion, the resonance energy of naphthalene is calculated to be 61 kcal/mole, 11 kcal/mole less than that of two benzene rings (2 * 36). The bromination is highly para-selective for aniline itself as well as for ortho- and meta-substituted anilines. By acetylating the heteroatom substituent on phenol and aniline, its activating influence can be substantially attenuated. Finally, the fourth example illustrates several important points. It is not surprising, therefore, that there is a rough correlation between the rate-enhancing effect of a substituent and its site directing influence. This is illustrated by clicking the "Show Mechanism" button next to the diagram. Because of their high nucleophilic reactivity, aniline and phenol undergo substitution reactions with iodine, a halogen that is normally unreactive with benzene derivatives. The electrophilic reactivity of these different reagents varies. Also, an animated diagram may be viewed. The lone pair on the nitrogen touches the delocalised ring electrons . . aniline is dissolved in 10 ml. The next two questions require you to analyze the directing influence of substituents. Electrophilic Substitution of Disubstituted Benzene Rings
When a benzene ring has two substituent groups, each exerts an influence on subsequent substitution reactions. proton loss). Also, as noted earlier, toluene undergoes nitration about 25 times faster than benzene, but chlorination of toluene is over 500 times faster than that of benzene. The smallest such hydrocarbon is naphthalene. Hydrolysis of Sulfonic Acids
The potential reversibility of the aromatic sulfonation reaction was noted earlier. The position of the tube D is adjusted until it touches the surface of the bromine layer. The trinitro compound shown at the lower right is a very strong acid called picric acid. Synthesis of 2, 4, 6-tribromoaniline from aniline, A g.mol of Aniline with 3 g.mol of Bromine yields a g.mol of Tribromoaniline, 159 g of Bromine yields Tribromoaniline = 329.8 g. If reported Practical yield is 8.5 g, then. Furthermore, SN1, SN2 and E1 reactions of benzylic halides, show enhanced reactivity, due to the adjacent aromatic ring. Bromination of both phenol and aniline is difficult to control, with di- and tri-bromo products forming readily. Note that if two different sites are favored, substitution will usually occur at the one that is least hindered by ortho groups.