Electrophilic aromatic substitution amines

Arylamines contain two functional groups the amine group and the aromatic ring they are difunctional compounds The reactivity of the amine group is affected by its aryl substituent and the reactivity of the ring is affected by its amine substituent The same electron delocalization that reduces the basicity and the nucleophilicity of an arylamme nitrogen increases the electron density in the aromatic ring and makes arylamines extremely reactive toward electrophilic aromatic substitution... 

Although It IS possible to prepare aryl chlorides and aryl bromides by electrophilic aromatic substitution it is often necessary to prepare these compounds from an aromatic amine The amine is converted to the corresponding diazonmm salt and then treated with copper(I) chloride or copper(I) bromide as appropriate... 

Tertiary alkylamines illustrate no useful chemistry on nitrosation Tertiary aryl-amines undergo nitrosation of the ring by electrophilic aromatic substitution... 

Another drawback to the use of amino-substituted benzenes in electrophilic aromatic substitution reactions is that Friedel-Crafts reactions are not successful (Section 16.3). The amino group forms an acid-base complex with the AICI3 catalyst, which prevents further reaction from occurring. Both drawbacks can be overcome, however, b3 carrying out electrophilic aromatic substitution reactions on the corresponding amide rather than on the free amine. 

The C-nitrosation of aromatic compounds is characterized by similar reaction conditions and mechanisms to those discussed earlier in this section. The reaction is normally carried out in a strongly acidic solution, and in most cases it is the nitrosyl ion which attacks the aromatic ring in the manner of an electrophilic aromatic substitution, i. e., via a a-complex as steady-state intermediate (see review by Williams, 1988, p. 58). We mention C-nitrosation here because it may interfere with diazotization of strongly basic aromatic amines if the reaction is carried out in concentrated sulfuric acid. Little information on such unwanted C-nitrosations of aromatic amines has been published (Blangey, 1938 see Sec. 2.2). 

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. 

Abstract Aldehydes obtained from olefins under hydroformylation conditions can be converted to more complex reaction products in one-pot reaction sequences. These involve heterofunctionalization of aldehydes to form acetals, aminals, imines and enamines, including reduction products of the latter in an overall hydroaminomethylation. Furthermore, numerous conversions of oxo aldehydes with additional C.C-bond formation are conceivable such as aldol reactions, allylations, carbonyl olefinations, ene reactions and electrophilic aromatic substitutions, including Fischer indole syntheses. 

The initial product is a dihydroquinoline it is formed via Michael-like addition, then an electrophilic aromatic substitution that is facilitated by the electron-donating amine function. A mild oxidizing agent is required to form the aromatic quinoline. The Skraup synthesis can be used with substituted anilines, provided these substituents are not strongly electron withdrawing and are not acid sensitive. 

Stack and co-workers recently reported a related jx-rf / -peroxodi-copper(II) complex 28 with a bulky bidentate amine ligand capable of hydroxylating phenolates at - 80 °C. At - 120 °C, a bis(yu,-oxo)dicopper(III) phenolate complex 29 with a fully cleaved 0-0 bond was spectroscopically detected (Scheme 13) [190]. These observations imply an alternative mechanism for the catalytic hydroxylation of phenols, as carried out by the tyrosinase metalloenzyme, in which 0-0 bond scission precedes C - 0 bond formation. Hence, the hydroxylation of 2,4-di-tert-butylphenolate would proceed via an electrophilic aromatic substitution reaction. 

An electrophilic aromatic substitution leads to a-chloro amines, which are rapidly hydrolyzed during work up to give the aldehyde ... 

The most common reason for reducing aromatic nitro compounds is to make substituted anilines. Much of this chemistry was developed by the dye industry, which uses aniline derivatives for azo coupling reactions (Section 19-17) to make aniline dyes. Nitration of an aromatic ring (by electrophilic aromatic substitution) gives a nitro compound, which is reduced to the aromatic amine. 

We have already described how nitration leads eventually to aromatic amines by reduction of the nitro group. In the next chapter you will meet the further development of these amines into diazoni-um salts as reagents for nucleophilic aromatic substitution by the S l mechanism with loss of nitrogen. In this chapter we need to address their potential for electrophilic aromatic substitution without the loss of nitrogen as this leads to the important azo dyes. Treatment of the amine with nitrous acid (H0N=0) at around 0°C gives the diazonium salt. 

The second route utilizes the introduction of the chlorosulfonyl substituent directly onto the aromatic nucleus. The reaction of substituted benzenes with chlorosulfonic acid gives good yields of arylsulfonyl chlorides however, the aryl substituent dictates the position of attachment of the chlorosulfonyl function in this electrophilic aromatic substitution.7 The method described herein allows replacement of a diazotized amine function by the chlorosulfonyl group. The ready availability of substituted anilines makes this the method of choice for the preparation of arylsulfonyl chlorides. 

The electrophilic, aromatic substitution of electron-rich arenes with the electron-deficient azodicarboxylate BTCEAD is a powerful method for the introduction, in a single operation, of a masked hydrazine or amino group.3 4 Several activators can be used for this amination reaction ZnCl2,4 BF3-Et20,4 LiCIO.4,3 and here, trifluoromethanesulfonic acid.5 Trifluoromethanesulfonic acid dramatically increases the rate of the amination reaction and makes possible the use of this methodology with poorly reactive substrates. 

A more interesting problem than the influence of substituents in the electrophilic reagent of azo coupling is the extremely high selectivity of the C-coupling reactions, relative to other electrophilic aromatic substitutions. Unsubstituted benzene does not react with any arenediazonium ion, 1,3,5-trimethoxybenzene reacts very slowly with strongly electrophilic diazonium ions only aromatic amines (e.g. N,N-dimethyl-aniline) or phenolate ions react very fast, in some cases close to diffusion control. 

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