Electrophilic substitution nitration

Electrophilic Aromatic Substitution. Electrophilic nitration using a combination of NO2CI and AgBp4 has been reported. Conversion of arylsilanes into iodides and bromides has been achieved using a combination of the halogen and AgBp4 (eq 13). ... 

Further evidence that the nitronium ion was not the electrophile in the uncatalysed reaction, and yet became effective in the catalysed reaction, came from differences in the orientation of substitution. The nitration of chlorobenzene in the uncatalysed reaction yielded only 43 % of the para compound, whereas, when the catalysed reaction was made important by adding some nitric acid, the ratio of substitution was that usually observed in nitration involving the nitronium ion ( 5.3.4). In the case of the uncatalysed reaction however, the reaction was complicated by the formation of nitrophenols. 

Other typical electrophilic aromatic substitution reactions—nitration (second entry) sul fonation (fourth entry) and Friedel-Crafts alkylation and acylation (fifth and sixth entnes)—take place readily and are synthetically useful Phenols also undergo elec trophilic substitution reactions that are limited to only the most active aromatic com pounds these include mtrosation (third entry) and coupling with diazomum salts (sev enth entry)... 

Electrophilic nitration of a substituted benzene may lead to ortho, meta or para products, depending on the substituent. According to the Hammond Postulate, the kinetic product will be that which follows from the most stable intermediate benzenium ion, i.e. 

Isoxazoles are known at present to undergo the following electrophilic substitution reactions nitration, sulfonation, halogenation, chloroalkylation, hydroxymethylation, and mercuration. Repeated attempts to effect the Friedel-Crafts reaction in the isoxazole series in the authors laboratory failed. The isoxazole nucleus seems not active enough to react with weak electrophilic reagents. 

Finally, we ask, if the reactive triads in Schemes 1 and 19 are common to both electrophilic and charge-transfer nitration, why is the nucleophilic pathway (k 2) apparently not pertinent to the electrophilic activation of toluene and anisole One obvious answer is that the electrophilic nitration of these less reactive [class (ii)] arenes proceeds via a different mechanism, in which N02 is directly transferred from V-nitropyridinium ion in a single step, without the intermediacy of the reactive triad, since such an activation process relates to the more conventional view of electrophilic aromatic substitution. However, the concerted mechanism for toluene, anisole, mesitylene, t-butylbenzene, etc., does not readily accommodate the three unique facets that relate charge-transfer directly to electrophilic nitration, viz., the lutidine syndrome, the added N02 effect, and the TFA neutralization (of Py). Accordingly, let us return to Schemes 10 and 19, and inquire into the nature of thermal (adiabatic) electron transfer in (87) vis-a-vis the (vertical) charge-transfer in (62). 

Electrophilic nitrations of aliphatic nitriles, carboxylic acids,carboxylic esters, ° and /3-diketones have been reported. The nitration of 2-alkyl-substituted indane-l,3-diones with nitric acid, followed by alkaline hydrolysis, is a standard laboratory route to primary nitroalkanes. ... 

Pyrazine and pyrimidine heterocycles, like pyridine, are electron deficient and need the presence of an activating/electron-releasing group to allow efficient electrophilic nitration to occur. An example of this strategy is seen during the synthesis of 2,6-diamino-3,5-dinitropyrazine (ANPz) (183) where one of the chloro groups of 2,6-dichloropyrazine (180) is substituted for a... 

When there is an electron-releasing substituent in the 4-position, the electrophile attacks the 1-position. This has been used as a convenient way of preparing 1-substituted dibenzofurans by removal of an amino group at the 4-position. Bromination, chlorination, and diazo coupling of 4-dibenzofuranol occur at the 1-position. Bromination and Vilsmeier-Haack formylation of 4-methoxydibenzofuran provide the 1-substituted derivatives. Nitration and bromination of 4-acetylaminodibenzofuran take a similar course. ... 

Treatment of bis(dimethylaminomethylene)pyrrolizinium perchlorate (29) with cyclopentadiene-NaH in DMF gave the diatropic cyclopenta-[fc]cycl[4,2,2]azine (77), which was also obtained from the fulvene derivative (78) and 3//-pyrrolizine (25). Electrophilic substitutions (deuteration, nitration, nitrosation, acylation, bromination, Mannich reaction) occur in the 6- and 8-positions.32... 

The observed effects of structure on rate and on orientation, confirmed by the Brown selectivity relationship, show that there is no basic difference between heterogeneous catalytic alkylation of aromatic compounds and homogeneous electrophilic aromatic substitution, cf. nitration, sul-phonation etc. This agreement allows the formulation of the alkylation mechanism as an electrophilic attack by carbonium ion-like species formed on the surface from the alkene on Br0nsted acidic sites. The state of the aromatic compound attacked is not clear it may react directly from the gas phase (Rideal mechanism ) [348] or be adsorbed weakly on the surface [359]. 

Cyclopentaf/z ][2.2.4]cyclazines (297), which are uncharged since there is an exocydic double bond at the [2.2.4]cyclazine periphery, have been prepared by the two routes shown in Scheme 46 <80JCS(Pl)l324, 79TL3405). Electrophilic substitutions (deuteration, nitration,... 

During the 1920s Ingold, Robinson, and others carried out extensive studies on aromatic electrophilic substitution, whereas in more recent years the work of Schofield, Ridd, Katritzky, and their co-workers have contributed so much to the body of data and to the understanding of aromatic electrophilic substitution, especially nitration. 

The imidazo[l,2-electrophilic substitution, but nitration (and bromination) is reported to give 5-substituted products (77G1). 

Know the meaning of electrophilic aromatic substitution, halogenation, nitration, sulfonation, alkylation, acylation, Friedel-Crafts reaction. 

The general aim of C-H transformation is to introduce groups with a higher complexity to hydrocarbon structures. Industrial processes therefore usually involve transformation of C-H groups starting from simple molecules. The reactions employed are selective oxidation, substitution (radical, electrophilic), nitration, ammoxidation, and sulfonation. The functionalized molecules are then further converted to more valuable products and intermediates by different reaction pathways. The latter often comprise further steps of C-H-activation. 

Pyridine is virtually inert to aromatic electrophilic substitution. Consider nitration of pyridine by nitric acid. First, as pyridine is a moderate base, it will be almost completely protonated by the acid, making it much less susceptible to electrophilic attack. Second, addition of the electrophile to the small amount of unprotonated pyridine present in solution is not a facile process. 

Electrophilic substitution (bromination, nitration) of 2-substituted 1,2,3,6,7,116-hexahydro-4//-pyrazino[2,l -a]isoquinolin-4-ones occurred on the aromatic moiety to give either 11- or 8-substituted derivatives the site was not determined (76GEP2441261). The nitro group was reduced to an amino group, which was alkylated, acylated, and converted to different groups via a diazonium group, and involved in diazonium coupling. 

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