Nitration phenyl ring

The nitration of nitro- and dinitro-biphenyls has been examined by several workers. i - As would be expected, nitration of the nitro-biphenyls occurs in the phenyl ring. Like a phenyl group, a nitrophenyl group is 0 -directing, but like certain substituents of the type CH CHA ( 9.1.6) it is, except in the case of w-nitrophenyl, deactivating. Partial rate factors for the nitration at o °C of biphenyl and the nitro-biphenyls with solutions prepared from nitric acid and acetic anhydride are given below. The high o p-v2X o found for nitration of biphenyl... 

The nitration of phenylpyridines and related compounds has attracted attention for a long time, and measurements of isomer proportions have been made for several compounds of this type. Nitration occurs in the phenyl ring. For 2-phenylpyridine and 2-phenylpyridine i-oxide measurements of the dependence of rate of nitration upon acidity in 75-81 % sulphuric acid at 25 °C show that both compounds are nitrated as their cations (table 8.1). The isomer distribution did not depend significantly upon the acidity, and by comparison with the kinetic data for quinolinium ( 10.4.2) the partial rate factors illustrated below were obtained.They should be compared with those for the nitration of 2-nitrobiphenyl ( 10.1). The protonated heterocyclic groups are much... 

Acetamidothiazole is nitrated in the same way (58, 378, 379). 2-Acetamido-4-phenylthiazole is reported to be nitrated on C-5 (380) as opposed to 2-amino-4-phenylthiazole, where nitration occurs on the phenyl ring (381). This latter result is not consistent with the other data on electrophilic reactivity in most cases 2-amino-4-arylthiazole derivatives react with electrophilic reagents at the C-5 position (see Sections rV.l.B and D). Furthermore, N-pyridy]-(2)-thiazolyl-2-amine (178) is exclusively nitrated on the thiazole ring (Scheme 113) (132, 382). 

Arylthiazoles are nitrated on the phenyl ring. The yields in sulfuric acid average 60 to 85% (248). Results are indicated in Table III-46 (250). 

Tlie products of nitration of 2-amino-5-phenyl-l,8-naphthyridin-7(8H)-one (63) vary depending on whether the reaction is carried out with nitric acid in sulfuric acid or in acetic anhydride (74GCI499). In sulfuric acid the phenyl ring was found to be nitrated more easily than the naphthyridine ring, yielding a mixture of 3- and 4-nitrophenyl derivatives (64) in acetic... 

Oxidation of 5-arylazo-6-aminoquinoline 146 with copper sulfate in pyridine gave the corresponding 2-aryltriazolo[4,5-/]quinolines 147. Condensation of halo-genated nitrobenzenes with triazolo[4,5-/]quinoline 145 yielded the appropriate 2H- and 3//-aryl derivatives. The nitration of 3-phenyl-3//-triazolo[4,5-/]quino-line 147 occurred at position 4 of the phenyl ring (Scheme 46) (73T221). 

Compounds 4 and 5 would be expected to be inert toward electrophilic substitution, and, in fact, sulfonation of the 2-phenyl derivative 201234 and nitration of the 1-phenyl derivative 202l69b lead to substitution on the phenyl rings. A series of electrophilic substitutions on the product (203) from 1 -(n-butyl)[l,2,3]triazolo[4,5-c]pyridine and dimethyl sulphate give 7-bromo-, 7-nitro-, and 7-chlorotriazolopyridin-4-ones the electrophilic attack may, in each case, be on the triazolopyridinone.169... 

When a competition with potential nitration of a phenyl ring exists, as in compound 39, the site of nitration is dependent upon the reaction conditions.25 In the presence of sulfuric acid, initial nitration takes place on the... 

The features of the electronic structure of aryl-substituted pyrazolines influence their chemical properties. For example, in the case of 3-substituted 7V-phenyl-pyrazolines 100 reactions of formylation, acylation, nitration, sulfonation, azocoupling and other electrophilic processes involve the para position of the 7V-phenyl ring, with formation of compounds 101 [103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113]. On the other hand, some electrophilic reactions, including nitration, bromination, chlorination, formylation and azocoupling, for 3-unsubstituted pyrazolines 102 occur at position 3, yielding heterocycles 103 and in some cases as a mixture with 104 [108, 114, 115] (Scheme 2.26). This fact provides evidence for orbital control of these reactions. 

Nitration of 2-methyl-3-phenylindole using potassium nitrate in sulfuric acid also yields a mixture of 2-methyl-3-(4-nitropheny )indole (13%) and 2-methyl-5-nitro-3-(4-nitrophenyl)indole (2%). This dinitro product is also obtained by a second nitration of the mononitro compound. However, nitration of 3-methyl-2-phenylindole under these conditions gives only the 5-nitro derivative (80%) with no nitration in the phenyl ring. 

Nitro-2-phenylindoles are obtained by electrophilic ipso-nitration of arylazo, hydroxymethyl, and acyl groups on treatment with two equivalents of 70% nitric acid in acetic acid at 25°C. No attack on the phenyl ring is observed under these conditions [80MI1 81JCS(P2)628]. Indolenines undergo nitration mainly at the 5-position (77-85%) (64TL803). 

In the nitration of methylphenylpyrazoles, Parrini [57AC(R)929] showed that a mixture of nitric and sulfuric acids leads to nitration first in the para position of the phenyl ring and second in the 4-position of the pyrazole ring. 4-Nitro-(4-nitrophenyl) derivatives were obtained from 3,5-dimethyl-1-phenylpyrazole and 3-methyl-5-phenylpyrazole. 

Ethyl-1-phenylpyrazole is nitrated in acetic anhydride producing the 3-nitropyrazole with no evidence for phenyl ring nitration (70TL479). 

In strongly acidic media the conjugate acid is nitrated leading to para substitution in the phenyl ring. In acetic anhydride an intermediate such as (28) may be formed, resulting in the favored 4-attack in the pyrazole ring (Fig. 9). 

The results are in accord with the observations above i.e., in mixed acid the pyrazole ring in protonated and the pyrazolium cation acts as a para director to the phenyl ring. In acetic anhydride pyrazoles are nitrated as free bases to yield 4-nitropyrazoles. 

These early nitrations were carried out by adding the imidazole nitrate salts to sulfuric acid at 100°C. Such a procedure results in phenyl ring substitution, the following results being recorded ... 

In another study of the nitration of 5-phenyl- and 3-methyl-5-phenylisox-azole the action of nitric acid sulfuric acid on 5-phenylisoxazoIe produced a 1 1 1 mixture of the ortho, meta, and para 5-(nitrophenyl) products with minor amounts of 4-nitro-5-(3-nitrophenyl)- and 4-nitro-5-(4-nitrophenyl)-dinitro products. The action of nitric acid acetic anhydride produced 4-nitro-5-phenylisoxazole as the major product with some nitrophenyl compounds as minor products. 3-Methyl-5-phenylisoxazole also gave a mixture of the ortho, meta, and para 5-(nitrophenyl) products when mixed acids were used, but no dinitro products were observed. The use of nitric acid acetic anhydride resulted in nitration at the 4-position of the isoxa-zole ring as the largely predominant product, with some phenyl ring substitution (89H1965). 

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