Amines, aromatic, hydrogenation

Fischer-Hepp rearrangement The nitros-amines of aromatic secondary amines when treated with hydrochloric acid give nuclear substituted nitrosoamines. Among the benzene derivatives, if the para position is free the -NO group displaces the hydrogen atom there in naphthalene derivatives it enters the 1-position ... 

Aromatic nitroso compounds usually are considered to be intermediates in the hydrogenation of a nitroaromatic compound to the aromatic hydroxyl-amine or amine. However, nitroso compounds do not accumulate in these reductions, suggesting that they are reduced more easily than are nitro compounds. Catalysts effective for the nitro group should also be effective for nitroso. 

Oxidative attack on a carbon-hydrogen bond of an alkyl group a to a nitrogen atom is not restricted to saturated aliphatic amines. In fact X in an X-N-CH- structural subunit can be virtually any common atomic grouping that can be found in stable organic molecules. For example, w-carbon hydrogens of Aralkyl-substituted aromatic cyclic amines (119), aryl amines (120), amides (121), amidines (122), A-nitrosodialkylamines (123), etc. are all subject to oxidative attack, carbinolamine formation, and in most cases release of an aldehyde or ketone depending on the substitution pattern (1° or 2°)... 

A different mode of reaction, however, is observed in photoreductions of nitroaromatics by aromatic tertiary amines. Irradiation of benzene solutions of N-methylated anilines and either m-chloronitrobenzene or 1-nitronaphthalene results in oxidative demethylation of the amines accompanied with reduction of the nitro compound to the corresponding arylamine 49). The authors suggest that hydrogen abstraction from the methyl group takes place as the primary chemical event. 

The effect which amino functionality has on the thermal and impact sensitivity of polyni-troarylenes (Section 4.8.1.4) makes amination by VNS a method with much future potential for energetic materials synthesis. Other carbon, nitrogen, oxygen and sulfur nucleophiles can displace aromatic hydrogen examples with 1,3-dinitrobenzene and 1,3,5-trinitrobenzene are extensive. 

The inhibition of hydrocarbon oxidation by aromatic tertiary amines which contain no labile hydrogen, such as N,N-dimethylaniline and N,N,N, N -tetramethyl-p-phenylenediamine, has been assigned to an electron-transfer process. However, this seems rather unlikely as pyridine... 

The synthesis of an N-alkylarylamine by the reductive alkylation of an aromatic primary amine with a ketone is used in the preparation of antioxidants for polymers and rubber. The alkylation of an amine with a ketone is typically carried out in the liquid phase using heterogeneous catalysts such as Pd, Pt, Rh, or Ru supported on carbon (1,2). The reaction of ADPA with MIBK yields an imine, which then is hydrogenated over a Pt or sulfur promoted-Pt catalyst to yield 6-PPD. 

The reaction appears to be applicable to a wide range of aromatic starting materials, exceptions being aromatic aldehydes and aromatic primary amines [96]. In effect, the aromatic compound to be converted is stirred with an aqueous solution of hydroxylamine hydrochloride in the presence of metallic ions such as copper ions [95-97] or complex ions such as the pentacyanoam-mine ferrate(II) ion [98]. The mixture is then treated with 30% hydrogen peroxide and a highly colored complex of the nitrosophenol forms. Presumably, the free nitrosophenol may be isolated by treatment of the complex with an acid (Eq. 50). 

Diazonium salts can be prepared directly by replacement of an aromatic hydrogen without the necessity of going through the amino group.136 The reaction is essentially limited to active substrates (amines and phenols), since otherwise poor yields are obtained. Since the reagents and the substrate are the same as in reaction 1-3, the first species formed is the nitroso compound. In the presence of excess nitrous acid, this is converted to the diazonium... 

With phenols either the phenolic nr nuclear hydrogens can react lo give benzylaryl ether or benzylated phenols. Reaction with NaCN gives benzyl cyanide (phenylacelonitrile) with aliphatic primary amines the product is (he N-alkylbenzylamine. and with aromatic primary amines N-benzylaniline is formed. Benzyl chloride is converted 10 butyl benzyl phlhalatc plasticizer and other chemicals. 

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

The one-electron oxidation of a secondary amine results in the formation of a secondary aminium ion which on deprotonation gives an aminyl radical (Scheme 1). The nature of the final products derived from these intermediates dqiends very much on the structure of the substrate and the reaction conditions. If the amine has a hydrogen atom on the a-carbon atom the major products usually result from deprotonation at this a-position. With aromatic secondary amines, products can result from coupling of the delocalized radicals at a ring carbon atom. The formal dimerization of aminyl radicals shown in Scheme 21 is therefore not often a useful method of preparation of hydrazines. Nickel peroxide has been used to oxidize diphenylamine to tetraphenylhydrazine in moderate yield, and other secondary arylamines also give... 

Hydrogen sulfide, + Ba(0H)i Halogen acid + pyridine + AcjO Carboxylic acid, (RCOOH) Phthalimide Ammonia Aliphatic amines, RNHj, RjNH Aromatic primary amines, PhNHj, etc, Diphenylamine, PhjNH Sodium alkoxide, NaOR tt-Amino acid esters, R(NHj) COOEt Phenols (PhOH, etc.) —SH —Cl, —Br, —I RCOO— C,H (C0),N— —NHj RNH—, R,N— PhNH—, etc. PhsN— —-OR —NHRCOOEt —OPh, etc. 86 86 86 87 7 88 89 90 7, 91 92 93... 

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