Amination Aromatic nitro groups

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

The catalytic effect of aromatic nitro groups in the substrate and product or in an added inert nitro compoimd (e.g., w-dinitrobenzene in 18) has been observed in the reaction of 2,4-dinitrochlorobenzene with an amine in chloroform. Hydrogen bonding to benzil or to dimethyl sulfone and sulfoxide also provided catalysis. It is clear that the type of catalysis of proton transfer shown in structure 18 will be more effective when hydrogen bonding is to an azine-nitrogen. 

In the first step tin(Il) chloride in acetic acid solution reduces the aromatic nitro groups to amino groups. The aromatic amines produced then react with fluorescamine in weakly basic medium to yield fluorescent derivatives (cf. reagent monograph Fluorescamine Reagent , Volume la). 

Almost all drugs that contain a primary aromatic amine or aromatic nitro group are associated with a significant incidence of adverse reactions (5), presumably because they are oxidized or reduced, respectively, to similar reactive intermediates examples are shown in Figure 8.5. 

Reductions with zinc are carried out in aqueous [160 as well as anhydrous solvents [163 and at different pHs of the medium. The choice of the reaction conditions is very important since entirely different results may be obtained under different conditions. While reduction of aromatic nitro groups in alkali hydroxides or aqueous ammonia gives hydrazo compounds, reduction in aqueous ammonium chloride gives hydroxylamines, and reduction in acidic medium amines (p. 73). Of organic solvents the most efficient seem to be dimethyl formamide [164 and acetic anhydride [755]. However, alcohols have... 

Monomers 111 (a -d), were prepared from the common starting material 15 by a potassium phenate displacement of the aromatic nitro group. The yields of the keto-ether amine products ranged from 90 to 100% and were of sufficient purity after extractive work up to be utilized directly in the synthesis of the various maleimide monomers. Imidization of the aminobenzocyclobutenes was accomplished using standard reaction conditions (maleic anhydride to form the amic acid followed by cyclodehydration with acetic anhydride and triethyla-mine) and provided the maleimide products in yields ranging from 60 to 90%. 

Aromatic amines are readily prepared by the reduction of aromatic nitro groups by Fe/HCl or Sn/HCl or by catalytic hydrogenation. 

The resin-bound perfluoroalkylsulfonyl linker is compatible with many common solid-phase reactions, such as tin dichloride-mediated aromatic nitro group reduction, trifluoroacetic acid-mediated tBoc deprotection, reductive amination reactions, acylation, and sulfonation. It is possible to perform several sequential synthetic reactions on the nonflate resin so that multistep syntheses can be carried out. The solid-phase approach provides an operationally simple, inexpensive, and general protocol for the cleavage... 

Reduction of aromatic nitro groups occurs in three steps, via nitroso and hydroxylamine intermediates, to the amine. The amine can go on to form polymeric residues by a mechanism analogous to that for oxidative coupling of phenols, as in Equation 2. Abiotic nitro reduction is well documented for pesticides that contain aromatic nitro groups, such as the phosphorothioate esters methyl and ethyl parathion (22, 30-33). 

The use of a strong base in the palladium-catalyzed amination of aryl halides precludes the use of many substrates, such as those with aromatic nitro groups or enolizable hydrogens, esters other than tert-butyl esters, and many substrates with base-sensitive stereochemistry such as some protected amino acids and heterocyclic substrates [191]. Thus, conditions that employ milder bases are required. A solution that involves reaction temperatures as low as those used for reactions conducted with sodium tert-butoxide has not been developed. However, carbonate and phosphate bases can be used with certain catalysts at reaction temperatures comparable to those of reactions involving the first- and second-generation catalysts. 

These compounds are aromatic amines with nitro groups in the 2.6 positions adjacent to the amino function. 

Dry ozonization is also an efficient proc ure for oxidation of aliphatic primary amines into nitro groups, with yields of about 70%. Arylamines are also oxidized to nitro aromatics, albeit with low yields. Ozone on silica gel has also been shown to oxidize arenes in some cases. ... 

Aromatic nitro groups Aromatic rings N-oxides Alkyl hydrazines Alkyl aldehydes N-methyl derivatives Monoalkenes p-Haloethyl mustards N-Chloroamines Alkyl N-nitrosoamines Alkyl esters of either phosphoric or sulfonic adds Aromatic mono- and dialkylamino groups Aromatic azo groups (because of possible reduction to aromatic amines) Aromatic and aliphatic aziridinyl derivatives Aromatic and aliphatic substituted primary alkyl halides Aromatic amines (including their N-hydroxy derivatives and the derived esters Propriolactones and propriosultones Derivatives of urethane (carbamates) Aliphatic and aromatic epoxides... 

Similarly selective hydrogenation of aromatic nitro groups was achieved [368] with [Ru3(CO)i2] as catalyst precursor in the presence of small amounts of certain amines (HN Pr2, HNBu2, NEt2 and piperidine). Other unsaturated groups such as C= 0, C=N, C=C and C=C were not effected at... 

Microcrystalline white powder when pure gray when aluminum impurity present. Monoclinic crystals, d 0.92. Stable in dry air at room temperature, decomp above 125, slowly loses hydrogen at 120. decomp in moist air. may ignite on grinding in air. Solv (parts/100 parts solvent) 30 (ether) 13 (tetrahydrofuran) 10 (dimethylcellosolve) 2 (dibutyl ether) 0.1 (dioxane). Reacts rapidly with water and alcohols reduces aldehydes, ketones, acid chlorides and esters to alcohols nitriles to amines aromatic nitro compounds to azo compounds. Does noi at lack olefinic double bonds unless they are conjugated with a phenyl group and a carbonyl or nitrile group. 

Similar studies, however, suggest that N-nitrosobutalin will be quite persistent in soils (Oliver and Konston, 1978). Reduction of N-nitrosopendimethalin has been observed in anaerobic soils (Smith et al., 1979). Product studies indicate, however, that the nitroso moiety remains intact and reduction of the aromatic nitro group in the 6-position occurs to give the aromatic amine (Equation 3.36). 

Alternatively, if such azides bear a l°-benzylic group they can be converted to A-methylanilines by reaction with EtsSiH and SnCl4. Wilkinson s catalyst and Et3SiH reduce aromatic nitro groups to their amines in moderate to good yields, while the combination of Pd(OAc)2 and EtsSiH in a THF-water mixture reduces aliphatic nitro groups to the A-hydroxylamines (eq 25). ... 

EC is most often used in the analysis of catecholamines and aromatic amines, since these compounds are easily oxidized at low potentials (Table 1). However, most alkaloids also contain oxidizable functional groups, and are well suited for oxidative EC detection. Many contain either a phenol group or an indole nucleus, and even more contain a tertiary aliphatic amine. In addition, many aliphatic alcohols and amines, which are oxidized at high potentials on carbon electrodes, can be detected at much lower potentials with gold or platinum electrodes (Sect. 2.4). Alkaloids, however, do not usually contain easily reducible groups like quinones or aromatic nitro groups. 

Procedures were proposed for the reduction of aromatic nitro groups to amines. Sodium dithionitei78 and a combination of sulfur and hydrazine on activated carboni79 are reported to provide anilines in good to excellent yields. From aliphatic nitro compounds (Eq. 66), primary amines could be obtained with "nickel boride", prepared from nickel chloride and sodium borohydride.i ... 

Primary Amines.—Cobalt polysulphide and ruthenium(iv) sulphide catalysts have been found to be selective for the preferential hydrogenation of aromatic nitro-groups in the presence of acetylenes/ Formamidinesulphinic acid/ phenylselenol in the presence of DABCO/ and sodium borohydride in the presence of [Cu(acac)2r also effect the aromatic nitro-to-amine conversion. 

In the reduction mode, electrochemical detectors can be used for detecting quinones, nitro compounds and consequently for the analysis of various forms of explosives (37). With the use of reagents containing aromatic nitro groups, derivatives of amines, ketones, and acids can also be detected by electrochemical detection. 

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