Nitroso compounds with hydroxylamines

While the condensation of amines with nitroso compounds appears to have wide applicability in the benzene series, it seems to lead to complex dye molecules in the naphthalene series. A method has been developed using a somewhat complex reaction between thionylamines and substituted hydroxylamines which does produce azo compounds derived from naphthalenes. This synthesis is of particular interest because it helped to settle the question whether true naphthylazo compounds with hydroxyl groups could exist [36]. 

Schenk et al. have used the a-chloro nitroso compound 93 for the reaction with cyclopentene 98 in order to solve the problem with the instability of the allyl amine product formed from the reaction with nitroso compounds [56c]. The product formed, 99, rearranges to the stable nitrone hydrochloride salt 100, which is easily hydrolyzed to the hydroxylamine 101 (Eq. (23)). 

Aromatic and aliphatic primary amines can be oxidized to the corresponding nitro compounds by peroxy acids and by a number of other reagents. The peroxy acid oxidations probably go by way of intermediate hydroxylamines and nitroso compounds (Scheme 2). Various side reactions can therefore take place, the nature of which depends upon the structure of the starting amine and the reaction conditions. For example, aromatic amines can give azoxy compounds by reaction of nitroso compounds with hy-droxylamine intermediates aliphatic amines can give nitroso dimers or oximes formed by acid-catalyz rearrangement of the intermediate nitrosoalkanes (Scheme 3). 

Functionalization of rubbers with nitroso compounds (174) involves two reaction steps [233] formation of a hydroxylamine derivative 175 and its... 

The domain of oxidations with silver oxide includes the conversion of aldehydes into acids [63, 206, 362, 365, 366, 367 and of hydroxy aromatic compounds into quinones [171, 368, 369]. Less frequently, silver oxide is used for the oxidation of aldehyde and ketone hydrazones to diazo compounds [370, 371], of hydrazo compounds to azo compounds [372], and of hydroxylamines to nitroso compounds [373] or nitroxyls [374] and for the dehydrogenation of CH-NH bonds to -C=N- [375]. Similar results with silver carbonate are obtained in oxidations of alcohols to ketones [376] or acids [377] and of hydroxylamines to nitroso compounds [378]. 

Sodium hypobromite, NaOBr, is prepared in situ from bromine and aqueous sodium hydroxide under cooling. Its almost exclusive application is the degradation of methyl ketones to acids with one less carbon [635, 735, 736, 737]. Such degradation is achieved not only with methyl ketones but also with other alkyl ketones [103, 160], Other oxidations, such as the conversion of hydroxylamines into nitroso compounds, are rare [738]. 

The oxidants dimethyl sulfoxide and nitroso compounds react easily with oL-bromo ketones and convert them into a-dicarbonyl compounds. The reaction with nitroso compounds is usually carried out in the presence of pyridine and proceeds through a nitrone stage. Phenacyl bromide (a-bromoacetophenone) is thus transformed first into phenacylpyridinium bromide and further, with nitrosobenzene, into a-ketoaldonitrone, which is subsequently treated with hydroxylamine to give phenylglyoxal monoxime or with phenylhydrazine to give phenylglyoxal osazone [985] (equation 411). 

The reaction of alkenes with nitroso compounds gives hydroxylamine products [47]. The process was thought to occur by either a one-step ene reaction (Eq. 4.56, below) or a two-step reaction via a transient aziridine oxide intermediate (Eq. 4.57). The following deuterium isotope effects were measured for the reaction of 2,3-dimethyl-2-butene and pentafluoronitrosobenzene. Explain the similarities and differences among these results in terms of one of these mechanisms. Use the results to exclude one mechanism. The first three cases are intramolecular competitions where is the rate of formation of the C=CH2 product and is the rate of formation of the = 0 alternative product. The last case is an intermolecular competition. The results were determined by H NMR analysis of the products. 

Reductive alkylations have been carried out successfully with compounds that are not carbonyls or amines, but which are transformed during the hydrogenation to suitable functions. Azides, azo, hydrazo, nitro and nitroso compounds, oximes, pyridines, and hydroxylamines serve as amines phenols, acetals, ketals, or hydrazones serve as carbonyls 6,7,8,9,12,17,24,41,42,58). Alkylations using masked functions have been successful at times when use of unmasked functions have failed (2). In a synthesis leading to methoxatin, a key... 

C-Nitroso compounds with an a-hydrogen atom rearrange readily to the corresponding oxime (/7y) and perhaps to the unsaturated hydroxylamine 145). Reduction of these is discussed in the chapter on oximes. 

In a reaction similar to 12-50, azoxy compounds can be prepared by the condensation of a nitroso compound with a hydroxylamine. The position of the oxygen in the final product is determined by the nature of the R groups, not by which R groups came from which starting compound. Both R and R can be alkyl or aryl, but when two different aryl groups are involved, mixtures of azoxy compounds (ArNONAr, ArNONAr, and Ar NONAr ) are obtained and the unsymmetrical product (ArNONAr ) is likely to be formed in the smallest amount. This behavior is probably caused by an equilibration between the starting compounds prior to the actual reaction (ArNO -I- Ar NHOH Ar NO - - ArNHOH). The mechanism has been investigated in the presence of base. Under these conditions both reactants are converted to radical anions, which couple ... 

Hydrazones of the form ArCH=NNH2 react with HgO in solvents such as diglyme or ethanol to give nitriles (ArCN). Aromatic hydroxylamines (Ar—NH-—OH) are easily oxidized to nitroso compounds (Ar—N=0), most commonly by acid dichromate. ... 

The mechanisms of these reductions have been very little studied, though it is usually presumed that, at least with some reducing agents, nitroso compounds and hydroxylamines are intermediates. Both of these types of compounds give amines when exposed to most of these reducing agents (19-43), and hydroxylamines can be... 

Nitroso compounds and hydroxylamines can be reduced to amines by the same reagents that reduce nitro compounds (19-41). One example reduces a hydro-xylamine to the amine with CS2 in acetonitrile. N-Nitroso compounds are similarly reduced to hydrazines ... 

Azoxy compounds can be obtained from nitro compounds with certain reducing agents, notably sodium arsenite, sodium ethoxide, NaTeH, NaBH4—PhTeTePh, and glucose. The most probable mechanism with most reagents is that one molecule of nitro compound is reduced to a nitroso compound and another to a hydroxylamine 119-42), and these combine (12-51). The combination step is rapid compared to the reduction process. Nitroso compounds can be reduced to azoxy compounds with triethyl phosphite or triphenylphosphine or with an alkaline aqueous solution of an alcohol. ... 

Alkyl and aryl C-nitroso compounds contain a nitroso group (-N=0) directly attached to an aliphatic or aromatic carbon. As compounds with a nitroso group attached to a primary or secondary carbon exist primarily as the oxime tautomer, the stable examples of C-nitroso compounds contain nitroso groups attached to tertiary carbons, such as 2-methyl-2-nitroso propane (1, Fig. 7.1) or nitroso groups attached to carbons bearing an electron-withdrawing group (-CN, -N02, -COR, -Cl, -OAc, Fig. 7.1). Oxidation of alkyl and aryl hydroxylamines provides the most direct route to alkyl and... 

Acyl nitroso compounds (3, Scheme 7.2) contain a nitroso group (-N=0) directly attached to a carbonyl carbon. Oxidation of an N-acyl hydroxylamine derivative provides the most direct method for the preparation of acyl C-nitroso compounds [10]. Treatment of hydroxamic acids, N-hydroxy carbamates or N-hydroxyureas with sodium periodate or tetra-alkyl ammonium periodate salts results in the formation of the corresponding acyl nitroso species (Scheme 7.2) [11-14]. Other oxidants including the Dess-Martin periodinane and both ruthenium (II) and iridium (I) based species efficiently convert N-acyl hydroxylamines to the corresponding acyl nitroso compounds [15-18]. The Swern oxidation also provides a useful alternative procedure for the oxidative preparation of acyl nitroso species [19]. Horseradish peroxidase (HRP) catalyzed oxidation of N-hydroxyurea with hydrogen peroxide forms an acyl nitroso species, which can be trapped with 1, 3-cyclohexanone, giving evidence of the formation of these species with enzymatic oxidants [20]. 

However, an improved electrochemical redox methodology using a flow cell fitted with two consecutive porous electrodes of opposite polarities (cathode then anode), allows a rapid and total oxidation at the anode of the hydroxylamine intermediate produced at the cathode. Various nitroso compounds may be obtained in high yields without... 

Nitroaromatic Reduction Nitroaromatics constitute an important class of potential environmental contaminants, because of their wide use in agrochemicals, textile dyes, munitions, and other classes of industrial chemicals. Reduction of nitroaromatics produces amines, throngh a series of electron transfer reactions with nitroso and hydroxylamines as intermediates (Fig. 13.1). Compared to the parent nitroaromatic compound, all intermediates typically reduce readily (Larson and Weber 1994). 

Since the hydroxylamine product is readily oxidized by air to the blue nitroso compound, these manipulations should be performed rapidly to minimize exposure of the product to atmospheric oxygen. Any nitroso compound formed at this stage will co-distil with the ether and is difficult to recover. 

Of trialkyl phosphites the most frequently used is triethyl phosphite (EtO)3P (M.W. 166.16, b.p. 156°, density 0.969) which combines with sulfur in thiiranes [291, 294] and gives alkenes in respectable yields. In addition, it can extrude sulfur from sulfides [295], convert a-diketones to acyloins [296], convert a-keto acids to a-hydroxy acids [297], and reduce nitroso compounds to hydroxylamines [298] Procedure 47, p. 111). 

Most reactions of nitroso intermediates are however too slow to compete with further reduction. In these cases it is necessary to carry out the tandem reduction to the hydroxylamine stage and then oxidation back to the nitroso compounds using the type of double-cell sketched in Fig. 11.2. The intermediate is then allowed to... 

Hydroxylamines are usually more accessible than the corresponding nitroso compounds, so only few examples of this reaction have been described in the literature. Aromatic nitroso compounds have been reduced into hydroxylamines with ascorbic acid, gly-oxylic acid and by NADH. It can be safely assumed that any reagent capable of reducing nitro compounds should reduce nitroso compounds as well. 

Tertiary and aromatic nitroso compounds react with aryl Grignard or aryl-lithium reagents giving the corresponding hydroxylamines . This reaction is useful for preparation of alkyl- and aiylhydroxylamines (e.g. 109, equation 80 and 110, equation 81) and can be considered as complementary to arylation of hydroxy lamines with activated aryl halides. It has been used for functionalization of cyclophanes with the hydroxy amino group. The main limitation of the reaction is the relatively restricted choice of available aliphatic nitroso components, so most of reactions were done with 2-nitroso-2-methylpropane. There is no literature data about the possibility of removal of the tert-butyl group from these compounds. 

Aliphatic and aromatic nitroso compounds are powerful dienophiles and react with a variety of acyclic, cychc and heterocyclic 1,3-dienes producing cyclic hydroxylamines. The reaction proceeds with a high regioselectivity at room temperature (equation 99 291-293 Asymmetric variation of the reaction with chiral copper-BINAP catalyst has been reported ". The cycloaddition is reversible and some amounts of diene and nitroso components may be observed in reaction products. 

Due to the restricted availability of nitroso components, it more convenient to prepare acylnitroso compounds in situ from iV-acyl or Af-carbamoyl hydroxylamines with NaI04 (equation 100) . Subsequent deprotection results in an Af-unsubstituted dihydro-1,2-oxazine cycle. The reaction is also commonly employed for intramolecular cyclo-additions ". ... 

Cycloaddition of enantiomerically pure a-chloro nitroso compounds derived from steroids and carbohydrates (e.g. 158, equation 102) proceeds with considerable stereoselectivity. Final removal of the chiral auxiliary results in Af-unsubstituted cyclic hydroxylamines of high ee. 

Although electrochemical oxidation of Al-cyclohexyl-Al-hydroxylamine in the presence of pyridine afforded the corresponding dimeric nitroso compound with a low yield, A-hydroxy t-alkylamines were transformed into the corresponding nitroso compounds (equation 8) . Similarly, A-phenylhydroxylamine was transformed into nitrosobenzene under similar reaction conditions. ... 

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