Phenylhydroxylamines

N-phenylhydroxylamine, PhNHOH and further reduction can give azoxybenzene, azobenzene, hydrazobenzene and aniline. The most important outlet commercially for the nitro-compounds is the complete reduction to the amines for conversion to dyestufTs. This is usually done in one stage with iron and a small amount of hydrochloric acid. 

Phenylhydroxylamine is formed when aniline is treated with a neutral reducing agent, e.g., zinc powder and aqueous ammonium chloride solution ... 

Add 4 4 g. of recrystaUised -phenylhydroxylamine to a mixture of 20 ml. of concentrated sulphuric acid and 60 g. of ice contained in a 1 litre beaker cooled in a freezing mixture. Dilute the solution with 400 ml. of water, and boil until a sample, tested with dichromate solution, gives the smell of quinone and not of nitrosobenzene or nitrobenzene (ca. 10-15 minutes). Neutralise the cold reaction mixture with sodium bicarbonate, saturate with salt, extract twice with ether, and dry the ethereal extract with anhydrous magnesium or sodium sulphate. Distil off the ether p-aminophenol, m.p. 186°, remains. The yield is 4-3 g. 

Cupferron, the ammonium salt of the N-nitroso derivative of phenylhydr-oxylamine, is prepared by passing ammonia gas into an ethereal solution of phenylhydroxylamine and n butyl nitrite ... 

Acyl derivatives, RCO—NH—OH and HjN—O—CO—R, are named as A-hydroxy derivatives of amides and as O-acylhydroxylamines, respectively. The former may also be named as hydroxamic acids. Examples are A-hydroxyacetamide for CH3CO—NH—OH and O-acetylhydrox-ylamine for HjN—O—CO—CH3. Further substituents are denoted by prefixes with O- and/or A-locants. For example, C5H5NH—O—C2H5 would be O-ethyl-A-phenylhydroxylamine or A-ethox-ylaniline. 

The single-step -duoroaruline [31-40-4] process based on duorodeoxygenation of nitrobenzene (via in situ generation of /V-phenylhydroxyl amine) in anhydrous hydrogen duoride (94—96) has not been commercialized primarily due to concurrent formation of aniline, as well as limited catalyst life. The potential attractiveness of this approach is evidenced by numerous patents (97—101). Concurrent interest has been shown in the two-step process based on /V-phenylhydroxylamine (HF-Bamberger reaction) (102—104). 

In the reduction of nitro compounds to amines, several of the iatermediate species are stable and under the right conditions, it is possible to stop the reduction at these iatermediate stages and isolate the products (see Figure 1, where R = CgH ). Nitrosoben2ene [586-96-9] C H NO, can be obtained by electrochemical reduction of nitrobenzene [98-95-3]. Phenylhydroxylamine, C H NHOH, is obtained when nitrobenzene reacts with ziac dust and calcium chloride ia an alcohoHc solution. When a similar reaction is carried out with iron or ziac ia an acidic solution, aniline is the reduction product. Hydrazobenzene [122-66-7] formed when nitrobenzene reacts with ziac dust ia an alkaline solution. Azoxybenzene [495-48-7], C22H2QN2O, is... 

The chemical production of aminophenols via the reduction of nitrobenzene occurs in two stages. Nitrobenzene [98-95-3] is first selectively reduced with hydrogen in the presence of Raney copper to phenylhydroxylamine in an organic solvent such as 2-propanol (37). With the addition of dilute sulfuric acid, nucleophilic attack by water on the aromatic ring of /V-phenylhydroxylamine [100-65-2] takes place to form 2- and 4-aminophenol. The by-product, 4,4 -diaminodiphenyl ether [13174-32-8] presumably arises in a similar manner from attack on the ring by a molecule of 4-aminophenol (38,39). Aniline [62-53-3] is produced via further reduction (40,41). 

The reaction of a dibromochalcone with hydroxylamine hydrochloride in pyridine gave three products with the expected 2-isoxazoline product as the predominate compound. A ring bromination product and an isoxazole were also isolated (70UC796). The reaction of hydroxylamine with /S-thiosulfates of propiophenone at reflux produced 3-phenyl-2-isoxazo-line (455). At room temperature a bis-Michael product (456) was produced. The reaction with N -phenylhydroxylamine yielded a mono-Michael type product (457) (74CPB1990). 

IV-Substituted derivatives have been prepared by the reaction of IV-methylhydroxylamine with phenylpropiolic esters or acid chlorides (71CPB1389), the cyclization of A"-substituted /3-ketohydroxamic acids or the reaction of phenylhydroxylamine with diketene (Scheme 150) 63GEP1146494). 

N-Hydroxyurea and acrylic esters produce 3-isoxazolidinones (equation 57) (76BSF1589). Phenylhydroxylamines react with diketene to provide 5-hydroxyisoxazolidones (80JHC727) which can be dehydrated to the corresponding 4-isoxazolin-3-ones (Scheme 160). 

Cupferon ammonium salt (7V-nitroso-7V-phenylhydroxylamine ammonium salt) [135-20-6] M 155.2, m 150-155°(dec), 162.5-163.5°, 163-164°, pK 4.16 (free base). Recrystd twice from EtOH after treatment with Norite and finally once with EtOH. The crystals are washed with diethyl ether and air dried then stored in the dark over solid ammonium carbonate. A standard soln (ca 0.05M prepared in air-free H2O) is prepared daily from this material for analytical work and is essentially 100% pure. [Anal Chem 26 1747 1954.] It can also be washed with Et20, dried and stored as stated. In a sealed, dark container it can be stored for at least 12 months without deterioration. Xmax 260nm (CHCI3). [Org Synth Coll Vol I 77 1948 J Am Chem Soc 78 4206 7956.] Possible CARCINOGEN. 

Nitiosobenzene, which shares the general character of nitroso-compoLinds in gnung rise to a gneen vapour or solution, is leadily reduced to phenylhydroxylamine and aniline. It condenses with ammo-compounds, yielding azo- or diazo-derivatives. 

Another method of obtain"ing vanillin from guaiacol is as follows Formic aldehyde is allowed to react with guaiacol in the presence of phenylhydroxylamine sulphonate —... 

Phenylhydroxylamine rearranges in sulfuric acid to give mainly p-aminophenol. Industrial routes to this compound have been developed in which phenylhydroxylamine, formed by hydrogenation of nitrobenzene in sulfuric acid over platinum-on-carbon, is rearranged as it is formed. Conditions are adjusted so that the rate of rearran ment is high relative to the rate of hydrogenation of hydroxylamine to aniline (15,17,86). An easy way to obtain a favorable rate ratio is to carry out the reduction with about 1% DMSO present in the sulfuric acid (79,81). 

Benzaldehyde, condensation with N-phenylhydroxylamine, 46,127 reaction with tnphenylphosphine and sodium chlorodifhioroacetate, 47, SO... 

B-Butyraldehyde, condensation with N-phenylhydroxylamine, 46, 96 -Butyric acid, reaction with iron powder to yield 4-heptanone, 47, 75 Butyric acid, 7-bromo-, ethyl ester, 46, 42... 

N, -Diphenylmtrone, by condensation of N-phenylhydroxylamine with bcnzaldchyde, 46,127 1,3-dipolar cycloaddition to styrene, 46,128... 

N Phenylhydroxylamine condensation, with benzaldehyde to form N,a-diphenylmtronc, 46,127 with n-butyraldehyde, 46, 96 Phenyl lsothiocyanate, 46, 21 Phenylhthium, 46, 109 N-Phenylmaleimide, conversion to 3-phenyl-3 -propylisoxazolidinc-... 

Cupferron (ammonium salt of N-nitroso-A -phenylhydroxylamine). The reagent is used in cold aqueous solution (about 6 per cent). Metal cupferrates are soluble in diethyl ether and in chloroform, and so the reagent finds wide application in solvent-extraction separation schemes. Thus Fe(III), Ti, and Cu may be extracted from 1.2 M HC1 solution by chloroform numerous other elements may be extracted largely in acidic solution. 

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