Hydroxylamino

It must be remembered, however, that nitroso, azoxy and azo compounds (which are usually more highly coloured than nitro compounds) may bo reduced by zinc powder to the corresponding hydroxylamino, hydrazo and hydrazine compounds respectively, all of which reduco Tollen s reagent in the cold. 

In catalytic hydrogenation, a compound is reduced with molecular hydrogen in the presence of a catalyst. This reaction has found appHcations in many areas of chemistry including the preparation of amines. Nitro, nitroso, hydroxylamino, azoxy, azo, and hydrazo compounds can all be reduced to amines by catalytic hydrogenation under the right conditions. Nitriles, amides, thioamides, and oximes can also be hydrogenated to give amines (1). Some examples of these reactions foUow ... 

The reactivity of halogens in pyridazine N- oxides towards nucleophilic substitution is in the order 5 > 3 > 6 > 4. This is supported by kinetic studies of the reaction between the corresponding chloropyridazine 1-oxides and piperidine. In general, the chlorine atoms in pyridazine A-oxides undergo replacement with alkoxy, aryloxy, piperidino, hydrazino, azido, hydroxylamino, mercapto, alkylmercapto, methylsulfonyl and other groups. 

In spite of the usefulness of the Beirut reaction, mechanistically it is not well understood. It has been suggested that the first step involves the nucleophilic attack by the enolate or the enamine at N-3 of the benzofuroxan to yield an intermediate iV-oxide (Scheme 50) which subsequently undergoes tautomerism to an hydroxylamino derivative. This intermediate then cyclizes to the dihydroquinoxaline 1,4-dioxide. This suggestion has not been proven, and indeed there is evidence that benzofuroxan is in equilibrium with 1,2-dinitrosobenzene... 

The first 5-isoxazolidinone was synthesized in 1912 by the cyclization of a-hydroxylamino-/3,/3-diphenylpropionic acid (62HC(l7)l,p. 7). The ester (541) underwent an intramolecular Michael cyclization to produce 2-methyl-3-phenyl-5-isoxazolidinone (542) (78TL3985). 

In all cases, a higher percentage of hydroxylamino trapping occurs in the presence of mineral acid, and the hydroxylamino trapping abilities of the carboxy derivatives increase as R = OH < OMe < NH2. Thi.s order is reversed in the absence of mineral acid. Presumably the carboxyl derivative is protonated in the presence of acid and thus becomes a better electrophile. 

Only in one case was the structure of the adduct rigorously established, but it would appear most likely that these adducts are 1-cyano- or 1 -hydroxylamino-1,2,3,4-tetrahydro-j8-carboline derivatives (308). 

Tiiazine A-oxides can be obtained by two general methods by direct oxidation of the parent 1,2,4-tiiazines with organic peracids, and by the formation of the A-oxide group of the 1,2,4-triazine ring by cyclization involving nitro, nitroso (isonitroso), or hydroxylamino groups. 

B. Synthesis of 1,2,4-Triazine 4-Oxides by Cyclization Involving Nitroso (Isonitroso) or Hydroxylamino Groups... 

It is known that 1,2,4-triazine 4-oxides, in contrast to 1,2,4-triazine 1- and 2-oxides, cannot be obtained by oxidation. Therefore, the only way to obtain 1,2,4-triazine containing the A -oxide group at position 4 of the heterocycle is to form the tiiazine ring by cyclization, starting from compounds bearing nitroso (isonitroso) or hydroxylamino groups. There are several ways to carry out such cyclizations. 

The 1,2,4-triazine 4-oxides 55 were synthesized by the reaction of nitrones 158 (generated from a-hydroxylamino ketones and aldehydes) with an excess of hydrazine, followed by the oxidation of the intermediate 4-hydroxy-2,3,4,5-tetrahydro-l,2,4-triazines 159 with lead(TV) oxide (73KGS134). 

Oxime-(9-sulfonic acid potassium salts of pyrido[3,2,l-(/]quinazolines 180 (X = H2, O) were obtained from 7-oxo derivatives 179 (X = H2, O) by reacting with hydroxylamino-O-sulfonic acid, then with K2CO3 (98EJM763). Reaction of 2,3,6,7-tetrahydro-l//,5//-pyrido[3,2,l-//]quinazo-line-l,3,7-trione with HONH2 HCI in boiling EtOH in the presence of NaOAc afforded 7-oxime derivative (01MI28). 

A convenient synthesis of , -diamino acids from azlactones involves catalytic hydrogenolysis of a hydroxylamino function over palladium-on-carbon 141). 

Hydroxylamino-3-methyI-4-phenyl-l-butene (8, R = C H5) Typical Procedure10 ... 

Chinon-acylhydrazone lassen sich in milder Reduktion durch Erwarmen mit Ascorbinsaure in waBriger Losung zu Aryl-hydrazinen reduzieren (s.ds. Handb. Bd. X/2, S. 233). Die Herstellung des sehr empfindlichen 2-Hydroxylamino-l-nitro-benzols ist aus 1,2-Dinitro-benzol mit Ascorbinsaure moglich (s. Bd. X/l, S. 1149). Aryl-diazoniumsalze werden liber Oxalsaure-monoarylhydrazide zu Aryl-hydrazinen reduziert (s.Bd. X/2, S. 219). 

Aus l,5-Dinitro-9,10-anthrachinon wird 5-Nitro-1 -hydroxyamino-9,10-anthrachinon erhalten (s.Bd. X/1,S. 1149), wahrend bei der Reduktion mit Zinn(II)-chlorid/Natron-lauge beide Nitro-Gruppen zur Hydroxylamino-Gruppe reduziert werdcn. Nitro-aroma-ten ohne Acyl-Substituenten werden dagegen zu Anilinen reduziert (s.ds. Handb. Bd. XI/1, S. 453). 

Zur Reduktion von l-(2-Nitro-phenyl)-alkenen zu l-(2-Hydroxylamino-phenyl)-alkenen (Zwischenstufe) s.S. 698. 

Durch Spaltung der Seitenkette kann 2-Hydroxylamino-benzaldehyd entstehen, der an-schlieBend zum Benzo-[d]-l,2-oxazol cyclisiert (s.S. 691). 

Phcnyl-3-(2-hydroxylamino-phenyl)- 698 2-Phenyl-3-(4-methyl-phenyl)- 553... 

Hydroxylamino-l-phenyl- 372 2-(2-Hydroxy-phenyl)-l-(2-hydroxymethyl-phenyl)-... 

Nitro-3,4-dimethoxy-phenyl)- 188 2-Nitro-l-(2-hydroxylamino-phenyl)- 694 2-Nitro-l-(2-nitro-phenyl)- 694... 

Phenyl- 50, 55, 398, 514, 522, 581, 633, 645ff. 2-Phenyl-l-(2-hydroxylamino-phenyl)- 698 2-Phenyl-1 -(2-nitro-phenyl)- 698 2-Phenyl-1 -(2-nitroso-phenyl)- 698 2-Phenyl- -sulfinsaure 461 2-Phenyl- -sulfonsSure-chlorid 461 2-Phenylsulfonyl-1,1 -diphenyl- 634 Phenylsulfonyl-triphenyl- 464 Tetraaryl-... 

Hydroxy- 146, 599, 743 4-Hydroxy- 286, 654 [Carbonyl-14C]- 182 2-Hydroxylamino- 695 4-Hydroxy-3-methoxy- 272, 286 -4-hydroxy-phenylimin 362 4-Isopropyl- 604, 655 Methoxy- 599... 

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