Nitrous acid oxidant and preparation

Nitrous acid. Only dilute solutions of nitrous acid have been prepared, and these rapidly decompose, evolving oxides of nitrogen. Two structures can be envisaged for the molecule of nitrous acid, the second of which could exist in cis and trans forms  

Cyclooctanone has been prepared by distilling the calcium and thorium salts of azelaic acid, by heating azelaic acid with barium oxide in the presence of iron, by the action of nitrous acid on l-(aminomethyl)-cycloheptanol, by Dieckman cyclization of azelaic acid dimethyl ester and diethyl ester, and by ring expansion of cycloheptanone with diazomethane.  

Diazo esters can also be prepared from glycine esters by treatment with nitrous acid [966] or with alkyl nitrites. Further methods include the oxidation of hydrazones, oximes (Forster reaction), and semicarbazones, the base-induced 

Nitrosyl chloride (178), nitrosyl chloride—hydrogen fluoride (NOF -3HF, NOF -6HF) (179), nitrous acid—hydrogen fluoride solutions (180,181), or nitrogen trioxide (prepared in situ from nitric oxide and oxygen) (27) can be used in place of sodium nitrite in the dia2oti2ation step. 

The glycamines may serve as intermediates in the s3mthesis of 2-deoxy-sugars. 2-Deoxy-D-ribose was prepared by nitrous acid oxidation of 2-amino-2-deoxyribitol (SS8), obtained from D-arabinose and D-ribulose. 

Several 5,6-disubstituted-3-azido[l,2,4]triazine-l-oxides 1021 were prepared (77JHC1221) by treatment of 1020 with nitrous acid. 3-Azido[l, 2,4]-triazine-2-oxide 1023 was prepared by reacting the corresponding 3-bromo derivative 1022 with either tetramethylguanidinium azide in chloroform or sodium azide in aqueous acetone. These azido derivatives were proven to exist in the open-chain form by H- and l3C-NMR and 1R spectra (77JHC1221) (Scheme 191). 

The earliest oxidations were effected with nitrous fumes and later with mercuric oxide and isoamyl nitrite.74 Lead tetraacetate in acetic acid is in many cases the reagent of choice, but the removal of by-products can present some difficulties.75 IV-Haloimides and amides in alcoholic solutions have been reported to yield essentially pure tetrazolium salts76 and have been found specially useful in the preparation of heteroaryl-substituted tetrazolium salt.77,78 The novel formazans 49 have been successfully oxidized to 50 using 7V-chloro succinimide (Eq. II).79 tert-Butyl hypo- 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid  

The presence of HMX as an impurity in RDX is not a problem when the product is used as an explosive. However, the need for an analytical sample of RDX makes other more indirect methods feasible. One such method involves the oxidation of 1,3,5-trinitroso-1,3,5-triazacyclohexane (109) ( R-salt ) with a mixture of hydrogen peroxide in nitric acid at subambient temperature and yields analytical pure RDX (74%) free from HMX." The same conversion has been reported in 32 % yield with three equivalents of a 25 % solution of dinitrogen pentoxide in absolute nitric acid. l,3,5-Trinitroso-l,3,5-triazacyclohexane (109) is conveniently prepared from the reaction of hexamine with nitrous acid at high acidity.  

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