4- Nitropyridine N-oxide

Because reduction of 2-nitrodiphenyl with hexamethyldisilane 857 does not give any carbazole, nitrene intermediates can probably be excluded. The very polar 4-nitropyridine N-oxide 1003 can be reduced by 857 only in the polar solvent N,N-di-... 

Intramolecular charge transfer in 4-nitropyridine N-oxide has been investigated by spectroscopic methods and by comparison with AMI and MNDO semi-empirical methods to obtain the vibrational force field225. The results obtained indicate that protic solvents (water, methanol) favour the mesomeric form 97 which is also favoured in the crystal, by an internal interaction between the nitro and TV-oxide groups226. 

It had been shown previously 7 ) that 4-nitropyridine-N-oxides 7 a—d are photo-reduced (> 300 nm) in ethanol solution to the corresponding 4-hydroxylamino-pyridine-N-oxides 2 a—d. Presence of oxygen was found to alter the course of the reaction. 

Jawdosiuk et al.220 have treated 4-chloro- and 4-nitropyridine N-oxides (145) with substituted phenylacetonitrile. This is in agreement with the well-known activating effect of N-oxides toward SNAr reactions the results show that nitro is a better leaving group than chloro. 

Dimethyl 3,5,6-trichloro-2-pyridyl phosphate, known as Fospirate or Dowco 217, is an rnsechcide useful rn anlrllea collars for dogs and cats. The compound 4-aminopyridine, known as Avilrol 100, and 4-nitropyridine-N-oxide, known as Avitrol 200, are useful as bird repellents. 

POM (3-methyl-4-nitropyridine-N-oxide) 53) is the only commercially available organic crystal for SHG, other... 

Selective silylation of ribonucleosides.2 Only the 5 -hydroxyl group of ribonucleo-sides is silylated by reaction with the reagent in THF in the presence of silver nitrate. On addition of pyridine to the reaction, 2, 5 -disilyl derivatives are formed in 80-90% yield. The actual reagent may be r-butyldimethylsilyl nitrate. Highly selective 3, 5 -disilylation can be achieved in the presence of several silver salts (AgN03, AgC104, and AgOAc) in the presence of either DABCO or 4-nitropyridine N-oxide. 

Methyl-4-nitropyridine N-oxide, 2310 A-Methyl-A-nitrosourea, 0871 Methylnitrothiophene, 1844... 

Dimethyl-4-nitropyridine-N-oxide-dimethyl sulfate adduct... 

To a suspension of 3,5-dimethyl-4-nitropyridine-N-oxide (150 g, 0.80 mole) in acetone (450 ml) was added dimethyl sulfate (90 ml, 0.95 mole). The mixture was heated to reflux until a clear solution was obtained and then allowed to cool to ambient temperature. An off-white crystalline solid separated out, which was filtered, washed with acetone and dried to yield 220 g of the adduct. Yield was 83.8% of theoretical. 

Dimethyl-4-nitropyridine-N-oxide-dimethyl sulfate adduct (220 g, 0.75 mole) was dissolved in methanol (1.0 Itr) and the solution heated to reflux. A solution of ammonium persulfate (140 gm) in water (200 ml) was added dropwise over 4 hours after which reflux was continued for 4 hours. Methanol was distilled off under reduced pressure and the residue was basified to pH 10 by addition of caustic lye (105 ml). The mixture was extracted with dichloromethane (2 times 400 ml). The dichloromethane layer was dried over sodium sulfate and filtered. The product was used as its solution in dichloromethane for the next reaction. 

Also the nitro group in 4-nitropyridine-N-oxide is very mobile (den Hertog and Combe [8a]). 

Pyridine /V-oxide is nitrated in the 4-position as the free base (9.81) [64CI(L)1577] and/p has been estimated as between 2.1 x 10"3 and 4 x 10"6 [66JCS(B)870 67JCS(B)1213], up to 95% yields of 4-nitropyridine N-oxide have been reported (51RTC581). 4-Nitration on the free base also occurs for the 3,5-dimethyl and 2,6- and 3,5-dichloro derivatives (9.82-9.84) [67JCS(B)1213]. 

Hypervalent Cl Sn—Cl bridges are also typical for pentacoordinate tin atoms. For example, the crystal structure of 20 and 21 comprise dimeric pairs of molecules bridged by weak intermolecular Cl Sn interactions. The Cl —Sn distances in 20 (2.475 A ), 21 (average 3.869 A ) and in MeSn(Ar)Cl2 (Ar = 3-methyl-4-nitropyridine-N-oxide) (3.934 A ) are longer than in most comparable structures The Sn NMR resonance (—285.7 ppm) for 21 suggests that it possesses a five-coordinate structure in solution . 

As yet, however, no reactive nitro-N-heterocycle, such as 5-nitropyri-midine (325), l-alkyl-5-nitropyrimidine-2-one, or 4-nitropyridine-N-oxide [or N-heterocycles containing other acceptor groups such as 2-methylsulfonylpyrimidine (265) or 3-methylsulfonyl-l,2,4-triazine (267)] have been aminated using this interesting new procedure. 

The nitro group of 4-nitropyridine-N-oxide (1) was hydrogenated preferentially over palladium in neutral medium -2 but in acid the N-oxide was also reduced (Eqn. 19.1).2 Hydrogenation of 1 or 4-nitroquinoline-N-oxide over Raney nickel at elevated temperatures and pressures resulted in the reduction of both the nitro group and the N-oxide.3.4 Hydrogenation of 2-nitropyridine-N-oxide gave only 2-aminopyridine.5... 

Problem 31.16 Pyridine N-oxides not only are reactive toward electrophilic substitution, but also seem to be reactive toward nucleophilic substitution, particularly at the 2- and 4-positions. For example, treatment of 4-nitropyridine N-oxide with hydro-bromic acid gives 4-bromopyridine N-oxide. How do you account for this reactivity and orientation ... 

Ochiai used phenylhydrazine in ethereal solution to reduce 4-nitropyridine-N-oxide to 4-hydroxylaminopyridine N-oxide in high yield. 

The oxidation of thiols is accelerated remarkably by traces of catalyst and this reaction forms the basis of petroleum sweetening processes. Although transition metal ions are the most effective catalysts, any additive capable of catalysing electron transfer accelerates the reaction. Nitrobenzene in dimethylformamide/potassium hydroxide [118], 2-nitro-thiophene, tetracyanoethylene, and 4-nitropyridine-N-oxide [118] are all good catalysts for the oxidation of 1-butane thiol. The alkaline hydrolysis of disulphides containing aryl, carbonyl, and alpha unsaturated groups also results in catalysis, apparently due to the setting up of a sulphinate—sulphenate redox cycle [119—121]. 

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