Nitrites preparation

The nitrites aie most conveniently prepared from the corresponding alcohols by treatment with nitrosyl chloride in pyridine. The crude nitrites can be precipitated by addition of water and recrystallized from appropriate solvents. However nitrites prepared from carbinols in which the adjacent carbon is substituted by halogen, free or esterified hydroxyl or a carbonyl function are very readily hydrolyzed and must be recrystallized with great care. In general the photolysis gives higher yields if purified and dried nitrites are used which do not contain acids or pyridine, although occasionally the addition of small amounts of pyridine is recommended in order to prevent hydrolysis of the nitrite. Traces of acids do in fact catalyze the thermal decomposition of secondary nitrites to equimolar amounts of alcohol and ketone. ... 

Far more numerous are the complexes of nickel(II) which contain a variety of either aliphatic or aromatic amines and coordinated nitrite (Table 82). Most of these complexes are prepared by the reaction of the amine in methanolic solution with a methanolic solution of nickel nitrite prepared metathetically from hydrated nickel nitrate and sodium nitrite.1654-1659... 

The dimer of (74) is isolated as one of the products. In the flow ESR spectra, nitroxides (76) and (77) can be recognized. These are proposed to arise by H-abstraction from (74) by a cyclobutoxy radical, giving (75), which either reacts with a further molecule of (74), yielding (76), or undergoes, 5-exo ring closure to (77). The steroidal nitrite (78) (Scheme 17) yields 50% of the ketone (79) and 16% of the alcohol (80) when photolysed in the solid state (X > 300 nm), but only 5% of (79) and 52% of the Barton-type product (81) when photolysed in toluene solution. It is usual for ketones to be produced only in low yields from photoreactions of nitrites in solution, and so the promotion of this reaction pathway in solid-state photolysis is of considerable interest. Similar results were obtained for the solid-state photolyses of a number of other steroidal nitrites, but nitrites prepared from acyclic alcohols showed much less selectivity in favour of the corresponding ketones. 

Even the purest nitrite preparations invariably show a slight nitrate content, which must be considered when testing for nitrates in the presence of nitrites. 

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