Nitrosobenzene Nitrosyl

Keywords anilines, nitrosobenzene, azomethine, nitrosyl chloride, nitrogen monoxide, diazotation, gas-solid reaction, solid diazonium salts... 

For example, the preparation of nitrosobenzene by the reaction of phenylmagnesium bromide with nitrosyl chloride was reported as long ago as 1909 [10], but has scarcely been further explored. 

The Regioselectivity ofHetero Diels-Alder Reactions. In a few cases, carbonyl, nitrosyl, cyano, and other double bonds with one or more electronegative heteroatoms have acted as dienophiles in Diels-Alder reactions. The carbonyl group has a HOMO and a LUMO as shown in Fig. 1.51. The energies of both orbitals are relatively low, and most of their Diels-Alder reactions will therefore be guided by the interaction between the HOMO of the diene and the LUMO of the carbonyl compound. This explains the regioselectivity in the cycloaddition of dimethylbutadiene 6.176 and formaldehyde, and between 1-substitituted butadienes 6.177 and nitrosobenzenes. 

Neurotoxin, frog, 86 Nitriles, 146-150 intramolecular, 149-150 Nitrosobenzene, cycloaddition, 72-78 Nitrosyl cyanide, 87... 

A novel synthesis of imidazoles was reported by Junjappa and co-workers [84JCS(CC)430], in which the reaction of enaminones 316 (R = H) with nitrosyl chloride gives the nitrosoenaminones 317, which are cyclodehy-drated to the -H imdazoles 318 in high yields. Scheme 89 (path a). The transformation can be done in one step with some of the enaminones under more forcing conditions (path b). Also, 1-phenylimidazoles 319 can be prepared by heating the enaminones 316 (R = H) with nitrosobenzene in sealed tubes (path c). The method was successfully extended to the synthesis of 2,2-disubstituted 2-H imidazoles 320 for enaminones 316 (R H) (87S547). Tetrahydrobenzimidazoles are prepared similarly from the cyclodehydration of a-nitroso enaminones derived from 1,3-cyclohexanediones (80JHC1723). 

With nitrosyl chloride or ethyl nitrite in place of nitrous acid, the same holds except for Cl or OC2H5 instead of OH. The nitrous acid in this reaction corresponds to the base, and the amine to the acid. This formulation also shows how general a classification may be developed from a simple scheme and that although the reactions of organic chemistry appear to be most complex and different, in reality a great many conform to simple fundamental principles and changes. If A = CeHs, then the reaction corresponds to the formation of nitrosobenzene, etc. 

The rate-determining step was proposed to be the third in the scheme (first deoxygenation of nitrobenzene). The so formed nitrosobenzene eomplex was said to be observable in solution based on the presence in the UV spectrum of the reaetion solution of an absorption at 316 nm, which was said to be characteristic of Ru-NO bonds. However, the examples mentioned in the literature cited only include nitrosyl complexes (Ru-NO), very different from an electronic point of view fi-om a nitroso complex (Ru-ArNO) as the one proposed to be formed. Moreover the frequencies of the bands reported in the references vary as much as from 220 to 350 nm. So an absorption at 316 nm is far from being characteristic of any complex and may arise from a variety of compounds. The observation of the nitrosobenzene complex in solution also contrasts with the assumption that the third step of the reaction is the rate-determining one since, in this case, no complex formed after this step should be observable in solution. 

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