Alkyl nitrites, -nitroso compounds

All N-nitroso compounds plus organic and inorganic nitrites, some nitrates, certain alkyl C-nitroso compounds and certain C-nitro compounds... 

Thus, the rate-determining step of alkane nitration is the formation of free alkyl radicals in (Equation 5.1), as well as in reaction of alkanes with O, NO3, OH, Cl and other active radicals. The reactions of R with NO, NO, O, N O [19], Br [20] and other components of the reaction system (including solvents) results in a mixture of nitro compounds, nitrites, nitroso compounds, and nitrates. All these compounds with the exception of RNO depending on the conditions undergo further conversions, resulting in the different composition of the end products of nitration. 

Under alkaline conditions, alkyl nitrites nitrosate imidazoles which possess a free NH group in the 4-position (70AHC(12)103). Nitrosation of 3,5-dimethylpyrazole gives the 4-diazonium salt by further reaction of the nitroso compound with more NO". 5-Pyrazolinones are often nitrosated readily at the 4-position. 3-Alkyl-5-acetamidoisothiazoles undergo 4-nitrosation. 

Carbons adjacent to a Z group (as defined on p. 548) can be nitrosated with nitrous acid or alkyl nitrites. The initial product is the C-nitroso compound, but these are stable only when there is no tautomerizable hydrogen. When there is, the product is the more stable oxime. The situation is analogous to that with azo compounds and hydrazones (12-7). The mechanism is similar to that in 12-7 R—H —> R + N=0 — R—N=0. The attacking species is either NO or a carrier of it. When the substrate is a simple ketone, the mechanism goes through the enol (as in halogenation 12-4) ... 

Other compounds with nitrogen-nitrogen bonds have been used instead of diazonium salts. Among these are N-nitroso amides [ArN(NO)COR], triazenes, and azo compounds. Still another method involves treatment of an aromatic primary amine directly with an alkyl nitrite in an aromatic substrate as solvent. ... 

Treatment of alkyl nitrites with arylsulfinic acids 194 generates the unstable nitroso compounds 195, which, in the presence of dienes, are trapped as cycloadducts 196 (equation 109)102. 

As indicated above, tertiary aromatic amines are directly C-nitrosated. The usual reagents are sodium nitrite and dilute hydrochloric acid, sodium nitrite and glacial acetic acid containing concentrated hydrochloric acid, and nitrite esters with hydrochloric acid [21a, 27]. While tertiary amines with such complex alkyl groups as found in A,A-di(3,5,5-trimethylhexyl)aniline are readily nitrosated [25], of the four A-butyl-A-methylaniline isomers, JV-r-butyl-A-methylaniline does not undergo the reaction, and even the nitroso compounds which did form were only unstable oils [27]. 

Irradiation of octyl nitrite has already been described Kabasakalian et al. have also studied the behavior of its lower homologs.24 It was observed that primary alkyl nitrites with more than four carbon atoms in a chain produced essentially identical yields (37 to 45%) of nitroso dimer formed by the Barton reaction until the minimum straight-chain length of four carbon atoms was reached. Butyl nitrite underwent internal hydrogen abstraction in poor yield. This is the result of a more difficult abstraction of a primary hydrogen as compared to a secondary hydrogen atom available in compounds with longer chains. Reaction paths 2 and 4 predominated to afford 1-butanol and butanal as the major products. 

This conversion has been rationalized33 as depicted in (a) to Id) the alkoxy radical (a) formed during the photolysis of the corresponding nitrite is favorably placed with respect to the 7r-system of the double bond to undergo an intramolecular addition, the resulting intermediate alkyl radical (b) then combines with NO to furnish the oxime (d) via the nitroso compound (c). 

Many compounds have been tested as ignition quality improvers—additives which shorten the ignition delay to a desirable duration. An extensive review in 1944 (6, 43) listed 303 references, 92 dealing with alkyl nitrates and nitrites 61 with aldehydes, ketones, esters, and ethers 49 with peroxides 42 with aromatic nitro compounds 29, with metal derivatives 28 with oxidation and oxidation products 22 with polysulfides 16 with aromatic hydrocarbons nine with nitration and four with oximes and nitroso compounds. In 1950, tests at the U. S. Naval Engineering Experiment Station (48) showed that a concentration of 1.5% of certain peroxides, alkyl nitrates, nitroaikanes, and nitrocarbamates increased cetane number 20 or more units. 

Method (d), based on UV photolysis-TEA detection, seemed to give positive response to alkyl nitrites and C-nitroso compounds. In this respect, it is less specific than the preceding two HX-catalyzed denitrosation techniques, which give either negligible or no response for such compounds. Data on the actual use of the methods mentioned in Table 2 for the determination of NOC in foods is, however, limited. 

Low yields of /i-chloro nitroso compounds are often obtained from racemic or optically active terpenes37. From optically active Iimonene using an alkyl nitrite and hydrochloric acid were produced two diastereomers, indicated as a and fi forms (dimers)38 which were separated due to their different solubilities in chloroform and diethyl ether. The predominant a-form from... 

Sulfonyl nitroso compounds have been used only rarely as dienophiles. ° One source of these species is from arylsulflnic acids and alkyl nitrites (equation 43). These compounds probably warrant further investigation. 

The aiyl radical thus formed attacks the substrate to give the intermediate 42 (see p. 940), from which the radical 41 abstracts hydrogen to give the product, 43. A -Nitroso amides probably rearrange to A -acyloxy compounds (44), which cleave to give aryl radicals. " There is evidence that the reaction with alkyl nitrites also involves attack by aryl radicals. ... 

In the Barton reaction, an alkyl nitrite is converted into an alcohol-oxime. The nitrite is photoexcited to a 1,2-diradical. It fragments to NO and an alkoxy radical (RO-), and the latter abstracts H- from the nearest C-H bond. The resulting alkyl radical then combines with NO to give a nitroso compound, which then tautomerizes to the oxime, probably by a polar stepwise mechanism. The Barton reaction has been used for the remote functionalization of hydrocarbons, especially steroids. 

The reaction of phenols with nitrous acid gives the ortho- and para-nitroso products, which are formed through a neutral dienone intermediate, the proton loss from the latter being the rate-limiting step" " . It has been shown that the nitrous acid can act as a catalyst for the formation of the nitro derivatives. Thus the conventional preparation of nitro compounds by the oxidation of nitroso compounds may be replaced by methods using an electron-transfer pathway in certain cases. In the latter method, the phenoxide reacts with nitrosonium ion to give the phenoxy radical and nitric oxide radical. The nitric oxide radical is in equilibrium with the nitronium radical by reaction with nitronium ion. The reaction of the phenoxy radical with the nitroninm radical resnlts in the formation of the ortho- and para-mixo prodncts" . Leis and coworkers carried ont kinetic stndies on the reaction of phenolate ions with alkyl nitrites and fonnd that the initially formed product is the 0-nitrite ester, which evolves by a complex mechanism to give the ortho-and the para-nitro products". ... 

The dimer 147 and the carbinolamine 140b reacted with alcohols in the presence of an acidic catalyst to give the corresponding alkoxymethyl derivatives, e.g., 140a. Nitrosation of the N—H group, to give the N-nitroso compound 18b, readily occurred when the dihydrothiazine 18a was treated with sodium nitrite and hydrochloric acid in aqueous dioxane. There is only one report of the A -alkylation of a dihydrothiazinone this involves the A/ -methylation of the derivative 80a in the presence of methyl iodide and sodium hydride. ... 

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