Nitroso compounds ketones

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) ... 

As in the Japp-Klingemann reaction, when Z is an acyl or carboxyl group (in the case of R2CH—Z), it can be cleaved. Since oximes and nitroso compounds can be reduced to primary amines, this reaction often provides a route to amino acids. As in the case of 12-4, the silyl enol ether of a ketone can be used instead of the ketone itself. Good yields of a-oximinoketones (20) can be obtained by treating ketones with fert-butyl thionitrate. ... 

A variety of double bonds give reactions corresponding to the pattern of the ene reaction. Those that have been studied from a mechanistic and synthetic perspective include alkenes, aldehydes and ketones, imines and iminium ions, triazoline-2,5-diones, nitroso compounds, and singlet oxygen, 10=0. After a mechanistic overview of the reaction, we concentrate on the carbon-carbon bond-forming reactions. The important and well-studied reaction with 10=0 is discussed in Section 12.3.2. 

Most UV absorption bands correspond to transitions of electrons from ra->7i, or n o molecular orbitals. Besides aromatic compounds, organic functional groups such as carbonyl, carboxylic, amido, azo, nitro, nitroso, and ketone groups have absorbance in the UV region. 

An analogous reaction is known with aromatic nitroso-compounds, but for it an exceptionally mobile hydrogen atom must be present in the ketone and hence no condensation occurs with simple ketones such Us acetone. The products of the reaction are, of course, azomethines. This condensation has made possible the synthesis of 1 2 3-triketones (F. Sachs), e.g. 

As such, a more thorough description of the energetics of nitroso compounds may well logically appear in a future Patai volume on functional groups devoted to carbon-containing double bonds such as monoalkenes, imines and ketones and aldehydes, since oximes would seem to belong with these functionalities. 

Primary and secondary nitroso compounds tautomerize to isonitroso compounds - oximes of aldehydes and ketones, respectively. Their reductions are dealt with in the sections on derivatives of carbonyl compounds (pp. 106,132). 

In the nitrosation of ethyl isopropyl ketone (Preparation 2-4), acetyl chloride is used as a catalyst. While aqueous hydrochloric acid has also been used to catalyze this reaction, anhydrous hydrogen chloride or acetyl chloride evidently is more effective as far as the yield is concerned. To be noted here is that the greater yield is that of the true nitroso compound. However, the secondary carbon atom of the ethyl group is converted into an oxime on nitrosation. 

The bimolecular reduction of aliphatic nitroso compounds is complex and somewhat unreliable. With careful control of reaction conditions, a-nitroso ketones (in dimeric form) may be reduced with stannous chloride in an acidic medium at room temperature to the azoxy compounds, while dimeric a-nitroso acid derivatives may be reduced at about 50°C [10, 35, 36]. Nitrosoalkanes, on the other hand, are decomposed at room temperature to alcohols and nitrogen, and are reduced to amines at 50°-60°C. It has been postulated that only the dimeric nitroso compounds can be reduced to azoxy compounds and, in fact, that the dimer has a covalent nitrogen-nitrogen bond. Equations (31)—(34) summarize these data [10]. 

Treatment of aliphatic active methylene compounds with such reagents normally leads to oxime formation. An exception is the nitrosation of compounds with active tertiary carbon atoms such as ethyl isopropyl ketone which are convertible into C-nitroso compounds. 

A related procedure, which may be of value from the preparative standpoint, involves the preparation of /rans-nitrosomethane dimer by adding a solution of diacetyl peroxide in sec-butyl nitrite to warm sec-butyl nitrite [50]. From the product of the reaction it has been assumed that this preparation involves the generation of free methyl radicals which react with the nitrite to give nitrosomethane and alkoxy radicals. The latter disproportionate to ketones and alcohols, while the nitroso compound dimerizes. 

The biradical intermediates have in some cases been detected by flash spectroscopy, or trapped by added reagents such as a t-alkyl nitroso compound. The enol produced by cleavage of the biradical is relatively inert at low temperatures, and it can be studied spectroscopically after irradiation of the ketone in solutions cooled below —50°C. There have been many mechanistic studies of the Norrish... 

The pyridazine dioxide derivative (108) was made by intramolecular nitroso compound dimerization as shown (Scheme 23). 1,2-Oxathiin 2,2-dioxides are obtained by the addition of sulfuric acid to a,(3-unsaturated ketones, e.g. (109) — (110) (66HC(21-2)774). 1,2-Dithiins are synthesized from conjugated diynes using benzyl thiol reductive debenzylation of intermediate (111) by sodium in liquid ammonia at - 70°C gives, after aerial oxidation, the 1,2-dithiin (112) (67AG(E)698). 

Amino groups react very easily with aldehydes or ketones, and with aldehydes in the presence of amines, they can be acylated by the usual acylating agents, and they react with amidacetals, Vilsmeier reagents and nitroso compounds (Scheme 12). As mentioned earlier, alkylation leads mainly to AT(2)-alkylated products. The hydrazino group reacts in the same way as the amino group with aldehydes or ketones, with acyl chlorides or carboxylic anhydrides, with sulfonyl chlorides, ortho esters, carbon disulfide and with nitrous acid. The last three reactions have mainly been used for the synthesis of condensed 1,2,4-triazines. 

Analogous compounds which are assumed to contain imines, diazenes, ketones and nitroso compounds -coordinated to the Ni(CNBut)2 moiety have been also reported.30... 

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. 

Oxidation of the TV-aryl azanols under controlled conditions yields nitroso compounds. This reaction is not unlike the oxidation of alcohols to ketones (Section 15-6B) ... 

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