Oximes Isonitroso Compounds

TABLE 95. OXIMES (ISONITROSO COMPOUNDS) TABLE 95. OXJMES (ISONITROSO COMPOUNDS)... 

There appears to be little reported work on S-nitrosation reactions of simple thioke-tones. Thiocamphor when treated with /50-amyl nitrite in fact gives the oxime58 (formerly called a isonitroso compounds), presumably via the tautomeric form of the thione, i.e. the enethiol. In this respect the reaction is very similar to the reactions of ketones59 which give oximes or C-nitroso compounds via the enol intermediates60. 

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). 

The situation with regard to aliphatic nitroso compounds was confused by the observation that oximes were frequently isolated from nitrosation reactions. In fact, many oximes were called isonitroso compounds. Until the middle 1950s, without adequate experimental evidence, it was generally believed that only tertiary aliphatic nitroso compounds (which obviously could not rearrange to oximes) had reasonable stability. More recent work has shown that a wide variety of aliphatic nitroso compounds can be produced and that they exhibit adequate stability. It was also discovered that many nitroso compounds are dimeric in nature. 

The nitrosation of aliphatic carbon atoms, particularly of carbon atoms activated by adjacent carbonyl, carboxyl, nitrile, or nitro groups, has been reviewed in great detail [2]. Judging from this review, with few exceptions, nitrosation of active methylene compounds leads to the formation of oximes (unfortunately termed isonitroso compounds in the older literature). The few exceptional cases cited in which true nitroso compounds (or their dimers) were formed involved tertiary carbon atoms in which no hydrogen atoms were available to permit tautomerism to the oxime or involved a reaction which was carried out under neither acidic nor basic conditions. 

Reaction of the chelate with HC1 gas in chloroform yields the dimeric product [Pd ULJ in which the oxime is protonated and the azooxime is bonded through N(azo) only. 1 Reactions of /3-diketones with nitrous acid yield oximes, derivatives which are more commonly referred to as isonitroso compounds.262 These bond to palladium through the nitrogen atom and one ketone group (41). 3-265... 

Aliphatic nitro compounds are reduced to various products, in all the published examples, only C-F bonds at a-positions are reduced, while the nitro group can be reduced in two steps. Catalytic hydrogenation of primary nitro compounds over palladium transforms them to the corresponding isonitroso compounds, i. e. oximes, while secondary nitro groups are converted into amines (Table 4). The reduction with Raney nickel alloy converts all types of nitro compounds into the corresponding amines, e. g. formation of 14.136... 

Primary amines form Schiff bases, (CH )2C=NR. Ammonia induces an aldol condensation followed by 1,4-addition of ammonia to produce diacetone amine (from mesityl oxide), 4-amino-4-methyl-2-pentanone [625-04-7], (CH3)2C(NH2)CH2COCH3, and triacetone amine (from phorone), 2,2,6,6-tetramethyl-4-piperidinone [826-36-8]. Hydroxylamine forms the oxime and hydrazine compounds (RNHNHJ form hydrazones (RNHN=C(CH3)2). Acetone and nitrous acid give the isonitroso compound which is the monoxime of pymvaldehyde [306-44-5], CH COCH=NOH. 

The hydroxyimino group attached to carbon (C=NOH) may be converted into an amino group by way of the intermediate hydroxyamino or imino group. The reduction of oximes can be conducted so as to yield (1) a synthesis of amines from carbonyl compounds, (2) introduction of amino groups into a compound containing active methylene groups (by way of the isonitroso compounds obtained by nitrosation), or (3) production of amines from the adducts of nitrogen oxides or nitrosyl chloride to olefins. 

Primary and secondary aliphatic nitroso compounds are usually present as dimers which can be converted into isonitroso compounds thermally or by irradiation.119 Thus aliphatic nitroso compounds are reduced in practice under the conditions described above for oximes. 

Compounds with a nitroso group on the primary or secondary carbon irreversibly isomerise to isonitroso compounds that are oximes of aldehydes or ketones ... 

Chlorine passed into a methanolic soln. of isonicotinaldehyde oxime at 5-10 for 15 min., the resulting crude isonicotinohydroxamic chloride hydrochloride collected (Y 83%) and added with vigorous stirring in a very efficient hood to a methanolic soln. of KCN, and warmed 1 hr. at 60 with occasional stirring a-isonitroso-4-pyridineacetonitrile. Y 54%.—Although the isonitrosation of acetonitriles is the most convenient general method for the prepn. of a-iso-nitrosoacetonitriles, certain hetero compounds can be better prepared by the above new method. F. e. s. E. J. Poziomek and A. R. Melvin, J. Org. Chem. 26, 3769 (1961). 

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