Ketoximes acidity

Satisfactory with 1 -phenylethanone (acetophenone) oxime and other diaryl ketoximes acid catalysts include HCI, H2S04, PCI5, H3PO< (Section 24-3C). 

When treated with certain reagents, the ketoximes in particular undergo the Beckmann rearrangement to isomeric acid amides (p. 227). 

Although 1,2-benzisothiazoles can be prepared by the oxidation method, they are also available by cyclization of o-mercaptobenzaldoximes and ketoximes with polyphosphoric acid (72AHC 14)43, 73JCS(P1)356, 77JCS(P2)1114). This method has been improved by the use of S-t- butyl analogues, which do not suffer from the instability of the free thiols (79SST 5)345). 

The rearrangement of oximes 1 under the influence of acidic reagents to yield A -substituted carboxylic amides 2, is called the Beckmann rearrangement. The reaction is usually applied to ketoximes aldoximes often are less reactive. 

The ketoxime derivatives, required as starting materials, can be prepared from the appropriate aromatic, aliphatic or heterocyclic ketone. Aldoximes (where R is H) do not undergo the rearrangement reaction, but rather an elimination of toluenesulfonic acid to yield a nitrile. With ketoxime tosylates a Beckmann rearrangement may be observed as a side-reaction. 

In recent years, possible alternatives to hydrazine have been suggested, and some have been used on plant. These include carbohydrazide (NH2NHCONHNH2), derivatives of hydroxylamine, e.g. diethyl hydroxy-lamine (HONfCiHjIi), ketoximes, and erythrobic acid (iso corbic acid). These are usually faster scavengers than hydrazine or activated hydrazine . 

Scholl et al (Refs 3 4) prepared the same compds by treating ketoximes (such as pina-colone) with nitrogen tetroxide, but he assigned them the structure R2C=N-N02 and called them nitrimines. One of the compds described by him in Ref 4, p 27 is a weak expl. It is the Ag salt of pinacolone-nitraminic acid which puffs off on rapid heating (this compd described below under List of Nitrimines ). Further work on... 

Certain ketoximes can be converted to nitriles by the action of proton or Lewis acids. Among these are oximes of a-diketones (illustrated above), a-keto acids, a-dialkylamino ketones, a-hydroxy ketones, p-keto ethers, and similar compounds. These are fragmentation reactions, analogous to 17-25 and 17-26. For example, ot-dialkylamino ketoximes also give amines and aldehydes or ketones besides nitriles. 

The reaction that normally occurs on treatment of a ketoxime with a Lewis or proton acid is the Beckmann rearrangement (18-17) fragmentations are considered side reactions, often called abnormal or second-order Beckmann rearrangements. Obviously, the substrates mentioned are much more susceptible to fragmentation than are ordinary ketoximes, since in each case an unshared pair is available to assist in removal of the group cleaving from the carbon. However, fragmentation is a side reaction even with ordinary ketoximes and, in cases where a particularly stable carbocation can be cleaved, may be the main reaction. ... 

The photochemical cyclisation of p.y-unsaturated ketoximes to 2-isoxazolines, e.g., 16—>17, has been reported <95RTC514>. 2-Isoxazolines are obtained from alkenes and primary nitroalkanes in the presence of ammonium cerium nitrate and formic acid <95MI399>. Treatment of certain 1,3-diketones with a nitrating mixture generates acyl nitrile oxides, which can be trapped in situ as dipolar cycloadducts (see Scheme 3) <96SC3401>. 

On treatment of trialkylsilyl nitronates 1043 with MeLi, LiBr, or BuLi in THF the resulting nitrile oxide intermediates 1044 afford, in dilute THF solution (R=Me) the ketoximes 1045 in ca 50-60% yield, whereas in concentrated THF solution the O-silylated hydroxamic acids 1046 are obtained as major products [144] (Scheme 7.35). Analogously, the silyl nitronate 1047 reacts with the 2,3,4,6-tetra-O-acetyl-/ -D-glucopyranosyl thiol/triethylamine mixture to afford, via the thiohydroxi-mate 1048, in high yield, a mixture of oximes 1049 which are intermediates in the synthesis of glucosinolate [145] (Scheme 7.35). 

Anhydrous peroxytrifluoroacetic acid is not easy to handle, but the procedure has recently been revised.121 Namely, reaction of urea-hydrogen peroxide complex (UHP) with tri-fluoroacetic anhydride in acetonitrile at 0 °C gives solutions of peroxytrifluoroacetic acid, which oxidize aldoximes to nitroalkanes in good yields (Eqs. 2.58 and 2.59). Ketoximes fail to react under these conditions, the parent ketone being recovered. 

The conversion of nitroalkanes to ketoximes can be achieved by the reduction with Zn in acetic acid,112 or Fe in acetic acid.113 Nitroalkenes are direcdy reduced into saturated ketoximes by these reagents, which are precursors for ketones (see Section 6.1.4 Nef reaction). Reduction of 3-O-ace-ty lated sugar 1 -nitro-1 -alkenes with Zn in acetic acid gives the corresponding 2,3-unsaturated sugar oximes in high yield, which is a versatile route to 2,3-unsaturated sugar derivatives (Eq. 6.58).114... 

Conceptually interesting is the synthesis of the oxazole system 94 through a Beckmann rearrangement of a-formyl ketoxime dimethyl acetals 93 which demonstrated the possibility of a non-amino acid pathway in the biosynthesis of marine derived oxazoles <06CC1742>. 

Ketoximes and oximes of 2-oxo-acids are hydrogenated to amines by [CoH(CN)5]3-. The latter reaction allows the preparation of a-amino-acids by reductive amination of 2-oxo-acids in aqueous ammonia. At 40-50 °C and 70 bar H2 the yields are ca. 90% [146]. 

Fischer formula, 4 697 a-Ketoxime, reduction, 2 572 Kettle soap making, 22 723, 736-737 Kettle-type reboilers, 79 510 Kevlar, 70 211, 212 79 742 20 79, 399 TD resins in, 22 589 Kevlar fibers, 73 373-376 26 760 Kew laboratories, 77 248—249 Key-and-lock principle, 7 574 Keyword-in-context (KWIC) index, 78 239 KF alumina, 5 337 Kharasch process, 79 114 Kidney, citric acid in, 6 632t Kidney Disease Outcome Quality Initiative (K/DOQI), 26 823 Kidney failure, 26 813 Kidney function, normal, 26 813 Kielselguhr 22 402... 

Several explosions or violent decompositions dining distillation of aldoximes may be attributable to presence of peroxides arising from autoxidation. The peroxides may form on the -C=NOH system (both aldehydes and hydroxylamines perox-idise [1]) or perhaps arise from unreacted aldehyde. Attention has been drawn to an explosion hazard inherent to ketoximes and many of their derivatives (and not limited to them). The hazard is attributed to inadvertent occurence of acidic conditions leading to highly exothermic Beckmann rearrangement reactions accompanied by potentially catastrophic gas evolution. Presence of acidic salts (iron(III)... 

This is the first example of a direct coupling of a diazo compound in a / position of the thiophene nucleus. The Beckmann rearrangement with the ketoxime of 2-thienylketone was found to give poor yields of the aceto-2-thiopheneamide. Furthermore, the Schmidt reaction using hydrazoic and sulphuric acids was investigated and did give rise to aceto-2-thiopheneamide but probably as an eutectic with the isomeric 2-thenoylmethylamide. 

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