oxime formation mechanism

Pyrolysis of formaldoxime and acetaldoxime was studied also in the presence of NO [1–3]. A one-pot synthesis of functionalized nitrones by zinc-mediated reduction of nitroalkanes in the presence of aldehydes has been devised. Nitrones are extremely useful synthetic intermediates, and their use in 1,3-dipolar cycloadditions <1998CRV863> and their reactions with organometallics <2002CUOC695, 1998CRV1407> and nucleophiles <2000S759> have been reviewed. Loss Prev., 1993, 6(2), 69. When R′ is an aryl group, the rate of crotyl transfer is probably faster than competitive imine isomerization. Carbohydrate-derived nitrones are an important tool for stereoselective cycloadditions, and their use has been reviewed <2002JCS(P1)2419>. Reaction (9.3.1) is also the main decomposition route for some aromatic aldoximes. The nitriles are generated by further OH• elimination, and this reaction sequence is shown below: The rate constant k for the reaction OH• + CH2NOH → H2O + CH•NOH was estimated at 300°C k = 3.8 × 10+ 8, and for the reaction OH• + CH3CHNOH → H2O + CH3C•NOH and the same temperature was estimated k = 1.3 × 10+ 9 [2]. Surface catalysis was considered as a favoring factor for these reactions. Here I subject the first step of this reaction to form a tetrahedral intermediate to quantum mechanical scrutiny. Reaction of aldehydes and ketones with hydroxylamine gives oximes. 2-Substituted-3H-indol-3-one-N-oxides can be obtained by the reductive cyclization of dione 10 (Equation (12)) <2001SL700>. 94d) is probably much more stable. Similar results regarding pyrolysis, with the generation of the corresponding nitrile, were obtained for propionaldehyde oxime [4,5]. Butyraldehyde oxime, 1650 ‘10-Carbon oxime’, 3356, 1-Hydroxyimidazole-2-carboxaldoxime 3-oxide, 1473, * N-Methoxy-N-methylbenzylidenimmonium methylsulfate, 3328, 2-Methyl-2-[4-(2-methylpropyl)phenyl]oximinoethane, 3608, 3-(2-Nitrophenyl)-2-hydroxyiminopropanoic acid, 3125, 2-Nitrosophenol (1,2-Benzoquinone monoxime), 2256, * 4-Nitrosophenol (1,4-Benzoquinone monoxime), 2257, 4-Oximino-4,5,6,7-tetrahydrobenzofurazan N-oxide, 2350, * Potassium 1-nitroethane-1-oximate, 0753, * Potassium cyclohexanehexone 1,3,5-trioximate, 2621, * Silver 3-methylisoxazolin-4,5-dione-4-oximate, 1405, Sodium 2-allyloxy-6-nitrophenylpyruvate oxime, 3499, * Sodium 3-methylisoxazolin-4,5-dione-4-oximate, 1415, * Sodium 3-phenylisoxazolin-4,5-dione-4-oximate, 3108, * Sodium 4-chloroacetophenone oximate, 2922, * Sodium tris(O,O′-1-oximatonaphthalene-1,2-dione)ferrate, 3865, S. Rossiter, A.P. Nitrolic acids (350) are prepared by addition of dinitrogen tetraoxide to oximes (349) <02CB3884, 61IZV477>, nitronic acids <52DOK(83)243, 60IZV1783> or nitronate salts <58ZOB2305> (Equation (103)). The mechanism of forming an oxime from nucleophilic addition of a hydroxylamine to a ketone is taught early on in most courses of organic chemistry. The reaction mechanism in this case seems to be the formation of iminoxyl radicals with the cleavage of the OH bond rather than the cleavage of NOH bond. Pyrolysis of oxime hydrochloride was reported for benzophenone oxime HCl [11]. Nitrones may also be prepared from disubstituted hydroxylamines by oxidation. Other oximes generate products influenced by the structure of the whole molecule. The formation of ammonia and ketone can be explained by the presence of small quantities of water formed during pyrolysis from secondary reactions such as alcohol decomposition. For some examples, thermolysis of these nitrones gives imidazoles <1997JCS(P1)3065> (Scheme 5). A phosphotungstate/ampiphilic polymer catalyst has been employed for this reaction <2002SL2031> and oxaziridines have been used as the oxidant <2000TL1583>. By continuing you agree to the use of cookies. For example, benzaldoxime generates in flash-vacuum pyrolysis (FVP) benzonitrile and benzoxazole. A nickel catalysed aldoxime rearrangement, to an amide, went out of control after changing the solvent employed. ), Vol. It is conceivable, therefore, that the overall rate of reaction via (94d) can be much faster than via (95a) even though the (Z)-imine cannot be detected in solution. Changing to a higher operating temperature restored control to the process [3].

The (E)-isomer of acetonitrolic acid (352) is prepared from nitroethane (351) and sodium nitrite in the presence of a base at low temperatures. Eng. Cyclic nitrones, e.g., 11, react with aldehydes in refluxing toluene to give the α,β-unsaturated nitrones 12 (Equation (13)) <2003S1367>. Oximes generally form a mixture of geometric isomers.

These radicals can decompose to generate either R1CN and R2• or R2CN and R1•. The driving force for imine isomerization is probably that complex (95a) is not very stable owing to the bulky 9-BBN unit positioned syn to R, while the complex of crotyl-9-BBN (47) and a (Z)-aldimine (e.g.

No clear stereochemical pattern, however, is apparent in the data. In Bretherick's Handbook of Reactive Chemical Hazards (Seventh Edition), 2007, Horner, L. in Autoxidation and Antioxidants, Lundberg, W. O. This was found to be due to a slow start and consequent accumulation of unreacted substrate. Although the resulting compounds in these pyrolytic reactions were rather complex, the formation of ketone imines and of corresponding ketones was the general reaction route (also proved for isodibenzosuberone oxime).

ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780444640000000093, URL: https://www.sciencedirect.com/science/article/pii/B0080447058001928, URL: https://www.sciencedirect.com/science/article/pii/B978012372563950046X, URL: https://www.sciencedirect.com/science/article/pii/B0080446558000568, URL: https://www.sciencedirect.com/science/article/pii/B9780080523491000238, Pyrolysis of Other Nitrogen-Containing Compounds, Pyrolysis of Organic Molecules (Second Edition), Synthesis: Carbon with Two Attached Heteroatoms with at Least One Carbon-to-Heteroatom Multiple Link, Comprehensive Organic Functional Group Transformations, Bretherick's Handbook of Reactive Chemical Hazards (Seventh Edition), Synthesis: Carbon With One Heteroatom Attached by a Multiple Bond, Comprehensive Organic Functional Group Transformations II, α,β-Unsaturated nitrone precursors to a series of 1,2-oxazin-6-ones were prepared by the photooxygenation of 2-methoxyfurans in the presence of, Techniques and Instrumentation in Analytical Chemistry. p-Toluenesulfonic peracid (TsOOH) can also oxidize amines to the corresponding nitrones <1996T5773>. This practical method uses air as economic and green oxidant, water as green solvent, and tolerates a wide range of substrates. This reaction is shown as follows: Formaldoxime generates mainly HCN and H2O. The first decision is to decide which atom of the hydroxylamine acts as the nucleophile. The diastereomeric ratios were determined by 1H NMR spectroscopy <2001TA3297>. The formation of benzoxazoles is similar to reaction (9.3.4) and is shown below: The formation of OH• free radicals is possible in ketoxime pyrolysis, and the reaction takes place as shown below: The formation of R1R2CN• iminyl free radicals accounts for various further reactions. α-Heteroatom-substituted nitrones have also been prepared <2002TL2445>. A novel synthesis of O-substituted nitrones has been achieved by the reaction of the anions of aliphatic nitro compounds with nitroso compounds <1996MI856>. N-Benzyl acyclic nitrones may be conveniently prepared by zinc chloride-catalyzed condensation of benzylhydroxylamine with aliphatic ketones <1995SC2275>. The reaction of (88) and oximes can be performed at room temperature if a pressure of several kilobars is applied.62a, The stereochemistry of the reactions of oxime ethers and crotylboronates (22)and(23) have been discussed earlier (Scheme 8).38 The reactions of the corresponding oximes with (22)and(23) appear to follow a similar stereochemical course (Scheme 14).38 Stereoselectivity, however, is not as high with the isobutyraldehyde and pentanal oximes as it is with phenylaldoxime. Besides the compounds shown in reaction (9.3.6), the pyrolysate of phenyl benzyl ketoxime contains NH3, 2,4,5-triphenyl-1H-imidazole and 2-phenylacetophenone. The main reaction in these molecules takes place with a free radical mechanism by the cleavage of the N OH bond and the formation of OH • free radicals. This seems unlikely, however, since the analogous transition state (29) is highly disfavored in the reactions of oximes and crotylboronates (Figure 8). https://www.khanacademy.org/.../v/formation-of-oximes-and-hydrazones For example, pyrolysis of 5H-dibenzo[a,d]cyclohepten-5-one oxime and of 10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5-one oxime was reported for a flow system working at 1.33 mbar and 650°C [7].

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