Acidity oxime substituent effects

The rates of deoximation of oximes using cetyltrimethylammonium dichromate in the presence of acetic acid and a cationic surfactant is sensitive to the concentrations of aU four substances substituent effects are also reported. The oxidant preferentially oxidizes oxime over hydroxyl groups. 

Suitable mechanisms have been proposed following determination of the kinetic and activation parameters for oxidation of 2-naphthol and cyclic ketones by nicotinium dichromate some a-amino acids by tripropylammonium fluorochromate " distyryl ketone by quinaldinium fluorochromate methanol by benzyltriethylammonium chlorochromate catalysed by 1,10-phenanthroline substituted benzyl alcohols by tetraethylammonium bromochromate L-cysteine by pyridinium bromochromate lactic acid and 3,5-dimethyl-2,6-diaryl piperidin-4-one oximes by pyridinium chlorochromate allyl alcohol by IDC benzophenoxime by bispyridine silver(I) dichromate and alkyl phenyl sulfides by cetyltrimethylammonium dichromate. A non-linear Hammett plot obtained for the oxidation of substituted benzyl alcohols by IDC has been attributed to the operation of substituent effect on two steps of the proposed mechanism. " Kinetic and activation parameters for oxidation of o-toluidine and of A-methyl-2,6-diphenyl piperidin-4-one oxime and its 3-alkyl derivatives by sodium dichromate have been determined and suitable mechanisms have been suggested. Micellar catalysis in the 1,10-phenanthroline-promoted chromic acid oxidation of propanol... 

The most widely used route to l-benzazepin-2-ones involves the Beckmann or Schmidt reaction of the easily accessible 1-tetralones. Many biologically active compounds described in this review have been prepared on the basis of these reactions they have been fully reviewed [2], In the Beckmann reaction of 1-tetralone oximes, polyphosphoric acid is used as a catalyst-solvent in most instances. Aryl migration generally takes precedence over alkyl migration under these reaction conditions, and various 1-tetralone oximes substituted on the aromatic and/or aliphatic rings can be converted to the appropriate 2,3,4,5-tetrahydro-l//-l-benzazepin-2-ones (51) [5, 20-23, 36, 59, 65, 80, 107-112]. Both courses of the rearrangement occur in some instances, yielding l-benzazepin-2-ones (51) and the isomeric 2-benzazepine-l-ones, probably due to electronic effects of the substituents [90, 113, 114]. 

B. Electrical Effects of Oxime, Hydroxamic Acid, Hydroxylamino and Related Substituents... 

Values of electrical effect substituent constants for oxime and hydroxylamino groups have been reported ° their values are set forth in Tables la-c. No value for the acid group, CO(NHOH), was available. We have estimated values for it they are given in Tables la-c. Also in Tables la-c are values for some other types of substituents either for purposes of comparison or because they were used in correlations in this work. 

Examples of the application of correlation analysis to oxime and hydroxamic acid pK data sets are considered below. In the best of all possible worlds all data sets have a sufficient number of substituents and cover a wide enough range of substituent electronic demand, steric effect and intermolecular forces to provide a clear reliable description of the kind and magnitude of structural effects on the property of interest. In the real world this is often not the case. We will therefore try to show how the maximum amount of information can be extracted from small data sets. 

In studies on the effect of functional groups in EM (1) derivatives, compounds having 9-oxime (11), (95)-9-amino (9a), 6-O-methyl (16a), (8S)-8-hydroxy (6a), and 11,12-cyclic carbonate (15a) substituents were found to stabilize the lactone ring from decomposition in acidic media [2]. Therefore, further improvement of activity and bioavailability in oral administration has been attempted. 

A number of carbamates have been used as insecticides and a few as herbicides. Kinetic parameters for several of these compounds are summarized in Table 8.6. Note that the base-catalyzed reaction is the more important, however, some reports indicate that for some compounds, the direct reaction with water can be significant with values of 6-7. Unfortunately, there is only limited information in this area. Note that these data also illustrate how the substituents on the N influence hydrolysis. The feb values for the dimethyl compounds are orders of magnitude lower than the methyl counterparts. Aldicarb represents a variation in that the ester component of the molecule is derived from an oxime (RCH=NOH) rather than an alcohol. It also illustrates the significance of hydrolysis in understanding its environmental behavior. Aldicarb has been very effective in controUing insect pests in potatoes, but because of its high water solubility (6000 ppm) has been detected as a contaminant in groundwater. This effect has been observed only in acid (pH 5.5) but not in basic (pH 8.0) soils. 

Chiral oxazaborolidine catalysts were applied in various enantioselective transformations including reduction of highly functionalized ketones/ oximes or imines/ Diels-Alder reactions/ cycloadditions/ Michael additions, and other reactions. These catalysts are surprisingly small molecules compared to the practically efficient chiral phosphoric acids, cinchona alkaloids, or (thio)ureas hence, their effectiveness in asymmetric catalysis demonstrates that huge substituents or extensive hydrogen bond networks are not absolutely essential for successful as5unmetric organocatalysis. 

In support of this mechanism is the fact that dialkyl ketoximes practically do not give 4-methylene-3-oxa-l-azabicyclo[3.1.0]hexanes under the studied conditions. For example, in the case of acetoxime, only negligible amounts (7%) of the corresponding bicyclohexane are detected in the reaction mixture ( H NMR). This corresponds to the weaker CH acidity of the dialkyl ketoxime and smaller positive charge at the oxime nitrogen atom owing to the electron-donating effect of both alkyl substituents. 

---