Oximes, aldehyde determination

Hydroxylamine serves as a useful probe for biosynthetic pathways involving aldehyde intermediates by reacting with free aldehydes to generate metabolically inactive oximes. To determine whether octanal is a precursor to both /2-heptane and 1-octanol, xylem sections were co-incubated with 5 pCi acetate and 0.1 to 1 M hydroxylamine. Radiolabel was incorporated into octyl oximes in coincubations with hydroxylamine, and increasing concentrations of the reagent inhibited radiolabel incorporation into /2-heptane and 1-octanol, with a corresponding accumulation of radiolabel into octyl oximes. 

One of the most important routes to isoxazole and isoxazoline rings involving the formation of the 1—5 and 2—3 bonds involves the condensation of hydroxylamine with a,/8-unsaturated carbonyl compounds. This method was previously widely used, but it is now of no preparative value, though it has been recently applied to determine the configuration of oximes. " The only new modification of this synthesis is the use of the acetals (27) of a,/8-acetylenic aldehydes for preparation of 5-substituted isoxazoles (28)... 

Acetylation.—Gitronellal may be quantitatively estimated by the ordinary acetylation process i when the aldehyde is quantitatively converted into isopulegyl acetate, which is then determined by saponification with potash in the ordinary way. Dupont and Labaume have attempted to base a method for the separation of geraniol from citronellal in citron-ella oils on the fact that the citronellal oxime formed by shaking with hydroxylamine solution at the ordinary temperature is not converted into an ester by subsequent acetylation, but into the nitrile of citronellic acid which is stable towards" alkali during the saponification process. 

Cullere, L., Cacho, J., and Ferreira, V. (2004a). Analysis for wine C5-C8 aldehydes through the determination of their 0-(2,3,4,5,6-pentafluorobenzyl)oximes formed directly in the solid phase extraction cartridge. Anal. Chim. Acta, 524, 201-206. 

According to Neogi and Adhicary (17) omega mononitrotoluene is readily prepared by the action of mercurous nitrate or benzyl chloride. Heim (18) concludes from a series of researches, that pure phenylnitro-methane is not subject to spontaneous decomposition, but a small amount of impurities may cause such action. Korwalloff (19) has determined that this substance, on reduction, yields the corresponding aldehyde and oxime. 

Beckmann Transformation The Beckmann transformation of dihydrocodeinone oxime was investigated by Schbpf [68] in an attempt to determine the point of attachment of the carbon end of the ethanamine side-chain. If the point of attachment is C-13 [xliv] the product of transformation should be ail aldehyde [xi.v], whoroas if it is C-5 [xltx] the product should bo a... 

Many aldehydes and ketones can be determined with a solution of hydroxylamine hydrochloride. The reaction, which produces an oxime, is... 

The p values for both the addition and elimination steps in oxime formation of aromatic aldehydes have been determined For addition, p is +1.21 (and the best correlation is with a ). This is due to the decreased reactivity of aldehydes having direct conjugation with donor substituents. For the dehydration step, p is —0.85, which is the result of stabilization of the developing C=N bond by conjugation with donor substituents. 

Contrary to some reports, electrophilic addition reactions may occur in other multiple-bond systems. In many of the reactions of aldehydes and ketones the first stage involves the addition of some entity across the carbon-oxygen bond, e.g., the formation of oximes, semicarbazones, hydrazones, hydrates (1,1-diols) and their ethers, and the aldol condensation. Most of these reactions entail a subsequent loss (elimination) of a small molecule e.g. water, ammonia, ethanol) and, while one must be careful to determine whether the rate-determining stage involves attack on the carbonyl compound or elimination from the adduct , there are some systems in which it is evident that electrophilic attack is involved in the slow stage of the reaction sequence. Examples of such reactions are the acid-catalysed formation of oximes of aliphatic - and aromatic carbonyl compounds, of furfural semi-carbazone , and of 1,1-diols from aldehydes or ketones . 

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