Beckmann transformation

The course of the reaction depends on several factors such as stereoisomeric forms of the a-dioximes, the nature of the substituents R and R, the nature of the dehydration agents. This phenomenon was interpreted as a Beckmann transformation [6, 8, 13, 33, 17, 48). For example, the rearrangement of a-benzildioxime at 120°, in polyphos-phoric acid yields 99% of diphenyloxadiazole [20 a). 

The Beckmann transformation of asymmetrical dioximes with phosphorus oxychloride has been studied by Durio (25) whose conclusions are the following ... 

Chloro and 3-bromo-5-phenyloxadiazole have been prepared by a Beckmann transformation of a-phenylglyoxime peroxide in the presence of benzoylchloride or phosphorus pentachloride [71, 78). o-Tolyl-glyoxime peroxide shows a similar behaviour [4) (seep. 828). 3-Chloro-... 

When phenyl-glyoxime peroxide is treated with dilute sodium hydroxide [66, 78) or when phenyl-hydroxy-glyoxime is treated with benzoyl chloride (66) a Beckmann transformation yields directly the 3-hydroxy-5-phenyloxadiazole (see p. 826, 828). Some 5-hydroxy isomer is also formed in these reactions. 

Beckmann Transformation.—When the cis and trans forms are treated with certain reagents (especially phosphorus pentachloride) a rearrangement takes place in the molecule. The hydroxyl group interchanges position with the radicle in the trans position, and this is followed by a transference of hydrogen from oxygen to nitrogen ... 

This so-called Beckmann transformation has been of great significance for the explanation of the constitution of the isomeric oximes. If- eg., phosphorus pentachloride is allowed to act on both of the above formulated stereoisomeric oximes of the brombenzophenone, the same compounds are not obtained from both, but two different ones, which, as follows from their saponification products, correspond on the one hand to the benzoyl derivative of bromaniline, and, on the other, to the brombenzoyl derivative of aniline ... 

Schopf sought to obtain direct evidence for the location of the side-chain at C-13 by subjecting dihydrocodeinone oxime to a Beckmann transformation, when, if the side-chain is located at C-13 [liv], an aldehyde [lv] would be the product, whereas if the point of attachment is C-14 [lvi] a ketone [lvii] would be formed. Neither the oxime nor its methyl ether yielded the desired proof directly, and it was only after a sequence of further degradations that the conclusion was drawn that the product was [lv], indicating C-13 as the point of attachment of the side-chain [85] (see Chap. X). 

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... 

The Beckmann transformation of flavothebaone trimethyl ether oxime yields an isoxime containing four methoxyl groups, which on treatment with methanol and hydrochloric acid yields a substance yrith one additional methoxyl. Both the isoxime and the methyl-derivative remain unchanged on heating with methanolic potassium hydroxide for seven hours [2],... 

Beckmann transformation of the oxime of 7,14-cyclocodeinone in methanol or ethanol gives the mixed acetals (94 R = Me) and (94 ... 

Victor Meyer thought structural isomerism was possible in the case of the benzaldoximes, and only one oxime of benzophenone was known. Auwers and Meyer soon confirmed Hantzsch and Werner s theory by discovering two oximes of -chlorobenzophenone. In the case of ketoximes Hantzsch used the Beckmann transformation (see p. 833) in assigning the syti - and anti-configurations, but Meisenheimer s discovery (see p. 833) modified his conclusions. Moore says Hantzsch s series is really in configuration,... 

Lobelanine dioxime, obtainable in poor yield, undergoes a Beckmann transformation into the dianilide of l-methylpiperidine-2 6-diacetic acid (lobelinic acid (III)). On oxidation by chromic acid in sulphuric acid lobelanine furnished l-methylpiperidine-2 6-dicarboxylic acid (scopolinic acid (IV)) and benzoic acid. 

All known ketenes dimerize when heated or when allowed to stand at room temperature or below for a sufficient length of time. The dimers of ketoketenes undoubtedly are derivatives of cyclobutanedione. For example, the dimer of dimethylketene has a pleasant odor similar to that of ketones it yields two isomeric (cis and trans) glycols upon reduction and it yields mono- and di-oximes which give the expected products in the Beckmann transformation. ... 

The mechanism of the Schmidt reaction has not been established with certainty. Schmidt proposed a mechanism in which the hydrazoic acid is cleaved by the strong mineral acid to nitrogen and the imide radical (NH). This radical is supposed to add to the carbonyl group, followed by a rearrangement either directly or by a Beckmann transformation of an intermediate oxime to the amide. ... 

Phosphorus pentachloride converts 2,5-di- and 2,4,5-tri-phenyl-3-nitroso-pyrrole into di- and tri-phenyl-hydroxypyrimidine, respectively. The existence of the nitroso compounds in isonitroso forms (p. 107) suggests a similarity between these reactions and Beckmann transformations. However, open-chain intermediates are known to be formed . 

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