Phosphorus pentachloride, reaction with oximes

Constitution. Pelletierine behaves as a secondary amine and the oxygen atom of the alkaloid is present in the form of an aldehyde group, since the base yields an oxime, convertible by the action of phosphorus pentachloride into a nitrile, b.p. 104-6°/13 mm., which is hydrolysed by caustic potash in alcohol to an acid, the ethyl ester of which is Loffler and Kaim s ethyl -2-piperidylpropionate. Pelletierine is not directly oxidisable to this acid. It also yields a liquid hydrazone, b.p. 130°/20 ram., which with sodium in alcohol at 136-70° reduces to dZ-eoniine. These reactions are explained by the following formulas, in which pelletierine is represented as -2-piperidylpropionaldehyde. 

C. Beckmann fission of 2-methoxycyclooctanone oxime. In a 500-ml., three-necked, round-bottomed flask equipped with a mechanical stirrer, a dropping funnel, and a calcium chloride tube is placed a suspension of 62.5 g. (0.30 mole) of phosphorus pentachloride (Note 4) in 150 ml. of absolute ether, and the reaction vessel is cooled with ice. A solution of 42.8 g. of crude 2-methoxycyclooctanone oxime (0.25 mole) in 100 ml. of absolute ether is added over 30 minutes with vigorous stirring and the reaction is continued for 50 minutes at 5°. The reaction mixture, which becomes a transparent reddish brown solution (Note 5), is poured with mechanical stirring into 500 g. of ice in a 2-1. beaker. Stirring is continued for 1.5 hours at 5° (Note 6). I he ether layer is separated and the aciueous layer is extracted with... 

Xanthone is unreactive towards hydrazine and phenylhydrazine. The oxime is obtained by reaction of xanthione (xanthene-9-thione) with hydroxylamine, or from xanthone and hydroxylamine in pyridine. When the oxime is heated in water with phenylhydrazine, the phenylhydrazone is formed. In acid solution, xanthone reacts normally with 2,4-dinitro-phenylhydrazine but xanthone-1 -carboxylic acid (435) gives the pyridazinone (436), possibly via the hydrazone (57JCS1922). When the oxime is heated with phosphorus pentachloride it undergoes a Beckmann rearrangement to give the amide (437) (70MI22300). 

In strong acids, or when treated with reagents such as thionyl chloride or phosphorus pentachloride, an oxime will react to give a rearranged amide. This is known as the Beckmann rearrangement. When the reaction gives products other than amides, these products are referred to as abnormal products. One such abnormal pathway is illustrated in Problem 4.14. 

Dimethylisoquinolines (161) are obtained in a one-pot reaction by treatment of the oximes (159) with phosphorus pentachloride. Beckmann rearrangement is followed by cyclization of the resulting imidoyl chloride (160) with phosphorus pentoxide (Scheme 65). ... 

It is not possible to dehydrate ketoximes but some cyclic ketoximes break down under Beckmann rearrangement conditions to give nitriles - a reaction which is sometimes called a Beckmann fragmentation. The oxime of 2-(l-cyclo-hexenyl)cyclohexanone when treated at 0° with phosphorus pentachloride in ether gave the nitrile (16) as the main product [67]. 

Fresenius, passing his pharmacy examination in 1877. He then joined Kolbe, and his assistant, Ernst von Meyer, and started work on the oxidation of dialkyl sulfides. For this research Beckmann received his PhD in July 1878. Beckmann tried to apply an already-known reaction to discriminate between aldehydes and ketones. This reaction involved the use of hydroxylamine to convert benzophenone into an oxime. Treating this oxime with phosphorus pentachloride he converted it into a substance already characterized by Wallach. This reaction is now known as the Beckmann rearrangement. 

The dehydration of oximes by such reagents as phosphorus pentoxide, thionyl chloride, acetic anhydride, acyl chlorides, and phosphorus pentachloride is well known [26]. In effect, this dehydration procedure permits the conversion of aldehydes to nitriles with the same number of carbon atoms. A modification applicable only to the aromatic series makes use of boiling acetic acid as a dehydrating agent [27]. With other dehydrating agents, aliphatic aldehydes also may be converted to nitriles. Oximes may be converted readily to nitriles by an acid-catalyzed reaction with ortho esters [28]. 

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