Phosphorus pentachloride with oximes

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. 

By treatment of this oxime with phosphorus pentachloride or thionyl fhloride in ether solution, smooth conversion into benzanilide, m.p. 163°, results. The change of any oxime into a substituted amide under the conditions mentioned is usually termed the Beckmann rearrangement. The above example may be represented ... 

Beckmann rearrangement of benzophenone oxime to benz-anilide. Dissolve 2 g. of benzophenone oxime in 20 ml. of anhydrous ether in a small conical flask and add 3 g. of powdered phosphorus pentachloride (or 3 ml. of pure tbionyl chloride). Distil off the solvent and other volatile products on a water bath CAUTION ether), add 25 ml. of water, boil for several minutes and break up any lumps which may be formed. Decant the supernatant liquid, and recrystallise, in the same vessel, from boiling alcohol. The product is benzanilide, m.p. 163° confirm this by a mixed m.p. determination with an authentic specimen. 

The oximes of ketones undergo the Beckmann rearrangement on treatment with phosphorus pentachloride (118). 

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. 

A weighed quantity of the oxime is dissolved in some cold ether, free from water and alcohol, and to the solution 1 -5 parts of finely powdered phosphorus pentachloride are gradually added. The ether is then removed by distillation and water Is added to the residue with cooling the ensuing precipitate is recrystallised from alcohol. Melting point 163°. 

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). 

Beckmann Rearrangement results when oximes of ketones are treated with certain reagents such as phosphorus pentachloride. 

To a solution of 1 gram of 16-dehydropregnenolon-3p-acetate in 10 ml pyridine is added 0.22 gram of hydroxylamine hydrochloride, and the mixture is allowed to stand at room temperature for four days. One gram of 16-dehydropregnenolon-3p-acetate oxime is dissolved in 30 ml of hot dioxane, and then the solution is cooled in an ice bath until about one-half of the dioxane has solidified. Then 1 gram of phosphorus pentachloride is added and the mixture is shaken until all the dioxane has melted. The mixture is maintained at 35°C, for seventy-five minutes, then an excess of ice is added and the solution is again allowed to stand at 35°C. After about thirty minutes, a solution of 5 ml of concentrated hydrochloric acid in 10 ml of water is added, and the mixture is diluted with water, extracted with ether and the ethereal extract washed with dilute sodium hydroxide solution. The ether is removed on a steam bath and the residue is worked up to yield dehydro-isoandrosterone. 

A -Butylpyridinium tetrafluoroborate, containing dissolved phosphorus pentachloride, allows catalytic Beckmann rearrangement of cyclohexanone oxime giving e-caprolactam with good conversion and selectivity <2001TL403>. The same ionic liquid containing dissolved ytterbium(m) trifluoromethanesulfonate was used to perform Friedel-Crafts acylation of furan and thiophene <2005JIG398>. 

Beckman rearrangement of cyclohexanone oxime in the presence of zinc oxide and without any additional solvent afforded the azocane-2-one 120 (Scheme 70 <2002S1057>). This is an environmentally friendly alternative to the usual Beckmann rearrangement performed with highly corrosive, strong Bronsted and Lewis acids, such as cone, sulfuric acid, phosphorus pentachloride in EtzO, or HG1 in acetic anhydride. 

By treating o-chloromethylaniline hydrochloride with cu-benzyloxy-butyro- and -valeronitriles in refluxing o-dichlorobenzene in the presence of stannic chloride, Mufloz and Madroilero obtained the tricyclic compounds 124 and 202, respectively. The pyrido[2,l- )]quinazolines 289 were prepared by refluxing o-chloromethylaniline hydrochloride in dichlorobenzene with 2-chloropyridine and its tetrahydro derivative. The latter was obtained in situhy Beckmann rearrangement of cyclopentanone oxime with phosphorus pentachloride. 

Beckmann130 treated benzophenone oxime in phosphoryl chloride with phosphorus pentachloride and isolated the imidoyl chloride, which he hydrolysed to benzanilide by aqueous alcohol ... 

---