Phosphorus pentachloride ketones

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

Tropic Acid. The constitution of both tropic and atropic acids is known from syntheses by Ladenburg et al. from acetophenone. The ketone (I) by treatment with phosphorus pentachloride was converted into a-dichloroethylbenzene (II), and this, by the action of potassium cyanide in alcohol, into ethoxycyanoethylbenzene (III), which on hydrolysis yielded ethylatrolactic acid (TV). The latter was converted by strong... 

After having determined the nature of the side reaction it became clear that in order to obtain the desired ethynylpyrazole 11 the reaction between the ketone and PCI5 would have to be performed at low temperature. Indeed, the reaction was carried out in CH2CI2 at room temperature and a mixture of chlorides 7 and 8 was obtained. Dehydrochlorination of this mixture gave 66% of 3,5-dimethyl-4-ethynylpyrazole (11). Thus, by varying the conditions it is possible to carry out the reaction of the ketone with phosphorus pentachloride selectively in any of the above-mentioned directions. 

The formation of the dichlorides is aided by increased temperature (60-80°C) and by an excess of PCI5 (2-2.3 moles/mole of 4-acetylpyrazole). With a larger excess of PCI5, further chlorination of the compounds occurs. With 3 moles of phosphorus pentachloride at 80°C in benzene, ketones 12a-d gave pyrazolyl-trichloroethylenes 16a-d in 75% yield. Then dichlorides 17a-d were converted quantitatively into pyrazolyltrichloroethylenes 16a-d in 1 h under the same conditions. 

Ketones can be converted to gem-dichloride through their reaction with phosphorus pentachloride which can be used to synthesize alkynes. 

Cyclic 1,3-diketones have been converted into / -halogeno-ketones (118) by tri-phenylphosphine dihalides in benzene or acetonitrile,100 although this paper adds little to previous work101 in this field. The reactions of phosphorus pentachloride with acetals have been extended to mixed acetals, such as (119).102 Only one product... 

Acylation of the keto acid (637) leads to the isobenzopyrylium salt (638) (77CHE1183). However, the isobenzopyrylium salt (639), a potential intermediate for the synthesis of analogues of berberine alkaloids, results from the formylation of the substituted ketone or the isochromanone (640) using dichloromethyl butyl ether (Scheme 251) (81CHE221). A second product, the 5-oxoniachrysene (641), is formed and this compound may also be obtained by reaction of the isobenzopyrylium salt with phosphorus pentachloride and then with triethylamine. The intermediacy of a cyclic vinyl ether is proposed. 

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

Exercise 30-6 Reduction of the ketone group of (—)-menthone, which has its alkyl groups trans to one another, gives two products, known as (—(-menthol and (+)-neomenthol. These two substances differ considerably in their reactions. (+)-Neomenthol undergoes dehydration either in methanoic acid or when treated with phosphorus pentachloride, whereas (—(-menthol gives a methanoate ester with methanoic acid and a chloride with phosphorus pentachloride. What is the relationship between neomenthol and menthol, and why do they behave differently with methanoic acid and phosphorus pentachloride What is the likely structure of the menthene from dehydration of neomenthol (Review Sections 8-8D, 12-3D, and 12-5.)... 

A simple method for introducing a triple bond into an organic compound is to treat an appropriate dihalide with a strong base. Since vicinal dihalides (usually the bromide) are readily formed by reaction of bromine with an alkene, and geminal dihalides from aldehydes or ketones with phosphorus pentachloride, the method is a useful general procedure for the preparation of terminal and non-terminal alkynes from readily available starting materials. 

Oximes of ketones undergo rearrangement (the Beckmann rearrangement) to amides under the influence of a variety of acidic reagents (e.g. sulphuric acid, hydrogen fluoride, acetic anhydride, phosphorus pentachloride, thionyl chloride, etc.). The process is illustrated by the conversion of benzophenone oxime to benzanilide in the presence of phosphorus pentachloride. 

A list of ketones which have been prepared by the Friedel-Crafts stannic chloride method may be found in Table VI. Yields marked by an asterisk were obtained from acid chlorides prepared by the phosphorus pentachloride procedure all others were obtained from acid chlorides prepared from thionyl chloride. 

The dichloride (347) is converted to (348) on heating, apparently again through an intermediate cyclobutenyl cation. Hydrolysis of either compound with water leads to the ketone (349), which is reconverted to the cyclobutene by treatment with phosphorus pentachloride 274). 

One of the most reliable methods for constructing the oxazole ring is the cyclodehydration of a-acylamino ketones, the Robinson-Gabriel synthesis (1909/1910) (equation 93). The reaction is usually conducted in the presence of sulfuric add or phosphorus pentachloride and more recently polyphosphoric add, phosgene or anhydrous hydrogen fluoride have... 

The chemical properties of metaphosphoric acid, apart from those which are due to the fact that dehydration has proceeded to a maximum, do not differ essentially from those of the other hydrates of phosphorus pentoxide. The acid dissolves freely in certain oxygenated organic compounds—aldehydes, ketones and anhydrides, e.g, benzaldehyde, benzophenone and acetic anhydride.1 It was chlorinated but not dehydrated by phosphorus pentachloride —... 

The reaction of phosphorus pentachloride with aliphatic aldehydes or ketones has been used to prepare gew-dihalides. These compounds are important intermediates in the synthesis of acetylenes (method 43). 

Often, a large quantity of hydrogen chloride is evolved with the formation of monochloroSlefins, RC(Cl) = CHR however, the resulting mixture is suitable for the acetylene synthesis. Small amounts of dichloro compounds of the type RCHCICHCIR are also formed. These side reactions ate limited by adding the ketone to the phosphorus pentachloride at 0° C... 

Phosphorus pentabromide causes mainly a-halogenation. Even phosphorus pentachloride leads to an a-chloro ketone in the case of ethyl t-butyl ketone. ... 

Schoberlh and Hanack have reported a simple synthesis of cyclopropylacetylene (11) from methyl cyclopropyl ketone (9), The ketone is converted into the dichloride (10) by treatment with purified phosphorus pentachloride in carbon tetrachloride, and this is then dehydrohalogenated with potassium r-buioxide in DMSO. 

Isatin Chloride.— Now isatin which is a di-ketone of di-hydro indole, or the tautomeric form, a mixed ketone and hydroxyl derivative of indole, yields a chloride when treated with phosphorus pentachloride. 

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