Phosphorus pentoxide amide dehydration with

By the dehydration of primary amides with phosphorus pentoxide or with thionyl chloride, for example ... 

Temperatures higher than 75° often cause yellowing of the amide and excessive foaming during the dehydration with phosphorus pentoxide. 

Conversion of amides into nitriles may be effected by treating them with a variety of dehydrating reagents. Among those that have been employed are phosphorus pentoxide, phosphorus pentachloride,170 ethyl polyphosphate,171... 

Nitriles can be prepared by the SN2 reaction of a cyanide ion with a primary alkyl halide. However, this limits the nitriles that can be synthesised to those having the following general formula RCH2CN. A more general synthesis of nitriles involves the dehydration of primary-amides with reagents such as thionyl chloride or phosphorus pentoxide ... 

Thiazolecarboxylic acids, esters or acid chlorides react readily with ammonia or various amines, affording the corresponding carboxamides. Dehydration of the amides with phosphorus pentoxide or phosphoryl chloride occurs readily and gives the corresponding nitriles (Scheme 99). Thiazolecarboxylic acid hydrazides are obtained in a similar way, using hydrazine or substituted hydrazines instead of ammonia or amines. The Raney nickel reduction of cyanothiazoles leads to the corresponding amino compounds, the 4-cyano derivative being the isomer most readily reduced. 

The dehydration of an amide containing an acid-sensitive acetal group to a cyano acetal like /3,/3-diethoxypropionitrile has been carried out with phosphorus pentoxide in the presence of triethylamine. ... 

Aromatic nitriles are also prepared by heating amides with phosphorus pentoxide, phosphorus oxychloride, phosphorus pentachloride, thionyl chloride, and ammonium sulfamate. In addition, the action of a double salt of aluminum and sodium chlorides, NaCl- AlClj, gives excellent yields of nitriles from both aliphatic and aromatic amides. Heating an amide with phthalic anhydride causes dehydration. A novel synthesis consists in treating a mixture of an aromatic acid and p-toluene-sulfonamide with phosphorus pentachloride the yields of nitriles range from 63% to 79%. ... 

Nitriles may be prepared from amides by dehydration with phosphorus pentoxide, phosphorus oxychloride or thionyl chloride (Scheme 3.87). 

If an add-amide is treated with a dehydrating agent, e.g., phosphorus pentoxide, it is converted into a nitrile ... 

When an amide is heated with a dehydrating agent, water is eliminated and a nitrile is formed. Acetonitrile can be prepared by distilling acetamide with phosphorus pentoxide —... 

When the same starting amide, that is, 3-methylbenzenecarboxamide, is treated with phosphorus pentoxide (P2O5 or P4O10), a triple bond is substituted for the amide and a nitrile (3-methylbenzonitrile) results. Although many schemes might be written to account for the dehydration of the amide to the nitrile (item 4 of Table 9.10), that depicted in Scheme 9.156 is frequently seen. 

An alternative preparation of a nitrile is illustrated by the reaction of the half-ester of 2,2-diethyl malonate 1.51) ivith SOCI2 and then NH3 to give the amide. Subsequent heating with phosphorus pentoxide led to dehydration and gave nitrile 1.52 Catalytic hydrogenation reduced the nitrile to an aminomethyl group, and acid hydrolysis gave 2,2-diethyl-3-aminopropanoic acid 1.53). 2-Ethyl-2-cyclohexyl-3-aminopropanoic acid and 2-ethyl-2-benzyl-3-aminopropanoic acid were also prepared by this method.30... 

The dehydration of amides is probably the best known of the elimination reactions for the preparation of nitriles. One method, the dehydration with phosphorus pentoxide, has been used for many years although it is undoubtedly one of the most messy synthetic procedures available. The procedure normally involves a dry distillation... 

---