Phosphorus pentoxide dehydrating agent

Dehydration of the corresponding acid amides. This process usually requires phosphorus pentoxide (correctly termed phosphoric anhydride) as a dehydrating agent. 

Various 10-substituted dibenz[/i,/]oxcpins 5 have been synthesized from 9-(hydroxymethyl)-xanthenes by treatment with dehydrating agents such phosphorus pentoxide.194,195... 

Phosphorus pentoxide has been used as dehydrating agent but the pentachloride method is much superior. With the pent-oxide method there is always trouble due to the formation of a black, sticky mass which swells up during the latter part of the experimentand often disrupts the apparatus. 

Phosphorus pentoxide is a very effective drying and dehydrating agent, also converts acids to their anhydrides. 

Sulfonic acids may be subjected to a variety of transformation conditions, as shown in Figure 2. Sulfonic acids can be used to produce sulfonic anhydrides by treatment with a dehydrating agent, such as thionyl chloride [7719-09-7], This transformation is also accomplished using phosphorus pentoxide [1314-56-3], Sulfonic anhydrides, particulady aromatic sulfonic anhydrides, are often produced in situ during sulfonation with sulfur trioxide. Under dehydrating conditions, sulfonic acids react with substituted aromatic compounds to give sulfone derivatives. 

Phosphorus pentoxide is an excellent dehydrating agent. For example, it can be used to remove water from nitric add. Write a chemical equation for this reaction. 

Instead of using chlorine, gaseous hydrogen chloride may be employed, provided that a strong dehydrating agent, phosphorus pentoxide or zinc chloride, is present to remove the water formed and so stop the right-to-left reaction in 1... 

BARDHAN-SENGUPTA SYNTHESIS. Phosphorus pentoxide and other powerful dehydrating agents act upon 2-beta-phenethyl-l-cyclohexanol to form oclahydrophenanlhrene compounds. 

Various dehydrating agents—concentrated sulphuric acid, zinc chloride, phosphorus pentoxide—can be used. Sulphuric acid, although perhaps the most convenient, has the disadvantage that it tends to sulphonate the aromatic substances employed. At a low temperature, however, diphenylmethane can be obtained from benzyl alcohol and benzene. At 140° phosphorus pentoxide condenses benzene and diphenylcarbinol to triphenylmethane (see B., 7,1204). Not only substituted benzyl alcohols, but even mandelic acid can be brought within the scope of the reaction, while in place of benzefte its nitro, amino or phenolic derivatives may be used. 

Do not allow perchloric acid to come in contact with strong dehydrating agents (concentrated sulfuric acid, anhydrous phosphorus pentoxide, etc.). 

Primary amides are dehydrated to nitriles using a dehydrating agent like thionyl chloride (SOCl3), phosphorus pentoxide (P2Os), phosphoryl trichloride (POCl3), or acetic anhydride o... 

Carboxylic acids can also be activated by converting them to their anhydrides. For this purpose they are dehydrated with concentrated sulfuric acid, phosphorus pentoxide, or 0.5 equivalents of SOCl2 (1 equivalent of SOCl2 reacts with carboxylic acids to form acid chlorides rather than anhydrides). However, carboxylic anhydrides cannot transfer more than 50% of the original carboxylic acid to a nucleophile. The other 50% is released—depending on the pH value—either as the carboxylic acid or as a carboxylate ion and is therefore lost. Consequently, in laboratory chemistry, the conversion of carboxylic acids into anhydrides is not as relevant as carboxylic acid activation. Nonetheless, acetic anhydride is an important acetylat-ing agent because it is commercially available and inexpensive. 

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