Why isn’t concentrated $\ce{H2SO4}$ used for the dehydration of carboxylic acids to anhydrides? What is special about $\ce{P2O5}$?
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1$\begingroup$ OK, thanks. Now to the point: you may use H2SO4, but how would you separate it from your anhydrides? $\endgroup$– Ivan NeretinApr 26, 2018 at 9:09
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1$\begingroup$ well i dont know $\endgroup$– amish duaApr 26, 2018 at 9:38
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2$\begingroup$ The advantage of P2O5 is that it is solid. Also, it is a stronger dehydrating agent than H2SO4. $\endgroup$– Ivan NeretinApr 26, 2018 at 9:44
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2 Answers
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Intermolecular forces are the reason. Carboxilic acids have capability of forming a dimer by hydrogen bonding. That enables a very stable arrangement. The hydrogen bonding stabilise the molecule, enabling the organic chain to form additional bonds by dispersion forces.Also dehydration of carboxylic acids with phosphorus pentoxide (P2O5) yields acid anhydrides,because it strong dehydrated anhydride ;P2O5 itself reacts with water molecules to form phosphoric acid. That enables it to remove free water molecules by a simple hydrolysis reaction,
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$\ce{P2O5}$ is a solid. Hence, it is easy to separate from reaction products. Moreover, $\ce{P2O5}$ is a stronger dehydrating agent than $\ce{H2SO4}$