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I have seen $\ce{P4O_{10}}$ and $\ce{HSO3Cl}$ being used to dehydrate carboxylic acids giving an anhydride and a ketene respectively.

Can we use them to dehydrate $\ce{-OH}$ (of aliphatic alcohol) group from an organic compound? I have never seen anyone do that. If we can, then please specify the appropriate conditions for the reaction to be carried out.

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  • $\begingroup$ $\ce{P4O10/P2O5}$ with some heating dehydrates alcohols. $\endgroup$ – Yashas Apr 7 '17 at 14:54
  • $\begingroup$ Look up Eaton's reagent $\endgroup$ – Waylander Apr 7 '17 at 15:02
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As you've noted, $\ce{P4O10}$ (or $\ce{P2O5}$ ) is a powerful dehydrating agent. According to the Chemical Book, it can actually dehydrate concentrated sulfuric acid to $\ce{SO3}$. So, it's not surprising that it can indeed dehydrate aliphatic alcohols. Using ethanol as an example, ethene can be produced by refluxing ethanol over $\ce{P4O10}$:

$$\ce{C2H5OH ->[P4O10] C2H4 + H2O}$$

Note that the reaction will proceed with gentle or no additional heating (the reaction itself is exothermic), it will just do so more slowly.

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