[noodlesoup]

hi all,
i have a question about dehydration reaction. the question might sound silly and simple but i want to make sure i get it straight and want to hear your thought. in a dehydration reaction, why would we use Phosphoric acid (H3PO4) rather than hydrochloric acid as a catalyst?. i was thinking that it has to do with the strength of the acid, since phosphoric acid is a stronger acid, it will make the reaction go faster, i'm not sure if my thought is right though, just want to hear your insight on it. thank you

[nj_bartel]

phosphoric acid is a weaker acid.  What differences are there between the states the pure forms of the two acids exist in at STP? Why would the useable form of one of the acids be an unideal reactant for a dehydration?  Think LeChatlier's.

[HP]

Also conc. phosphoric acid is hygroscopic and nonvolatile. Polyphosphoric acids are even beter dehydrating/catalytic agent.