Another form of dehydration uses POCl3 to convert alcohol to a good leaving group.
Concept: General features of dehydration with phosphoryl chloride.2m
So it turns out that there's another set of reagents that can also do a dehydration of alcohol and these reagents aren't going to involve an acid at all. In fact, the reason that we would use this alternative reaction is because some molecules happen to be sensitive to acid and in the presence of acid they could decompose.
So instead of using that, for these what we're going to use is phosphoryl chloride. And what phosphoryl chloride looks like is basically POCl3. That's what we're going to talk about right now.
So it turns out that POCl3 in unison with pyridine, which what is that? That's basically just a benzene ring with a nitrogen on it. And you don't have to necessarily memorize that right now, I just want you to recognize what it is. So POCl3 and pyridine are going to do an elimination reaction on an alcohol and make a double bond. That's all you need to know right now in terms of the general reaction.
Now any time that we're doing an elimination, that does bring up the whole possibility of Zaitsev, Hofmann, stuff like that. And it turns out that for these reactions we're always going to favor the Zaitsev product. Zaitsev's rule still applies. So what that means is the most substituted product is the one that I favor.
So in terms of the general reaction as long as you just know that those two reagents with an alcohol give you a Zaitsev double bond, that's great.
Concept: General features of dehydration with phosphoryl chloride.5m
Nucleophilic Attack + Deprotonation
E2 β-Hydrogen Elimination