Dehydration of secondary alcohol via E1 mechanism


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> Write the mechanism for this reaction:
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> [![enter image description here](https://i.stack.imgur.com/EnPbQ.png)](https://i.stack.imgur.com/EnPbQ.png)
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I am trying to do a dehydration of an alcohol using the reagents sulfuric acid and acetic acid. I don't know how I am supposed to use the acetic acid, instead I've been using water. This is my proposed mechanism:


[![enter image description here](https://i.stack.imgur.com/OTD9n.png)](https://i.stack.imgur.com/OTD9n.png)


But it doesn't include the acetic acid, and it doesn't say in the question whether it is done in solution with water or not but I only know how to do it with $\ce{H2O}$. My main issue is that I need to put the acetic acid into the mechanism.




Your proposed mechanism looks reasonable. I think that acetic acid primarily serves as an acidic solvent for the reaction. However, in the presence of concentrated sulfuric acid, $\ce{CH3CO2H}$ can be protonated by $\ce{H2SO4}$, like in the [first step of this esterification](http://www.chemguide.co.uk/physical/catalysis/esterify.html). The resulting resonance-stabilized cation is strongly acidic ($\mathrm{p}K\_\mathrm{a} = -6.1$ according to [this source](http://books.google.de/books?id=iVr0HWkAdS8C&pg=PA31&lpg=PA31&dq=protonated%20acetic%20acid%20pka&source=bl&ots=W-BnYnwvJ2&sig=uTs_TyUGscu3_Uub9Clb0SR0n4A&hl=de&sa=X&ei=zwZlVNGKAue7ygO074CYBw&ved=0CDgQ6AEwAw#v=onepage&q=protonated%20acetic%20acid%20pka&f=false)), and should readily protonate the alcohol. This would be a possibility to include acetic acid into the mechanism.


$$\ce{CH3CO2H + H2SO4 <=> CH3C(OH)2^{+} + HSO4-}$$


![enter image description here](https://i.stack.imgur.com/PyGk6.gif)


([Image source: ChemGuide](http://www.chemguide.co.uk/physical/catalysis/esterify.html))


So in the first step, the alcohol can either be protonated by $\ce{H2SO4}$ or $\ce{CH3C(OH)2^{+}}$, and in the end, the eliminated proton can either be picked up by $\ce{HSO4-}$ or $\ce{H2O}$.


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