Dehydration/hydration of ethanol. (1 Viewer)

[undalay]

I understand why the acidic catalyst is required, however;

why does dehydration require a concentrated acidic catalyst, and why does hydration require a dilute acidic catalyst.

 

[munchiecrunchie]

I think it has to do with the strength of the bonds - don't quote me on that though.

 

[minijumbuk]

Well, I know that concentrated sulfuric acid is a strong dehydrating agent, ie. removes water from molecules. That's an elementary description, and I'm pretty sure you know it.

If you're asking for a more in-depth explanation that is beyond the HSC standards, trying asking here:

http://www.chemicalforums.com

 

[brenton1987]

Dehydration requires the removal of water from the molecule. To do this the hydroxyl group needs to be protonated because it is a very poor leaving group while water is a good leaving group. The more concentrated the acid the more protons are in solution to protonate the hydroxyl groups to promote their leaving.

In hydration electrons in the electron rich pi bond attack protons in the acid causing them to bind to the molecule. The conjugate base deprotonates water leaving a hydroxide ion and the original acid. Nucleophilic attack of the hydroxide ion onto the carbocation creates the hydroxyl group. More water is need for the production of hydroxide.

 

[Undermyskin]

"electrons in the electron rich pi bond" sorry but what is it meant?

 

[brenton1987]

"electrons in the electron rich pi bond" sorry but what is it meant?

Ethene has the double bond that contains four electrons. That is more unstable than multiple single bonds because there is more negative charges in a small area.
The electrons are nucleophilic meaning they will attack and bind to an electrophile (proton) to create bonds.

A nucleophile is electron rich looking for another nucleus to bind. An electrophile is electron poor and looking for electrons.

 

[samwell]

i think the explanation is provided by the modelling dehydration/hydration prac. concentrated H2SO4 has a high number of H+ ions per given volume compared to dilute muriatic acid. This makes it a very good substance to dehydration by converting the hydroxyl end of ethanol to H2O.
I think dilute HCl/H2SO4 isd used in the hydration reaction to aid in the addition reaction of H2O and ethene. [remember ethylene has high reactivity when it becomes a free radical] am not 100% sure about the hydration reaction.

 

[Pwnage101]

I think to fully understand why, u must first understand how each reaction occurs, ie LOOK AT THE MECHANISMS, but this is not required for the HSC Chemistry course, however they are interesting if u have a read of them - just google 'mechanism for acid catalysed hydration of ethene' etc