Acid catalyzed condensation vs. Dehydration of alcohol

[JustwantDDS]

when do you know if the product will be an ether or alkene

ROH + H2SO4 could be dehydration or acid cat. condensation......to give symmetrical ether

is it when you have heat-- condensation?

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[needzmoar]

when do you know if the product will be an ether or alkene

ROH + H2SO4 could be dehydration or acid cat. condensation......to give symmetrical ether

is it when you have heat-- condensation?

There's a competition between the addition/elimination. In order for bimolecular dehydration to occur, the substrate must be unhindered AND the temperature must be carefully controlled. If it's hindered or if too much / too little heat is added then equilibrium is shifted towards elimination.

edit: forgot to address the second part of your question.

Both requires heat.

 

[needzmoar]

There's a competition between the addition/elimination. In order for bimolecular dehydration to occur, the substrate must be unhindered AND the temperature must be carefully controlled. If it's hindered or if too much / too little heat is added then equilibrium is shifted towards elimination.

This type of synthesis rarely comes up though (aside from industrial processes). It's usually the elimination product unless you see 2 molar equivalence of the primary alcohol.

 

[JustwantDDS]

so something like
2 ethanol + H2SO4/ 103degrees will be ether synthesis right?

 

[PooyaH]

In addition, when the reaction takes place at 140 degrees Celsius, the product will be an ether. When the reactions takes place at 180 degrees Celsius, the product will be an alkene.

 

[needzmoar]

so something like
2 ethanol + H2SO4/ 103degrees will be ether synthesis right?

Right, that two molar equivalence usually indicates that it's going to be a bi-molecular dehydration to form a symmetrical ether. iirc the temp should be around 140C. don't quote me on that though, check wiki or something.

 

[needzmoar]

In addition, when the reaction takes place at 140 degrees Celsius, the product will be an ether. When the reactions takes place at 180 degrees Celsius, the product will be an alkene.

okay since pooyah said so, too, it must be 140

 

[PooyaH]

so something like
2 ethanol + H2SO4/ 103degrees will be ether synthesis right?

Yeah, you'd get a diethyl ether.

 

[JustwantDDS]

thanks guys!!!