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Topic: SN1 reaction: Solvent - methanol vs ethanol  (Read 16131 times)

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Offline matxjos

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SN1 reaction: Solvent - methanol vs ethanol
« on: July 25, 2011, 10:44:59 PM »
Hello, I have been searching around and cannot find an answer to this question.  Why is ethanol used instead of methanol in SN1 reactions?  Isn't methanol more polar and protic?  I haven't seen a case yet of methanol being used, why?

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Offline Guitarmaniac86

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Re: SN1 reaction: Solvent - methanol vs ethanol
« Reply #1 on: July 26, 2011, 06:43:54 AM »
It depends on the reaction you are carrying out as there are many factors that affect the SN1 reaction.

For an SN1 reaction to occur, you want a poor nucleophile/weak base in a solvent that will dissolve the nucleophile, and the solvent should have sufficient polarity to help pull the reactant molecule apart.

However, methanol may have sufficient reactivity as a poor nucleophile to interact with the reaction leading to the wrong product (and act as a competing nucelophile), whereas ethanol is not reactive enough to interfere with the reaction.

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Offline key435

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Re: SN1 reaction: Solvent - methanol vs ethanol
« Reply #2 on: July 26, 2011, 12:00:33 PM »
I do not know the subtances you use there. But methanol is more polar than ethanol and the struture is small, so it's easy to attack the carboncation. I think both can be used for this reaction. Althought methanol is hazard and ethanol is safe. ^^.

Offline orgopete

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Re: SN1 reaction: Solvent - methanol vs ethanol
« Reply #3 on: July 26, 2011, 03:47:25 PM »
The original poster has asked what seems like a reasonable question, but the answer follows a different train of thought. One could easily use methanol in an SN1 reaction in place of ethanol. It would work as expected.

When one studies organic chemistry and the reactions in textbooks, the purpose of a given reaction isn't always explained. One does not do SN1 reactions in ethanol in a desire to prepare an ethyl ether, especially as E1 reactions compete. Usually, there are better ways. So ethanol or methanol are not being chosen as the preferred reaction to prepare a methyl or ethyl ether. The solvents are chosen to study the reactions themselves. The most sought after value is generally the reaction rate. So, the solvent choice is to compare different reactions, is A faster than B? Even though a slow reaction could be accelerated in methanol, how would you compare B (methanol) is faster than A (ethanol).

Perhaps a better question might be why might one chose ethanol rather than methanol to study reaction rates? I can think of several reasons.
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