Sn1 Substition of Alcohols

[pnoybballin]

Hello everyone. I was reading ahead in my Ochem book and I had one quick question. In using Alkyl Sulfonates, particularly TsCl and MsCl, I noticed two compounds CH2Cl2 and NEt3 used w/ MsCl. I was just wondering what these were used for because my book sadly does not explain what these are and just happen to add them along with the reaction. Thanks.

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[QofQuimica]

Hello everyone. I was reading ahead in my Ochem book and I had one quick question. In using Alkyl Sulfonates, particularly TsCl and MsCl, I noticed two compounds CH2Cl2 and NEt3 used w/ MsCl. I was just wondering what these were used for because my book sadly does not explain what these are and just happen to add them along with the reaction. Thanks.

CH2Cl2 is dichloromethane (aka methylene chloride); it's the solvent that the reaction is being run in. It's polar aprotic, making it great for an Sn2 reaction.

NEt3 is triethylamine, which is a hindered base. It is used to pick up the protons that need to be removed after the alcohols react with tosyl chloride or mesyl chloride. Think about the reaction mechanism here. The alcohol first reacts with MsCl in an Sn2 rxn where the alcohol serves as a nucleophile. However, the hydroxyl group is still protonated and now carries a positive charge. So where does that proton go? The base (triethylamine) picks it up. 🙂

 

[west nile]

Wow, is this orgo II stuff? I am in orgo I and I haven't seen MsCl or NEt3 used in the SN2 rxns we studied.

 

[markneil]

Wow, is this orgo II stuff? I am in orgo I and I haven't seen MsCl or NEt3 used in the SN2 rxns we studied.

that's orgo I. know these reactions well.

 

[babycapybara]

in o-chem 1 now, and all we've learned is that tosylates and other sulfanates make good leaving groups. doesn't that mean they won't be good nucleophiles?

i'm still at the point where i have all this info spinning around in my brain and it hasn't quite congealed into usable knowledge yet.

 

[killinsound]

in o-chem 1 now, and all we've learned is that tosylates and other sulfanates make good leaving groups. doesn't that mean they won't be good nucleophiles?

i'm still at the point where i have all this info spinning around in my brain and it hasn't quite congealed into usable knowledge yet.

Iodide is a good leaving group. It's also a good nucleophile.

 

[babycapybara]

yeah, but wouldn't the strength of iodide as a leaving group or nucleophile depend on the substrate and on the solvent? i mean it can't be a good nucleophile and leaving group in the exact same reaction, can it? that doesnt make sense. but tosylates are usually always just good leaving groups...
(please correct me if i'm wrong!)

 

[QofQuimica]

yeah, but wouldn't the strength of iodide as a leaving group or nucleophile depend on the substrate and on the solvent? i mean it can't be a good nucleophile and leaving group in the exact same reaction, can it? that doesnt make sense. but tosylates are usually always just good leaving groups...
(please correct me if i'm wrong!)

No, you're right. Tosylate isn't nearly as good of a nucleophile as it is a leaving group.

 

[ILPsychDoc]

CH2Cl2 is dichloromethane (aka methylene chloride); it's the solvent that the reaction is being run in. It's polar aprotic, making it great for an Sn2 reaction.

NEt3 is triethylamine, which is a hindered base. It is used to pick up the protons that need to be removed after the alcohols react with tosyl chloride or mesyl chloride. Think about the reaction mechanism here. The alcohol first reacts with MsCl in an Sn2 rxn where the alcohol serves as a nucleophile. However, the hydroxyl group is still protonated and now carries a positive charge. So where does that proton go? The base (triethylamine) picks it up. 🙂

So can MsCl, TfCl and TsCl act as both a nucleophile and a leaving group when reacting with an -OH? Under which conditions will it behave in a certain way??😕