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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: HongKongALevelboy on October 19, 2004, 03:56:07 AM

Title: mechanism of this reaction
Post by: HongKongALevelboy on October 19, 2004, 03:56:07 AM

can anyone tell me the mechanism for the conversion of triphenylmathanol to triphenylmethoxymethane , thx !

Title: Re:mechanism of this reaction
Post by: movies on October 19, 2004, 04:34:51 PM

The mechanism depends on what reagents you use.  The simplest method would be NaH + MeI.  The mechanism involves deprotonation of the alcohol, then S_N2 attack of the alkoxide on the methyl iodide.

Title: Re:mechanism of this reaction
Post by: Mitch on October 19, 2004, 09:00:22 PM

This doesn't scream carbocation intermediate to you?

Title: Re:mechanism of this reaction
Post by: movies on October 19, 2004, 10:07:45 PM

Depends how you do it, right?  If you used MeOH/HCl, then it would certainly be an S_N1 reaction mechanism, for sure.

Title: Re:mechanism of this reaction
Post by: Mitch on October 19, 2004, 11:53:35 PM

Perhaps, but I think this was how they trapped the first carbocations. I'll double check tomorrow, before I stick my foot any deeper.

Title: Re:mechanism of this reaction
Post by: HongKongALevelboy on October 20, 2004, 07:14:30 AM

sorry , i add something to my question , the catalyst is HCl , the reaction involves protonation of OH and it s a Sn1 reaction , that s all the question tells me . thx

Title: Re:mechanism of this reaction
Post by: movies on October 20, 2004, 01:12:27 PM

Okay, under those conditions it's definitely a carbocation intermediate.

I don't see how you could get to a carbocation if you used a base to deprotonate the alcohol though.

Title: Re:mechanism of this reaction
Post by: Mitch on October 20, 2004, 02:21:01 PM

I think when he says OH he means protonation of alcohol and not the addition of OH-

Title: Re:mechanism of this reaction
Post by: movies on October 20, 2004, 08:16:57 PM

Yeah, I think so too.

Title: Re:mechanism of this reaction
Post by: Donaldson Tan on October 22, 2004, 08:02:46 PM

let @ represent benzene ring

(1) @₃C-OH + H⁺ -> [ @₃C-OH₂ ]⁺

(2) [ @₃C-OH₂ ]⁺ -> [@₃C]⁺ + H₂O

(3) CH₃OH + [@₃C]⁺ -> @₃C-O-CH₃ + H⁺

The -OH group is protonated by aq HCl in reaction (1)
The protonated triphenylmethanol dissociates to form the carbocation and water in reaction (2).
A lone pair on the oxygen from methanol attacks the carbocation to form a C-O bond, thus cleaving the O-H bond in methanol to regenerate H⁺, in reaction (3).

This is a SN1 mechanism