Comments on: Tosylates And Mesylates

By: dowob

dowob — Fri, 06 Mar 2026 17:03:51 +0000

Nothing much, I think it’s just nitpicking to show more clearly that it’s the lone pair that does the attack and not the “charge”. I myself have also been teached to start the attack from the lone pairs and not the charge.
I guess in a way some might assume if the arrow can start from a charge then why not from positive charge as well, this is of course just an assumption.

By: James Ashenhurst

James Ashenhurst — Sun, 09 Nov 2025 10:23:20 +0000

In reply to MrX. It's in section 3, but I grayscaled it because it's less commonly seen in introductory organic classes.

By: MrX

MrX — Sat, 08 Nov 2025 19:42:50 +0000

You should also mention “triflate” -SO2CF3 as an often used even better leaving group than mesylate and tosylate. Works better in some reactions and is also useful in catalyzed cross-coupling reactions. It is a leaving group one should definitively know.

By: James Ashenhurst

James Ashenhurst — Wed, 09 Jul 2025 20:06:31 +0000

In reply to anon. What's wrong with starting the arrow at the charge symbol?

By: anon

anon — Wed, 09 Jul 2025 17:12:56 +0000

Might want to start that arrow at the lone pair on the chloride, not the charge symbol for the mechanism shown in “4. How Do We Make Mesylates And Tosylates From Alcohols”

By: Jessica Reel

Jessica Reel — Thu, 02 May 2024 15:29:07 +0000

Hi James, thank you for the excellent resource, as always.

A student came to me with a question that makes perfect sense, but I don’t have the level of background knowledge to explain. Given that one of the products of reacting an alcohol R-OH with TsCl is Cl- (chloride anion), would that not be a strong enough nucleophile to immediately displace the OTs group in an SN2/SN1 type of reaction, since OTs is such a good leaving group? How is it possible that we can isolate the tosylate without this happening?

Thank you for any answer!

By: dave t

dave t — Tue, 09 Nov 2021 19:15:08 +0000

There is about 1.2 equ of Tosyl chloride, in pyridine / DMAP. The product is a pivalic acid methyl ester derivative (so more ‘Tosylate’ than other molecule if you see what I mean). The chromatography is on silica, with ethyl acetate / hexane as eluent. I have tried the use of finely devided filter paper to consume the excess tosyl chloride and this seems a promising pathway, prior to chromatography.

By: James Ashenhurst

James Ashenhurst — Tue, 09 Nov 2021 18:22:52 +0000

In reply to dave t. How much excess TsCl did you add? What's the molecule and what kind of solvent system are you using? Cutting your solvent system with a little bit of benzene / toluene will likely help with separation of aromatic groups.

By: dave t

dave t — Sun, 07 Nov 2021 10:44:15 +0000

what is the best way to remove excess tosyl chloride from the reaction mixture. My tosylated product moves at about the same rate as tosyl choride on chromatography.

By: James Ashenhurst

James Ashenhurst — Tue, 02 Jun 2020 15:29:14 +0000

In reply to Bhavana Uppalapati. In real life, substitution reactions on secondary carbons can be tough. What's your substrate and nucleophile? If there's any steric hindrance, and if the nucleophile is at all basic, it will be tough to avoid elimination as a significant byproduct.