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Organic Reagents

By James Ashenhurst

Reagent Friday: TsCl (p-toluenesulfonyl chloride) and MsCl (methanesulfonyl chloride)

Last updated: February 27th, 2016 |

In a blatant plug for the Reagent Guide, each Friday  I profile a different reagent that is commonly encountered in Org 1/ Org 2.
A friend of mine works in human resources at a company that runs huge warehouses, and they have a lot of staff turnover. He told me about one forklift driver whose favorite habit was to speed by groups of guys in the warehouse,  give them the double finger salute, and yell, “F*** you, bitches!!!” as he sped by, laughing. My friend and his co-workers in upper management were like, “what can we do to get rid of this guy?”.

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Alcohols: there are times you need to get rid of them too. Except there’s one problem. They’re terrible leaving groups. Remember that good leaving groups are weak bases? Hydroxide ions are strong bases, and therefore very poor leaving groups.

However there’s a way to turn the OH group into a good leaving group – if you can convert it into a weaker base.

One practical way this is done is with the sulfonates p-toluenesulfonylchloride (TsCl) and methanesulfonylchloride (MsCl).

1-TsMs

Treatment of an alcohol with TsCl or MsCl, usually in the presence of a weak base such as pyridine, results in the sulfonate esters.

2-tsms

Conversion to the sulfonate esters does one thing: the conjugate bases – toluenesulfonate and methanesulfonate are now extremely weak bases, since they’re heavily stabilized by resonance.

Weak bases, you say? That makes them great leaving groups. And you are right. The sulfonate esters participate easily in reactions such as substitution and elimination reactions.

3-tsms

And there you go.

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So in the end it turned out that the crazy forklift driver insulted the wrong guy. He called one of co-workers a “dick”, and he then complained to management. (“Bitch” was OK, but “dick” was insulting, apparently).  The management wanted to “terminate”, as they say, but my friend told them they didn’t have legal grounds to do so yet: instead, they gave the employee a written warning. He explained it to them this way.  “Think of it like putting him on the tee, so that the next time he screws up, we send him down the fairway of life”.

That’s what TsCl and MsCl do. They take an alcohol and put it on the tee, so that the next reaction can send it down the fairway of life.

P.S. You can read about the chemistry of TsCl and more than 80 other reagents in undergraduate organic chemistry in the “Organic Chemistry Reagent Guide”, available here as a downloadable PDF.

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7 thoughts on “Reagent Friday: TsCl (p-toluenesulfonyl chloride) and MsCl (methanesulfonyl chloride)

  1. Mestyl chloride and the tosyl chloride can be used for the protection of amino acid and in which condition?

    1. You probably don’t want to use them as protecting groups unless you are comfortable with using a reagent like sodium amalgam to remove them, which can be strongly basic. There are much better protecting groups for amines, like carbamates.

  2. Hey quick question about using TsCl to convert the alcohol into a better leaving group. If your keeping track of absolute stereochem on a problem and the alcohol is wedged, will converting it to OT’s switch it to dashed. I am working on a synthesis problem along these lines.
    Thank You.
    -Matthew

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