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Topic: Problem with tritylation reaction  (Read 3728 times)

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Offline zorkion

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Problem with tritylation reaction
« on: July 10, 2013, 11:44:57 AM »
Hey guys, its my first time here, though I've lurked on occasion, so hello.

Anyways, I'm having some difficulty with a tritylation reaction that I'm doing.  I'm reacting cysteamine hydrochloride with triphenylmethanol using TFA as a solvent, and stirring it for an hour.  After that, the procedure says that the workup should be 4 washes with 3N NaOH, 2 with water, and then one each with sodium bicarb and brine.  After that, the organics are collected and set to crystallize in the fridge.

So I tlced the reaction after an hour and I observed the product spot and an absence of a spot for the triphenylmethanol, but then sticking it in the fridge didnt crystallize anything.  So I figured it was maybe too dilute, so I did a recrystallization on it with ethyl acetate, and bingo, lots of crystals form when its stuck in the fridge.  However, the real kicker is that these dont seem to be the product, but rather the starting material, based on tlc. 

This reaction is supposed to proceed in ~100% yield, and I cant figure out whats going wrong here.  Thoughts?

Offline opsomath

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Re: Problem with tritylation reaction
« Reply #1 on: July 10, 2013, 11:51:26 AM »
Are you running TLC on the reaction during its course to see if the reaction is going at all?

If so, make sure the product doesn't hydrolyse on silica. Add a tiny bit of triethylamine to your TLC solvent is one thing people do.

Offline zorkion

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Re: Problem with tritylation reaction
« Reply #2 on: July 10, 2013, 12:56:20 PM »
Are you running TLC on the reaction during its course to see if the reaction is going at all?

If so, make sure the product doesn't hydrolyse on silica. Add a tiny bit of triethylamine to your TLC solvent is one thing people do.

The reaction is definitely proceeding via TLC, and I can see the product forming.  It matches up exactly with a standard I have of the product.  Also, for the procedure, theres not really even supposed to be any silica at all.  I know I may have to end up running a column on the crude product, but per literature, the product is just supposed to crystallize out of the solution :/

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