[roomsearching]

Hello
I am trying to reproduce a reflux reaction from a paper. I am heating chlorendic anhydride in equimolar triethylamine with 6 hexanoic acid in 15 ml of toluene as solvent in a sealed pressure tube ( qtube). In the paper it says reflux for 8 h in a dean stark apparatus but temperature is not specified. I tried heating for 12 hours at 105 degrees and then next morning for 6 hours at 150 degrees. The overnight reaction didn't change anything in the original black solution.  But when I changed the temperature to 150 I could see bubbles and light brown colour. Towards the last one hour before I stopped,  the solution had turned totakly black and black stuff could be seen sticking to the walls above the liquid surface. I don't know what has happened.  Could anybody suggest the right temperature and know when to stop ?

[Arkcon]

noun
Chemistry
noun: reflux

    1.
    the process of boiling a liquid in such a way that any vapor is liquefied and returned to the stock.

Once in a while, we get the same question as you just posted.  And I never understand why.  The temperature to reflux is the boiling point of the solvent.  That's it.  If you get it hotter ... you don't get it hotter.  Because a solvent never gets hotter than its boiling point.  What you did was essentially boil away solvent, or decompose solvents and reactants into something else with a higher boiling point.  Unless the reaction was supposed to produce a black substance, its should be easy for you to see "what has happened."

For an analytical test, I routinely reflux glycerol with the organic base-ether morpholine.  I heat it until it starts to boil, then adjust the heat so the solvent condenses back down for 3 hours.  I routinely check the open top of the condenser, to be sure morpholine isn't escaping as a vapor, or else other people in the lab will yell at me.  After 3 hours, I cool and test the mixture for free chloride ions liberated by the boiling morpholine.  I don't reflux longer because I don't have to. 

In the paper it says reflux for 8 h in a dean stark apparatus but temperature is not specified. I tried heating for 12 hours at 105 degrees and then next morning for 6 hours at 150 degrees. The overnight reaction didn't change anything in the original black solution.

Why did you heat for 12 hours, when the protocol said to heat it only for 8?

[Dan]

I am trying to reproduce a reflux reaction from a paper. I am heating chlorendic anhydride in equimolar triethylamine with 6 hexanoic acid in 15 ml of toluene as solvent in a sealed pressure tube ( qtube). In the paper it says reflux for 8 h in a dean stark apparatus

So you modified the procedure and got a different result. That should not come as a huge surprise.

A Dean-Stark apparatus has a purpose. Look it up and it should become apparent that substituting it for a sealed vessel is probably a bad idea.

Try performing the reaction as it was reported before you make modifications.

[DrCMS]

The Dean - Stark is designed to remove water from the reaction at the toluene/water azeotrope temperature of ~85°C.

In the first overnight heating you got the reaction to start and go to equilibrium but without removing the water formed it will not go further no matter how much you heat it.  When you pushed the temp up higher you decomposed some or all of the reagents. 

You should read and understand it BEFORE you try a reaction not afterwards.  This time you just wasted a night and day and trashed the reagents but next time you might have a more serious incident.