[AlphaScent]

I did a large scale reaction (> 1 Kg) of tetrahydrofurfuryl alcohol and thionyl chloride in pyridine.  Excess amounts of pyridine.  Stoichimetric amounts results in tars being formed.

I then set up a large scale simple distillation under aspirator vacuum.  I use ice and cold water to get the best vacuum.  The B.P. of the chloride is given as 45°C/10 mmHg.  I raise the temperature very slowly over a 2 hour period until I start collecting.  My observed B.P. was 54°C.  I do not have a monometer for my aspirator vacuum.  I use it for high vac. only.  My variak is only on 60 and about half way through the distillation the temperature raises to 98°C.  I keep the water cold and change it out do get rid of solvent in the water.  So I know my vacuum is not far off.  The pot turned black and GC shows no chloride.  Where did I go wrong?

Using a heating mantle with no sand? Not using a water or oil bath? 

This is what I believe my mistake was.  I recovered about 900 g of the chloride in 98% purity.  But that is below 50% yield.

What do you guys think? 

[discodermolide]

That's quite a reactive mixture you have there. Looks like the reaction mass started to polymerise as the temp went to 98°C. You may have been lucky to get anything out at all.
Keep the temperature down as far as possible, use a better vacuum and an efficient trapping system.
How much thionyl chloride did you use?

[AlphaScent]

I should give all the conditions, including work-up.

I treated 1745 g/17 mole of THF-alcohol, dissolved in 4.2 liters of pyridine, with 2236 g/18.8 mole of thinoyl chloride added dropwise over 4 hours.  The mixture turns a black color after about 5 hours.  This is normal.  It is monitored by GC until Starting material is gone.  About 6 hours.  The thionyl chloride is killed and reaction quenched with 5 liters of ice cold water.  Aqueous layer extracted with ether.  Organic washed with 1N HCl, water, brine, dried and solvent removed i.v. 

This is all based on a book by Brandsma.  Practical Acetylenic Chemistry. 

There may have been polymerization.  With the heat maybe.  I think using sand would have been better.  When it is just the heating mantle and the vessel there can be hot spots.  It was just so damn large.  Wanted magnetic stirring.  Should have just used boiling chips. 

It is my fault.

[discodermolide]

You should persuade your boss to buy some double-mantle reaction vessels, they are not too expensive. They look like small versions of pilot plant reactors. There you can use efficient mechanical stirring and with the double mantle efficient heat control.

[AlphaScent]

Could you by chance post a link for double-mantle heating vessel and pilot plant reactors, Disco?

I am ignorant to these things, I apologize.

[AlphaScent]

Ok, well I just read and know about pilot systems in industry.  Could you still post a link for double-mantle heating?

[discodermolide]

Ok, well I just read and know about pilot systems in industry.  Could you still post a link for double-mantle heating?

You need something like this. http://www.grupo-selecta.com/pdfs/en/cats/catpdf_en_30.pdf
Two of them at least, then you can do solvent extractions as well. You need a good heating cooling system such as http://www.alibaba.com/showroom/lab-thermostat.html

One of the larger ones about $5000. Of course there are many other suppliers, these two I found by a quick Google.