Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: why heat after reflux
andre178
Hazard to Self
**




Posts: 61
Registered: 11-12-2009
Location: San Diego, CA
Member Is Offline

Mood: pacified

[*] posted on 13-2-2011 at 17:28
why heat after reflux


I have a harder time deciphering older publications, and I don't want to mess up the reaction so I have a syntax problem in the below step of synthesis.


Screen clip 64.jpg - 39kB

I am performing a practice run using non-tritiated benzoic acid. The step itself is simple, adding thionyl chloride to benzoic acid. Reflux for 30 minutes / 80 deg Celsius.

What I don't understand is the 2nd part, heat it at 110 deg for 60 more minutes. Do I take off the water condenser once I finish refluxing and let some of the thionyl chloride evaporate?

The reflux 80 degrees should be the liquid or the vapor (like in sep distillation)? Since I'm working with such small amounts (150 microliters) how can I find the correct temperature?

I hope these questions are not too stupid.
View user's profile View All Posts By User
starch
Harmless
*




Posts: 33
Registered: 13-3-2010
Member Is Offline

Mood: No Mood

[*] posted on 13-2-2011 at 23:32


dude read it, it makes perfect sence :)

reflux it for 30 at 80c, then turn the temp up to 110c for a further 60 mins.

yes still in reflux aparatus

View user's profile View All Posts By User
matei
Hazard to Others
***




Posts: 205
Registered: 16-9-2006
Member Is Offline

Mood: No Mood

[*] posted on 14-2-2011 at 07:16


In the second step you have to replace the reflux condenser with a distillation head and distill off the excess of thionyl chloride. This is the standard procedure for making acid chlorides.
EDIT: I assumed you were going to scale up that procedure. If you use just 0.15 mL of thionyl chloride you can just evaporate the excess.

[Edited on 14-2-2011 by matei]
View user's profile View All Posts By User
andre178
Hazard to Self
**




Posts: 61
Registered: 11-12-2009
Location: San Diego, CA
Member Is Offline

Mood: pacified

[*] posted on 15-2-2011 at 09:47


thanks matei
View user's profile View All Posts By User
unionised
International Hazard
*****




Posts: 4934
Registered: 1-11-2003
Location: UK
Member Is Offline

Mood: No Mood

[*] posted on 15-2-2011 at 12:17


If you are going to do that with radiolabelled material it is probably better to use a condenser and catch the by-products I know that shouldn't have any activity, but I'd not want to bet on it. Also, I think that one of the by-product will be tritiated HCl (TCl?)which would need proper disposal.
View user's profile View All Posts By User

  Go To Top