Author Topic: Distilling problem  (Read 141 times)

superlative

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Distilling problem
« on: February 06, 2012, 12:59:50 AM »
if trying to distill ketone from extraction with Toluene under vacuum pulls Toluene at 34^C, Ketone should come over at around 130^C+. After all the Toluene came over nothing more happened. The heat was turned up until it was maxed out at 300^C on the heater. The thermometer in the sand/oil bath was maxed out at 160^C but the thermometer in the claisen adapter never moved above 35^C and nothing would come over. Never ever had this problem before. Any ideas?
« Last Edit: February 06, 2012, 01:02:36 AM by superlative »

RoidRage

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Re: Distilling problem
« Reply #1 on: February 06, 2012, 07:06:03 AM »
Posted the exact same reply at the other site:

You're not too clear in your writings but I suppose you're talking about crude MDP-2-P distillation...The answer to your question is pretty simple...There is no molecule boiling at 130C+ in your flask, or there is a leak in your setup...Since you seems to imply that that the toluene still cames over at the temp it normally comes over, logic shows you either failed your reaction or extraction...What's left in the distillation flask? (I bet black tar  >:( ;D)

NeilPatrickHarris

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Re: Distilling problem
« Reply #2 on: February 06, 2012, 12:52:03 PM »
if you're using a vac pump you shouldn't distill the toluene under vacuum, it will destroy your vac pump.  if you have an aspirator you can though.

without doing any math, that ketone bp prediction in comparison to the toluene's bp under reduced pressure sounds about right.  it will be slow to distill over, i agree with RR to check for leaks.  the way you grease your joints is very important with vac distillations, also what you use to grease your joints with is important too.  i used to get leaks in my apparatus because i was in a habit of using silicone grease then twisting the joints to spread the silicone grease evenly but by doing that i was creating little spiral airways which caused tiny leaks and i couldn't get the ketone to distill over either.  after reading on how to properly grease joints for use in a reduced pressure atmosphere, i did it properly and had no issues.  do you have a gauge you can check the pressure with?

java

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Re: Distilling problem
« Reply #3 on: February 06, 2012, 04:38:15 PM »
if trying to distill ketone from extraction with Toluene under vacuum pulls Toluene at 34^C, Ketone should come over at around 130^C+. After all the Toluene came over nothing more happened. The heat was turned up until it was maxed out at 300^C on the heater. The thermometer in the sand/oil bath was maxed out at 160^C but the thermometer in the claisen adapter never moved above 35^C and nothing would come over. Never ever had this problem before. Any ideas?


.....do you have some air coming into your flask to allow for air movement .....see

Zubricks  book,

The Organic Chem Lab Survival Manual: A Student's Guide to Techniques ...page 160





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.......you will see the difference....java
« Last Edit: February 06, 2012, 04:40:41 PM by java »
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superlative

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Re: Distilling problem
« Reply #4 on: February 06, 2012, 05:18:20 PM »
Thanks guys.
What came out of the reaction is yet unknown;) but i still get a strong smell of Safrole when opening the lid. Like i said toluene came over right above 30C so vacuum should be ok. All joints are greased with grease and sealed with silicone sealer that is hardened. Should be tight as a teen. If there was a leak the toluene wouldnt come over at 30C would it? The ketone/aldehyde mix is swimming in a high boiling petroleum oil as a buffer. Could the setup be too big for the amount? its started as 1 liter mix in a 4 liter rbf now its maybe 200 ml left in there. 60 of which should be goodies. I started out with a sandbath in a stainless dog water tray and added motor oil suspecting the sand wasnt conducting the heat good enough so the heat escaped through the stainless tray. The temperature in the sand/oil mixture was over 160C and the hotplate was on full(300C surface temp)so if boiling at 250c at normal pressure it should come over anyhow in my logic. i dont have a temperature measurement in the pit. the temperature at distilling head never got above 40C...i can see my hair getting gray.   Should i try a pure oil bath? or steam distill maybe? I guess i have to redo all the joints to be sure anyways.

thanx again:)

pyramid

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Re: Distilling problem
« Reply #5 on: February 06, 2012, 09:32:21 PM »
You expect about 60ml of product, and you are using a 4L flask??

Switch to a smaller flask, yo
« Last Edit: February 06, 2012, 09:34:25 PM by pyramid »

Wizard X

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Re: Distilling problem
« Reply #6 on: February 07, 2012, 12:18:55 AM »
Using TLC will determine the substrates, or reaction products BEFORE YOU distil.  You'll save time and not waste $$$ distilling!!
Albert Einstein - "Great ideas often receive violent opposition from mediocre minds."

superlative

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Re: Distilling problem
« Reply #7 on: February 19, 2012, 02:40:30 AM »
I changed the setup to a proper size and it came over easily.

Is there a preferred eluent for TLC on these substances?

Thanx you guys!

jon

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Re: Distilling problem
« Reply #8 on: February 19, 2012, 09:43:30 AM »
typically for amines 4/1 chloroform methanol.

lugh

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Re: Distilling problem
« Reply #9 on: February 19, 2012, 02:19:18 PM »
Quote
Is there a preferred eluent for TLC on these substances?

The search engine is your friend:

http://127.0.0.1/talk/index.php/topic,336

the subject has been discussed by the swarm in the past:

http://parazite.nn.fi/hiveboard/methods/000304428.html

The attached documents have more information  8)
« Last Edit: February 19, 2012, 03:08:51 PM by lugh »
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