Magpie
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quinoline
For those who are curious about the synthesis of the heterocycle quinoline here are my results: I used the Skraup method which starts with aniline,
nitrobenzene, glycerol, and con sulfuric acid. Ferrous sulfate is used to moderate the reaction. It is thought that the sulfuric acid makes acrolein
out of glycerol which provides the needed 3 carbons. The nitrobenzene acts as oxidizer to close the ring.
The workup required 2 steam distillations (extra work for me as my 3-neck is only 500 mL), a diazotization to get rid of unused aniline, and a final
simple distillation. I substituted DCM for CCl4 in the extraction from water. My yield was low but the product did boil at 236C (normal bp = 237C).
Contrary to a claim in my procedure I did not find the smell to be disagreeable. I think it smells more like napthalene than pyridine.
[Edited on by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Sauron
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How low was low yield?
Cf Vogel.
Do you think the losses were in workup?
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vulture
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Hey, it's the skraup method...throw some nice mess together and let it rip. Then process the resulting mess. No high yields, but it works.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Magpie
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I think vulture's description is pretty accurate. There is a lot of tar generated, I suppose by the hot sulfuric acid. The reaction mix is dark
brown almost black when acid and goes to chocolate brown when made alkaline.
My procedure (Brewster et al) says that the normal yield is 10 to 12 mL. I estimate by eye that I got half of that. I think the excessive handling
due to my small steam distillation batches contributed. I also didn't collect my final distillate soon enough, ie, when it became yellow. I was
waiting for the boiling point to better approach 237C.
It's interesting to compare the various procedures I have for the Skraup: Brewster, Vogel, OrgSyn, and Cummings. They all have pretty much the same
"unit processes" but arranged in different order. Vogel, Cummings, and OrgSyn call for reaction periods of ~5 hrs IIRC, whereas Brewster calls for 40
minutes to accommodate student lab periods.
I could calculate a %yield based on the aniline charged if someone is interested. But the fact I only had a 40 minute reaction time would have to be
considered.
The single most important condition for a successful synthesis is good mixing - Nicodem
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vulture
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According to some sources skraup methods can be varied at nauseam, you use whatever oxidizer you like or you believe that works. Nobody's going to
complain because every method produces tar anyway.
It's really a reaction for people who like to get their hands dirty and don't mind a nice chemical shower in the fumehood. 
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Magpie
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Vulture you sound like you are speaking from experience about the chemical shower. I had nothing of that sort in fact at no time was the reaction self-sustaining - I always had to give it some heat.
It's a dirty looking mix alright. And it is a lot of work - but that is all part of the fun.
The single most important condition for a successful synthesis is good mixing - Nicodem
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guy
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How low was the yield? I have a new Vogel edition that uses a slightly different method which gives 50% yield.
Equip a 250 mL three necked flask with a double surface condenser, a sealed stirrer and a screw capped adapter carrying a thermometer postioned so
that subsequently the temperature of the reaction mixture may be noted. Place 10.0g of pure aniline, 15.0g of glycerol, and 0.5 g of iodine in the
flask. Stir the mixture and add down the condenserfrom a dropping funnel 30g of concentrated sulfuric acid. Reaction soon commences, the temperatre
rises to 100-105oC. Heat the flask gradually, with stirring, in an air bathor oil bath to 140oC; the reaction proceeds with the evolution of SO2 and
a little I2 vapor and the liquid refluxes. Continue heating at 170oC for 1 hour, allow to cool and cautiously add with stirring, sufficient 5M NaOH
until solution is alkaline. Rearrange for steam distillation and distill until no more oily drops pass over. The distillate contains quinoline and a
little aniline. Extract the distillate with three 25mL portions of ether, combine the ethereal extracts and remove the ether on a rotary evaporator.
<b>Removing Aniline</b>
Dissolve crude quinoline in 100mL dilute (1:4 by volume) HCl. Heat to 60oC. Add with stirring, 13g(0.095mol) of ZnCl2 in a 22mL portion of diluted
HCl. Cool in ice until crystallization is complete. Filter the bis-quinolium tetrachlorozincate.
Add the precipitate to a little water and add 10% NaOH until Zn(OH)2 completely dissolves. Extract quinoline with three 25mL ether. Dry with
anyhrous calcium sulfate Remove ether by flash distillation using a 10 mL falsk and finally distil the residue from an air bath using an air
condensor. Collect the quinoline at 236-238oC as a colorless liquid; yield is 6.9g (50%).
[Edited on 5/19/2007 by guy]
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Magpie
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Yield was 22% based on the aniline charged.
I can still smell traces of it in the lab, around my sink.
The single most important condition for a successful synthesis is good mixing - Nicodem
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