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Topic: Benzylbarbituric acid  (Read 8295 times)

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Offline SwedishChef

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Benzylbarbituric acid
« on: April 10, 2009, 04:33:44 PM »
I've selected to synthesize barbituric acid, 5-benzyl- for my special project in organic chem. II. The structure for this particular compound can be viewed at:
http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=260790&loc=ec_rcs#Properties

The mechanism for the reaction is nucleophilic acyl substitution.

Sodium metal is dissolved in absolute ethanol to produce the alkoxide, followed by the addition of dry diethyl benzylmalonate, and a hot solution consisting of dry urea dissolved in absolute ethanol.
The mixture is then refluxed for 2 hrs using the appropriate apparatus(water-cooled condenser & calcium chloride drying tube). Upon completion of the reaction, the solution is acidified with 3 M HCl and then the volume of the mixture is reduced to 1/2 by removal of the ethanol via evaporation utilizing a rotary evaporator.
Solution is then cooled in an ice bath until no more product crystallizes. Product is collected by vacuum filtration on a Buchner funnel and then rinsed with ligroin(hexanes) to remove unreacted diethyl benzylmalonate.
Product is recrystallized from boiling water, collected by vacuum filtration, and allowed to dry.

This may be a stupid question, but here it goes.
I already have the necessary equipment cleaned and set up, and all of the reagents except for one. The experiment calls for dry diethyl benzylmalonate. The only thing my college has stocked in the chemical room for this experiment is a liquid solution of 98% diethyl benzylmalonate. Am I screwed or is there a way that I can prepare it from this within a 45-minute time period?
Originally, I was thinking about just using it anyway & make the necessary calculations for the actual amount to be added, but I don't think it would be wise.

Offline Squirmy

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Re: Benzylbarbituric acid
« Reply #1 on: April 10, 2009, 08:50:24 PM »
You should look into buying a new bottle and see what's available...I think it should provide some insight.

Offline lutesium

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Re: Benzylbarbituric acid
« Reply #2 on: April 11, 2009, 04:36:27 AM »
No. No question is stupid.
But it may be wise to learn that NaOEt wants dry conditions because NaOEt + H2O ===> NaOH + EtOH
So the strength of base is diminished.
But you can prepare him from

ChloroAcetic Acid + NaCN ===> + NaOH ===> +H2SO4 + EtOH ===> Diethyl Malonate

Look at vogel for the procedure.

Hope these helps!


Lutesium...

Offline lutesium

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Re: Benzylbarbituric acid
« Reply #3 on: April 11, 2009, 11:40:35 AM »
While looking at a synthetic scheme you have came to my mind (I've found something that may be useful for you.)

But be careful as the last step involves a CO formation!!!

And the only step missing is the condensation of urea with DiEthyl Phenyl Malonate.



Lutesium...

Offline SwedishChef

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Re: Benzylbarbituric acid
« Reply #4 on: April 11, 2009, 10:19:05 PM »
Thank you all for the responses!

Squirmy, unfortunately, that isn't an option at this point. Because of the college's messed up policy, I wasn't able to find out until last Thursday that it was the only thing they had in the chem storage room. I had to go in with the lab manager and look around. Organic chem lab is simply horrible here since we don't have open labs, so we're usually allowed 3.5 hours at the most (or rather 2 hrs since the professor gives quizzes & lectures on the lab before we actually start).

Lutesium, it doesn't look like the reaction in the image will produce what I need. There's suppose to be a CH2 bridging a benzyl and the tertiary carbon. heh, we can probably thank the multiple nomenclature systems for that. When I looked up the compound diethyl benzylmalonate, I was getting structures that were either missing the secondary carbon at that position or had a different group there. I had a hell of a time trying to find the correct structures to go with the names in order to look up data. Anyway, the lab is taken from Kenneth L. Williamson's "Organic Experiments" 9th edition, Chpt 42, 2. Benzylbarbituric Acid. That's what I have to follow, otherwise my professor will go ape if I start changing reagents and deviating too much from the procedure.

Vogel? Haha! We're lucky we have a couple of Merck Indices, a few CRCs, and some C/H-NMR and IR spec reference books from the 60's and 70's. Our college library has even less! I could have the library order it in for me, but I wouldn't get it in time, lol.

ChloroAcetic Acid + NaCN ===> + NaOH ===> +H2SO4 + EtOH ===> Diethyl Malonate

I would still need to add a benzylmethyl group, and besides, it would take too much time. I only have 3 hours to complete the lab with 2 of them being used up for refluxing during the reaction process(any suggestions to speed it up?), ~15-20 minutes on the rotary evaporator, and 30 minutes for recrystallization. If we go over that allotted time on our special lab, we lose points ( 5 for every ten minutes or something like that).

heh, a silly suggestion, but maybe if I ran the diethyl benzylmalonate solution through some anhydrous calcium chloride before adding it. It would take care of any water, but it probably wouldn't help, lol.

Offline Squirmy

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Re: Benzylbarbituric acid
« Reply #5 on: April 11, 2009, 10:52:40 PM »
I just said look into buying to see what's available...I thought you could figure out that buying it wasn't actually necessary ;)

In Aldrich's online catalog, there are only two entries:

Quote
Diethyl benzylmalonate (2)
   13532   purum, ≥98.0% (GC) (Fluka)      
   135542   98% (Aldrich)

Bottom line: the bottle you have is good enough...98% is the purity and that's pretty high for that compound. You could look at it as a concentration, too, and take it into consideration when you calculate amounts.

Drying it wouldn't hurt, but it's probably not critical.

Offline lutesium

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Re: Benzylbarbituric acid
« Reply #6 on: April 12, 2009, 06:05:52 AM »
You can't use a Metal Alkoxide in a humid environment: This is a fact! Do a google search for vogel practical organic chemistry you'll find results that'll be useful for you. Or else you can concentrate the solution that you've got in your lab but preferably under vacuum (faster and safer due to the probability of decomposition). Or the best inside a rotovap    but be sure that you remove the last bits of water or the yields will drop. Every bits of water means drops in the yield.


Lutesium...

Offline SwedishChef

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Re: Benzylbarbituric acid
« Reply #7 on: April 14, 2009, 01:09:37 PM »
:Update:

Actually, Squirmy was correct in that I could use the 98% diethyl benzylmalonate. What I did was, since the recipe called for 5.0 g, I measured out ~6.0 g, calculated the maximum amount of water(by mass) possible contained in the reagent, and added the necessary amount of calcium chloride( 1 to 2 ratio). Then I decanted out ~5.0 g of the diethyl benzylmalonate.
Cutting the Na metal was a ball ache. I had to cut the cake in half I dig out the "clean" stuff.

heh, I must have put a little bit too much cotton in the bottom of the drying column, because some of the drying agent shot out of the top from pressure building up in the apparatus, lol. Nevertheless, the experiment seemed to have went well. I had to cut the reflux time down from 120 minutes to 100 minutes due to time constraints. It looked like I recovered quite a bit of product after rinsing it with ligroin, but I'm not sure how much I'll get after recrystallization or how pure it is.

The benzylbarbituric acid, which is normally insoluble in water, is suppose to be recrystallized from boiling water. lol, I had to use about 100 mL & 7 minutes of boiling before the stuff completely dissolved, and then had to put the solution in the refridgerator since it was time to clean up & leave. Fortunately, I'm getting a little bit more time for the lab... 15 minutes.
In the event that I had used too much solvent, would it be possible to boil off some of the water without having a significant loss in product, or maybe add something to it to bring the product out of solution without contaminating it?

Offline Squirmy

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Re: Benzylbarbituric acid
« Reply #8 on: April 14, 2009, 02:28:09 PM »
Yes, you can boil off excess water. However, if you get crystals from your solution, it's probably best to go ahead and collect them. You could then try to get a second crop by boiling off water from the filtrate. The second crop is often less pure, so you should check purity before combining it with the first one.

Offline lutesium

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Re: Benzylbarbituric acid
« Reply #9 on: April 15, 2009, 05:26:29 AM »
You can't use a Metal Alkoxide in a humid environment: This is a fact! Do a google search for vogel practical organic chemistry you'll find results that'll be useful for you. Or else you can concentrate the solution that you've got in your lab but preferably under vacuum (faster and safer due to the probability of decomposition). Or the best inside a rotovap    but be sure that you remove the last bits of water or the yields will drop. Every bits of water means drops in the yield.


Lutesium...

That's what I've also said!


Lutesium...

Offline SwedishChef

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Re: Benzylbarbituric acid
« Reply #10 on: March 08, 2010, 01:07:45 PM »
Update for this particular experiment: Synthesis of Benzylbarbituric acid(mp. 206 deg. C)

Calcium chloride anhydrous can be placed in a long-stemmed funnel set up on a ring stand, and the 98% diethyl benzylmalonate solution slowly poured through the funnel and drained into a graduated cylinder until the desired volume is reached.
98% diethyl benzylmalonate solution: 1.064 g/mL at 25 °C(lit.)
  Source: http://www.sigmaaldrich.com/

Any remaining trace amounts of the solution can be rinsed out of the graduated cylinder and into the alkoxide rxn mixture with hot absolute ethanol.

The lab manual says to recrystallize the synthesized product from boiling water, however, I found it required an absurd amount of water, and found that a solvent pair consisting of n-propanol(bp. ~97.8 deg. C) and water worked even better. I first added enough n-propanol, the better solvent, until approx. half of the product dissolved during boiling, and then added boiling water until the rest dissolved and the solution became very cloudy. Seems to have worked with minimal loss of product. Now I just have to wait on the NMR spectra to see how this turned out.

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