Sciencemadness Discussion Board

Phenylacetic acid + Lead acetate

gambler - 23-9-2006 at 03:12

Ok a quick question. Hopefully, not to stupid and someone can assist SWIM with the tools at his disposal so to speak..

Ok Phenylacetic acid (i have) Lead acetate (i can easily acquire)


Now i have read the various documents regarding this on the Rhodium mirror.


However, i still have a couple of unanswered questions (somewhat stupid) before i proceed.

The synthesis goes something like this..


Place 1000g phenylacetic acid and 3000g anhydrous (or trihydrate) lead acetate in a distillation apparatus and heat. First an amount of water will distill, and next phenyl-2-propanone in this destructive distillation, which requires liberal application of heat. The distillate will separate into two layers. The organic layer is separated and redistilled to give pure phenyl-2-propanone, bp 105癈/10 mmHg or 216癈 at atmospherical pressure.

Straight from the rhodium archives.
So realistically it is a 3:1 ratio and i assume it can be attempted on a small scale to trial run it?
Say 20g phenylacetic acid and 60g lead acetate. (both in solid phase) are placed in a
Standard distillation setup and heated MP for phenylacetic = 76-77 °C and lead acetate is 75 °C. Assume both will both move to liquid phase
SO heat past this and assuming water will come across followed by organic layer when around 216 degree mark is reached. Remove from heat and two layers will have formed?

Does anyone have another document regarding this synth?

Furthermore any advice or hints for SWIM?

Is that all there is to it?

not_important - 23-9-2006 at 06:17

Lead acetate loses acetic acid between 100 and 200 C, and free phenylacetic can displace acetic above the boiling boint of acetic; expect some acetic acid that to come over as well.

That's about 2.8 moles of lead actatic per mole of phenylacetic, as I remember MW, 5.6 moles of acetic per mole phenylacetic.

It is yet another reaction similar to the distillation of the calcium/barium/manganese/unobtainium salts of carboxylic acids, or the passing of the mixed vapours of the acids over hot thorium/Mn(II)/Ba/whatever oxide.

The phrase "this destructive distillation, which requires liberal application of heat" means you are going to have to getting really hot, well past the boiling point of the product you seek. The vapour phase variants run at 400 to 500 C. Yields vary all over the place.

The flask may get ruined. This is going to form lead oxides, when when hot make good glass solvents. You could try lining the flask with aluminium foil as is suggested when heating lead nitrate, or make a metal flask from pipe (which I'd still line with foil as it makes clean-up easier.)

The mole ratio of the acids might be a bit on the low side, scaling down could result in more bibenzyl ketone. Only trying will tell.

Lead is toxic enough that some care should be taken. Don't let dust from the compounds drift about. Don't dump the waste out, recover the lead compounds with medium strength nitric acid - makes cleaning out the flask easier; the lead nitrate form can be converted back to the acetate. Strong acetic acid might do the job, directly giving crude lead acetate, although I suspect it would take a long reflux followed by a rinse and then nitric acid to finish the job.

If you are not careful with the lead compounds, the children who suffer brain damage from it will come to you in your old age trying to sell you insurance, get you to vote for them, and convert you to their religion. Note that your old age may come more quickly, from exposure to said lead compounds.

Don't do this in living/eating areas, unless your intent is gene pool improvement.

I would not swim while doing chemical experiments, the reactants get diluted by the pool water. Also strongly heated objects may result in steam explosions. Do the work in a lab, and as yourself as that is less confusing.

solo - 23-9-2006 at 06:49

Reference Information

Oxidation of Alkyl Radicals from Decarboxylation of Acids
by Lead(1V) and Copper(I1)
JOHND. BACHAAN D JAYK . KOCHI
The Journal of Organic Chemisty VoZ. 33, No. 1, pg 83, January 1968


Excerp
..............a-Dimethylphenylacetic acid was readily decarboxylated by Pb'" at 60 or 80" in a 16 vol. yo acetic acid-benzene solution. The primary products were cumyl acetate (65%) and a-methylstyrene (13%) .(7) The latter is slowly oxidized by Pb'" to phenylacetone.(8)

(7) All yielda are based on motes of products per mole PbIV, irreapeotive
(8) H. Hock and H. Kropf, Be?.. Sl, 1681 (1958).

[Edited on 23-9-2006 by solo]

Attachment: Oxidation of Alkyl Radicals from Decarboxylation of Acids .pdf (1.4MB)
This file has been downloaded 1546 times

not_important - 23-9-2006 at 07:37

Ah, but that Pb(IV) free radical, while his reaction uses Pb(II) thermal.

Note that Pb(IV) carboxylates do not have to be isolated, mixing the free acide with "red lead", minium - Pb3O4 - plumbous plumbate, and mild heat will do the trick; sometimes added methanol helps. This has been used in the alkylation of quinones by carboxylic acids.

solo - 23-9-2006 at 07:51

Aside fromthe toxic effects of lead ..I'm left to wonder why the Dakin-West reaction, where ketones are synthesied with ease by refluxing the PAA with sodium acetate and GAA for 18 hours and a fine product of phenyacetone is made, isn't used?.......solo

Richy - 23-9-2006 at 22:35

If i recall correctly, the Dakin-West requires acetic anhydride, not GAA. Lead acetate is easier to aquire for your average, budding P2P cook.

Additionally, lead poisoning might prove useful in desensitizing one to the crippling neurological damage thats resulted from their 2-year meth binge.

solo - 24-9-2006 at 09:24

I stand corrected .....it's been a while since I looked at that ..............solo

MEXCHEM2006 - 26-9-2006 at 16:19

I have made this reaction before ,usually I mix 400 gr PAA and 1,200 gr of Lead Acetate in a 2 L round bottom flask , in a cooking oil bath , i use a calcium chloride ice water mixture and run it thru the bulb condenser , you will first have water coming , after all the water has come out you start a partial vacuum (5" Hg suction on a standard gauge), at approx 195°C (temperature of the oil bath ) a white liquid will distill (if your condenser isnt cold enought you will have toxic lead fumes coming out of your condenser) , once you reach 240 °C (temperature of the oil bath) the p2p will come over , it takes like an hour for all to come over , once it stops distilling ,, you will have in the receiving flask 2 phases (the top yellow phase is the p2p) , the yield is in the range of 60-70 % depending on your skills.

MEXCHEM2006 - 26-9-2006 at 16:24

You can mix PAA , acetic anhydride , 1-methylimidazole or bezimidazole under a nitrogen atmosphere and get yields in the range of 93-98%.

gambler - 3-10-2006 at 14:26

Quote:
Originally posted by not_important
Lead acetate loses acetic acid between 100 and 200 C, and free phenylacetic can displace acetic above the boiling boint of acetic; expect some acetic acid that to come over as well.

That's about 2.8 moles of lead actatic per mole of phenylacetic, as I remember MW, 5.6 moles of acetic per mole phenylacetic.

The phrase "this destructive distillation, which requires liberal application of heat" means you are going to have to getting really hot, well past the boiling point of the product you seek. The vapour phase variants run at 400 to 500 C. Yields vary all over the place.



Thanks for the excellent response firstly. However, just one question remains in my mind.
Why is there a need to drive the temp so high considering the fairly low boiling points of the two substances? Just curious thats all.

In addition would yields simply suffer if i dropped the temp? Or do i need to drive to 400 - 500 degrees simply for distillation to occur?

Thanks again for my somewhat simple question :)

MEXCHEM2006 - 3-10-2006 at 15:03

You dont need 400-500 degrees for the lead acetate PAA method (you need 220 degrees and vacuum), this is for the tube furnace method
From Uncle festers Secrets of X
"In this process, a mixture of phenylacetic acid and glacial acetic acid is slowly dripped into a Pyrex combustion tube which is filled with pea-sized pumice stones covered with a coating of either thorium oxide or manganous oxide catalyst. This bed of catalyst is heated to a high temperature with a tube furnace and the vapors of phenylacetic acid and acetic acid react on the surface of the catalyst to produce ketones"