Piperonylic acid from Black Pepper:
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Preparation of Piperine

One ounce (28 grams) of standard black pepper was placed in a 500 ml flat bottom
flask along with 250ml Everclear to which a condenser was attached to prepare
for standard reflux. With vigorous magnetic stirring, the mixture was refluxed
at just above boiling temperature for 3 hours, allowed to cool, and the mixture
was suction filtered to retrieve the filtrate. Standard distillation
concentrated the filtrate to approximately 20 ml. The concentrated extract was
then added to 20 ml of 10% KOH in Everclear which was heated on a low setting on
a hot plate. To this mixture, water was added dropwise to form a yellow
precipitate until no more precipitate formed. This was suction filtered and
recrystallized with 30 ml of hardware-store acetone made anhydrous by drying
with epsom salts. Yield was approximately 1.3g of crude piperine, which was
stored in a dark place overnight. (approximate because the scale in question was
at best accurate to tenths of grams.) You can do this a couple of times in a
night without much effort, which can effectively yield 2.5 grams.

Hydrolysis of Piperine to Piperic Acid and Piperidine

2 grams of piperine was placed in 20 ml of a 10% KOH in Everclear solution in a
125 ml Erlenmeyer flask and was refluxed using a standard reflux setup for 2
hours. The original article recommends refluxing under reduced pressure, but
there should not be a problem with standard reflux. It's your choice. There is
no shortage of duct tape or chemical burns around these parts, so don't listen
to the author.

The solution was then transferred to a suitable vacuum distillation apparatus
(a 100ml flask would be ideal) and the distillate was collected in an ice cooled
receiving flask. The remaining undistilled residue was scraped out of the
distillation flask and placed in 100 ml of H2O. The solution was acidified with
HcL. The yellow precipitate was vacuum filtered and recrystallized with hot
Everclear to yield approximately 1.5 grams of predominantly piperic acid, which
was confirmed by a melting point of 213 degrees.

Phase Transfer Oxidation Of Piperic Acid

"In a 250 ml two- or three-necked round bottomed flask, place 1.0g of piperic
acid, .1 g of Adogen 464, 10-15 ml of benzene, and a magnetic stirring bar.
Attach a thermometer to the flask through a cork or adapter as well as a small
dropping funnel. Add to this stirred mixture 4.4g of potassium permanganate
dissolved in 50-60 ml of water at such a rate that the reaction temperature
remains below 30 degrees. After all of the potassium permanganate has been
added, stir at room temperature for 90 minutes. Finally, add about 10-20 ml of
saturate sodium bisulfite solution to the reaction mixture and collect the
preciptated manganese dioxide by suction filtration. Wash the precipitate with
10 ml of benzene. Place the filtrate in a separatory funnel, separate the
layers, and wash the benzene layer three times with 10ml of 10% NaOH solution.
Wash the base solution once with 20ml of ether. Carefully acidify the base
solution to pH 1-2 with 6M HcL and extract the acid solution with 3x25ml ether.
Dry the ether solution over magnesium sulfate, filter, and then remove the ether
by use of a rotary evaporator. The yield was approx. .3 grams piperonylic acid."
Obviously, some sort of scale up is necessary to get an amount of product for a
workable synth.

Reference: Page 527 of _Laboratory Experiments In Organic Chemistry_
           by Mohrig and Neckers, no doubt long out of print.


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