We know you've been waiting for this one.
We've been playing around a bit and we're now going to show you the next step in our
reaction sequence that started all the way back with white peppercorns.
Just to recap, first of all we extracted piperine from white pepper using ethanol, and recrystallised
it.
We then took the piperine and hydrolyzed this in an ethanolic alkali solution to form piperidine,
which we separated, and piperinic acid.
So here's a couple of samples of piperinic acid that we've obtained.
The one on the left is very clean and yellow coloured, and originates from white pepper.
The one on the left is slightly more brown coloured and originates from black pepper.
There's obviously still a little bit of the dark colouring that's made it all the way
through the process.
We're going to use the darker sample for this experiment, but there's really no difference.
So here goes, our starting material which is 3.7 grams of piperinic acid, prepared as
per our previous experiment.
It's lumpy looking, but it's quite a dry solid as you can see.
Here's the chemical structure.
What we're going to attempt to do is a fairly violent oxidation reaction where we'll try
to oxidise the two double bonds in the side chain of the molecule, and the result will
be various different products, however we're hoping that one of them will be piperonal,
an aromatic aldehyde.
1.
The first step is to get the piperinic acid into aqueous solution.
To do this we're going to convert it into the sodium salt which is water soluble.
So here's 0.69 grams of sodium hydroxide.
The same molar amount as our piperinic acid.
We'll make these into a solution using a large beaker which will end up being our reaction
vessel.
We'll need at least 700 mils of volume in here.
And we'll use 100 mils of water to get these into the solution.
Use a large stirrer as stirring is important for the reaction.
First we'll add the piperinic acid.
As you can see, it's pretty much insoluble in water as it is in the acid form.
So now we'll add the sodium hydroxide to the mixture.
Immediately you can see the color change and the solids start to dissolve.
Normally the solution is a yellow color, but we've obviously got dark colored impurities
in here so we've got a darker colored solution.
Get the stirring up, and leave this for 10 minutes to make sure that everything has dissolved.
The mixture goes a little foamy.
If after a few minutes you've still got lots of solids in there, you can add a little bit
of hydrogen peroxide.
Then it's possible your previous hydrolysis step wasn't complete and you've still got
piperine in the mixture.
This is looking good though.
So the next step is to prepare our oxidizing agent.
We've played around with a few things here and we've got a combination which gives a
fairly low but reasonably consistent yield.
So here it is.
Double trouble.
On the left we've weighed out 3.9 grams of potassium periodate.
One mole equivalent.
We prepared this in previous videos, starting all the way back from iodine, so go back and
take a look for more info.
And on the right we've got 5.4 grams of solid potassium permanganate crystals.
This is two mole equivalents compared to the piperinic acid.
Permanganate on its own can apparently be used for this reaction, but we've tried it
and we get lower yields than with this combination.
We think that these reagents work in conjunction to perform the oxidation process and break
those two double bonds up.
In the first step, permanganate reacts with a double bond, forming a diol as an intermediate.
This will then react further with both permanganate and periodate to break and form two carbonyl
compounds.
Neither of these are very soluble in water, and in addition we want to keep the concentration
of the mixture low in order to minimize excessive oxidation.
So we've got a combination of these two.
So here's 500 ml of water at about 20 degrees C. Let's go.
It takes a few minutes before the crunching sounds go away and we've got a deep purple
colored solution.
Ok here we go!
This is now ready to kick some double bond ass.
We've got our two reactant solutions ready.
We need to prepare one more thing though.
One of the risks with this reaction is that the products are themselves very prone
to oxidation.
So we need to stop the reaction after a period of time and quench any excess oxidizing agent.
Ok... we're good.
We'llestrapped.com.
on the left we've got 2.1 grams of solid sodium hydroxide and on the right 5.3
grams of sodium bisulfite which is sodium hydrogen sulfite we'll get these
dissolved in about 75 mils of water
together these will form sodium sulfite in solution which is our reducing agent
to quench the reaction they dissolve easily note that we don't use sodium
bisulfite itself to quench because although it would work it could also
react with our aldehyde product to form an adduct which we don't want okay well
that's a lot of preparation for a reaction but it's worth spending the
time to get everything ready here's our three solutions let's start with our
sodium piperonate solution in the large beaker
you
just to help moderate the reaction a bit we add three ice cubes to this and
start stirring
stir the oxidizing agent solution with a glass rod and make sure that there's no
solid settled on the bottom and now with vigorous stirring we add this to the
piperonate solution
and we're going to wait now for two minutes for the reaction to proceed you
can see a color change starting to take place in the mixture and a brown color
forming there's also a brown colored precipitate once you see this on the
sides of the beaker it's time to stop the party here we go after about two
minutes
so now we add the quench solution
so now we add the quench solution
so now we add the quench solution
pretty soon the mixture starts to settle
pretty soon the mixture starts to settle
and you can see a light colored solution
and you can see a light colored solution with a fairly heavy precipitate in it so
let's start by filtering this and
separating the filtrate from that
separating the filtrate from that
precipitate
We first wash the precipitate with a little
water.
Then once it's relatively dry, we're going to wash it using an organic
solvent to make sure that we've got any possible products out of here. We'll use
two portions of 30 mils of dichloromethane and wash the precipitate
thoroughly with each one.
we now take the filtrate and place it into a separating funnel hopefully it
will just fit. There's a nasty black precipitate left in the filter but we're
not totally sure what it is. It's not manganese dioxide, so it might be organic
by-products or something. There's a nasty black precipitate left in the filter, but we're not totally sure what it is. It's not manganese dioxide, so it might be organic by-products or something.
some other insoluble product the DCM forms a nice obvious bottom layer we
shake the mixture up for a minute to allow maximum extraction and then let it
separate again and we separate the bottom DCM layer
we do another extraction of the aqueous mixture in the funnel using another 15
minutes just to demonstrate the aqueous mixture left in the funnel is still
fairly alkaline what this means is that any acidic byproducts over oxidized
compounds or starting material from the reaction should have remained in the
aqueous layer here's our DCM extract we dry this using a small amount of
anhydrous magnesium sulfate
and then evaporate off the solvent let's see what we get
we get an oily residue which at room temperature solidifies and forms a
beautiful crystalline mass the melting point is somewhere just above room
temperature but we'll come on to this in a moment it's all solid as well with no
oily component remaining so enjoyed the view from the DCM extract video if you liked this video please subscribe to my channel and hit the bell icon to get notified of future videos
a minute or two and then broke up the solid and scraped it out of the
container
it's quite solid and crystalline as you can see not really waxy at all
and this is our crude product 0.5 grams exactly of crude pipe ronal as a yellow
colored solid this is a yield of 20%
from the starting piper inic acid nothing spectacular but it's the best
we've been able to manage from this reaction but it's still worth it why well
the aroma is simply incredible the first thing that hits you is a wave of
jelly belly toasted marshmallow beans it's got that buttery richness to it and
it's slightly vanilla like as well but it's also got a fruity edge to it as
well like maraschino cherries
overall like a rich homemade cherry bakewell tart with almonds vanilla
cherries butter and toasty aromas Wow and what's fascinating is having been
through the process first of all from the spicy white pepper the fruitiness of
the pure pipe rind then to the relatively unscented piper inic acid and
now to this beautiful concoction okay we know what you're thinking cut the poetic
bullshit and show us some proof okay here's our
DIY melting point setup let's get some product in the tube and a thermometer in
there and set up and we'll warm this now very very slowly and gently at 27 degrees
C now and the product in the tube is still completely solid getting up
towards 30 degrees and soon we've got our first sign that something is
happening there's some solid that looks wet on the side of the tube and what's
and we've definitely got the start of a melting point range here temperature is
34 degrees C and now it's completely melted 37 degrees C well the textbook
says 37 degrees C for pipe ronal that's pretty impressive our measurement is
slightly on the low side but it melts pretty sharply and it's very close so
ladies and gentlemen this is the real deal we're really pleased we did get a
way to go all the way from peppercorns to pipe ronal even though the yield is
not great it's something we really hoped we could achieve and capture on film
there are probably other ways to do this but copper sulfate didn't work for us
and plain permanganate was lower yielding and unpredictable
stay tuned