Phenol has a wide variety of uses and
it's a precursor to many things like
plastics or pharmaceuticals.
Phenol is normally a white crystalline
solid but it's susceptible to oxidation
in air and old phenol tends to be a little bit discolored.
When phenol is oxidized by oxygen in the air it tends to form para-benzoquinone
which has a yellow color.
However, phenol is also capable of
undergoing a polymerization reaction.
The polymer that the phenol forms has a
brown or black color.
In air without a catalyst the polymerization is really
really slow so it's only a problem with old samples.
Just by the color of the
phenol that I have here it's pretty easy
to tell that it's heavily contaminated.
The brown color indicates that we have
polymerised phenol present but we're
also going to have benzoquinone and
other oxidation products.
Luckily for us though it's pretty easy
to clean up the phenol and all we need
to do is a quick distillation.
The phenol in this video was used to make an anisole.
Which I just posted a video about.
In a future video I'll use this phenol to
make a plastic called bakelite.
Right now the phenol in this bottle is a
solid chunk and to get it out we're
going to have to melt it a little.
Luckily for us phenol has a pretty low
melting point so this can be easily done
with some hot water.
I don't show it here but I let the
bottle sit in hot water and using a
metal spatula I was able to loosen
things up.
I dumped the loose phenol into a glass
funnel and I blasted it with a heat gun
to melt it.
I didn't use a huge funnel so I couldn't
add everything at once and I had to do
it in something like three separate batches.
As the phenol was added it got
progressively blacker and blacker and I
think this is because when I originally
melted the phenol and added it to the
bottle a lot of the polymer sank to the bottom.
Anyway, I was eventually done melting and
adding everything and I was left with a
flask of super dirty black liquid phenol.
I remove the funnel and I melted the
phenol on the side of the flask just to
try to clean things up a little bit.
I then went ahead and set things up for
a short path vacuum distillation.
The setup is almost the same as a simple
vacuum distillation except we don't
include a condenser here. A normal cold
water condenser would cause the phenol
to freezing it, so it's really not a good
idea to use one.
It is an option to include warm water in
the condenser which would cool down the
hot phenol vapors but not freeze it but
I don't really think it's worth it.
The benefit of a warm water condenser
would be fewer phenol vapors passing
into your vacuum pump, but if you set up
a proper trap that shouldn't really be
an issue anyway.
To get a better separation and a potentially cleaner
product you could also use a fractional column.
We use a vacuum distillation here
for two main reasons: the first one being
that it greatly reduces the boiling
point of the phenol and it also prevents
the phenol from reacting with oxygen.
I do have a feeling though that it's
possible to distill it without a vacuum
but I've never really tried this so I
can't really comment on the purity or
the quality that you'll get out of it.
Once under vacuum I turn on the heating
mantle and the stirring and we can get
the distillation started.
It doesn't take long before it's boiling
quite nicely and we start to get some stuff passing over.
It should be noted that water and phenol
form and azeotrope, so any water that's
present is going to codistill with the phenol.
For what I plan to use it for
I don't need and high dry phenol, so this
is ok, but if you do need absolutely dry
phenol, you're going to have to use a
slightly different process.
I assume that the procedure would involve using some
sort of drying agent before distillation,
but I'm not exactly sure of the details.
The heating mantle was occasionally
adjusted to maintain a good rate of
distillation, but for the most part were
on autopilot
To condense as much of the phenol as
possible I set up a ghetto paper towel
condenser. I place a cold towel on the
apparatus and it actually works pretty well.
Near the end of the distillation I've
collected a very nice amount of crystal
clear colorless phenol.
I was very excited about this but unfortunately
disaster struck, and I distilled things too far.
I should have stopped it earlier but by
letting it go on a little bit too long
I started to collect some yellow stuff.
I stopped the distillation immediately
and in the distilling flask you can see
we're left with some reddish brown or
black goo and unfortunately our
receiving flask is tainted a little bit yellow.
This really isn't the end of the
world and the contamination level is
really low, but it's still a little bit disappointing.
With that being said the two ways to
have prevented this was to either stop
the distillation earlier or to use a
fractionating column.
A column probably would have prevented the contaminants
from coming over with the last bit of
phenol, but I don't really know for sure.
If we look at the bottom of the
receiving flask we can see that the
phenol is already starting to crystallize,
so it's probably a good idea to transfer
it to a bottle before it completely
solidifies in the flask.
The phenol is poured into a pyrex bottle
and we wait for it to crystallize.
(music)
Before it completely solidifies it's a
good idea to break things up.
This way, once things have completely
solidified will be left with a jar of
loose phenol and not a solid chunk.
Our final phenol product is an off white crystalline solid.
Pure phenol is as white as the paper below the jar but
unfortunately the contaminants make it a
little bit yellow. I did consider
redestilling everything to clean up the
phenol, but I decided that it really just wasn't worth it.
The amount of contamination is extremely
low compared to the crude stuff that we
started with and for what i'm using it
for, it really shouldn't have much of an impact.
In my last video I asked you guys to
give me the mechanism for the first step
of this reaction. I thought it was kind
of a tough question and I was happy to
see that a lot of you were able to come
up with something.
Before I go over the answer I like the most though I want to
make it clear that the exact mechanism
is not known. I did some research and I
couldn't find any real experimental data,
so we're mostly just theorizing here.
There were two main mechanisms that were
proposed and I'm going to quickly go
over both. The first one is my preferred
one and it was submitted by the
Whysalmon﻿. I looked over all the comments
and submissions and I think he or she
was the only one to suggest this type of
mechanism.
To start off the aldehyde is protonated
and the partial positive carbon of the
carbonyl is attacked by the nucleophilic
anisole ring.
The hydrogen is picked up most likely by
water and its electrons are donated back
to the ring to regenerate aromaticity.
The hydroxyl group that we form is then
protonated under the acidic conditions.
The methoxy group of the anisole again
donates electrons to the ring, which
results in the kicking of the water molecule.
A chloride ion from hydrochloric acid comes along and
attacks the double bond and the
aromaticity of the system is regenerated.
The only issue that I immediately see
with this mechanism is that an aldehyde
isn't the strongest electrophile
The methoxy group of the anisole is
extremely strongly activating though and
it might be able to make up for this.
Here's the second mechanism that was
suggested by a lot of people.
This one in particular was made by Timothy Morrison.
Other people submitted some very nice ChemDraw mechanisms but
unfortunately I can't show them all.
Like the other mechanism this one also
starts with the protonation of the aldehyde.
In this case however we get an
attack by the chlorine and the formation
of an alkyl halide. The alcohol is then
protonated and it leaves to form a carbocation.
The carbocation is a
relatively good electrophile and the
activated anisole ring can attack it.
The attack by the anisole ring is
activated by the methoxy group which
donates electrons, but I think he forgot
to show it here. After the electrophilic
aromatic substitution, the extra hydrogen
is picked up and the aromaticity is regenerated.
There are a few errors in this mechanism
but I'm only going to address what I see
is a major problem. In part one, after the
loss of water, we form a carbocation but
this is a primary carbocation.
Primary carbocations are not very stable and
the likelihood for this to form
especially with an electron-withdrawing
group like chlorine attached, is extremely low.
If this carbocation were
to form we would probably get a hydride
shift and the positive charge would move
over to the secondary carbon.
With a positive charge on the secondary carbon
we wouldn't form our desired product.
Because of my major concern with the
second mechanism I think the Whysalmon
has the best idea.
So now that we've seen these two
possible mechanisms I want to know what you guys think.
Do you agree with me that the first one
might be the best or do you think that
the second one is still good despite my concern?
Like I said before I don't really have a
concrete answer for this and I'm looking
mostly to just have a discussion.
On a side note I'm thinking about removing
the whole reward thing for answering the questions.
I honestly like the idea of
giving out prizes, but it's just really
hard to do fairly. People who submit
their answer later could potentially
work off previously submitted answers.
To remedy this I said that the best answer first would
win but this kind of ruins the fun for
people who can't watch the video
immediately after its posted.
I feel like the idea of having to race to give the
best answer first is kind of not good either.
And having to choose just one person to
give a prize to out of 5 or 10 people
who might have had just as good an answer,
is kinda just not fair.
With that being said I'll still give up
the beakers to the people I featured in
this video, 'cause I promised in the last one.
But in the future i'm pretty sure i'm going to stop.
Besides the whole fairness issue I feel
like my entire purpose of asking a
question was to get discussions going in
the comments and offering a prize kind
of detract from this purpose.
Anyway, the next video that I post is going to be on
the production of ammonia meta vanadate.
As usual I'd like to thank everyone
who's supporting the on Patron.
Everyone who supports me with five
dollars or more will get their name at
the end like you see here.
I know I've been seeing it forever but I
really am trying to work on other tier
rewards and to add more rewards to the
one dollar and five-dollar levels.
Anyway these are the videos that I've
filmed and the ones that I plan to film,
if you have any suggestions please let
me know in the comments.