today we're continuing the journey from
aspirin to acetaminophen in the previous
video I extracted acetyl salicylic acid
from aspirin pills and now I'm going to
hydrolyze everything that I recovered to
salicylic acid also from this point on
I'm going to refer to acetyl salicylic
acid by its abbreviated form a sa to
carry out the conversion from a sa to
salicylic acid we need to do an ester
hydrolysis in general ester groups are
sensitive to both acidic and basic
conditions I've actually already made a
video where I hydrolyze a si using base
but acid hydrolysis is much easier and
faster so that's what I'm going to do in
this video
in terms of chemicals I only really need
two things all of the a si that I
recovered in the previous video and some
hydrochloric acid
I don't showed here but I also used at
least 1300 milliliters of distilled
water the procedure that I'm following
was written out by the user
unintentional chaos on the science
madness forums and I'll provide a link
to that in the description
I didn't have a flask that was large
enough so I had to split things into two
separate batches starting with the flask
on the Left I loaded about forty seven
point five grams of a si
I then pour in about six hundred and
fifty milliliters of water followed by
twelve milliliters of hydrochloric acid
once everything's been added I transfer
the funnel to the flask on the right and
I do the exact same thing the only real
difference is that this time the a si
got stuck in the funnel but it's really
not a problem and it's easily just
loosened up using a spatula
once everything had been loaded I
prepared the flask on the left for a
reflux the contents of the flask will be
brought to a boil and the cold water
condenser that I've attached above will
rican dents any water that comes off
when things are heated up the a si will
dissolve into solution and will increase
the reaction rate at room temperature it
would take a really long time for the
reaction to reach equilibrium but under
reflux conditions it takes less than 30
minutes unfortunately I only have one
heating mantle so I can't reflux both at
the same time I chose to start out with
the one on the left and what I've done
refluxing it I'll transfer the heating
mantle and the reflux column to the one
on the right
when we're ready to get started I turn
on the stirring and the heating mantle
as we get closer and closer to the
boiling point more a si should dissolve
and we should eventually be left with a
crystal clear solution
okay so as I said before what we're
doing here is an acid-catalyzed ester
hydrolysis
in these hot and acidic conditions the a
essay will be hydrolyzed to form
salicylic acid as well as acetic acid
salicylic acid is not very soluble in
cold water so as the solution cools our
salicylic acid will slowly crystallize
out but the acetic acid will remain
dissolved now I'm just going to quickly
go over the mechanism if you're not
interested in seeing in detail what's
happening here
you can just skip ahead
in the first step the oxygen of the
acetyl group will pick up an acidic
hydrogen water will attack the partially
positive carbon of the carbonyl and the
electrons of the double bond will go
back to the oxygen another water
molecule will come along and it will
pull a hydrogen from the water that just
attacked the oxygen of our salicylic
acid will then be protonated to form a
good leaving group one of the other
oxygens will donate electrons to form a
double bond and the bond between our
acetyl group and the salicylic acid will
be broken this will form our final
salicylic acid but the acetic acid
that's formed will have a protonated
carbonyl a water molecule will come
along and pick up this proton to give us
our final acetic acid and regenerate the
acid catalyst
as I mentioned before this entire
reaction is an equilibrium reaction the
reverse of this reaction is known as a
Fisher of Stara fication and it's
actually a pretty common way to make
esters the direction that the reaction
takes you know whether we're making an
ester or hydrolyzing one depends on a
lot of factors with organic esters
though there is one major determining
factor and that's water by including a
lot of water we favor the hydrolysis
reaction but if we were to keep water
content to a minimum the formation of an
ester would be favored so in theory if
we wanted to do this reaction in Reverse
we would start with salicylic acid and
acetic acid the acetic acid will be used
as the solvent and we'll use a huge
excess because water is produced in the
reaction and we want to keep the
concentration of water at a minimum just
as a quick aside even though the reverse
reaction does work it's not the best way
to make a si starting with salicylic
acid the most commonly used method is to
react acetic anhydride with salicylic
acid and this reaction is not in
equilibrium so the yield is much higher
anyway once we get things to a reflux
and we have water steadily recondense
again to the flask we can turn on our
timer and keep things going for about 30
minutes a 30 minute reflux is probably
more than is needed and unintentional
chaos mentions this in this procedure
the 30 minute reflux is really just to
make sure that it reaches equilibrium
and realistically 30 minutes isn't very
long
after the 30 minutes the reflux column
and the heating mantle is transferred to
the flask on the right the exact same
thing is repeated here where the
contents of the flask is heated to a
reflux for about 30 minutes
as the contents of the flask on the
right are heated the solution on the
left is going to cool down as the
solution cools the solubility of
salicylic acid will decrease and it will
slowly crystallize out what's kind of
interesting is that the flask on the
Left becomes almost completely opaque
around the same time that the flask on
the right fully clears up the piece of
paper towel above the flask on the left
is just to prevent any dirt or dust from
falling in it's not really a good idea
to use a stopper here because as the
water and the air and the flask cool it
will pull a slight vacuum and it might
make it hard to take the stopper out
anyway just like before we get things to
a steady reflux and we keep it here for
about 30 minutes
then after 30 minutes we remove the
heating mantle and we let things cool
down
you
once things have cooled down to around
room temperature I didn't bother putting
the flasks in a fridge or an ice bath
because the solubility of salicylic acid
in water is super low if I were to chill
both of these flasks to about zero C I
would probably be gaining an extra maybe
two grams in total this represents
something like 3% of the total yield so
the time it would take to chill things
just to get an extra 3% in my mind it's
not really worth it here
anyway I first tried breaking up the
crystals using a spatula but it honestly
didn't work very well the best way was
to just take the flask off the stand and
to shake it around a little bit after
shaking around the flask on the right I
realized it was actually warmer than I
thought it was and it wasn't quite room
temperature I placed it back on the
stand for something like an hour or so
to cool down just to make sure that
everything is crystallized before I move
on to filtering
so about an hour later I come back and
it's time to filter off the water I
didn't have a really big filtration
flask so I have to filter the crystals
from each round bottom separately
the general procedure is pretty simple I
just keep adding and pulling off the
water until almost all of the crystals
have been transferred
I then use a small amount of ice-cold
water to wash out any crystals that
remain in the flask it took something
like two or three washings to get out
almost all of the crystals
now that all of the crystals are in the
filtration flask I add some distilled
water to wash them the major side
product in this reaction is acetic acid
and we want to make sure we get rid of
as much of it as possible
the vacuum is then turned on and the
water is pulled off I keep the vacuum
running for something like 5 to 10
minutes just to try to get the crystals
as dry as possible
the crystals are then transferred to a
piece of paper and I move on to
filtering the second batch
process here is exactly the same as the
first one so I'm not going to bore you
guys by going over it again
after we're done filtering and watching
the crystals I transfer them to the
paper and combine it with the other
batch some crystals remain stuck to the
flask but this represents a very small
amount
using a spatula I spread out the
crystals and I let them air-dry for a
few days
the final yield was sixty two point six
grams of salicylic acid which represents
percent yield of about eighty six
percent the procedure that I'm following
claims a yield of around ninety five
percent but I've repeated this procedure
a few times and it's always between 85
and 90 for me at this point our overall
yield of the process is around 82
percent and we get this by multiplying
the 95 percent I got in the first step
and the 86 percent I got in this step
with every coming step I will tally up
the overall yield and you'll see that
it's slowly going to be whittled down
the next step is the conversion of the
salicylic acid to phenol and this step
is usually around 50 to 60 percent
efficient so it's going to be a big hit
on my yield there anyway with that being
said I'll have you guys determine what
the next video we'll be using the
strawpoll link in the description I have
a feeling that you guys will vote for
the next video in this series but I also
did distill mercury so maybe you guys
will want to see that one instead
as usual I'd like to thank everyone
who's supporting me on patreon anyone
who supports me with $5 or more will get
their name at the end of the video like
you see here eventually I hope to get
some higher tears going and also add
some more rewards to the $1 and $5 tier
anyway these are the videos that have
already filmed and the ones that I
planned to film if you have any
suggestions please let me know in the
comments also if you haven't already you
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and this month there will probably be
some doubling up some weeks