Here's the general reaction
to form nitrate esters from alcohol. So we have our alcohol
over here on the left. And we react that with some
concentrated nitric acid and concentrated sulfuric
acid as our catalyst. And I believe this
reaction is reversible. So we could think about that. We would form our nitrate
ester over here on the right. We would also form
water in the process. So the water molecule's
going to come from this hydrogen on
the alcohol and this OH on our nitric acid. Let's take a look
at the mechanism to form nitrate esters. And so I'll start by redrawing
our nitric acid molecule here. And I think this is the correct
mechanism, although I tried to look up the mechanisms
in some textbooks, and I could not find
this mechanism anywhere. So I hope that the one that I
show you is the correct one. All right. Well, if I think about nitric
acid and sulfuric acid, sulfuric acid is actually
the stronger acid. So sulfuric acid is
going to donate protons, and the nitric acid is going
to accept those protons. The nitric acid is actually
going to function as a base. So a lone pair of
electrons on the oxygen are going to pick
up that proton. So now, oxygen has three bonds. Right? Two to hydrogens and one
still to this nitrogen here. It still has a lone
pair of electrons on it, which give it a plus
1 of formal charge. This nitrogen over here is still
double-bonded to one oxygen. And it's still bonded to this
oxygen over here-- a negative 1 formal charge and a plus 1
of formal charge, like that. So that was our first
step of our mechanism-- an acid/base reaction. In the next step,
if we look closely, we can see that we kind of
have water as a leaving group. If a lone pair of
electrons in our oxygen move in here to
form a new pi bond, that can kick these electrons
in here off onto the oxygen. And water has now left. So let's go ahead and
draw the results of that. All right. So now we have H20
as a leaving group. So H20 has left. We now have nitrogen- which
was double-bonded to an oxygen up here. It's now double-bonded to
another oxygen down here. And it still has a plus
1 formal charge now. So this is called
the nitronium ion. And since the nitrogen
is positively charged, it wants electrons. So it's going to function
as an electrophile in the next step
of the mechanism. When an alcohol
molecule comes along, alcohols have these lone
pairs of electrons here. We know that
negatively-charged electrons can function as nucleophiles. So the negatively-charged
electron is attracted to the
positively-charged nitrogen. And nucleophilic attack will
kick these electrons off onto your oxygen. Let's go ahead and
draw the product of that nucleophilic attack. All right. So now, we have our R
group bonded to an oxygen. And our oxygen is now bonded
to this nitrogen here. And this oxygen is also
still bonded to a hydrogen, giving it a plus
1 formal charge. And our nitrogen still has
a double-bond to the top oxygen here. And it now has a
single-bond to this oxygen, giving this a negative 1 formal
charge, giving this nitrogen a positive formal charge. Like that. So we've almost formed
our nitrate, ester. If we look at this,
all we have to do now is an acid/base reaction to take
this proton off of our oxygen. So water is a decent base. And a lone pair of
electrons on our oxygen can take this proton,
leaving these electrons behind on this oxygen here. And we would form
our nitrate ester. All right. So now, we have
R with an oxygen, and then, N02, like that. So once again, I think this
is the correct mechanism, but I'm not 100% sure. The formation of nitrate esters
has a few very famous examples. Let's look at the
most famous reaction where a nitrate ester is formed. Let's look at what would happen
if we started with this alcohol as our reactant. This is called
glycerol or glycerine. It has three OH groups on it. And if you react glycerine
with excess nitrate acid and also sulfuric acid--
all concentrated-- well, we would form a nitrate ester
at each one of our OH groups. So we're going to form a nitrate
ester at each of our OH groups to form this as our product. Right? We put nitro groups
onto glycerine, so this is called nitroglycerin. So of course, everyone
knows about nitroglycerin, a very famous high explosive. It's a liquid. It's extremely shock-sensitive,
so it's extremely dangerous. Nitroglycerin is not
something that anyone should attempt to make at home. So it's not a good demonstration
for chemistry instructors. A much better demonstration
for chemistry instructors would be to form another
nitrate ester starting from cotton or cellulose. So here we have the
cellulose polymer. It's made up of a bunch
of glucose molecules. So here's a glucose molecule. Here's a glucose molecule. And if you stick a whole
bunch of glucose molecules together in some
giant polymer, you form cellulose, otherwise
known as cotton. So if you take a
bunch of cotton balls and you mix them with
concentrated nitric acid and concentrated
sulfuric acid, you can put nitro groups in each
one of those alcohol groups. You can form nitrate esters. So each of these
alcohol groups gets turned into a nitrate ester. So I can go ahead and
put my nitrate esters in. You notice there are three
nitrate esters for each glucose molecule. So we form nitrocellulose
as our product, otherwise known as guncotton. Guncotton is much more
stable than nitroglycerin is. You can store
guncotton overnight. And if you ignite
it, it will give you a nice little fireball. So it's an excellent
demonstration for chemistry students.