Make Luminol - The Complete Guide

Uploaded by NurdRage on 07.03.2011

Greetings fellow nerds.
In this video, we’re going to make luminol,
a really famous chemiluminescent substance.
First I need to crush your expectations:
Okay, first let’s plan out our strategy.
Our synthetic approach is going to start from diethylhexyl phthalate,
then we hydrolyze and neutralize it to disodium phthalate,
acidify it to phthalic acid,
dehydrate it to phthalic anhydride,
nitrate it to 3-nitrophthalic anhydride,
hydrolize it to 3-nitrophthalic acid,
condense it with hydrazine,
then finally reduce the nitro group to amine and form our target luminol compound.
While there are shorter routes to luminol,
this approach can be performed with domestically available chemicals.
So let’s get started.
First we need to get diethylhexyl phthalate.
This is actually found in vinyl gloves.
and these are usually sold in pharmacies.
Look for ones that say they are made with PVC.
PVC, or polyvinyl chloride, is a very rigid polymer.
So to make the gloves flexible diethylhexyl phthalate is added.
To extract it we get 50g of worth of gloves and cut them up.
Then we add isopropanol, also known as rubbing alcohol,
to completely cover the gloves and then boil the mixture.
I’ve put this round bottom flask of cold water on top
to condense the alcohol vapors and reduce loses.
As it boils, the alcohol leaches out the diethylhexyl phthalate.
This should be done for about an hour or so.
After the mixture is cool filter the mixture and retain the alcohol solution of diethylhexyl phthalate.
Here we are.
There is a lot of alcohol in it so boil it or evaporate it until it reaches half its volume.
When that’s finished we can go to hydrolyzing it.
Get an equal volume of water, in this case about 200mL
and add to it about 10g of sodium hydroxide, which is available as drain cleaner.
Stir it up until it dissolves and then add it to the alcohol mixture.
Turn on the heat and once again place a flask of cold water over it
to condense the vapors and prevent excessive evaporation.
Boil the mixture for about half an hour to an hour.
What’s happening here is that we are performing a base catalyzed ester hydrolysis
on the diethylhexyl phthalate to make phthalic acid and 2-ethylhexanol.
To help separate the two products we’re using an excess of sodium hydroxide
which in turn reacts with the phthalic acid to make disodium phthalate.
When that’s done, take it off heating and let it cool to room temperature.
The mixture will separate into two layers.
the bottom layer has the disodium phthalate that we want,
and the top layer has the mixture of alcohols.
Pour off the alcohol layer or use a separatory funnel.
We won’t need the alcohols so we can get rid of that.
Now with the disodium phthalate solution,
we add to it 25mL of concentrated 12 molar hydrochloric acid,
also known as muriatic acid.
Stir the solution and put it into the refrigerator or an ice bath to cool.
The reaction of disodium phthalate with hydrochloric acid
produces sodium chloride and phthalic acid.
Since phthalic acid has low solubility in cold water, it will eventually precipitate out.
Pour off the excess liquid.
Now this phthalic acid is impure and we want phthalic anhydride.
So we’re going to purify and convert it to phthalic anhydride by distillation.
Place the phthalic acid on a hot plate and heat it to boil off the water.
Eventually the phthalic acid will dry and will melt again as the temperature increases.
At this point place a flask of cold water over the beaker.
The phthalic acid will dehydrate into phthalic anhydride and boil off
where it condenses on the top flask and the sides of beaker as crystals.
When a good amount has deposited, take it off heating and let it cool.
You can see inside the cotton candy like deposit of phthalic anhydride.
Carefully scoop out just the phthalic anhydride,
be careful not to contaminate it with the impure stuff at the bottom,
and then place it into a vial.
Go back and vaporize and collect more phthalic anhydride until very little comes out.
While you’re doing it be careful not to wait too long for it to deposit
or the deposit will get so heavy that it falls back onto the bottom, wasting your time.
Eventually with enough collection you’ll get a sizeable quantity of pure phthalic anhydride.
If your yields are low you’ll need to convert more gloves before continuing.
Now we need to nitrate it.
We have here a beaker with a glass encapsulated digital thermometer
and a hotplate stirrer with a stir bar.
Now take 45mL of sulfuric acid
and add to it 13g of the phthalic anhydride
and 19g of sodium nitrate.
I got the sulfuric acid from liquid drain cleaner.
But if you want to make it yourself you can do so from previous videos I've made.
The sodium nitrate was made in another video
from instant cold packs and sodium hydroxide.
Anyway, after all the ingredients are added
the mixture will heat up at first by itself
so keep stirring it until the temperature stops rising and starts to fall.
Now turn on the hot plate and ramp the temperature up slowly over an hour to 110 Celsius.
The important thing is not to overshoot.
I raised the temperature at a rate of one degree per minute.
Once it’s stabilized at 110 Celsius continue heating for another hour.
A couple of things are happening.
First, the sodium nitrate is reacting with the sulfuric acid
to make nitric acid and sodium bisulfate.
But under these extremely acidic and dehydrating conditions
of excess hot concentrated sulfuric acid
the nitric acid reacts to produce nitronium ions.
The phthalic anhydride reacts with the nitronium ions
to nitrate the 3rd position on the aromatic ring.
Alot of other products are also produced like adding the nitro group to the 4th position.
But the 3 nitro product is what we want.
Now take it off heating and allow it to cool.
The mixture will become thick and gel-like.
Scrape it out and pour it into 150mL of cold water.
Don't add the water to the acid mixture as the excessive self-heating is dangerous.
Vigorously stir the mixture to break up all the chunks and form a slurry.
Nitrogen dioxide will be emitted so this must be done in a fumehood.
What’s happening is the mixture is hydrolyzing
and the 3-nitrophthalic anhydride is converting to 3-nitrophthalic acid.
But more importantly we’re separating it from the various other components
such as sulfuric acid, nitric acid, sodium sulfates, 4-nitrophthlalic acid
and various other organic side products.
Most of them are very soluble while our 3-nitrophthalic acid has a lower solubility.
Anyway, allow the mixture to stand overnight so it fully hydrolyzes.
Here we are the next day.
Shake and then vacuum filter the mixture.
Wash the residue with two 50mL portions of water
and allow it to dry under the air stream.
Scoop it out into a container. And that is 3-nitrophthalic acid.
Now we condense hydrazine with the 3-nitrophthalic acid.
First we need a source of hydrazine.
We’re going to use the hydrazine sulfate I already made in a previous video
using methyl ethyl ketone, ammonia, bleach and sulfuric acid.
So to do the condensation get 1 gram of 3-nitrophthalic acid,
616mg of hydrazine sulfate and 1.4g of sodium acetate trihydrate
that we made for our hot ice experiments in another video.
Add the ingredients together in one container along with 1mL of water.
Now to heat it up.
Setup a digital thermometer and using a heat gun we gently boil the mixture until it dries.
What’s happening is the sodium acetate reacts with the hydrazine sulfate
to produce hydrazine acetate and sodium sulfate.
Now we add 4mL of brake fluid.
Make sure it has a boiling point above 230 Celsius
and that it’s made from polyethylene glycol.
We need to use this as a solvent
since the reaction works best at temperatures far above the boiling point of water.
Now start heating it up and try to keep it between 200 and 230 Celsius.
Continue heating for ten minutes.
If the reaction is working it’ll become a dark red.
The hydrazine acetate reacts with the 3-nitrophthalic acid
to produce 3-nitrophthalhydrazide, water and acetic acid.
The water and acetic acid boil off at these temperatures
and thus drive the reaction to completion.
After ten minutes of heating let the mixture cool to below 80 degrees Celsius before handling it.
Now we have to turn the nitro group on the 3-nitrophthalhydrazide into an amine group.
After the hydrazine condensation the mixture is quite gooey
so transfer it to a larger container by mixing it and washing it out with water.
Add additional water until the total volume is about 100mL.
Now add in 13g of sodium hydroxide.
Shake it up until it completely dissolves.
The mixture will turn a very dark red as it reacts with the sodium hydroxide.
Now add in 10g of sodium metabisulfite,
this is sold as stump remover or a chemical for home brewing.
Mix it in and be sure to break up any large chunks.
Add in another 50mL of water and keep mixing until everything is dissolved.
Now the next step needs to be done fairly quickly
so everything should be prepared first.
Get a round bottom flask of cold water that’s bigger than your beaker.
We need this to condense the water vapor as the mixture boils later.
Also get a flask or beaker that’s small enough to fit inside the larger beaker
but big enough to hold down the aluminum we’ll be adding later.
Now get a few square feet of aluminum foil, about 5 grams worth,
and tear it up into a dozen or so smaller pieces.
Now get ready,
quickly jam the aluminum foil into the beaker and press down with the flask,
then place the cooling flask on top.
The reaction starts up as the aluminum foil is dissolved
by the sodium hydroxide to produce hydrogen gas.
This reaction is very exothermic and heats up to boiling temperatures.
This is useful because it helps the aluminum react with the sulfite ions
in a complicated reaction to convert the nitro group
on the luminol precursor into an amine group.
It is this step where we are making luminol.
Let the reaction proceed until it stops bubbling.
It’s still strongly orange meaning it still isn’t complete.
So open it up and add in another 4 grams worth of aluminum foil and start again,
letting it run until it stops bubbling.
repeat the aluminum addition until you see no further color change in the mixture.
I added aluminum two additional times for a total of four in this particular run.
Now we have luminol, but it’s mixed in with a large amount of contaminants,
by products and side products.
As well as being deprotonated under these alkaline conditions.
So we have do a few steps of separation and an acid work-up.
After stirring the mixture to break up the chunks, filter it out.
When all the liquid has gone through,
add 50mL of water to the residue to wash out any additional soluble chemicals.
This is what the leftover residue looks like with large amounts of aluminum oxide
and unreacted aluminum.
You won’t need this so throw it away.
Now if you look closely at the filtrate it has these dark floating oils.
We don’t want this side product so get a paper towel and carefully dab it away.
Alternatively use a separatory funnel if you have one.
Now get a large container with 25g of sodium bisulfate.
This is normally sold as pH lowering chemical for swimming pools.
Dissolve it in a total of 200mL water, and then add in 100mL of acetone,
this is sold as a solvent in hardware stores.
Now get the luminol mixture and add it to the acid and acetone solution.
Stir it up to thoroughly react the chemicals.
The basic sodium aluminates and hydroxides
react with the acidic sodium bisulfate
to form a slurry of aluminum oxide hydrates and sodium salts.
Meanwhile the luminol is protonated
and has increased solubility in the acetone-water solution.
Now carefully pour off the upper liquid layer into a large evaporating dish.
The slurry is waste and may be discarded.
Let the luminol solution evaporate until it’s dry.
Here we are a couple of days later.
Break up the cake of luminol and transfer it into a beaker.
Wash the dish with a bit of water to get out as much of the luminol as you can
and transfer the washings to the beaker.
Stir up the mixture and break up the luminol flakes.
There should be a fine suspension of luminol but no large pieces.
Add in more water if the flakes are not breaking up.
I needed a total of 100mL of water for my run.
What we’re doing is washing out any remaining salts from the luminol.
Luminol has low solubility in water but the salt impurities have high solubility.
The opposite of the situation with acetone
and this gives us excellent separation of the luminol from the impurities.
You can see here the fine suspension of luminol.
Now simply vacuum filter the mixture and draw air through to dry it.
And there we have it, luminol made from domestically available chemicals.
Now to test it.
The first test is to place a few milligrams in a vial and add about 10mL water.
Only a tiny bit of luminol is soluble in water
but if we shine an ultraviolet light on it
we can see it has a strong blue fluorescence compared to regular water.
Now add in 200mg of sodium hydroxide, the exact quantity isn’t critical.
Shake it up and the undissolved luminol should now dissolve.
The luminol is no longer fluorescent under basic conditions like this.
Now for the ultimate test of chemiluminescence.
Get about 5mL of household bleach and turn off the lights, add it directly in.
The flash of blue chemiluminescent light shows that we have successfully made luminol.
Granted, it’s much easier and cheaper just to buy a glow stick
or buy luminol directly online.
But our objective here was to demonstrate synthetic organic chemistry
using domestically available chemicals.
And to show the amount of theory and planning that goes into a simple synthesis.
For those of you looking for a career in organic chemistry,
this is the most basic of what you’ll have to do, it only gets harder from here
Anyway, that’s luminol.
Thanks for watching the complete guide.