If you've been following this column for a while, you'll know that I have a
bit of a thing for things that glow – whether it be luminol, luminol again, or
singlet oxygen chemiluminescence. But I've never actually got around to doing
an actual glow stick reaction, so here we are.
So this reaction is based on one that was developed by Roger Nixon as part of a workshop that he did out of
Oxford University when he was schoolteacher fellow there, based around 2010–2011.
And you can go and read the original article he wrote up in School Science Review.
But the thing about the original set-kup was that they were using some fairly expensive dyes
and some solvents that weren't necessarily appropriate for use in a
school, such as dichloromethane. So I wanted to see whether or not it was
possible to sort of get this glow stick reaction at a reasonable price point and
get an approximation of something that was going to be satisfactory to students
and potentially initiate some ideas for some research for them to go and work on
in the future. These commercial glow stick systems tend to be based
around the chemistry of oxalate esters. The one we're going to be using
today, it's TCPO – trichlorophenyl oxalate. Now, it's going to be much easier
and cheaper for you to be able to make this in school than it would be for you
to buy it on its own, and that's a synthesis that's simple enough that even
a sixth-former or an IB student could do actually under fairly close supervision.
You'll get a fairly decent yield out of a respectable amount of starting material.
And once you've got that, this stuff will be fairly shelf stable for a
number of months and that's what makes this one particularly suitable for the
starting point for these kinds of investigations.
I also have some solvents and we'll see the effects of the solvent shortly.
Today we're going to be using a 50:50 mixture of ethyl acetate and ethanol
and I've got those separately here 5 ml of each just to
illustrate why we want both in the mix. I've also got some sodium acetate and
that's going to catalyse the reaction for us. And 2 cm3 of
10 vol hydrogen peroxide made up in ethanol, rather than being made up in water.
So all we need to initiate the reaction is a sample vial and
basically half a spatula of the TCPO, that's about 0.1 g.
And once you've got that you will add in, in order:
I'm going to begin with the ethyl acetate.
Now, if I add in the dye to the ethyl acetate, you'll notice
I've got about the tip of the splint here,
it's about 0.05 g of the dye, and you can see here
it's not really dissolving in the ethyl acetate on its own. The dye that I'm using
here to accept the energy from this chemiluminescent reaction is rhodamine B
also known as rhodamine 610, it's a laser dye. There are loads of different
fluorescent dyes that will actually facilitate this reaction and get a glow
for you. This one's going to glow a pinky red colour, the other dyes tend
to be a little bit better if I'm honest, but a lot more expensive. So to start off
with, rhodamine B is a good place to go. But you can see here, the ethyl
acetate that we want to actually dissolve our TCPO up into, the rhodamine being
not so interested in that. A little bit of ethanol here and immediately you can
see that the the dye is doing its business.
As I said, the end of a the splint of catalytic sodium acetate
and because I'm going to be working in fairly dim conditions I have my peroxide
already measured up in a syringe for me so it's nice and easy for me to work
with. I'll clear the other stuff out of the way and we'll have a look and see
what the reaction looks like.
Okay, so I've dimmed the lights
and as I mentioned, what we're looking out for here is the idea that we've got
this chemiluminescent reaction. There is going to be some catalytic
behaviour from our sodium acetate dye and so we might notice that actually more of
the glow is taking place around the dye itself. First of all, I'm going to
just put in the peroxide relatively slowly so we don't mix the liquid up too much.
And you can see we've got some glow taking place up at the top and if we mix
this through so the sodium acetate and the various components are thoroughly mixed
we get a nice glow there, coming from the peroxide and the reaction.
Now what's good about this demonstration is that it can be used a great launching point for any
number of different investigations for science clubs or for students who are
working on individual projects. First of all, you've got the idea of the synthesis
in the first place, things that affect the yield, the rate of that reaction, the
thing that you're actually synthesising as well – this is not the only oxalate ester
that actually has a chemiluminescent reaction. The one that was chosen today
was taken for its balance of shelf life and the strength of the glow associated
with it, but other ones are available. You can even look at green alternatives
using vanillin rather than the trichlorophenyl as an alternative.
Of course, other fluorescent dyes are available and you can look at the effects of those as
well as solvent effects – so there's a whole range of different things that can
be tried out and so definitely worth actually showing to students to see if
they want to take it anywhere. Give it a go.