We are going to do the classic benzoin condensation reaction.

This is done in schools using thiamine, vitamin B1. But this is a bit woozy, so we

decided to try it the proper old-school way using cyanide as the catalyst.

The first thing you'll need is one gram of an alkali cyanide salt. We've used our

mixed sodium potassium cyanide and it's from an impure batch so it's a yellow

color. But it should work fine.

As always be very careful when handling cyanides as they are very toxic. This

little bit of powder is enough to kill you, probably five times over. Dispose of

any waste solutions using hypochlorite bleach which oxidizes the cyanide into

much less toxic cyanate before disposing. I'll measure out three mils of water.

Add this to the cyanide and stir to make a solution. It should all dissolve.

Here we go. Now measure out 10 grams of benzaldehyde. Ours is slightly yellow

colored and it's from the reaction we did in a previous video which used

benzyl alcohol and manganese dioxide. Check it out at the link here. Now measure

out 20 mils of ethanol. It doesn't matter if this isn't dry. Add the ethanol to the

benzaldehyde solution in the flask. And now add the aqueous cyanide solution to

the flask containing the ethanol and benzaldehyde. To begin with you won't

see much happen. The solution is just a slight yellow color at this stage. Set up

for reflux with the flask on a hot plate and very gently refluxing the solution.

It doesn't need to be too fast. Just a slow and steady reflux. If you are doing

the reaction using only a few grams of benzaldehyde, you can get away with

heating in a conical flask and using only a few grams of benzaldehyde.

We are going to leave this refluxing now for a total of two hours.

Throughout this period you will notice the color of the reaction mixture slowly

turn a darker orange color. Here we are after two hours. At this point we removed

the condenser and allowed some of the alcohol to evaporate off the reaction.

Once we saw solid forming on the side of the flask, we removed the flask from the

heat. Here's the flask cooling down. The contents get down to just above room

temperature but are still quite liquidous. You can see here it's fun to

make our product crystallize on demand. We scratched the flask with a glass rod.

Very quickly crystals start to form. And then suddenly the whole mass

crystallizes. The contents of the flask are pretty solid as you can see. We tip

the contents into a cinter and filter them off.

Wash the flask out with a little cold water. Then use this to wash the solid in

the filter. This will remove any cyanide salts left. Then finally wash with 10

mils of ice-cold ethanol. Dry the solids well on the pump to create a fine

powder. And here's a portion of our product. We got 7.2 grams of benzoin

which is a 72% yield on starting benzaldehyde.

We could recrystallize this but the product seems pretty pure as it is.

It has quite a delicate faint aromatic aroma and no almond like benzaldehyde

smell remaining. We'll use this for some future experiments.