In this video we'll show you how to produce a decent sized quantity of .

aldehyde by the oxidation of benzyl alcohol using ammonium persulfate.

Do note that this is a difficult reaction to get, right? .

It took us 12 attempts before we got it, to work every time, and over 2 months of work, .

to get it to video.

So watch carefully, and we'll try to explain everything in, detail.

At the end we'll show you some of our, failed attempts so you can learn from these too.

Start by weighing out 180 grams of aldehyde.

85 grams of ammonium persulfate.

This will be our oxidizing agent for the reaction.

Place a stir bar into a large beaker with the, persulfate and add 150 mils of water.

Get stirring and apply a little heat, the water won't, be enough to dissolve the persulfate .

just yet.

Our aim is to dissolve in the minimum amount of, water at room temperature as possible.

More water is you need, and you, should end up with about 300 mils of solution like, this.

Now prepare the reaction vessel, you'll need a 1 liter, 2 or 3 neck flask with strong stirring, .

a thermometer, inside, and an addition funnel.

This needs to fit into a hot water bath.

Measure out 85 mils of benzyl alcohol.

Benzyl alcohol doesn't mix with water, which is one reason, why we need to add a little .

stirring for this reaction to, work.

Add the benzyl alcohol to the liter flask.

And now add 100 mils of water to the flask.

We find this helps dilute, the oxidizing power of the, first portion of persulfate added, .

and stops the reaction getting, out of control.

These form separate layers, so lower the apparatus into the, water bath and start, stirring vigorously.

This will help dilute the oxidizing power of the, first portion of persulfate added, .

and stop the reaction getting, out of control.

Now make sure your addition funnel tap is closed, and, fill it up with the persulfate .

solution.

Persulfate is an oxidizing agent, but its reactions seem to, be initiated and propagated .

by a free radical mechanism.

This gives us a problem, because the radicals are only, generated in a reasonable amount .

in solution above a certain, temperature.

But once the radicals are formed they can cause a, reaction.

Chain reaction and rapidly cause an out of control reaction.

So temperature control is absolutely critical and you'll need to, watch very carefully.

Heat the water bath up so that both the water, bath and the flask contents, are at around .

52, 55 degrees C.

Now measure out 20 mils of methanol, methanol here is, going to help act as a solvent for .

the benzyl, alcohol.

But its on the, top, bottom.

going to provide protection it's relatively low non azeotropic boiling .

point will help stop the flask temperature rising too fast if anything .

goes wrong and it's out of control so add this to the flask now with the .

temperature between 50 and 55 degrees C it's time to add our first portion of .

persulfate open the tap and allow about 15 mils of the solution into the flask at .

this point the temperature is too low for a fast reaction so now get the .

stirring as fast as possible and slowly increase the temperature aiming for the .

low 60s from this point keep a constant watch to notice there is any temperature .

difference between the water bath and inside .

the flask .

and here's our first sign a two degree difference in the flask the contents are .

heating at this point you'll start to see a slight yellow color in the flask .

as well as the radical reaction kicks off the .

temperature rises up but not too high at this point start adding persulfate .

solution to the flask steadily not too fast and not too slow .

you .

want to keep the temperature in the flask about three to four degrees above .

the temperature in the water bath add too slowly and the temperature will drop .

and the reaction will stall this is dangerous because persulfate will build .

up in the flask and when it all reacts it could get out of control .

it's a delicate balance and you'll have to experiment to find the right point if .

the temperature does shoot up .

the persulfate and let it run its course until the temperature drops again use .

some ice to cool the water bath down and then start again add a portion of .

persulfate and then warm until you find the kickoff temperature then start .

addition again now we're radical surfing our kickoff temperature was about 65 .

degrees and awards the end of the addition the water bath was at 68 as you .

complete addition took about an hour we then left the solution stirring in the .

water bath and slowly cooling for 30 minutes switching off the stirring you .

can see that the top layer has turned a nice orange color we then place the .

flask in a cool water bath and allowed it to cool for another 30 minutes you .

can allow it to cool without the water bath but be careful and watch the .

temperature .

in one experiment we did this and the reaction kicked back off again we'd .

accidentally build up a large excess of persulfate in the solution which was .

unreacted .

place the room temperature reaction mixture into a separating funnel .

just fit allowed the layers to separate completely then drain off the aqueous .

bottom layer you could extract the .

water from water weER Cobb aqueous bottom layer you could extract the aqueous bottom layer you can extract the aqueous bottom layer you can extract the aqueous providers run inि .

layer using dichloromethane but we've found in practice it doesn't make much .

difference to the yield so we're just going to discard this here's our top .

layer with an incredible strong sweet almond smell of benzaldehyde we are .

going to create a bisulfite a duct to purify this weigh out 110 grams of .

sodium bisulfite this is excess to what we need but it will help a duct .

now we need to make a saturated solution start with about 150 mils of .

water and vigorous stirring add more water as you need you should end up with .

about 250 mils of a solution like this now set up your separating funnel so you .

can slowly add the benzaldehyde to the bisulfite solution add the benzaldehyde .

slowly with constant strong .

stirring you'll start to see a pale yellow precipitate forming in the .

solution this is our bisulfite a duct forming keep the stirring going for a .

good 20 minutes to ensure complete formation use a metal spatula to break .

up any lumps if they form now set up for vacuum filtration there's a lot of a .

duct so be generous with the filter .

get the product as dry as you can on the pump to begin with allowing it to .

dry for at least 15 minutes .

then wash out the flask with 50 mils of cold water and use this to wash this .

solid in the funnel again get the solid as dry as you possibly can now we need .

to wash the a duct we'll use 50 mils of dichloromethane to do this how well .

this step will determine the color of your final product mix the solid really .

well and smooth out any lumps now filter again and allow to dry for 30 minutes on .

the pump repeat this process if you want a less orange colored product a lot of .

the color he has come out in the wash our duct looks okay so we'll stop at one .

wash this time we broke up our reduct and allowed it to air for a few hours to .

remove any residual dichloromethane now weigh out 120 grams of anhydrous sodium .

carbonate if you're using hydrate then adjust accordingly add 200 mils of water .

and as before stir to .

form a warm saturated solution adding more water is needed then with vigorous .

during add the bisulfite adduct to the sodium carbonate solution to start with .

this will form a suspension but you'll immediately smell the benzaldehyde being .

reformed keep stirring for a good 20 minutes to lava adducting hydra lies we .

then added an extra 100 mils of water to .

aid separation of the benzaldehyde when stirring is stopped the product starts .

to form as a top layer on the liquid it takes a little while to separate .

completely so finally we place back into the separating funnel allow the layers .

to separate completely and then drain off the aqueous layer then we collect .

our product in a storage bottle .

and here it is slightly brown colored but otherwise quite pure benzaldehyde 74 .

grams which is a spectacular 86 percent yield on starting benzyl alcohol this .

reaction is tricky to get right but yields rewards when you learn its .

secrets it definitely requires some chemical surfing to get right .

now let's show you some of the ways you can mess it up .

the easiest mistakes are either using too high a temperature or taking too .

long to do the addition you'll see the liquid turn orange then brown above 70 .

to 75 degrees the oxidation of the benzaldehyde becomes very rapid and you .

end up with benzoic acid and organic char .

go too slow on addition .

and you're giving more time for oxidation to occur your reaction mixture .

could end up looking like this and your workup will be even worse .

the product no longer smells of benzaldehyde but has an unpleasant burn .

aroma even slightly Phenolic .

keep the reaction as short as you can but it as low a temperature as possible .

here's another example we kept the temperature at 60 degrees .

degrees but added very slowly over four hours thinking that this might work the .

result on cooling was beautifully solidified benzoic acidous a top layer .

finally we tried using 50% methanol as a co-solvent to see if this would speed up .

the reaction but on separating a product we got this again massive over oxidation .

of the benzaldehyde to benzoic acid so start out small and try this out good luck .

you .