In part 1 of this video we'll prepare what is known as active or chemical .

manganese dioxide. This has an extremely high surface area. To begin with weigh out .

50 grams of potassium permanganate into a large 600 ml beaker. Then add a magnetic .

stir bar and place this on a hot plate. Now add 150 ml of warm water and .

commence stirring vigorously whilst heating the mixture gently. It is very .

easy to dissolve. Otherwise we'll have permanganate crystals in our product .

and these will mess up subsequent reactions. At around 60 degrees and .

adding a little more water if you need to you should get all the crystals to .

dissolve. At this point the crunching sounds from the stir bar will disappear.

Now weigh out 70 grams of manganese sulfate monohydrate crystals into .

the water. If you have anhydrous salt or a different hydrate then adjust accordingly.

Dissolve these in as small an amount of water at room temperature as you can.

This will take quite a bit of stirring so be patient. In our case it took around 150 ml of .

water to dissolve and form a nice pink solution. Now slowly add the manganese sulfate solution to .

solution the reaction will produce a bit of heat so go slowly and don't allow .

this to boil you'll see a dark colored precipitate forming in the beaker this .

will gradually get thicker and thicker as you add the manganese sulfate .

solution and you will see the purple color of the permanganate slowly .

disappear allow to stir for a good hour and you'll end up with a dark brown mud .

a bit like this ours was quite warm and bubbled when agitated we think this may .

be oxygen gas being produced by slight decomposition now filter the mud we use .

the strengthened filter paper for this but be aware that the mixture is quite .

acid and may dissolve paper filtration is slow .

and takes a lot of time.

It takes a few hours to get a semi-dry product don't worry if the filtrate is .

slightly pink with unreacted permanganate now watch the semi-dry .

product with 400 mils of cold water and green filter your filtrate at the end of .

the wash should be colorless the brown mud will stain all your glassware and .

equipment here's a tip on how to clean it off .

prepare a dilute solution of sodium bisulfide in water use this to wash your .

glassware or stained equipment magic after a few more hours of filtration you .

will have a semi-solid attractive-looking brown paste place this .

into an oven at 150 degrees C every hour check on the solid and use a spatuline.

to break it up eventually you'll get a fine powder and some small solid lumps .

pulverize these into a very fine dry powder and here's our chemical manganese .

dioxide around 65 grams are produced from the preparation which is pretty .

much quantitative considering that it's probably not 100% dry and maybe contain .

some salt impurities as well it's good enough for the .

the next step though .

in part two we're now going to use our active manganese dioxide to prepare .

benzaldehyde we decided to use all the manganese dioxide we prepared in the .

next step in order to do a test of its oxidizing power in theory two moles are .

needed to oxidize one mole of benzaldehyde .

alcohol but the efficiency may depend on the available surface area. We measured .

out 30 mils of benzyl alcohol. This was added into a three-neck flask fitted .

with a stir bar and on a water bath. We then measured out 80 mils of .

dichloromethane to act as the solvent. Our theory was that dichloromethane .

would dilute the alcohol and thus prevent overoxidation to benzoic acid. In addition, .

we figured that its low boiling point would stop the reaction mixture getting .

too warm and again protecting against overoxidation. Once this was added we set .

up the flask with a reflux condenser. Using ice and the cooling water and with .

vigorous stirring we bought the mixture up to reflux. We then oven dried a small .

glass of water for 20 minutes, taking it out of the oven, and then placed it in the .

funnel which would fit in one of the spare necks of the flask. Removing the .

stopper and working quickly we then added a small amount of the manganese .

dioxide into the flask and then restoppered the neck. Either due to a .

reaction taking place or a seeding effect we noticed an immediate increase .

and reflux. We continued with the process of slowly adding the manganese .

dioxide powder over the following hour. Once it was all added the magnetic .

stirring continued to work well and we left the flask refluxing for a further .

hour on the water bath then allowed it to cool slowly down to room temperature.

Cooling took place.

It took a while as if the flask was still producing some heat due to the .

reaction taking place. Here's the final reaction mixture in the flask.

By the way the manganese dioxide gets everywhere you least expect it to so .

have some sodium bisulfite solution handy for cleanup.

We then filtered the reaction mixture using a filter pump compared to the .

filtration in the flask.

In part one this was pretty simple with the dichloromethane solvent and took a .

few minutes. The reaction flask was a mess so we used a further 50mL of DCM to .

wash this out thoroughly.

As you can see the filtrate had a yellow-orange color.

We then switched off the pump and thoroughly mixed the black solid with a .

further 40ml of DCM.

in order to get all our product out then filtered again we then repeated the DCM .

wash and then got the solid completely dry on the pump the black solid is now a .

mixture of manganese oxides and we saved it because we're sure we can recycle .

this back into manganese sulfate and then more manganese dioxide here's our .

filtrate we placed this on a hot water bath and evaporated off the DCM using a .

vacuum pump you could also distill the solvent off if you wanted to recycle it .

we ended up with an amber colored oil which we measured and was 27 mils and .

volume this had a very strong sweet almond aroma .

you .

to purify this you could vacuum distill it but we decided to do a bisulfite .

purification .

prepare 150 mils of a saturated sodium bisulfite solution in water .

this takes around 80 grams and lots of stirring .

add the crude benzaldehyde to this solution and then stir well for a period .

of 15 minutes .

be patient as it can take a while for the adduct to form and it requires a lot .

of stirring and breaking up any lumps to get it to completely react the adduct .

isn't completely crystalline so we can see that there's probably some residual .

benzal alcohol in here as well as benzaldehyde we gave this a really .

thorough stirring and then filtered the solid adduct to form we have this very .

through a glass sinter.

We then washed this twice using around 20 ml of dichloromethane.

Thoroughly stirring together, the idea was that this would remove any benzyl alcohol .

and other organics trapped in the adduct.

The adduct as you can see was quite a nice, pure white color and a crystalline solid.

Now we prepared a saturated solution of sodium carbonate and 150 ml of water as before, make .

sure the solution is saturated.

Add the crystalline bisulphide adduct from the filter into this solution and stir well, .

again being patient.

As it can take a while to completely react, the adduct first floats and then over 10 minutes .

with stirring dissolves and separates into a layer of our benzaldehyde product.

We placed the mixture into a separating funnel and drained off the bottom aqueous layer.

We allowed the mixture to stand to let as much water separate as possible, then drained .

the product into a container.

We then poured the mixture into a small flask.

We used some anhydrous magnesium sulfate to remove all water, present, and then filtered .

into a storage container.

And here's our product, 12.6 grams of benzaldehyde.

This is a 43% yield on our starting benzyl alcohol, which isn't too bad and is actually .

comparable to the real-life yields produced by some other oxidizing agents.

The benzaldehyde is a very good solution for the adduct.

It can be used in a variety of ways, such as per sulfate and copper or iron nitrate.

We'll keep playing around and seeing if we can get the stoichiometry just right on this .

one because it seems to a very convenient method and doesn't seem to over oxidize.