Here we will synthesize mandelic acid and interesting aromatic alpha-hydroxy, .

acid.

First measure out 15 grams of benzaldehyde ours is a bit discolored but relatively pure .

and free from benzoic acid.

First we need to create the bisulfide adductive benzaldehyde, so weigh out 30 grams of sodium .

bisulfite this is more than we need but the adduct forms better if you use an excess quantity.

Add a stir bar and then add 50 ml of water.

Need to dissolve the bisulfide in order to make a saturated solution, stir well and add .

water as needed to dissolve but go slowly as the dissolution will take some time.

We needed just over 60 ml of water and about 10 minutes of stirring.

Now with vigorous stirring slowly add the benzaldehyde to the saturated solution once .

all added you'll see the adduct forming as a cream colored.

Add crystalline lumpy solid in the beaker, and you'll notice the temperature of the .

beaker rise.

Once formed it's very important to use a spatula to break up all the lumps in order .

to ensure all the benzaldehyde reacts.

Spend some time doing this properly.

Keep stirring for at least 15 minutes and baking up the lumps and you should end up .

with a very fine precipitate like this.

Once completed.

You'll notice a quite significant temperature increase.

Filter the precipitate, allow to dry and then wash with 10 ml of cold water.

It's worth noting that if you ever want to purify an adduct such as this, you can wash .

it with cold ether or dichloromethane in order to remove unwanted organics without dissolving .

the adduct.

The next step is to nucleophilically attack our adduct.

Using an alkali cyanide salt.

We are using 15 grams of mixed sodium potassium cyanide.

This is in excess to what we need to use but the reaction goes faster.

Add 40 ml of water to dissolve most of the cyanide.

Be sure to take care with cyanide salts and solutions.

Place the adduct into a 200 ml beaker and add a magnetic stir bar.

Add the cyanide solution and begin rapid stirring.

The adduct will slowly dissolve and form an orange colored mixture.

Continue stirring for 20 minutes at the end of this period.

You should see the mixture separate into two layers.

Place the mixture into a separating funnel and separate in.

Reserve the oily top brown layer.

This contains our crude mandelonitrile intermediate.

Add the cyanide solution and begin rapid stirring.

Place the aqueous layer back into the funnel and then wash this with 50 ml of toluene.

This will extract out any dissolved mandelonitrile.

Separate the toluene layer and carefully dispose of the aqueous layer containing cyanide.

Combine the product and toluene layers in the funnel and wash with 10 ml of saturated .

sodium bisulfite.

Add 50 ml of saturated sodium chloride solution.

This will remove any unreacted benzaldehyde.

Finally, wash the product and toluene mixture with 50 ml of saturated sodium chloride solution.

Reserve the orange top layer and place into a 250 ml round bottomed flask.

The next stage of the reaction is to hydrolize the mandelonitrile.

Add 40 ml of concentrated hydrochloric acid to the The next stage of the reaction is .

flask this will form a lower layer .

stir the mixture using a magnetic stir bar .

and set up for simple distillation we will distill off the toluene .

from the mixture and perform the hydrolysis at the same .

time .

as you distill you'll see a mixture of toluene and .

water coming off which will form layers in the receiving .

flask a lot of HCl fumes are also produced so .

be sure to use ventilation .

after about an hour you should have distilled off all the toluene .

at this point add a further 20 mils of hydrochloric acid to the boiling flask .

and continue to heat for a further hour .

then transfer the remaining liquid into a 200 mil beaker .

and boil it down on a hot plate until only 15 .

to 20 mils of liquid remains .

as the liquid starts to cool you'll immediately see crystals .

appearing add a few grams of salt to saturate the .

remaining hot liquid this will help all the mandelic acid .

to precipitate .

chill the mixture down to form a thick slurry of .

crystals .

place these into a filter center and then use vacuum .

to get as much of the orange liquid off as possible .

it turns out that mandelic acid is not soluble in cold chloroform so we can use this to .

get rid of some of the organic impurities .

add 15 mils of cold chloroform and break up the solid in the center .

then turn on the pump again and dry the solid as much as possible .

we're now left with a crude mixture of mostly inorganic salts and mandelic acid .

mandelic acid is soluble in diethyl ether whereas the inorganic .

salts are not, so we can use this to extract .

our product .

add 50 mils of yether to the solid obtained .

you'll see a large portion dissolving immediately .

stir the mixture well to get as much solid dissolved as possible .

then filter off the ether containing all of the orange and this will give us the final arm of the mix .

product the solid remaining should be washed with a further 40 mils of ether .

and this filtered through again combine the ether portions and evaporate the .

dryness be careful not to allow the mixture to absorb moisture and be very .

careful with inflammable ether vapor use gentle heat when removing the last bit .

of ether from the crystals but don't go too hard or the crystals will melt and .

potentially decompose we now need to remove organic impurities we do this by .

adding 15 mils of chloroform to the product and then gently heat until .

boiling on a hot plate using a spatula to break up all the lumps carefully then .

chill this mixture down for 30 minutes until it is ice-cold and then filter the .

crystals .

you can see the orange color fading wash the crystals again with two .

portions of 15 mils of ice-cold chloroform drying thoroughly in between .

each wash on the final wash you'll see most of the yellow disappear and the .

crystals will be almost white if you have no chloroform then die chloromethyl .

will also work but you will encounter greater losses of product here's our .

final dried product off white and odorless crystals of mandelic acid .

we obtained 8.94 grams of product which corresponds to a 42% yield from .

starting benzaldehyde this is okay but we are sure it can be improved we will .

keep trying .

literature references suggest recrystallization from benzene but this .

seems difficult and the quantities of solvent required are large this approach .

may be the next best alternative note that the we have created a mixture of .

optical isomers of the product fifty percent of each an antium or of mandelic .

acid .

you .

Thanks for watching! .