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

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