Materials I used
Thymol 15g
phthalic anhydride 30g
Concentrated 98% Sulfuric acid 5ml
Acetone 25ml
The reaction is very similar to the synthesis of phenolphthalein and the reaction mechanism is also exactly the same.
Start by finely grinding together thymol and phthalic anhydride in a mortar .I did a mistake without doing that and I ended up in a much low yield.
After grinding them together to an intimate powder it was added to a round bottom flask. Then 5ml of 98% Sulfuric acid was added and then mixed well.
The flask was placed in an water bath and heated to around 90°C for 15minutes. By this time the contents in the flask would liquefy and attains a
beautiful red color. This indicates the formation of thymolphthalein insitu and the red color is the color of thymolphthalein in highly acidic media.
After 15minutes the flask was allowed to cool down to room temperature.
NOW THE QUESTION IS HOW TO SEPERATE AND ISOLATE THE COMPOUND
I first tried using boiled water
The Melting point of thymol is around 50°C
But thymolphthalein has high mp around 230°C.
So on adding bot boiling water the residual thymol would melt and it can be discarded by decanting the liquid.
But a better option I found was to just keep the flask in boiling water bath.
After keeping the flask for 1hr in the water bath probably most of the phthalic anhydride would have dissolved in it and thymol got liquified and was
removed
The compound was then filtered and washed with more water
Then the product was dried and dissolved in acetone. Acetone is pretty useful here as it selectively dissolved thymolphthalein (and probably thymol if
anything is present !!!)
And the phthalic anhydride was left undissolved. It was then filtered and then the solution was recrystallized to obtain much pure thymolphthalein.
It's a pretty useful indicator to identify superacids.
It's used as disappearing ink as some amount of thymolphthalein dissolved in sodium hydroxide gives a deep blue color. It was then painted on some
paper and then after sometime it disappears as the pH gets lowered by reaction of atmospheric air gases like CO2 /SO2 .
Amateur chemist. Doctor by profession
Have a small cute home chemistry lab.
![[*]](images/xpblue/default_icon.gif){kind=icon}
