Sciencemadness Discussion Board

Diethyl Phthalate Acid Hydrolysis

Abromination - 24-7-2019 at 21:31

I recently came across a cheap source for diethyl phthalate and am planning to hydrolyze it to phthalic anhydride synthesis. Would it be better to mix the diethyl phthalate directly with the HCl and reflux or first dissolve the phthalate in isopropanol?

Tsjerk - 24-7-2019 at 23:06

Why don't you use NaOH? The product of the hydrolysis will be soluble so you have a nice visual endpoint and you can heat the reaction without producing clouds of HCl.

Making the anhydride is a nice experiment! The anhydride sublimes and solidifies as beautiful needles upon cooling, you could use techniques described for purifying iodine.

Abromination - 25-7-2019 at 14:22

I see no problem with base hydrolysis, I do suppose having a visual endpoint would be nice. I have made it from extracting the DEHP plasticizer from PVC and hydrolyzing with base, so it should be fine. I just love the crystal shape of the anhydride, it almost looks like glass wool.
I have a fume hood now, but avoiding the HCl would be nice.

DavidJR - 25-7-2019 at 14:49

I would advise using acid hydrolysis with HCl rather than base hydrolysis. I've tried both (albeit with a different phthalate ester) and found acid hydrolysis to be more convenient, even though it's theoretically reversible. In practice, the equilibrium is driven by the fact that the product phthalic acid is insoluble in both ester and aqueous layers. It can be filtered off and used directly without the need to acidify later so it's faster, more convenient, and less wasteful.

Beware though that converting the acid to the anhydride by heating and subsequent sublimation of the anhydride is VERY tedious and time consuming for quantities of more than a couple of grams of product. I suggest using a dean stark trap + mixed xylenes (not toluene, on account of lower boiling point) to remove the water formed by dehydration instead of trying to sublime off the product anhydride.

Oh, nearly forgot to answer the question. There is no need to add isopropanol.

Of course the other option is to just buy the anhydride - I got a kilo from Sigma for a surprisingly cheap price.

[Edited on 25-7-2019 by DavidJR]

Abromination - 25-7-2019 at 18:13

Quote: Originally posted by DavidJR  
I would advise using acid hydrolysis with HCl rather than base hydrolysis. I've tried both (albeit with a different phthalate ester) and found acid hydrolysis to be more convenient, even though it's theoretically reversible. In practice, the equilibrium is driven by the fact that the product phthalic acid is insoluble in both ester and aqueous layers. It can be filtered off and used directly without the need to acidify later so it's faster, more convenient, and less wasteful.

Beware though that converting the acid to the anhydride by heating and subsequent sublimation of the anhydride is VERY tedious and time consuming for quantities of more than a couple of grams of product. I suggest using a dean stark trap + mixed xylenes (not toluene, on account of lower boiling point) to remove the water formed by dehydration instead of trying to sublime off the product anhydride.

Oh, nearly forgot to answer the question. There is no need to add isopropanol.

Of course the other option is to just buy the anhydride - I got a kilo from Sigma for a surprisingly cheap price.

[Edited on 25-7-2019 by DavidJR]


I didn't think so, although some methods suggest adding the isopropanol to increase solubility, although usually for different plasticizers. I am glad to go without.
I only need a few grams at a time, I am not planning on a mass synthesis, most of my projects are on small and quantitative scales.
I see no reason to try both methods, although I have had problems with base hydrolysis with other phthalate plasticizers.

Tsjerk - 26-7-2019 at 01:40

Cool! keep us updated!