Sciencemadness Discussion Board

Phthalic Anhydrid is red?

Takron - 3-11-2011 at 18:41

When I started heating my Phthalic acid to make anhydride, all it did was fog up inside the beaker and condensed on the flask as a very hard yellow cake that I had to scrape off repeatedly through the process. After doing this and getting no anhydride crystal formation. The cloud turned red and how there is an orange condensate forming inside the beaker and the crystals are red-orange. If I had to describe it, it looks like bromine when its in the liquid phase. The crystals forming are equally red-orange.

Bot0nist - 3-11-2011 at 18:50

Did you synthesize it? Which isomer?

Takron - 3-11-2011 at 18:54

Yes I did. I believe it was ortho-phthalic acid.

woelen - 3-11-2011 at 23:52

Phtalic anhydride is white. I have a commercial sample of this chemical.

Probably you heated too strongly and your material started charring somewhat.

[Edited on 4-11-11 by woelen]

DJF90 - 4-11-2011 at 00:18

Quote:
When I started heating my Phthalic acid to make anhydride, all it did was fog up inside the beaker and condensed on the flask as a very hard yellow cake that I had to scrape off repeatedly through the process. After doing this and getting no anhydride crystal formation.


The "condensate" is actually a sublimate, and is your product anhydride. Turn down the heat and it shouldn't char so much. I think Magpie has done the phthalic acid -> anhydride prep here somewhere, look through his posts on the topic to find details that you need. What colour was your starting phthalic acid? Did you follow a published procedure (e.g. journal or textbook)?

Takron - 4-11-2011 at 07:40

I followed NurdRage's procedure for luminol and just was going to stop at the anhydride step. My phthalic acid was white and needly. When I heated it there was a dense white fog inside the beaker for a time but it was comming out the beaker like smoke and I got a few tiny bits of anhydride forming by the spout of the beaker but nothing ever looked like cotton candy inside the beaker. I am pretty sure it was some kind of condensate at the end because very red liquid was running down the sides of the beaker on the inside and very red crystals formed on the cooler at the top and if I'm not mistaken, sublimation is a solid to a gas.

Bot0nist - 4-11-2011 at 09:14

Did you use a controlled method of heating, or did you use open flame? Maybe try using a tall narrow beaker. Put a little foil skirt around the bottom 1/4 of the beaker, then cool the upper 3/4 of the beaker with moving air, a wet tissue, or both.

DJF90 - 4-11-2011 at 14:27

You said it condensed as ahard yellow cake...

Takron - 5-11-2011 at 08:40

semantics. The point of my question isnt' about the name of what happened its about why it was yellow and then turned red. it should have been white, and I don't know what would have caused this to be dark red. There was only phthalic acid and sodium chloride in the mix.