jamit
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identifying phthalic acid
today i acquired a melting point apparatus and so i decide to test it out using phthalic acid (MP ~207C) which I extracted from vinyl gloves several
years ago. What I thought was "phthalic acid" would not melt even at 340C, so I realize that it must be massively contaminated or it may not even be
phthalic acid at all.
My question is, how can I find out if my sample is phthalic acid? Is there a chemical test for phthalic acid? I googled it but the results came out
negative. If someone could steer me in the right direction, I would appreciate it. thanks.
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Volanschemia
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ortho-Phthalic Acid (what most people refer to when they say Phthalic Acid) will melt at 207C and will then decompose to Phthalic Anhydride and
sublimate. To test if it is Phthalic Acid, heat some up in a beaker and when it melts, put a round bottomed flask filled with cold water on top. If
it is o-Phthalic Acid, you will get cotton candy like crystals of Phthalic Anhydride condense on the bottom of the RBF.
If it doesn't melt and sublimate then it is not o-Phthalic Acid, but it could quite possibly be another isomer (iso- or tere-) or not even Phthalic
Acid at all.
Another way you could test it (which I have never done, but I think it would work), is to place a small amount in a flask with some Phenol and a
couple of drops of conc. H2SO4. If you get the red colour of Phenolphthalein form, then it should be Phthalic Acid.
Someone please correct me on that if it is plain wrong.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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UC235
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Is it possible that you also did a hydrolysis of PET plastic and may have your jars mixed up? Terephthalic acid sublimes at 400C.
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CharlieA
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Quote: Originally posted by TheAustralianScientist  |
Another way you could test it (which I have never done, but I think it would work), is to place a small amount in a flask with some Phenol and a
couple of drops of conc. H2SO4. If you get the red colour of Phenolphthalein form, then it should be Phthalic Acid.
Someone please correct me on that if it is plain wrong.
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Wouldn't you have to basify the phenolphthalien to observe the red/pink color? I believe that phenolphthalien is colorless in acidic solution.
I also wonder if this might be a way to synthesize phenolphthalein relatively cheaply. With my wife's appetite for Mountain Dew, I have an endless
supply of PETE starting material!
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gdflp
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PETE is polyethylene terephthalate, or polyethylene para-phthalate so that won't work. Phenolphthalein is prepared by the
condensation of phenol with ortho-phthalic acid.
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CharlieA
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Of course! Duh!!!!!! I guess my head us up my....My only defense is not enough coffee at the time of the post...or too much wine?
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Volanschemia
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| Quote: Originally posted by CharlieA |
Wouldn't you have to basify the phenolphthalien to observe the red/pink color? I believe that phenolphthalien is colorless in acidic solution.
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I think it would have to be in aqueous solution to go colourless, and as there is extremely little water in the reaction, most of the Phenolphthalein
formed is not dissolved.
I'm not sure if that's correct, but I know that the Phenolphthalein is dark red when it forms in the reaction between Phenol and Phthalic Acid.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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jamit
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Thanks guys. I'll give it a try this weekend.
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