TheNaKLaB
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Terephthalic Acid to Phthalic Anhydride
Hey ScienceMadness,
Would it be possible to turn Terephthalic Acid into Phthalic Anhydride? Or could Terephthalic Acid can be heated and turned into its Anhydride. Wiki
says that Terephthalic Acid sublimes at 402 degrees Celsius, but I'm unsure if it will dehydrate into it's anhydride (if it has one)
It would be very much appreciated if someone could help! Thank you for your time.
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kavu
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Phthalic acid anhydride is the anhydride of ortho-phthalic acid. Orto-phthalic acid (or commonly phthalic acid) is the only one of the three
benzenedicarboxylic acids to form an intramolecular anhydride. This is purely for steric reasons. For condensation to occur in an intramolecular
fashion the carboxylic acid groups have to be in close approximity for orbitals to overlap. This is not the case for terephthalic acid where
carboxylic acid groups are far apart in para-position. Heating will ultimately lead to degradation of the acid.
[Edited on 22-12-2011 by kavu]
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TheNaKLaB
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Ohk so if I heat it, it wont change the structure of the molecule. Would there be any way of changing the terephthalic acid to ortho-phthalic acid?
Bringing the carboxylic groups closer together from para to ortho?
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kavu
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Benzene rings are rigid systems stabilized by aromaticity. There is no simple way of swaping the position of carboxylic acid groups within the ring. A
DIY synthesis of o-phthalic acid from o-xylene might be one of the easiest. Oxidation of alkyl subsituted aryl compounds (for example with KMnO4) will
lead to cleavage of the alkyl chain and formation of COOH group.
Another method is the extraction of o-phtalic acid from vinly gloves as shown in many videos on youtube.
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TheNaKLaB
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I might try oxidizing o-xylene to make phthalic acid. Thanks for you help! very much appreciated!
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