RabbitTy
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Why some compounds may disappear in TLC?
TLC is always be using as monitor method.I found that some compound would disapear in TLC after several hours.However, The boiling point of these
compounds is not that low.
Can someone help me explain the mechanism?
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Ubya
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an example of a compound that does this would be helpful
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feel free to correct my grammar, or any mistakes i make
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Metacelsus
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Sometimes compounds react with silica gel and decompose.
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Cactuar
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If you are using fluorescent TLC plates they show spots by glowing under UV-light, but any aromatic compound (or in other way conjugated) will absorb
this light, showing dark spots. Any compound with a significant vapor pressure will eventually evaporate if it's not polar enough to be held by the
silica. Xylenes boil at around 140 C and would probably disappear within 10 minutes. If you ever eluate anything with toluene you wont be able to read
the TLC the first few minutes until it evaporates. When synthesizing small simple aromatics you quickly learn to circle any spots with a pencil.
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RabbitTy
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O-chlorobenzonitrile is one of them
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RabbitTy
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O-chlorobenzonitrile is one of them
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RabbitTy
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Quote: Originally posted by Cactuar  | | If you are using fluorescent TLC plates they show spots by glowing under UV-light, but any aromatic compound (or in other way conjugated) will absorb
this light, showing dark spots. Any compound with a significant vapor pressure will eventually evaporate if it's not polar enough to be held by the
silica. Xylenes boil at around 140 C and would probably disappear within 10 minutes. If you ever eluate anything with toluene you wont be able to read
the TLC the first few minutes until it evaporates. When synthesizing small simple aromatics you quickly learn to circle any spots with a pencil.
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Thus its not depend on the boiling point solely. Thanks a lot
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RabbitTy
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O-chlorobenzonitrile is solid at r.t.Benzoonitrile is liquid ar r.t.
However, Benzoonitrile wont disappear in TLC, O-chlorobenzonitrile will.
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unionised
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Other possibilities are oxidation or hydrolysis catalysed by SiO2
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