njl
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O-Cresol from Salicylic acid
To the point: Can I reduce salicylic acid to cresol or will I just end up with a bunch of phenols?
Forgive me if this is a silly question. Inspired by my father who used to work in the fragrance industry, I recently began an adventure into smelly
chemicals. In particular, those derived from plants (essential oils, "essence's") and currently my attention is on Oreganol (cymophenol). Following a
paper I've found, O-Cresol is a good starting point and I'm wondering if it would be possible to reduce Salicylic acid in order to obtain the cresol.
PS: As a very inexperienced amateur, I have a few more semi-related questions. Again, I apologize in advance if these are silly.
1. Say I have a cresol in an acidic solution. What group gets protonated (If any)? Is protonated the right word to use here?
2. Say I instead have just Salicylic acid in solution. Of the 2 Hydroxyl groups (does the part of the carboxyl group count as a hydroxyl group?) which
is more likely to be protonated?
3. I have read that leaving group behavior is different between aliphatic and aromatic compounds due to electron withdrawing behavior. My
understanding of this is probably weak, but from what I can wrap my head around the aromatic ring has a stronger hold on the electrons shared between
the carbon and (potential) leaving group. Why is this? For example, why does a hydroxyl group leaving hexanol behave differently than one leaving
phenol?
I am a junior in high school so while I would say I'm a bit more knowledgeable than my classmates, I'm generally unfamiliar with stuff like this so
any help is appreciated. Happy Holidays!
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DraconicAcid
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Reducing a carboxylic acid to an alkane is not easy. You'd have to turn it into an ester, use lithium aluminum hydride to reduce it to an alcohol,
and then get rid of the hydroxyl. The best way i can think of to do that would be to convert it into a halide, react that with magnesium to get the
Grignard, and hydrolyze it. That won't work with a phenol in the molecule.
If you have a cresol or salicylic acid in strongly acidic solution, the phenolic oxygen will get protonated.
A phenol will have some of its electron density shared with the carbons of the aromatic ring through resonance. Aliphatic alcohols don't. This makes
phenols stronger acids than alcohols, weaker bases than alcohols, and it's far less likely to get the hydroxyl to act as a leaving group (after you
protonate it, of course). Also, if you protonate off the hydroxyl of, say, cyclohexanol, you get a secondary carbocation (unstable but managable)
intermediate. If you do the same with a phenol, you get a phenyl carbocation, which is far less stable- the sp2 hybridized carbon is far less
willing to host a positive charge. This means it's much harder to form (and unlikely).
If you want to make things that smell nice, it's easier to focus on esters to start with.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Alucard
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Better policy to obtain o-cresol should be to start from toluene, as well by following route of synthesis :
Toluene -> o-nitrotoluene -> o-toluidine -> o-cresol
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njl
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| Quote: |
o-toluidine -> o-cresol
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This is interesting. I found a report on orgsynth for the para isomer but not the ortho. Would you mind filling me in on that procedure?
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Alucard
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p-cresol is a bit easier, because it may be derived from p-toluenesulphonic acid, easily made from toluene and sulphuric acid.
Both isomers -p and -o toluidine may be diazotized to yield corresponding cresol isomer. Even despite I'm not sure that o-nitrotoluene can be reduced
with Na2S to o-toluidine, you can surely do it by using metallic tin or iron, although p-nitrotoluene is compatible with Na2S and reduction occur
under Zinin reduction conditions.
So, generally yes - I think you have to try to perform diazotization of o-toluidine under ordinary conditions, say like the same way p-toluidine
diazotization should occur.
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