macckone
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Benzoic Acid Synthesis options
The traditional method of benzoic acid synthesis is via potassium permanganate. However this is quite expensive if you want to produce larger
quantities.
It can be bought as sodium benzoate but at a cost of $6/lb for USP/FDA grade.
Toluene is relatively inexpensive $5/gal.
I am exploring options for cheap conversion.
Vapor phase air oxidation seems like the cheapest alternative but requires a relatively complex setup. This is the commercial method.
I have come across a high pressure liquid phase method with MnO. Which requires an autoclave.
As well as a hydrogen peroxide method. But hydrogen peroxide can get expensive in large quantities.
Does anyone have any other methods?
I am currently looking at lower temperature liquid phase catalysts but they tend to be exotic, expensive compounds.
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CobaltChloride
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Using oxone (chlorine free pool disinfectant) might work, although I'm not 100% sure it will. It is similar to hydrogen peroxide in many organic
oxidations.
[Edited on 6-9-2018 by CobaltChloride]
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SWIM
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Okay, I'm gonna have to look this up to find some more details,but there's a method that uses sulfur.
I think it just came down to sulfur, water, and toluene in an autoclave heated to something like 280 or 300C. For a few hours.
Result: benzoic acid and hydrogen sulfide.
It was a reversible reaction, and getting high yields involved some trick to deal with the hydrogen sulfide and shift the equilibrium so the reaction
would run to completion.
I'm pretty sure it's in one of the books I have around. Maybe the supplement to Feiser's advanced organic topics (Or something like that.)
Of course I realize this is a nasty process for home use, but hey, sulfur, water, toluene...that is a truly OTC ingredients list.
edit: temps were 200C to 400C, and the reaction was driven to completion by sulfur dioxide which reacted with the sulfide to make more sulfur.
And yeah, it does sound like a lot of pressure.
But doing high pressure work with home-made gear can be fun.
Nothing like sitting around waiting to see if it''s going to rupture or not.
(Don't sit right next to it.)
[Edited on 7-9-2018 by SWIM]
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Xrpdguy
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The easiest way to obtain a benzoic acid is from sodium benzoate which as you said you can buy a supply store and it isn't very expensive. You have
to know that benzoic acid is insoluble in cold water so before doing the whole process you will need to boil a water and disolve sodium benzoate in
it. Then let it cool to about 50°C and add 18% hydrochloric acid which was from refrigerator (acid MUST be cold). Immediately white precipitate with
faint odor will be produced.
You can easily calculate the amount of sodium benzoate and hydrochloric acid you need for the reaction.
To separate benzoic acid from the solution (which will be I suppose sodium chloride) you can use vacuum filtration or a gravity filtration with coffee
filter.
Purifying of benzoic acid you can do by recrystallize from the water.
Then just dry the crystalls.
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DraconicAcid
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Water and toluene at 280 oC? That's going to be pretty high pressure- 63 atm for the water, and a similar amount for the toluene. Unless you're
working with very small quantities.
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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Sulaiman
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What kind of volumes are you considering synthesizing ?
Unless this is a commercial venture I can not imagine diy being cheaper than commercial
e.g. https://www.ebay.co.uk/itm/600g-Benzoic-Acid-99-6-high-purit...
... I assume that you do not intend to work at large scale due to your per lb. cost of sodium benzoate
https://www.ebay.co.uk/itm/1kg-Sodium-benzoate-food-grade-hi...
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clearly_not_atara
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There's no method using toluene that will be cheaper than buying sodium benzoate. If you want to do it anyway, you could try using photocatalytic
oxidation over nanostructured TiO2, which is available for purchase as a heterogeneous catalyst or can be prepared by the sol-gel process:
http://www.plasmachem.com/shop/en/-type-p25/283-pl-tio-p25.h...
This might become economical if you intend to produce more than 20 kg of benzoic acid -- God knows what for, but I should warn you it won't be
considered food-grade without a government certification.
[Edited on 04-20-1969 by clearly_not_atara]
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macckone
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Sulaiman - those prices aren't very good for the US.
Clearly_not_atara - cool catalyst
SWIM and Draconic Acid - unfortunately an autoclave isn't in the cards.
Cobalt Chloride - that might actually work, I think the oxi-clean (sodium percarbonate) would be cheaper though as the potassium persulfate (oxone) is
outrageously expensive.
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CuReUS
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Go through the benzaldehyde thread.Most of the methods to make benzaldehyde give benzoic acid if overdone.My favourite is this -https://www.sciencemadness.org/whisper/viewthread.php?tid=22... (Apparently they used to make bathtubs of benzaldehyde by this method  )
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JJay
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Phenylmagnesium bromide + carbon dioxide
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macckone
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The homemade persulfate is an interesting twist. A couple of solar panels and that would be zero cost beyond equipment.
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