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Sciencemadness Discussion Board » Fundamentals » Organic Chemistry » Help in synthesis of Benzoic acid from Benzaldehyde

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vibbzlab

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posted on 21-5-2020 at 21:38

Help in synthesis of Benzoic acid from Benzaldehyde

Hello friends
I was looking for the preparation steps of oxidation of Benzaldehyde to benzoic acid using KMnO4 as oxidising agent.
I checked a lot of books and pdf. I couldnt find an exact synthesis steps and stoichiometry. can anyone give a detail on that. I am not looking for the cannizaro reaction, but the direct oxidation using permanganate
Thank you friends in advance

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karlos³

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posted on 21-5-2020 at 22:13

You can use this orgsyn procedure: http://www.orgsyn.org/demo.aspx?prep=cv2p0315
Heptanal is only slightly more soluble in water as benzaldehyde(1,25g/l opposed to 0,3g/l), so it should pose no problem.

If in doubt, you can employ a two-phase system using the aq. KMnO4 layer and an organic layer with the aldehyde and strong stirring.
A PTC agent will obviously help, but it is not needed.
I've oxidised a cinnamaldehyde analogue that is insoluble in water using KMnO4, in a two-phase system with DCM, and this worked good too despite not using a PTC agent.

So, whatever you decide to use, it will likely be easy and a success.
When I did the mentioned oxidation, I did so without having any reference for it, but I knew how it should be done, I could calculate how much would be needed to achieve that, and then simply tried it in the way I had imagined it.
And it did work like I thought about it, the yield could have been higher though, but at least I got some yield out at all.
And when you're in doubt, you can always draw a sample and check the reaction progress on a plate.

This is really pretty basic chemistry, and you can probably succeed without relying on a "recipe".
Just put your own method together and do a small trial run, because its really not hard.
After all, the experiment is king in chemistry, one can argue theory all day, but a little experiment and everything will be quickly settled.

Fery

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posted on 22-5-2020 at 04:43

wibbzlab, such a pitty converting benzaldehyde to benzoic acid... you can oxidize more available toluene with solution of KMnO4 (neutral initially which changes to alkaline during the reaction) - I did that oxidation with toluene decades ago (if you are interested I can post the method)
is your goal just to demonstrate the aldehyde -> carboxylic acid oxidation step ?
when oxidizing in alkaline the Mn7+ reduces to Mn4+ and necessity to process nasty fine MnO2 on which some product always adheres
when oxidizing in acidic the Mn7+ reduces to Mn2+

Boffis

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posted on 22-5-2020 at 06:25

Curiously I am currently doing a write-up for this forum on the Cannizzaro reaction which is the conversion of some aldehydes into an equimolar mixture of acid and alcohol, effectively a disproportionation reaction. I hope to post it in the next day or so.

In this case the source material was a small c100ml very old bottle of benzaldehyde that had acquired a crust of benzoic acid crust inside. Rather than purify it I thought I would simply try Cannizzaro's reaction on it. My aim is then to convert the benzyl alcohol into benzyl bromide using NaBr and H2SO4 and then convert this without isolation or purification into phenylacetonitrile. Watch this space.

TGSpecialist1

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posted on 22-5-2020 at 13:21

You can just use alkaline H2O2.