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cinnamic acid

lilly - 29-8-2009 at 14:11

The mild oxidation of cinnamaldehyde should obviously yeild
cinnamic acid. I have read of no one doing this.I think a rhodium file I read said permanganate on a solid support oxidized a cinnamic acid to the benzaldehyde.
Can anyone suggest a procedure with a good chance of
oxidizing to the acid with out touching the double bond.
i have Mno2 and peroxide any ideas as to best solvents and reagents to try would be most helpful.

DJF90 - 29-8-2009 at 15:36

All you need is an oxidant that does not cleave or alter double bonds. MnO2 is no good as it is designed to oxidise allylic alcohols without overoxidation to the acid (i.e. it stops at the aldehyde). Perhaps jones reagent is applicable here, although id double check that... Sodium chlorite (NaClO2) is also used specifically for this kind of transformation (i.e. aldehyde to acid, in the presence of a,b-unsaturation amoungst other things). Workup would be much easier and cleaner than using jones reagent/chromic acid.

In fact, conversion of allylic alcohol to allylic acid is preferably done in two stages using MnO2, then NaClO2, rather than the "simpler oxidation" with chromic acid because it is generally cleaner and higher yielding. Obviously you wouldnt need the MnO2 oxidation as you're starting with the aldehyde.

[Edited on 29-8-2009 by DJF90]

Klute - 29-8-2009 at 16:20

I guess you could use H2O2 with a iron catalyst, have a look in the "oxidation of benzylic alcohols" thread for details, I don't think you will have epoxidation in none-basic envinronement. Hey even NaOCl could do the job, if buffered.

DJF90 - 29-8-2009 at 16:27

Yes H2O2 oxidation in a non-basic environment may also work, but dont adjust the pH too low or you will have significant decompostion of the peroxide. I don't even think an iron catalyst would be needed Klute, but I havent seen the thread so I'm not in a great position to comment on that. There are numerous reagents that will work for the reaction, its just a matter of finding the one that works best, and often one method will excel far above the others.

cinnamic acid via the Perkin reaction

Magpie - 4-9-2009 at 12:51

I have recently prepared cinnamic acid via the Perkin reaction per Brewster et al, 1960. This a base (NaOAc) catalyzed condensation reaction between benzaldehyde and Ac2O.

In an 8" x 1" test tube 10.1 mL of benzaldehyde (homemade), 11 mL Ac2O (homemade), 1 mL pyridine (homemade) a catalyst, and 12g of technical anhydrous NaOAc were mixed with a stirring rod. The NaOAc did not dissolve well, most remaining as a slurry.

The reaction tube was equipped with an air condenser and placed in a hot oil bath (silicone brake fluid, DOT 5). The bath was placed on a stirrer hotplate. The hotplate was powered through a PID controller with a thermocouple for temperature control. The heating schedule was: 2 hours at 145C followed by 5 hours at 175C. Some tar formed right away and turned the reaction mix dark brown. Also, much of the NaOAc settled to the bottom of the tube. See photo below:

Temperature control was quite satisfactory throughout. When the gummy reaction mix had cooled it was laboriously removed from the test tube via spatula and placed in a 1000 ml RBF with 250 mL distilled water. The tarry mix was then steam distilled to remove unreacted benzaldehyde. This produced about 125mL of condensate. The product was then basified with NaOH solution. This was then filtered into a 1000mL Erlenmeyer flask:

[Edited on 4-9-2009 by Magpie]

[Edited on 4-9-2009 by Magpie]

The filtrate was then acidified by addition of muriatic acid. This resulted in the formation of a massive amount of fine flake crystals of cinnamic acid. This was Buchner filtered and the cake redissolved in 850 mL of boiling water. The flask was allowed to sit for a few hours while the cinnamic acid recrystalized. The crystals were again Buchner filtered then allowed to dry overnight.

The 3.7g of crystals were very light and fluffy, and had a slight yellow cast, which I suspect is from residual tar. Melting point was 134C which is in agreement with literature values for trans-cinnamic acid. Expected yield was 61%, actual yield was 25%, based on the amount of benzaldehyde charged.

[Edited on 4-9-2009 by Magpie]

Discussion
Although Brewster mentioned that there would possibly be some tar I was very surprised at the amount. Perhaps my homemade, somewhat impure, reactants contributed to this.

All the undissolved NaOAc was also somewhat plagueing. This residual just formed a hard mass on the bottom of the tube. I doubt the procedure authors intended that result.

Next time I would pour the reaction mix into the RBF before it had a chance to cool and solidify.

When I saw the heavy tar formation early in the heating period I didn't have much hope for any yield. I am happy with the product as the mp indicates high purity despite its yellow cast.

I'm looking forward to making some hopefully nice smelling esters with the product using methyl, ethyl, and benzyl alcohols.

A 2007 mechanism:

[Edited on 4-9-2009 by Magpie]

[Edited on 4-9-2009 by Magpie]

from: http://www.springerlink.com/content/h45v0h1782637462/

[Edited on 4-9-2009 by Magpie]

jon - 4-9-2009 at 13:57

hmm jon is interested in cinnamic acid esters also cinnamic anhydride is easily prepared from this by forming the mixed anhydride with acetic anhydride.
the boiling point of acetic anhydride is very close to the m.p. of cinnamic acid the reaction is driven by distillation of thelower boiling acetic acid b.p. 118 this may work since the mixed anhydride is a different animal.
the procedure calls for piping the anhydride into heated cinnamic acid.
jon thinks it could be added dropwise or just added in portions.
but propionic anhydride seems prefereable.
since it's b.p is 172 and propionic acid boils at 130~ or so the points are broader and the acid distills closer to the m.p. of cinnamic acid.

entropy51 - 5-9-2009 at 11:12

Magpie, your yield is much better than mine was. I followed the procedure in Vogel 4th edition on a scale of 21 gm benzaldehyde. I used NaOAc (purchased, anhydrous) instead of KOAc. All reagents were purchased commercially. The procedure looks very much like yours, but there is no pyridine. I can't tell if you used stirring during the reflux, I suppose you did; I did stir it magnetically. My notes say the reaction turned yellow, not dark brown, for what its worth. My notes don't mention how much tar was produced, but it was filtered, per Vogel, to remove "resinous byproducts".

After recrys. from H2O/EtOH, the mp was low (124 vs 133) so the recrys. was repeated using only water. Yield was 2.8 g (9.6%) and mp = 131-132 C. Vogel gives the expected yield as 18 g (62%).

All in all, I think you did a great job. This prep is a Dog.

crazyboy - 5-9-2009 at 11:21

Anything interesting that cinnamic acid can be used for? Google didn't yield much.

Magpie - 5-9-2009 at 11:50

re: entropy51

Thanks for the comparison of results. As you can see my reaction mix wasn't just yellow, it was dark brown. What amazed me is how fast the tar formed even at 145C. But it probably doesn't take much to cause heavy coloration.

No, I had no stirring of the reactants in the test tube. A stir bar was used to keep the silicone oil temperature uniform. Stirring of the reactants looks like a good idea although Brewster did not call for it.

I agree that this procedure has a canine pedigree.

It was probably my dirtiest synthesis ever. But it did give some product.

Did your NaOAc give the appearance of not dissolving?

entropy51 - 5-9-2009 at 13:10

Brewster didn't mention stirring because college labs didn't have magnetic stirrers in those days. But you're too young to remember that.

My notes didn't mention anything about the NaOAc not dissolving, but it's been too long for me to remember. I probably would have noted it if that had happened.

From my perspective, you did a fine job. With stirring you might get even more.

jon - 5-9-2009 at 14:15

that's a tough mechanism to pick apart.

Magpie - 5-9-2009 at 14:25

Quote:

Brewster didn't mention stirring because college labs didn't have magnetic stirrers in those days. But you're too young to remember that.

That's true and was my guess too. I wonder what Perkin used. We didn't have ground glass fittings either - just bored stoppers.

I checked my Vogel and it specifies 12g of NaOAc. This is the same amount that Brewster specifies yet the benzaldehyde and Ac2O are about half those of Vogel. That may be an error in scaling down and would explain what appeared to be a gross quantity of NaOAc.

jon: Right, I gave up on trying to understand it after about the first line or so. But I thought I should present what appears to be the latest thinking on the Perkin reaction.

[Edited on 5-9-2009 by Magpie]

entropy51 - 6-9-2009 at 10:20

Quote: Originally posted by Magpie

We didn't have ground glass fittings either - just bored stoppers.

I'll bet you didn't have heating mantles either. We used bunsen burners for everything in my organic class. Surprisingly we never had an ether fire, but we did have one benzen fire during the two semester course. The TA put the fire out in about 30 seconds.

When we did Grignards we flame dried the glassware. Before they brought the ether in the TA went around and confiscated all the burners. Worked quite well to prevent accidents.

Everado E. Dinavo - 9-9-2009 at 16:19

Cinnamaldehyde is also oxidized by atmospheric O2 to cinnamic acid rather rapidly. I have observed this occur on glasswhere where some cinnamaldehyde traces were left on overnight, resulting in pale yellow, nearly white crystals with a much different odor. Also, the lid of cinnamaldehyde bottles can be found to have these crystals and the odor if they have been aged for a few years. I am fairly certain this is not the aldehyde hydrate that is forming, because I have specifically read that cinnamaldehyde needs to be stored away from oxygen to prevent oxidation. I never actually tried to identify the crystals, but I might give it another try since it requires about no work, provided you already have the cinnamaldehyde (which you say you have, Lilly). Just pour out a thin layer of cinnemaldehyde into the bottom of a beaker or petri dish, or even a plate and just leave it until it turns into crystals. The conversion should be good as long as the surface area is high.

[Edited on 9/10/2009 by Everado E. Dinavo]

zed - 9-9-2009 at 19:58

Got aniline? Under the proper conditions, Diazonium Salts, couple nicely with acrylic acid esters, to form cinnamic acid esters. Good yields.

True, aniline is impressively toxic, but reactions of this type, can be used to produce materials, that are very interesting, and very hard to produce by other methods.

Sleipnir - 11-9-2009 at 00:52

maybe a oxidation with hydrogen peroxide could be appropriate like in "Hydrogen peroxide oxidation of aldehydes to carboxylic acids: an organic solvent-, halide- and metal-free procedure "
by Kazuhiko Sato, Mamoru Hyodo, Junko Takagi, Masao Aoki and Ryoji Noyori

(can't read the paper actually)

since i haven't got malonic acid i like the idea of making cinnamic acid from cinnamaldehyde ...

[Edited on 11-9-2009 by Sleipnir]

zed - 11-9-2009 at 17:18

On the other hand, utilizing the diazotization of the amino-acid Phenylalanine, you could form either the halo-acid, or the hydroxy-acid.

Upon dehydration, or de-hydro-halogenation, cinnamic acid should be produced.

This might appear to be an expensive method for producing cinnamic acid.

But, if feasible, there is a rationale for the approach.

In this era, of difficult reagent accessibility, Phenylalanine is very easy to acquire.

There are no shipping problems. And, it isn't very expensive. With almost no effort, I was able to find DL Phenylalanine for sale, for 39.99/Kilo or 15.00/300grams.

[Edited on 12-9-2009 by zed]

JohnWW - 11-9-2009 at 20:03

By DL-phenylalanine, I presume you mean the racemic mixture of its two stereoisomers, marketed as a nutritional supplement for its supposed analgesic and antidepressant activities, which must be produced synthetically as only the L-stereoisomer occurs naturally as one of the about 20 essential amino-acids constituting natural proteins. I am somewhat surprised that it is still so readily available, though, because of its potential for conversion to phenethylamine, and possibilities for conversion of this by methyl or methoxy etc. substitutions to amphetamine or methamphetamine or related psychoactive compounds.

zed - 11-9-2009 at 22:01

Phenylalanine is not easily convertible to any amphetamine. Though it can be done.

It is however, readily convertible to phenethylamine.

Fortunately, most chemists have chosen to NOT pursue, the unenlightened path, of phenethylamine based analgesic synthesis.

More specific to this thread, Phenylalanine might serve as a practical starting material for a fairly simple cinnamic acid synthesis.

Phenylalanine is readily available, at least, here in the States, and the acquisition of reagents like Benzaldehyde or Acetic Anhydride, can be fairly difficult .

[Edited on 12-9-2009 by zed]

benzylchloride1 - 16-9-2009 at 21:08

I recently conducted two experiments with the Perkin Reaction. I attempted to synthesize cinnamic acid from benzaldehyde, acetic anhydride and triethylamine as a base. 10ml of benzaldehyse, 15ml acetic anhydride and 7 ml of triethylamine where heated together with stirring in a 100ml rbf with condenser for 3 hours. The mixture was then added to water, steam distilled and a large amount of unreacted benzaldehyde was recovered and used for a synthesis of alpha phenyl cinnamic acid. The resulting residue in the still pot was boiled with decolorizing charcoal, filtered and strongly acidified with 12m HCl. After cooling, 0.24g of producted crystallized, for a incredible percentage yield of 2%! I have not taken the Mp yet.
My synthesis of alpha cinnamic acid was much for successful.
5.0g of phenyl acetic acid, awful smell, 6.0 ml benzaldehyde, 4.0ml of triethylamine and 4.0ml of acetic anhydride were heated together in a 50ml rbf with condenser for 1.5 hours. The work up was according to the procedure specified in Williamson, Microscale and Macroscale Organic Experiments, since it is to long winded to repeat at this moment. 3.56g of product was obtained in a percent yield of 47%, I have both E and Z isomers isolated according to the procedure, I still need to take melting points.

[Edited on 17-9-2009 by benzylchloride1]

Waffles SS - 24-1-2014 at 10:17

My experience:
Benzaldehyde 63 gr,90 gr Ac2O, 33gr Sodium acetate ,2gr pyridine
reaction time:6hour
Yield: 58gr impure(30gr pure)
According to Vogel 5th.experiment 6.138.page1038

[Edited on 24-1-2014 by Waffles SS]

DraconicAcid - 24-1-2014 at 11:12

Cinnamic acid is nicely oxidized by chlorite; you just have to have a scavenger in there to make sure any hypochlorite that is generated doesn't attack the double bond or chlorinate the ring.

I took 6.3 mL of cinnimaldehyde, 1.6 g sodium dihydrogen phosphate, dissolved them in 20 mL water and 30 mL isopropanol, and added 6 mL of 30% hydrogen peroxide. In a separate flask, I dissolved 8.0 g sodium chlorite in 50 mL water, and slowly added this, with stirring to the first solution. I let it stir an hour (it warmed up, and gave an orange oil that floated on top). After cooling well in an ice bath, I got 6.58 g of off-white crystals (89% yield), mp 131.5-133.2 oC).

Recrystallizing it from isopropanol (3.8 g in 20 mL, heat to dissolve, cool in ice to precipitate) gave a much smaller yield (0.9 g) of white crystals (mp 132.2 - 133.9 oC).

I tried a similar trial with a few drops of phosphoric acid added, thinking that a slightly lower pH would speed up the reaction. It gave similar yield and mp, but the initial foaming and evolution of an orange-yellow gas put me off of trying that again.

DJF90 - 25-1-2014 at 10:56

If you're following a literature procedure please provide a reference. Do you really think you need so much hydrogen peroxide as a scavenger in the Pinnick oxidation?

Chlorite reacts with acid to liberate ClO2, hence the yellow-orange gas you observed with phosphoric acid.

DraconicAcid - 25-1-2014 at 11:19

Quote: Originally posted by DJF90

If you're following a literature procedure please provide a reference. Do you really think you need so much hydrogen peroxide as a scavenger in the Pinnick oxidation?

I'm not an organic chemist- I was following this patent:
http://www.freepatentsonline.com/4549025.html

If you've got a better reference, I'd be delighted to read it.

Quote:

Chlorite reacts with acid to liberate ClO2, hence the yellow-orange gas you observed with phosphoric acid.

Yes, I figured that out myself, thanks.

[Edited on 25-1-2014 by DraconicAcid]

Hoffnung - 30-1-2014 at 10:59

Hi all,

I will be also interested in preparing cinnamic acid from cinnamaldehyde soon, surely the next Spring. Since I don't have chlorites I am looking up for feasible alternatives. I wonder if anyone have tried this one yet:
http://www.freepatentsonline.com/4778924.html
The 8 h of reaction time is discouraging, but I guess that 40ºC is more or less the same as leaving it on the sun in Summer, so it looks interesting.

I'm looking for a reference on the method that Everado E. Dinavo said but I can't find it.

Another method I found in a book is the oxidation using the Tollens reagent, but there aren't any details/recipe.

Well, I'm posting my method and results as soon as I make it. See you.

ChemistryGhost - 13-10-2014 at 08:38

Can cinnamic acid be obtained from cinnamaldehyde by reacting with aqueous sodium hydroxide. Would it yield sodium cinnamate and cinnamyl alcohol?

Dr.Bob - 13-10-2014 at 08:48

Quote: Originally posted by ChemistryGhost

Can cinnamic acid be obtained from cinnamaldehyde by reacting with aqueous sodium hydroxide. Would it yield sodium cinnamate and cinnamyl alcohol?

I am guessing that would yield a mess. Aldehydes are one of the easiest things around to oxidize. Just leave the bottle open to the air a while, and it will be partially oxidized to the acid. If you want to speed it up, you can use any strong oxidant, Jones, likely permanganate, or even just bubble air through the aldehyde. It is hard to seal a bottle of aldehyde well enough to prevent this from happening even due to traces of air.

Amos - 13-10-2014 at 12:41

Quote: Originally posted by crazyboy

Anything interesting that cinnamic acid can be used for? Google didn't yield much.

Esters. Esters that smell nice. Maybe some more practical things too...

bbartlog - 13-10-2014 at 20:00

Quote: Originally posted by ChemistryGhost

Can cinnamic acid be obtained from cinnamaldehyde by reacting with aqueous sodium hydroxide. Would it yield sodium cinnamate and cinnamyl alcohol?

Cannizzaro Reaction. No. Cinnamaldehyde has a hydrogen in the alpha position and therefore is not part of the scope of this reaction.

Oxidation should work, you just have to figure out which reagent would minimize attacks on the double bond and arene ring. Basic reaction conditions seem unlikely to be favorable ... maybe one of these two:

http://en.wikipedia.org/wiki/Pinnick_oxidation
http://dx.doi.org/10.1002/cjoc.200890199 (but I don't trust this paper)

UnintentionalChaos - 13-10-2014 at 20:41

Quote: Originally posted by bbartlog

Quote: Originally posted by ChemistryGhost

Can cinnamic acid be obtained from cinnamaldehyde by reacting with aqueous sodium hydroxide. Would it yield sodium cinnamate and cinnamyl alcohol?

Cannizzaro Reaction. No. Cinnamaldehyde has a hydrogen in the alpha position and therefore is not part of the scope of this reaction.

*buzzer*

Cinnamaldehyde -is- subject to the Cannizzaro reaction as it is a non-enolizable aldehyde. It may have a hydrogen on the alpha-position, but keto/enol tautomerism is never going to make an allenyl alcohol from the vinyl proton.

Of course, you have a competing retro-aldol condensation to benzaldehyde and acetaldehyde. detailed elsewhere on this site. Refluxing carbonate solution works best if this is desired, IIRC. Room-temp grinding with NaOH or KOH would probably best promote the Cannizzaro.

DraconicAcid - 8-5-2015 at 16:56

Quote: Originally posted by Amos

Quote: Originally posted by crazyboy

Anything interesting that cinnamic acid can be used for? Google didn't yield much.

Esters. Esters that smell nice. Maybe some more practical things too...

I made some methyl cinnamate. A solid at room temperature, which really didn't smell like anything to me.

Magpie - 8-5-2015 at 17:47

I made ethyl cinnamate from cinnamic acid by mimicing a procedure in Pavia et al for methyl salicylate. According to my notebook: "Ester had a rich fruity smell."

Texium - 8-5-2015 at 18:43

Maybe it will smell stronger if dissolved in some methanol. I wouldn't imagine that the pure solid ester would have much of an odor to it.
Although I imagine that at some point in the production of it you would have had such a solution that you would have smelled, so perhaps not.

DraconicAcid - 8-5-2015 at 18:56

Tried that. Even put some on a filter paper and waved it under my students' noses to see if they could detect anything. Nope.

Pumukli - 9-5-2015 at 03:17

Hm. Last year someone posted a report on an odorless raspberry ketone batch. Now this odorless cinammic esther. Doesn't it ask for a deeper investigation?

zed - 16-5-2015 at 13:08

I would imagine Hydrogen Peroxide would perform this oxidation nicely. Or not.

I doubt that low concentration H2O2 would have enough punch to effect that double bond. Though maybe. Performic acid surely would.

Magpie - 12-6-2017 at 06:07

Over the last few days I made another batch of cinnamic acid per Brewster (exp 71). Per procedure I used a paraffin bath to hold a temperature of 175°C for 7hrs with the help of a PID controller. Again, there was a massive amount of undissolved NaOAc. I still suspect this is a mistake by Brewster, ie, charging so much NaOAc (12g). The benzaldehyde charge was 10.1ml, and Ac2O 11ml.

The yield was 5.7g (Brewster 9g) for a %yield of 38.5%. This is much better than my previous yield of 25% (see upthread).

I was fastidious in my lab technique but my homemade benzaldehyde and pyridine are several years old, so am surprised by the better yield. MP was 134°C per literature.

[Edited on 12-6-2017 by Magpie]

DraconicAcid - 12-6-2017 at 08:08

Quote: Originally posted by DraconicAcid

Tried that. Even put some on a filter paper and waved it under my students' noses to see if they could detect anything. Nope.

Just following up on this- I found that if I put a bit of the solid in a beaker of warm water, it smelled nicely of strawberries.

Chemi Pharma - 21-7-2017 at 17:22

A mild oxidant to obtain aldehydes or acids from alcohols and acids from aldehydes is nickel peroxide, or nickel oxide hidroxide, made from nickel salt and bleach.

It's an OTC procedure to produce cinamic acid from cinnamaldehyde or cinnamyl alcohol, among an extense row of aldehydes or acids from it's alcohols or aldehydes, depends upon wich enviroment to use:

Alkaline aquous enviroment afford acids salts from alcohols and aldehydes and anhydrous organic solvents enviroment such as benzene, ether, dichlorometane or petroleum ether gives aldehydes from alcohols.

Although this method gives poor yields starting from aliphatic saturated alcohols, the yields increases with benzilic and insaturated alcohols.

The studies sais also that low temperatures helps the oxidation, by this method, of benzilic alcohols with aliphatic chain, like 2-phenetyl alcohol and 3- phenylpropyl alcohol into the respective acids withouth the cleavage of the methylenic groups adjacent to the benzilic ring, like happens with common oxidating agents as KMnO4, Jones reagent, persulfate, oxone or peroxides.

Great way to afford kilos of phenyl acetic acid from the common and cheap 2-phenetyl alcohol, sold at perfumary fragrance stores.

I'm bringing below two papers attached that studies the mechanims of the reactions and show examples how to exactly produce cinnamic acid from cinamyl alcohol and cinnamaldehyde in excellent yields at the experimental section:

Attachment: alcohol Oxidations with nickel peroxide (NICL2 + NAOCL).pdf (567kB)
This file has been downloaded 527 times

Attachment: Alcohol Oxidation to acids with NiCl2 + hypochlorite.pdf (653kB)
This file has been downloaded 577 times

Loptr - 28-3-2019 at 09:00

I am in the middle of moving and can't test this out since everything is packed away, but based on some reading about the oxidation of aldehydes through their hydrates, wouldn't it be feasible to prepare cinnamic acid using a modification of this synthesis of coumarin? Is an actual oxidizing reagent actually needed for this reaction?

Replace the chlorosulfuric acid with p-toluenesufonic acid. Addition of the p-toluenesulfonic acid to the cinnamic acid shouldn't take place, and coumarin won't form.

Quote:

Synthesis of coumarin
This reaction was conducted by adopting method from Sudarma.

To stirred solution of cinnamaldehyde (1) (1003 mg, 7.8mmol) in dichloromethane (20mL) was added chlorosulfuric acid (2mL) drop by drop. The solution was stirred at room temperature for 30 min then refluxed for 15 min. The solution was evaporated and water (10mL) then added, basified to pH 8 with 1M sodium hydroxide, then extracted with dichloromethane. The organic phase was dried and evaporated to dryness to give brown gum (685mg).

TLC and GC-MS analysis showed coumarine (44.63%).GC-MS: M+ .146, cal for C9 H6 O2. Major fragments: 118 (base peak), and 65 (Figures 3 & 4).

[Edited on 28-3-2019 by Loptr]

DraconicAcid - 28-3-2019 at 12:34

You mean this paper? lupinepublishers.com/chemistry-journal/pdf/AOICS.MS.ID.000144.pdf

I don't know how reliable their results are, but their proposed mechanism is crap. They show "scheme 1" for the oxidation of cinnamaldehyde to cinnamic acid by the addition of a hydroxide ion to the carbonyl, and then a hydride ion just "falls off" with no oxidizing agent. You need an actual oxidizing agent.

Loptr - 28-3-2019 at 12:49

Quote: Originally posted by DraconicAcid

You mean this paper? lupinepublishers.com/chemistry-journal/pdf/AOICS.MS.ID.000144.pdf

I don't know how reliable their results are, but their proposed mechanism is crap. They show "scheme 1" for the oxidation of cinnamaldehyde to cinnamic acid by the addition of a hydroxide ion to the carbonyl, and then a hydride ion just "falls off" with no oxidizing agent. You need an actual oxidizing agent.

Yeah, that is the paper that grabbed my interest. I understand the proposed mechanism is crap, and why I didnt post the actual paper. However, I do know how sensitive aldehydes are to oxidation, so I was curious if it was possible for the oxidizer to be oxygen from the air at reflux temperatures in this case.

Of course the oxygen is going to oxidize the aldehyde, but is this effective?

[Edited on 28-3-2019 by Loptr]

DraconicAcid - 28-3-2019 at 13:05

Not if you actually want it to. If you want your cinnamaldahyde to stay pure, then of course it will oxidize to the acid. If you're trying to oxidize it to the acid, it will just sit there thumbing its carbonyl at you. I tried several different oxidants before settling on sodium chlorite (see the previous page of this thread, where I'm told it's the well-known Pinncik reaction and that I was doing it wrong).

Loptr - 28-3-2019 at 13:11

Quote: Originally posted by DraconicAcid

Not if you actually want it to. If you want your cinnamaldahyde to stay pure, then of course it will oxidize to the acid. If you're trying to oxidize it to the acid, it will just sit there thumbing its carbonyl at you. I tried several different oxidants before settling on sodium chlorite (see the previous page of this thread, where I'm told it's the well-known Pinncik reaction and that I was doing it wrong).

Yes, I am familiar with your work on cinnamaldehyde oxidation with sodium chlorite. I have done this reaction myself as well. Very simple.

I was also thinking of trying out the NiCl2/NaOCl method posted here recently, too.

How were you doing it wrong?

DraconicAcid - 28-3-2019 at 13:17

Apparently I was using far too much hydrogen peroxide. But, hey, it still works for the majority of my students, and if it isn't broken, why fix it?

Fery - 8-7-2020 at 03:32

I did the same synthesis as Magpie and Waffles SS, just without pyridine.
The catalyst base I used was Na acetate, no need to use pyridine. K acetate should be better as K cinnamate is better soluble than Na acetate. Neither me achieved the yield claimed in literature.
At first I post all links and info I had available, then my experiment itself in the following post
https://webcache.googleusercontent.com/search?q=cache:MsU4k3...
https://labmonk.com/synthesis-of-cinnamic-acid-from-benzalde...
benzoic acid (contaminant) solubility in water 1.7 g/L (0 °C) 2.7 g/L (18 °C) 3.44 g/L (25 °C) 5.51 g/L (40 °C) 21.45 g/L (75 °C) 56.31 g/L (100 °C)
route from benzaldehyde and ethylacetate into ethyl cinnamate using sodium+absolute ethanol (very likely the base is Na ethoxide):
http://orgsyn.org/demo.aspx?prep=cv1p0252
http://orgsyn.org/Content/pdfs/procedures/cv1p0252.pdf

here look for page 181, chapter 4.7.7 Perkin reaction, this seems to be superior source for this synthesis with a lot of practical + explanation, if you would like to read only 1 source from all here available, read this one
https://www.pdfdrive.com/advanced-practical-medicinal-chemis...
https://www.pdfdrive.com/download.pdf?id=41004348&h=ebab...
I'm attaching the book for case it will disappear
Attachment: Advanced Practical Medicinal Chemistry ( PDFDrive.com ).pdf (3MB)
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Fery - 8-7-2020 at 04:12

To 250 ml RBF (perhaps 100 ml is better, less air, less benzaldehyde oxidation to benzoic acid, on the other hand the reaction was quite spattering so 250 ml volume helped here a bit) was placed 20 g benzaldehyde (0,188 mol) + 30 g acetic anhydride + 10 g powdered anhydrous Na acetate (12 g K acetate should be better). Condenser attached (air condenser should be enough but I used Claisen condenser with water circulation) and closed with drying tube filled with anh. CaCl2. The flask was heated on oil bath warm 180 C for 8 hours (T varied between 175-185 C, variation does not have significant impact on the reaction as the temperature inside flask depends on refluxing temperature inside). Still warm reaction mixture was poured into 200 ml of cold water in 1 L beaker (do not allow the product to cool down in the flask as it solidifies) and the flask was washed with little of boiling water which was added into the beaker too. To the beaker was slowly added concentrated solution of 87 g Na2CO3 . 10 H2O in water with CO2 evolution - cinnamic acid neutralized to litmus indicator paper. NaOH cannot be used (Cannizzaro, unreacted benzaldehyde would produce benzoic acid and contaminate the product). It was poured into 1 L flask, volume adjusted to 600 ml and unreacted benzaldehyde was steam distilled out, approx 250 ml of distillate collected from which recovered 6,1 g benzaldehyde as bottom layer (wet weight, not purified further), most of it was in first 100 ml of distillate, then slightly turbid distillate came from condenser but after 250 ml the turbidity was very small and no scent of benzaldehyde. As cinnamic acid is in Na salt that prevents it from steam distilling.
Volume in flask adjusted to 400 ml, heated to boil and immediately very quickly filtered using heated funnel. On cooling down Na cinnamate tends to crystallize (perhaps it could be purified in the form of its Na salt). 60 ml of 35% HCl added into hot solution (to congo red indicator) at which the cinnamic acid precipitated. The volume was adjusted with water and heated to boil so all the product dissolved (1400 ml total volume). Then it was slowly cooled down to room temperature and then put into fridge overnight at 4 C. Crystals obtained in a form of lustrous leaves, vacuum filtered, they had a volume of approx 25 ml on the sintered glass funnel. Recrystallized from 1400 ml of boiling water, now the crystals in very fluffy form, with a total volume of approx 150 ml. Air dried on filter paper until the weight stopped to cease (man, 5 days !!!), then packed into 50 ml vial pressing crystals by a spoon.
Yield 11,4 g (0,077 mol = 41%)
m.p. 134-135 C.

The benzaldehyde used for the reaction should be free of benzoic acid (contamination of the product). It was purified by washing with solution of Na2CO3, drying with anh. Na2SO4, vacuum distilled (vacuum is preventing oxidation to benzoic acid).
But according the solubility of benzoic acid, 5 g of benzoic acid could be removed from the product in almost 3 L of water used for 2 crystallizations as 1 L of water dissolves 1,7 g of benzoic acid at 0 C.
Solubility of cinnamic acid is only 0,5 g in 1 L of water at 25 C (better soluble in boiling water).

the method which I used from my chem book (sorry, it is not in eng)

reaction (the oil in bath is very old and dark)

reaction done

getting rid of unreacted benzaldehyde by steam distillation

Na cinnamate in solution prior acidfication with HCl

first crystallization