okelly4408
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Nickel Boride Catalyzed Hydrogenation of Cinnamaldehyde
Hello.
I got some helpful replies on a previous post I had made here:
https://www.sciencemadness.org/talk/viewthread.php?tid=16103...
But just wanted to start a new thread as this is a slightly different topic. I want to definitely come back to the Raney nickel method though and will
soon.
Special thanks to @bnull if you are reading for recommending that book "Catalytic Hydrogenation". Ended up picking it up on Amazon and am determined
this weekend to construct a makeshift Brown hydrogenation system.
But before that I did a test of nickel boride based hydrogenation w/ in situ H2 production to reduce the alpha-beta conjugated double bond present in
trans-cinnamaldehyde.
I charged a 1000 mL 3-neck round bottom flask with around 300 mL of cold methanol, 50 mL ice cold H2O, 2 grams of NaOH, ~9 grams of nickel (II)
chloride hexahydrate, and about a gram of slightly wet chromium (III) chloride that I prepared from a little dichromate. A paper I read on the subject
of nickel-boride catalysis mentioned the use of promoter salts of various metals to aid in reduction so I decided to give this a try with the chromic
chloride hydrate.
(not particularly relevant but who doesn't love green crystals?)
I placed the flask in an ice bath and attached a stirrer bearing (a rather cheap PTFE one that I have since replaced with a CG-2077 as there was
definitely some significant H2 leakage) with a glass shaft set to around ~450 RPM throughout the reaction and a reflux condenser. The reflux condenser
had an outlet adapter leading to some tubing, a check valve, and finally to a wash bottle containing a ~10 cm head of silicone oil.
For the substrate I dissolved ~50 grams of the cinnamaldehyde in 200 mL dry, cold methanol and added this to the stirring reaction mixture.
Finally, I dissolved around ~40 grams of sodium borohydride in a 250 mL 0.1 M NaOH 4:1 MeOH : H2O solution and poured this into a pressure equalized
addition funnel that I then attached to the flask.
Temperature in the flask was kept to around 5 C as all of the borohydride was added to the flask over the course of around 25 minutes. During this
time period, bubbling in the flask was very light but I was concerned as to why there wasn't any bubbling in the wash bottle like at all. Soapy water
test revealed a slight leak in the tubing coming out the reflux condenser take off adapter with which it was plugged (rookie move, I know) and after
fixing this hastily I did get some light pops of H2 bubbles but still not as much as I'd expect. Ended up diagnosing this later as the stirrer bearing
rocking too much causing me to spend a little more than I had planned on aforementioned chemglass part.
After all of the borohydride was added, I allowed the reaction to warm up to at a max 35 C. Under 32 C it seemed to proceed quite slowly. I performed
TLC throughout and after an additional shot of borohydride just to soothe my mind and around 4 hours I decided chasing the complete disappearance of
the last of the unreacted cinnamaldehyde still showing up on the plates to not be in the cards that night.
(Two TLCs taken during the process. Left Lane "A" is the cinnamaldehyde, right lane "B" is the sample from the reaction. Included both (poorly)
vanillin and KMnO4 stained examples)
After neutralizing the borohydride with some ammonium chloride and filtering out the black granules of Ni B catalyst, I was left with a large amount
of hazy ammonia smelling liquid.
I added cold water, extracted with some ether and ethyl acetate, and washed with brine. After removing the solvent, I was left with an only faintly
cinnamon but newly floral and a little...balsamically smelling orangish liquid weighing around 39 grams
TLC still shows cinnamaldehyde but upon staining the spot is noticeably ghostly and only lightly oxidized by KMnO4. UV light reveals a very non-polar
impurity as well of some sort. I will clean this up with a chromatography column or vacuum distillation when I get a chance to isolate the pure
hydrocinnamaldehyde.
As mentioned earlier, I plan to repeat but this time keep the H2 creation to a separate flask and set up borohydride addition in such a way that only
more H2 is generated when some gets consumed by the catalyzed reduction.
Apologies for the messiness of the post/images. Please let me know if you have any tips or tricks that you think might be helpful. Thanks for reading.
[Edited on 16-5-2025 by okelly4408]
[Edited on 16-5-2025 by okelly4408]
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DraconicAcid
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Are you sure you got the hydrocinnamaldehyde, and not cinnamyl alcohol? I wouldn't expect the two aldehydes to have very different Rf values. I know
the alcohol is quite floral (literature smell is hyacinth, but I tried an entire class of students, and half of them said it smelled like flowers, and
the other half like roses).
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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okelly4408
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Quote: Originally posted by DraconicAcid  | | Are you sure you got the hydrocinnamaldehyde, and not cinnamyl alcohol? I wouldn't expect the two aldehydes to have very different Rf values. I know
the alcohol is quite floral (literature smell is hyacinth, but I tried an entire class of students, and half of them said it smelled like flowers, and
the other half like roses). |
I am not certain but due to the selectivity of the catalyst, the blue-ish color produced by the vanillin stain, and the amount of oxidation by the
KMnO4 I suspect is the aldehyde. The Rf difference between the two if the product is indeed the aldehyde could be down to my eluent which is slightly
on the polar side (4:1.5 hexane:ethyl acetate + a little DCM) producing a noticeable delta w.r.t. the more polar saturated one. Interesting point on
the smell, definitely could be mistaken.
I plan on confirming the identity with some Schiff's reagent once I clean up my sample so I'll let you know if you are interested.
Thanks!
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