Sciencemadness Discussion Board

Reduction of Ketones to alcohols in Tween 20 vs THF

FragranceLover89 - 29-10-2020 at 15:28

I am trying to reduce some ketones and diketones to alcohols using Zinc/ NH4Cl/THF. However, I want to use Tween 20 instead of THF to lower cost and because I don't want THF contaminating my product. I believe THF is somewhat critical due to its ability to act as a lewis base complexion agent. Can Tween 20 do the same thing?

Attachment: Hekmatshoar2002_Article_Zinc-PromotedReductionOf12-Dik.pdf (35kB)
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Texium - 29-10-2020 at 20:09

I highly doubt that it’s been tried before. Why don’t you give it a go?

FragranceLover89 - 29-10-2020 at 20:18

I want advice before I try it.

Texium - 29-10-2020 at 20:25

Well my advice is to try it.

It’s a very unconventional choice of solvent you have, so it’s hard to say whether it will work or not. It contains many ethers, so in theory it could plausibly serve the same purpose as THF, but it also has a much, much higher BP, so your alcohols better be volatile or you won’t have much chance of isolating them. I think it’s an interesting idea.

FragranceLover89 - 29-10-2020 at 20:47

I tried it today (incorrectly). One of the signs of progress is the disappearance of Zn metal. I cannot say whether any Zn reacted.

- Initially I let it stir for 3 hrs at room temperature but saw no color change.

- I was worried about tween being too acidic so I mistakenly added some NaHCO3, which produced ammonia with NH4Cl.

- I added more NH4Cl

- I put it on heat and I accidentally let it go to dryness (tween gets soapy). When I re-hydrated it the color had become darker.

- The paper says ketones are only reduced at 60C so I have to try this again with heat.

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Corrosive Joeseph - 29-10-2020 at 21:12

Mandal, T., Jana, S., & Dash, J. (2017). Zinc-Mediated Efficient and Selective Reduction of Carbonyl Compounds.
European Journal of Organic Chemistry, 2017(33), 4972–4983.

Abstract :
Simple yet unknown! Aldehydes and ketones can be easily reduced to the corresponding alcohols with Zn/NH4Cl, which is used for pinacol coupling reactions. Chemoselective reduction of aldehydes in the presence of ketones is achieved. Isatins can be efficiently reduced at the C3 position.



/CJ


Attachment: Zinc-Mediated Efficient and Selective Reduction of Carbonyl Compounds.pdf (1.3MB)
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FragranceLover89 - 29-10-2020 at 21:21

I will try again tomorrow.

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Boffis - 30-10-2020 at 04:13

Wouldn't PEGs (polyethylene glycols) and Glymes (alkoxyglycols) be a simpler choice or do you have a lot of tween 20?

FragranceLover89 - 30-10-2020 at 07:12

I already have a lot of tween 20. I found research saying tween 20 at 200 ppm offered maximal corrosion resistance to carbon steel by complexion with Zn2+ ions. Higher concentrations had diminishing returns. This might be the concentration I should aim for. Earlier I added 50% tween 20 to 50% aqueous NH4Cl, which might lead to monolayers of tween coating the zinc surface. Perhaps I need only a catalytic amount because tween can form micella above it's critical concentration.

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FragranceLover89 - 30-10-2020 at 07:36

I forgot to mention this reaction may have worked. The problem is I don't know how to distinguish between the alcohol and ketone I had. I read PQQ is a dione with different colored redox states. Maybe I should try that.

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FragranceLover89 - 30-10-2020 at 08:29

Here is the new reaction.
Collected some zinc fillings. Weight is less than 0.1 g. Put it in a jar with some (~7-8 ml) saturated NH4Cl solution. Small amounts of tween from yesterday coated the pipette and was enough to cause bubbles to form in solution. No excess tween was added. A few dashs of turmeric were added as a visual indicator of reduction. Heating was turned on (not sure what temp I have a really cheap setup)

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FragranceLover89 - 30-10-2020 at 08:51

Maybe this was not the smartest reduction. I cannot find any information of curcumin with only the ketone groups selectively reduced. It might not be possible due to the aromaticity. I will try PQQ or acetone.

FragranceLover89 - 30-10-2020 at 09:26

The solution has gotten lighter. Either this method works or the curcumin is being degraded in solution.

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FragranceLover89 - 30-10-2020 at 11:03

The solution eventually turned almost colorless. It was taken off heating and let sit for ~1 hr with Al foil sitting on top. When I returned some NH4Cl crystallized out and the color slightly returned to a darker yellow. Does this mean some of the curcumin alcohol reoxidized? There is also an unusual smell I suspect is degradation of curcumin but it might also be NH4Cl.

I decided to add some PQQ to see if it can be reduced. The PQQ comes in small pink capsules that turned the solution brown with a light pink hue. I added two (10 mg) capsules along with more NH4Cl solution.

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FragranceLover89 - 30-10-2020 at 11:10

After a few minutes of stirring it has developed into a red solution.


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FragranceLover89 - 30-10-2020 at 11:26

for reference this is the color of vitamin c mixed with PQQ -> PQQH2


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FragranceLover89 - 30-10-2020 at 11:31

This is PQQ unreduced.

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FragranceLover89 - 30-10-2020 at 11:37

My camera does not do it justice but the PQQ in the zinc reduction (right) mixture looks more golden than the unreduced PQQ (Left).

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FragranceLover89 - 30-10-2020 at 12:11

I am setting up the experiment again. This time with golden PQQH2 (Pipette on left) and pink PQQ (Pipette on right and pink cup) references.

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FragranceLover89 - 30-10-2020 at 12:17

It has been 5 minutes and the color of the zinc redux seems more golden on camera than the unreduced PQQ form. In addition a red precipitate has formed in the zinc redux very similar to a red precipitate formed in the PPQH2 reference. I don't know what this red precipitate is; a metal complex?

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FragranceLover89 - 30-10-2020 at 12:22

Some more photos.

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FragranceLover89 - 30-10-2020 at 13:10

Ok so I played around and found that adding household ammonia (with some surfactant) caused the zinc redux to turn golden.

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FragranceLover89 - 30-10-2020 at 13:15

Ammonia on it's own induces this color change so it has nothing to do with the zinc redux.

FragranceLover89 - 30-10-2020 at 14:19

I think I have figured it out. Adding a citric acid ammonium hydroxide buffer solution (slightly acidic) makes PQQ reduce to PQQH2. I think citric acid cleans the zinc metal increasing the reaction rate. I was able to get this color change without making the solution basic. The key is citric acid. Acidifying the solution also probably stabilizes the reduced form through hydrogen bonding.

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FragranceLover89 - 30-10-2020 at 14:54

I found an even better way to do this reaction without NH4Cl. Lol.
L-alanine + zinc + tween 20 produced a better product than the NH4Cl method.

Zinc redux left PQQ Right

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FragranceLover89 - 30-10-2020 at 15:02

So to summarize my findings. You don't need citric acid or ammonia. All you need is L- alanine, tween 20, and zinc metal. Below I have attached two images of the same solutions. The only difference is that the golden one (right) has zinc metal in it. The gold color is due to the reduction of PQQ into PQQH2. Thank the chemistry gods!!! I am so fortunate to have had this beta alanine sent to me by accident after I canceled the order a few weeks ago! What a coincidence. Ok now where is my nobel prize. Hahaha

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FragranceLover89 - 30-10-2020 at 15:30

If any of you guys are planning on publishing this reaction I would really appreciate if you mentioned me (email me for my information). I am trying to get into graduate school for chemistry and I really need some credit.

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FragranceLover89 - 30-10-2020 at 16:29

I have found that the concentration of tween 20 plays a huge role in the stabilization of PQQH2. Without tween 20 PQQ is reduced to PQQ semiquinone radical, which I believe is responsible for the deep blue color the PQQ + Zinc + L-alanine solution. Adding tween 20 and a sufficient amount of water gets rid of the blue and the pink PQQ is instead reduced to the golden color of PQQH2. Adding heat is important as well.

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FragranceLover89 - 30-10-2020 at 16:42

I realized that the color of my "golden solution" was a little more greenish blue than I thought suggesting the presence of semiquinone radicals. This implied that more proton source (L-Alanine) was needed. I did not want to waste my L-alanine so I added NH4Cl and put it back on the hot plate. In a few seconds this brought the color to the true golden color of PQQH2. Perhaps what is needed is only a catalytic amount of L-alanine, and the rest can be NH4Cl. I also found that the blue products from earlier turned into golden PQQH2 so maybe only a super small catalytic amount of tween 20 is needed.

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Texium - 30-10-2020 at 16:47

Quote: Originally posted by FragranceLover89  
If any of you guys are planning on publishing this reaction I would really appreciate if you mentioned me (email me for my information). I am trying to get into graduate school for chemistry and I really need some credit. This new reaction is called Yahya's reduction BTW.
Your results might be interesting, but they need to be followed up on with further experiments and actual isolation and characterization of products. You don't get to declare victory and claim a new named reaction just because you observed a color change.

FragranceLover89 - 30-10-2020 at 17:07

If this was 1920 I could name it. Seems like I did most of the preliminary work, which no labs would care to do without some evidence of it working. I bet you money if you asked any chemist at MIT if they thought it was possible to replace sodium borohydride with zinc in 90% water they would laugh at you and tell you to spend your time on research that will reliably give you results. Everyone knows the hard part is convincing your PI for funding.

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Texium - 30-10-2020 at 18:13

You're missing the point: you didn't prove anything

Corrosive Joeseph - 30-10-2020 at 18:58

/CJ

Attachment: Reduction of C=X to CHXH by Dissolving Metals and Related Methods - J.W. Huffman.pdf (2.9MB)
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FragranceLover89 - 30-10-2020 at 19:07

When Bouveault–Blanc reduction was discovered in 1903 they just demonstrated it with reduction of ethyl oleate to it's corresponding alcohol. I have not heard of direct reduction of ketones using amino acids in water. In order to get published in 2020 you need to study a couple different skeleton structures and then diversity within those groups. Lets be honest if you get published you can call it whatever you want even if you did not discover what amino acids work or what surfactants work or how to show that it works with a redox sensitive dye. You probably did more work than me in a professional setting and that matters more in 2020 there is no reason to get angry.
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Texium - 30-10-2020 at 20:04

Quote: Originally posted by FragranceLover89  
I have not heard of direct reduction of ketones using amino acids in water.
I have not either. And you haven't yet proven that you've accomplished it. All you have right now is a cup of soapy yellow water.

FragranceLover89 - 30-10-2020 at 20:15

The point of using PQQ was to show that you can reduce diones to quinones. Sorry if I offended you. I thought when i said "if it was 1920 i could name the reaction" pretty much showed I am not as serious about the name of the reaction as you.

HeYBrO - 30-10-2020 at 20:20

Quote: Originally posted by FragranceLover89  
The point of using PQQ was to show that you can reduce diones to quinones. Sorry if I offended you. I thought when i said "if it was 1920 i could name the reaction" pretty much showed I am not as serious about the name of the reaction as you.


You got a colour change, you need to isolate and characterise your product before you claim you did what you said.


EDIT: I skimmed through your thread and it was very difficult to follow what you were doing. You added some turmeric? this isn't pure curcumin... Also, the ketones you are trying are often very different, i.e. alpha beta unsaturated, conjugated systems etc.

Here is what I would do:

draw a scheme of what you are trying to achieve (by hand or with chemdraw etc)- you can also give a proposed mechanism. write down all conditions, i.e. the number of moles, the equivalents of each reactants, the mole % of your Tween 20, reaction temperature, reaction concentration and the reaction time.

Start with pure chemicals, weigh them accurately, do your procedure at conditions that can be easily reproduced, isolate your product and give some sort of characterisation data. These are the three typical steps of any reaction- synthesis, isolation and characterisation. Without them, the knowledge you are trying to produce is not any help to us.

I hope this helps...





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Texium - 30-10-2020 at 20:48

Quote: Originally posted by FragranceLover89  
The point of using PQQ was to show that you can reduce diones to quinones. Sorry if I offended you. I thought when i said "if it was 1920 i could name the reaction" pretty much showed I am not as serious about the name of the reaction as you.
Everything that HeYBrO just said perfectly illustrates what I’m trying to tell you. I don’t care about the name of this reaction that may or may not even happen. I’m not offended. I’m just trying to explain that you’ll need to research this more if you want to find out whether this can accomplish what you think it does. You haven’t discovered a new reaction either by 2020 or 1920 standards of evidence.

FragranceLover89 - 30-10-2020 at 21:12


As a rough estimate I would say 1 ml tween 20, 8 ml H2O, 0.7 g L-alanine, 0.7 g NH4Cl, 0.07 g Zinc, 5 mg PQQ. Reaction took 15-30 minutes with stirring. The solution got warm on the hot plate but could be held in the hand so 40-60 C? To be honest the concentration of tween in my opinion has not mattered significantly since even a little (6 drops in 10 ml) allows the reaction to occur. It has a relatively low CMC compared to other common surfactants like SDS. The concentration of the ammonium salt does not matter either. Just add it until no more goes into solution. Adding excess zinc cannot hurt either since in the paper by Dash et al. they added 5 molar equivalent and they reused it between separate runs. The limiting reagent is the ketone and or dione.

The solution goes through a yellow orange phase (in the pictures I showed) but after letting it stir longer turned a deeper orange more similar to the vitamin C PQQ solution color.

Altogether it was very simple. Add 10/90 L-alanine NH4Cl until no more goes into solution. Add 5% by volume tween. Add some zinc and your ketone/dione of choice. Sorry if this reaction does something random and the PQQ decomposes or something. I am sure the tween 20 can come in handy and you can just buy some THF and follow the correct protocol in the paper by Dash et Al. Hopefully the authors are being truthful.

In the image below I compare old PQQ+vitamin c solution (sep funnel) and the zinc redox solution (on hot plate). The opaque precipitate that is a red color is from some thing in the vitamin C tablets I am using precipitating PQQ. The clear aqueous layer has a similar orange color as the zinc redox solution.

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FragranceLover89 - 30-10-2020 at 21:40

This describes PQQH2 as yellowish brown, similar to the product I produced especially when you compare it to the PQQ solution I showed earlier.

http://scripts.iucr.org/cgi-bin/paper?S2052520617002281

FragranceLover89 - 30-10-2020 at 22:00

Thank you for your concerns. I hope I am not endangering my health from these experiments.

When I mixed PQQ + Zinc + NH4Cl + Tween 20 nothing happened after continuous high heating for 1-2 hrs.
When I added some L-alanine the color very quickly changed to yellow with mild heating or at room temperature. I know this is not a direct reaction between L-alanine and PQQ, Tween, or NH4Cl because that solution is pink and turns yellow upon addition with Zn. The next possibility is that there is an oxidative deamination requiring the presence of PQQ, Zn, and L-alanine simultaneously. This solution is a deep blue rather than the yellow seen previously suggesting that deamination is not the common cause of color change seen in L-ala solutions with or without tween.
Research by Senda et al. 1990 show that the PQQ semiquinone radical is stabilized in aqueous solutions with 2+ metal cations. Perhaps this explains why the variation in tween concentration caused this color difference from deep blue to yellow. My hypothesis is that Tween can complex Zn2+ or form micelles to capture the quinol form of PQQ.

This only leaves a few more possibilities on the table. I know PQQ is not directly reacting with Zn because that solution remained pink.
Worst case scenario: L-alanine radicals are forming and reacting with PQQ to form some weird compound?

Things I have tried
PQQ + Zinc + NH4Cl (saturated) + Tween 20 Pink (Baseline) stays even with heating
PQQ + ammonia Golden color
PQQ + citric acid Golden color
PQQ + Zinc + NH4Cl (saturated) + L-alanine Deep blue color
at room temperature
PQQ + Zinc + NH4Cl (saturated) + L-alanine + Tween Bright Yellow color at room temperature or with heating depending on NH4Cl concentration

What to try next
Zn + L-alanine + Tween 20
Zn + NH4Cl + L-alanine + Tween 20
Catalytic amount of L-alanine

Addendum

I have read that [Zn(ala)2] is colorless.





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FragranceLover89 - 31-10-2020 at 09:20

Your hunch was correct. Someone has already done this reaction and it is not producing PQQH2. The yellow color is an oxazole

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FragranceLover89 - 31-10-2020 at 14:34

Ok sorry my earlier posts are kinda crappy. I was just experimenting around and thought I had the right product. I was wrong. PQQH2 should precipitate out of solution as a brown material as described in this paper by Ikemoto et al. That is the brown material I saw when I mixed an excess of vitamin C with PQQ earlier. In addition I was very wrong about that bright yellow product being PQQH2. It is actually an Oxazole formed by reaction between L-alanine and PQQ in the presence of Zn2+. The paper I attached above describes what was observed pretty well. I believe there is still hope for tween 20 + Zn + NH4Cl as a reducing agent for ketones. I have attempted the reaction again with better descriptions of the reagents.

PQQH2 synthesis pt 2:

I opened a capsule of 10 mg stated PQQ and dissolved it in 33 ml of water with gentle stirring for 10 minutes to create a 0.0009177 molar solution(Pic 1). While I waited for the pill filler to settle out I added 1 drop of tween 20 to a glass container with a significant amount of zinc powder (Pic 2). 2 ml of water were left over in this container from when I washed the zinc powder with water earlier. I added NH4Cl until no more would dissolve in the solution. To this I added 6 ml of the PQQ solution prepared earlier (5.5*10-6 moles).
The color changed instantly to a brown yellow color (pic 3).

Next I will try to determine the volume of 1 drop of tween and repeat the experiment with fresh zinc weighed out to see if this was the result of L-alanine residue.


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FragranceLover89 - 31-10-2020 at 14:47

Using the same pipette I used add a drop of tween 20, I found there are 43 drops per 1 ml so 1 drop is .02 ml. This means that the reaction above contained a 0.3% (solute/solution) tween 20.

FragranceLover89 - 31-10-2020 at 14:54

It is hard to see but in the 20 minutes since this reaction started. A red-brown precipitate has begun to form in the liquid.

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FragranceLover89 - 31-10-2020 at 15:22

As a quick update all the PQQ has formed into an insoluble copper red precipitate with no pink left in solution. Here is an image of this precipitate in a pipette.

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FragranceLover89 - 31-10-2020 at 16:41

When the initial PQQ solution was saturated with NH4Cl the color changed from pink to peach, however, no precipitate was noted. This means the orange precipitate is either PQQH2, the zinc complex of PQQ, or something else. Pic below is a PQQ NH4Cl solution without precipitate.

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FragranceLover89 - 31-10-2020 at 17:13

The addition of a Zinc acetate solution was added to the PQQ NH4Cl solution. A white precipitate was observed.

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