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Author: Subject: Camphor reduction to borneol/isoborneol
stamasd
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[*] posted on 8-12-2018 at 04:30
Camphor reduction to borneol/isoborneol


I need some borneol and/or isoborneol. They are hard to find and expensive, while the corresponding ketone (camphor) is not.
The 2 described methods for camphor reduction are:

1. MPV reaction which needs aluminum isopropoxide (not difficult to make but adds an extra step) and continuous distillation of the secondary ketone (acetone if using isopropanol) during the reaction to drive the equilibrium in the desired direction, or

2. NaBH4 which I don't have and can't acquire.

Wondering if it's possible to instead use:
3. Urushibara nickel reduction which would be technically much easier for me to do. If so, would U-Ni-A or U-Ni-B preferred? I'm tending to think that U-Ni-A.

Then of course remains the problem of separating the product(s) from the unreacted camphor. The boiling points of camphor and (iso-)borneol are ridiculously close so fractional distillation is not really an option. Would probably need to exploit either:

a. differential solubility in solvents - does anyone have any information on that pertaining to camphor vs. (iso-)borneol?
or
b. chemical differences in reactivity e.g. converting the borneols to alkoxides and differential extraction with solvents

Comments are welcome.

(to clarify, it doesn't matter too much if I get borneol, isoborneol or a mixture of the two)

(edit) Actually U-Ni-B may be preferred for the reduction of ketones according to the Hata book.

[Edited on 8-12-2018 by stamasd]
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[*] posted on 8-12-2018 at 09:47


Sodium borohydride is likely to be the easiest option by far. It will not require separating unreacted camphor because as long as you use enough NaBH4 then you'll get complete conversion. It's fast, selective for ketones/aldehydes/carbonyl groups, and even though it seems pricey per gram, you tend to need so little of it that it's a cheap option. Honestly, it's one of my favourite reagents.

Where are you located? Perhaps we may be able to direct you to a source for NaBH4.
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stamasd
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[*] posted on 8-12-2018 at 10:11


Thanks for the reply. About NaBH4, it's not that it's impossible for me to get, but I'm low on funds and that won't change anytime soon. I could get it from Amazon at about $60 for 100g... But I can't spare that money now.
OTOH I have everything I need for the Urushibara pathway and wouldn't need to spend any money on that. Plus it would open a new avenue.
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DavidJR
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[*] posted on 8-12-2018 at 10:33


Quote: Originally posted by stamasd  
Thanks for the reply. About NaBH4, it's not that it's impossible for me to get, but I'm low on funds and that won't change anytime soon. I could get it from Amazon at about $60 for 100g... But I can't spare that money now.
OTOH I have everything I need for the Urushibara pathway and wouldn't need to spend any money on that. Plus it would open a new avenue.


For reference, you could probably get away with using 0.3 mol of NaBH4 per mol of camphor (i.e. 7.5g of NaBH4 per 100g of camphor).

However hydrogenation with Urushbara nickel catalyst can probably work but I've never done any hydrogenations so I can't really help with that, sorry.
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[*] posted on 8-12-2018 at 11:19


Quote: Originally posted by stamasd  

Wondering if it's possible to instead use:
3. Urushibara nickel reduction which would be technically much easier for me to do. If so, would U-Ni-A or U-Ni-B preferred? I'm tending to think that U-Ni-A.


(edit) Actually U-Ni-B may be preferred for the reduction of ketones according to the Hata book.

[Edited on 8-12-2018 by stamasd]


The original Urushibara paper makes it clear that the U-Ni-B catalyst performs similarly to Raney nickel catalysts in the reduction of ketones to alcohols; specifically, they claim that 2g of cyclohexanone in 20mL EtOH was reduced successfully to cyclohexanol in approximately 45min utilizing the B catalyst at RT and 1atm pressure, so that's what I would recommend if you want to follow that synthetic pathway. It should give quantitative yield so separation wouldn't be an issue.

Have you considered synthesis of your own sodium borohydride? You could presumably synthesize it from a trimethylborate and sodium hydride using a shortened Schlesinger process.



Ref:
THE URUSHIBARA CATALYSTS
Urushibara, Yoshiyuki. Annals of the New York Academy of Sciences Volume: 145 Issue 1 catalyti (1967) ISSN: 0077-8923 Online ISSN: 1749-6632


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[*] posted on 8-12-2018 at 11:33


You are in luck i was browsing this guys website yesterday for silicon oil when this caught my eye https://www.ebay.com/itm/Bing-Pian-Borneol-flakes-Essential-Volatile-Aroma-100gm-FREE-world-SHIPPING-/143035473165?_ul=US



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stamasd
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[*] posted on 8-12-2018 at 11:53


Thanks again.

I looked around more and I did in fact find a source of isoborneol that isn't outrageously expensive (about $1/g).
But since I already have everything (including the camphor) I think I'll go ahead and attempt hydrogenation anyway. No downside to it. :)

I think I'll use U-Ni-B or U-Ni-BB (or for more fun I may even attempt to make U-Ni-CB which should be even more active)and then hopefully after alkaline treatment be able to extract aqueous (iso-)borneol alkoxide and regenerate the alcohol with acid then organic phase extraction.

I'll post back if successful.

Quote: Originally posted by nux vomica  
You are in luck i was browsing this guys website yesterday for silicon oil when this caught my eye https://www.ebay.com/itm/Bing-Pian-Borneol-flakes-Essential-Volatile-Aroma-100gm-FREE-world-SHIPPING-/143035473165?_ul=US


That is not borneol. I have browsed those ebay listings; what they call "borneol" is in fact camphor intended for edible applications. It's used in India for desserts/sweets.

Quote: Originally posted by Nakhimov  

Have you considered synthesis of your own sodium borohydride? You could presumably synthesize it from a trimethylborate and sodium hydride using a shortened Schlesinger process.


No I haven't; I'll look into it but for now I'll try the catalytic way. Thanks for the heads-up.



[Edited on 8-12-2018 by stamasd]
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[*] posted on 8-12-2018 at 20:00


Quote: Originally posted by stamasd  


Quote: Originally posted by nux vomica  
You are in luck i was browsing this guys website yesterday for silicon oil when this caught my eye https://www.ebay.com/itm/Bing-Pian-Borneol-flakes-Essential-Volatile-Aroma-100gm-FREE-world-SHIPPING-/143035473165?_ul=US


That is not borneol. I have browsed those ebay listings; what they call "borneol" is in fact camphor intended for edible applications. It's used in India for desserts/sweets.


I would guess that is actual borneol. It is almost definitely synthetic, as natural borneol is very expensive in high purity.

More importantly it looks nothing like camphor, and everything like borneol. The two look nothing alike.

Of course I wouldn't be surprised if the pictures and the listing text were just copy/pasted from the internet.

Borneol is used in flavoring and food, I order it (and camphor) by the kilo for my work, so I know a bit about the market.
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[*] posted on 8-12-2018 at 20:01


If you can find camphene it undergoes a very clean rearrangement in acetic acid to borneol acetate. No need for reducing agents. Camphene is used by some perfumers and I bought some from a perfumers site. It is actually quite cheap. One of the problems I have with so-called pure camphor is that it contains a significant amount of menthol and probably other terpenes which leads to complications.

AvB
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stamasd
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[*] posted on 8-12-2018 at 20:09


I never thought to look for camphene though I knew about the bornyl acetate rearrangement... As for the camphor purity, it turns out that menthol as an impurity would not affect at all my intended final application. :)

(edit) Yes I think I found the place you bought it from, or a close relative. Indeed it's about 10 times cheaper than isoborneol.

But nonetheless I think I'll go ahead with the hydrogenation. For science! :D

Quote: Originally posted by happyfooddance  
Quote: Originally posted by stamasd  


Quote: Originally posted by nux vomica  
You are in luck i was browsing this guys website yesterday for silicon oil when this caught my eye https://www.ebay.com/itm/Bing-Pian-Borneol-flakes-Essential-Volatile-Aroma-100gm-FREE-world-SHIPPING-/143035473165?_ul=US


That is not borneol. I have browsed those ebay listings; what they call "borneol" is in fact camphor intended for edible applications. It's used in India for desserts/sweets.


I would guess that is actual borneol. It is almost definitely synthetic, as natural borneol is very expensive in high purity.

More importantly it looks nothing like camphor, and everything like borneol. The two look nothing alike.

Of course I wouldn't be surprised if the pictures and the listing text were just copy/pasted from the internet.

Borneol is used in flavoring and food, I order it (and camphor) by the kilo for my work, so I know a bit about the market.


OK I'll believe you. I ordered a smaller sample from the same seller, we'll see what it is when it gets here sometime next year. :D


[Edited on 9-12-2018 by stamasd]
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[*] posted on 9-12-2018 at 02:33


Why don't you just reflux camphor with dithionite ?
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[*] posted on 9-12-2018 at 02:40


Quote: Originally posted by CuReUS  
Why don't you just reflux camphor with dithionite ?

An answer might be that it is documented not to work, at least under the conditions given here
http://about.mdma.ch/picproxie_docs/000427794-Reduction_of_a...

It may be possible to get success with a different solvent etc.
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stamasd
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[*] posted on 9-12-2018 at 04:08


^that, plus at this point I'm more or less looking for an excuse to use a Urushibara catalyst. :)
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[*] posted on 9-12-2018 at 10:23


Quote: Originally posted by AvBaeyer  
If you can find camphene it undergoes a very clean rearrangement in acetic acid to borneol acetate.

AvB


This is good to know! I use camphene at work, too. And bornyl acetate...

Also, alpha-pinene (which is by far the cheapest of the terpenes mentioned in this thread) can be converted to camphene by addition of HCl followed by elimination. Might be of use to the O.P.



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[*] posted on 11-12-2018 at 01:29


Hello everyone, my first post on this board :)

Sauce to the MPV route - https://patents.google.com/patent/WO2016119270A1/en Patent's English seems a bit broken, unfortunately (even more than mine :P).

I've found one old thread (http://www.sciencemadness.org/talk/viewthread.php?tid=17712#...), where Adas mentioned camphor reduction with ascorbic acid.

What also comes to my mind, camphor could be reduced by Na-MgO aggregate (https://www.youtube.com/watch?v=ZXCSL0r4aqg) in alcohol medium.

In Vogel I've also found the description of photocatalytic reduction of ketones by alcohols. However, I'm afraid that camphor absorbs UV too inefficiently to keep the reaction going. And even if the reduction was indeed the case in such conditions, skeletal rearrangements still seem to be an option, due to radical mechanism.

Does anyone know how stable is camphor in alkaline environment? Maybe a Zn/OH- route would be viable?

Now a bit OT part - "Common Fragranceand Flavor Materials" http://www.cffet.net/ait/M1_book.pdf states that "levorotatory borneol
is synthesized industrially from levorotatory pinenes by Wagner-Meerwein rearrangement with dilute acid, followed by hydrolysis of the resulting esters" and German Wiki provides similar information https://de.wikipedia.org/wiki/Campher#Gewinnung_und_Darstell... but I can't find the source article with synthesis description (apparently B. Masumoto, T. Funahashi, JP 5368, 1952; Chem. Abstr. 48 (1954) 8263g). Anyone with the access?

Edit: adding 2 useful camphor related links to keep everything in one place
http://www.edu.utsunomiya-u.ac.jp/chem/v18n1/102Ponomarev/Po... Camphor and its Industrial Synthesis
http://www.sciencemadness.org/talk/viewthread.php?tid=12470 Camphor from turpentine

[Edited on 11-12-2018 by oberkarteufel]
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stamasd
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[*] posted on 11-12-2018 at 04:02


I don't think that the redox power of ascorbic acid would be enough for this reaction.

I'm in the middle of making the Urushibara catalyst. It turns out that I didn't have nickel chloride, only sulfate - so I'm converting the sulfate to chloride via carbonate. Had to let the carbonate dry overnight (or else the chloride solution would end up too diluted) hence the delay.
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[*] posted on 11-12-2018 at 04:49


Quote: Originally posted by oberkarteufel  

In Vogel I've also found the description of photocatalytic reduction of ketones by alcohols. However, I'm afraid that camphor absorbs UV too inefficiently to keep the reaction going. And even if the reduction was indeed the case in such conditions, skeletal rearrangements still seem to be an option, due to radical mechanism.


This might work - I did a bunch of experiments on the photocatalytic reduction of benzophenone by isopropanol. On a very small scale (0.5g) you can easily get quantitative yields, but scaling up presents serious problems. I was never able to get more than about 50% conversion on a 50g scale, even with over a month of exposure under a UV-B lamp.

I ended up just using NaBH4.

[Edited on 11-12-2018 by DavidJR]
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[*] posted on 11-12-2018 at 05:20


Outta curiosity why do you need borneol? Seems rather specific.
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stamasd
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[*] posted on 11-12-2018 at 06:45


Quote: Originally posted by nora_summers  
Outta curiosity why do you need borneol? Seems rather specific.


It does, doesn't it?
*cough*NurdRage*cough*
Menthol is another option, but I happen to be allergic to it. That's actually how I know the camphor I'm using isn't contaminated by menthol. I'm not breaking out in hives on contact. :)

[Edited on 11-12-2018 by stamasd]
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[*] posted on 11-12-2018 at 18:26


What did nurdrage do exactly? I don't watch his shit.
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[*] posted on 11-12-2018 at 18:52


Quote: Originally posted by stamasd  
I'm in the middle of making the Urushibara catalyst. It turns out that I didn't have nickel chloride, only sulfate - so I'm converting the sulfate to chloride via carbonate. Had to let the carbonate dry overnight (or else the chloride solution would end up too diluted) hence the delay.
Won't the sulphate also work?



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[*] posted on 11-12-2018 at 23:33


Quote: Originally posted by nora_summers  
What did nurdrage do exactly? I don't watch his shit.
A simple pocess for metallic sodium, using reagents as OTC as possible. Newest video of the sodium cycle, referencing borneol https://www.youtube.com/watch?v=PxPjBz_8S3c
Calling his experiments and research "shit" seems wildly uninformed or unnecessarily rude.

@stamasd - I second fusso's question - shouldn't sulphate be good enough for the catalyst synthesis?
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[*] posted on 12-12-2018 at 03:05


According to Hata's book chloride is best for making Urushibara-type catalysts. Sulfate works but results in a catalyst with significantly reduced activity.
(edit) Acetate would be adequate too but I don't have that either.


[Edited on 12-12-2018 by stamasd]
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[*] posted on 12-12-2018 at 03:31


If you're doing NurdRage's sodium metal production reaction with borneol, it is possible that camphor may work, if a hypothesis of mine is correct. I hypothesise that it is the enolate that is the active catalyst, and borneol (or another secondary alcohol) is just a pre-catalyst. The enolate would be formed from the corresponding ketone via alpha-hydrogen elimination.



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stamasd
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[*] posted on 12-12-2018 at 03:33


Quote: Originally posted by 12thealchemist  
If you're doing NurdRage's sodium metal production reaction with borneol, it is possible that camphor may work, if a hypothesis of mine is correct. I hypothesise that it is the enolate that is the active catalyst, and borneol (or another secondary alcohol) is just a pre-catalyst. The enolate would be formed from the corresponding ketone via alpha-hydrogen elimination.


I know of one way of testing that hypothesis. :) But I need borneol for that. :D
(7 years of graduate school has taught me the importance of controls)

[Edited on 12-12-2018 by stamasd]
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