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Hilski
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Benzyl Alcohol -> Benzaldehyde via Silica Gel Supported Jones Reagent
Anyone ever try this? Seems way too easy to be true.
Representative Procedure
Dry silica gel (5 g) was placed in a 100-mL round-bottom flask containing a magnetic stirring bar and fitted with a rubber septum. Jones reagent
(1.5mL, 12 mmol) was added slowly from a syringe to the vigorously stirred silica gel. After complete addition of the reagent, stirring continued
until a free-flowing orange powder was obtained (less than 5 min). Methylene chloride (25 mL) was added to the above flask. A solution of benzyl
alcohol 1a (396 mg, 3.66 mmol) in methylene chloride (5 mL) was added slowly from a syringe through the rubber septum to the stirred heterogeneous
mixture. The orange SJR turned dark green/brown immediately. After complete disappearance of the starting benzyl alcohol as indicated by TLC (10 min),
the reaction mixture was filtered through a sintered glass funnel, the solid residue was washed with methylene chloride (75 mL) and the washings were
added to the filtrate. Solvent was removed from the solution under vacuum to produce a colorless oil (331.6 mg, 85.3% yield) which was pure
benzaldehyde according to NMR and IR data.
More details from Erowid:
http://www.erowid.org/archive/rhodium/chemistry/alcohol2alde...
-Hilski
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Hilski
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Seems the answer was right here all along. Or at least something close. I suppose that as long as no water is allowed into a Jones-type oxidation,
then it should work OK?
https://sciencemadness.org/talk/viewthread.php?tid=5839
The last 4 or 5 posts in that thread is a discussion about variations of a Jones oxidation.
Quote: "Use of CrO3 with NaHSO4.H2O (Sodium Bisulfate Monohydrate) in 1:1:1 ratio will give you bezaldehyde by 95% yield. ( Im still using it
myself,trust it)"
'Tis worth looking into I would say. I wonder if dichromate would also work in this case as well?
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redox
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I have performed this exact synthesis before, and it works like a dream. Isolation of product is trivial, and the whole reaction is clean and easy.
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mario840
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better is PCC (pyridinum chlorochromate) , easy synth reagent and easy synthesis oxidize
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redox
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The only problem with PCC is that it is much more difficult to acquire than silica gel.
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simba
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Why not use calcium/sodium hypochlorite? The link below says it is possible and gives 98% yields, though it says that benzyl alcohol is the only (or
one of the few) primary alcohol(s) that can get oxidized into an aldehyde using hypochlorites.
http://www.erowid.org/archive/rhodium/chemistry/ether2ester.hypochlorite.html
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redox
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I would love to try this, but the synthesis calls for acetonitrile, which I cannot make nor purchase. I wonder if a different compound could be
substituted in its place....
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Melgar
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Does anyone have experience with the procedure in the attached pdf? It uses iodine radicals to oxidize benzyl alcohol to benzaldehyde, then the
iodide is oxidized back to iodine by molecular oxygen. Seems pretty easy, especially if you have access to a source of pure oxygen.
Attachment: benzaldehyde.pdf (146kB)
This file has been downloaded 1427 times
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simba
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Quote: Originally posted by redox  | | I would love to try this, but the synthesis calls for acetonitrile, which I cannot make nor purchase. I wonder if a different compound could be
substituted in its place.... |
I'm pretty sure acetonitrile is just a solvent they decided to use for adding the menthol dropwise, since pure menthol is a waxy solid. But you don't
need it for working with benzyl alcohol since its a liquid already.
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redox
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In that case, I will be attempting this procedure with benzyl alcohol post-haste. 
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simba
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Ok I tried today the oxidation of benzyl alcohol with calcium hypochlorite and I can only classify it as 'disastrous success'.
I mixed 155g of 65% calcium hypochlorite from bleaching powder with 600ml of water and 110g of benzyl alcohol. The reaction went smooth in the
beginning, with no heating evolved, and I could smell benzaldehyde being formed...then after 2 hours I heard an explosion. I went to see what happened
and my laundry room was entirely painted with spills from the reaction mixture and the smell was so strong I could barely breath.
It seems the reaction spontaneously boiled to the point of exploding in a volcanic stream of benzaldehyde. I just want to know what the fuck
happened...I know calcium hypochlorite is known for undergoing self heating, but I added just the enough for the reaction...does anyone have a clue of
what happened?
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DJF90
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For a start, the paper claims acetic acid is required for the oxidation. Secondly, the paper runs the reaction in an ice bath. And finally, your
volume of solvent is far off if a direct scale-up is attempted. Perhaps you should try new reactions following the experimental procedure outlined in
the reference and on a small scale to avoid such dangerous situations and the large waste of materials.
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Nicodem
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| Quote: Originally posted by shivas | I mixed 155g of 65% calcium hypochlorite from bleaching powder with 600ml of water and 110g of benzyl alcohol.
...then after 2 hours I heard an explosion. I went to see what happened and my laundry room was entirely painted with spills from the reaction mixture
and the smell was so strong I could barely breath. |
Sorry for being offensive, but I just can't help not saying: "What an idiot!"
How could you expect anything else but a runaway could happen by doing an oxidation on a one mol scale under totally uncontrolled
conditions? I have to restrain myself of not telling you what I think of such a behavior. Could you have done this in any more stupid way?
Only by doing it on 10 mol!
Well, at least you had the luck of not being present at the moment of the accident.
TO ALL: Don't scale up exothermic reactions without process research!
I can't believe these things still happen after so many safety warnings. Does nobody ever UTFSE by using keywords like: runaway, mishap, safety,
accident, scale up...
http://www.sciencemadness.org/talk/viewthread.php?tid=3698
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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simba
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Yeah, I can only agree about that, epic idiocy, and nothing more. I could try to justify it, but its just unjustifiable really, I don't even know what
I was thinking at the time I made that post, I guess I was just knocked out by the strong smell of benzaldehyde in my house.
But well, what does not kill you...makes you learn.
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DJF90
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Its not the fact you made the post thats the problem, and so you cannot blame the smell of benzaldehyde. What you did was really inconsiderate,
running a new reaction on the molar scale without even following the same procedure that was used. The large amount of water used in the paper is
NECESSARY as there is a large amount precipitate formed during the reaction, which may prevent/hinder magnetic stirring. Towards the end of the
reaction all of this precipitate is redissolved. I'd suggest overhead stirring for anything over about 100mmol.
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simba
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| Quote: Originally posted by DJF90 | | Its not the fact you made the post thats the problem, and so you cannot blame the smell of benzaldehyde. What you did was really inconsiderate,
running a new reaction on the molar scale without even following the same procedure that was used. The large amount of water used in the paper is
NECESSARY as there is a large amount precipitate formed during the reaction, which may prevent/hinder magnetic stirring. Towards the end of the
reaction all of this precipitate is redissolved. I'd suggest overhead stirring for anything over about 100mmol. |
The reason I feel stupid about that post is just because I said I had no clue of what had happened. I was already expecting some highly exotermic
reaction, but I could feel the smell of benzaldehyde and no rise in temperature, so I just assumed nothing would happen thereafter, I was very wrong
then.
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MolecularArchitect
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@redox Do you have any experience with scaling up the procedure herein mentioned?
"Practical application is found by not looking for it, and one could say that the whole progress of civilization rests on that principle." -Jacques
Hadamard
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redox
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Somewhat. I performed the synthesis on a two-times scale, which was about 7.32 mmol benzyl alcohol (some [read: most] might still consider this small
scale  ). Once I get some more silica gel, I will try it again on a .25 mol
scale or near that.
[Edited on 10-8-2011 by redox]
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MeSynth
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After doing a bit of math I discovered that if you wanted to scale this up say... 1000x ( in order to produce 300ml of benzaldehyde ) your going to
need A LOT of silica gel... if you found a good supplier of silica gel then it would be ok the next problem is the large flask you would need. Glass
punch bowl? or one of those glass water jugs that Chunk drops in The Goonies.
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redox
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| Quote: Originally posted by MeSynth | | After doing a bit of math I discovered that if you wanted to scale this up say... 1000x ( in order to produce 300ml of benzaldehyde ) your going to
need A LOT of silica gel... if you found a good supplier of silica gel then it would be ok the next problem is the large flask you would need. Glass
punch bowl? or one of those glass water jugs that Chunk drops in The Goonies. |
I think its clear that this synthesis was not designed to be scaled up. Plus, who needs 300mL of benzaldehyde?
It would be interesting to do some experiments to see if the ratio of silica gel to Jones' Reagent could be lowered, to save some of the valuable
silica gel.
Does anyone have a good source for the gel? My only source was ~55$ for 300g silica gel! Of course, this was for very fine mesh, I think 0.4 um -
0.63um, or something like that.
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MeSynth
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| Quote: Originally posted by redox | | Quote: Originally posted by MeSynth | | After doing a bit of math I discovered that if you wanted to scale this up say... 1000x ( in order to produce 300ml of benzaldehyde ) your going to
need A LOT of silica gel... if you found a good supplier of silica gel then it would be ok the next problem is the large flask you would need. Glass
punch bowl? or one of those glass water jugs that Chunk drops in The Goonies. |
I think its clear that this synthesis was not designed to be scaled up. Plus, who needs 300mL of benzaldehyde?
It would be interesting to do some experiments to see if the ratio of silica gel to Jones' Reagent could be lowered, to save some of the valuable
silica gel.
Does anyone have a good source for the gel? |
Would it be possible to lessen the amount of silica gel used? Why don't you find out how the reaction works, tell us =P, and then we can answer your
question.
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redox
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| Quote: Originally posted by MeSynth | | Quote: Originally posted by redox | | Quote: Originally posted by MeSynth | | After doing a bit of math I discovered that if you wanted to scale this up say... 1000x ( in order to produce 300ml of benzaldehyde ) your going to
need A LOT of silica gel... if you found a good supplier of silica gel then it would be ok the next problem is the large flask you would need. Glass
punch bowl? or one of those glass water jugs that Chunk drops in The Goonies. |
I think its clear that this synthesis was not designed to be scaled up. Plus, who needs 300mL of benzaldehyde?
It would be interesting to do some experiments to see if the ratio of silica gel to Jones' Reagent could be lowered, to save some of the valuable
silica gel.
Does anyone have a good source for the gel? |
Would it be possible to lessen the amount of silica gel used? Why don't you find out how the reaction works, tell us =P, and then we can answer your
question.
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The reaction works by forming an intermediate chromate ester which is cleaved, giving an aldehyde and a less oxidized oxochromium acid.
I personally don't understand why silica gel lessens the activity of and raises the selectivity of the Jones' reagent. Does anybody out there in the
internet know?
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MeSynth
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Silica gel used in the oxidation reactions, as solid support, was MN-Kieselgel 60 (0.04–0.063mm mesh size) supplied by Fisher Scientific.
------------------------------Taken from the link in the original post
Used as a solid support. Maybe plain old glass dust would work.
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redox
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| Quote: Originally posted by MeSynth | Silica gel used in the oxidation reactions, as solid support, was MN-Kieselgel 60 (0.04–0.063mm mesh size) supplied by Fisher Scientific.
------------------------------Taken from the link in the original post
Used as a solid support. Maybe plain old glass dust would work. |
Well, it is obviously a solid support. Dust won't work. Dust is made up mostly of dust, hair, and skin cells. Silica gel is very
porous with an enormous surface area, which adsorbs (or absorbs? not sure) the Jones reagent. My question was why it modifies the activity of
the Jones Reagent.
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questions
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Our friend "cyclonknight" described an attractive process for making benzaldehyde from cinnamon oil by slowly dripping the cinnamon oil into the
already boiling water with dissolved NaOH at around a PH of 12 to 13.
What I dont understand is that on the wikipedia they say that benzaldehyde is converted into two other chemicals when exposed to highly concentrated
NaOH, and I quote
"Benzaldehyde undergoes disproportionation upon treatment with concentrated alkali (Cannizzaro reaction): one molecule of the aldehyde is reduced to
the corresponding alcohol and another molecule is simultaneously oxidized to sodium benzoate."
So if the cinnamon oil is being converted to benzaldehyde, and is steam disstilled out, why isn't the benzaldehyde being converted into other products
as described by the wikkipedia?
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