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mbrown3391
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Ethanol + H2O2
Just a quck question-- how does ethanol react with hydrogen peroxide with an acid catylist? i basicly followed the synthesis for acetone peroxide but
used ethanol instead of acetone. When I came back to my basement an hour after i added the sulfuric acid, the entire room smelled recognizably sweet.
I cant put my finger on the smell, but it smells almost like some sort of artificially flavored drink. But esters are formed with carboxylic acids, so
it couldn't be an artificial flavor. Any idea what was formed?
Note: the ethanol i used was 4% methanol.
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Drone
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The peroxide will oxidise the ethanol into ethanal and acetic acid.
The odour you are smelling is probably the ethanal, which is very votatile (b.p. 21 deg.C).
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guy
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It is probably ethanal (acetaldyhyde) and ethyl acetate. Both smell fruity.
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Pyridinium
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You might be getting esterification of AcOH (formed by oxidation) with some unreacted EtOH to give ethyl acetate. With conc. sulfuric this is
possible.
I wouldn't be surprised if you're getting a whole mix of reaction products. H2O2 and conc. H2SO4 together is not very particular about what it
oxidizes. Nor is it very safe.
-------
No offense intended, but I wish people would stop trying to make AP. It's not going to do hobby chemistry any favors in the arena of public opinion.
Some of the EM people on here might take issue with my statement, but everyone's entitled to their opinion 
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woelen
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| Quote: | I wouldn't be surprised if you're getting a whole mix of reaction products. H2O2 and conc. H2SO4 together is not very particular about what it
oxidizes. Nor is it very safe.
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What you are talking about is very different from what mbrown3391 is talking about. He is talking about dilute H2SO4/H2O2, and I have very strong
doubts that any ethyl acetate will be formed in such aqueous solution.
I would ask mbrown3391 to repeat the experiment with the same denatured ethanol, dilute H2SO4 and K2Cr2O7 or KMnO4 as oxidants. Probably the smell
will be very similar. I know that smell and I think it is a mix of ethanol, ethanal and the products added to the ethanol to make it denatured.
| Quote: | | No offense intended, but I wish people would stop trying to make AP. [...] |
No one is making AP over here, it just is mentioned for describing how this ethanol/H2O2/H2SO4 mix looks like.
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Pyridinium
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| Quote: | Originally posted by woelen
What you are talking about is very different from what mbrown3391 is talking about. He is talking about dilute H2SO4/H2O2, and I have very strong
doubts that any ethyl acetate will be formed in such aqueous solution. |
I missed the 'dilute' part, must not have been paying attention.
You're right, there probably won't be much EtOAc formed in dilute solution. I also missed the 'catalytic' part of H2SO4.
Probably acetaldehyde (ethanal) etc. There can still be hard-to-predict products when H2O2 goes to work.
When someone says they followed an AP synthesis.... we're off on the wrong foot to begin with.
Edit: I'm curious what the denaturant is in his alcohol. It isn't always MeOH. I have used a variety that gives a peculiar, somewhat disagreeable
odor on prolonged contact with alkali, and I don't think it's from either EtOH or MeOH.
Edit2: I saw he says 4% MeOH, that's what I thought mine had too, but I'm not really sure.
[Edited on 19-6-2007 by Pyridinium]
[Edited on 19-6-2007 by Pyridinium]
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not_important
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acetone, MEK, methyl isobutyl ketone, diethyl phthalate, ethyl acetate, gasoline, kerosene, citronella, pyridine bases, soaps, crude wood alcohol,
brucine sulfate, denatonium benzoate have all been used to denature ethanol; in many countries dyes are added as well.
The pyridine family is pretty smelly, ketones could undergo condensation in the presence of alkali.
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Pyridinium
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@woelen: I have been thinking about this some more, and I've decided to stand by what I originally said about ester formation.
There is a common tendency to think that you need conc. H2SO4 to absorb all the water from the reaction. That is simply not true.
Methyl, ethyl, and I believe n-propyl esters can all be made even with dilute acid (even HCl) if there is a large excess of alcohol. I checked up on
this, and the yields are not bad (more than enough to make the noticeable fragrance). The excess of alcohol sounds counter-intuitive, but according
to my McMurry Organic Chem textbook (a good text!) that is precisely what is needed.
The ester is then separated by fractionation.
@not_important: that is quite a list of denaturants.
I have an old edition of Lange's that has a good sized list of denaturants and the amounts required, but I don't have it in front of me. I wish I
knew what that weird, nasty smell was that happens from denat. EtOH and KOH. It's like a nasty, almost mustard-like odor (reminds me vaguely of honey
mustard & onion pretzels, but not in a pleasant way)
[Edited on 19-6-2007 by Pyridinium]
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woelen
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Pyridinium, that sounds interesting. Indeed, I always thought that concentrated acid and waterfree (or at least very low in water) conditions were
required.
I'll try tonight with 30% acetic acid (photograde stop bath, no fragrances added, pure, only containing water and acetic acid) to which I'll add some
37% H2SO4 and excess 96% EtOH (not denatured). I'll report back on this tomorrow.
[Edited on 19-6-07 by woelen]
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woelen
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I did the experiment, and indeed it works nicely. I just mixed the chems as described in my previous post and stoppered the test tube. I put the
stoppered test tube in a beaker with hot water (70 C or so) and left it over there (slowly cooling down to room temperature). After two hours of
standing in this beaker (the water cooled down to room temperature) there was a strong smell of ethyl acetate when I unstoppered the test tube,
unmistakenly. I learnt something again  .
I did not attempt to isolate the ethyl acetate, I have 250 ml of this liquid, so this experiment was just done out of curiousity to see whether this
esterification reaction indeed can happen in aqueous medium.
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Pyridinium
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| Quote: | Originally posted by woelen
I did the experiment, and indeed it works nicely. I just mixed the chems as described in my previous post and stoppered the test tube. I put the
stoppered test tube in a beaker with hot water (70 C or so) and left it over there (slowly cooling down to room temperature). After two hours of
standing in this beaker (the water cooled down to room temperature) there was a strong smell of ethyl acetate when I unstoppered the test tube,
unmistakenly. I learnt something again . |
I couldn't resist trying it myself as well. After 5 hours of standing and some shaking at room temp., I noticed a very definite smell of EtOAc also.
My rxn mix was 5 drops conc. H2SO4, about 2 mL 95% EtOH, about 0.5 mL glacial acetic, and perhaps 0.5 mL H2O.
I tried the same experiment with isopropyl, but I didn't smell anything different. McMurry lists MeOH, EtOH, and 1-propanol but not 2-propanol.
Although I am not giving up just yet. I might try heating under reflux for a bit.
What I did notice also was that acetic acid droplets tended to accumulate at the mouth of the test tube. Perhaps some ester condensed there,
hydrolyzed, and the more volatile alcohol evaporated, leaving the HOAc behind. ? I'm not sure.
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not_important
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Yes, esterfication happens in aqueous medium, it's an equilibrium condition. Excesses of one or more of the reagents forces the reaction to the other
state, as does removal of one or more of the reagents.
One method of making oxalic acid esters is to use an excess of alcohol and saturate it with hydrogen chloride. The HCl ties up the water formed,
driving the reaction over to the ester side.
With the smaller alcohols and acids, the esters are fairly volatile. Even if only a tiny amount of ester is formed, the reaction still goes. If that
ester can evaporate from the reaction mix, its removal drives the reaction in the direction of ester formation. And with much headspace above the
reaction mix, a sniffable amount of ester can be formed. And of course a large excess of alcohol helps.
With a decent fractionating column you can pull methyl acetate, methyl formate, and ethyl formate, out of their reaction mixtures. You will also get
some of the alcohol and water. but lacking a catalyst the mixture is stable enough for collection and further isolation.
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S.C. Wack
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Related to the last few posts, with 28.6% acetic acid + "concentrated" HCl -
Preparation of Ethyl Acetate in the Presence of Water
Mix in a 500 ml flask 50 g of ethyl alcohol, 60 g of glacial acetic acid, 150 ml of water and 20 ml of concentrated hydrochloric acid. To ensure even
boiling put in the flask a small piece of porous tile. Place a thermometer in the flask to observe the temperature of the vapor, and connect it with a
water-cooled condenser. Distil not faster than 1 drop per second.
[Transfer the distillate to a separatory funnel and shake it with 50 ml of a solution of sodium chloride prepared by dissolving 60 g of salt in 200 ml
of water. Draw off the salt solution and repeat the washing three times. At the end of the fourth treatment leave about 5 ml of the salt solution in
the funnel, and add about 0.5 g sodium bicarbonate. Put the stopper in the funnel, invert it, open the stop-cock, and shake cautiously. Enough of the
bicarbonate should be used to neutralize the small amount of acid left after the first washings. When no more carbon dioxide is evolved draw off the
aqueous solution and run the ester into a distilling flask, and add about 15 g of calcium chloride. Let the product stand for at least 2 hours and
distil from a water-bath.]
The yield is about 50 per cent of the theoretical.
Norris - Experimental Organic Chemistry 3rd ed 1933. Exp. #109 [#108]
Norris is right on with the bp of the ternary azeotrope (70.3C) but way off in its composition according to Lange's.
[Edited on 19-6-2007 by S.C. Wack]
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12AX7
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Speaking of ethanol and oxidizer, last night I took a sample of nasty ethanol ("solar" distilled from fermented sugar, see the ethanol thread), added
a few grains (i.e., crystals, not the unit of weight) of potassium dichromate, and dripped in some not-very-pure ~50% sulfuric acid. Over about ten
minutes, it warmed up and turned from orange to dark green, taking on a burnt smell reminiscient of burning charcoal (either complex products, or
oxidized impurities) and an irritating odor I suppose reminiscient of apples (being the ever-special ethanaldehyde). I left it on the warm spot over
night, leaving, I suppose, potassium and chromium sulfates and some acetate. Not much acetic acid was formed, that I can tell, given the green goo
has little odor now.
Tim
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mbrown3391
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This is only slightly related, but im trying to synthesize acetic anhydride, and i found this reaction:
http://www.chemthes.com/rxn_dp.php?id=3348
The reaction uses ethanal and looks easy enough to do at home, but i dont quite understand it. Anybody know how this would work. Also, it looks like
the reaction produces acetic anhydride and water. Wouldn't the acetic anhydride hydrolyze right back into acetic acid?
[Edited on 20-6-2007 by mbrown3391]
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woelen
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The reaction only is possible in the presence of a compound, which takes away the water. Maybe with H2SO4 or P4O10.
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mbrown3391
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What is the actual chemical equation representing the the ethanol/h2o2 reaction? The only thing i can think of is maybe the ethanol is dehydrated by
the sulfuric acid and then immediately oxidized by the hydrogen peroxide.
CH3CH2OH --> CH3CH
CH3CH + H2O2 --> CH3CHO + H2O
Just a guess. If anyone knows the correct formula please post it.
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woelen
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In dilute acid, the ethanol certainly is not dehydrated. It simply is oxidized by the hydrogen peroxide to ethanal (and possibly further to acetic
acid):
CH3CH2OH + H2O2 ---> CH3CHO + 2H2O
Ethanal may in turn be further oxidized to acetic acid.
CH3CHO + H2O2 ---> CH3COOH + H2O
I can also imagine that ethanal forms peroxo-compounds, a little bit like acetone forms peroxo-compounds, in the presence of acid.
In concentrated H2SO4, the reaction between ethanol and H2O2 is explosive. If you ever mix some "piranha's solvent" (mix of H2O2/conc. H2SO4) with
ethanol, then a violent explosion occurs. In that case there definitely is not a clean simple oxidation of ethanol.
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mbrown3391
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thats weird, i used conc. sulfuric acid. Does the explosion only occur if the reaction is allowed to get hot?
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woelen
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What is the concentration of your H2O2? You certainly can make explosive mixes with 30% H2O2 and concentrated H2SO4. This is called "piranha
solution". Mixing this with organics like acetone or ethanol is extremely dangerous and may lead to violent explosions.
If you only use 3% H2O2, then it will be too dilute and too much water will be added, then I don't think you can make an explosive mix.
Also, something which is dangerously explosive does not always explode. That makes stuff like piranha solution so dangerous.
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mbrown3391
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i used 40 volume h2o2. no idea what that means
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woelen
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That is appr. 12% H2O2. N-volume H2O2 means that a volume of this liquid gives an N-fold volume of oxygen at room temperature, when completely
decomposed. 3% H2O2 is appr. 10 volume.
Probably your 12% H2O2 is not sufficiently concentrated.
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mbrown3391
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So what explosive would form if i used conc. H2O2? or would the solution just explode?
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woelen
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With the concentrated acid, and H2O2 of sufficient concentration, you would get Caro's acid, H2SO5. The solution obtained in this way is called
"piranha solution" or "piranha solvent". Just google on this and you'll find a lot of information.
This liquid itself is not explosive, but accidental mixing with organics may lead to explosion. The liquid reacts VERY violently with organics, and
this violent reaction may set off the whole amount.
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16MillionEyes
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So the production of ethanal can be done by making a solution of ethanol, hydrogen peroxide and some diluted strong acid? What concentration must the
ethanol be?
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