Sciencemadness Discussion Board

Ethanol + H2O2

mbrown3391 - 18-6-2007 at 11:32

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.

Drone - 18-6-2007 at 12:17

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).

guy - 18-6-2007 at 13:56

It is probably ethanal (acetaldyhyde) and ethyl acetate. Both smell fruity.

Pyridinium - 18-6-2007 at 14:11

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 :P

woelen - 18-6-2007 at 22:52

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.

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.

Pyridinium - 18-6-2007 at 23:34

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]

not_important - 19-6-2007 at 00:17

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.

Pyridinium - 19-6-2007 at 00:32

@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. :P

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]

woelen - 19-6-2007 at 01:21

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]

woelen - 19-6-2007 at 13:55

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.

Pyridinium - 19-6-2007 at 14:03

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. :D
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.

not_important - 19-6-2007 at 15:18

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.

S.C. Wack - 19-6-2007 at 15:23

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]

12AX7 - 19-6-2007 at 15:58

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

mbrown3391 - 20-6-2007 at 10:00

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]

woelen - 20-6-2007 at 13:31

The reaction only is possible in the presence of a compound, which takes away the water. Maybe with H2SO4 or P4O10.

mbrown3391 - 21-6-2007 at 13:11

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.

woelen - 22-6-2007 at 02:10

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.

mbrown3391 - 22-6-2007 at 07:35

thats weird, i used conc. sulfuric acid. Does the explosion only occur if the reaction is allowed to get hot?

woelen - 22-6-2007 at 13:15

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.

mbrown3391 - 22-6-2007 at 15:45

i used 40 volume h2o2. no idea what that means

woelen - 23-6-2007 at 03:18

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.

mbrown3391 - 24-6-2007 at 08:07

So what explosive would form if i used conc. H2O2? or would the solution just explode?

woelen - 25-6-2007 at 00:58

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.

16MillionEyes - 13-7-2007 at 10:37

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?

Nerro - 13-7-2007 at 11:10

It doesn't seem to be very important to me what concentration the ethanol is. The reaction will be driven by the fact that ethanal evaporates very readily. The more dilute the ethanol is the slower the reaction will procede.

16MillionEyes - 14-7-2007 at 07:44

I think I'll try that. I also have some 40 volume hydrogen Peroxide the same one the original post was talking about so I'll see if it works as well.

16MillionEyes - 14-7-2007 at 14:18

By the way, I've read is really toxic. Did any of those who've produced it get any side effects?

Nerro - 14-7-2007 at 15:41

Aldehydes aren't exactly healthfood but if you work in a reasonably ventilated space or outside you'll probalby be fine. Docters in training smell of formaldehyde all the time and it generally doesn't seem to kill them :)

16MillionEyes - 14-7-2007 at 20:57

MSDSs can really scare you away sometimes. I normally look at those for precaution anyway but sometimes I just have to make sure.