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Hockeydemon
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Butyric acid from butanol & KMnO4
I was trying to make some butyric acid by oxidizing butanol with KMnO4, but I have had no such luck.
I figured I could simply add a hot solution KMnO4 to butanol, and the stopping point would become apparent by the smell. Because of this I didn't
really take note of how much KMnO4 I added in total, but I started with 100mL of butanol, and I added an absurd amount of KMnO4 solution relative to
the 100mL of butanol.
A reaction was clearly taking place because of how exothermic the addition of KMnO4 was. But no matter how much I seemed to add I never really got
anywhere.
It had crossed my mind that I allowed the reaction to get too hot which caused the butanol to boil off, but at the same time in order for that heat to
be generated in the first place wouldn't some of the butanol had to have been oxidized to butanoic acid?
The KMnO4 is a very pretty purple color in solution, and when added to the clear butanol a brown sludge is formed.
On a side note I took about 2mL of that sludge, and added ~1mL of nitric acid to it. The mixture instantly started to bubble, then went clear &
formed 2 layers. Any clue as to what took place in that reaction?
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bfesser
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Which isomer of <a href="https://en.wikipedia.org/wiki/Butanol#Isomers" target="_blank">butanol</a> <img src="../scipics/_wiki.png"
/> do you have? What were the approximate temperature and concentration of your <a href="http://en.wikipedia.org/wiki/Potassium_permanganate"
target="_blank">potassium permanganate</a> <img src="../scipics/_wiki.png" /> (KMnO<sub>4</sub> solution?
In the reaction, the KMnO<sub>4</sub> would be reduced to <a href="http://en.wikipedia.org/wiki/Manganese(IV)_oxide"
target="_blank">manganese(IV) oxide</a> <img src="../scipics/_wiki.png" /> (MnO<sub>2</sub>, this is your brown sludge.
[Edited on 7/20/13 by bfesser]
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Hockeydemon
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I figured I'd need to have provided more detail to get any real answers. I guess I was more looking for X was wrong in your process.
I'll have to redo it to give you the conc of the KMnO4 (any recommendation?). The temp was at least 100C since it was at a boil. It is 1-butanol.
The solution containing the butanol & KMnO4 was very hot, and steaming quite a bit.
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bfesser
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I'd recommend a little lit. research before you proceed. <a href="http://library.sciencemadness.org/library/books/vogel_practical_ochem_3.pdf"
target="_blank">Vogel's Bible</a> <img src="../scipics/_pdf.png" /> has a few KMnO<sub>4</sub> oxidations (including one of
isobutanol).
[Edited on 7/20/13 by bfesser]
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Hockeydemon
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I know I'll be reading up a bit more before I give it another go - it just appeared to be really straight forward when I read about it initially.
I was wondering though.. After I form butanoic acid I should have a solution of that + MnO2 (& H2O & K). Could I distill off the butanoic
acid, and then use nitric acid to nitrate the MnO2 to form manganese nitrate + H2O? Since they are immiscible I could separate the two, and be left
with manganese nitrate?
Or does HNO3 + MnO2 not form manganese nitrate since you edited that part out of your post?
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Lambda-Eyde
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Quote: Originally posted by Hockeydemon  | | I was wondering though.. After I form butanoic acid I should have a solution of that + MnO2 (& H2O & K). Could I distill off the butanoic
acid, [...] |
Obviously not, since butyric acid has a boiling point that is 63 degrees higher than that of water. If you had checked Wikipedia (for instance) in
advance, you would have known that. You also would have known that alkaline permanganate oxidizes butyric acid to carbon dioxide. I don't know if this
is what happened here (seemingly in neutral conditions), but it might be a possibility. Dichromate would anyways be a better oxidizing agent.
What sort of apparatus are you doing this in? An open beaker? How do you think you're going to tackle the overpowering smell of 100+ g of hot butyric
acid as the reaction proceeds? I'd do it in a two- or three-neck flask, alternately a flask with a claisen adapter with an attached reflux condenser
leading to a trap filled with a lye solution, and an addition funnel in the remaining neck. After adding all the oxidant and letting the reaction come
to the halt, I'd probably distill off the water, then the acid, and finally dry and distill again. All done in an apparatus sealed with an alkaline
lock, of course (and don't forget the suck-back traps).
But these are just my personal ramblings and gut-feel. Look up a tried and true published procedure.
No, manganese dioxide contains Mn(IV), while manganese nitrate contains Mn(II). You'd have to reduce the dioxide first. There is a prep for preparing
manganese(II) sulfate from manganese(IV) dioxide using sulfuric acid and hydrogen peroxide. I do not know if you can do the same with nitric acid.
Your check-list for next time:
Gather all relevant physical data such as boiling points, molecular weights, concentrations etc.
Look up a published procedure for this procedure or an analogous one (e.g. the oxidation of 1-propanol to propanoic acid) and follow it. Write
out your steps. Know what to do in order to handle smells and eventual spills.
Consider scaling down from your original scale. You've just wasted 100 mL of butanol and a considerable amount of permanganate. Had you done it
at 1/10 of the scale you would have wasted less reagents. Also, 10 mL of butyric acid is a whole lot less unpleasant to spill than 100 mL of that
beast.
Don't you ever again think that organic chemistry is easy or straight forward. It never is 
This just in: 95,5 % of the world population lives outside the USA
Please drop by our IRC channel: #sciencemadness @ irc.efnet.org
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Magpie
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KMnO4 is a strong oxidant and can indeed be used to chew up organics and spit them out as CO2.
I suggest you try a milder oxidant - say nitric acid. Here's a procedure for conversion of an alcohol to an acid which may prove beneficial:
http://www.sciencemadness.org/talk/viewthread.php?tid=13122
Runaway reactions, even explosions, are a risk when mixing an alcohol (a fuel) with a strong oxidant. I think the best technique is to get the
oxidant up to reaction temperature and then very gingerly and slowly add the alcohol to keep the reaction going. When all the alcohol has been added
and the reaction seems to have stopped, then apply some heat to assure maximum completeness of the reaction.
[Edited on 20-7-2013 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Acidum
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First thing - KMnO4 is very powerful oxidizer, and it also has several levels of oxidizing depending on reaction conditions. Depending on
pH, concentrations and temperature, it can do things from mild oxidations to formations of carboxylic acids to total oxidation of organic compounds to
CO2. So, check on conditions BEFORE trying to synthetize something. Most likely You created vast amounts of CO2...
Oh, and definitely this:
| Quote: Originally posted by Lambda-Eyde |
Your check-list for next time:
Gather all relevant physical data such as boiling points, molecular weights, concentrations etc.
Look up a published procedure for this procedure or an analogous one (e.g. the oxidation of 1-propanol to propanoic acid) and follow it. Write
out your steps. Know what to do in order to handle smells and eventual spills.
Consider scaling down from your original scale. You've just wasted 100 mL of butanol and a considerable amount of permanganate. Had you done it
at 1/10 of the scale you would have wasted less reagents. Also, 10 mL of butyric acid is a whole lot less unpleasant to spill than 100 mL of that
beast.
Don't you ever again think that organic chemistry is easy or straight forward. It never is
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...and then I disappeared in the mist...
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Hockeydemon
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Firstly - thank you for all of the helpful responses. I'm just now starting O-chem so my apologies on my naivety.
| Quote: Originally posted by Lambda-Eyde | | What sort of apparatus are you doing this in? An open beaker? How do you think you're going to tackle the overpowering smell of 100+ g of hot butyric
acid as the reaction proceeds? I'd do it in a two- or three-neck flask, alternately a flask with a claisen adapter with an attached reflux condenser
leading to a trap filled with a lye solution, and an addition funnel in the remaining neck. After adding all the oxidant and letting the reaction come
to the halt, I'd probably distill off the water, then the acid, and finally dry and distill again. All done in an apparatus sealed with an alkaline
lock, of course (and don't forget the suck-back traps). |
I was just doing it in a beaker yes. I had an aspirator next to me that I was going to throw on once I smelled anything foul.
I have a 3-neck flask that I can setup with an addition funnel, & reflux condenser. Why would my reflux condenser lead to a solution of lye? I
understand the premise of neutralizing the acid, but the acid should never leave the reflux condenser? I'm also unfamiliar with an 'alkaline lock'
& wasn't able to turn anything up readily with google.
| Quote: Originally posted by Magpie | KMnO4 is a strong oxidant and can indeed be used to chew up organics and spit them out as CO2.
I suggest you try a milder oxidant - say nitric acid. I think the best technique is to get the oxidant up to reaction temperature and then very
gingerly and slowly add the alcohol to keep the reaction going. When all the alcohol has been added and the reaction seems to have stopped, then
apply some heat to assure maximum completeness of the reaction. |
Adding the alcohol to the oxidant would only be viable with HNO3 correct? If I have the KMnO4 in excess and add the alcohol to it wouldn't it proceed
to 'chew up' the alcohol producing CO2?
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Can someone correct anything I get wrong in the following.. Forgive me if this is a vast over simplification.
The butanol is first oxidized to the aldehyde butanal with the addition of permanganate because the electron rich single bonded oxygen atom cleaves
off two hydrogen from the butanol leaving butanal & H2O. This changes the oxidation state of the Mn to +6 (from +7).
Why is the aldehyde able to pull off another oxygen atom from the manganese trioxide?
-----
I looked up the isobutyric acid synthesis in Vogel's book (pg. 668 exp:5.122). His uses fairly large quantities, of everything & ends up with a
yield of only 45g isobutyric acid which isn't very much. I can of course scale his synthesis down (I would have to - I don't have a 5L rb flask). But
I would like to use the product to make other aromatic compounds.
-----
If I used nitric acid as the oxidizer would each HNO3 molecule only be able to perform one oxidation? In other words an oxygen molecule would be
liberated from the HNO3 to form butanal, and the HNO2 would simply decompose (2HNO2 -> H2O + NO + NO2)? Then another HNO3 molecule would give up
an oxygen atom to form the carboxylic acid?
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bfesser
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It is clear from the context what you mean by "aromatic compound," but in the future, be careful with that term, as it's a synonym for <a
href="http://en.wikipedia.org/wiki/Aromaticity" target="_blank">arenes</a> <img src="../scipics/_wiki.png" />.
Also, when <strong>Lambda-Eyde</strong> wrote "alkaline lock," what he meant (archaically) was the gas trap which will neutralize acid
vapor ("a trap filled with a lye solution").
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woelen
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May I suggest that next time you do the reactions first on a small scale. It is a pity that you spoilt 100 ml of 1-butanol and an insane amount of
KMnO4. This failure must have cost you quite some money. Bad bad bad.
Next time take 2 ml or so in a test tube and add a little amount of oxidizer. This saves you a lot of money and it strongly reduces the risk of severe
fire and/or explosion.
Another thing is that KMnO4 as solid oxidizer, mixed simply with an organic compound does not yield nice results. You get a horrible black/brown
slurrie and you rip apart most of the organic molecules leaving you with useless crap and a lot of CO2 and H2O.
I'm quite sure that you can get much better results if you dissolve 1-butanol in dilute sulphuric acid and then add KMnO4. In sufficiently acidic
aqueous solution the KMnO4 will be reduced all the way down to Mn(2+) instead of MnO2 and the reaction is much more controlled. The alcohol-group
first is oxidized to an aldehyde-group and after that it is oxidized to the acid. So, you'll first get CH3CH2CH2C(=O)H and then you'll get
CH3CH2CH2COOH. There is no ripping apart of the C-skeleton under these conditions.
Try this in small quantities in a test tube and see whether you obtain the smell of the acid before you continue with larger amounts. Isolating the
acid from the mix will require a decent distillation setup. You first boil off water, then the acid and you'll be left with excess H2SO4 and
MnSO4/K2SO4 mix. Do not boil off to dryness, because that will lead to charring of the butyric acid.
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Magpie
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| Quote: Originally posted by Hockeydemon |
Adding the alcohol to the oxidant would only be viable with HNO3 correct? If I have the KMnO4 in excess and add the alcohol to it wouldn't it proceed
to 'chew up' the alcohol producing CO2?
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Not necessarily. This is likely concentration dependent.
At this point, where you are exploring to find what works at a small scale, I wouldn't worry too much about stoichiometry. I would base my initial
testing on what has worked for others in similar alcohol oxidations. In the oxidation of 1,3 propanediol to malonic acid I assumed the reaction shown
was appropriate stoichiometry. But the actual ratio of HNO3/OH that I used was twice that shown in my equation. My choice was totally based on what
worked in the reference by Seymour where he was making oxalic acid.
As Lambda-Eyde says, in organic chemistry what works is often not terribly predictable.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Hockeydemon
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Okay I went ahead a tried again small scale in 3 test tubes. Each test tube contained 4mL of 1-butanol.
In test tube 1 I had 2mL of 18M H2SO4, and proceeded to slowly add 4mL of HNO3 with frequent stirring. I allow this to happen in the open atmosphere
which allowed the reaction to get fairly hot but still touchable. This resulted in a loss of liquid in the end. I ended up with ~3mL of a dark black
liquid that had a slightly sweet syrupy smell to it. It also of course evolved a lot of NO & NO2 during the addition. Thoughts?
In test tube 2 I had 2mL of 18M H2SO4 along with the addition of less than 1g of KMnO4. I heated this with a Bunsen burner for a little bit with
frequent stirring. Not too much happened other than dark purple/gray liquid formed. I'm guessing since there was a bit of dark purple remaining that I
did not allow the reaction to complete?
In test tube 3 I only added HNO3, and I kept the test tube in cold tap water so the reaction did not get past luke warm. After the first 2mL of HNO3
was added two layers formed. The top layer was a dark green color, and the bottom layer was a light green color. After ~4mL of HNO3 was added it was
all the light green color, but a reaction was still occurring because it would gradually heat up if I took it out of the water & vigorous stirring
would increase the evolution of NO & NO2 gas. After ~7mL of HNO3 was added the solution was a light yellow color, and it would continue to heat up
if not in the water bath, stirring still exacerbated gas evolution. I then placed a stirbar into the test tube, and while in the water bath allowed it
to vigorously stir until I could no longer get a gas to evolve. I then took it out of the water, and allowed the stirring to continue & I applied
heat to the test tube. This caused quite a bit of gas to evolve, but I noticed no real chance to the solution even after I allowed it to cool back
down to room temperature.
None of these variations or steps produced anything that smelled unpleasant. Any thoughts or suggestions? I am curious what the various intermediates
I formed in test tube 3 are if I did not form butyric acid. Is the green the formation of the aldehyde?
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Magpie
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Try this:
Place 3-4mL of 6M HNO3 in a test tube. Add to this 1-2 drops of your butanol. Heat up carefully using a hot water bath until you can see a vigorous
reaction taking place. See if it smells of butyric acid.
The single most important condition for a successful synthesis is good mixing - Nicodem
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woelen
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I see you don't use any water at all. All of these reactions are a form of destuctive oxidation and do not yield what you want. The black stuff you
obtain sometimes is called 'gunk' or 'goop'  and is totally useless. The sweet
smell may be due to broken down molecules having nitro-groups or nitrate groups attached to them. Beware, some of these compounds are very toxic and
strong carcinogens.
Try the following:
Take 3 ml of water and add 1 ml of conc. H2SO4. This will cause the liquid to heat up considerably. Then add 0.5 ml of 1-butanol. Next add a small
spatula of KMnO4 and swirl gently. Assure that you have excess 1-butanol. It may take quite some time and quite some shaking/stirring before all of
the KmnO4 has dissolved. Smell the liquid. I'm quite sure that this reaction leads to formation of butyric acid. If it indeed works, then the next
step is to work towards a mechanism with precisely determined stoichiometry, the first step I described here is checking whether the reaction works.
[Edited on 23-7-13 by woelen]
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Magpie
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| Quote: Originally posted by Hockeydemon |
I looked up the isobutyric acid synthesis in Vogel's book (pg. 668 exp:5.122). His uses fairly large quantities, of everything & ends up with a
yield of only 45g isobutyric acid which isn't very much. I can of course scale his synthesis down (I would have to - I don't have a 5L rb flask). But
I would like to use the product to make other aromatic compounds.
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I looked up the preparation of isobutyric acid in Vogel in the forum library. It gives a preparation using alkaline permanganate that gives a 92.5%
yield. What more could you want. Scale it down if it is too large a batch.
BTW I wouldn't waste any more effort on using nitric acid. Not when you have a procedure provided in detail in Vogels.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Waffles SS
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Nitric acid usually use for oxidation Diol alcohol and i think this is not common method for oxidation Primary alcohol to Carboxylic acid but i like
to try it for oxidation 1-Butanol next week and i will share the result.
I dont suggest Alkaline/Permanganate oxidation method because:
-You should use huge amount of water for making only small amount of carboxylic acid(you need 100lit of water for 1 kg of Carboxylic acid !)
-You should cool huge amount of water and also reduce it by vacuum for best performance
-This method take lot of time(~12hours)
Nitric acid oxidation will be great if it can oxidize primary alcohol to carboxylic acid safe and fast
@Magpie,
Have you ever tried this method for primary alcohol?
[Edited on 23-7-2013 by Waffles SS]
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Magpie
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No, waffles, malonic acid is the only acid I have made using nitric acid. As you say, it was made from a diol. The procedure is convenient because
the workup is so simple.
Brewster gives a procedure for converting sucrose to oxalic acid using nitric acid. I suppose sucrose could be considered a polyol.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Hockeydemon
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Okay I performed another round of experiments with multiple variations with no luck thus far.
Trial 1: I did exactly as Magpie suggested with the HNO3. I place 4mL of 6M HNO3 in a test tube. Then I added 4 drops of 1-butanol and suspended this
in a flask of water. I then heated the flask of water with a Bunsen burner for awhile. The water was just about to boil (small bubbles forming on the
inside of the flask) when the solution in the test tube abruptly started to boil vigorously. I then removed the heat source and allow the reaction to
continue. The reaction continued for about 15 minutes (new bubbles formed). During the reaction oxides were released. The end result was a clear
liquid with a faint NO2 smell though it is a reasonable assumption this could be just remnant of the gas evolved.
Trial 2: I did what Woelen said (same measurements & .5g KMnO4 in each) with two variations. The first variation I allowed to react with no
cooling which allowed the reaction to get quite hot. The solution went very dark at first, and after several minutes it formed two layers. The top
layer was roughly .5mL of a tan liquid. The bottom layer was clear, and made up the majority of the solution.
The second variation I did the whole reaction at 5C in an ice water bath. After about 10 minutes of vigorous stirring in the ice bath I removed the
solution. The solution was a very dark color - I'd say a dark brown. This also formed two layers with the top one being comprised of roughly .5mL of
the same tan liquid. The bottom one was of course the dark brown liquid.
Neither of these produced any unpleasant smells. I also made sure to pull a small amount of the bottom layer out with a pipette, and I placed that on
a paper towel to see if it smelled any different. I did not notice any difference. Since nothing occurred in either test tube variation I decided to
heat both solutions with a torch (gradually). Once the solutions both got up to temperature a reaction took place that made each solution go clear.
The first variation test tube (not cooled) was crystal clear with a small dark ring of residue around the top of the liquid (this is possibly just
KMnO4 dust that was on the walls of the test tube). The second variation (cooled test tube) also went clear, but had a slight tan tint to it.
Both liquids smelled quite pleasant. I can't think of anything that it reminds me of, but I did think it smelled good enough that I was upset I was
limited to wafting the odor towards my face rather than actually smelling it. I wish I knew what it was (I know you said possibly toxic molecules with
nitrate groups attached).
----
On top of those I also did a 1% scale of Vogel's isobutryic acid synthesis (obviously using 1-butanol instead). I placed 1mL of 1-butanol, and ~.1-.2g
(non-mg scale) of sodium bicarbonate into 1.5mL of water. I placed this into a 100mL round bottom flask which I suspended in a 1L beaker of iced salt
water over a stir-plate. I then added 1.4g of KMnO4 to 27.5mL of water and mixed until dissolved. I then added this to the rxn vessel which was at 5C.
The instructions say to continue stirring for 3-4hrs, and then allow the rxn to come to room temperature over the next 12 hours. I will however be
leaving for work shortly so the rxn will continue stirring for the next 8-9 hours. I will stop it when I get home, and it will sit for another 7 hours
while I sleep. I will then continue with Vogel's instructions from there & let you know of the results.
[Edited on 25-7-2013 by Hockeydemon]
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woelen
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Did you use dilute sulphuric acid and added 1-butanol to that, and then added KMnO4? This is as I described it.
I am surprised that you did not get any butyric acid with my method. I have the impression that you obtain an ester (n-butyl butyrate), but this would
surprise me, given all the water present in the mix.
If you indeed obtain an ester, then the reaction does work, but immediately after formation of the butyric acid it reacts with excess 1-butanol to
obtain the ester. This, however, is not something which I would expect, but it is the only explanation which I have for what you observe. Especially
because you obtain a clear liquid in the end and not some black gunk.
In the experiments with KMnO4 as oxidizer you can smell safely, you do not have to worry about very toxic compounds in the mix. The formation of the
strongly carcinogenic compounds only occurs when there is destructive oxidation with HNO3 (if you get plumes of NO2, together with white fumes, then
you'd better leave the place for a while and allow the fumes to diffuse away).
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Hockeydemon
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I added H2O to the test tube, then H2SO4, then butanol, and then while stirring added the KMnO4.
After reading the scent profile of n-butyl butyrate I would say that is a fair description of what I smelled. Am I correct in assuming that the top
.5mL of the solution would be the butyl butyrate ester, and the bottom layer was mostly water?
Since the butyric acid is reacting with excess 1-butanol should I try running the experiment again, and half the 1-butanol quantity?
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woelen
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I do not think that the top 0.5 ml is pure n-butyl butyrate, but it most likely contains quite some of this ester. I expect it to be a mix of the
ester and 1-butanol.
Maybe you could get better results when you use less 1-butanol, but you still have the complication that the ester is formed. This is something which
complicates things a lot. I myself have experience with ethanol being oxidized to acetic acid and there, the problem of formation of ethyl acetate in
the aqueous solutions is nearly non-existent. I expected it to be the case with 1-butanol as well, but apparently things are otherwise.
I am afraid that an organic chemist must jump in with good ideas.
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DutchChemistryBox
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Maybe you can try to make the Butyl butanoate on purpose with the description of woelen but then with less water.
And seperate the ester from the rest and then add natriumhydroxide to make Sodium butanoate.
After that you can evaporate the solution so you'll have an almost alcohol and water free solid.
If you distill this with concentrated H2SO4 I would say that your product is butanoic acid.
Or am I thinking way out of the box?
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Hockeydemon
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I've just allowed the mixture described in Vogel's book to sit for 12+ hours, and I have a few questions going forward with the instructions.
It says to then filter off the manganese dioxide, and concentrate the filtrate under reduced pressure then cool.
This is simply saying distill the filtrate under reduced pressure right? Does what pressure I get to matter?
It then says cover the solution with a layer of ether, and acidify with dilute sulfuric acid.
I don't have ether or any non-polar solvents currently. I have several aprotic, and protic polar solvents. I guess I could make some ether - I do have
some pure ethanol in the freezer. Is this the only way around this?
It also doesn't give a quantity for what acidifying the solution requires. Is this something that I'm supposed to know?
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adamsium
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Concentrating the solution under reduced pressure means to remove some of the solvent and possibly excess reagents under vacuum, leaving a more
concentrated solution of the product. This is what you would often do on a rotary evaporator (though not to dryness in this case, it seems).
It's probably sufficient to acidify until the solution is just acidic.
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