shaheen16
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Oxidation of Ethanol to Ethanal?
Hi guys,
I NEED HELP! I have a presentation tommorow on the oxidation of ethanol to ethanal and I'm lost :/
Firstly, I need to know the reaction mechanism involved. Does anyone know the steps on how to get from ethanol to ethanol?
I know the reaction is something along the lines of:
3CH3CH2OH + CR2O7 + BH --> 3CH3CHO + 2CR3 + 7H20
but I need to know what's happening step by step. I've searched everyone on the internet and I cant find anything!
Not only that, I need to know the curly arrows involved too!
Can someone please help me out 
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mnick12
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This took me a gut-wrenching 3 minutes to find: http://www.springerlink.com/content/u14n74051g547p07/ .
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madscientist
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Thread Moved
7-2-2011 at 20:11 |
shaheen16
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sorry but what is that? :/
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mnick12
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what is what?
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madscientist
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That is the mechanism!
I weep at the sight of flaming acetic anhydride.
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shaheen16
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I'm so confused
what's a mechanism? Like a catlyst? or something...
ahhhhhhhh
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mnick12
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Oh boy, if you are not sure what mechanism means then I am afraid any attempt to explain the oxidation of primary alcohols to aldehydes would be a
waste of time. At least in this sense, a mechanism could be thought of as the way the chemical reaction proceeds, meaning how you go from A to B with
all the steps in between.
Good luck!
Oh and just a tip, it would be prudent of you to NOT to wait until the night before your presentation to ask for help. Humans need much more time to
memorize and understand things than a single night
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Cuauhtemoc
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You're still in highschool right?
A mechanism explains step-by-step what is going on with the molecules involved.
Each of the curly arrows show a pair of electrons moving.
So in the first step you have a pair of electrons of the oxygen(represented by the two dots, each dot is an electron) "attacking" the Cr atom, this on
the other hand causes a pair of electron that was making the double bound between Cr and O go back to the oxygen.
Cr can make 6 bonds, as a new bond is made another one is broken.
Each bond is made by two electrons in this case one from oxygen and another one from chromium, as the bond is broken the two electrons migrate to the
oxygen atom which in turn can make a bond with a single hydrogen.
And so on, just follow the arrows.
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madscientist
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Is this the first time you looked at any of the material for your class?
You already were given the answer. If you can't recognize that, you're going to have to do some reading. If explanations are not given in your
textbook, which I find hard to believe, here's some helpful articles:
http://en.wikipedia.org/wiki/Reaction_mechanism
http://en.wikipedia.org/wiki/Arrow_pushing
http://www.chem.wisc.edu/areas/reich/handouts/elecpush/epush...
You're on your own until you can show you learned something. Sciencemadness is not Academic Dishonesty 911 - no one here is going to make a
presentation for you.
I weep at the sight of flaming acetic anhydride.
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shaheen16
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So that's the general mechanism of an alchohol to an aldehyde? Is the same thing applied to ethanol to ethanal then?
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madscientist
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Yes.
I weep at the sight of flaming acetic anhydride.
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shaheen16
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I'm not asking anyone to make my presentation for me, nor am I looking at the material for the first time. I had thought I had the right reaction
until I was proved otherwise. I'm just looking for someone to help me figure it out.
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shaheen16
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My reaction doesnt use acetone thought, does it make a difference?
Oh sorry I forgot to say, thanks for those links!
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madscientist
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No, it doesn't.
I weep at the sight of flaming acetic anhydride.
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Cuauhtemoc
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Acetone is just the solvent, it doesn't make a difference in your case.
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shaheen16
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Thanks for the help everyone! 
I have one more question, does anyone know what enviormental conditions must be in place for oxidation to occur?
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peach
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EthanOL can be converted to it's aldehyde (ethanAL) by passing it over hot copper as a catalyst.
This is called dehydrogenation, as a pair of hydrogens are removed by the copper.
Count all the hydrogens on ethanOL in this picture. The O-H on the right is the functional group, and here it is an alcohol group. You can have
alcohols of lots of different things, so long as they have this O-H group sticking off them.
This is ethanAL. The left side carbon of the molecule has stayed the same, but the one on the right has changed, there is now only one hydrogen left
and the oxygen has double bonded to the carbon on the right - this is because carbon likes having four bonds and oxygen can make two. With two of the
hydrogens missing, the oxygen makes up for the lack. If you count the number of bonds to the right hand carbon in ethanOL and then ethanAL, you'll see
they're the same; four. The only thing that's changed is the number of hydrogens present.
This catalytic method is very simple. Ethanol is blown into solid copper turnings, wire, powder or (far more effective) copper that's deposited on a
type of sponge (zeolite - which is also used in kitty litter and washing powder).
The copper is heated to around 300C.
The two hydrogens that get removed from each molecule of ethanOL come out of the process as hydrogen, H2.
Zeolite is a mineral you find in rock. If you roast it, it becomes microporous. When you look at it under a microscope, it will be full of billions of
tiny holes. When the copper is deposited on that, it gives the copper a gigantic surface are.
Both the bulk production methods for ethanAL use catalysts. But this copper one is not how ethanal is typically produced on a bulk scale, but bulk
quantities of it have been made from surplus grain alcohol (ethanol), using this process.
The alternative method starts from ethylene and uses a palladium (platinum) catalyst and oxidation, as it's cheaper when you're running huge plants
that can handle stranger materials.
There are, I suppose, three main stages to your level of knowledge in chemistry.
To begin with, you'll be mixing things and only know very roughly what is happening.
By the time you're 16-18, you should know what functional groups are and be starting to understand how they swap and why they're important.
As you're going from 17 to 18 to university, you should know what mechanisms are and have studied at least one of them. The mechanism tells you
precisely how the things are swapping electrons and parts of the molecules around.
Mechanisms aren't chemical by chemical things, they apply to broad spectrums, since the specific chemical doesn't matter so much as what functional
groups are on it; and there aren't anywhere near as many functional groups as there are different molecules with different combinations of them
present.
They are called functional groups because they are the part of the molecule that is typically involved in a reaction; that gives it it's main
characteristics.
E.g. EthanOL and ethanAL are very similar, the only change is in their functional group. One makes you drunk and the other makes you feel very sick if
you drink it.
YOUR BODY ENZYMATICALLY CONVERTS ETHANOL TO ETHANAL WHEN YOU DRINK ALCOHOL, AS IT TRIES TO BREAK DOWN THE CHEMICAL
Which is part of the reason for feeling so nasty once the ethanol is gone.
These are called tautomers. The molecules are virtually identical. The only change is the state of their functional group. And it's
also a simple change. The functional group is being oxidised, from ethanOL to ethanAL (a higher oxidation state).
If it oxidises a step further, it because ETHANoic acid.
This is what's in vinegar. And wine that hasn't been sealed up properly, or that's been left open for too long, will sometimes smell a bit like
vinegar, as this is what's happened.
The ethanOL has oxidised to the higher oxidation state, the acid. There are some bacteria that will do this if they get into the wine, and it's one
way of making vinegar (dilute ethanoic acid).
Ethanoic acid;
Here is some zeolite. It looks pretty boring, but is used for a lot of chemistry work due to it's special microscopic pore structures. It can do some
amazing things given how simple it is.
Pure, specific forms of zeolite are usually used to carry catalysts like copper, and they are powdered by grinding them, to give them an even larger
surface area. Here's what the grains look like under an electron microscope.
The topic of making ethanAL, and the various different methods, has been discussed a lot on this forum. You can find them by searching for ethanal and
aldehyde (although the latter will bring up things related to other aldehydes as well). Here is a link to one such thread, showing people actually
trying the different ideas
[Edited on 8-2-2011 by peach]
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shaheen16
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THANK YOU SO MUCH! that helped out alot, thank you!!!
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Sedit
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Your searches will yeild alot more useful information I believe if you use the term Acetaldehyde instead of Ethanal since some search engines may see
it as a typo and yeild you many useless pages.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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