[guybrush]

I have been asked to interpret the following reaction:

Ethanol (C2H6O)was pipetted into a tube, solid potassium dichromate crystals (K2Cr2O7) were added followed by drops of sulphuric acid (H2O4S).

The odour from the tube was now slightly different than from the start (stronger and sweeter smelling)

After heating the liquid in the tube turned slightly green and gave an odour that was similar to a whiteboard marker  pen (cant remember the actual name).

I am not sure what to say about this reaction. Is it to do with the intermolecular structure of the compounds? What made it turn green?

[Smrt guy]

You're clearly supposed to identify the products.  As a general rule, pure organics are colorless, so your first bet should be that the green color is from the metal.  What is dichromate used for?

[guybrush]

Its used for oxidizing experiments in the lab as well as uses in the outside world.

This means it requires an extra oxygen molecule to complete the reaction.

ch3ch2oh + (O) = ch3C=Oh + h2o

The product changes to ethyl aldehyde and of course water. Is this correct? This is the basic equation of what happens (without inserting the remnants of the Chromium).  The lecturer did not mention any further oxidation which would take it to ethanoic acid so im not sure whether to put the 2nd part of the reaction in, or the Chromium in the 1st equation.

[orgopete]

@guybrush
I sort of agree with what you have written, but it is possible to write this example without the loss of water. Since dichromate is technically an anhydride of chromic acid. The proton being removed concomitantly with the electrons being accepted by the chromium need not generate a water molecule (though that is commonly found in a mechanism).

There are two proton transfer reactions, one with the formation of a chromate ester (the CH3CH2OH) and the second to generate CH3CHO + H⁺. It is possible to remove one or both with a chromate oxygen and not water. I am not arguing that water must be avoided, only that it can be avoided. If it were avoided, then acetaldehyde is a more likely product because water can easily form a hydrate with acetaldehyde to form acetic acid. 

[guybrush]

Just to further this.

I have a dehydration elimination reaction:

Ethanol is in a tube and is dehydrated leaving a gasesous product. This product is bubbled through bromine solution. A vacuum is formed and pulls the Bromine solution up the pipe.

My answer is that H2O is eliminated from ethanol (dehydration) so this gives a Carbon Double bond with the addition of Bromine coming up the pipe which will become Bromo-ethene. Is this correct? What is the gas that is being expelled?

[srihari]

bromo-ethene ?? do think again you're almost there
a bit more you'll easily get it
( the carbon carbon double bond is formed , just go ahead and
think just a little bit more )

regards
Srihari

[guybrush]

hmmm, the other that comes to mind is dibromo-ethene. But what makes me unsure is that it is not pure bromine is it? Its a bromine vapour gas, like HBr but then that would not make a difference to bromoethene would it.

[Smrt guy]

If the bromine solution is nonaqueous (and not alcholic), then you would get dibromoethane, not ethene