Alright, Oxidation is one key Concept in Organic Chem, we can to get it right in a few SIMPLE steps 🙂
starting with PRIMARY alcohol, we will go through the common oxidation performed.
Next up, we have the brother of Primary Alcohol…… Secondary Alcohol!!!
It is important to take note that Secondary alcohols are NEVER found at the extreme left or right ends of a hydrocarbon chain!
That is because to be a secondary alcohol in the first place, the carbon that bonds to our OH group has to be happily sandwiched in between 2 other carbon atoms!
Now, also take note that Ketones CANNOT be oxidised any further 🙂
Alright! Lets move on to the more confusing part of alkylbenzene Oxidation!!!
First up, lets take note of the very special points of AlkylBenzene oxidation
So far we learn that straight-chain alkyl groups cannot be oxidised but alkylbenzene can.
under (KMnO4 , acid catalyst and heat)
Now, let us consider how the above mentioned process can help us in reducing number of carbon atoms!
Great! now we know that oxidation of alkyl group is actually not that difficult!
The number of carbon atoms in the alkyl groups should not hold you back when you KNOW you can oxidise the whole alkyl group no matter how many carbon atoms it has to just a SIMPLE COOH group!
Next, using what we have learnt from above, and adding the new ingredient of functional groups, we shall sample the results below!
It is important to not feel unsettled by the functional groups present!
Because the final product of oxidation of alkylbenzene in most A level questions is in most cases just our very humble and simple benzoic acid!
next up, we will turn our attention from KMnO4 to K2Cr2O7!
Right now, it is useful to do a comparison between the effects of oxidation of KMnO4 and K2Cr2O7 which are our 2 important oxidising agents on alkylbenzene.
If you have noticed so far, we have only discussed about oxidation of Alkylbenzene,
yet there are 2 exceptions in straight chain carbons whereby
KMnO4 (H2SO4 (aq) and heat)
will oxidise the following to CO2 and H2O!
OXIDATION of ALKENES
All right! Oxidising Alkenes are a great way to
* shorten the carbon chain*
= you will use it super often in A levels! trust me
recall that the only other 2 ways are oxidising alkylbenzenes, which we covered in front, and using Iodine!
take note that K2Cr2O7 CANNOT oxidise alkenes AT ALL!!!
without further ado, lets proceed to the main part!
Great we are nearing the end of our Oxidation POST!
Now you were be introduced to the “3 musketeers” of oxidising agents……
Namely, Fehling, Tollen and I2
Last but not least!!!
our final contestant is I2
Oh right! hey guys, take note that iodine can
1) oxidise 3 different functional groups
– namely KETONE, ALCOHOL and ALDEHYDE!
2) But for iodine to oxidise those mentioned above, the functional group has to be attached to a METHYL GROUP!
detailed explanation can be found here, *winks*
3) Therefore, ethanal (above) which is the only aldehyde with an CHO (aldehyde) group and a METHYL r group ,
is THE only aldehyde that can be oxdised by iodine
4) If the above points have not yet wowed you, the oxidation product of all 3 functional groups turn out to be the SAME! yeah! which is RCOO-
5)In addition,our amazing iodine, which can oxidise 3 good old functional groups to the SAME thing, can only work when it has an ALKALI catalyst.
So your in your final answer, the product of oxidation is not COOH but COO-
6) Iodine is apparently a good friend of Tollen and Fehling, not just that all 3 require alkali catalyst, they also share another common reagent and condition : temperature gotta be WARM
7) Finally, to the horror of students, IODINE is going to appear in the exams!
because other than oxidising ALKENES…………….. using IODINE to oxidise our organic compounds is………
THE only other way to SHORTEN the carbon chain – by ONE carbon atom!
also, it is a very useful Distinguishing test! because CHI3 is a yellow precipitate