K2Cr2O7 synonymous with CrO3?

[pineappletree]

It seems that (according to Practice problem #94 in chapter 5 of the Berkley review) that K2CrO7/H2SO4 is the same thing as CrO3/H2SO4


What sequence of reagents will convert an aldehyde into an amide?
A.) 1.NH3 2.SOCl2
B.) 1.CrO3/Pyridine/HCl 2.SOCl2 3.NH3
C.) 1.CrO3/H2SO4 2.NH3 3.SOCl2
D.) 1.CrO3/H2SO4 2.SOCl2 3.NH3

The answer is D


I was wondering if this kind of reagent switching is prevalent on the MCAT. I know that D really is the only answer you can come up with (PCC doesn't take aldehydes to Carboxylic Acids), but I would like to know.


Also, side note question:
Can KMnO4 oxidize aldehydes to Carboxylic acids as well? (or are they restricted to reactions with alcohols?)

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[Rayhaan]

There are many many many oxidizing agents beyond KmNO4. Pretty much if you see lots of oxygens then its an oxidizing agent. PCC is the important one which can't oxidize to carboxylic. And yes KmNO4 will fully oxidize to the carboxylic.

Just for other information, the reason why there are multiple oxidizing agents is because it might be necessary given the pH of the solution; some don't work at all pH. In this reaction the use of Cro3 is better due to the fact you are working with amines (but this isn't knowledge you need to have unless its stated in the passage).

 

[orgohacks]

It seems that (according to Practice problem #94 in chapter 5 of the Berkley review) that K2CrO7/H2SO4 is the same thing as CrO3/H2SO4


What sequence of reagents will convert an aldehyde into an amide?
A.) 1.NH3 2.SOCl2
B.) 1.CrO3/Pyridine/HCl 2.SOCl2 3.NH3
C.) 1.CrO3/H2SO4 2.NH3 3.SOCl2
D.) 1.CrO3/H2SO4 2.SOCl2 3.NH3

The answer is D


I was wondering if this kind of reagent switching is prevalent on the MCAT. I know that D really is the only answer you can come up with (PCC doesn't take aldehydes to Carboxylic Acids), but I would like to know.


Also, side note question:
Can KMnO4 oxidize aldehydes to Carboxylic acids as well? (or are they restricted to reactions with alcohols?)

Just a note, H2SO4 will convert K2Cr2O7 to 2 molecules of CrO3 in situ through loss of H2O.

As far as other oxidizing agents you learn besides KMnO4, there is also the Tollens reagent but that is generally used as qualitatively, not preparatively.