[minimal]

I have some questions that particularly can be made in reference to formamide, n-methyl-formamide, and dimethylformamide.
DMF seems to be the most widely used of the three as a solvent.  My question is why?  What is it about those two (or one) extra methyl groups that makes it the first choice as a solvent in so many reactions?  Does it have anything to do with the resonance structure?
They are all aprotic, so they would all work well in SN2 correct? I don't see why any additional alkyl groups would change the compound that much...steric hindrance wouldn't have an affect in most cases would it?  And if it did, I don't see how it would be positive as a solvent. 
Thanks for the info in advance.

[agrobert]

What is the definition of an aprotic solvent?

What is the pK_b of formamide? of NMF?

How might a nucleophilic base interfere with S_N2 reactions?

What properties does an ideal S_N2 solvent have?

How does hydrogen bonding ability change the boiling point of a solvent? (formamide, DMF)

[minimal]

An aprotic solvent is a solvent that does not have a hydrogen bonded to an oxygen or similar electronegative element.  Essentially a molecule that cannot be the hydrogen part of a hydrogen bond. 

Regarding the pkb of formamide and nmf, where would I find that information online? 

A nucleophilic base might interfere with SN2 reactions because it would compete for the nucleophile?

The ideal SN2 solvent is polar and aprotic afaik.

Hydrogen bonding raises the boiling point of a liquid.

[agrobert]

Correct, now apply this information to your original question.  Do you know now?

The pK_b doesn't matter much, I was trying to get you to realize that formamide and NMF are basic.

[sjh9]

I think that it is because DMF is the easiest to remove (lowest BP).

[minimal]

Correct, now apply this information to your original question.  Do you know now?

The pK_b doesn't matter much, I was trying to get you to realize that formamide and NMF are basic.

Ahh I see, the nitrogen in dmf is less basic? Would that be due to steric hindrance?  Or because there is slightly less polarity in a N-C bond than there is in an N-H bond?  Or both?

[DrCMS]

An aprotic solvent is a solvent that does not have a hydrogen bonded to an oxygen or similar electronegative element. 

Would the nitrogen in an amine be a similar electronegative element to oxygen? So do amines always meet your definition of an aprotic solvent?

Agrobert has been trying to get you to realise that primary and secondary amines are protic solvents only tertiary amine are aprotic solvents. 

Think about the definitions you use for longer than it takes to cut and paste them, maybe if you'd read and understood it properly you'd have been able to answer you're own question.

[minimal]

An aprotic solvent is a solvent that does not have a hydrogen bonded to an oxygen or similar electronegative element. 

Would the nitrogen in an amine be a similar electronegative element to oxygen? So do amines always meet your definition of an aprotic solvent?

Agrobert has been trying to get you to realise that primary and secondary amines are protic solvents only tertiary amine are aprotic solvents. 

Think about the definitions you use for longer than it takes to cut and paste them, maybe if you'd read and understood it properly you'd have been able to answer you're own question.

Don't be so presumptuous.  I appreciate the help, but I haven't cut and pasted a single thing.  I'm doing this entirely from memory, and I had the impression that nitrogen was not electronegative enough to have a connecting hydrogen form a hydrogen bond.

[agrobert]

I think that it is because DMF is the easiest to remove (lowest BP).

Minimal

It is the application of all these properties that DMF is a favorable solvent.  Of course being polar and aprotic it has a low boiling point due to the fact that it can not hydrogen bond with the carbonyl.  Low boiling solvents are favorable because they are easily evaporated.  Although when using DMF it is common to evaporate off with a azeotropic mixture with xylene as DMF will decompose before boiling.

[DrCMS]

An aprotic solvent is a solvent that does not have a hydrogen bonded to an oxygen or similar electronegative element. 

Would the nitrogen in an amine be a similar electronegative element to oxygen? So do amines always meet your definition of an aprotic solvent?

Agrobert has been trying to get you to realise that primary and secondary amines are protic solvents only tertiary amine are aprotic solvents. 

Think about the definitions you use for longer than it takes to cut and paste them, maybe if you'd read and understood it properly you'd have been able to answer you're own question.

Don't be so presumptuous.  I appreciate the help, but I haven't cut and pasted a single thing.  I'm doing this entirely from memory, and I had the impression that nitrogen was not electronegative enough to have a connecting hydrogen form a hydrogen bond.

In that case stop doing it from memory and use your computer and internet connection to:
Look up the electonegativity of nitrogen and oxygen. 
Read up on hydrogen bonding in general and amines in particular.

[minimal]

.

[lutesium]

As far as I know these reagents are widely used in Vilsmeier - Haach reaction!!!

Chemical reaction of a substituted amide with phosphorus oxychloride and an activated arene to produce an aryl aldehyde or ketone the reaction of a substituted amide with phosphorus oxychloride gives a substituted chloroiminium ion, also called the Vilsmeier reagent. The initial product is an iminium ion  which is hydrolyzed to the corresponding aromatic ketone or aldehyde.


Lutesium...