Nitrogen compounds as acids and bases

Removing a proton from an amine is very difficult as the anion (unfortunately called an amide anion) is very unstable and very basic. The only way to succeed is to use a very strong base, usually an alkyllithium. The anion then has a N-Li bond and is soluble in organic solvents. This example, known as LDA, is commonly used as a strong base in organic chemistry. 

The basicity of amines as neutral compormds is measured by the pK of their conjugate acids—so, for example, the pK associated with the protonation of triethylamine, a commonly used tertiary amine, is 11.0. 

Chemists often say things like the pK of triethylamine is about 10. (It s actually 11.0 but 10 is a good number to remember for typical amines). This may surprise you as triethylamine has no acidic hydrogens. What they mean is of course this the pK of the conjugate acid of triethylamine is about 10. Another way to put this is to write the pX n of triethylamine is about 10. The subscript aH refers to the conjugate acid. 

It s OK to say the pK of triethylamine Is about 10 as long as you understand that what Is really meant Is the pKa of the triethylammonlum Ion Is about 10 , which can also be expressed thus  

When a molecule is both acidic and basic, as for example aniline, it is important to work out which pJCj is meant as again chemists will loosely refer to the pAC of aniline is 4.6 when they mean the pK of the conjugate acid of aniline is 4.6. Aniline is much less basic than ammonia or triethylamine because the lone pair on nitrogen is conjugated into the ring and less available for protonation. 

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