In this article regarding low-boiling point amine-catalyzed biodiesel transesterification reactions, it is stated that,

"From Table 1, we can also see that, for the isomers, the branched amines always showed higher yields of methyl acetate than the normal amines. For example, the yields of methyl acetate for n-dipropylamine, n-butylamine, and n-propylamine were 25.3%, 46.1%, and 48.2%, respectively, while those for diisopropylamine, tert-butylamine, and isopropylamine were 42.1%, 49.6%, and 50.7%, respectively. This was probably due to the high pH values of the branched amines than the normal amines."

Why is this the case? Why do high pH values correlate to higher yields? Does the geometry (branched or linear) of the amine play a role in this?


Branched amines are more basic than their linear counterparts because inductive effect of alkanes places more electron density in the adjacent carbon atom. The higher the electron density near/at the amine group, the higher its pH will be.

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  • $\begingroup$ Also, steric factors also make the amine more planar, so the lone pair orbital is going to have less mixing/stabilization from the orbitals of the other substituents. $\endgroup$ – Zhe Oct 26 '16 at 17:35

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