Recently, I learnt about the Schotten-Baumann synthesis method. I know that this synthesis method was invented to overcome the problem of neutralising the acidic by-products of the amide synthesis reaction without introducing strong basic nucleophiles to compete with the amines. The alternative to this synthesis method would be to use two equivalences of the amine, allowing the 2nd equivalence of the amine to act as a base to neutralise the acidic by-product. I would like to enquire more about the differences between these two synthesis methods. In particular, I would like to know the advantages and disadvantages of each of these synthesis methods.

  • $\begingroup$ You do need a base (non-nucleophilic) to absorb the acidic proton, or the reaction doesn't proceed. It often uses a 2-phase solvent system, consisting of water and an organic solvent. The base within the water phase neutralises the acid, generated in the reaction, while the starting materials and product remain in the organic phase. $\endgroup$ – getafix Jan 1 '18 at 7:06
  • $\begingroup$ @getafix But if u add a 2nd equivalence of amines, then it could act as a base as well. Why do we need another base? Amines are basic enough. $\endgroup$ – Tan Yong Boon Jan 1 '18 at 7:54
  • $\begingroup$ Well, synthetic chemistry is a practical science. Your amine starting material might be expensive, or difficult to synthesise. You wouldn't want to waste it, or spend time recovering it from the reaction mixture. $\endgroup$ – getafix Jan 1 '18 at 7:57
  • $\begingroup$ This is quite correct, if you've spent 2 weeks synthesising your amine you will not use 2 eq of it. In the real world of the lab we rarely use S-B prefering to use a single phase system and an equivalent of a second organic base. Triethylamine or N-methyl morpholine are often used $\endgroup$ – Waylander Jan 1 '18 at 9:50
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    $\begingroup$ No. Not if you use tertiary bases with significant steric hindrance around the basic nitrogen. $\endgroup$ – Waylander Jan 1 '18 at 10:38

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