ABSTRACT
In this chapter, prebiotically feasible reactions “on water,” reactions under hydrothermal conditions, solventless reactions, and solid-solid reactions are reviewed. Such reactions expand the repertoire of prebiotic chemistry. Among “on water” reactions, Diels-Alder and Passerini multicomponent reactions are highlighted. Although the starting materials for “on water” reactions are not water-soluble, the reactions nevertheless occur smoothly, in a selective manner, and give high yields. Reactions in superheated water are also significant for prebiotic chemistry. Properties of superheated water, under certain conditions of temperature and pressure, enable water to dissolve organic compounds, since water changes its polarity and behaves as acetone. In addition, superheated water can also act as an acid/base catalyst as its Kw changes. Solventless and solid-solid reactions are relevant to the chemistry on asteroids, in addition to the general prebiotic chemistry. Selected examples of the key organic reactions that occur under these conditions are shown. They include esterifications, etherifications, aldol-type condensations, and preparations of the large cyclic molecules. The latter could serve as primitive enzymes.
