Multiphasic Solvent Systems

The idea to use solvent systems enabling homogeneous reaction conditions at elevated temperatures and liquid/liquid phase separation at lower— preferably room—temperature seems to be obvious. Nevertheless, it is only recently that thermomorphic solvent systems gain attention [30-33] for product separation or multiphase catalysis [34,35]. The main reasons for the delayed engagement is that an efficient choice of a useful solvent system is not easy to achieve. There is also a lack of experience with thermomorphic systems in general. Reactions are optimized to be carried out in solvents having certain distinct solubility and polarity characteristics. A thermomorphic solvent system of choice will have to fulfill these requirements and to show the thermomorphic effect in addition. 

Ruy et al. have performed a similar reaction under microreactor conditions in a multiphase solvent system containing an ionic liquid as the catalyst carrier and reaction promoter [35]. Their system consisted of two T-shaped micromixers (i.d. 1,000 and 400 pm) and a capillary stainless steel tube as an RTU (1,000 pm i.d. and 18 m length, giving a 14.1 ml volume), equipped with pumps and control valves. Under the optimized conditions, Pd-catalysed carbonylation of aromatic iodides in the presence of a secondary amine provided only the double carbonylated product, ot-ketoamide, while the amide obtained by the single carbonylation was observed in high quantities only when the reaction was performed in batch (Scheme 13). 

The microstructure of the multiphase media is often the product of phase transitions, e.g. (i) capillary condensation in the porous media, (ii) phase separation in polymer/polymer and polymer/solvent systems, (iii) nucleation and growth of bubbles in the porous media, (iv) solidification of the melt with a temporal three-phase microstructure (solid, melt, gas), and (v) dissolution, crystallization or precipitation. The subject of our interest is not only the topology of the resulting microstructured media, but also the dynamics of its evolution involving the formation and/or growth of new phases. 

Higher rates Different selectivities Fewer reaction steps Additional safety Enhanced separation Continuous-flow operation Miscibility with gases, rapid mass transfer Weak coordination, pressure tuning In-situ protection of amines No toxicity, inertness, good heat transfer Tunable solvent properties, multiphase systems Multiphase systems, mass transfer... 

Addition of hydrogen cyanide to aldehydes by means of oxynitrilases gives cyanohydrins in high yields and high optical purity. It is often unnecessary to work with free hydrogen cyanide instead, the cyanohydrin of acetone can be used to form hydrogen cyanide in situ, which is then reacted with the aldehyde. The oxynitrilases are compatible with organic solvents or multiphase solvent systems. [Ill, 112]... 

Mizoroki Heck Reactions Modern Solvent Systems and Reaction Techniques 517 15 43 Nonaqneous Multiphase Systems... 

---