Triethylamine is more often thought of as a reactant or acid trap. It is inexpensive enough, however, to be considered for a role as a reaction solvent.
Triethylamine has a critical solution temperature with water. Below 18°C they are miscible but immiscible above this temperature. Thus it is thermomorphic and this provides a potential for simplified isolations.
Triethylamine is likely to dissolve neutral or basic substrates which can deliver hydrogen bonds without actually causing proton transfer. Alcohols, phenols, amides, N-hydroxyl amides, thioamides, primary and secondary amines, meet the criterion.
As a solvent it could not be used in oxidizing environments because of the ease of forming an N-oxide or the loss of one of its lone pair electrons.
A reducing environment would not cause any problems. Its' use would be problematic in the presence of electrophiles since it would tend to compete to react with them. Halides, epoxides, etc. are incompatible. With acidic substrates it would be inclined to form salts. It should be compatible with organometallic agents and indeed may stabilize these.
Triethylamine has a boiling point of 90°C. It does not form explosive peroxides like diethyl or diisopropyl ethers. It can be expected to be close to diethylether in solution properties. It might be useful as an extraction solvent so long as the substrate being isolated is not electrophilic. In the same way that liquid ammonia can be a reaction solvent so could triethylamine.
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