nonaqueous

Nonaqueous (often written non-aqueous) describes environments, solvents, reagents, or reactions conducted in the absence of water or with very low water content. The term emphasizes excluding water as a solvent or reactant and is used to distinguish these systems from aqueous, water-based ones. Nonaqueous conditions are chosen when water would interfere with solubility, reactivity, stability, or selectivity.

Non-aqueous solvents include a broad range of compounds. Polar aprotic solvents such as acetonitrile, dimethyl sulfoxide, and dimethylformamide are common in synthesis and electrochemistry because they dissolve many salts and stabilize reactive intermediates without donating protons. Polar protic solvents like methanol and ethanol are also used in some non-aqueous contexts, though moisture control is critical. Nonpolar solvents such as toluene or diethyl ether are employed when nonpolar solubility is required. In all cases, the solvent system is dried and handled under inert conditions to minimize water uptake.

Water activity is kept very low in non-aqueous work by drying reagents, using desiccants, distillation, or molecular sieves, and storing materials under inert gas or in moisture-controlled environments. Water content is typically measured by Karl Fischer titration or other moisture analysis methods.

Applications span organic synthesis, catalysis, and analytical chemistry, as well as electrochemistry and energy storage, where non-aqueous electrolytes enable different redox behavior and stability compared with aqueous systems. Because acid-base behavior is solvent-dependent, non-aqueous chemistry often relies on solvent-specific pKa scales rather than water-based references. Safety considerations include flammability and toxicity, with heightened emphasis on moisture exclusion to prevent hydrolysis or degradation of sensitive species.