<p>Among imines, nitrogen-unprotected ketimines (<i>N</i>–H ketimines) are valuable precursors to nitrogen-containing compounds. However, their applications are limited compared with those of nitrogen-protected ketimines (<i>N</i>–R ketimines) owing to difficulties in synthesis and purification. We develop remarkably simple methods for synthesizing and isolating high-purity <i>N</i>–H ketimines and <i>N</i>–H ketimine hydrochlorides via the dehydration–condensation of ketones with stoichiometric ammonia, generated in situ with inorganic solid acid catalysts. Our methods offer exceptionally broad substrate scope, use non-toxic and reusable catalysts, do not require tedious synthetic steps, are inexpensive, and are suited to large-scale production. Additionally, ketones can be easily converted to <i>N</i>–R ketimines, α-aminonitriles, and hydantoins in one pot via <i>N</i>–H ketimines. All products can be isolated by filtration or concentration; other purification methods, such as column chromatography, are not required. This study guides the advancement of the design of new transition metal catalysts and pharmaceutical synthesis.</p>