定义Definition
托伦试剂是新配制的银氨溶液 [Ag(NH₃)₂]OH。醛（及甲酸、还原糖）能把其中的 Ag⁺ 还原为金属银，在洁净试管内壁形成光亮的银镜，酮一般不反应，因此用于区别醛和酮。
Tollens' reagent is freshly prepared ammoniacal silver hydroxide, [Ag(NH₃)₂]OH. Aldehydes (and formic acid and reducing sugars) reduce Ag⁺ to metallic silver, which deposits as a bright mirror on a clean tube; ketones generally do not, so the test distinguishes aldehydes from ketones.
配制与原理Preparation and principle
向 AgNO₃ 溶液中滴加氨水，先生成棕色 Ag₂O 沉淀，继续滴加至沉淀恰好溶解，得到 [Ag(NH₃)₂]⁺。醛被氧化为羧酸铵盐，Ag(I) 被还原为 Ag。
Ammonia is added to AgNO₃ solution: brown Ag₂O forms first and redissolves as [Ag(NH₃)₂]⁺ with more ammonia. The aldehyde is oxidised to an ammonium carboxylate while Ag(I) is reduced to silver.
由来Origin
德国化学家伯恩哈德·托伦（1841–1918）提出。化学镀银制镜的原理早在 1835 年由李比希提出。
Introduced by the German chemist Bernhard Tollens (1841–1918); chemical silvering of mirrors goes back to Liebig in 1835.
安全注意Safety
试剂必须现配现用。久置会析出雷酸银等爆炸性的氮化银化合物；实验后应立即用稀硝酸处理残液。
Prepare the reagent fresh. On standing it can deposit explosive silver nitride (‘fulminating silver’); destroy residues promptly with dilute nitric acid.
反应Reactions
洁净试管，温水浴加热
A clean test tube warmed in a water bath
配制银氨溶液。
Prepare the diamminesilver solution.
醛被氧化为羧酸根。
The aldehyde is oxidised to a carboxylate.
Ag⁺ 被还原为银，附着在管壁形成银镜。
Ag⁺ is reduced to silver, which coats the glass.
甲醛可被氧化到碳酸盐，消耗 4 倍银。
Formaldehyde is oxidised all the way to carbonate, consuming four Ag⁺.
年表Timeline
- 1835
李比希发明化学镀银
Liebig develops chemical silvering
- 1880s
托伦提出用于检验醛和糖的试剂
Tollens introduces the reagent for aldehydes and sugars