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反应 · 有机化学 · 氧化还原 Organic chemistry · Redox reactions

坎尼扎罗反应Cannizzaro reaction

拼音Pinyin kǎn ní zhā luó fǎn yìng　别名Also 康尼查罗反应；歧化反应（醛）； aldehyde disproportionation

定义Definition

坎尼扎罗反应是没有 α-氢的醛（如甲醛、苯甲醛）在浓碱中发生歧化：一分子被氧化为羧酸盐，另一分子被还原为醇。

The Cannizzaro reaction is the disproportionation of an aldehyde lacking α-hydrogens (formaldehyde, benzaldehyde) in concentrated base: one molecule is oxidised to a carboxylate and another reduced to an alcohol.

机理Mechanism

OH⁻ 加成到醛羰基生成四面体负离子；它把碳上的氢以氢负离子形式转移给第二分子醛（决速步），自身成为羧酸，另一分子成为醇盐；质子交换得羧酸盐和醇。用 D₂O 实验证明转移的氢来自醛而非溶剂。

Hydroxide adds to the aldehyde; the tetrahedral anion transfers its C–H as a hydride to a second aldehyde (rate-determining), becoming the acid while the other becomes an alkoxide; proton exchange gives carboxylate and alcohol. Labelling in D₂O shows the hydride comes from the aldehyde, not the solvent.

由来Origin

意大利化学家斯坦尼斯劳·坎尼扎罗于 1853 年用苯甲醛与碳酸钾得到苯甲醇和苯甲酸。坎尼扎罗更以 1860 年卡尔斯鲁厄会议上复兴阿伏加德罗假说、确立原子量而闻名。

Discovered in 1853 by Stanislao Cannizzaro, who obtained benzyl alcohol and benzoic acid from benzaldehyde and potassium carbonate. He is better known for reviving Avogadro’s hypothesis at the 1860 Karlsruhe Congress.

交叉坎尼扎罗反应Crossed Cannizzaro

甲醛最易被氧化，与其他醛混合时甲醛优先作还原剂（自身变成甲酸），使另一醛定量还原为醇。工业上季戊四醇的合成（乙醛 + 4HCHO）即包含羟醛反应与交叉坎尼扎罗步骤。

Formaldehyde is the most easily oxidised, so in mixtures it acts as the reductant (becoming formate) and reduces the partner aldehyde to the alcohol. Industrial pentaerythritol (acetaldehyde + 4 HCHO) combines aldol and crossed Cannizzaro steps.

反应Reactions

2 ArCHO + OH− ⟶ ArCOO− + ArCH2OH

浓 NaOH 或 KOH（50%），室温至加热

Concentrated (≈50 %) NaOH or KOH, room temperature to heating

  1. OH⁻ 加成到羰基。

    Hydroxide adds to the carbonyl.

  2. 四面体负离子向第二分子醛转移氢负离子。

    The tetrahedral anion transfers hydride to a second aldehyde.

  3. 质子交换得羧酸盐和醇。

    Proton exchange gives carboxylate and alcohol.

2 HCHO + NaOH ⟶ HCOONa + CH3OH

甲醛的歧化。

Disproportionation of formaldehyde.

反应机理图Mechanism

红色弯箭头表示一对电子的移动方向：从电子来源（孤对电子或化学键）指向电子去向。Red curly arrows show where an electron pair moves: from its source (lone pair or bond) to its destination.

1

OH⁻ 加到无 α-H 的醛上

OH⁻ adds to an aldehyde with no α-H

2

四面体中间体把负氢转移给另一分子醛

The tetrahedral intermediate transfers a hydride to a second aldehyde

质子交换H⁺ transfer
3

一分子被氧化成苯甲酸根，另一分子被还原成苯甲醇

One molecule is oxidised to benzoate, the other reduced to benzyl alcohol

年表Timeline

  • 1853

    坎尼扎罗发现该反应

    Cannizzaro discovers the reaction

  • 1860

    坎尼扎罗在卡尔斯鲁厄会议上阐明原子量

    Cannizzaro clarifies atomic weights at Karlsruhe