脱羧反应Decarboxylation

β-酮酸经六元环状过渡态，羧基 H 转移给酮羰基氧，同时 C–C 断裂放出 CO₂，生成烯醇，互变异构为酮。这是乙酰乙酸乙酯合成法、丙二酸酯合成法的最后一步。

β-Keto acids lose CO₂ through a six-membered cyclic TS in which the carboxyl H moves to the ketone oxygen as C–C breaks, giving an enol that tautomerises to the ketone — the final step of the acetoacetic and malonic ester syntheses.

碱石灰与羧酸钠共热得烷烃（如乙酸钠 + NaOH → CH₄，中学实验室制甲烷）；电解脱羧偶联（柯尔贝电解）；巴顿脱羧；现代光氧化还原脱羧偶联以羧酸为自由基前体。

Heating sodium carboxylates with soda lime gives alkanes (sodium acetate + NaOH → CH₄, the school preparation of methane); Kolbe electrolysis couples radicals; Barton decarboxylation; modern photoredox decarboxylative couplings use acids as radical precursors.

丙酮酸脱羧（乙醇发酵，需焦磷酸硫胺素）、氨基酸脱羧生成神经递质（多巴 → 多巴胺、组氨酸 → 组胺、谷氨酸 → GABA，需磷酸吡哆醛）、三羧酸循环中的氧化脱羧都是关键代谢步骤。

Pyruvate decarboxylation (ethanol fermentation, thiamine pyrophosphate), amino-acid decarboxylations to neurotransmitters (DOPA → dopamine, histidine → histamine, glutamate → GABA, pyridoxal phosphate) and oxidative decarboxylations in the citric-acid cycle are key metabolic steps.