| 词条 | Varrentrapp reaction |
| 释义 |
The Varrentrapp reaction, also named Varrentrapp degradation, is a name reaction in the organic chemistry. It is named after Franz Varrentrapp, who discovered this reaction in 1840. It is an organic reaction involving the chemical decomposition of an α,β-unsaturated acid into two other acid fragments by action of molten alkali.[1] General Reaction SchemeBecause of the complex structure of this reaction it is shortened in the following scheme. The reaction conditions are harsh: medium molten potassium hydroxide at temperatures in the range of 250 to 300 °C. Likewise cinnamic acid is converted to benzoic acid.[2] Reaction MechanismBelow, the reaction mechanism is shown with (E)-4-hexenoic acid.[3] First, the hydroxyl reacts with the caustic potash 1. After two condensations a compound with two mesomers is build 3a and 3b. After another condensation a negative charged carbon-atom is generated 4. After a rearrangement the intermediate compound (5) is built. This reacts with a hydroxydion of the caustic potash 6. In the next step the molecule dissociates into two pieces 7 and 8. (8) is protonated and builds the acetic acid derivative (9). The second compound (7) reacts with a hydroxidion and a shortened carbonic acid is generated 10. ApplicationsThe reaction has been of some importance in structure elucidation of certain fatty acids but has no practical synthetic use.[4][5] The original 1840 Varrentrapp reaction concerned the conversion of oleic acid to palmitic acid, acetic acid and hydrogen gas: References1. ^F. Varrentrapp, Ann., 36, 196 (1840) 2. ^{{citation|surname1=Windholz, M.|title=The Merck Index |publisher=Merck & Co|publication-place=Rahway|pages=ONR-90|isbn=0-911910-26-3|date= 1976|language=German}} 3. ^{{citation|surname1=Wang, Zerong|title=Comprehensive Organic Name Reactions and Reagents |publisher=John Wiley & Sons|publication-place=New Jersey|pages=2864-2868|isbn=978-0-471-70450-8|date= 2009|language=German}} 4. ^Organic reactions in strong alkalis-I : Fission of ethylenic acids (the varrentrapp reaction) Tetrahedron, Volume 8, Issues 3–4, 1960, Pages 221–238 R. G. Ackman, Patrick Linstead, B. J. Wakefield and B. C. L. Weedon {{doi|10.1016/0040-4020(60)80031-2}} 5. ^A Mechanism for the Cleavage of Unsaturated Acids with Molten Alkali William A. Bonner, Robert T. Rewick J. Am. Chem. Soc.; 1962; 84(12); 2334–2337. {{DOI|10.1021/ja00871a013}} 2 : Elimination reactions|Name reactions |
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