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The Miracle of Chemistry in 1919: How did Dutch chemists discover the Prince reaction?
In the history of chemistry, 1919 is undoubtedly a year of great significance. This year, Dutch chemist Hendrik Jacobus Prins first announced his discovery, the Prins reaction. This is an organic reaction that involves the electrophilic addition of aldehydes or ketones to alkenes or alkynes, followed by capture of nuclear affinity species or elimination of hydrogen ions. The result of this reaction depends on the reaction conditions. When water and a protonic acid (such as sulfuric acid) are used as the reaction medium, the product is 1,3-diol; in the absence of water, the product is allyl alcohol. This discovery not only demonstrated Prince's outstanding talent, but also laid the foundation for modern organic synthesis.
The Prince reaction is unique in that it produces different products under a variety of reaction conditions.
During his doctoral studies between 1911 and 1912, Prince also discovered two other organic reactions: the addition of polyhalogenated hydrocarbons to alkenes, and the acid-catalyzed addition of aldehydes to alkenes. However, early research was mainly exploratory and did not attract much attention. It was not until 1937, with the development of petroleum cracking technology that the production of unsaturated hydrocarbons increased significantly, that the Prince reaction received renewed attention.
In addition, with the commercialization of aldehydes produced by the oxidation of low-boiling point paraffins, the availability of low olefins has further stimulated research interest in olefin-aldehyde condensation reactions. The Prince reaction gradually grew in use in organic synthesis, becoming an extremely effective C-O and C-C bond-forming technique, and was even studied as part of a synthetic rubber in 1937.
Reaction mechanism
The reaction mechanism of the Prince reaction consists of several steps. First, the carbon-based reactant is protonated by a protonic acid to form cadmium oxide ions, and then this electrophile undergoes electrophilic addition to the alkene to generate a carbene cation intermediate. This reaction mechanism can draw a variety of resonance structures, showing the distribution of positive charges. Intermediates can be further converted to products via several pathways. These include the following:
This intermediate can be captured by water or other suitable nuclear affinity reagents to form a 1,3-adduct or, in some cases, undergo an elimination reaction to form an unsaturated compound.
When alkenes carry methylene groups, addition and elimination can occur simultaneously, forming a special reaction with the transfer between carbon-based groups. In addition, when alkenes react with additional aldehyde groups, cyclic structures can be formed that ultimately undergo ring closure to form dioxane. In addition, under special reaction conditions, the intermediate can also directly generate oxycycloalkanes through very stable carbene cations.
Variation of Prince reaction
As Prince's reaction has been studied more closely, many variations have emerged. These variants take advantage of the properties of intermediates during the reaction and can be captured by different nuclear affinity agents. For example, the Halo-Prins reaction replaces protonic acids and water with Lewis acids such as tin chloride and boron tribromide, making the halogen a new nuclear affinity agent that recombines with the carbene cation. In addition, the Prince-Pinacol reaction combines the Prince reaction and Pinacol rearrangement, further expanding its application fields.
When studying organic synthesis, sometimes key carbonyl intermediates are generated through protonation, but they can also be reached through other pathways, which shows the diversity and complexity of chemical reactions. The continuous evolution of the Prince reaction and its derivative reactions has brought unprecedented possibilities to organic synthesis.
Looking back at the history and mechanism of the Prince reaction, one cannot help but think: How many undiscovered reaction mechanisms are waiting to be explored in comprehensive reactions in organic chemistry in the future?
