Synthesis and Spectroscopic Analysis of a Cyclic Acetal: A Dehydration Performed in Aqueous Solution

• David M. Collard ^[1] ; Adolphus G. Jones ^[1] ; Robert M. Kriegel ^[1]
  1. [1] Georgia Institute of Technology

     Georgia Institute of Technology

     Estados Unidos

     
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 78, Nº 1, 2001, pág. 70
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • The treatment of aldehydes (and ketones) with diols in the presence of acid gives acetals (and ketals) in an equilibrium reaction. Treatment of pentaerythritol with benzaldehyde in aqueous acid gives the monoacetal, 5,5-bis(hydroxymethyl)-2-phenyl-1,3-dioxane. The reaction has a number of interesting features. The isolated product is the monobenzal not the dibenzal, and the reaction, a dehydration, is performed in water. The reaction proceeds to provide the acetal owing to the insolubility of the product in the aqueous reaction medium, thus removing the product from the equilibrium. This experiment is suitable for incorporation into the undergraduate organic laboratory as the synthesis of a product for characterization by melting point, solubility, and proton nuclear magnetic resonance. Only through recognition of the three-dimensional structure of the dioxane ring can students explain the appearance of the 1H NMR spectrum of the product. The hydroxymethyl groups of the product are inequivalent, as are the hydrogens of the methylenes in the ring. The experiment may also be presented as a group exercise to optimize the conditions of a reaction to maximize the yield of the desired product.