2017 Volume 90 Issue 12 Pages 1318-1324
The reactivity of formaldehyde (HCHO) adsorbed in the supercages of zeolite NaY toward α-methylstyrene for the carbonyl-ene reaction was very dependent on the loading amount of HCHO in the NaY pores. We first prepared a series of NaY samples with different amounts of HCHO, and applied them to the carbonyl-ene reaction with excess amounts of α-methylstyrene to evaluate their intrinsic reactivities. It was found that one formaldehyde molecule adsorbed in one supercage of NaY produced 3-phenylbut-3-en-1-ol in the highest yield (83%), while for higher loading amounts of HCHO on NaY, lower yields of the product were obtained because the supercages were narrowed by the HCHO molecules as well as the homoallylic alcohol product and its over-reaction products. We next investigated their states of HCHO adsorbed in the pores by 13C DD/CP MAS NMR analysis. When three HCHO molecules were adsorbed in a supercage, it was clarified that all the HCHO was exclusively encapsulated in a monomeric form, while most of the adsorbed HCHO with much higher loading amounts was transformed into 1,3,5-trioxane inside the supercages of NaY as well as paraformaldehyde outside the supercages.
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