Formose Formation in the Presence of Hydroxy Oxo Compounds at High pH Region

Abstract

Equilibrium constants were evaluated in H₂ O and MeOH-H₂O solutions saturated with Ca (OH)₂ for 1 to 1 complex formations between dissolved Ca (OH)₂ and formaldehyde (C_1A ); a feed stock for formose formation, known accelerators such as 2-hydroxyacetophenone (HAP), DL-glyceraldehyde (C_3A ), 1, 3-dihydroxyacetone, D-glucose (Glu), and D-fructose, or 2, 3dihydroxypropiophenone (DHPP); a C_1A addition product to HAP. The initial rate of C_1A conversion to formose was measured using HAP, C_3A and Glu as accelerators, in the presence of Ca(OH)₂ or NaOH at the pH region of 11.5 to 12.5, in order to elucidate kinetically whether the complex between dissolved Ca (OH)2 and accelerator might enhance the formose f ormation. The order of acceleration efficiency and that of complex formation constants were strictly in reverse, and DHPP revealed a great acceleration effect in spite of no binding ability to Ca (OH)₂. Moreover, the reaction kinetics were first order each with [uncomplexed accelerator], [C_1A], and [OH-]. These results indicate that the formose formation in a high pH region proceeds mainly through OH- catalyzed aldol reaction.