603. Kinetics of the aldol condensation of acetaldehyde

Abstract

Measurements are reported on the initial reaction rates of the aldol condensation of acetaldehyde and of the reaction of acetaldehyde with formaldehyde, in sodium hydroxide solutions and in borate and carbonate buffers. The acidic properties of acetaldehyde and formaldehyde have been investigated, and the results are used to correct the hydroxide-ion concentrations in the kinetic experiments. The corrected results show that the aldol condensation is almost of the second order with respect to aldehyde, though the apparent order decreases slightly with increasing aldehyde concentration. The aldol condensation in buffer solutions exhibits general base catalysis, but does not obey the usual quantitative laws.The results are interpreted by assuming that the ionization and condensation steps of the aldol condensation have comparable rates, the former being the faster under most conditions. A similar interpretation applies to the previously unexplained kinetics of the acid-catalysed decomposition of the diazoacetate ion.19 The rate of reaction between acetaldehyde and formaldehyde is proportional to the first power of the acetaldehyde concentration, but independent of formaldehyde concentration, and is therefore governed by the rate of ionization of acetaldehyde. The value thus found for the rate of ionization is similar to that for acetone, and is consistent with the observed kinetics of the aldol condensation.

Abiotic CC bond formation under environmental conditions: Kinetics of the aldol condensation of acetaldehyde in water catalyzed by carbonate ions (CO3 2− )

“…In recent years, we have identified several new types of catalysts able to make these reactions fast in natural environments: amino acids [3,4], inorganic ammonium ions, NH + 4 [5][6][7][8], and carbonate ions, CO 3 2− [8]. Carbonate ions are present in atmospheric aerosols [9] and in hyperalkaline surface and spring waters in New Caledonia (pH 9.2-10.8) [10], the United States (pH 10) [11,12], Cyprus (pH 9.5-11.6) [13], and Jordan (pH 12.1-12.7) [14,15], at concentrations between 0.1 mM and 1 M. But, with a few exceptions [16], their catalytic properties have been studied only under conditions very different from environmental ones: in organic solvents [17,18] or at high temperature [19]. Moreover, as will be discussed in this work, most previous studies of the base-catalyzed aldol condensation [16,20], usually using OH − as catalyst, appeared to be flawed.…”

Phenol Group in Pyridoxamine Acts as a Stabilizing Element for Its Carbinolamines and Schiff Bases

“…In aqueous solutions, FA occurs largely (ca. 98%) in hydrated from, and the CO species is, therefore, the minor form [29]. A nucleophilic attack of the NH 2 group in PM on the CO group of FA produces a carbinolamine (CA) dehydration of which leads to a Schiff base, SB.…”

The Aldol Condensation of Acetaldehyde: the Equilibrium Constant for the Reaction and the Rate Constant for the Hydroxide Catalyzed RetroAldol Reaction

“…-condensation is usually described as "irreversible" (6)(7)(8). For reasons of experimental practicality the reaction has been studied in rather concentrated solutions' and these studies have had to contend with the notorious (6,7,9) complexity of the acetaldehyde-water-hydroxide system. Nevertheless it is curious that the statement that the self condensation of acetaldehyde is "irreversible" is so widely accepted, since all the information needed to evaluate the equilibrium constant is available in the literature.…”

“…Condensation of acetaldehyde with itself is of the thermochemically estimated equilibrium one of the simplest and most thoroughly studied constant and the known rate constant for the (1)(2)(3)(4)(5)(6) examples of the aldol reaction. This condensation step (k,,) (1,5) led to the conclusion that the rate of the retroaldol step (k,,)…”