No abstract

The oxidation of trichloroethylene (TCE) by permanganate proceeds in three sequential reaction steps. In the initial step, a cyclic hypomanganate ester is formed via an activated organometallic complex. The activation parameters for this step were determined to be E a = 41.46 kJ/mol, ΔH ⧧ = 39 kJ/mol, and ΔS ⧧ = −14 J/mol. The initial reaction is a rate-limiting step (second-order rate constant k 1p = 0.65−0.68 M-1 s-1 at 21 °C) and independent of pH. In the second step, the decomposition of the cyclic ester with complete chlorine liberation proceeds quickly via various reaction pathways to form four carboxylic acids. Approximately 77% of the TCE was transformed to formic acid at pH 4, while 95−97% of the TCE was transformed to oxalic and glyoxylic acids at pH values of 6−8. Kinetic data suggest that the decomposition rate of the cyclic ester is at least 100 times higher than its formation rate. In the final step, all carboxylic acids are oxidized by permanganate to the final product, CO2. Second-order rate constants of k 3ap = 0.075−0.35 M-1 s-1, k 3bp = 0.13−0.37 M-1 s-1, and k 3cp = 0.073−0.11 M-1 s-1 over a pH range of 4−8 at 21 °C were estimated for oxidation of formic, glyoxylic, and oxalic acids, respectively. The oxidation rate of carboxylic acids and accumulation rate of CO2 increase with decreasing pH. The kinetic model that was developed, formulated, and solved analytically on the basis of the understanding of various processes is consistent with results obtained in the kinetic experiments.

Substituent changes in the ligand (L) backbone and the chelating phosphorus atoms of the classical DIOP ligand result in dramatic changes in the enantioselectivity of Rh(+)L-catalyzed enamide hydrogenations.

[structures: see text] Enantioselectivities and yields comparable to the best catalysts reported previously can be achieved in the addition of potassium dimethyl malonate to diphenylallyl acetate by the use of Pd(0) complexes of bis-phospholanes prepared from D-mannitol. By appropriate changes in the C2-C5 substituents, rare example of a useful monophosphine can also be prepared by a similar route. In both instances chirality of C3 and C5 oxygen seems to play a crucial role in the asymmetric induction.

A series of water-soluble chelating bis-phosphinite ligands have been prepared from D-salicin (2-(hydroxymethyl)phenyl beta-D-glucopyranoside). The 4- and 6-hydroxyl groups of salicin were protected as a cyclic ketal. Mitsunobu reaction with phthalimide at the benzylic position was used to install the aminomethyl side-chain in the C(1)-aromatic substituent. Formation of the bis-2,3-O-diarylphosphinite was accomplished by reaction of the resulting diol with chlorodiarylphosphine. Quaternization with Meerwein's salt (Me(3)O(+) BF(4)(-)) followed by reaction with Rh(+)(COD)(2) BF(4)(-) gave precatalysts with limited aqueous solubility. Deprotection of the ketal group with acidic resin in methanol gave water-soluble cationic Rh complexes that are competent to carry out highly efficient hydrogenation of acetamidoacrylic acid derivatives in organic, aqueous, or biphasic media. However, enantioselectivities of these reactions in neat aqueous or biphasic media are generally lower than those observed in organic medium.