Chiral ligands derived from Abrine 8. An experimental and theoretical study of free ligand conformational preferences and the addition of diethylzinc to benzaldehyde.

Three structurally similar series of 1,2,3,4-tetrahydro-beta-carboline ligands, 4a-d, 6a-d and 7a-d, and two series of chiral oxazolidines, 8a-d and 9a-g, were synthesized and used as chiral catalysts in the addition of diethylzinc to benzaldehyde. The enantioselectivities of the resulting 1-phenyl-1-propanol were obtained in each case, and these ee values were, in most cases, related to the conformational populations of the free ligand as expressed by the calculated differences in the energies of the ligand conformations formed by inversion at nitrogen. This suggested the possible existence of a linear free energy relationship. The effect on enantioselectivity of the carbon chain length of the R group located (1) on the C-3 substituent of 4a-d, 6a-d, and 7a-d or (2) at C-5 in 8a-d and 9a-g was studied in detail. On the basis of the correlations observed and the ligands' structural characterization, a structure was proposed for the transition state during ethyl group transfer when using ligands 8a-d. Furthermore, the change in enantioselectivity was successfully predicted when diastereomeric ligands 11 and 12 were compared in this chiral addition.

Dechlorination of polychlorobiphenyls using NaBH(4) and NaBH(4)/LiCl at 120-310 degrees C in glyme solvents.

High temperature PCB dechlorination (Aroclor 1016) occurred using NaBH(4) alone in tetraglyme at 290-310 degrees C within 2h in a sealed tube. Aroclor 1016 dechlorination was also quantitatively achieved using NaBH(4)/LiCl/glyme solvents (di-, tri-, or tetraglyme) at 125-135 degrees C. The best results were obtained by prestirring NaBH(4), LiCl and the glyme solvent at room temperature before heating at 125-135 degrees C. At equivalent conditions, PCB dechlorination rates were found to depend on solvent in the order: tetraglyme>triglyme>diglyme. At 130 degrees C, Aroclor 1016 can be dechlorinated in NaBH(4)/LiCl/tetraglyme in 4h. 2-Chlorobiphenyl and 2,2'-dichlorobiphenyl were the least reactive congeners in dechlorinations with NaBH(4)/LiCl in diglyme. Competitive dechlorinations with NaBH(4)/LiCl in diglyme showed 3-chloro- and 4-chlorobiphenyl reacted faster than 2-chlorobiphenyl at 130 degrees C. The reactions were clean with no solvent decomposition in the range of 120-162 degrees C.

Destruction of halogenated hydrocarbons with solvated electrons in the presence of water.

Model halogenated aromatic and aliphatic hydrocarbons and halogenated phenols were dehalogenated in seconds by solvated electrons generated from sodium in both anhydrous liquid ammonia and ammonia/water solutions. The minimum sodium required to completely dehalogenate these model compounds was determined by increasing the Na/substrate ratio until halogen loss was complete. Minimum sodium consumptions were determined in both anhydrous liquid ammonia and with a (5, 20, 50-fold molar excess of water per mole of halide). While more Na was consumed in the presence of water, these dehalogenations were still efficient when a 50-fold water excess was present. Dehalogenation is faster than competiting reactions with water. CCl4 and CH3CCl3 in the presence of a stoichiometric deficiency of sodium produced only CH4 and CH3CH3 and recovered CCl4 or CH3CCl3, respectively. No partially dechlorinated products were detected, indicating dechlorination was diffusion controlled. Na consumption per chlorine removed (as NaCl) was lower than that of Li, K or Ca and this advantage increased in the presence of water. Na consumption was lower using Na chunks instead of a thin Na mirror. Chloroaromatic compounds gave the parent aromatic hydrocarbon and aminated products in anhydrous ammonia but aminated products did not form when water was present.