Epimerization-Crystallization Method in Optical Resolution of 2,2'-Dihydroxy-1,1'-binaphthyl, and Kinetic Study

Article abstract of DOI:10.1246/bcsj.66.2002

Optical resolution of 2,2'-dihydroxy-1,1'-binaphthyl (1) with (R,R)-1,2-cyclohexanediamine (2) in toluene yielded optically pure (R)-1 in a yield of 160percent based on the theoretical amount of the enantiomer contained in the racemate by selective crystallization of a less soluble complex, (R)-1*(R,R)-2, and epimerization of more soluble complex, (S)-1*(R,R)-2.Also optically pure (S)-1 was obtained with the same enantiomer of the resolving agent, (R,R)-2, in a yield of 154percent. (R,R)-1,2-Diphenyl-1,2-ethanediamine (3) was a suitable resolving agent for both 1 and 6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl.Kinetic study indicated that the reversible first-order rate constants for the epimerizations of (S)-1*(R,R)-2 and (S)-1*(R,R)-3 were larger than that for the racemization of (S)-1.The activation energy and frequency factor for the epimerization of (S)-1*(R,R)-2 were 109 kJ mol^-1 K^-1 and 3E10 s^-1, respectively, and those for (S)-1*(R,R)-3 were 96 kJ mol^-1 and 1E8 s^-1, while those for the racemization of (S)-1 were 85 kJ mol^-1 K^-1 and 9E5 s^-1, respectively.