Structural Requirements for Glyme Catalysis in Butylaminolysis of Aryl Acetates in Chlorobenzene. Identification of -OCH2CH2OCH2CH2OCH2CH2O- as the Optimal Subunit for Catalysis

Article abstract of DOI:10.1021/jo00008a044

The catalytic behavior of linear (open-chain) polyethers (glymes) in butylaminolysis of 4-nitrophenyl acetate carried out in chlorobenzene has been reexamined (J.Am.Chem.Soc. 1980, 102, 2865-2866).The observation of a break in a plot of the catalytic rate constant vs chain length indicates that four oxygens in a -OCH2CH2OCH2CH2OCH2CH2O- subunit are necessary for optimal catalysis.The break, occuring at four oxygens in the profile (corresponds to triglyme), has been verified by a Hammett analysis, which employed four additional aryl acetates (3-chlorophenyl, 3-bromphenyl, 3-cyanophenyl, and 4-cyanophenyl).This break was missed in a previous study (J.Am.Chem.Soc. 1980, 102, 2865-2866) because differing amounts of impurities in the glymes increased the experimental scatter of the data.The Hammett study supports the conclusions of others that breakdown of the zwitterionic tetrahedral intermediate is rate-limiting.The break in the polyether plot implies a specific structure for a glyme-zwitterionic tetrahedral intermediate complex, which contains an ammonium ion that hydrogen bonds to the ether oxygens.