Aggregation and reactivity of the dilithium and dicesium enediolates of 1-naphthylacetic acid.
UV-vis spectra of the dilithium, 1-Li, and dicesium, 1-Cs, enediolates of alpha-naphthylacetic acid show no systematic change with concentration in dilute THF solution, but addition of small amounts of HMPA causes a bathochromic shift in the spectrum of 1-Li. These results indicate that these salts are aggregated and that HMPA breaks up the aggregates of 1-Li. The quantitative effect of small increments of HMPA indicates that 1-Li is a dimer. Alkylation reactions of 1-Cs show half-order kinetics in enediolate indicating that this salt is also dimeric but that the small amount of monomer in equilibrium is the actual reactant. Alkylation of 1-Li, however, is much slower and shows first-order kinetics interpreted as a direct reaction of the dimer; the amount of monomer in this case is too small to compete. A solution of 1-Li in THF containing 10% HMPA is much more reactive in alkylation than 1-Li alone and the first-order dependence in 1-Li is now interpreted as reaction of the monomer. Compound 1-Li is found to form a mixed aggregate with LDA, a finding that has possible synthetic significance since enediolates used in syntheses are frequently prepared using LDA. Structures of these compounds are suggested based on model ab initio computations.
Streitwieser
Andrew
A
Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA. astreit@socrates.berkeley.edu
Husemann
Marc
M
Kim
Yeong-Joon
YJ
D000478:Alkylation; D002586:Cesium / Q000737:chemistry*; D019281:Dimerization; D007700:Kinetics; D008094:Lithium / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009280:Naphthaleneacetic Acids / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
D009280:Naphthaleneacetic Acids; D009942:Organometallic Compounds; D002586:Cesium; C034182:1-naphthaleneacetic acid; D008094:Lithium