(Dimerization of o-quinodimethanes)
Using stopped-flow uv-visible spectroscopy, it was determined that the dimerization of o-xylylene (1) follows second-order kinetics with a rate constant of 9.94 +- 0.32 x 10/sup 3/ liter mol/sup -1/ s/sup -1/ at 25/sup 0/C in CH/sub 3/CN. Two ring-alkylated derivatives of 1, 4-butyl-1,2-xylylene (28) and 3.4-(1,1,3,3-tetramethyltrimethylene)-1,2-xylylene (29) were generated and observed by uv-visible spectroscopy. The rate constant for the dimerization of 28 was 3.90 +- 0.15 x 10/sup 3/ liter mol/sup -1/ s/sup -1/ at 25/sup 0/C and that for 29 was 5.59 +- 0.21 x 10/sup 3/ liter mol/sup -1/ s/sup -1/ at 25/sup 0/C. The similar rate constants indicate that when undergoing dimerization the o-quinodimethane monomers prefer a non-endo approach. The dimerization kinetics of 5-ethylidene-6-methylene-1,3-cyclohexadiene (9) and 5,6-bis(ethylidene)-1,3-cyclohexadiene (10) were studied by stopped-flow uv-visible spectroscopy. At 25/sup 0/C in CH/sub 3/CN k/sub 9//k/sub 1/ = 0.59 and k/sub 10//k/sub 1/ = 0.016. The dimerization of 9 and 10 led predominantly to one stereoisomer. The rate constants indicated a stepwise mechanism for the dimerization of benzenoid o-quinomethanes. The fluoride-ion induced 1,4-elimination methodology used in the generation of o-xylylene (1) was used to form 1,2-napthoquinodimethane (2) and 9,10-phenanthroquinodimethane (3). o-Quinodimethane (2) was observed in solution by uv-visible spectroscopy while 3 was observed by /sup 1/H NMR spectroscopy. Both of these species were considerably more stable than 1, with k/sub 1//k/sub 2/ = 163 and k/sub 1//k/sub 3/ = 590,000 at 25/sup 0/C. Both 2 and 3 dimerized following second-order kinetics.
- Research Organization:
- Ames Lab., IA (USA)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 6322767
- Report Number(s):
- IS-T-1294; ON: DE87011256
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
AROMATICS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
DIMERIZATION
HYDROCARBONS
KINETICS
NMR SPECTRA
ORGANIC COMPOUNDS
POLYCYCLIC AROMATIC HYDROCARBONS
POLYMERIZATION
REACTION KINETICS
SPECTRA
YIELDS