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Published on: May 27, 2015
Decomposition of malonic anhydrides.
Charles L Perrin1, Agnes Flach, Marlon N Manalo
1Department of Chemistry, University of California-San Diego, La Jolla, California 92093-0358, USA. cperrin@ucsd.edu
Malonic anhydrides decompose into ketene and carbon dioxide. Methylmalonic anhydride decomposes fastest due to its lower activation energy, while dimethylmalonic anhydride is slowest.
Area of Science:
- Organic Chemistry
- Chemical Kinetics
Background:
- Malonic anhydrides are known to decompose readily.
- Understanding their decomposition mechanisms is crucial for synthetic chemistry.
Purpose of the Study:
- To investigate the thermal decomposition kinetics of malonic, methylmalonic, and dimethylmalonic anhydrides.
- To elucidate the factors influencing the decomposition rate and mechanism.
Main Methods:
- Rate constants were measured using Nuclear Magnetic Resonance (NMR) spectroscopy.
- Activation parameters were determined from the temperature dependence of the rate constants.
- Computational methods were employed to support mechanistic interpretations.
Main Results:
- Methylmalonic anhydride exhibited the fastest decomposition rate.
- Dimethylmalonic anhydride showed the slowest decomposition rate.
- A nonlinear dependence of decomposition rate on the number of methyl groups was observed.
Conclusions:
- The decomposition proceeds via a concerted cycloreversion mechanism.
- A twisted transition-state structure is proposed, supported by computational data.
- The substitution pattern significantly impacts the decomposition pathway and kinetics.
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