Malonic Anhydrides, Challenges from a Simple Structure

Area of Science:

• Organic Chemistry
• Chemical Synthesis
• Physical Chemistry

Background:

• Monomeric malonic anhydrides have long been challenging to synthesize.
• Previous attempts at preparation were unsuccessful.

Purpose of the Study:

• To report the first successful synthesis of monomeric malonic anhydrides.
• To characterize the stability and decomposition kinetics of these compounds.

Main Methods:

• Ozonolysis of ketene dimers was employed for synthesis.
• Infrared (IR) and Raman spectroscopy were used for structural elucidation.
• Kinetic studies and computational analysis were performed to understand decomposition.

Main Results:

• Monomeric malonic anhydrides were successfully prepared and characterized.
• These anhydrides are unstable, decomposing below room temperature into ketene and carbon dioxide.
• The dimethyl derivative was slightly more stable than the parent compound.
• The monomethyl derivative exhibited the fastest decomposition rate, with a low enthalpy of activation (12.6 kcal/mol).

Conclusions:

• The synthesis of monomeric malonic anhydrides is now achievable.
• Decomposition follows a concerted [2s + 2a] cycloreversion pathway.
• Computational studies rationalize the observed stability trends based on transition state organization.