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J Am Chem Soc. 2012 Jun 13;134(23):9698-707. doi: 10.1021/ja301867s. Epub 2012 Jun 4.

Decomposition of malonic anhydrides.

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1
Department of Chemistry, University of California-San Diego, La Jolla, California 92093-0358, USA. cperrin@ucsd.edu

Abstract

Malonic anhydrides decompose at or below room temperature, to form a ketene and carbon dioxide. Rate constants for the thermal decomposition of malonic, methylmalonic, and dimethylmalonic anhydrides were measured by NMR spectroscopy at various temperatures, and activation parameters were evaluated from the temperature dependence of the rate constants. Methylmalonic anhydride is the fastest, with the lowest ΔH(‡), and dimethylmalonic anhydride is the slowest. The nonlinear dependence on the number of methyl groups is discussed in terms of a concerted [2(s) + (2(s) + 2(s))] or [2(s) + 2(a)] cycloreversion that proceeds via a twisted transition-state structure, supported by computations.

PMID:
22625847
DOI:
10.1021/ja301867s
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