Enthalpies of Formation and of Functionalization Reactions for Bingel-Type Monoadducts of C60 and C70 Using Microcalorimetry

• Published in: Journal of physical chemistry. C 2011-11, Vol.115 (43), p.20849-20855
• Main Authors: Martínez-Herrera, Melchor, Amador, Patricia, Rojas, Aarón
• Format: Article
• Language: English
• Subjects: C: Nanops and Nanostructures
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp2045349

The molar standard enthalpies of combustion and formation of the Bingel-type monoadducts diethyl 1,2-methano[C60]fullerene-61, 61-dicarboxylate, C61(COOEt)2, and diethyl 1,2-methano[C70]fullerene-71, 71-dicarboxylate, C71(COOEt)2, have been determined as 1613.4 ± 37.6 and 1847.2 ± 37.0 kJ·mol–1, respectively. These values were obtained based on their energies of combustion, as measured by microcombustion calorimetry. With these values and the molar standard enthalpies of formation for C60 and C70, the enthalpic contributions for the functionalization of both fullerenes were calculated as Δfunct H°m[C60(cr) → C61(COOEt)2(cr)] = −679.7 kJ·mol–1 and Δfunct H°m[C70(cr) → C71(COOEt)2(cr)] = −690.2 kJ·mol–1. The standard enthalpies associated with the functionalization reactions were found to be Δr H°m[C60(cr) → C61(COOEt)2(cr)] = −34.5 kJ·mol–1 and Δr H°m[C70(cr) → C71(COOEt)2(cr)] = −45.0 kJ·mol–1. These results show that the insertion of the bis(ethoxycarbonyl)methane group on the C70 sphere to obtain C71(COOEt)2 produced an enthalpic change that was more exothermic than that produced when the same group was inserted on C60. Thus, the formation of C71(COOEt)2(cr) was favored over C61(COOEt)2(cr) by 10.5 kJ·mol–1. Theoretical enthalpies and Gibbs energies of the functionalization reactions, computed using density functional theory (DFT) at the B3LYP/3-21G*, B3LYP/6-31G, and B3LYP/6-31G* levels of theory, agreed with the experimental results presented here.