Reaction of silver(I) and (II) fluorides with C-60: thermodynamic control over fluorination level

Silver(I) fluoride is shown to be a weak fluorinating agent (FA) for C-60 and gives mainly C60F18. Fluorination with silver(II) fluoride yields C60F44, a new compound, as the predominant product (> 80% in the crude). Fluorination degree of fullerenes in reaction with binary metal fluorides is found to be mainly thermodynamically controlled. The correlation between the level of C-60 fluorination and oxidising fluorinating strength of the metal fluorides used for fluorofullerene preparations is discussed, permitting development of a self-consistent quantitative scale for inorganic FAs

Saturated vapor pressure and sublimation enthalpy of C60F18

The Knudsen effusion-mass loss method was used to determine the saturated vapor pressure and molar enthalpy of sublimation for C60F18, fluorofullerene. The average molar mass of the effusing vapor was checked by an independent torsion effusion-mass loss experiment. The vapor pressure against temperature dependence is described by the equation ln(p/Pa) = -(23739 +/- 1234) (.) (K/T) + (33.23 +/- 1.97) in the temperature range (591 to 671) K. The anomalously high value of the sublimation enthalpy of C60F18 {Delta(sub)H(m)(o) (627 K) = (197 +/- 10) kJ (.) mol(-1)} compared with the values found for the parent fullerene C-60 and the other fluorofullerenes C60F48 and C60F36 so far studied, may be explained by the high polarity of the C60F18 molecule. (C) 2002 Elsevier Science Ltd, All rights reserved

Trifluoromethylation of Fullerenes: Kinetic and Thermodynamic Control

We present a survey and theoretical interpretation of the experimental results on trifluoromethylation of fullerenes. A thermodynamic model has been developed to describe the C_60/70(CF₃)_<i>n</i> condensed phase mixtures capable of free exchange of addends and, consequently, of isomerization and changing the degrees of addition. It was found that the purely thermodynamic model affords at least satisfactory prediction of composition of products even for apparently nonequilibrium syntheses. Special cases can be identified by means of detailed kinetic modeling based on the BEP approach, which includes stepwise energetic analysis of the possible trifluoromethylation sequences. This analysis reveals two types of reactions with remarkable difference in rates: direct trifluoromethylation and rearrangements of the CF₃ groups. Whenever a particular group of compounds is interrelated through direct addition/abstraction of CF₃ groups, it is more or less safe to assume that the said group is in equilibrium describable by the thermodynamic model. In the same time, the slower migration of addends is controlled kinetically, and interference of the sublimation processes frequently prevents its equilibration. Among the most illustrative examples of hindered formation via rearrangements in absence of sufficiently favorable direct trifluoromethylation pathways are certain isomers of the <i>C</i>_3<i>v</i>–C₆₀(CF₃)₁₈, C₇₀(CF₃)₁₈, and C₇₀(CF₃)₂₀ compounds