The reaction of xenon difluoride with chloroform

Vessel effects in organic chemical reactions; a century-old, overlooked phenomenon

One of the most intriguing aspects of synthetic chemistry is the interplay of numerous dependent and independent variables en route to achieve a successful, high-yielding chemical transformation. The experienced synthetic chemist will probe many of these variables during reaction development and optimization, which will routinely involve investigation of reaction temperature, solvent, stoichiometry, concentration, time, choice of catalyst, addition sequence or quenching conditions just to name some commonly addressed variables. Remarkably, little attention is typically given to the choice of reaction vessel material as the surface of common laboratory borosilicate glassware is, incorrectly, assumed to be chemically inert. When reviewing the scientific literature, careful consideration of the vessel material is typically only given during the use of well-known glass-etching reagents such as HF, which is typically only handled in HF-resistant, polyfluorinated polymer vessels. However, there are examples of chemical transformations that do not involve such reagents but are still clearly influenced by the choice of reaction vessel material. In the following review, we wish to condense the most significant examples of vessel effects during chemical transformations as well as observations of container-dependent stability of certain molecules. While the primary focus is on synthetic organic chemistry, relevant examples from inorganic chemistry, polymerization reactions, atmospheric chemistry and prebiotic chemistry are also covered.

Synthesis of [F]Xenon Difluoride as a Radiolabeling Reagent from [F]Fluoride Ion in a Micro-reactor and at Production Scale

[(18)F]Xenon difluoride ([(18)F]XeF(2)), was produced by treating xenon difluoride with cyclotron-produced [(18)F]fluoride ion to provide a potentially useful agent for labeling novel radiotracers with fluorine-18 (t(1/2) = 109.7 min) for imaging applications with positron emission tomography, Firstly, the effects of various reaction parameters, for example, vessel material, solvent, cation and base on this process were studied at room temperature. Glass vials facilitated the reaction more readily than polypropylene vials. The reaction was less efficient in acetonitrile than in dichloromethane. Cs(+) or K(+) with or without the cryptand, K 2.2.2, was acceptable as counter cation. The production of [(18)F]XeF(2) was retarded by K(2)CO(3), suggesting that generation of hydrogen fluoride in the reaction milieu promoted the incorporation of fluorine-18 into xenon difluoride. Secondly, the effect of temperature was studied using a microfluidic platform in which [(18)F]XeF(2) was produced in acetonitrile at elevated temperature (≥ 85 °C) over 94 s. These results enabled us to develop a method for obtaining [(18)F]XeF(2) on a production scale (up to 25 mCi) through reaction of [(18)F]fluoride ion with xenon difluoride in acetonitrile at 90 °C for 10 min. [(18)F]XeF(2) was separated from the reaction mixture by distillation at 110 °C. Furthermore, [(18)F]XeF(2) was shown to be reactive towards substrates, such as 1-((trimethylsilyl)oxy)cyclohexene and fluorene.