DOI: 10.1002/celc.201300065 Catalyst-Free Electrochemical Grignard Reagent Synthesis with Room-Temperature Ionic Liquids Daniel Luder, [a] Alexander Kraytsberg, [b] and Yair Ein-Eli* [a, b] Some of the widely used materials in the chemical and phar- maceutical industries are metalorganic compounds. One of the most common types of such metalorganic compounds is the Grignard reagent (GR), generally formed by the reaction of an organic halide with Mg. [1] GR is used in numerous reactions in- volving C ÀC bond formation in these industries. Examples in- clude the synthesis of tramadol [2] and various organotin com- pounds [3] used as stabilizers for vinyl chloride resins. One of the important issues in GR synthesis is the synthesis solvent media, which has an important role in GR formation. Typically, the most suitable solvents are ethers, [1] most commonly being tetrahydrofuran (THF) or diethyl ether. Practically, the produc- tion of GR is challenging to a certain degree, since Mg surfaces are usually covered with a layer composed of hydroxides and oxides, [4] which impair the reaction of Mg with organic hal- ides. [1] In particular, when Mg is in contact with different organ- ic media, a non-conductive passivation layer is present, slow- ing down or completely preventing reactions that would oth- erwise occur in its absence. [5, 6] To overcome this, catalysts and other initiating methods have been introduced to the synthesis procedure, such as the use of iodine, heat, environmental dryness and various chemi- cal initiators. [4] Elsewhere, it has been speculated that GR may be formed without catalysts when magnesium is polarized in ethers containing GR precursors, [5] but no substantial evidence of this has been found or presented. The electrolyte media used is based on room-temperature ionic liquids (RTILs), a class of solvents that have been re- searched seriously for the past two decades as an electrolyte media. [7–10] Generally speaking, these solvents are liquids at room temperature and are purely composed of ions. The cation is typically a bulky and asymmetric organic molecule such as modifications of pyrolidinium. [11, 12] The anion is an or- ganic or inorganic molecule, ranging from a simple halide to the larger charge delocalized bis(trifluoromethylsulfonyl)imide (TFSI) anions. [11, 12] These liquids are advantageous for many ex- isting and potential applications owing to their characteristics, such as chemical and thermal stability, a wide electrochemical window, [11] high conductivity, low vapor pressure, non-flamma- bility and the ability to adjust different properties by minutely adding or subtracting functional groups on the cation. [11] Be- cause of these properties, RTILs have found many applications in diverse areas such as bioscience, CO 2 capture, organic syn- thesis, and energy management. [13] In particular, a large number of uses have been found in electrochemistry for appli- cations such as electrodeposition, batteries, fuel cells, solar cells, and capacitors. [14–16] In the area of Mg electrochemistry, certain non-acidic ionic liquids such as [1-butyl 1-mthyl pyroli- dinium bis(trifluoromethylsulfonyl)imide] (BMPTFSI) and [N,N- diethyl-N-methyl-N-(2-methoxyethyl) ammonium-bis(trifluoro- methylsulfonyl)imide] (DEMETFSI) have been found to be suita- ble as co-solvents for externally added GRs such as phenyl- magnesium bromide (PeMgBr) and ethyl-magnesium bromide (EtMgBr). [8, 10] In the current process, an RTIL-based electrolyte has been applied for the electrochemical organic synthesis of the GR EtMgBr. The electrolyte is composed of BMPTFSI, the GR pre- cursor bromoethane (EtBr) and THF as a product stabilizer, a common and less volatile ether than alternatives such as di- ethyl ether. During the reaction, Mg actively dissolves at the electrode surface after the application of a positive potential and reacts with EtBr, forming the final GR product without the presence of any chemical catalysts. For electrochemical processes in general, particularly those requiring dryness, it is desirable to use non-aqueous electro- lytes with wide electrochemical windows. In Figure 1 are pre- sented the electrochemical windows of BMPTFSI and an elec- trolyte composed of BMPTFSI + THF in 1:1 volume ratio. A particularly wide electrochemical window of ~ 5.5 V can be observed for BMPTFSI. This result is in good agreement with previous studies, [12] making it advantageous as a stable electro- lyte co-solvent for the synthesis of GR when compared to other RTILs. The presence of THF in the solution is intended for stabilizing the GR product [4] as well as for increasing elec- trolyte conductivity. [8] It is, however, observable from Figure 1a that the addition of THF in 1:1 volume ratio to BMPTFSI nar- rows the solution’s electrochemical window by ~ 1.9 V. In order to synthesize the EtMgBr, a cell was assembled with the electrolyte BMPTFSI + THF + EtBr at a volumetric ratio of 1:1:0.3 respectively. Figure 1 b presents the results of two CVs conducted with the mentioned cell and electrolyte; the work- ing electrode was Mg, and the counter electrode was Pt and Mg in two separate CVs (anodic direction first). The electro- chemical window of the electrolyte is presented for compari- son as well. In contrast to expectations with organic electrolytes, upon the activation of a CV, no anodic or cathodic reaction overpo- [a] D. Luder, Prof. Y. Ein-Eli The Nancy and Stephen Grand Technion Energy Program Technion Israel Institute of Technology Haifa 32000 (Israel) Fax: (+ 972) 77-8871977 [b] Dr. A. Kraytsberg, Prof. Y. Ein-Eli Department of Materials Science and Engineering Technion Israel Institute of Technology Haifa 32000 (Israel) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/celc.201300065.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemElectroChem 2014, 1, 362 – 365 362 CHEMELECTROCHEM COMMUNICATIONS