title: Concentration determination of methyl magnesium chloride and other Grignard reagents by potentiometric titration with in-line characterization of reaction species by FTIR spectroscopy.
abstract: A potentiometric titration method for methyl magnesium chloride and other Grignard reagents based on the reaction with 2-butanol in THF has been developed and validated. The method employs a commercially available platinum electrode, using an electrolyte compatible with non-aqueous solvents. Well-defined titration curves were obtained, along with excellent method precision. The endpoint was precisely determined based on the first derivative of the titration curve. Different solvents such as THF, diethyl ether and methylene chloride provided similar results with regard to sharpness of the endpoint and method precision. The method was applied to a wide array of Grignard reagents including methyl magnesium bromide, ethyl magnesium chloride, propyl magnesium chloride, vinyl magnesium chloride, phenyl magnesium chloride, and benzyl magnesium chloride with similar precision and accuracy. Application of in-line FTIR was demonstrated for in situ monitoring of the titration reaction, allowing characterization of the reaction species. An authentic spectrum of the MeMgCl-THF complex was obtained using spectral subtraction and the vibrational absorbance bands were identified. FTIR also provided an alternative for detecting the titration endpoint, and the titration results so obtained, provided a cross-validation of the accuracy of the potentiometric titration.
authors.affiliation: Analytical Research Department, Merck Research Laboratories, PO Box 2000, RY818-C220, Rahway, NJ 07065, USA. yadan_chen@merck.com
authors.forename: Yadan
authors.initials: Y
authors.lastname: Chen
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.forename: Roy
authors.initials: R
authors.lastname: Helmy
authors.forename: George X
authors.initials: GX
authors.lastname: Zhou
authors.forename: Rosario
authors.initials: R
authors.lastname: LoBrutto
mesh_terms: D000440:Butanols / Q000737:chemistry; D004566:Electrodes; D007202:Indicators and Reagents / Q000032:analysis* / Q000737:chemistry; D015636:Magnesium Chloride / Q000032:analysis* / Q000737:chemistry; D011199:Potentiometry; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000440:Butanols; D007202:Indicators and Reagents; D015636:Magnesium Chloride; C043958:2-butanol