Attenuated total reflection infrared difference spectroscopy (ATR-IRDS) for quantitative reaction monitoring.

Monitoring of chemical reactors is key to optimizing yield and efficiency of chemical transformation processes. Aside from tracking pressure and temperature, the measurement of the chemical composition is essential in this context. We present an infrared difference spectroscopy approach for determining the reactant (cyclooctene) and product (cyclooctane) concentrations during a catalytic hydrogenation reaction in the solvent cyclohexane, which is present in large excess. Subtracting the spectrum of the pure solvent from the reactor mixture spectra yields infrared (IR) spectra, which can ultimately be evaluated using a curve-fitting procedure based on spectral soft modeling. An important feature of our evaluation approach is that the calibration only requires recording the pure component spectra of the reactants, products, and solvent. Hence, no time-consuming preparation of mixtures for calibration is necessary. The IR concentration results are in good agreement with gas chromatography measurements.

Determination of glucose and cellobiose dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate using Fourier transform infrared spectroscopy.

The conversion of biogenic carbohydrate feedstock to chemicals or energy equivalents is a promising approach to solve the problem of limited fossil fuel reserves. Some concepts to accomplish these transformations are based on ionic liquids (ILs) due to their ability to dissolve biopolymers, such as cellulose, and even complex biopolymer mixtures, such as wood. However, concerning control of such conversions, a reliable tool for process analytics is required. In this paper we demonstrate the applicability of Fourier transform infrared (FT-IR) spectroscopy to perform quantitative concentration measurements of glucose and cellobiose as two examples of carbohydrates dissolved in the room-temperature ionic liquid [EMIM][OAc] (1-ethyl-3-methylimidazolium acetate). For this purpose, binary mixtures in the range 0-20 wt% have been studied. A previously developed method for the data analysis, which was based on the Beer-Lambert relation, has been universalized by employing empirical correlations between the measured quantity (i.e., extinction) and the carbohydrate concentration. In the entire spectral range under investigation (500-4000 cm(-1)) numerous individual wave-numbers have been identified, allowing quantitative measurements with high accuracy and precision.

Infrared spectroscopy of a Wilkinson catalyst in a room-temperature ionic liquid.

Homogeneous catalysis in room-temperature ionic liquids (ILs) constitutes a most interesting field of research with high potential in technical applications. As concerns the hydrogenation of unsaturated hydrocarbons, Wilkinson's compound RhCl(PPh(3))(3) represents a catalyst that provides high selectivity and activity. Herein, we demonstrate the application of infrared spectroscopy to the quantitative analysis of the Wilkinson catalyst in the IL 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]). Our study demonstrates for the first time the quantitative, accurate and reproducible determination of the concentration of a rhodium catalyst by means of IR spectroscopy and, moreover, allows the investigation of intermolecular interactions. Spectral features, located mainly in the fingerprint region of the IR spectrum, are identified revealing the influence of the dissolved catalyst on the IL's vibrational structure. In particular, the ring-bending mode of the imidazolium ring shows a frequency shift as a function of catalyst concentration, probably due to hydrogen-bond formation between the IL cation and the Rh complex. The results show the potential of IR spectroscopy both for application as a quick process control technology in catalytic processes and as a tool for better understanding of IL-catalyst interactions.

Quantitative analysis of alpha-D-glucose in an ionic liquid by using infrared spectroscopy.

The applicability of infrared (IR) spectroscopy for quantitative concentration measurements in mixtures of carbohydrates and ionic liquids (ILs) is investigated. The compound 1-ethyl-3-methylimidazolium acetate, [EMIM][OAc]-an "enzyme-friendly" ionic liquid with great application potential in the dissolution of various biomasses-is used as solvent in combination with alpha-D-glucose. Our study establishes a new way to monitor the concentration of sugars in ILs, thus providing a convenient method to follow the kinetics of, for example, enzymatic reactions in [EMIM][OAc]. As a first step, we present the IR spectrum of pure [EMIM][OAc] (this constitutes the first vibrational study of this particular IL). Although numerous lines overlap in the fingerprint region of the spectrum, characteristic features can be assigned to the corresponding vibrational modes of both ions. Secondly, we study different mixtures of the IL with alpha-D-glucose (in the concentration range: 0-20 mass % glucose) and analyze them by means of IR spectroscopy, followed by computational methods, thus demonstrating the great potential of this spectroscopic technique in quantitative measurements.