NMR for Reaction Monitoring

Luisa Ciobanu, Jonathan V. Sweedler, and Andrew C. Webb 

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J. Chin, B. Fell, M. J. Shapiro, J. Tomesch, J. R. Wareing and A. M. Bray, Magic angle spinning NMR for reaction monitoring and structure determination of molecules attached to multipin crowns, J. Org. Chem., 1997, 62, 538-539. 

Chinl997 Chin, J., Fell, B., Shapiro, M.J., Tomesch, J., Waring, J.R. and Bray, A.M., Magic Angle Spinning NMR for Reaction Monitoring and Structure Determination of Molecules Attached to Multipin Crowns, J. Org. Chem., 62 (1997) 538-539. 

In this context it is important to note that the detection of this land of alkali cation impurity in ionic liquids is not easy with traditional methods for reaction monitoring in ionic liquid synthesis (such as conventional NMR spectroscopy). More specialized procedures are required to quantify the amount of alkali ions in the ionic liquid or the quantitative ratio of organic cation to anion. Quantitative ion chromatography is probably the most powerful tool for this kind of quality analysis. 

In this section we have not endeavoured to give a comprehensive review of methods which can be used for reaction monitoring, but we have described the most universal and commonly used modern techniques. Various other monitoring methods can be devised for specific reactions. For instance ultraviolet (uv) spectroscopy can be used if one strong chromophore is being converted to another, but the disadvantage of spectroscopic methods is that they do not indicate how many products are being produced. Nmr spectroscopy can also be employed and this is mentioned further in Chapter 12. 

GEL-PHASE NMR SPECTROSCOPY FOR REACTION MONITORING AND QUANTIFICATION OF RESIN LOADING... 

Referring to magnetic resonance methods, nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy, and particularly NMR, is widely used for reaction monitoring however, it is not applicable to all nuclei, and quenching problems may occur in the presence of paramagnetic species. On the other hand, EPR spectroscopy can only detect systems with unpaired electrons. This limits the application potential for this method, and additional complementary... 

Flow and High-Pressure NMR Spectroscopy for Reaction Monitoring... 

Fisher at al. [17] reported the use of on-line NMR spectroscopy with a flow probe for supercritical fluid chromatography (SFC) used for reaction monitoring purposes. They monitored aliphatic amines in SCCO2. A typical NMR spectrum reahzed both in classical media and in SCCO2 is presented in Fig. 5.6. 

For reactions monitored by NMR, thermolyses were carried out in acetonitrile or ace tonitrile-d in sealed... 

R 501 D. Sakellariou, C.A. Meriles and A. Pines, Advances in Ex-Situ Nuclear Magnetic Resonance , C.R.Phys., 2004,5,337 R 502 J.M. Salvino, F Gel-Phase NMR Spectroscopy for Reaction Monitoring and Quantification of Resin Loading , Chem.Anal., 2004,163,37 R 503 A. Schenck and G. Solt, Study of Multipolar Effects in Rare Earth and Actinide Intermetallic Compounds by pSR , J.Phys.-Con-dens.Mat. 2004,16,S4639... 

Online detection using 4H nuclear magnetic resonance (NMR) is a detection mode that has become increasingly practical. In a recent application, cell culture supernatant was monitored on-line with 1-dimensional NMR for trehalose, P-D-pyranose, P-D-furanose, succinate, acetate and uridine.33 In stopped-flow mode, column fractions can also be analyzed by 2-D NMR. Reaction products of the preparation of the neuromuscular blocking compound atracurium besylate were separated on chiral HPLC and detected by 4H NMR.34 Ten isomeric peaks were separated on a cellulose-based phase and identified by online NMR in stopped-flow mode. 

Standard conditions acetone (or -cf), water (5 equiv) and 2 mol % catalyst, initial alkyne concentration 0.50 M, reaction temperature 70 2 °C, reaction monitored by ll NMR or GC using appropriate internal standards. b In situ generation of catalyst see text for further details. 

Fig. 10.9 (a) Schematic arrangement for the NMR-spectro-scopic monitoring of gas-consuming reactions under catalytic conditions according to [50]. (b) Gas flow during the measurement (a - argon, b - hydrogen). 

Scheme 8.1 Synthesis of a sialyl-Lewis tetrasaccharide employing C-enriched protecting groups for the quantitative reaction monitoring using gated decoupling NMR spectroscopy.

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