26 Analytical Instrumentation
Figure 3: NMR spectra of 16-OMC and various coffee samples from Derfernez et al [2].
Figure 6: Schematic (above) and physical set-up (below) in a fume hood showing how fl ow chemistry is incorporate.
Table 2: Temperature dependent variation in rate constant.
Figure 4: ¹H NMR spectra of 3-Dimethylaminoacrolein in CDCl₃, over a temperature range of +2 to +48°C.
Table 2 shows the temperature dependent variation in rate constant. NMR additionally enables determination of enthalpy (∆H), entropy (∆S) (associated with reaching the transition state from the reactants, and the Gibbs Free Energy (∆G). For more information on how this was calculated please see our app note here.
Conclusion Figure 5: Flow rate and temperature dependent esterifi cation of ethanol and ethanoic acid catalysed by sulphuric acid.
experiments can now follow a similar pattern with prediction, experiment, and result happening in the same session.
Reaction Monitoring
The ability to easily integrate fl ow cells into benchtop NMR also extends the benefi ts for both research and teaching beyond structural elucidation. With benchtop NMR, analysis can be run in minutes to determine the success of a reaction – no more running down to the user facility or sending samples to external companies for routine analysis.
One simple example is the fl ow rate and temperature dependent esterifi cation of ethanol and ethanoic acid catalysed by sulphuric acid (reaction shown in Figure 5). The product synthesised, ethyl ethanoate, a solvent that is used for varnishes, lacquers, dry cleaning, stains, fats, and nitrocellulose.
To investigate the rate constant dependence on temperature, a fl ow cell set-up (Figure 6) was used with X-Pulse and the reaction performed at varying temperatures.
The availability of cryogen free, benchtop NMR has enabled analytical scientists, university teaching courses, and industrial research facilities to bring the NMR technique right into the heart of their labs. Benchtop NMR has removed the high upfront and maintenance cost of traditional high-fi eld NMR, and with the arrival of the true broadband X-Pulse NMR incorporating comprehensive fl ow and temperature control, a single instrument now addresses needs ranging from student teaching, right through to high end R&D and industrial QA/QC.
References 1. E. O. Stejskal & J. E. Tanner, J. Chem. Phys., 1965, 42, 288-292.
2. M. Defernez; E. Wren; A. D. Watson; Y. Gunning; I. J. Colquhoun; G. L. Gall; D. Williamson & E. K. Kemsley, Food Chem., 2017, 216, 106-113
Author Contact Details William G. Hale, James T. Sagar, Rosie E. Jones, Robin J. Blagg, Oxford Instruments Magnetic Resonance
PIN OCTOBER / NOVEMBER 2024
READ, SHARE or COMMENTon this article at:
petro-online.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
