Surface Enhanced Raman Spectroscopy Coupled with High Performance Liquid Chromatography for Real-time Monitoring of Suzuki Coupling Reaction

Abstract

The surface enhanced Raman spectroscopy (SERS) has been employed in the structural characterization successfully due to its ultra-high sensitivity. However, it is still remained the significant difficulties in the precise interpretation of spectroscopy. Thus, it was not developed as the promising tool for monitoring the organic reaction directly. Herein, by using the two dimensional Au nanoparticles array film as substrate, the SERS was hyphenated with high performance liquid chromatography (HPLC). The individual advantages of high sensitivity of SERS and high efficiency in separation of HPLC were combined together, and it was extended successfully to real-time monitor of a Suzuki coupling reaction between 3-bromopyridine and phenylboronic acid. Firstly, the retention time and SERS spectra of standard solution of 3-bromopyridine and phenylboronic acid were performed respectively. It was beneficial for distinguishing the reactants of the current Suzuki reaction. After the reaction was proceeded for about 5 min, the mixture was sampled for the HPLC-SERS detection. It demonstrated that the chromatogram peaks located at 2.1 min and 2.8 min were contributed to phenylboronic acid and 3-bromopyridine, while 3.6 min and 15.3 min were originated from the reaction products. The solution collected at different retention times were then flowed through the catheter and dropped to the surface of Au nanoparticles arrays sequentially. The SERS spectra features were well agreement with that of 3-bromopyridine at 2.8 min, while the SERS spectra was absent for phenylboronic acid at 2.1 min due to its weak adsorption on Au surface. For the products, the typical vibrational modes of 3-phenylpyridine and diphenyl were observed in the SERS spectra, suggesting the composition of the product and byproduct. Meanwhile, the final product was confirmed by NMR spectroscopy, proving a structure of 3-phenylpyridine. Finally, the SERS results were well associated with the chromatographic peaks in a certain duration. It indicated that the HPLC-SERS technique would be a promising tool as a complementary approach to traditional techniques (such as LC-MS) for on line monitoring the organic reaction processes.

Construction of a HPLC-SERS hyphenated system for continuous separation and detection based on paper substrates

“…In the follow up investigation, replaceable SERS substrates on a manual rotating disk were used to on-line monitor reaction processes of o -aminothiophenol with o -iodobenzoyl chloride. 26,27 By using the magnetic Fe 3 O 4 @Ag core–shell nanoparticles as SERS substrates, the on-line detection was reached by applying a magnetic field to enrich the nanoparticles for detection. After removing the magnetic field, the enriched nanoparticles were then washed with water to eliminate the memory effect.…”

Real-time visualization of the Suzuki reaction using surface enhanced Raman spectroscopy and a moveable magnetic nanoparticle film

“…The bands at 1292 cm À1 and 1595 cm À1 originating from the C-C vibration of the ring and vibration of the monosubstituted benzene ring served as the characteristic peaks of the product 3-phenylpyridine, and the band at 1000 cm À1 was assigned to the vibration of the benzene ring of the byproduct diphenyl. 28,29 1.83 mmol phenylboronic acid, 1.67 mmol BrPy and 0.33 mmol NaHCO 3 (in the same amounts for all reactions below unless otherwise specified) were dissolved in 30 mL of ethanol/water mixed solution with a volume ratio of 2 : 1, then 0.002 g PdCl 2 was added and the reaction mixture was heated to 90 1C from room temperature. Fig.…”

“…The bands at 1292 cm −1 and 1595 cm −1 originating from the C–C vibration of the ring and vibration of the monosubstituted benzene ring served as the characteristic peaks of the product 3-phenylpyridine, and the band at 1000 cm −1 was assigned to the vibration of the benzene ring of the byproduct diphenyl. 28,29…”