156 Figure diastere
157 Representative pulse experiment in flow conditions: Uniqsis FlowSyn reactor was equipped with a transparent 5 mL HT-PFA reactor coil and a 100 psi back pressure regulator, and then the system completely flushed with glacial AcOH which was used as the system solvent. Stock solutions of vanillin and HNO3 of desired concentrations in AcOH were prepared to separate volumetric flasks. The reactor was primed to the desired temperature and flow rate, after which 1 mL of both stock solutions was injected to the reactor via injection ports equipped with proper injection loops. After the indicated residence time, the reaction mixture was collected to a separate beaker. The initiation of the reaction was observed by a color change to yellow either in the beaker after collection was ended, right after the reaction stream exited the bpr, or in the reactor coil.
Representative continuous experiment: Stock solutions of vanillin and HNO3 in AcOH were prepared in separate volumetric flasks. Uniqsis FlowSyn reactor was equipped with a 10 mL stainless steel reactor coil and a 100 psi back pressure regulator, and then the system was completely flushed with glacial AcOH which was used as the system solvent. The reactor was primed to the desired temperature and flow rate, after which the stock solutions were fed through the pumps into the reactor. The exiting reacted mixture was collected to a separate beaker partially filled with H2O. The outbound stream was analyzed with HPLC by collecting the mixture into a 10 mL volumetric flask for a few seconds, and then diluting to indicated volume with 1:1 H2O:MeCN. The output stream was collected for an indicated time, then cooled to 0 °C in an ice bath for 1 hour, filtered, and washed with ice cold H2O and EtOH.
The yellow powder was dried in a vacuum oven and analyzed with HPLC.
HPLC analyses: The reactions were characterized by reverse phase HPLC analyses with Waters Alliance 2695 system uding a Symmetry Shield RP8 column (3.5 Pm, 4.6 x 150 mm) and PDA 996 UV detector (O = 284 nm). Eluent A for gradient elution was H2O:MeCN:TFA 850:150:1, and eluent B was MeCN:TFA 1000:1, and elution speed was 1.5 mL/min. The gradient was as follows:
Minutes A(%) B(%)
0-2 100 0 2-20 50 50
20-22 15 85
22-27 15 85
27-29 100 0 29-35 100 0
158
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