Researcher

Khalid Mirza

Objective

To estimate the concentration of dissolved Ugi product UC176C in the supernatant of a 4-component Ugi reaction mixture in benzene. Reactions are carried out at four concentrations, 0.4M, 0.3M, 0.1M and 0.03M

Procedure

A 0.4M equimolar solution of phenenthrene-9-carboxaldehyde, furfurylamine and phenylacetic acid was prepared in benzene. Serial dilution was performed to obtain 0.3M, 0.1 and 0.03M solution, To each solution a molar equivalent of butylisocyanide was added. The solutions were vortexed and left overnight for precipitation of the Ugi product (UC176C). Next day, the solutions were sonicated for 1min in a water bath at 25C. Supernatants from the solutions were collected and HNMR was obtained to estimate the amount of dissolved Ugi product (UC176C) in each solution.

Results

Spreadsheet Exp159-i A&B
Spreadsheet Exp159-ii-C&D
Estimated second order kinetics for the Ugi reactions A, B and C using K= 6.2x10-3M-1 min-1.

ONSCExp159-plot-i.jpg
Figure 1. Estimated Ugi reaction kinetics at three concentrations, 0.4M (red), 0.3M (blue) and 0.1M (purple)

Discussion

From UsefulChem Exp249; it is known that the rate constant of this Ugi reaction is K= 6.2x10-3M-1 min-1. It is also known that at 0.4M concentration the product starts to precipitate out after 6h in to the reaction.
Based on the above mentioned data and the actual starting concentrations used in this experiment (ONSCExp159-A-2, 0.4M; ONSCExp159-B-2, 0.3M; and ONSCExp159-C-2, 0.1M), a second order kinetics plot was plotted (Figure 1). From the plot, concentration of the starting materials after 500min in to the reactions had been estimated as 0.18M, 0.16M, 0.08M for ONSCExp159-A-2, ONSCExp159-B-2 and ONSCExp159-C-2 respectively.

Experimental results for the concentration of the starting materials does (eg, phenylacetic acid) correlate with the estimated molar concentration of the reactants, ONSCExp159-A-2, 0.18M; ONSCExp159-B-2, 0.18M and ONSCExp159-C-2, 0.1M (within +/-0.02M), thus justifying not only second order kinetics but also the rate constant K for the Ugi reaction.

Reconciling solubility and kinetics:


Conclusion

Log

2009-01-12
11:30 Made-up a 0.4M solution of phenanthrene-9-carboxaldehyde (132mg) , phenylacetic acid (218mg) and furfurylamine (141uL) in benzene in a 4mL volumetric flask. The solution was vortexed for about a minute when all components dissolved freely. This solution is labeled ONSCExp159-A
12:00 Dissolved 100uL ONSCExp159-A solution in 500uL DMSO-d6 in a clean NMR tube and obtained a HNMR.
12:45 Serial dilution of ONSCExp159-A was performed as given below. One mL of resultant solutions
Solution ID
Stock concentration (M)
stock volume (mL) used
Final Volume
Final
Conc per component
ONSCExp159-A
0.4
4
4
0.4
ONSCExp159-B
0.4
1.5
2
0.3
ONSCExp159-C
0.3
0.67
2
0.1
ONSCExp159-D
0.1
0.6
2
0.03
14:00 Obtained HNMRs of the dilute solutions. ONSCExp159-B, C and D. Concentrations of each component was verified by SAMS
18:20 To vial containing ONSCExp159-A added butylisocyanide (44.1uL, 0.4mmol). Vortexed the solution for 30s and left it in the hood.
To vial containing ONSCExp159-Badded butylisocyanide (32.5uL, 0.4mmol). Vortexed the solution for 30s and left it in the hood.
To vial containing ONSCExp159-C added butylisocyanide (8.4uL, 0.4mmol). Vortexed the solution for 30s and left it in the hood.
To vial containing ONSCExp159-D added butylisocyanide (3.1uL, 0.4mmol). Vortexed the solution for 30s and left it in the hood.
2009-01-13
10:50 Vials 1 and 2 appeared to contain a small amount of ppt at the bottom. However not ppt was observed in vials 3 and 4.
11:00 Set vials 1 and 2 in a sonicator bath at 25C and sonicated them for one minute.
11:25 Sonciated vials 3&4 for one min. Then left the samples undisturbed in a fume hood.
20:20 By now a whole lot of solid had formed in vials A and B, obtained pictures of the vials containing the reaction mixtures.
20:30 Vortexed the vials A and B, then centrifuged them.
20:45 Obtained four clean and dry NMR tubes, labeled A, B,C and D. Pitpetted out 500uL DMSO-D6 in them and transferred approximately 150-200uL of the supernatants from vials A and B in the NMR tubes. Also pipetted out C and D solutions in the tubes
22:00 Obtained HNMRs of the solutions.