phenylacetaldimine.JPG

Objective

To study the formation of an imine from phenylacetaldehyde and tert-butylamine to confirm formation in the Ugi reaction.

Procedure

CDCl3 solutions of phenylacetaldehyde (240 ul in 2 mL, 1 M) and t-butylamine (146 ul in 2 mL, 0.7 M) are prepared in separate 1 dram vials. One mL of each solution are used to obtain initial H and C NMR spectra. The remaining 1 mL of each solution are mixed in a 1 dram vial and shaken vigorously. The resulting solution is transferred to an NMR tube and the reaction is monited by H and C NMR.

Results

t-butylamine solution (BA)

HNMR 1.27 (br s, NH2), 1.15 (s, CH3)

phenylacetaldehyde solution (PA)

H-NMR 9.71 (t, J=2.3Hz, CHO, 0.65H), 7.30 (m, 3H), 7.19 (d, J=7.5 Hz, 2H), 3.65 (d, J=2.3 Hz, CH2, 2H)

42A 5 min

HNMRsmall new peaks 9.76 (t), 7.79 (d), 7.73 (d), 7.65 (t, J=5.3 Hz), 3.57 (d, J=5.3 Hz),1.19 (s) and many other peaks in the 2-6 ppm region
From PA and BA: 9.73 (t), 7.1-7.4 (m, more than just PA), 3.67 (d), 1.18 (s)

42B 11 min

HNMR

42C 28 min

CNMR

42D 30 min

HNMR

42E 42 min

HNMR a multitude of peaks, especially 2-6 ppm region

42F 65 min

CNMR

42G 110 min

CNMR

42H 15hr 18 min

CNMR

42 I 15hr 23 min

HNMR

42 J 16hr30 min

HNMR

Discussion

  1. With an excess of aldehyde, we expect to see leftover aldehyde peaks in all the spectra, which is the case.
  2. Imine formation should result in the formation of a triplet and a doublet coupled to each other and after 5 min we do see the appearance of a triplet at 7.65 ppm and a doublet at 3.57 ppm with the same coupling constant of 5.3 Hz. However, this does not seem to be the major process operating, with many other peaks appearing immediately and increasing over time until after 42 minutes the HNMR spectrum is intractable.
  3. The formation of a carbinolamine intermediate (before dehydration to the imine) should have generated 3 sets of double doublets with correlating coupling constants, given that the hydrogens on the methylene group would be diastereotopic. These were not observed.
  4. The underintegration (0.65H) of the aldehyde hydrogen in the pure phenylacetaldehyde solution should be noted and has previously been observed on our 500 Mz instrument with this aldehyde as well as 5-methylfurfurylamine. The parameters for the NMR experiment are available on the header information when viewing the spectra through JSpecView. Any recommendations about modifying these parameters to obtain accurate integration would be helpful.
  5. If this is a general problem with phenylacetaldehyde because of aldol chemistry, it may prove to be a difficult to use in Ugi reactions. It should be noted that Ugi reactions are generally run in methanol, not chloroform. Also, other less sterically hindered amines should be tried.

Conclusion

Phenylacetaldehyde and t-butylamine react but do not cleanly form an imine in CDCl3.

Log

2006-11-14

1. 16:00] A 1M solution of phenylacetaldeyde was prepared by adding 240uL of phenylacetaldehye in 2ml of CDCl3 in vial. Another solution (less than 1M) of tert-butylamine was made by adding 146uL of tert-butylamine in 2ml of CDCl3.
2.16:45] A H-1 NMR of CDCl3 as a blank sample was obtained.
3. 17:00] A H-NMR of tert-butylamine was obtained.
4.17:15] A H-NMR of phenylacetaldehyde was obtained.
5. 18:15] 1ml of 1M phenylacetaldehyde solution (made previously) was added to 1ml of 1M tert-butylamine to obtain 42A.
6. 18:20] A HNMR of 42A was obtained; -- 5 min
7. 18:26] Another HNMR was obtained; -- 11 min
8. 18:43] A CNMR was obtained; -- 28 min
9. 18:45] A HNMR was obtained; -- 30 min
10. 18:57] A HNMR was obtained; -- 42 min
11. 19:20] A CNMR was obtained; -- 65 min
12. 20:05] A CNMR was obtained; -- 110 min

2006-11-15

13. 09:33] A CNMR was obtained; --15hr 18min
14. 09:37] A HNMR was obtained; 15hr 23min
15. 10:45] A HNMR was obtained; 16hr 30min

Tags

phenylacetaldehyde InChI=1/C12H17N/c1-12(2,3)13-10-9-11-7-5-4-6-8-11/h4-8,10H,9H2,1-3H3/b13-10-
tert-butylamine InChI=1/C4H11N/c1-4(2,3)5/h5H2,1-3H3
imine InChI=1/C8H8O/c9-7-6-8-4-2-1-3-5-8/h1-5,7H,6H2