1370
Machacek, Cegan, Halama, Roznavska, Sterba:
For compound Va the 1H NMR spectrum: 15.88 b, 1 H (NH); 7.29 and 7.30 AA′BB′, 4 H (4-
chlorophenyl); 6.76 and 7.18, AA′XX′, 4 H (4-tolyl); 2.54 s, 3 H (COCH3); 2.35 s, 3 H (ArCH3);
2.30 s, 3 H (=NCCH3). 13C NMR spectrum: 20.63 (C-1), 165.56 (C-2), 133.48 (C-3), 198.02 (C-4),
27.02 (C-5), 143.38 (C-7), 120.92 (C-8), 129.73 (C-9), 129.59 (C-10), 20.87 (C-11), 142.45 (C-12),
117.25 (C-13), 129.42 (C-14), 134.64 (C-15).
3-Phenylhydrazono-2,4-pentanedione (VIb) and 3-(4-chlorophenylhydrazono)-2,4-pentanedione
(VIc) were prepared by azo coupling of benzenediazonium chloride and 4-chlorobenzenediazonium
chloride, respectively, with 2,4-pentanedione in a known way16,17. For compound VIb: m.p. 87–88 °C,
ref.16 gives m.p. 89 °C; for compound VIc: m.p. 135–137 °C, ref.17 gives m.p. 132–133 °C.
1
For compound VIc the H NMR spectrum: 14.65 b, 1 H (NH); 7.34 and 7.35 AA′BB′, 4 H (Ar);
2.59 s, 3 H (CH3); 2.47 s, 3 H (CH3). 13C NMR spectrum: 31.53 (C-1), 197.92 (C-2), 133.21 (C-3),
196.65 (C-4), 26.43 (C-5), 139.98 (C-6), 117.12 (C-7), 129.56 (C-8), 130.74 (C-9).
Kinetic Measurements
The kinetic measurements were carried out at 25 °C with the use of a Specord UV-VIS spectro-
photometer. The solutions of substituted benzenediazonium salts IIIa–IIIc and IIIf (4-CH3, H, 4-Cl,
3-NO2) were prepared in the following way: 0.05 mol amine was dissolved in 50 ml 2.5 M HCl and
diazotized by adding 20 ml 2.5 M NaNO2 at 0 °C. The excess nitrous acid was removed by addition
of amidosulfonic acid, and the solution volume was adjusted to 100 ml by adding ice water.
The azo coupling rate of enamine I with the diazonium ions IIIa–IIIc was measured in a water–
methanol mixture (20% (v/v) methanol): 1.6 ml aqueous acetate buffer [CH3COONa]/[CH3COOH] = 10
or 5, [CH3COONa] = 0.1 mol l–1 (the ionic strength was adjusted at I = 0.5 mol l–1 by adding NaCl
solution) was placed into a quartz cell, and 0.1–0.4 ml methanolic solution of enaminone (5 . 10–3 mol l–1)
and 0.3–0.0 ml methanol were added thereto (final volume 2 ml), whereupon 30 µl 0.002 M diazo-
nium salt solution (IIIa–IIIc) was injected. The absorbance increase was measured at λ 375 nm. The
rate constants kobs were calculated from the relation
k
obst = –2.3 log (A∞ – At) + const.
Reaction of enamine I with 3-nitrobenzenediazonium chloride (IIIf) in 20% (v/v) methanol: at the
time t = 0, 0.2 ml 0.01 M diazonium salt IIIf was added to a mixture of 3 ml aqueous acetate buffer
[CH3COONa]/[CH3COOH] = 10; [CH3COONa] = 0.5 mol l–1, 13 ml aqueous 0.5 M NaCl, and 4 ml
0.001 M enaminone I in methanol. After a certain time interval ∆t (∆t = 0–10 s), 5 ml 0.01 M 4,5-di-
hydroxynaphthalene-2,7-disulfonic acid was added, and the absorbance was measured at 510 nm. In
this way, a series of measurements were carried out with various ∆t intervals. The rate constant kobs
was calculated from the equation
k
obst = –2.3 log (At – A∞) + const.
Reactions of enaminones IIa–IIe with substituted benzenediazonium ions in aqueous 2-methyl-2-
propanol (50% (v/v)): 0.1 or 0.2 ml aqueous acetate buffer ([CH3COONa]/[CH3COOH] = 0.2;
[CH3COONa] = 0.1 mol l–1), 1.2 ml mixture 2-methyl-2-propanol–water (5 : 1 (v/v)), 0.05–0.20 ml
0.1 M NaOH, 0.1–0.4 ml 0.05 M 4-chlorobenzenediazonium chloride, and water (up to the total volume
of 2 ml) were mixed in a quartz cell (d = 1 cm). A drop of 0.005 M enaminone IIa–IIe was added to
this mixture, and the absorbance–time dependence was measured at 375 nm. The amount of 0.1 M
Collect. Czech. Chem. Commun. (Vol. 60) (1995)