SYNTHESIS OF N-ISOBUTYLANILINES SUBSTITUTED IN THE BENZENE RING
1249
(tertiary amines) and unreacted amines IIa IId was
perfomed by GLC. The yields of target secondary
amines IVa IVd were always close to 100%.
An electron-donor substituent (4-Me) in arenesulfonyl
chloride Vb decreases reaction rate and the same
substituent in amine Vb increases it compared with
the reaction rate for unsubstituted reagents IVa
and Va.
Amines IVa IVd were separated from the catalyst
and reacted with benzenesulfonyl chloride (V) and its
monosubstituted derivatives in 2-propanol.
The effect of substituents in the benzene ring of
the arenesulfonylating agent is nicely described by the
Hammett equation:
SO2C6H4R
IVa IVd + R C6H4SO2Cl
RC6H4N
(1)
HCl
Bu-i
VIa VIj
Va Vd
log k = log k0
+
.
(4)
V, R = H (a), 4-Me (b), 3-NO2 (c), 4-NO2 (d); VI, R = H,
R = H (a), R = H, R = 4-Me (b), R = H, R = 3-NO2 (c),
R = H, R = 4-NO2 (d), R = 4-Me, R = H (e), R = 4-Me,
R = 4-Me (f), R = 4-Me, R = 3-NO2 (g), R = 4-Me, R =
4-NO2 (h), R = 4-MeOCO, R = 3-NO2 (i), R = 4-EtOCO,
R = 3-NO2 (j).
Here is the sensitivity of the reaction to substituent
effect and is the Hammett constant of the substi-
tuent [8]. With amines IVa IVd we used constants,
since they account for conjugation of substituent with
reaction center. Equation (4) takes forms (5) (7) for
amines IVa, IVb, and sulfonyl chloride Vc, respec-
tively.
The kinetics of reaction (1) were studied by spectro-
photometry [7] using lithium 2,6-dinitrophenolate as
indicator. Preliminary experiments showed that this
indicator exerts no catalytic effect.
log k = ( 2.35 0.03) + (0.76 0.07) ;
r 0.980, s 0.046, n 4.
(5)
(6)
(7)
The arenesulfonylation rate fits the second-order
kinetic equation (2):
log k = ( 2.05 0.04) + (0.76 0.07) ;
r 0.990, s 0.056, n 4.
dcV/d = kcIVcV.
(2)
log k = ( 1.87 0.11)
(1.36 0.11)
,
r 0.962, s 0.169, n 4.
Here k is the acylation rate constant and cIV and cV are
the current concentrations of amine IVa IVd and
sulfonyl chloride Va Vd, respectively.
Alkyl substituents in the primary amino group of
arylamine increase the electron density on the nitrogen
atom and accelerate acylation reactions; thus, the rate
constant ratio for the reactions of aniline and N-
The initial concentration of alkylarylamine IVa
IVd in all kinetic experiments was 102 103 times
higher than the initial concentration of arenesulfonyl methylaniline with benzoyl chloride in benzene is
chloride Va Vd, which allowed the pseudo-first-order
rate constant k1 to be calculated by the Guggenheim
7.65 [2, 9]. At the same time, as shown in [10], with
branched alkyl substituents in the amino group of
method and the second-order rate constants, by Eq. (3). aromatic amines, steric factor takes significance. Thus,
the rate constant ratio for the reactions of aniline and
k = k1/c 0IV
.
(3)
N-isobutylaniline with phenacyl bromide is 0.33. In
our case, the k value for the reaction of aniline with
benzenesulfonyl chloride is ca. 10 times that for the
reaction with N-isobutylaniline, i.e. the steric factor
exerts a stronger kinetic effect than the electronic
effect of the alkyl substituent.
Here c0IV is the initial concentration of aliphatic
aromatic amine IVa IVd.
The error in k was calculated at a confidence level
of 0.95, and the random error in k was no higher than
2 3%. Given are amine no., arenesulfonyl chloride no.,
and arenesulfonylation rate constant k 102
The kinetics of arenesulfonylation of amines IVa
IVd with sulfonyl chloride Vc in 2-propanol were
studied at 298 318 K. The table lists the rate constants
k, errors in their determination, and activation para-
meters of the reactions studied.
(l mol 1 s ): IVa, Va, 0.729 0.005; IVa, Vb, 0.772
1
0.009; IVa, Vc, 3.476 0.073; IVa, Vd, 3.209 0.038;
IVb, Va, 0.374 0.011; IVb, Vb, 0.446 0.010; IVb,
Vc, 0.813 0.022; IVb, Vd, 1.127 0.031; IVc, Vc,
0.216 0.006; and IVd, Vc, 0.156 0.002.
As seen from the table, the arenesulfonylation reac-
tion features low activation energies and changes in
the activation entropy. The activation parameters ob-
tained in the present work are nicely consistent with
those reported in [2, 11].
As seen from these data, the effects of substituents
in the benzene rings of amines IVa IVd and arene-
sulfonyl chlorides Va Vd are opposite to each other:
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 8 2002