Solvent interactions in the allylation of piperidine

Article abstract of DOI:10.1002/kin.20410

The reaction between allylbromide and piperidine has been studied in different protic and aprotic solvents. The reaction is first order with respect to [allylbromide] and [piperidine]. A correlation analysis of the rate data with solvent properties shows that polarity (Y ), polarizability (P), and electrophilicity (E) of the solvent simultaneously influence the rate of reaction. From the regression analysis, information regarding the relative solvation of the reactants and the activated complex is obtained and a solvation model is proposed.

Full text of DOI:10.1002/kin.20410

Solvent Interactions in the
Allylation of Piperidine
T. DEVENDER, P. MANIKYAMBA
Department of Chemistry, Kakatiya University, Warangal 506 009, India
Received 11 May 2008; revised 1 November 2008; accepted 30 November 2008
DOI 10.1002/kin.20410
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The reaction between allylbromide and piperidine has been studied in different
protic and aprotic solvents. The reaction is first order with respect to [allylbromide] and
[piperidine]. A correlation analysis of the rate data with solvent properties shows that polarity
(Y), polarizability (P), and electrophilicity (E) of the solvent simultaneously influence the rate
of reaction. From the regression analysis, information regarding the relative solvation of the
ꢀ
C
reactants and the activated complex is obtained and a solvation model is proposed. 2009
Wiley Periodicals, Inc. Int J Chem Kinet 41: 421–425, 2009
equation introduced by Koppel and Palm [5] as
INTRODUCTION
In any reaction, the interactions of reactants and acti-
vated complex with the solvent molecules are exten-
sive and complex. The solvent–solute interactions are
of two types, namely specific and nonspecific [1]. All
solvents interact with substances nonspecifically. The
intensities of these interactions are measured in terms
of polarity (Y) [2] and polarizability (P) [2] of the
solvent. The specific solvent–solute interactions are
short-range forces and are chemical in nature. Specific
solvation of the substance primarily occurs when the
solvent interacts with a specific charged atom or group
in a molecule. The intensities of these interactions are
measured in terms of electrophilicity (E) [3], nucle-
ophilicity (B) [3], hydrogen-bond donor ability (α)
[4], hydrogen-bond acceptor ability (β) [4], and spe-
cific polarizability and dipolarity parameter (π∗) [4] of
the solvent. So the general-term polarity of the solvent
means the overall solvation ability of the solvent due to
either all or some of these properties. Hence the effect
of solvent on the reaction rate has to be presented not by
a single parameter equation but by a multiparametric
log k = log ko + yY + pP + bB + eE + · · · (1)
In the above equation, k is the rate constant of the
reaction in any solvent and ko is the rate constant in
an inert solvent that does not solvate at all, taken as
a reference state. Y, P, B, and E are different solva-
tion parameters of the solvent under consideration. The
coefficients y, p, b, and e are the susceptibilities of k
to the respective solvent–solute interaction parameters.
These coefficients indicate the differential solvation of
the reactants and the activated complex and the mode
of solvation. The results on such studies have been re-
ported earlier [6–14] using different nucleophiles and
substrates. Similar studies of solvent effects on the ki-
netics of the allylation reactions are limited. Hence, the
reaction between allylbromide and piperidine has been
studied in 16 different protic and aprotic solvents and
the results are presented.
EXPERIMENTAL
Allyl bromide (Merck, Mumbai, India) and piperidine
(Sd-fine, Mumbai, India) were used without further
purification. Methanol, ethanol, n-propanol, n-butanol,
Correspondence to: P. Manikyamba; e-mail: mani prerepa@
yahoo.co.in.
2009 Wiley Periodicals, Inc.
c
ꢀ

422
DEVENDER AND MANIKYAMBA
sec-butanol, i-butanol, t-butanol, and cyclochexanone
were Sd-fine samples of AR grade. Acetone, ethyl
methyl ketone, N,N-dimethylformamide, dimethyl-
sulfoxide, formamide, acetonitrile, i-propanol, and
benzyl alcohol are Merck samples. These solvents were
purified if necessary after checking their boiling points.
The solutions of the reactants of required concentra-
tions were prepared by dissolving known volumes of
allylbromide and the nucleophile piperidine in a known
volume of the solvent. The reactions were initiated by
mixing the thermally equilibrated solutions of allyl-
bromide and the nucleophile at required temperature.
Preliminary studies indicated that HBr is one of the
products of the reaction. Hence, the course of the re-
action was followed by measuring the conductance of
the reaction mixture at different time intervals using a
conductivity bridge (Century make) in the temperature
range 303–318 K. The temperature was maintained
constant within 0.5◦ using an Insref thermostat.
The conductance of the reaction mixture was mea-
sured at the beginning of the reaction (C0), at different
known time intervals (Ct ), and also after completion of
substrate allylbromide undergoing solvolysis in the sol-
vents usedinthe present study was checkedbystudying
the conductance of the solution of allylbromide in each
solvent in the absence of the nucleophile. There was
a slow change in the conductance due to liberation of
HBr. Estimation of the rate constants of this process in-
dicated that the solvolysis rate constants are more than
100 times less than the substitution reaction rate con-
stants under similar experimental conditions. Hence
the solvolysis rates are neglected while calculating the
substitution rate constants. The package data analysis
that is part of MS Excel was used to carry out the linear
multiple regression analysis. The F-test and t-test [16]
were used to test the validity of the multiparametric
equation.
The product separated at the end of the reaction
was identified as the corresponding allyl piperidine
from its IR spectral analysis. Its IR spectrum does not
show any sharp absorption band around 3300 cm−1 due
to the N H bond, while this band is observed in the
reactant. Furthermore, the IR absorption around 2800
cm−1 confirms the presence of a N CH2 group [17].
the reaction (C ). The order of the reaction was estab-
∞
lished by studying the reaction at 0.02 mol dm−3 allyl-
bromide and 0.1, 0.2, and 0.4 mol dm−3 piperidine con-
centrations. In each set, the plot of log((C∞ − Ct )/Ct )
against time was linear, suggesting the first-order na-
ture of the reaction with respect to allylbromide. The
first-order rate constants determined from the slopes
of the above linear plots are 1.65, 3.36, and 6.67 ×
RESULTS AND DISCUSSION
The second-order rate constants determined in 16 dif-
ferent solvents are presented in Table I. A glance at
these values indicates that the rate constants are highly
dependent on the nature of the solvent. To know the
influence of the solvent on the rate, these rate constants
are correlated individually with the solvent parameters
Y, P, E, and B as well as α, β, and π∗. The correspond-
ing correlation coefficients (r) obtained are 0.77, 0.55,
0.63, 0.32, 0.49, 0.25, and 0.07, respectively. These
correlations are not satisfactory, suggesting that the
variation in the rate due to change in the nature of
the solvent cannot be described by a single property of
the solvent. Hence, the data are analyzed by taking two
parameters each time. Some of the successful correla-
tions obtained with meaningful correlation coefficients
are given below.
10−2 −1, respectively, in methanol at 303 K. These
s
data suggest that the order with respect to the nucle-
ophile is also one. Since the overall order is two, the
present reactions were conducted at [allylbromide] =
[piperidine] = 0.02 mol dm−3 and the second-order
rate constants k were calculated using the relation [15]
1
Ct
k =
(2)
at C∞ − Ct
where a is the initial concentration of the reactants.
The rate constants thus determined were found to be
reproducible within 5% error. The possibility of the
log k = −8.33 + 14.37Y − 5.89 × 10−4B; R = 0.77
(3)
(4)
(5)
(1.73) (3.57)
(13.69 × 10−4
)
(0.19)
log k = −7.77 + 12.98Y − 1.40 × 10−3P; R = 0.78
(1.88) (4.06)
(1.70 × 10−3
)
(0.19)
log k = −7.26 − 2.70 × 10−2E + 12.31Y; R = 0.88
(1.25) (0.83 × 10−2
)
(2.60)
(0.15)
International Journal of Chemical Kinetics DOI 10.1002/kin

SOLVENT INTERACTIONS IN THE ALLYLATION OF PIPERIDINE
423
Table I Second-Order Rate Constants and Activation Parameters in the Reaction between Allyl Bromide and
Piperidine in 16 Different Solvents
k × 103 dm3 mol−1
s
−1/(K)
314
E
a
ꢀH=
(kJ mol−1) (kJ mol−1 a
ꢀS=
(J K−1 mol−1 a
ꢀG=
(kJ mol−1 a
Solvent
303
308
313
)
)
)
δꢀG=a
Methanol
Ethanol
11.67 16.21 25.00
14.16 33.11 66.66
16.67 23.44 31.66
10.01 19.95 35.00
10.06 17.85 27.83
9.13 19.05 33.33
20.01 26.91 35.83
10.23 16.21 24.15
16.43 23.98 34.20
34.61
134.89
42.65
63.09
42.68
60.35
46.88
36.30
49.07
60.25
141.25
51.28
141.25
40.73
33.11
144.54
57.44
95.73
47.87
76.54
71.80
79.65
43.46
63.82
57.44
31.78
38.29
31.91
57.44
47.86
38.29
31.91
54.92
93.21
45.35
74.02
69.28
77.13
40.94
61.30
54.92
29.26
35.77
29.39
54.92
45.34
35.77
29.39
−101
27
85.51
84.97
84.57
85.83
83.52
86.08
84.10
85.84
84.61
82.96
81.52
80.90
82.19
84.73
84.55
80.59
0.00
−0.54
−0.94
0.32
n-Propanol
i-Propanol
n-Butanol
Sec-Butanol
i-Butanol
t-Butanol
Benzyl alcohol
Dimethylformamide 31.26 40.73 50.01
Dimethylsulfoxide 59.42 87.09 108.82
Acetone
−129
−39
−47
−1.99
−29
0.57
−142
−81
−1.41
0.33
−98
−0.90
−2.55
−3.99
−4.61
−3.32
−0.78
−0.96
−4.92
−177
−151
−170
−90
26.61 32.35 41.05
45.39 86.86 99.59
Acetonitrile
Ethylmethyl ketone 16.48 22.38 30.66
Cyclohexanone
Formamide
−130
−161
−169
16.66 22.35 27.50
77.06 97.72 110.85
[Allyl bromide] = [piperidine] = 0.02 mol dm−3
.
a At 303 K.
The values in parentheses are standard errors of the
corresponding coefficients. The analysis is further ex-
tended using three parameters as the correlation coeffi-
cients of the above biparametric equations are not satis-
factory. The following are some of the results obtained:
correlation coefficient value of R = 0.91, the standard
errors are higher than the coefficient of the parameter
itself. Hence the above four-parameter equation (9) is
rejected and only Eq. (8), in which the rate is simul-
taneously correlated with polarity (Y), polarizability
log k = −8.76 + 4.26 × 10−4B − 18.82 × 10−3E + 15.33Y; R = 0.83
(6)
(7)
(8)
(1.42) (18.17 × 10−4
)
(9.54 × 10−3
)
(3.14)
(0.17)
log k = −10.45 + 16.30Y + 6.89P − 1.52 × 10−3B; R = 0.86
(1.43)
(2.86)
(2.46)
(1.80 × 10−3
)
(0.15)
log k = −10.26 + 16.24Y + 5.68P − 16.99 × 10−3E; R = 0.91
(1.20)
(2.36)
(1.95)
(7.31 × 10−3
)
(0.13)
Thus log k is better correlated with Y, P, and E. To
know whether a fourth parameter would improve the
strength of the correlation or not, the analysis is further
extended using four parameters. The following result
is obtained:
(P), and electrophilicity (E) of the solvent, is consid-
ered. This equation explains 83% of experimental data
as indicated by the R value.
The applicability of Eq. (8) to the present system is
confirmed by subjecting the data to the following tests:
log k = −10.50 + 16.86Y + 6.46P − 1.46 × 10−3B − 16.78 × 10−3E; R = 0.91
(9)
(1.23)
(2.47)
(2.12) (1.57 × 10−3
)
(7.31 × 10−3
)
(0.13)
1. To apply the linear multiple regression analysis,
the primary requirement is that the individual
Although the rate constant data are correlated using
the four parameters equation with the linear multiple
International Journal of Chemical Kinetics DOI 10.1002/kin

424
DEVENDER AND MANIKYAMBA
independent variables used in the analysis should
not bear any meaningful relationship among
themselves. This analysis results in the following
correlation:
suggests that Y is significant at 99.95% confi-
dence level, whereas P and E are significant at
95% confidence level. Thus, these tests confirm
the applicability of the above LSER (Eq. (8)) to
the present system. The contributions of these
three parameters in this LSER are found to be
Y = 53%, E = 21%, and P = 26%.
Y = −0.48−0.08P + 3.33 × 10−3E; R = 0.16
(0.04) (0.22) (0.85 × 10−3
) (0.02)
The following conclusions, regarding the mode of
the differential solvation of the reactant and the acti-
vated complex, can be drawn from the above LSER:
A low correlation coefficient (0.16) among
these three parameters used in Eq. (8) sug-
gests that the above linear solvation energy
relationship (LSER) is not a result of chance
correlation.
1. The rate of the reaction is strongly influenced by
the polarity of the solvent (Y). The positive value
of the coefficient of Y in the above LSER sug-
gests that the activated complex is more strongly
solvated than the reactants due to the polarity of
the solvent.
2. log kcal using the above LSER for each solvent
used in the present system is correlated with the
experimentally determined kꢂ, i.e. log kobs. This
results in the following equation:
2. The rate of reaction is also influenced by polar-
izability (P) of the solvent. Positive value of the
coefficient of P in the above LSER suggests that
the activated complex is more strongly solvated
than the reactants.
3. The reaction rate is influenced by the elec-
trophilicity (E) of the solvent. The negative value
of the coefficient of E in the LSER suggests that
the reactants especially the nucleophilic center is
more strongly solvated than the activated com-
plex due to the electrophilic nature of the solvent.
log kobs = 0.99 log kcal; r = 0.99
This excellent correlation is an indication of the
applicability of the above equation (Eq. (8)) to
the present system.
3. The calculated statistical F is compared with the
table value. Fcal (18.43) is greater than the Ftable
(5.95) at 1% level of significance.
4. The significance of each independent variable
used in the above LSER is confirmed by com-
paring the statistical t-values calculated for each
parameter (tcal) with the statistical table values
(ttable), tcal are 6.88, 2.92 and 2.32 for Y, P, and
E terms. Comparison of these values with ttable
In view of these observations, the following solvation
model can be proposed in the reaction of allylbromide
with piperidine.
≠
C H 2
C H 2
+
C H
C H
N
C H
B r
N
C H 2
H
B r
H
S o lv a tio n d u e to e lec tro p h ilicity
o f th e so lv en t
N o n sp ecific so lv atio n d u e to
p o la rity an d p o lariza b ility o f th e
so lv en t
H B r
+
N
H
2 C
C
H
C H 2
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SOLVENT INTERACTIONS IN THE ALLYLATION OF PIPERIDINE
425
From the temperature effect on the rate data, the en-
ergy of activation Ea, enthalpy, entropy and free energy
of activation ꢀH=, ꢀS= and ꢀG= are computed and
presented in Table I. The ꢀS= evaluated in different
solvents indicate that these are highly dependent on
the nature of the solvent. The ꢀG= computed is nearly
constant (83.33 2.74 kJ mol−1), suggesting a unified
reaction scheme in all the solvents. The differential free
energy δꢀG= values computed taking methanol as the
reference solvent are all negative except in i-propanol
and t-butanol, suggesting that the activated complex is
more stabilized when it is changed from methanol to
other solvents.
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Org Chem 2001, 14, 884.
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International Journal of Chemical Kinetics DOI 10.1002/kin