Effect of binary aqueous-organic solvents on the reaction of phenacyl bromide with nitrobenzoic acid(s) in the presence of triethylamine

Article abstract of DOI:10.1002/kin.20012

Second-order rate constants (k₂) of the reaction between phenacyl bromide and equimolar mixture of nitrobenzoic acid(s)-triethylamine have been determined in dimethyl-formamide (DMF)/acetonitrile (ACN)/acetone and aqueous mixtures of these solv

Full text of DOI:10.1002/kin.20012

Effect of Binary
Aqueous-Organic Solvents
on the Reaction of Phenacyl
Bromide with Nitrobenzoic
Acid(s) in the Presence of
Triethylamine
M. NALLU, M. SUBRAMANIAN, N. VEMBU, A. AKBER HUSSAIN
Department of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, India
Received 16 December 2002; accepted 10 March 2004
DOI 10.1002/kin.20012
ABSTRACT: Second-order rate constants (k2) of the reaction between phenacyl bromide and
equimolar mixture of nitrobenzoic acid(s)–triethylamine have been determined in dimethyl-
formamide (DMF)/acetonitrile (ACN)/acetone and aqueous mixtures of these solvents by con-
ductometric method at 30◦C. The rates of nitrobenzoic acids are found to be in the order:
4-NO2 > 3-NO2 > 3,5-(NO2)2. Changes in the rate just by the addition of water (1% (v/v)) into
organic component is rationalized. Decrease in the values of k2 on increasing water content
in organic solvent is explained on the basis of preferential solvation phenomenon. Single and
dual regression analysis using the various solvent parameters of aqueous mixtures (ET(30), Z,
π∗, β, α, and Y) resulted in π∗ and α as the best parameters to explain solvation of nitroben-
zoates. ꢀ 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 401–409, 2004
C
erties at microscopic and macroscopic levels was not
successful [1–4]. Triethylammonium carboxylate was
considered as an active nucleophile which exists in
different forms such as tight ion-pair, solvent sep-
arated ion-pair, proton-transferred hydrogen bonded
complex, and hydrogen bonded complex in different
solvents [1–4,12,13]. So far, a little work has been
done to provide kinetic evidence for structural identifi-
cation of acid-amine complexes through solvent effects
in acetone–water binary solvents [1–4,12,13]. There-
fore, it is planned to study the effect of binary solvents
on the reaction of phenacyl bromide with nitrobenzoic
acid(s) in the presence of triethylamine. We report here
the findings of the title reactions.
INTRODUCTION
Kinetics of the reaction of phenacyl bromide with p-
substituted benzoic acids [1,2], cinnamic acids [3], and
acetic acid [4] in the presence of triethylamine were
studied in various solvents. It was suggested that car-
boxylic acids form complexes with amine. The struc-
tural and spectral characteristics of these complexes
in aprotic solvents have been extensively studied [5–
11]. The correlation of rate data with solvent prop-
Correspondence to: M. Nallu; e-mail: nallu46@rediffmail.com.
2004 Wiley Periodicals, Inc.
c
ꢀ

402
NALLU ET AL.
The product analyses of the reaction of 3-nitro- and
3,5-dinitrobenzoic acids in acetone were performed as
above. The yield, m.p., and spectral data are listed be-
low:Theproductof(3-NO2)wasidentifiedasphenacyl
3-nitrobenzoate, yield 0.129 g (90%), m.p. 97–99◦C,
IR: 1735 νCO (–OCOAr), 1690 νCO (–CH2COAr)
EXPERIMENTAL
Materials
Phenacyl bromide was prepared as reported elsewhere
[14]. Nitrobenzoic acids, triethylamine, solvents such
as DMF, ACN, and acetone were purified by recrys-
tallization or distillation until their physical constants
(m.p./b.p.) remained constant and agreed with the lit-
erature value [15]. Elix and Milli-Q water was used.
Aqueous–organic binary solvent mixtures were pre-
pared volumetrically.
1
cm−1; H NMR: δ 9.0 (s, 1H, C2–H), 8.50 (d, 1H,
C4–H), 8.00 (d, 1H, C6–H), 7.92 (dd, 1H, C5–H), 7.69–
7.20 (m, 5H, –COAr), and 5.65 (s, 2H, –CH2CO) ppm.
The product of (3,5-(NO2)2) was identified as phenacyl
3,5-dinitrobenzoate (Fig. 1), yield 1.52 g (92%),
m.p. 131–133◦C, IR: 1743 νCO (–OCOAr), 1695 νCO
1
(–CH2COAr) cm−1; H NMR: δ 9.20 (s, 1H, C4–H),
8.00 (s, 2H, C2–H, C6–H), 7.90–7.70 (m, 5H, –COAr),
and 5.72 (s, 2H, –CH2CO) ppm.
Kinetic Measurements
The solutions of phenacyl bromide and nitrobenzoic
acid(s)–triethylamine (25 mL, 0.020 mol dm−3) in ace-
tone were prepared. The rates were followed conducto-
metrically[13]andthek2 valueswereobtainedfromthe
rate equation derived on the basis of Guggenheim prin-
ciple [13,16]. The experiments were also performed
in DMF, ACN, and aqueous mixtures such as DMF–
water, ACN–water, and acetone–water (v/v) binary
solvents.
The products isolated in the reactions of phenacyl
bromide with triethylamine–nitrobenzoic acids (4-
NO2, 3-NO2, and 3,5-(NO2)2) in DMF, ACN and their
aqueous mixtures at all ranges of water content were
found to be the corresponding phenacyl nitrobenzoates.
They were identified from mixed melting point and Co-
TLC tests.
RESULTS AND DISCUSSION
Product Analysis
Second-order rate constants (k2) of the reaction
of phenacyl bromide with equimolar mixture of
triethylamine–nitrobenzoic acid(s) (4-NO2, 3-NO2,
and 3,5-(NO2)2) in aprotic solvents (DMF, ACN, and
acetone) and in DMF–water, ACN–water, and acetone–
water solvent mixtures upto water content 25% (v/v)
have been determined by the conductometric method
at 30◦C. The rate data are presented in Table I.
The conductance of the solution of phenacyl bro-
mide in DMF/ACN/acetone was too low to measure.
This indicates that there may be no solvent interaction
with phenacyl bromide. Control experiments were car-
ried out to check the solvolysis of phenacyl bromide
by aqueous-organic solvent mixtures at all ranges of
water content. No solvolysis of phenacyl bromide was
noticed in all the cases.
The rate of the reaction between phenacyl bromide
andnitrobenzoate(s)at30◦Cwasfoundtoincreasewith
increase in the polarity of the medium. This is due to
decrease of solvation of nitrobenzoate anion by aprotic
solvent. This charged anion is solvated less in more
polar aprotic solvents which is almost desolvated [2].
The order of desolvation of nitrobenzoate anion in the
aprotic solvents is DMF > ACN > acetone.
Equal volumes of equimolar solutions of phenacyl bro-
mide and 4-nitrobenzoic acid–triethylamine (25 mL,
0.020 mol dm−3) in acetone were mixed under kinetic
conditions and kept overnight with constant stirring
at about 30◦C. The reaction mixture was slowly di-
luted with water (about 100 mL) to dissolve the amine
salt. The solid product separated was filtered off and
dissolved in dichloromethane (50 mL). The solution
was washed with aqueous solution of sodium bicar-
bonate, followed by water. The resulting solution was
dried to get a solid product, which was recrystallized
from ethanol, yield 0.131 g (92%), m.p. 123–125◦C.
TLC test on the product using ethyl acetate as elu-
ent showed single spot. The product was identified
as phenacyl 4-nitrobenzoate (Fig. 1) on the basis of
1
IR (KBr) and H NMR (200 MHz, CDCl3) data. IR:
1728 νCO (–OCOAr), 1697 νCO (–CH2COAr) cm−1
;
1H NMR: δ 8.32–8.29 (m, 4H, –OCOC6H4–NO2–4),
7.95–7.26 (m, 5H, –COAr), 5.65 (s, 2H, –CH2COAr)
ppm.
The order of reactivity of nitrobenzoates in
DMF/ACN/acetone is 4-NO2 > 3-NO2 > 3,5-(NO2)2.
The variation in the values of rate constants (k2) of these
benzoates in DMF is very small. In ACN, the values
Figure 1 X = 4-NO2, 3-NO2, 3,5-(NO2)2.

REACTION OF PHENACYL BROMIDE WITH NITROBENZOIC ACID(S)
403
Table I Log k2 and ET(30), Z, π∗, β, α, and Y values for DMF/ACN/Acetone–Water Binary Mixtures
3 + log k2
Solvent Parameters
% of Organic
Solvent
X2 Mole Fraction
of Organic Solvent 4-NO2
3-NO2 3,5-(NO2)2
Z
ET(30)
π∗
β
α
Ya
DMF
100
99
97
95
90
85
80
75
1.0000
4.0593 4.0249
4.0414 4.0124
4.0000
3.9927
3.7815
3.5843
2.6876
2.5877
2.4216
2.3060
–
–
–
–
–
–
–
–
43.8
44.2
45.3
46.0
47.6
48.9
50.0
51.2
0.89 0.77 0.00
0.90 0.79 0.05
0.91 0.78 0.11
0.92 0.76 0.16
0.94 0.74 0.27
0.97 0.72 0.33
1.01 0.70 0.37
1.04 0.69 0.40
–
–
–
–
–
–
–
–
0.9587
0.8834
0.8165
0.6783
0.5703
0.4837
0.4127
ACN
4.0399 3.8056
3.8779 3.7076
3.6368 3.6435
3.3424 3.3010
2.8960 3.1189
2.5152 2.8239
100
99
97
95
90
85
80
75
1.0000
0.9714
0.9172
0.8668
0.7550
0.6599
0.5780
0.5067
Acetone
1.0000
0.9605
0.8880
0.8233
0.6882
0.5815
0.4951
0.4238
3.4116 3.3791
3.2304 3.2140
2.8788 2.7686
2.5705 2.4637
2.3979 2.4404
2.3464 2.1884
3.1106
2.8391
2.4586
2.4128
2.3222
2.1818
2.0269
1.7657
71.70
73.24
75.13
76.89
80.79
83.44
84.45
85.33
44.7
48.3
50.6
51.8
53.3
54.0
54.5
55.1
0.75 0.47 0.25
0.77 0.51 0.34
0.79 0.53 0.46
0.80 0.54 0.57
0.84 0.58 0.78
0.88 0.61 0.81
0.82 0.58 0.84
0.84 0.59 0.86
–
–
–
–
–
–
–
–
2.3077
–
–
–
100
99
97
95
90
85
80
75
3.0414 3.0043
3.1461 3.0889
2.9542 2.9477
2.7696 2.7566
2.6522 2.6689
2.5590 2.4409
2.4815 2.3534
2.4690 2.1389
2.6021
2.6767
2.4928
2.3263
2.2596
2.1523
2.1153
1.9841
65.70
69.53
71.41
73.09
77.10
79.29
81.06
82.52
42.2
44.8
47.4
48.4
50.2
51.2
51.8
52.2
0.69 0.56 0.08
–
0.70 0.60 0.30 −4.881
0.72 0.61 0.38 −2.760
0.74 0.62 0.44 −2.620
0.78 0.63 0.58 −1.860
0.80 0.64 0.68 −1.310
0.84 0.66 0.72 −0.670
0.87 0.66 0.76 −0.310
a Y-value was predicted by linear regression analysis method for 99 and 93% (v/v) mixtures.
of k2 of 4-NO2 and 3-NO2 are the same while that of
3,5-(NO2)2 is about twofold less. A similar trend is also
observed in acetone. This observation can be explained
by electronic effect of nitro group on the reaction cen-
ter. 4-Nitrobenzoate and 3-nitrobenzoate anions are in
different electronic environments such as –R and –I
effects respectively. 4-Nitrobenzoate is expected to be
more stable by −R effect and less reactive. However,
the relative rates of 4- and 3-nitrobenzoate anions are
almost in the same order in DMF/ACN/acetone. This is
due to the fact that the –NO2 groups at 4-position may
not fully exhibit −R effect and it may also influence a
small + R effect on the reaction center [17] (Fig. 2).
The rate of 3,5-dinitrobenzoate is about twofold
less to that of 4-nitro- and 3-nitrobenzoates in
ACN/acetone. The nitro groups at 3- and 5-positions
can influence –I effect fully on the reaction center
which may cause less reactivity. However, in DMF,
the observation is different which may be due to some
factors other than electronic effects.
The presence of water (1% v/v) in DMF does not af-
fect the rates significantly whereas in ACN it decreases
to about 32–47% and in acetone it increases to about
30% (Table I). These observations may be explained in
terms of preferential solvation and solvent–solvent in-
teractions[18]. DMFisadipolarionizingsolvent. Itun-
dergoes autoprotolysis which results in its more basic
character than water [19]. Therefore, the small amount
of water interacts more with DMF rather than with ni-
trobenzoates, hence, not affecting the rate. ACN is a
protogenic solvent [20]. Water is the cosolvent which
is protic. Just addition of water (1% v/v) may facilitate
the solvation of nitrobenzoates by H-bonding or other
interactions which cause for diminishing the speed of
the reactions. The unexpected increase of rate in binary
mixture acetone–water (1% v/v) may be explained in
Figure 2 Canonical structure of triethylammonium-4-
nitrobenzoate.

404
NALLU ET AL.
terms of solvation nature which depends on the inter-
molecular forces as well as hydrogen bonding. The
added water (1% v/v) makes the acetone more polar
specifically by forming hydrogen bond with carbonyl
group. In this situation, acetone–water (1% v/v) mix-
ture may selectively solvate the counter ion of nitroben-
zoate which causes the loss of hydrogen bond already
existing between nitrobenzoate anion and triethylam-
moniumcation. Hence, thenitrobenzoateanionismade
free to react with phenacyl bromide, thus accelerating
the reaction.
The rate of reaction is very much affected when the
concentration of water is increased in the binary sol-
vent mixtures. The rate constant (k2) attains a steady
value at a higher concentration of water. The rate con-
stant values attain constancy when the water content is
more than 5% (v/v) in ACN–water. On the other hand
the values of k2 remain constant after the addition of
10% water (v/v) into DMF–water and acetone–water
(Table I). The plot of k2 against solvent composition
(Figs. 3–5) of DMF–water/ACN–water/acetone–water
indicates the solvent dependence of the rate constant.
The decrease in rate with increasing ionizing power on
the binary solvent mixtures was accounted on the basis
of Hughes–Ingold theory [20,21] for SN2 reactions.
The correlation method has been employed to know
the influence of solvent properties at microscopic
and macrosopic levels on the rate. In the present
study, attempts have been made to correlate the sol-
vent polarity in terms of Dimroth–Reichardt ET(30)
value, the Kosower Z value, the Kamlet–Taft dipo-
larity/polarizability π∗ scale, hydrogen bond accept-
ing ability β, and hydrogen bond donating ability α of
aqueous mixtures with reaction rate.
Calculation of Solvatochromic Parameters
by Forming Regression Equations
Marcus [22] reported solvatochromic parameters for
aqueous mixtures of several organic solvents. When the
entire range of mole fraction of water in the binary mix-
ture (Xw = 0–1.0) was considered, any solvatochromic
parameter did not vary linearly with the mole fraction.
However, for a very small range of mole fractions such
as 0.9–0.6 or 0.6–0.3 etc., there appears to be a linear
correlation. This formed the basis for the calculation
of several solvatochromic parameters for the solvent
mixtures used in the present study. Regression equa-
tions were formed between Xw and the reported values
of a parameter [22] for small ranges of mole fractions
of aqueous mixtures of solvents under consideration.
From the regression equation the values of the parame-
ters were predicted for the solvent mixtures within the
specific range. In several instances the correlation co-
efficient of the regression equations formed using the
reported values were 0.995–1.000. The parameters cal-
culated by the above method must therefore be reliable
and could be used in regression analyses. The calcu-
lated values of the parameters namely ET(30), Z, π∗,
β and α for aqueous mixtures of DMF, ACN, and ace-
tone are given in Table I along with the value of log k2.
The results of the regression analyses for log k2 of the
Figure 3 k2 vs percentage of DMF in DMF–water.

REACTION OF PHENACYL BROMIDE WITH NITROBENZOIC ACID(S)
405
Figure 4 k2 vs percentage of ACN in ACN–water.
reaction against solvent parameters of aqueous mix-
tures are presented in Table II. The best single and dual
parameter regression equations are shown in boldface.
the same as that of Z (Table II). The Eqs. (1) and (4)–(7)
are found to be the best fit among the single parameter
regression (Table III). The good correlation between
ET(30) and log k2 (3,5-(NO2)2) with less standard esti-
mation of error (s = 0.150) and high value of goodness
of fit (F = 162.90) (Eq. (1)) shows that the contribu-
tion of ET(30) over the reacting species is significantly
felt. The correlation coefficient is not improved even
Correlation with ET(30)/Z
The effect of solvent polarity ET(30) of ACN–water
and acetone–water on the rates is found to be almost
Figure 5 k2 vs percentage of acetone in acetone–water.

406
NALLU ET AL.
Table II Results of Regression Analyses for log k2 Against Solvent Parameters of Aqueous Mixtures
Parameters
r
n
s
F
Eq. No.
DMF-Water
ET(30)
0.931
(0.956)
[0.982]
0.995
(0.991)
[0.918]
0.966
(0.969)
[0.982]
0.935
(0.956)
[0.984]
0.995
8
0.230
(0.137)
[0.150]
0.063
(0.622)
[0.316]
0.178
(0.127)
[0.162]
0.245
(0.150)
[0.154]
0.066
39.29
(54.11)
[162.90]
596.42
(332.95)
[31.96]
35.22
(38.00)
[69.26]
17.43
(26.72)
[77.84]
272.98
(146.32)
[24.79]
384.20
(162.06)
[76.99]
(8)
[8]
8
(8)
[8]
8
(8)
[8]
8
(8)
[8]
8
(8)
[8]
8
(8)
[8]
1
2
3
π∗
ET(30) + β
ET(30) + α
π∗ + β
14
(0.992)
[0.953]
0.997
(0.992)
[0.984]
(0.664)
[0.264]
0.056
(0.632)
[0.154]
π∗ + α
11
12
13
ACN–Water
ET(30)
0.975
(0.935)
[0.910]
0.942
7
0.108
(0.186)
[0.192]
0.164
96.68
(27.98)
[29.03]
39.40
4
5
(6)
[8]
7
Z
(0.933)
[0.944]
0.878
(6)
[8]
7
(0.189)
[0.153]
0.234
(26.99)
[49.12]
16.80
6
π∗
(0.917)
[0.800]
0.976
(0.946)
[0.914]
0.978
(0.969)
[0.967]
0.956
(0.940)
[0.945]
0.985
(0.952)
[0.946]
0.958
(0.940)
[0.950]
0.978
(6)
[8]
7
(6)
[8]
7
(6)
[8]
7
(6)
[8]
7
(6)
[8]
7
(6)
[8]
7
(0.210)
[0.279]
0.112
(0.196)
[0.206]
0.114
(0.149)
[0.130]
0.160
(0.207)
[0.167]
0.093
(0.186)
[0.166]
0.158
(0.207)
[0.159]
0.114
(21.10)
[10.67]
39.64
(12.83)
[12.77]
44.39
(25.27)
[35.99]
21.45
(11.38)
[20.72]
65.95
(14.42)
[21.12]
22.11
(11.43)
[23.13]
44.35
ET(30) + β
ET(30) + α
Z + β
17
Z + α
π∗ + β
π∗ + α
15
16
(0.951)
[0.945]
(6)
[8]
(0.187)
[0.166]
(14.32)
[20.78]
Acetone–Water
ET(30)
0.940
(0.925)
[0.942]
0.952
8
0.963
(0.139)
[0.089]
0.087
45.77
(35.34)
[46.94]
57.76
(8)
[8]
8
Z
7
(0.950)
[0.957]
(8)
[8]
(0.115)
[0.077]
(55.22)
[64.81]
Continued.

REACTION OF PHENACYL BROMIDE WITH NITROBENZOIC ACID(S)
407
Table II Continued.
Parameters
r
n
s
F
Eq. No.
π∗
0.951
(0.985)
[0.966]
0.955
(0.934)
[0.951]
0.981
(0.959)
[0.966]
0.965
(0.969)
[0.968]
0.963
(0.983)
[0.969]
0.952
(0.988)
[0.966]
0.956
8
0.087
(0.063)
[0.687]
0.092
(0.144)
[0.090]
0.061
(0.114)
[0.076]
0.081
(0.997)
[0.073]
0.084
(0.073)
[0.072]
0.095
(0.062)
[0.075]
0.091
57.36
(195.51)
[83.64]
25.81
(17.02)
[23.61]
62.63
(28.55)
[34.54]
34.12
(38.02)
[37.24]
31.92
(72.87)
[38.52]
24.12
(102.49)
[34.95]
26.45
8
9
10
(8)
[8]
8
(8)
[8]
8
(8)
[8]
8
(8)
[8]
8
(8)
[8]
8
(8)
[8]
8
ET(30) + β
ET(30) + α
Z + β
18
Z + α
20
19
π∗ + β
π∗ + α
(0.986)
[0.966]
(8)
[8]
(0.067)
[0.073]
(88.75)
[37.13]
Value in open is for 4-NO2.
Value in parenthesis is for 3-NO2.
Value in square brackets is for 3,5-(NO2)2.
Best regression models are shown in boldface.
by the inclusion of either one of β or α to ET(30) or
Z. However, Eqs. (15)–(18) (Table III) indicate that the
inclusion of the parameter α improved the correlation.
The solvents ACN and acetone are dipolar, strong hy-
drogenbondacceptors, andpoorhydrogenbonddonors
[23]. Theirhydrogenbonddonatingabilityincreasesby
increasingtheamountofcosolventwater. Theimprove-
ment in correlation on using α brings out the prefer-
ential solvation of nitrobenzoate ion by water through
H-bonding.
Correlation with Y
The Grunwald–Winstein Y is a solvatochromic param-
eter derived on chemical basis [24]. This parameter
can be used to know whether reaction follows SN1 or
SN2 type in aqueous binary solvent mixtures. Acetone–
water is taken as a model for the present study. Some of
the Y values for acetone–water pairs are not available.
A regression model was formed between mole frac-
tions and reported Y values [4,25] to get the required Y
values. The seven data points (Table I) were fitted into
the Grunwald–Winstein Eq. (21),
Correlation with π∗
The parameter π∗ of DMF–water/acetone–water is
more effective on the rate than ET(30) and Z (Eqs. (2),
(3), and (8)–(10)). On the other hand, it is poor in ACN–
water mixtures (Table II). The Eq. (2) is one of the best-
fit single parameter regressions with very low value of s
(0.063) and very high value of F (596.42). This reflects
the effectiveness of polarity and polarizability of these
aqueous mixtures on the reactive species. By introduc-
ing the parameter α to π∗, the correlation improved
significantly (Eqs. (11)–(13) and Table II). Hydrogen
bond donor ability and polarity/polarizability of aque-
ous mixtures are the preferred parameters for better
solvation of triethylammonium nitrobenzoate(s).
log k2 = log ko + mY
(21)
which gave the regression Eqs. (22)–(24) for 4-NO2,
3-NO2, and 3,5-(NO2)2 respectively. The results are
shown below:
log k2
r
n
s
F
Eq. No.
2.394–0.162 Y
2.197–0.212 Y
1.979–0.154 Y
0.969
0.979
0.981
7
7
7
0.072
0.075 136.92
0.051 153.82
91.33
(22)
(23)
(24)

408
NALLU ET AL.
Table III The Best-Fit Regression Equation in Predicting the Effect on Preferential Solvation
Parameter
Log k2
r
n
s
F
Eq. No.
DMF–Water
ET(30)
π∗
16.336 − 0.280 ET(30)
13.685 − 10.695 π∗
11.025 − 7.884 π∗
0.982
0.995
0.991
8
8
8
0.137
0.063
0.622
54.11
596.42
332.95
1a
2b
3c
ACN-Water
ET(30)
Z
8.292 − 0.108 ET(30)
8.332 − 0.110 ET(30)
8.406 − 0.076 Z
0.975
0.935
0.944
7
6
8
0.108
0.186
0.153
96.68
27.98
49.12
4b
5c
6a
Acetone–Water
Z
π*
5.893 − 0.042 Z
5.655 − 3.773 π*
6.559 − 5.061 π*
5.085 − 3.594 π*
0.952
0.951
0.985
0.966
8
8
8
8
0.087
0.087
0.063
0.687
57.76
57.36
195.51
83.64
7b
8b
9c
10a
DMF–Water
π∗ + α
15.239 − 12.487 π∗ + 0.681 α
9.254 − 7.029 π∗ + 1.293 α
3.160 + 1.159 π∗ − 5.151 α
8.308 − 0.095 ET(30) − 3.154 α
0.997
0.992
0.984
0.984
8
8
8
8
0.056
0.632
0.154
0.154
384.20
162.06
76.99
11b
12c
13a
14a
ET(30) + α
77.84
ACN–Water
Z + α
0.059 Z − 3.057 α − 0.112
2.691 − 0.017 Z − 2.274 α
0.250 ET(30) − 5.789 α − 7.089
0.985
0.952
0.967
7
6
8
0.093
0.186
0.130
65.95
14.42
35.99
15b
16c
17a
ET(30) + α
Acetone–Water
ET(30) + α
π∗ + β
25.616 − 0.549 ET(30) + 7.605 α
6.007 − 6.035 π∗ + 2.088 β
8.654 − 1.377 α − 0.094 z
0.981
0.988
0.969
8
8
8
0.061
0.062
0.072
62.63
102.49
38.52
18b
19c
20a
a Represents 4-NO2.
b Represents 3-NO2.
c Represents 3,5-(NO2)2.
The correlation between log k2 and Y is only fair
in all three equations (r = 0.969–0.981). The very low
value of m (−0.154 to −0.212) indicates that the bond
breaking and bond making would proceed to the same
extent, which is characteristic of SN2. Based on this
result, the proposed mechanism of the reaction under
study is shown below (Scheme 1):
CONCLUSION
The rate of the reaction between phenacyl bromide and
nitrobenzoic acid(s) (4-NO2, 3-NO2, and 3,5-(NO2)2)
in the presence of triethylamine in DMF–water, ACN–
water, and acetone–water binary solvent mixtures has
been determined by conductometric method at 30◦C.
Scheme 1

REACTION OF PHENACYL BROMIDE WITH NITROBENZOIC ACID(S)
409
The second-order rate constant (k2) of the reaction(s)
has been evaluated from conductivity data by an appro-
priate equation derived from Guggenheim principle.
The phenacyl nitrobenzoate is found to be the product
of the reaction. Thus, triethylammonium benzoate is
considered to be the active nucleophile. The variation
in the rates of these reactions in a medium is explained
in terms of electrical effects of nitro group. The dif-
ference in the rate of reaction in DMF/ACN/acetone
is attributed to the phenomenon of desolvation of ni-
trobenzoate anion by the aprotic solvents. Addition of
1% water (v/v) to acetone gives the unexpected results.
The decrease in the rate with increase of water content
in aqueous mixtures is attributed to the preferential sol-
vation of nitrobenzoate anion. Correlation technique is
employed to quantify the solvent effects. Values of sol-
vatochromic parameters such as ET(30), Z, π∗, β, and
α of aqueous mixtures are correlated with log k2 val-
ues of these reactions. The correlation of π∗ and α is
found to be good. This indicates that the nitrobenzoate
ion is preferentially solvated by water through hydro-
gen bonding. The correlation with Y supports the SN2
mechanism.
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