Physicochemical properties of benzoic acid N,N-dialkylhydrazides

Article abstract of DOI:10.1134/S1070363209050120

Benzoic acid N,N-dialkylhydrazides of the general formula C ₆H₅C(O)NHNR₂, R = C₄H₉, C₆H₁₃, C₈H₁₇, C₁₀H ₂₁, were obtained,. Their solubility, acid-base properties, stability against hydrolysis, distribution between organic and water phases were studied.

Full text of DOI:10.1134/S1070363209050120

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 5, pp. 940–943. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © V.Yu. Gusev, A.V. Radushev, V.N. Vaulina, T.D. Batueva, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 5,
pp. 768–771.
Physicochemical Properties
of Benzoic Acid N,N-dialkylhydrazides
V. Yu. Gusev, A. V. Radushev, V. N. Vaulina, and T. D. Batueva
Institute of Technical Chemistry, Ural Division of Russian Academy of Sciences,
ul. Koroleva 3, Perm, 614013 Russia
e-mail: cheminst@mpm.ru
Received October 6, 2008
Abstract―Benzoic acid N,N-dialkylhydrazides of the general formula C6H5C(O)NHNR2, R = C4H9, C6H13,
C8H17, C10H21, were obtained,. Their solubility, acid-base properties, stability against hydrolysis, distribution
between organic and water phases were studied.
DOI: 10.1134/S1070363209050120
In [1, 2] benzoic acid N,N-dialkylhydrazides were
shown to be promising extraction agents of copper(II)
from ammonia media. However they were not
systematically explored: Some properties important for
practical use were not studied, influence of hydro-
carbon radical length was not revealed. This work is
devoted to the study of some physicochemical
properties of benzoic acid N,N-dibutyl- (I), dihexyl-
(II), dioctyl- (III), and didodecylhydrazides (IV).
Acid–base properties of these compounds were
examined by spectrophotometric method [4]. The UV
spectra of neutral, acidic and basic solutions of com-
pound I are shown in Fig. 1. The spectra are different
indicating that in these solutions various forms of
reagent are in acid-base equilibrium characterized by
pKa1 and pKa2 values.
–H+, pKa2
–H+, pKa1
H2L+
HL
L–.
(1)
The explored compounds are white crystalline
substances. They are insoluble in water, but well
soluble in isopentyl alcohol and aromatic hydrocarbons
(Table 1). The solubility passes through a maximum
(compound II). The presence of a maximum is due to
the increase in hydrophobicity of compounds at the
elongation of the hydrocarbon radical, but at further
growing of hydrocarbon chain the solubility decreases
because of stronger intermolecular interaction. The
solubility of no less than 0.05–0.1 mol l–1 is necessary
for the use of reagents in extraction processes. By this
characteristic all of the compounds studied are
applicable except for compound IV. The data obtained
are quite unlike the benzylhydrazide solubility, which
is well soluble in water and virtually insoluble in
aromatic hydrocarbons [3]. Thus, introducing two
alkyl radicals into the benzylhydrazide molecule
increases hydrophobicity of compounds obtained and
improves their compatibility with organic solvents that
permits their application to the extraction processes
and leads to the decrease in the water phase losses.
Here HL is N,N-dialkylhydrazide molecule, H2L+ and
L– are its protonated and deprotonated forms
respectively. The spectra of other compounds are
similar.
The dependence of optical density of the reagent
solutions on the medium acidity was determined for
pKa1 and pKa2 calculation. The acidity was controlled
by addition of HCl solutions or saturated water-alcohol
solution of KOH. Measurements were accomplished in
the water–alcohol solutions at the wavelengths where
Table 1. Solubility of N,N-dialkylhydrazides at 20±1°C
Solubility, g l-1
Comp.
no.
water
0.26
hexane
0.08
1.9
i-AmOH
35.24
toluene
51.08
51.90
39.90
17.04
p-xylene
–
I
IIa
III
IV
0.2
177.8
48.60
27.39
11.80
insol.
insol.
1.8
96.18
1.12
14.66
а Data are taken from [1].
940

PHYSICOCHEMICAL PROPERTIES OF BENZOIC ACID
941
A
A
1.0
1.2
3
0.8
1
2
0.8
0.4
0
0.6
0.4
0.2
1
2
250
260
270
280
290
300
λ, nm
0
0
4
8
12
16
pH ← | → H
Fig. 1. Electron absorption spectra of compound I solution
in the mixture water–EtOH (1:3), CI = 5×10–4 mol l–1, l =
1 cm. (1) рН = 1.97; (2) pH = 6.60; and (3) 3.15 mol l–1 of
KOH.
Fig. 2. The dependence of optical density (А) on рН for
compound I in water:EtOH (1:3) medium, СI = 5×10–4 mol l–1,
l = 1 cm. (1) λ = 262 nm, and (2) λ = 286 nm.
the difference in optical density of two reagent forms
was maximal. The reagent concentrations are (4–5)×
10–4 mol l–1 and l = 1 cm. It is seen from Fig. 2 that the
process of proton elimination from the protonated
molecule begins at рН~2 and completes at pH ~5;
deprotonation of neutral molecule begins at рН~13 and
completes at 4.5–5 mol l–1 of KOH (while working
with concentrated solutions of alkali we use Hammett
function for the calculation). Therefore there are
protonated (pН < 2), neutral (pH 5–13) and depro-
tonated (CKOH > 5 mol l–1) forms of compound I. Ana-
logous results were obtained for the other compounds.
(diethylhydrazide) [2]; 3.16±0.02 (compound I); 2.83±
0.04 (compound II) [1]; 2.66±0.05 (compound III);
2.63±0.04 (compound IV), for all of the found values
R = 0.95, n = 5; pKa2 values: 14.94±0.04 (benzoic acid
dethylhydrazide) [2]; 14.6±0.2 (compound I); 14.6±0.2
(compound I); R = 0.95, n = 9 and 6, respectively. In
the series of benzoic acid N,N-dialkylhydrazides the
basic properties characterized by pKa1 become weaker
as the hydrocarbon radical length is increased, whereas
the acidic properties characterized by pKa2 almost do
not change. For benzylhydrazide pKa1 equals 3.27 and
pKa2 is 12.2 [3]. Thus, N,N-alkylation of benzylhyd-
razide reduces negligibly the basic properties of com-
pounds obtained and decreases substantially their acidic
properties. The decrease in acidic properties is caused
by a positive inductive effect of alkyl substituents that
makes difficult to eliminate a proton from the neutral
molecule. The basic properties weakening is probably
associated with steric hindrances growing as the
hydrocarbon radical length increases, which imparts the
proton addition to the neutral molecule of the reagent.
The values of pKa2 and pKa2 were calculated by
formulas (2) and (3).
AHL – A
pKa1 = pH + log
pKa2 = pH + log
,
(2)
(3)
A – AH L
+
2
–
AL – A
.
A – AHL
Here pKa1 and pKa2 are negative logarithms of
dissociation constants of N,N-dialkylhydrazides pro-
Chemical stability of hydrazides in acid and alkali
is characterized by hydrolysis index, which in turn
determines their suitability as extraction reagents.
Presumably, the hydrolysis of N,N-dialkylhydrazides
would proceed similarly to that of the unsubstituted
hydrazides [5].
tonated and neutral forms, respectively; AH L
+
, AHL, AL
–
2
are optical densities of solutions containing, respec-
tively, protonated, neutral and deprotonated forms of
the reagents; A is the optical density of solution
containing two forms of reagent at a certain pH value.
Hydrolysis was carried out by refluxing a solution
of reagents in 0.5 М H2SO4 and 1М NaOH for 2 h.
For the benzoic acid N,N-dialkylhydrazides the
following pKa1 values were obtained: 3.24±0.02
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 5 2009

942
GUSEV et al.
compound III, to 1.1%. In NaOH it equals to 6.6, 4.0,
log D
and 2.6%, respectively. Evidently, the hydrolysis index
decreases as the alkyl radical chain elongates that can
be due to the increased steric hindrances.
2.5
2.0
1.5
1.0
0.5
An important characteristic of reagents used in
liquid extraction is their distribution between organic
and water phases. Dependence of logarithm of
distribution coefficient (log D) of I on pH and
ammonia concentration is presented in Fig. 3.
From this figure it is obvious that at pH ≥ 3 the
values of log D remain constant due to the presence of
neutral reagent form in this region. When pH is
decreased, values log D are also decreased that is
caused by protonation of the reagent. The obtained
data on N,N-dialkylhydrazides distribution are given in
Table 2. By these data, log D increases as the mole-
cular mass, i. e. hydrophobicity, increases.
0
0
4
8
0.5 1.0
pH
CNH , mol l–1
3
Fig. 3. Dependence of logarithm of distribution coefficient
(log D) of compound I between organic and water phases
on medium acidity, CI = 0.05 mol l–1 (p-xylene), I = 0.2
(KCl). Vо.ph.:Vw.ph. 1:1, stirring for 3 min.
EXPERIMENTAL
The 1Н NMR spectra were registered on a
MERCURY-plus300 spectrometer (300 MHz) in
CDCl3 relative to internal HMDS. The IR spectra were
obtained on an IFS 66/S Fourier-spectrometer (Bruker,
Germany) from mulls in mineral oil. The UV spectra
were taken on an SF-26 spectrophotometer. Values of
рН were measured on an I-160M ionometer with a
glass and silver chloride electrodes. Optical density
was measured on a KFK-3-01 photocolorimeter.
Conductometric titration was accomplished on a ОK-
102/1 conductometer. Elemental analysis was carried
out on a CHNS-932 LECO Corporation analyser.
Thin-layer chromatography was fperformed on a Silufol
plates in m-xylene–BuOH system (2:1) using phos-
phomolybdenum acid as a detecting agent. We used
our own extraction-photometry method to determine
reagents content in the water phase on studying
hydrolysis and reagents distribution between water and
organic phases. This method is based on an ability of
N,N-dialkylhydrazide to form colored complexes with
copper(II) ions in ammonia medium when extracted
with p-xylene.
PhCOOH + NH3+ NR2
H3O+
PhCONHNR2_
(4)
OH
PhCOO_ + NH2NR2
The amount of nonhydrolyzed reagent was
determined by the extraction-photometry method we
had de-veloped. The extent of hydrolysis was
calculated by formula (5).
m1 – m2
h =
×100%.
(5)
m1
Here m1 is mass, g, of the taken hydrazide sample, m2
is the hydrazide mass, g, determined after hydrolysis.
In H2SO4 the hydrolysis index of compound I
equals to 6.0%; of compound II, to 5.3%; of
Table 2. Values of logarithm of distribution coefficient
(log D) of N,N-dialkylhydrazides, Vo:Vw = 1:1, stirring 3–
5 min, I = 0.2 (KCl)
Procedure of extraction-photometry determina-
tion of N,N-dialkylhydrazides. Into a separating
funnel (50 ml) were placed 25 ml of water phase
containing 1 ml of 10% copper(II) salt and a calculated
volume of ammonia to its concentration 0.1–1 mol l–1
in the final volume. To this mixture was added a
sample of reagent or its water solution aliquot, or
solution in p-xylene, and 10 ml of pure p-xylene. This
log Dav
Comp. no.
M
рН ~4
NH3, 0.1 M
2.34
H2SO4, 0.5 M
0.47
2.34
248
304
360
I
2.58
2.58
2.58
2.63
1.93
2.60
II
III
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 5 2009

PHYSICOCHEMICAL PROPERTIES OF BENZOIC ACID
943
mixture was stirred for 3–5 min. Then the extract was
filtered through cotton wool, diluted with p-xylene to
25 ml and photometrically measured depending on
N,N-dialkylhydrazide content at λ 330 (determination
interval 0–0.03 mmol) or 460 nm (determination
interval 0.03–0.5 mmol) in optical cell with l = 1 cm.
Reagent content was determined using the calibration
plot. The relative error of measurements did not
exceed 5%.
[20H, CH3(CH2)5], 1.45–1.56 m (4H, NCH2CH2), 2.75
t (4H, NCH2, J 7.8 Hz), 6.62 s (1H, NH), 7.3–7.46 m
(3H, Ph), 7.66 d (1H, Ph, J 8.4 Hz), 7.67 d (1H, Ph, J
7.8 Hz). The base compound content: 99%. Found, %:
C 76.50; H 11.04; N 7.74. C23H40N2O. Calculated, %:
C 76.67; H 11.11; N 7.78.
Compound IV. Yield 54%, mp 69–71°С (acetone).
Rf 0.73. IR spectrum, ν, cm–1: 3228 (NH); 1652 (amide
I); 1544 (amide II). 1Н NMR spectrum, δ, ppm: 0.80 t
(6H, CH3, J 6.9 Hz), 1.18 br. s [28H, CH3(CH2)7],
1.44–1.56 m (4H, NCH2CH2), 2.75 t (4H, NCH2, J 7.5
Hz), 6.51 s (1H, NH), 7.30–7.46 m (3H, Ph), 7.66 d
(1H, Ph, J 8.4 Hz), 7.67 d (1H, Ph, J 7.8 Hz). The base
compound content: 98%. Found, %: C 77.38; H 11.21;
N 6.67. C27H48N2O. Calculated, %: C 77.88; H 11.54;
N 6.73.
Reagents syntheses were carried out similar to
procedure [2].
Compound I. Yield 59%, mp 98.5–99°С (EtOH–
H2O 2:1), Rf 0.73. IR spectrum, ν, cm–1: 3250 (NH);
1660 (amide I); 1550 (amide II). 1Н NMR spectrum, δ,
ppm: 0.83 t (6H, CH3, J 7 Hz), 1.22–1.36 m (4H,
CH3CH2), 1.43–1.53 m (4H, NCH2CH2), 2.75 t (4H,
NCH2, J 6.9 Hz), 6.75 s (1H, NH), 7.30–7.45 m (3H,
Ph), 7.67 d (2H, Ph, J 6.9 Hz). The base compound
content determined by conductometric titration [6] is
98%. Found, %: C 72.41; H 9.34; N 11.04. C15H24N2O.
Calculated, %: C 72.58; H 9.68; N 11.29.
REFERENCES
1. Radushev, A.V., Gusev, V.Yu., Batueva, T.D., Bogo-
mazova, G.S., Shabalina, L.S., Tyryshkina, V.N., and
Karmanov, V.I., Zh. Neorg. Khim., 2006, vol. 51, no. 12,
p. 2096.
Compound II. Yield 62%, mp 77–78°С [1]. IR
spectrum, ν, cm–1: 3240 (NH); 1652 (amide I); 1538
(amide II). Н NMR spectrum, δ, ppm: 0.86 t (6H,
2. Radushev, A.V., Gusev, V.Yu., Baigacheva, E.V., and
Batueva, T.D., Zh. Prikl. Khim., 2007, vol. 80, no. 10,
p. 1744.
1
CH3, J 6.8 Hz), 1.24–1.37 m [12H, CH3(CH2)3], 1.52–
1.61 m (4H, NCH2CH2), 2.82 t (4H, NCH2, J 7.6 Hz),
6.60 s (1H, NH), 7.36–7.52 m (3H, Ph), 7.73 d (2H,
Ph, J 6.9 Hz). The base compound content: 99%.
Found, %: C 74.59; H 10.22; N 9.17. C19H32N2O.
Calculated, %: C 75.00; H 10.53; N 9.21.
3. Popel, А.А. and Shchukin, V.A., Zh. Neorg. Khim.,
1975, vol. 20, no. 7, p. 1917.
4. Bernshtein, I.Ya. and Kaminskii, Yu.А., Spektro-
fotometricheskii analiz
v
organicheskoi khimii
(Spectrophotometric Analysis in Organic Chemistry),
Leningrad: Khimiya, 1986, p. 116.
5. Grekov, А.P., Mavrenik, О.V., and Malyushenko, S.A.,
Zh. Org. Khim., 1970, vol. 6, no. 1, p. 94.
6. Radushev, А.V., Chekanova, L.G., Gusev, V.Yu., and
Sazonova, Е.А., Zh. Anal. Khim., 2000, vol. 55, no. 5,
p. 496.
Compound III. Yield 64%, mp 87.5–88°C
(acetone–H2O, 4.5:1). Rf 0.73. IR spectrum, ν, cm–1:
3224 (NH); 1652 (amide I); 1544 (amide II). 1Н NMR
spectrum, δ, ppm: 0.80 t (6H, CH3, J 6.9 Hz), 1.18 br.s
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 5 2009