Physicochemical properties of 4-tert-butylbenzoic acid N′,N′- dialkylhydrazides

Article abstract of DOI:10.1134/S1070363214060085

Properties of hydrazides of 4-tert-butylbenzoic acid, important for their application in extraction technology, have been studied: solubility, acid-base properties, distribution between immiscible liquids, and hydrolytic stability. pH ranges of existence

Full text of DOI:10.1134/S1070363214060085

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 6, pp. 1101–1105. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © D.A. Pashkina, V.Yu. Gusev, A.V. Radushev, 2014, published in Zhurnal Obshchei Khimii, 2014, Vol. 84, No. 6, pp. 918–922.
Physicochemical Properties of 4-tert-Butylbenzoic Acid
N',N'-Dialkylhydrazides
D. A. Pashkina, V. Yu. Gusev, and A. V. Radushev
Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences, ul. Koroleva 3, Perm, 614013 Russia
е-mail: info@itch.perm.ru
Received September 23, 2013
Abstract—Properties of hydrazides of 4-tert-butylbenzoic acid, important for their application in extraction
technology, have been studied: solubility, acid-base properties, distribution between immiscible liquids, and
hydrolytic stability. pH ranges of existence of different forms of the compounds have been determined. The
6
N',N'-dialkyl derivatives with alkyl chains longer than C are readily soluble in nonpolar solvents, are not
transferred into aqueous phase, and are stable with respect to hydrolysis in acidic and basic media. Linear
correlations of the studied physicochemical parameters with the compounds structure and the medium
properties have been elucidated.
Keywords: hydrazide of 4-tert-butylbensoic acid, solubility, distribution coefficient, acid-base properties
DOI: 10.1134/S1070363214060085
Extraction of Cu(II) compounds from their solution
is an important stage of the solvent extraction–
eleсtrowinning method of copper production. In order
to isolate copper from its ammoniacal media, two types
of extracting agents are commonly used: oxyoximes
and β-diketones [1]. Even though efficiency of the
extraction with oxyoximes is sufficiently high, this
class of extracting agents suffers from a serious
drawback: they form a salt upon interaction with
ammonia [2], which deteriorates the solution
properties essential for further electrolysis stage.
Hence, using of oxyoximes requires additional stage of
copper production flowchart: the removal of the salt
and regeneration of the extracting agent by washing
the organic phase. In contrast to the oxyoximes, β-
diketones do not react with ammonia, but their
efficiency towards Cu(II) extraction is a lot lower.
Similarly to β-diketones, the carboxylic acid N',N'-
dialkylhydrazides are inert towards ammonia and are
efficient extracting agents for Cu(II) [3, 4]. It has been
shown that 4-tert-benzoic acid N',N'-dialkylhydrazides
containing linear alkyl substituents are better
extracting agents than β-diketones [5].
instance, from solubility in various media, distribution
between immiscible liquid phases, acid-basic
properties, and stability with respect to hydrolysis. In
this work we determined these properties of com-
pounds I–VII.
O
R
HN
N
R
R = Н (I), CH
3
(II), i-С Н
4 9
4 9 6
(III), С Н (IV), C H13 (V),
8
С Н17 (VI), С10Н21 (VII).
Solubility. The studied compounds I–VII were
white crystalline solids. Their solubility in the common
laboratory solvents (water and ethanol) as well as in
the widely used extraction media (isoamyl alcohol,
hexane, kerosene, and o-xylene) was determined
gravimetrically; the results are collected in Table 1.
As seen from Table 1 compound I was readily
soluble in aliphatic alcohols, being poorly soluble in
water or hydrocarbons. Its N',N'-dialkyl derivatives
were practically insoluble in water. With increasing
chain length of the alkyl substituents, the compounds
solubility in hydrocarbons increased, being the highest
in the case of compound IV. Further increase in the
Besides a direct technological experiment, the
potential of the extracting agents application may be
estimated from their physicochemical properties, for
1
101

1
102
PASHKINA et al.
a
Table 1. Solubility of compounds I–VII at 25±1ºC, g/L (mol/L)
Comp.
no.
Water
1.0 (0.005)
0.85 (0.0039)
insoluble
insoluble
insoluble
insoluble
insoluble
Ethanol
Isoamyl alcohol
52.0 (0.27)
157.1 (0.71)
182.4 (0.60)
410.4 (1.35)
437.4 (1.21)
–
o-Xylene
Hexane
0.2 (0.001)
Kerosene
–
I
263.6 (1.37)
8.6 (0.045)
II
285.8 (1.29)
9.7 (0.044)
1.8 (0.008)
–
III
IV
V
142.2 (0.46)
116.2 (0.38)
6.4 (0.021)
8.5 (0.028)
16.2 (0.053)
>1020 (>2.83)
>1380 (>3.32)
>590 (>1.25)
475.2 (1.56)
230.0 (0.76)
13.7 (0.045)
>930 (>2.23)
>1000 (>2.40)
>450 (>0.95)
–
–
–
–
–
–
VI
VII
–
a
(
“–”) Not determined, “insoluble” the solubility is too low and cannot be determined with any available method.
alkyl chain length reduced the solubility due to
enhanced intermolecular interactions. The presence of
branched alkyl substituents (compound III) led to
decrease in the solubility as compared with that of the
derivative containing linear alkyl groups. Hence, the
studied compounds with n-hexyl (or longer) alkyl
substituents were readily soluble in hexane and
kerosene, being promising for extraction applications.
Acid-base properties. The unsubstituted hydra-
zides and their N',N'-dialkyl derivatives are capable of
proton attachment or elimination to form protonated and
deprotonated forms, respectively. The acid-base equi-
libriums in their solutions are represented as follows:
+
HL, the hydrazide neutral form; H L , the hydrazide
2
protonated form; L¯, the hydrazide deprotonated form.
+
+
Figure 1 displays solubility S of compound IV as a
function of the Hildebrand parameter δ of the solvent
–
H ; pKa1
–H ; pKa2
+
H
2
L
HL
L¯.
(
δ values were taken from [6]). The experimental data
were well fitted with the linear equation: log S = 1.98δ –
7.76 (r = 0.9918). It is seen that the compound
In this work we studied the hydrazides acid-base
properties by means of spectrophotometry [7].
1
solubility increased with the growing Hildebrand
parameter.
In order to determine the pH ranges of existence of
different acid-base forms of the studied compounds
and to calculate the corresponding acidity constants we
analyzed the solutions absorbance as a function of pH
and the Hammett constant. The measurements were
carried out at wavelengths where the difference of
different forms absorptivity was the highest. The
medium acidity was altered by addition of HCl or
KОН solutions. A representative example of the
observed profiles is shown in Fig. 2 (compound II).
log S, mol/L
1/2
–3/2
δ, J cm
p-xylene
From the plots in Fig. 2 it is seen that proton
+
hexadecane
detachment from H L occurred at pH of 2.5–4.5,
2
whereas deprotonation of the neutral molecule HL took
place at рН 13–14.5 (the latter value corresponded to
hexane
1.8 mol/L KОН). Hence, at рН < 2.5 compound II
+
existed in the protonated form H L , the neutral form
2
Fig. 1. Solubility of compound IV as a function of the
Hildebrand parameter of the solvents.
HL prevailed over pH range of 4.5–13, and the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 6 2014

PHYSICOCHEMICAL PROPERTIES OF 4-tert-BUTYLBENZOIC ACID
1103
pKa1
II
III
V
VI
VII
Н
0
E
s
Fig. 2. Absorbance of solution of compound II as a
function of pH and the Hammett acidity function (Н ).
1) сII = 4 × 10 mol/L, λ = 245 nm; (2) сII = 1 × 10 mol/L,
0
–5
–4
Fig. 3. pKa1 of compounds II–VII as a function of steric
(
constant of the substituent.
λ = 237 nm. EtOH–H
2
O (3 : 1), l = 1 cm.
–
deprotonated form L was found in the alkaline
medium at cKOH > 1.8 mol/L. The calculated acidity
constants pK and pK are collected in Table 2.
the +I effect of the substituent, the values of σ were
taken from [6]). The experimental data were well fitted
f
with the linear equation: pKa2 = –1.30σ
.9986).
+ 12.59 (r =
a1
a2
f
0
From data in Table 2 it is seen that alkylation of the
unsubstituted hydrazide I significantly decreased its
acid (pK ) as well as basic (pK ) properties. In the II–
VII series, the longer alkyl fragment led to weakened
base properties due to steric hindrance towards proton
attachment to the agent molecule. Figure 3 displays the
compounds pKa1 value as a function of the alkyl
substituent steric constant (E ) (E were taken from
Distribution between immiscible phases. A
a2
a1
compound distribution between organic and aqueous
phases is an important parameter for estimating the
extracting agent possible application. In this work we
used either p-xylene or hexane as the organic phase
and solution of HCl (0.5 mol/L) or NH (1 mol/L) in
3
s
s
water as the aqueous phase to determine the
distribution coefficients. The obtained results are
collected in Table 3; it was found that the compounds
distribution coefficients DHL increased with the
growing molecular mass M. The lower values of log
DHL in the case of aqueous HCl were due to formation
of the hydrazides protonated form facilitating transfer
of the hydrazide to the acidic aqueous phase. The
[
6]). The experimental data were well fitted with the
linear equation: pK = 0.88E + 3.27 (r = 0.9985).
a1
s
The weakening of acid properties was due to +I
effect of the alkyl substituents impeding the proton
detachment from the substituted hydrazide molecule.
Figure 4 shows the studied compounds pKa2 as a
function of the Kabachnik constant σ (characterizing
f
Table 2. pKa1 and pKa2 of compounds I–VII (P = 0.95, n = 5–9)
pK
a
I
II
III
IV
V
VI
VI
pKa1
pKa2
3.63±0.03
3.28±0.07
2.47±0.01
3.20±0.03
3.09±0.03
2.98±0.01
2.93±0.03
12.6±0.1
13.8±0.1
14.3±0.1
14.2±0.1
14.6±0.1
–
–
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 6 2014

1
104
PASHKINA et al.
pKa2
III
IV
log D
VII
II
VI
V
IV
I
log M, g/mol
σ
f
Fig. 5. Distribution coefficient of compounds IV–VII
between p-xylene and aqueous hydrochloric acid solution
as a function of the compound molecular mass.
Fig. 4. pKa2 of compounds I–IV as a function of the
Kabachnik constants.
amount of the com-pounds transferred to the aqueous
ammonia phase was so immaterial that it could not be
detected in certain cases.
Hydrolytic stability. Stability of the extracting
agents with respect to hydrolysis determines the
possibility of their industrial application. Hydrazides
acid or base hydrolysis can be represented as follows
Figure 5 displays log DHL (p-xylene/aqueous HCl)
of the n-alkyl derivatives as a function of log M. The
experimental data were well fitted with the linear
equation: log DHL = 15.6log M – 37.48 (r = 0.9918).
This parameter of the compounds VI and VII exceeds
respective values of the industrial extractants of the
oxyoxime class.
[8].
+
+
2
R'CONHNR
2
+ H
3
O ⇄ R'COOH + NH
3
NR
,
–
–
R'CONHNR
2
+ OH ⇄ R'COO + NH
2
NR
2
.
Hydrolytic stability of the studied compounds was
expressed as the degree of hydrolysis after 4 h of
refluxing in 0.5 mol/L aqueous H SO or 1 mol/L
2
4
aqueous KOH. Degree of hydrolysis of the un-
substituted hydrazide was determined via titration of
the formed carboxylic acid with alkali. Hydrolysis of
the dialkyl derivatives was monitored using the extrac-
tion-spectrophotometry method from the decrease of
the initial compound concentration. The so obtained
results are given in Table 4.
Table 3. Distribution coefficient of compounds III–VII
between immiscible phases
a
log DHL
Comp. no. HCl 0.5 mol/L
NH
3
1 mol/L
hexane
p-xylene
p-xylene
III
IV
V
2.7
1.4
2.1
3.3
4.4
3.1
–
3.9
3.8
Table 4. Hydrolysis degree (α, %) of compounds I, IV, and
V after 4 h refluxing
not found
not found
not found
4.7
a
Medium
I
IV
V
VI
VII
not found
not found
1
0
mol/L KОН
90
0.5
–
.5 mol/L H
2
SO
4
31
3
–
a
(
“–”) Not determined; (“not found”) amount of the compound
transferred to aqueous phase is too low and cannot be
determined with any available method.
a
(“–”) Hydrolysis products cannot be determined with the method
used.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 6 2014

PHYSICOCHEMICAL PROPERTIES OF 4-tert-BUTYLBENZOIC ACID
1105
From Table 4 it is seen that the alkylation of the
unsubstituted hydrazide I significantly improved the
compounds hydrolytic stability. In the case of
compound V, the degree of hydrolysis was so low that
we failed to quantify it. The improvement of the
hydrazides stability was due to two major reasons.
Firstly, alkyl substituents sterically hampered the
reactants contact by shielding of the reactive centre
from water molecules. Secondly, the +I effect of the
alkyl substituents increased the electronic density at
carbon atom of the carbonyl group, preventing its
interaction with nucleophilic oxygen atom of water.
alkylation of the unsubstituted hydrazide at its β-
nitrogen atom with the corresponding alkyl halides [5].
In order to determine the distribution coefficients,
concentration of the compounds in the aqueous phase
was measured by the extraction-photometry method
[9].
REFERENCES
1
2
3
. Kordosky, G.A., J. Miner. Metals Mater. Sci., 1992,
vol. 44, no. 5, p. 40.
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vol. 4, no. 2, p. 135.
. Gusev, V.Yu., Radushev, A.V., Verkholantseva, T.A.,
and Batueva, T.D., Russ. Chem. Bull., 2008, no. 2,
p. 389.
EXPERIMENTAL
Electronic spectra were recorded with the SF-2000
4
5
. Gusev, V.Yu., Radushev, A.V., Bogomazova, G.S., and
Batueva, T.D., Izv. Vuzov, Ser. Khim. i Khim. Tekhnol.,
spectrophotometer
(OKB-Spectr,
St-Petersburg).
Absorbance was measured with the KFK-3-01
photometer. рН values were measured using the I-
2
010, vol. 53, no. 1, p. 21.
. Gusev, V.Yu., Radushev, A.V., Muksinova, D.A., and
Vaulina, V.N., Russ. J. Inorg. Chem., 2012, vol. 57,
no. 5, p. 738.
1
60M ionometer (ANTEKh, Belarus) equipped with
glass and silver chloride electrodes.
6
7
. Shmidt, V.S., Ekstraktsiya aminami (Extraction by
Amines), Moscow: Atomizdat, 1980.
. Bernshtein, I.Ya. and Kaminskii, Yu.A., Spektrofoto-
metricheskii analiz v organicheskoi khimii (Spectropho-
tometric Analysis in Organic Chemistry), Leningrad:
Khimiya, 1986.
The following solvents and chemicals were used:
isoamyl alcohol, chloroform, and KOH (analytical
pure grade); p-xylene, hexadecane, and H SO (pure
grade); hexane (the highest purity); kerosene (aviation,
rectificate); ethanol (rectificate).
2
4
Unsubstituted 4-tert-benzoic acid hydrazide I was
prepared via the Curtius reaction (interaction of propyl
-tert-butylbenzoate with hydrazine hydrate). The
N',N'-dialkyl derivatives of I were prepared via direct
8. Grekov, A.P., Mavrenik, O.V., and Malyushenko, S.A.,
Zh. Org. Khim., 1970, vol. 6, no. 1, p. 94.
9
. Muksinova, D.A., Gusev, V.Yu., and Radushev, A.V.,
4
Butlerovsk. Soobshch., 2011, vol. 24, no. 2, p. 113.
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