Study of methanol catalyzed reaction between sodium 1,2-naphthoquine-4-sulfonate and hydroxyl ion and its application in the determination of methanol

Article abstract of DOI:10.1016/j.saa.2007.12.017

A novel and simple spectrophotometric method for the direct determination of methanol with 1,2-naphthoquinone-4-sulfonate (NQS) is developed in this paper. It is based on the fact that methanol can catalyze the reaction between 1,2-naphthoquinone-4-sulfonate and hydroxyl ion to form 2-hydroxy-1,4-naphthoquinone in buffer solution of pH 13.00. Beer's law is obeyed in a range of 0.26-15.8 mg/ml at the maximal absorption wavelength of 454 nm. The equation of linear regression is A = 0.01998 + 0.05944C (mg/ml), with a linear regression correlation coefficient of 0.9977. The detection limit is 0.25 mg/ml (3σ/k), while R.S.D. is 2.0% and the recovery rate is in a range of 96.5-103%. The detailed mechanism for the formation of the products is proposed and discussed.

Full text of DOI:10.1016/j.saa.2007.12.017

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 71 (2008) 245–251
Study of methanol catalyzed reaction between sodium
,2-naphthoquine-4-sulfonate and hydroxyl ion and its application
in the determination of methanol
1
∗
Quanmin Li , Huanhuan Zhang
College of Chemistry and Environmental Science, Henan Normal University, Henan Key Laboratory for
Environmental Pollution Control, Xinxiang, Henan 453007, PR China
Received 12 June 2007; received in revised form 15 December 2007; accepted 17 December 2007
Abstract
A novel and simple spectrophotometric method for the direct determination of methanol with 1,2-naphthoquinone-4-sulfonate (NQS) is developed
in this paper. It is based on the fact that methanol can catalyze the reaction between 1,2-naphthoquinone-4-sulfonate and hydroxyl ion to form
2
-hydroxy-1,4-naphthoquinone in buffer solution of pH 13.00. Beer’s law is obeyed in a range of 0.26–15.8 mg/ml at the maximal absorption
wavelength of 454 nm. The equation of linear regression is A = 0.01998 + 0.05944C (mg/ml), with a linear regression correlation coefficient of
.9977. The detection limit is 0.25 mg/ml (3σ/k), while R.S.D. is 2.0% and the recovery rate is in a range of 96.5–103%. The detailed mechanism
for the formation of the products is proposed and discussed.
2008 Elsevier B.V. All rights reserved.
0
©
Keywords: Methanol; Sodium 1,2-naphthoquine-4-sulfonate; Catalytic reaction; 2-Hydroxy-1,4-naphthoquinone; Spectrophotometry
1
. Introduction
HPLC, expensive apparatus needed in other methods make them
inapplicable in common laboratory.
Methanol is one of the most popular organic solvents and
finds extensive applications in industries and household uses [1].
As for its determination, chromotropic acid colorimetric method
2] based on that methanol’s oxidization to formaldehyde has
been recommended as official methods by AOAC [3] and ISO
4]. However, this method requires long operation time (more
than 4 h), a painstaking process to treat formic acid which was
formed during the oxidation process [5]. In the mean time, meth-
ods based on high performance liquid chromatography (HPLC)
It was reported in 1894 that 1,2-naphthoquinone-4-sulfonate
(NQS) could react with amino group of primary amine deriva-
tive in nucleophilic substitution reaction [10]. However, to the
best of our knowledge, compounds containing hydroxyl group
have not been determined by using NQS. It is showed in our
study that methanol can catalyze NQS to react with hydroxyl
[
[
−
ion (OH ) in buffer solution of pH 13.00, providing a novel
and sensitive method for the determination of methanol. This
method was studied in detail and reported in this paper. Through
our study, it is shown that the reaction product from NQS and
[
1], selective flow-injection [6], enzymatic method [7], Fourier
−
transform infrared spectrometric [8] or GC–MS [9] are also
used for the determination of methanol. However, selective flow-
injection method based on that methanol’s oxidation to formic
acid with alcohol oxidase-catalysed [6] and enzymatic method
based on methanol oxidase in combination with basic fuchsin
hydroxyl ion (OH ) is 2-hydroxy-1,4-naphthoquinone (law-
sone, Fig. 1, λmax = 454 nm), which was characterized by means
1
of MS, IR, H NMR analysis. Beer’s law is obeyed in a range of
0.26–15.8 mg/ml. The detection limit is 0.25 mg/ml (3σ/k) and
R.S.D. is 2.0%. In contrast with the method mentioned above
[1–9], this new procedure is simple, sensitive and can be carried
out in short time. At the same time, it has a wide line range and
does not need expensive apparatus. All these advantages make
it applicable in common laboratory, and it is expected that it
will get an important practical value for the determination of
methanol.
[
7] cannot be used for the direct determination of methanol.
On the other hand, besides pre-treatment of the samples with
∗
Corresponding author. Tel.: +86 373 3326336; fax: +86 373 3326336.
E-mail address: mercury6068@hotmail.com (Q. Li).
1
386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.12.017

2
46
Q. Li, H. Zhang / Spectrochimica Acta Part A 71 (2008) 245–251
Beijing, China and Tianjin Deen Chemical Regent Plant) was
accurately weighted using a BS 110 s electro-analytical balance
Beijing Sartorius balance Ltd., Beijing, China), and then trans-
(
ferred to 100 mL volumetric flask. Subsequently, the solution
was diluted to volume with distilled water and mixed well.
2.4. Procedure
About 1.00 ml of 4% methanol solution was transferred into
5 ml color comparison tube. Subsequently, 2.50 ml of buffer
2
solution of NaOH–KCl (pH 13.00) and 5.00 ml of solution of
Fig. 1. The structure of lawsone.
−
3
NQS (5.0 × 10 M) were added to the same tube and diluted
to the mark of 12.5 ml with water and mixed well. This solution
was stood for 45 min at room temperature, and the absorbance
of the solution was measured at 454 nm against a reagent blank
with the same concentration without methanol.
2
. Experimental
2
.1. Apparatus
A model 752s spectrophotometer (Shanghai Lengguang
Technique Instrument Plant, Shanghai, China) was used for
photometric measurements. Absorption spectrum was recorded
with a TU-1810 ultraviolet–vis spectrum spectrophotometer
3. Results and discussion
3.1. Analysis of reaction mechanism
(
General Instrument Plant, Beijing, China). A model CS-501
3.1.1. Detection of sulfurous ion (SO32 ) in sample
solution (methanol + NQS + NaOH–KCl buffer solution of
pH 13.00)
−
super constant temperature instrument (Chongqing Experiment
Equipment Plant, Chongqing, China) was employed for tem-
perature measurement. All pH measurements were made with a
pH-3C digital pH meter (Shanghai Lei Ci Device Works, Shang-
hai, China); IR spectrum was taken by the KBr pelletization
method using FTS-40 Fourier transform infrared spectrometric
(
trum was recorded in Bruker 400 MHz ultra shield
spectrometer (The Bruker Companies, Germany) using CD3OD
as the solvent; 6890GC-5973N GC–MS (Agilent Technologies
Company, California, USA) was used to carry on MS spectrum
analysis.
According to the procedure detailed in Section 2.4,
sample solution (methanol + NQS + NaOH–KCl buffer solu-
tion of pH13.00, solution I) and reagent blank solution
(NQS + NaOH–KCl buffer solution of pH 13.00, solution II)
were prepared, respectively. These solutions were stood for
1
American BIO-RAO Company, USA); The H NMR spec-
TM
NMR
◦
20 min at 35 C in aqueous thermostat. Then 5.00 ml of solu-
tion of barium chloride (BaCl2, 10%) was added into solutions I
and II, respectively, shaking these solutions in order to mix well.
It was found that white precipitation appeared in solution I, but
the phenomena did not appear in solution II. After centrifu-
gal separation, the white precipitation obtained from solution
I was divided into two portions. To one portion, solution of
hydrochloric acid (0.20 M) was added. It was then observed that
a pungent gas evolved and the white solid dissolved. The gas
can make basic fuchsin discolor, indicating that the gas is sul-
fide dioxide (SO2). This shows that the precipitation is barium
sulfite (BaSO3); to the second portion of the white precipita-
tion, 1.00 ml of solution of hydrogen peroxide (3%) was added.
Subsequently a solution of hydrochloric acid (0.20 M) was also
added into the above solution and it was found that the precipita-
tion did not dissolve. This indicates that barium sulfite (BaSO3)
is oxidized by hydrogen peroxide to barium sulfate (BaSO4)
which is insoluble in hydrochloric acid. Therefore, it is pre-
2
.2. Reagents
Sodium 1,2-naphthoquine-4-sulfonate (NQS) standard solu-
−
3
tion (5.0 × 10 M) was prepared by dissolving 0.3252 g NQS
(
from ACROSORGANICS) in 250 ml distilled water (the solu-
◦
tion was preserved at 4 C in dark). Methanol standard stock
solution (4%, m/m) was prepared by transferring 5.00 ml
High-liquid-chromatographic-grade methanol (99.9%, Tian-
jin Kermel Chemical Reagents Development Center, Tianjin,
China) into 100 ml volumetric flask and diluted to the mark with
distilled water and mixed well. Buffer solution of pH 13.00 was
prepared by mixing 125 ml solution of KCl (0.20 M) and 330 ml
solution of NaOH (0.20 M) in 500 ml volumetric flask [11], and
adjusted by a pH 3C digital pH meter (Shanghai Lei Ci Device
Works, Shanghai, China). Buffer solutions of pH 1.00–12.00
were also prepared according to literature method [11]. Unless
otherwise stated, analytical reagent-grade chemicals and dis-
tilled water were used throughout.
sumedthatthereissulfurousion(SO32 )insolutionIcontaining
methanol. In other words, in NaOH–KCl buffer solution of pH
13.00, 4-sodium sulfonate of NQS was substituted by hydroxyl
ion (see Section 3.1.3) into solution in form of sulfurous ion
−
(SO32 ) in presence of methanol.
−
1
2
.3. Sample preparation
3.1.2. IR, MS, H NMR spectrum analysis
About 15.00 ml of methanol was transferred into 50 ml
beaker. Subsequently, 5.00 ml of buffer solution of NaOH–KCl
(pH 13.00) and 5.00 ml of solution of NQS (0.05 M) were added
Prior to analysis, 3.9420 g of the certified material of
methanol (analytical reagent-grade, Beijing Chemical Plant,

Q. Li, H. Zhang / Spectrochimica Acta Part A 71 (2008) 245–251
247
Fig. 3. IR spectrum of product.
of methanol. The residual obtained was used for MS spectrum
analysis. Comparing with MS spectrum of NQS, it can be found
that MS spectrum of the residual (see Fig. 6a) is the same
with that of NQS (see Fig. 6b). This indicates that the residual
obtained is still NQS in absence of methanol.
3.1.3. Absorption spectrum
The absorption spectrum of the system of NQS–methanol–
NaOH–KCl buffer solution (pH 13.00) against reagent
blank and NQS, lawsone against NaOH–KCl buffer solution
(
pH13.00) were recorded, respectively. The result was shown in
Fig. 7.
As shown in Fig. 7, the shape of the absorption peak of
the system of NQS–methanol–NaOH–KCl buffer solution (pH
3.00) is very similar to lawsone and both of them have a
1
maximal absorption wavelength of 454 nm. This indicates that
the product of methanol–NQS–NaOH–KCl buffer solution (pH
1
3.00) system should be lawsone. The conclusion is in agree-
1
ment with IR, MS and H NMR spectrum analysis. Furthermore,
when the concentration of lawsone is the same with NQS,
maximum absorption wavelength (454 nm) of lawsone shifts
Fig. 2. Standard spectrum of lawsone.
125 nm to long wave against the λmax of NQS (329 nm) and
to the same tube and mixed well. After stood for 45 min at room
temperature, the solution was adjusted to acidic by using 3.00 ml
of solution of hydrochloric acid (0.20 M). And then the solution
was heated until almost dryness under constant temperature of
absorbance of lawsone is much larger than that of NQS. In
term of chromogenic reaction used in spectrophotometry, dif-
ference of the absorbance between the reaction product and
chromogenic reagent should be larger than 60 nm. Thus the sys-
tem of NQS–methanol–NaOH–KCl buffer solution (pH 13.00)
can be used to determine methanol very well due to formation
of lawsone in this reaction system. In order to obtain high sen-
sitivity and eliminate interference, all following measurements
were carried out at 454 nm.
◦
3
5 C condition. After washed with distilled water to neutral-
ity (washings is neutrality), the reaction product obtained was
◦
dried for 1 h at constant temperature of 35 C. The product was
1
characterized with IR, MS, H NMR and absorption spectrum
analysis, respectively. In comparison with standard spectrum of
lawsone (Fig. 2), it is found that the characteristic peak of IR
spectrum (Fig. 3) and MS (Fig. 4) are almost the same with
3.2. Reaction mechanism
1
that of lawsone. And it is also seen from H NMR spectrum
(
Fig. 5) of the reaction product that the number of proton is
According to literature [10], 4-sodium sulfonate of NQS can
be substituted by amino group to form russety N-alkyl-amino-
naphthoquinone in alkaline solution (pH > 8.00), indicating that
4-sodium sulfonate of NQS cannot be replaced directly by
hydroxyl ion to form lawsone in alkaline solution. And in this
paper, the experiment results also show that in buffer solution
in accord with that of lawsone which was shown in its stan-
dard spectrum. This indicates that the reaction product should
be lawsone.
Keeping other condition unchanged, the residual was pre-
paredaccordingtotheexperimentalmethodaboveintheabsence

2
48
Q. Li, H. Zhang / Spectrochimica Acta Part A 71 (2008) 245–251
Fig. 4. MS spectrum of product.
−
3
(2) Reaction between CH O and NQS
of pH 13.00, NQS cannot react directly with hydroxyl ion, only
in the presence of methanol can NQS react with hydroxyl ion
to form lawsone. Thus it is presumed that methanol acts as cat-
alyzer in this reaction. At the same time, similar with amino
−
group, methoxyl (CH3O ), taking on nucleophilicity due to
the lone electron pair of oxygen atoms, tends to attack on the
electron-deficient center in NQS, namely the No. 4 carbon atom.
−
So it is concluded that methoxyl (CH3O ) formed by ioniza-
tion of methanol [12] reacts with NQS to form intermediate
−
(
C) and then it is replaced by OH to form unsymmetrical 4-
(3) Intermediate converted into lawsone
hydroxy-1,2-naphthoquinone, and furthermore is converted into
-hydroxy-1,4-naphthoquinone. It seems reasonable that the
2
reaction equation is as follows (arrowheads in reaction equation
indicate transfer of charge)
(
1) Ionization of methanol in alkaline solution
−
−
CH3OH + OH ꢀ CH3O + H2O
In light of the expression method of rate equation in literature
13], rate equation of the catalytic reaction should be
[
r = k2CDCC
(1)
Positive reaction rate is the same with reverse reaction rate
in reversible reaction (k1CACB = k−1CC), so
k1CACB
CC =
(2)
Fig. 5. 1H NMR spectrum of product.
k
−1

Q. Li, H. Zhang / Spectrochimica Acta Part A 71 (2008) 245–251
249
Fig. 6. MS spectrum of reagent blank and NQS. (a) MS spectrum of reagent blank and (b) MS spectrum of NQS.
Then the equation of r = (k2k1/k−1)CACDCB = KCACDCB can
ferent reaction time in initial rate method. ln(Amax − A)/Amax
has been plotted as function of t (min), and a line was
obtained. Obviously, the reaction order of the system of
methanol–NQS–NaOH–KCl buffer solution (pH 13.00) is one.
According to discussion in Section 3.2, the amount of NQS
be obtained from (1) and (2). In light of ionization constant
−
16
of methanol (Ka = 3.16 × 10 ) [12], when the amount of
−
methanol (4%) is 1.00 ml (0.10 M), the concentration of CH3O
−
4
ionized partly by methanol (CH3OH) is about 3.2 × 10 M in
−
3
the buffer solution of pH 13.00. Hence, the amount of NQS
(2.0 × 10 M) and hydroxyl ion (0.10 M) is superfluous rel-
−3
−
(
2.0 × 10 M) and hydroxyl ion (0.10 M) is superfluous rel-
ative to CH3O . Therefore, this reaction can be regarded
−
ative to CH3O and its concentration variation is relatively
as pseudo first order reaction. The reaction rate equation is
−
ꢀ −
d[Product]/dt = k [CH3O ].
small. Namely, the rate equation is r = KCB = K[CH3O ]. The
rate equation shows this reaction is first order reaction. The con-
clusion is in agreement with experimentation result of kinetic
curve of reaction. This indicates that the reaction is catalytic
reaction.
3
.3.2. Apparent rate constant and activation energy
The absorbance of solution was determined in different tem-
perature according to the procedure (Fig. 8). By dealing with
A–T data obtained above, the apparent rate constant at 30 C and
4
◦
3
3
.3. The study of kinetic property
.3.1. Kinetic curve of reaction
◦
0 C can be obtained. Then in light of Arrhenius Formula of
ꢀ
ꢀ
Ea = RT2T1/(T2 − T1) ln k /k and different pair of K–T data,
2
1
In accordance with the procedure, keeping the temperature
the activation energy of the nucleophilic substitution reaction
between methanol and NQS was given in Table 1.
◦
at 25 C, the absorbance of product was determined at dif-

2
50
Q. Li, H. Zhang / Spectrochimica Acta Part A 71 (2008) 245–251
−
4
Fig. 7. Absorbance spectrum. (a) Absorption spectrum of NQS (5.0 × 10 M)
against buffer solution (pH 13.00); (b): absorption spectrum of the system of
methanol–NQS–buffer solution (pH 13.00) against reagent blank; (c) absorption
spectrum of lawsone (5.0 × 10− M) against buffer solution (pH 13.00).
Fig. 9. Effect of pH on absorbance of product. Methanol: 1.00 ml; NQS
−
3
(5.0 × 10 M): 1.00 ml; buffer solution: 2.00 ml; volume of solution: 12.5 ml;
reaction time: 45 min.
4
−
CH3O increased when the pH is increased. Thus it is the more
−
easily the nucleophilic substitution reaction between CH3O
and NQS goes. Based on the above observations and calcula-
tion results it is not unreasonable to say that methanol which
−
exists in form of CH3O cannot react with NQS when pH is
less than 12.00. Only when pH is more than 12.00, lawsone
can be formed effectively and consequently the absorbance of
methanol–NQS–buffer solution system is increased markedly.
In order to keep the high sensibility for determination of
methanol, pH 13.00 was chosen as optimum for consequent
experiments.
3.5. Effect of amount of NQS and buffer solution
Fig. 8. Effect of temperature. Methanol (4%, m/m): 1.00 ml; KCl–NaOH buffer
The absorbance was determined when the amount of
−3
solution (pH 13.00): 2.50 ml; NQS (5.0 × 10 M): 5.00 ml; volume of solution:
2.5 ml; reaction time: 10 min.
methanol was kept unchanged and the amount of NQS and
buffer solution increased gradually, respectively. Absorbance of
the product increases with the rise of the amount of NQS and
buffer solution. When the amount of NQS and buffer solution
is more than 5.00 ml and 2.50 ml, respectively, the absorbance
of the product becomes maximal and stable. Therefore, 5.00 ml
and 2.50 ml were selected as the optimum volume of NQS and
buffer solution for throughout the research.
1
3
.4. Effect of pH
The effect of pH on the determination of methanol was exam-
ined by varying pH from 1.00 to 14.00. As shown in Fig. 9,
the absorbance is close to 0 at pH 1.00–12.00, indicating that
under this condition it is difficult for the catalytic reaction to take
place. The possible reason is that the concentration of methoxyl
−
3.6. Effect of temperature and standing time
(
CH3O ) ionized by methanol (CH3OH) is lower when pH
is less than 12.00. So its nucleophilic capacity on 4-sodium
sulfonate of NQS was depressed and the nucleophilic substi-
tution reaction does not take place easily. When pH is more
than 12.00, the absorbance of the product begins to increase
corresponding to the rise of pH and reaches maximal at pH
Keep other condition unchanged, the absorbance of the prod-
uct was measured after standing for different time period at
room temperature. The experimental results show that methanol
can catalyze hydroxyl ion to react immediately with NQS
at room temperature. The absorbance reaches maximum and
constant after 45 min (the absorbance is 0.473) and remains
constant for at last 2 h. Then the absorbance of the product
was determined at different temperature with 10 min reaction
time (Fig. 8). It shows that the absorbance of product is greatly
affected by temperature and gets to the top when the tem-
1
3.00–14.00. The reason behind this change is that the amount of
Table 1
The apparent rate constant and activation energy
ꢀ
−1
−1
Ea (kJ mol )
The certified
Methanol
k (s
)
◦
◦
◦
30 C
40 C
perature is 50 C (the absorbance is 0.357). Hence, the room
temperature and 45 min standing time were chosen as the opti-
mum.
2.47 × 10−
3
4.37 × 10−3
36.23

Q. Li, H. Zhang / Spectrochimica Acta Part A 71 (2008) 245–251
251
Table 2
is in agreement with those obtained by the literature method
Table 2). The recovery tests of standard addition were also car-
Determination results of samples
(
Sample
The certified
% m/m)
Present method
(% m/m)
Literature3
method (% m/m)
ried out on the samples and the result was also been shown in
Table 3.
(
2
2
2
2
0,020,313
0.96
0.96
0.96
0.96
0.98
1.01
0.95
0.97
1.00
0.98
0.97
0.99
4
. Conclusions
0,060,518
0,051,021
0,060,922
It is reported for the first time that methanol can catalyze
reaction between NQS and hydroxyl ion to form lawsone and
this catalytic reaction has been developed as a novel method
for the determination of methanol. Moreover, this method can
also be used to determine compounds containing hydroxyl group
Table 3
The result of the recovery tests of standard addition
Sample
Sample
content
Added (%, Found (%, R.S.D. Recovery
(sugars, alcohol, hydroxybenzene and some drugs containing
m/m)
m/m)
(%)
(%) (n = 5)
hydroxyl group) in a similar manner. Due to its simple proce-
dure and other merits, this method is expected to be able to find
practical uses in both laboratories and industries.
(
%, m/m)
2
2
2
2
0,020,313 0.473
0,060,518 0.473
0,051,021 0.631
0,060,922 0.315
0.158
0.315
0.315
0.473
0.163
0.304
0.318
0.471
3.8
3.4
4.9
2.3
103
96.5
101
99.6
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3
.7. Performance of the proposed method
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[
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[
[
1
conclusions were reached: (1) the absorbance of the sys-
tem methanol–NQS was proportional to the concentration
of methanol in the range of 0.26–15.8 mg/ml. (2) A lin-
ear regression equation attained from the calibration curve
is A = 0.01998 + 0.05944C (mg/ml) with a linearly correlation
coefficient of 0.9977. (3) The detection limit of this proposed
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.8. Sample analysis
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[
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[
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