A Green and Simple Process for Preparation of Tetraalkylammonium Azide with Excellent Environmental Factor: Comparison of Batch and Flow Column Reactor

Article abstract of DOI:10.1021/acs.oprd.8b00230

This study presents a green and efficient process for the preparation of tetraalkylammonium azide applicable in large scale under mild conditions. Moreover, the purity of the product and the reaction yield were significantly high. In this regard, two reactors are compared: batch and flow column reactor. Results demonstrated the greater efficiency of the flow column reactor. Strong base anion exchange resin was used as catalyst. The reusability of the resin was excellent. The environmental factor of this process is 0.85, which is excellent for a chemical process in industrial scale. Accordingly, this method involved almost all principles of Green Chemistry, which is unique for its type.

Full text of DOI:10.1021/acs.oprd.8b00230

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Full Paper
A green and simple process for preparation of
Tetraalkylammonium Azide with excellent environmental
factor; comparison of batch and flow column reactor
Abdolrahman Shalibor, and Ali Reza Modarresi-Alam
Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.8b00230 • Publication Date (Web): 19 Nov 2018
Downloaded from http://pubs.acs.org on November 20, 2018
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A green and simple process for preparation of tetraalkylammonium azide
with excellent environmental factor; comparison of batch and flow column
reactor
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a
a,b,
Abdolrahman Shalibor and Ali Reza Modarresi-Alam 
aOrganic and Polymer Research Laboratory, Department of Chemistry, Faculty of Science,
b
And Renewable Energies Research Institute, University of Sistan and Baluchestan, Zahedan,
Iran.

Corresponding author; Tel.: +98-54-33431146, Fax: +98-54-33446565, E-mail: modaresi@chem.usb.ac.ir
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Abstract
This study presents a green and efficient process for the preparation of tetraalkylammonium azide
applicable in large scale under mild conditions. Moreover, the purity of the product and the reaction
yield were significantly high. In this regards, two reactors are compared: batch and flow column reactor.
Results demonstrated the more efficiency of the flow column reactor. Strong base anion exchange resin
was used as catalyst. The reusability of the resin was excellent. The environmental factor of this process
is 0.85 that is excellent for a chemical process in industrial scale. Accordingly, this method involved
almost all principles of Green Chemistry, which is unique of its type.
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Keywords
Tetraalkylammonium azide, Ion exchange resin, Green synthesis, environmental factor
Introduction
Organic azides and hetrocycles such as triazoles and tetrazoles are used as important functional groups
in chemical and pharmaceutical industries.1 Due to the biological properties of triazoles and tetrazoles,
they are extremely used in medicinal chemistry.1-4 in preparation of these materials, sodium azide is
used as nitrogen source.5-11 Sodium azide is an inorganic material which hardly dissolves in organic
solvents. It just dissolves in high polarity solvents such as dimethylformamide (DMF) and
-4
12
dimethylsulfoxide (DMSO). These solvents are hazardous and problematic. In addition to their high
boiling point, the presence of small amount of water leads to product purification problems and a
5
decrease in yield of reaction. Therefore, using alkylammonium azides instead of sodium azide is a
good alternative because of its better solvation in organic solvents. Additionally, tetraalkylammonium
salts are excellent phase transfer catalysts and in some cases used as ionic liquids. Although
tetraalkylammonium azide (TAAZ) salts have been known since 1918, there is limited information and
few applications reported about them. Thus far, several methods have been reported for the preparation
of TAAZ.13-20 However, these methods suffer from hazardous procedures and shock-sensitive and
expensive materials. In most procedures, TAAZ are prepared by neutralization of tetraalkylammonium
hydroxide with hydrazoic acid in water or methanol (Scheme 1).13-16
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Hydrazoic acid is highly toxic and explosive. Its vapor causes headache, low blood pressure, bronchitis
21
and irritation of eyes, skin and lungs. It has boiling point of 36 °C and therefore is extremely volatile
and if its concentration exceeds 8-15 v% in air, leads to formation of explosive gas mixture.22
Another method for the preparation of tetramethylammonium azide (TMAZ) was carried out by using
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the reaction of AgN
has some problems such as purification of the product from extra reactants and the use of shock-
sensitive material such as AgN
3
with tetramethylammonium iodide in water or ethanol (Scheme 2). This method
3
.
In another procedure, TMAZ was prepared by the reaction of tetramethylammonium fluoride
) in acetonitrile at room temperature (Scheme 3).18
(
N(CH
3
)
4
F) and trimethylsilyl azide (Si(CH3)
3
N
3
1
2
This method also has problems such as need to dry the solvent, utilization of problematic solvent, and
corrosive reagent (hydrofluoric acid), which is needed in the synthesis of N(CH3)
starting materials.
4
F as one of the
Scheme 1: Preparation of TMAZ via neutralization of trtramethylammonium hydroxide with hydrazoic acid.
3
Scheme 2: Preparation of TMAZ using the reaction of AgN with tetramethylammonium iodide.
Scheme 3: Preparation of TMAZ via reaction of trimethylsilyl azide and tetramethylammonium fluoride.
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Recently a method has been presented which in firstly tetramethylammonium sulfate is produced via
the reaction of tetramethylammonium hydroxide with sulfuric acid, and then the produced
tetramethylammonium sulfate reacts with sodium azide or barium azide to produce TMAZ (Scheme
4
).19-20 In this method, the stoichiometric ratios of the reactants should be determined properly,
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otherwise further purification of the product from the extra reactants would be necessary.
Scheme 4: Preparation of TMAZ by two-step reaction via exchange of sulfate ion by azide.
In Green Chemistry there are two major green metrics methods to measure greenness of chemical
2
3
procedure: Environmental Factor (EF) and Atom Economy (AE). The latter was proposed by Trost in
2
4
1991 which is defined as molecular weight of product per the sum of total molecular weight of all
2
5
substances formed in the stoichiometric equation. EF was presented by Sheldon in 1992 and up to
date it is the most efficient method for greenness criterion assessment of chemical procedures. EF is
calculated by dividing the mass of waste by mass of product, which in the waste is defined as everything
but the product with the exception of water. Sheldon descripted EF considering with and without water.
In our opinion, since water is a major part of environment and it is recovered in chemical process, it
should not be calculated in EF. Sheldon represented two benefits of EF compared with AE, (1) in
description of EF waste is everything included all auxiliary components, e.g. solvent losses, by-
products, excess reagents and chemicals used in work-up (2) AE is applied to individual steps but the
EF can easily be applied to a multi-step reactions.
In our proposed method, TAAZ was prepared in a multi-step reaction. In the first step after regeneration
of anion exchange resin with aqueous solution of sodium hydroxide (2% w/w), azide ion is adsorbed
by this resin (step one in Scheme 5). In the second step, the resin is incubated with aqueous solution of
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tetraalkylammonium bromide (TAAB) (step two in Scheme 5). As a result, bromide ion is exchanged
by azide ion rapidly with 99.9% purity and conversion degree. This method is efficient for the
preparation of TAAZ both in laboratory and industrial scale.
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Scheme 5: Preparation of TAAZ via azide-bromide exchange by anion exchange resin.
Results and Discussion
Process
In this study, we applied two processes: Batch and flow process. The batch process was carried out in
250 to 1000 ml glass flasks as batch reactor (BR) under mechanical stirring at ambient temperature and
pressure. The anion exchange resin after the regeneration with NaOH, is incubated with aqueous
solution of sodium azide (step one, Scheme 6). Then, this resin is washed with deionized water and
incubated with TAAB aqueous solution (step two, Scheme 6).
The flow process, as shown in Scheme 7, was carried out in glass columns of 1.5 to 5 cm in diameter
and 15 to 70 cm height as flow column reactor (FCR) which was packed with anion exchange resin.
After the regeneration of the resin, firstly azide ion is adsorbed by the anion exchange resin while
sodium azide aqueous solution passes through the FCR (step one). Then, TAAB solution was passed
through the FCR as well (step two).
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Scheme 6: Preparation of TAAZ in a two-step reaction in the batch process.
Scheme 7: Preparation of TAAZ in a two-step reaction in the flow process.
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Assessment of azide adsorption capacity of the resin
Figure 1 demonstrates the amount of azide adsorbed per unit weight of the resin in every moment of
the reaction time in BR. As shown, the maximum absorption of azide by the resin (azide adsorption
capacity) is independent of initial azide concentration. However, the increase in initial azide
concentration significantly shortens the time to reach maximum adsorption and causes an increase in
slope of the adsorption curve. For example at 300 mg/L and 5000 mg/L of sodium azide concentrations,
the time to reach maximum adsorption (azide adsorption capacity) were 50 and 16 min, respectively
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(
Table 1). As shown in Table 1, the average of azide adsorption capacity of the resin in BR is 1.76
miliequivalent of sodium azide per unit weight of the resin. Moreover, this test was carried out in
different resin weights from 0.5 to 5 g dry resin, which similar results were obtained.
Figure 1: Monitoring sodium azide weight which adsorbed per unit weight of the resin during the reaction in BR.
Table 1: Azide adsorption capacity of the resin in BR.
Initial sodium azide
concentration (mg/L)
The time to reach
maximum adsorption
Azie adsorption
capacity (mg/g resin)
Azide adsorption
capacity (meq/g
resin)
(
min)
3
5
00
00
50
115
116
1.77
1.78
35
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00
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1.75
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1.78
1.77
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Table 2: Azide adsorption capacity of the resin in FCR.
a
The reactor column height (cm) Feed flow rate (ml/min)
Azide adsorption capacity
(
meq/g resin)
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1.90
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1.91
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15-20
30-35
3-5
15-20
30-35
60
a
For each feed flow rate range, for example 3 to 5 ml/min, the experiment was repeated at least three times and
similar results were achieved for azide adsorption capacity of the resin hence, for the latter, the mean value is also
reported.
Table 2 shows azide adsorption capacity of the resin in FCR under various conditions such as different
reactor column height and feed flow rate. This data have been obtained once by changing in the resin
height at constant feed flow rate and again by changing the feed flow rate at constant the resin height
in the reactor. Maximum azide adsorption capacity of the resin in FCR is 2.37 meq/g. This result has
been obtained at feed flow rate of 3-5 ml/min and 60 cm reactor column height. As can be seen in Table
2
, with increasing the resin height in the reactor at constant feed flow rate, azide adsorption capacity of
the resin increases. In addition, at constant reactor column height, increasing the feed flow rate leads to
a decrease in azide adsorption capacity of the resin. Increasing in the reactor column height or/and
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decreasing in feed flow rate cause an increment in the contact time between the feed solution and the
resin which lead to an increase in ion exchanging. This experiment also was carried out in reactors with
column height higher than 60 cm which similar results obtained.
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Comparing data listed in Tables 1 and 2, revealed that azide adsorption capacity of the resin in FCR is
higher than BR. This is due to the accumulation of hydroxide ions in the reaction media in BR, since
azide adsorption by the resin is an equilibrium reaction. This accumulation of hydroxide ions reverses
the direction of the reaction to the left (step one in Scheme 5).
Assessment of azide – bromide exchange yield
For this purpose, tetraethylammonium bromide (TEAB) and tetrabutylammonium bromide (TBAB)
were used. Table 3 shows azide – bromide exchange yield and the maximum residence time of the feed
solution in BR. After the incubation of the feed solution with the resin in the reactor was started, samples
were withdrawn to analyze their azide and bromide concentration. The incubation of feed solution and
the resin was terminated after the concentration of azide and bromide was constant. The maximum
residence time was defined as time range from the beginning incubation until the concentration of azide
and bromide was constant. The results also indicate that residence time for TBAB and TEAB are
similar. However, the residence time is related to the molar ratio of TAAB to the adsorbed azide by the
resin. When molar ratio of TAAB to azide adsorbed by the resin is increased, the exchange yield
decreases. The reason is attributed to accumulation of azide ions in the reaction media in BR. Since
azide – bromide exchange reaction is an equilibrium reaction (step two in Scheme 5).
Tables 4a, 4b and 4c show the yield of azide – bromide exchange under various conditions in FCR with
the resin height of 10, 30 and 60 cm, respectively. The results indicate that increasing in the reactor
column height and/or decreasing in feed flow rate cause an increment in the exchange yield. This is due
to the contact time between feed solution and the resin in the reactor. Another effective parameter in
azide-bromide exchange yield is the molar ratio of TAAB in feed solution to azide adsorbed in the
reactor column. The results indicate that the lower molar ratio cause higher azide-bromide exchange
yield.
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Table 3: Azide – bromide exchange yield in BR.
TAAB molar ratio
per adsorbed azide
Maximum
residence time
(min)
Azide– bromide
exchange Yield (%)
for TEAB
Azide– bromide
exchange Yield (%)
for TBAB
(
%)
3
5
0
0
20
20
30
35
45
77.5
72.6
71.2
70.3
58.5
79.9
70.2
72.6
71.4
56.1
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70
100
Table 4a: The yield of azide–bromide exchange in FCR with 10 cm the resin height.
Feed flow rate
TAAB molar ratio Azide– bromide
Azide– bromide exchange
per azide
adsorbed (%)
exchange Yield
(%) for TEAB
Yield (%) for TBAB
a
(ml/min)
3
3
3
-5
-5
-5
40
50
70
50
70
50
70
99.9
95
99.9
99.9
95.5
94.3
78
75
1
1
3
3
5-20
5-20
0-35
0-35
90
71
83
89.5
77
65
a
For each feed flow rate range, for example 3 to 5 ml/min, the experiment was repeated at least three times and
similar results were achieved for azide adsorption capacity of the resin hence, for the latter, the mean value is also
reported.
Table 4b: The yield of azide–bromide exchange in FCR with 30 cm the resin height.
Feed flow rate
TAAB molar ratio Azide–
bromide Azide–
bromide
per adsorbed azide exchange Yield (%) for exchange Yield (%) for
a
(ml/min)
(
%)
TEAB
99.9
92
TBAB
99.9
3
3
-5
-5
70
75
98.7
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
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3
3
4
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4
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5
5
5
5
5
5
6
3
1
1
3
3
-5
80
70
75
70
60
85
95
91
82
98
94
5-20
5-20
0-35
0-35
98
98.6
94
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
99.6
a
For each feed flow rate range, for example 3 to 5 ml/min, the experiment was repeated at least three times and
similar results were achieved for azide adsorption capacity of the resin hence, for the latter, the mean value is also
reported.
Table 4c: The yield of azide–bromide exchange in FCR with 60 cm the resin height and higher.
Feed flow rate
TAAB molar ratio per Azide–
azide adsorbed (%)
bromide Azide–
exchange Yield (%) for exchange Yield (%) for
bromide
a
(
ml/min)
TEAB
99.9
96
TBAB
99.9
96.2
97.5
98.4
99.5
93
3-5
90
95
90
85
80
80
70
3
1
1
1
3
3
-5
5-20
5-20
5-20
0-35
0-35
94
98
99.5
88
92
97
a
For each feed flow rate range, for example 3 to 5 ml/min, the experiment was repeated at least three times and
similar results were achieved for azide adsorption capacity of the resin hence, for the latter, the mean value is also
reported.
According to the results obtained in BR for TEAB and TBAB, the azide – bromide exchange yield is
similar, whereas in FCR the exchange yield of TBAB is higher than TEAB. This may be related to the
size of butyl relative to ethyl, which keep away azide ion from the center of the positive nitrogen. In
this case, the azide ion is freer and easily adsorbed by the resin.
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The best result, 99.9% yield, was obtained when experiment was run in FCR under condition using a
reactor with 60 cm height and 3-5 ml/min flow rate. Under these conditions, the molar ratio of TAAB
in feed solution to azide adsorbed by the resin in the reactor was 90%.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Comparing the data in Table 3 with data in Tables 4a, 4b and 4c demonstrate that exchange yield in
FCR is higher than in BR. The maximum exchange yield in BR is 79.9% whereas in FCR is 99.9%.
This difference in exchange yield of two reactors is due to the equilibrium state of azide–bromide
exchange. In FCR unlike the BR, azide ion does not accumulated in the reaction media. As above have
been mentioned, azide ion accumulation in the reactor causes to reverse the equilibrium reaction to the
left.
Reusability of the resin assessment
For this purpose after regeneration of the resin in FCR, the adsorption process of azide ion by the resin
was done and the resin regenerated again. This cycle was repeated several times and in each cycle azide
adsorption capacity of the resin was calculated. Data are shown in Figure 2. As shown the capacity of
the resin no remarkably changed.
Figure 2: Exchange capacity of the resin, after several exploitations in FCR with 60 cm reactor column height
and 5 ml/min feed flow rate.
Greenness criteria assessment of the process
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6
26
According to 12 principles of Green Chemistry and its definition , this paper presents a green and
simple process for the preparation of TAAZ under mild conditions such as ambient temperature and
pressure, neutral pH (high energy efficiency), green solvent (water), and absence of harmful by-
products. Moreover, the reactant materials are not corrosive and have non-toxic vapor. This method
also renders high purity of product and high conversion degree. In addition, this process has been
designed in order to be sampled, tested, or stopped at any moment. In addition, since reaction is carried
out at ambient temperature and pressure, there is no risk of explosion or accident.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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9
0
1
2
3
4
5
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8
9
0
1
2
3
4
5
6
7
8
9
0
To calculate the EF of the process, total mass of the product and all wastes based on one-gram resin in
FCR under optimum condition was calculated and shown in Table 5. For regeneration of this amount
of the resin, 5ml solution of NaOH 2% was consumed that include 0.103 gr NaOH. It was found that
0
.095g sodium hydroxide was adsorbed by resin and 0.008g was excess. In optimum conditions, the
azide adsorption capacity is 2.37 meq/gr of resin and azide–bromide exchange yield is 99.9% which
yielded in 0.408 gr tetraethylammonium azide (TEAZ) as product. In addition, 0.243 gr of NaBr was
produced as waste. Accordingly, the EF was calculated as 0.85, which is excellent according to Sheldon
reports, Table 6.23, 25
Table 5: Total mass of all the reagents and the products (including product and wastes) based on one-gram resin
in FCR under optimum condition according to Scheme 5.
Materials
Mass of reactants (g)
Mass of product and wastes (g)
Regeneration
Step one
__
Step two
__
Regeneration
Step one
0.095
__
Step two
NaOH
NaN3
TEAB
TEAZ
NaBr
0.103
__
0.008
__
__
__
0.154
__
__
__
0.497
__
__
__
__
__
__
__
__
0.408
__
__
__
__
0.243
__
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Table 6: EF in the chemical industry.23,25
Industry segment
Oil refining
EF ( kg waste per kg product)
<0.1
Bulk chemicals
Fine chemicals
Pharmaceuticals
<1-5
1
1
1
1
1
1
1
1
1
1
2
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2
2
2
2
2
2
2
2
3
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4
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4
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5
5
5
5
5
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0
1
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9
0
1
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9
0
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9
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4
5
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
5-50
25- >100
Characterization of the products
1
Characterization of the products including TEAZ and TBAZ were done by DSC, FT-IR, H-NMR, CHN
analysis and melting point measurement that are completely in agreement with previous studies.13-16
Table 7 shows CHN analysis of Tetraethylammonium azide (TEAZ) and tetrabutylammonium azide
(
TBAZ) that clearly demonstrates compounds structure. Figure 3 indicates DSC analysis of TEAZ (a)
and TBAZ (b). As shown for TEAZ one pick is observed at 245 °C that is associated with decomposition
temperature that is in agreement with melting point measurement. However, for TBAZ two picks are
observed at 89 °C and 196 °C, which are melting point and decomposition temperature, respectively,
and consistent with melting point value.
Table 7: CHN analysis data of the products
Element
TEAZ
TBAZ
Weight %
calculated)
Weight %
(found)
Weight %
(calculated)
Weight %
(found)
(
N
C
H
32.56
55.81
11.63
32.10
55.41
11.82
19.7
67.6
12.7
19.4
66.8
13.2
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
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3
3
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3
4
4
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9
0
1
2
3
4
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3: DSC curve of (a) TEAZ and (b) TBAZ.
1H-NMR and FT-IR main peaks of TEAZ (available in Supporting Information) as typical product are
given as follow:
1H-NMR (CDCl
, 250 MHz): δ; 1.34 (t, 3H, J = 7.3 Hz), 3.39 (q, 2H, J = 7.3 Hz). FT-IR spectrum
3
-1
-1
shows a wide peak at about 3400 cm and two sharp peaks at 3356 and 2020 cm indicating the
-1
presence of azide in product. Also absorptions at 2987, 1491 and 1391 cm corresponds to C-H bond
in methyl and methylene groups.
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Impact sensitivity risk of the products
To evaluate the explosive potential of the products towards impact, Hammer test was used. The results
revealed no sensitivity to impact for both TEAZ and TBAZ.
1
1
1
1
1
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1
1
1
1
2
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0
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0
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8
9
0
Conclusions
In this paper, preparation of TAAZ was carried out via batch and flow process. In the present study,
unlike the previous methods, materials with no toxic vapor, corrosive and shock-sensitive properties
were used. In this way, the products with 99.9% purity and yield are obtained. The results demonstrated
that FCR is more efficient than BR. This procedure has advantageous including excellent EF, reusability
of resin, simplicity and safety as well as applicability in both laboratory and industrial scale. As a result,
this process involved almost all principles of Green Chemistry that is unique of its type.
Experimental Section
Material and equipment
Caution: All compounds containing azide ion are toxic, so careful attention is required while using
them. It should be avoided from skin contact or swallowing.
TEAB, TBAB, sodium azide and all reagents were purchased from Merck Company. Industrial grade
strong base anion exchange resin, Amberlite IRA 402 CL, with a clear gel structure prepared from
Rohm and Haas Company. According to manufacturer data sheet, resin seeds have uniform particle size
with a 600 to 750 µm diameter and 1.063 g/ml bulk density. This resin made of styrene/ divinyl benzene
+
copolymer with –N (CH
3
) as functional group.
3
Characterization
DSC analysis of the products carried out in nitrogen gas media with a heating rate of 10 °C /min by
DSC200 F3Maia in range of temperature 0-300 °C according to standard method of ASTM D3418-15.
1H-NMR Spectrum was recorded at room temperature in CDCL
on AV250-MHZ spectrometer. FT-IR
3
spectrum was recorded from KBr plate on JASCO 460 spectrophotometer. The elemental analysis was
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6
performed by elemental analyzer system VarioEL. The concentration of azide and bromide in all
samples and standard solutions were measured by HACH DR 5000 UV-Vis spectrophotometer.
Hammer test
0
1
2
3
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5
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8
9
0
1
2
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9
0
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9
0
1
2
3
4
5
6
7
8
9
0
The sensitiveness to impact of the products (TEAZ and TBAZ) was tested by the fall-hammer method.
Approximately 20 mg of samples are subjected to the action of falling 2 Kg weight and 50 cm drop
height according to ASTM E680.
Azide concentration measurement
The azide concentration of all samples during experimental tests was measured by use of UV-Vis
2
7
spectrophotometer. Azide samples have a strong absorption at 222 nm. To determine its concentration,
firstly sodium azide was dried at 110 °C in an electric oven for over 2h and put in a vacuum desiccator
for cooling. Then, the stock solution was prepared by dissolving certain amount of this sodium azide in
deionized water. The azide standard solutions were prepared with 0 to 500 mg/L concentration from
stock solution. Finally, the absorption of the standard solutions was taken and the UV-Vis
spectrophotometer was calibrated. The azide concentration of all samples, were measured by its
absorption against absorption of the standard solutions. In addition, the absorption of samples
containing bromide ion, was taken at 238 nm (after calibration) because bromide ion has also strong
absorption at wavelength of 222 nm.
Bromide concentration measurement
According to standard method for determination of bromide concentration, the samples were evaluated
as follow: 28
The concentration of bromide in all samples was measured by UV-Vis spectrophotometer. Firstly,
potassium bromide, as standard source for bromide ion, dried at 130 °C in oven for 2h and put in vacuum
desiccator for cooling. The stock solution was prepared by dissolving certain amount of this potassium
bromide in deionized water. Then, standard solutions were prepared up to 1.00 mg/l of bromide
concentration from stock solution. To 50.0 mL of standard solution the following solutions were added:
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2
mL buffer solution (90 g NaCl and 68 g sodium acetate trihydrate were dissolved in deionized water
and then 30 mL glaciale acetic acid was added and make up to 1 L for stabilizing pH at 4.6-4.7), 2 mL
phenol red solution (21 mg phenolsulfonephthalein sodium salt was dissolved in deionized water and
diluted to 100 mL) and 0.5 mL chloramine-T solution (500 mg chloramine-T and sodium p-
toluenesulfonchloramide were dissolved in deionized water and diluted to 100 mL). Exactly 20 min
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
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5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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8
9
0
1
2
3
4
5
6
7
8
9
0
after adding chloramine-T, 0.5 mL of Na
2
S
2
O
3
solution (49.6 g Na
2
S
2
O
3
.5H O was dissolved in
2
deionized water and diluted to 100 mL) was added. Finally, the absorption of standard solution was
measured at 590 nm and the UV-Vis spectrophotometer was calibrated. All samples containing bromide
ion were treated as above and then their absorption were taken. The concentrations of all samples were
measured by its absorption against absorption of standard solutions.
Regeneration of resin
Certain amount of the anion exchange resin was washed with acetone and deionized water to remove
all impurities on its surface. The resin was transferred to FCR and according to manufacturer
regeneration guide, five-fold of resin-volume rinsed with 2% (w/w) aqueous solution of sodium
hydroxide in flow rate of 3 ml/min. Next, it was washed with deionized water until the pH of solution
which passed through the reactor column reached to 6. This resin was used as regenerated resin.
Determination of azide adsorption capacity of regenerated resin
In BR: 0.5 to 5 grams of dry regenerated resin were put in BR under mechanical stirring at room
temperature. Next, aqueous solution of sodium azide (1.2 fold of resin exchange capacity) was added
to reactor and then well stirred. After the start of incubation, samples were taken out periodically and
azide concentration was determined. This process was continued until the concentration of azide was
constant. This test was repeated for various concentrations of sodium azide from 300 to 10000 mg/L.
The azide adsorption capacity of the resin is defined as equivalent weight of azide adsorbed by unit
weight of the resin (step one in Scheme 6).
In FCR: Certain weight of the resin was transferred in FCR. After the regeneration, aqueous solution
of sodium azide (1.2 fold of the resin exchange capacity) was passed through the reactor and then
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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4
4
4
4
4
4
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5
6
collected. The collected solution was evaluated for determination of azide concentration. This test was
run for various feed flow rates from 3 to 35 ml/min with azide concentration from 1000 to 10000 mg/L
and the resin height in the reactor from 10 to 60 cm. The azide adsorption capacity is defined as
equivalent weight of azide adsorbed by unit weight of the resin (step one in Scheme 7).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Assessment of azide – bromide exchange yield
Firstly azide ion was adsorbed by regenerated resin. This resin called as pretreated resin. Then certain
amount of this pretreated resin was applied for determination of azide – bromide exchange yield. Azide-
bromide exchange yield is defined as equivalent bromide ion exchanged by azide ion per unit weight
of pretreated resin. This experiment was performed in two reactors as follow:
In BR: 0.5 to 5 g of pretreated resin was put in the reactor at room temperature on a mechanical stirrer.
Then, 0.5 to 0.9-fold equivalent of azide adsorption capacity of the resin, was taken from aqueous
solution of TAAB, and added to the reactor and stirred. After the start of incubation, samples were taken
out periodically to determine the concentration of azide and bromide. This procedure was continued
until the concentration of azide and bromide was constant (step two in Scheme 6).
In FCR: Certain weight of the dry regenerated resin was transferred to the reactor. Then calculated
amount of sodium azide aqueous solution in concentration of 1% (w/w) was passed through the column
with 3-5 ml/min flow rate. Next, it was washed with deionized water and finally azide adsorption
capacity of resin was calculated. Accordingly, 0.5 to 0.95-fold of azide adsorption capacity of resin was
taken by aqueous solution of TAAB, which passed through the reactor. Collected solution was assessed
for determination of azide and bromide concentration. This analysis was repeated with various feed
flow rates from 3 to 35 ml/min and the resin height in the reactor from 10 to 60 cm (step two in Scheme
7).
Isolation of products
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In this study two ways were evaluated for isolation and storage of the products: Extraction and
Evaporation.
Evaporation: For this purpose 100 ml of TEAZ aqueous solution as a product with concentration of 10
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
g/L was put in evaporation apparatus according to Scheme 8. The evaporation was run under reduced
pressure at constant temperature of 60 °C. Since in the evaporation procedure a small amount of HN
gas can be produced, as can be seen in Scheme 8, after the condenser and collector of condensed water,
two traps for adsorption of produced HN installed in the path of vacuum. In each trap was put 50 mL
aqueous solution of 0.1N NaOH. After the evaporation procedure finished the solution of two traps and
condensed water evaluated for amount of produced HN by UV-Vis spectroscopy and the results have
3
3
3
been summarized in Table 8. As can be seen in Table 8, for 1000 mg of TEAZ only 1.9 mg HN
produced namely less than 0.2% of TEAZ, which it can easily trapped in NaOH solution.
3
gas is
A white precipitation was achieved after evaporation under reduced pressure and cooling under vacuum.
The products, especially TBAZ, are very hygroscopic therefore they should be stored in solution
otherwise they have to be stored in sealed packing and kept away from moisture.
Scheme 8: Isolation of the products by evaporating method in the presence of two NaOH traps.
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Table 8: The amount of azide in aqueous solution of TEAZ as well as it was trapped in NaOH solution and
condensed water after evaporation.
Solution
TEAZ
Solution volume (mL)
Amount of azide (mg)
100
50
1000
1.3
0
1
2
3
4
5
6
7
8
9
0
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0
Trap 1
Trap 2
50
0.2
Condensed water
97
0.4
Extraction into an organic solvent: Extraction, the other way for withdrawing the products from
aqueous solution into dichloromethane (DCM) or chloroform (CF), also was evaluated in this paper.
The extraction was run in three consecutive stages for 25 mL of TEAZ aqueous solution with
concentration of 10 g/L in deionized water by use of a extraction funnel, so that in each stage was used
of 25 ml DCM or CF. To assay the extraction yield the azide concentration in aqueous phase was tested
by UV-Vis spectroscopy in each stage. The results indicated that, in the first stage, only 30% of TEAZ
is extracted into DCM or CF as well as in 2 and 3 stages 23% and 17% of it is extracted respectively.
Based on the above data, it is concluded that the evaporation way in comparison with extraction,
benefits from higher yield and more safety under the condition because in extraction we have to use
hazardous solvents, which has environmental problems.
Supporting Information
1
Experimental procedure for determination of regenerated resin exchange capacity, H-NMR, and FT-
IR spectra of TEAZ.
Authors Information
Corresponding Author:
Ali Reza Modarresi-Alam;
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Organic and Polymer Research Laboratory, Department of Chemistry, Faculty of Science, And
Renewable Energies Research Institute, University of Sistan and Baluchestan, Daneshgah street,
Zahedan, Iran
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Tel.: +98-54-33431146
Fax: +98-54-33446565
E-mail: modaresi@chem.usb.ac.ir
Co-author:
Abdolrahman Shalibor;
Organic and Polymer Research Laboratory, Department of Chemistry, Faculty of Science, University
of Sistan and Baluchestan, Daneshgah street, Zahedan, Iran,
E-mail: shaliborabdolrahman@yahoo.com
Notes
The authors declare no competing financial interest.
Acknowledgements
Special thanks to Dr. Mohammad Hossein Keshavarz from Malek-ashtar University of Technology,
Shahin-shahr, Iran, for his help to conduct impact sensitivity test of product. This research supported
by the National Nanotechnology Initiative Council funded by Iranian government and the Graduate
Council of University of Sistan and Baluchestan because of the financial support.
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