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First time determination of important catalyst Sodium Methoxide used in biodiesel by Colorimetric Method Sabir Khan, Matthieu Tubino, Marta M. D. C. Villa, and Flavio A. Bastos Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b05445 • Publication Date (Web): 13 Feb 2018 Downloaded from http://pubs.acs.org on February 13, 2018
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Analytical Chemistry
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First time determination of important catalyst Sodium Methoxide used in biodiesel
2
by Colorimetric Method
3
Sabir Khana,c, Matthieu Tubinoa, Marta M. D. C. Vilab, Flavio A. Bastosa
4
a
Institute of Chemistry, State University of Campinas, 13083-970 Campinas, São Paulo, Brazil
5 b
6
University of Sorocaba, CEP-18023-000, Sorocaba, SP, Brazil
c
Department of Analytical Chemistry, Institute of Chemistry, UNESP – University
7 8
Estadual Paulista, Araraquara, SP, Brazil
9
*
[email protected]
10
A simple and selective spectrophotometric method for the first time has been
11
developed for the determination of sodium methoxide in methanol solution in the
12
presence of sodium hydroxide. he developed method involves the formation of a pink
13
species by the reaction between sodium methoxide and α-santonin. The pink color
14
compound formed shows absorbance maximum at 513 nm. N,N–dimetilformamide and
15
methanol were used as solvents and the reaction was performed at different temperature
16
and 25ºC was selected for further experiment. The pink color compound formed, dried
17
and then was studied using FTIR and mass spectrometry. The calibration curve was
18
constructed from 0.10 to 0.30 % (m/v) sodium methoxide in methanol and the standard
19
deviation is 0.010 %. Similarly relative standard deviation for 28%, 26% and 24% of
20
sodium methoxide obtained in the range of 0.4 to 1.9 %. Correlation coefficient of the
21
analytical curve r = 0.9997; limit of detection, LOD is ca. 1.1 × 10-3 % w/w; limit of
22
quantification, LOQ is ca. 3.2 × 10-3 % w/w. Results of analysis were validated
23
statistically. Keywords: Spectrophotometry, sodium methoxide, α-Santonin, N,N–dimetil
24 25
formamide, methanol solution.
26 27 28 29
*
30
Corresponding author2 :
[email protected]
31
Institute of Chemistry, University of Campinas, P.O. Box 6154, 13083-970, Campinas,
32
SP, Brazil
Corresponding author 1:
[email protected]
33
Tel: + 55-19-3521-3133
34
Fax: + 55-19-3521-3023
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1.
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Introduction
36 37
Petroleum is obtained from non-renewable geological sources. Its fuel fraction
38
contains gasoline and diesel which is costly and causes severe environmental problems.
39
Biodiesel is a renewable and alternative source to petroleum. It is prepared from
40
vegetable oils and from animal fats. Besides that, biodiesel is related to great economic
41
and social impacts (Tubino et al., 2011; Boog et al., 2011; Froehner et al., 2007;
42
Dabdoub et al., 2009).
43
The production of biodiesel in Brazil is continuously increasing attaint 2.917 billion
44
liters in 2013. This means that presently it is the second biggest world producer of such
45
biofuel (http://www.udop.com.br/index.php?item=noticias&cod=1110872#nc; accessed
46
30/09/2014;http://mcgroup.co.uk/news/20140905/europe-unrivalled-leader-global-
47
biodiesel-market.html; accessed 30/09/2014 ; Leoneti et al., 2012; Balat & Balat.,
48
2010).
49
According to the Brazilian law nº 11.097 that treats about the introduction of
50
biodiesel in the energetic system in Brazil, the term biodiesel is defined as: “a biofuel
51
derived from renewable biomass to be used in engines with internal ignition by
52
compression or, according to the regulation, to the generation of another type of energy,
53
that can replace partially or totally the fuels from fossil origin” (Brazil, 2005).
54
At Brazil, the National Program of Production and Use of Biodiesel (PNPB, 2010)
55
stimulates the production of biodiesel by means of the transesterification process which
56
consists in a chemical reaction between a vegetable oil or an animal fat with a low chain
57
alcohol, yielding the respective esters (biodiesel) from the corresponding fatty acids
58
(Resende et al., 2005).
59
Most industrial production processes for biodiesel are currently using sodium
60
methoxide (sodium methylate) to catalyze the reaction. It is a very active catalyst
61
offering high yields (> 99 %) under mild reaction conditions. The sodium methoxide
62
that is employed industrially corresponds to a 30 % (w/w %) solution of NaOCH3 in
63
CH3OH (Bastos et al., 2013, Moura et al., 2010).
64
Despite its great importance in industrial processes, the quantitation of the
65
methoxide present in such solutions is done indirectly through an acid-base titration that
66
give the total alkalinity expressed as percentage in weight of sodium methoxide in
67
methanol(includes NaOH and Na2CO3). In order to obtain the true methoxide
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concentration in the methanol solution, gaseous HCl or alternatively a solid acid as, for
69
example, the benzoic, is added to an amount of the methanol solution. In this process
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benzoic acid is transformed to sodium benzoate; sodium methoxide is transformed to
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methanol; NaOH is transformed to sodium benzoate and H2O; Na2CO3 is transformed to
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sodium benzoate and to H2O and CO2. The H2O formed in these reactions is correlated
73
to NaOH and to Na2CO3 present in the solution. It is quantified thorough Karl-Fischer
74
titration and the partial alkalinity correspondent to NaOH and to Na 2CO3 is calculated,
75
in percentage in weight, as being simply NaOH. This value is then transformed, by
76
molar relation, in percentage in weight of NaOCH3 and subtracted from the total
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alkalinity obtained through the acid-base titration. The result is the alkalinity due to the
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actual concentration of sodium methoxide in the methanolic solution (Rizescu and
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Lessen, 1974).
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In face of such situation, aiming to directly distinguish methoxide from
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hydroxide in its industrial solutions in methanol, we decided to do efforts in order to
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develop alternative procedures for the selective quantitative analysis of such ion.
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The importance of this substance in the production of biodiesel, due to its catalysis
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characteristics in comparison to hydroxyl ions, justifies the development of an
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analytical method that can directly discriminate methoxide in the presence of hydroxide
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in the methanolic solution. Therefore, the aim of this work was to develop a simple, fast
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and low cost analytical method for the specific determination of sodium methoxide in
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methanolic industrial solutions used as catalyst in the synthesis of biodiesel and also in
89
pharmaceuticals production.
90 91
2.
Experimental
92 93
2.1 Chemicals
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Methanol: HPLC grade (Synth, Diadema, SP, Brazil); α-santonin: Sigma Aldrich
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with minimum of 99 % purity (St. Louis, MO, USA); sodium methoxide: 30% w/w
96
(Vetec, Duque de Caxias, RJ, Brazil); metallic sodium in bars (Merck, Darmstadt,
97
Germany)
98
Stock solution of sodium methoxide 30 % w/w: A standardized stock solution of sodium
99
methoxide 30 % w/w in methanol was used to prepare other solutions, through dilutions
100
with methanol. The total alkalinity of the stock solution was determined by titration
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with an HCl solution previously standardized (0.10210.004 mol L-1) against anhydrous
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Na2CO3 as usual (Skoog et al., 1991).
103 104
Sodium methoxide standard solution (CH3ONa, molar mass: 54.02 g mol-1): 0,9496 g
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(0.04131mol) of solid sodium (molar mass 22.99 g mol -1) was dissolved in HPLC grade
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methanol previously dried with anhydrous Na2SO4 and the volume was completed to
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250 mL in a volumetric flask up to the mark with methanol, forming a 0.165 mol L-1
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solution. Lower concentrations were prepared by adequate dilutions with the same
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solvent as used for standard solution.
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NaOCH3 solutions in presence of NaOH: Variable concentrations NaOCH3 solutions in
111
presence of NaOH were prepared by adding adequate quantities of pure water (Milli Q
112
Plus; accurately weighed to 0.0001 g) to the stock 30% w/w solution.
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α-santonin (C15H18O3, molar mass: 246.3 g mol-1): 0.1 g (4×10-4 mol) were dissolved in
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N,N–dimethylformamide solvent and diluted up to 50 mL with this solvent in a
115
volumetric flask forming an 8×10-3 mol L-1 working solution.
116 117
2.2 Apparatus Pipettes: Eppendorf 0.5 to 10 L and 2.0 to 20 L; Biohit Proline 100 to 1000
118 119
L.
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Mass Spectrum: the mass spectrum was recorded using Waters Mass Analyzer Quattro
121
micro API with Masslynx Software.
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Infrared spectra: FTIR spectrum (KBr pellets) of the pink compound formed by the
123
reaction between α-santonin and methoxide were obtained by accumulating 32 scans in
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a Bomem Spectrophotometer, MB-series; 4000 to 400 cm-1 range and 4 cm-1 of
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resolution. The spectrum of α-santonin was obtained in the same conditions.
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A single beam spectrophotometer model (FEMTO 600) with 1.000 cm quartz cell was
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used for the absorbance measurements in the visible region of the spectrum. An
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Ultrospec 200 Pharmacia Biotech spectrophotometer was used to obtain spectra.
129 130
2.3 Preparation and isolation of the pink colored compound
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The compound was prepared by mixing of 15 mL of standard α-santonin
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solution (8 mmol L-1) and 5 mL of sodium methoxide (0.17 mmol L-1) in a 25 mL
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volumetric flask. The reaction system was allowed to react during 25 minutes to
135
complete the reaction and finally the volume was completed up to the mark with
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methanol in order to obtain similar conditions as done in the analytical procedure. This
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solution was transferred to a 50 mL round bottom flask and dried under low pressure
138
(about 25 mmHg) during 4 hours continuously initially at room temperature (25oC).
139
When a small quantity of solvent remained in the flask a gentle heating and slowly
140
increased the temperature up to 70 oC was used to dry the pink color compound
141
completely. The obtained solid product was used for further analysis as described
142
below.
143 144
2.4 Analytical Curve
145
Different volumes of the sodium methoxide standard solution (120, 150, 180,
146
210 and 240 µL) were placed in 10 mL volumetric flasks and 1mL of α-santonin
147
(810-3 mol L-1) solution in N,N-dimethylformamide was added in each one. After
148
waiting for 25 minutes to complete the reaction and the volume was completed to the
149
mark with methanol. The absorbance measurements were performed in the
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spectrophotometer at 513 nm using a 1.000 quartz cell.
151 152
2.5 Interference of the hydroxide
153
In order to verify the specificity of the reaction of α-santonin with respect to
154
methoxide in presence of hydroxide, water was added to methanol solution of sodium
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methoxide to form hydroxide anions in conformity to the reaction –OCH3 + H2O =
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HOCH3 + -OH. The sodium methoxide solution in methanol was prepared by diluting
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1.00 mL of 1 % w/w stock solution.
158
A 2.50 × 10-3 mol L-1 solution was prepared from the 1 % w/v sodium methoxide
159
solution which by its turn was prepared from the 30% w/w industrial grade sodium
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methoxide solution. For the preparation of 1 % w/v sodium methoxide solution 0.3300
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mL of 30% w/w sodium methoxide solution were placed in a 10 mL volumetric flask
162
and diluted the volume with HPLC grade methanol. Then four aliquots of 140 µL
163
(containing 2.50 × 10-2 mol of sodium methoxide each) were taken from the above 1%
164
w/v sodium methoxide solution and separately placed in four 10 mL volumetric flasks.
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Sequentially, 0, 10.0, 20.0 and 30.0 µL of deionized water were added respectively to
166
each one, following shaking to homogenize. Then it was added 1.00 mL of α-santonin
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solution (40 ppm). The reaction was allowed to occur by 25 minutes and then the
168
solution was completed to the mark of the flask with methanol. The absorbances of the
169
solutions were read after 5 minutes at 513 nm and the results were tabled.
170 171
2.6 Influence of the temperature
172
The effect of temperature was also investigated from 25 o C to 60 o C and along
173
the time. It was noted that color form quickly when solution is heated, but at 25 o C, the
174
compound is stable up to 25 minutes while at higher temperature the complex is less
175
stable, i.e., up to 3-5 minutes. Due to this reason 25 oC, temperature close do the
176
environmental, was selected for the further analytical experiments.
177 178
3.
Results and Discussion
179 180
3.1 About the pink colored product
181
The proposed method is based on the reaction between sodium methoxide and α-
182
santonin which forms of a pink colored compound. According to Edwards and Davis,
183
basic reagents attack carbon (1) of α-santonin (Edward and Davis, 1978). Therefore it
184
can be suggested that CH3O- reacts with the carbon C (1) of the α-santonin (I) resulting
185
in the formation of an intermediate species (II). Sequencially, this intermediate
186
dimerases resulting the formation of the pink compound (III) which shows maximum
187
absorbance at 513 nm. The proposed reaction scheme of the formation of the pink color
188
product is shown in Figure 1.
189 190
3.2. Interference of the hydroxide
191
The possible interference of the hydroxide ion was investigated by adding
192
known quantities of water in a solution of sodium methoxide in methanol 0.147 mol
193
L1. As water reacts with methoxide resulting –OH, known concentrations of such ion
194
are formed and known quantities of methoxide remain in the solution. By the addition
195
of the analytical reagent, α-santonin, if the hydroxide interferes in the reaction no
196
correlation between the resulting concentration of methoxide in the final solution and
197
the measured absorbance at 513 nm would be found.
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In Table1 are shown the obtained results. Considering the precision of the
199
measurements a constant difference in the absorbance is observed between each two
200
contiguous solutions, meaning that there is a linear correlation with respect to the
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concentration of methoxide and the absorbance. The results also suggest that at the used
202
concentrations the reaction is not quantitative as the methoxide concentrations obtained
203
are a little smaller than the calculated. However, despite this fact, it became clear by the
204
obtained results that the ion hydroxide does not reacts with α-santonin meaning that the
205
reaction occurs specifically with α-santonin .
206
As expected the reaction of formation of the pink compound depends on the
207
concentration of the reagents. Increasing the concentration of -santonin with respect
208
to a fixed concentration of methoxide as shown in the Figure 2.
209 210
3.3
Stability of the formed compound over the time
211 212
The reaction was completed within 20-25 minutes maximum at room
213
temperature (25 oC) and the complex was stable for more than 10 minutes at the same
214
condition after that the absorbance slowly decreasing beyond this time. As shown in the
215
Table 2.
216 217
3.4
Effect of temperature
218 219
The effect of temperature was also investigated from 10 oC to 60
o
C. It was
220
noted in Table 3 that the pink colored compound forms more quickly when solution is
221
heated. However the temperature increase means less stability of the formed species: 3
222
to 5 minutes at 60 oC. Therefore, due to this reason, and for practical purposes in the
223
handling, room temperature was selected for the further experiments.
224 225
3.5 Analytical Curve
226 227
The equation that describes the analytical curve, from 0.010 to 0.030 % w/w is
228
described by the equation A = 0.0378 + 20.03 C, at 513 nm where C is the
229
concentration in % w/w of the sodium methoxide in the methanol and A is the measured
230
absorbance.
231
The coefficient of correlation is r = 0.9994; the limit of detection, LOD ca
232
-3
1.0×10 % w/w; the limit of quantification, LOQ ca is 3.0×10-3 % w/w %.
233 234
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235 236
3.6 Study of the pink compound
237 The compound formed by the reaction of α-santonin and methoxide was studied.
238 239
The visible spectrum was obtained and the maximum was found at 513 nm (Figure 3). The FTIR and mass spectra were also obtained and are shown in Figure 4 for
240 241
pure α-santonin and Figure 5 for complex respectively.
242
The IR spectrum of the pure α-santonin (Figure 4) and that of the pink
243
compound (Figure 5) were compared. The IR spectrum of pure α-santonin shows a band
244
at 1784 cm-1 corresponding to the carbonyl of the ketonic group at the carbon 11 in the
245
α- santonin molecule and the band at 1316 cm-1 can be attributed to the symmetric
246
stretching of the C-O-C bond. After the reaction this band disappeared. This carbonyl is
247
converted to a carboxylic group as became evident by the large and broad band with
248
minimum of transmittance at 3398 cm-1 that appeared in the spectrum of the formed
249
compound (Figure 5). The enlargement of the band occurs probably due to the
250
dimerization of the compound III through the carboxylic groups
251
The band at 1647 cm-1 can be assigned to the stretching vibration of carbonyl
252
carbon of the carboxylate, which is mostly appeared in IR spectrum at lower value than
253
that of carbonyl carbon for ketonic group. The band at 1400 cm-1 can be due the bridge
254
carboxylate of two molecules of the formed compound as in phase symmetric stretching
255
usually absorbs near this frequency. The band at 1316 cm-1 can be attributed to the
256
symmetric stretching of the C-O-C bond that links two molecules of the original α-
257
santonin in the formed compound III.
258
Furthermore, the mass spectrum of the formed compound also suggests that two
259
α-santonin molecules condensate in the presence of sodium methoxide, forming in the
260
solid state the sodium salt of the compound III, as the molecular mass of 579 is
261
observed in the spectrum (Figure 6). Some observed main fragments of the molecule are
262
shown in Table 4.
263 264 265
4.0
Analytical procedure
266
Different volumes, i.e., 1.66, 2.50, 3.30, 4.16 and 5.00 µL were taken from the
267
30 % w/w sodium methoxide in methanol solution and putted separately in 5 mL
268
volumetric flasks. Then 1 mL of the α-santonin 40 ppm solution in dimethylformamide
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was added. After waiting for 25 minutes the volume was completed with methanol.
270
Which results the formation of pink color complex and the concentration were
271
determined as given in the Table 5.
272
Different concentrations solution of sodium methoxide i.e. 28 %, 26 % and 24 % w/w
273
were prepared from the 30 % w/w sodium methoxide in methanol solution. For the
274
preparation of 28 % sodium methoxide solution 9.33 mL was taken from 30 % sodium
275
methoxide industrial grade solution in 10 mL volumetric flask and the volume was
276
completed with methanol up to 10 mL. Then 3.57 µL from the above 28 % solution of
277
sodium methoxide was taken in a 5 mL volumetric flask then added 1 mL α-santonin
278
solution (40 ppm) also added 10, 20, 30 µL of double distilled water, waited up to 30
279
minutes and then diluted the volume with methanol up to 5 mL. The absorbance was
280
read after 5 minutes. Concentrations are given in Table 6.
281
For the preparation of 26 % sodium methoxide solution 8.66 mL was taken from
282
30 % sodium methoxide industrial grade solution in a 10 mL volumetric flask and the
283
volume was completed with methanol up to 10 mL.
284
Then, solution of 3.8461 µL from the above 26 % of sodium methoxide solution
285
was taken in a 5 mL volumetric flask then added 1 mL of α-santonin solution (40 ppm)
286
also added 10, 20 and 30 µL of double distilled water, waited up to 30 minutes and then
287
diluted the volume with methanol up to 5 mL. Read the absorbance after 5 minutes and
288
the results of concentrations are given in the Table 6.
289
For the preparation of 24 % sodium methoxide solution 8.00 mL was taken from
290
30 % sodium methoxide industrial grade solution in a 10 mL volumetric flask and the
291
volume was completed with methanol up to 10 mL.
292
Then solution 4.166 µL from the above 24 % of sodium methoxide solution was
293
taken in a 5 mL volumetric flask then added 1 mL α-santonin solution (40 ppm) also
294
added 10, 20 and 30 µL of double distilled water. Waited up to 30 minutes and then
295
dilute the volume with volume methanol up to 5 mL. Read the absorbance after 5
296
minutes and the results of concentrations are given in the Table 6.
297 298
5.0 Conclusion
299
The proposed method for the determination of sodium methoxide is simple,
300
selective and sensitive. The reagent used in this method has the advantage of high
301
sensitivity, selectivity and have more specific with sodium methoxide instead of sodium
302
hydroxide. Moreover with the addition of calculated amount of double distilled water
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absorbance decreases. The developed method does not involve any stringent reaction
304
conditions and offers the advantages of high color stability (up to 30 minutes), the
305
synthesis as it is cost-effective and eco-friendly because small quantities of chemicals
306
has been used and also the confidence and the rapidity of such kind of procedure. The
307
solid pink color compound can easily be stored at environmental temperature. The
308
proposed method can be successfully applied for the determination of industrial grade
309
of sodium methoxide solution.
310
6.0 Acknowledgments
311
The authors are grateful to TWAS & CNPq for financial support and
312
fellowships. They also thank FAPESP for financial aid and Prof. Dr. Carol H. Collins
313
for English revision of the manuscript.
314 315
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Balat M, Balat H. Progress in biodiesel processing. APPL ENERG 2010; 87: 1915-35.
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Quantitative Selective Analysis of Sodium Methoxide in Methanol Industrial
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Boog J.H.F.; Silveira E.L.C. ; Caland L.B.; Tubino M. Determining the residual alcohol
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in biodiesel through its flash point. Fuel, 2011, 90, 905–07.
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Brazil, Ministério de Minas e Energia Lei nº 11.097, de 13 de janeiro de 2005. Dispõe
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sobre
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(http://www.planalto.gov.br/ccivil_03/_ato2004-2006/2005/lei/l11097.htm)
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Dabdoub M.J.; Bronzel J.L.; Rampin, M.A. Biodiesel: visão crítica do status atual e
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Skoog, D.A.; West, DM, Hollee, FJ. Fundamentals of Analytical Chemistry, 6nd ed.,
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USA: Sauders College Publishing, 1991.
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Moura, C,V.R.; Castro, A.G.; Moura, E.M.; Santos Jr , Moita Neto, J.M. Heterogeneous
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catalysis of babassu oil monitored by thermo gravimetric analysis. Energ. Fuel 2010,
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24, 6527–32.
344
Programa Nacional de Produção e Uso do Biodiesel (http://www.biodiesel.gov.br/).
345 346
Rezende, S.M.; Soares B. G.; Coutinho, F.M.B; Reis, S.C.M.; Reid, M.G.; Lachter,
347
E.R.; Nascimento, R.S.V. Aplicação de resinas sulfônicas como catalisadores em
348
reações de transesterificação de óleos vegetais. Polímeros 2005, 15, 186-92.
349
Rizescu I, Lessen T. Consideratii asupra metodelor de analizã pentru metilat de sodiu.
350
Rev. Chim., 1974, 25,335-36.
351
Tubino M.; Aricetti, J.A. A green method for determination of acid number of biodiesel.
352
J. Braz. Chem. Soc., 2011, 22, 1073-81.
353 354 355 356 357 358 359 360 361 362 363 364
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365
Table 1. Determination of methoxide concentration with santonin in different solutions
366
in methanol prepared by addition of known quantities of water in 75 mL of an initial
367
solution of concentration 1 % w/w (0.147 mol L-1). Con Initial aproximate CH3O- 2.5 ×
Solution
Water added (µL)
water (10-3 mol)
Conc Final aprox. CH3O(10-3mol L-1)
0
0
0
2.50
1
10.0
0.556
2.15
2
20.0
1.111
1.85
3
30.0
1.667
1.54
368
10-3 mol L-1
369
a
Abs
abs
Conca from curve CH3O(10-3mol L-1)
0.301 ± 0.260 ± 0.223 ± 0.186 ±
0
2.200.04
-
-
0.041
1.940.06
0.26
0.26
0.037
1.710.05
0.23
0.49
0.037
1.480.04
0.23
0.72
Diference (10-3mol L-1)
Meaured triplicate
370 371 372
Table 2. Stability of the formed compound over the time
373
Solution
Time / min
Absorbance 513 nm
1
5
0.233
2
10
0.427
3
15
0.488
4
20
0.599
5
30
0.604
6
40
0.584
7
50
0.556
8
60
0.509
374 375 376 377
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Diferenc acumulati
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Analytical Chemistry
Table 3. Effect of temperature on absorbance measured after the mixing of reagents. Solution
Temperature / o C
At 513 nm
1
10
0.427
2
20
0.466
3
30
0.607
4
40
0.765
5
60
0.920
379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405
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406
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Table 4. Mass fragments of the formed pink compound. S.No
M. weight
Structure H
HO
1
279
OH O O
Na 2
H
287
OH
O
O CH
3
Na O OH 3
301
O O
HO HO
4
318.9
O
O Na
CH
3
O Na O
5
450
O
O
H3C
O O
OH
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410
Table 5. Concentration of the different volumes taken from 30 % w/w sodium
411
methoxide solution. Concentration (%)
SD
RSD %
0.008
4.3 × 10-3
2.40
2.50
0.013
2.6 × 10-3
0.99
3
3.33
0.017
2.6 × 10-3
0.74
4
4.17
0.024
2.1 × 10-3
0.46
5
5.00
0.028
2.6 × 10-3
0.48
Solution
Volume taken (µL)
1
1.66
2
w/w
412 413 414
Table 6. Concentration of the stock solution prepared from 30 % sodium methoxide
415
solution like 28%.26% and 24 %. Solution
Water added (µL)
SD
Concentration ( %)
RSD (%)
28 % sodium methoxide solution 1
0
0.0249
3.1 × 10-3
0.9
2
10
0.0165
3.2 × 10-3
1.0
3
20
0.0150
1.6 × 10-3
0.5
4
30
0.0137
5.4 × 10-3
1.9
26 % sodium methoxide solution. 1
0
0.0162
2.2 × 10-3
0.66
2
10
0.0152
2.1 × 10-3
0.85
3
20
0.0143
2.6 × 10-3
0.90
4
30
0.0130
5.5 × 10-3
1.3
24 % sodium methoxide solution 1
0
0.0149
1.24 × 10-3
0.40
2
10
0.0136
4.49 × 10-3
1.18
3
20
0.0126
2.80 × 10-3
1.07
0.0110
-3
1.03
4 416
a
30
2.40 × 10
Meaured triplicate
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419 420
Figure 1. Reaction sequence for the formation of the pink color compound.
0.65 0.60 0.55 0.50
Absorbance
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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0.45
Volum 100 250 500 750 1000
0.40 0.35 0.30
Absor 0.233 0.323 0.421 0.54 0.604
0.25 0.20 0
200
400
600
800
1000
Amount of santonin / µL
421 422
Figure 2. Effect of the α-santonin concentration on absorbance.
423
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424 425
Figure 3. Visible spectrum of the pink compound formed by the reaction of αsantonin
426
with sodium methoxide solution.
427
70 60
Transmittance / %
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Analytical Chemistry
50 40 30 20 10
-1
1784 cm 0
500
1000
1500
2000
2500
3000
Wave Number / cm
3500
4000
4500
-1
428 429 430
Figure 4. FTIR Spectrum of the pure α-santonin
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35
30
Transmittance / %
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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25
20
1316 nm
15
3398 cm
10
1400 cm
5 500
1000
-1
1647 cm
1500
-1
-1
2000
2500
Wavenumber / cm
3000
3500
4000
-1
431 432 433
Figure 5. FTIR spectrum of the formed pink compound.
434 435
436
Figure 6. Mass spectrum of the formed pink compound.
437 438
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