Cardanol-based bis(azo) dyes as a gasoline 91 colorant

Article abstract of DOI:10.1007/s11746-011-1912-y

Novel bis(azo) dyes were successfully prepared from the coupling of either natural cardanol or its hydrogenated derivative with a series of diazotized aromatic amines and diamines. These new dyes were fully characterized by NMR, infrared and UV-visible spectroscopy and mass spectrometry. The dyes are highly soluble in a variety of common organic solvents and gasoline as a consequence of the cardanol unit. The physical properties of gasoline according to American Society for Testing and Materials standard were unaffected by the presence of the bis(azo) dye derived from 1-(4aminophenylazo)-2-naphthol at a concentration of 6 ppm and the dye showed excellent stability over a 3 month period. AOCS 2011.

Full text of DOI:10.1007/s11746-011-1912-y

J Am Oil Chem Soc (2012) 89:321–328
DOI 10.1007/s11746-011-1912-y
ORIGINAL PAPER
Cardanol-Based Bis(azo) Dyes as a Gasoline 91 Colorant
•
Pimpaporn Paebumrung Amorn Petsom
•
Patchanita Thamyongkit
Received: 20 April 2011 / Revised: 3 July 2011 / Accepted: 19 July 2011 / Published online: 10 August 2011
Ó AOCS 2011
Abstract Novel bis(azo) dyes were successfully prepared
from the coupling of either natural cardanol or its hydro-
genated derivative with a series of diazotized aromatic
amines and diamines. These new dyes were fully charac-
terized by NMR, infrared and UV–visible spectroscopy and
mass spectrometry. The dyes are highly soluble in a variety
of common organic solvents and gasoline as a consequence
of the cardanol unit. The physical properties of gasoline
according to American Society for Testing and Materials
standard were unaffected by the presence of the bis(azo)
dye derived from 1-(4aminophenylazo)-2-naphthol at a
concentration of 6 ppm and the dye showed excellent sta-
bility over a 3 month period.
Introduction
In most countries, motor gasoline tends to be classified
into grades according to an octane number (e.g., premium
and regular). Dye additives are used to differentiate the
different grades of the gasoline so the consumers can
visually recognize the gasoline grade they are using.
However, gasoline is really colorless to pale yellow and
therefore has to be intentionally blended with a colorant
to enable identification of grades and manufacturing
sources. Solvent Red 164 and 26 (Chart 1) are amongst
the most common colorants in use today [1]. However, it
is clear that these could be superseded by cheap new dyes
having higher molar absorptivities and hydrocarbon-sol-
ubilities. In general, an inadequate solubility becomes
problematic when a high concentration of dye is required
to get the desired color intensity in the gasoline, while
dyes that may be soluble enough but have a low
absorptivity may have to be used at concentrations so
high that they interfere with the fuel properties. Thus any
new gasoline colorant should have a high absorptivity and
organic solubility, while maintaining a low production
cost and high stability with respect to both light and
humidity during storage.
Keywords Cardanol ꢀ Bis(azo) dye ꢀ Gasoline colorant ꢀ
Cashew nut shell liquid ꢀ CNSL ꢀ Red dye
Electronic supplementary material The online version of this
article (doi:10.1007/s11746-011-1912-y) contains supplementary
material, which is available to authorized users.
P. Paebumrung
Program in Petrochemistry and Polymer Science,
Faculty of Science, Chulalongkorn University,
Bangkok 10330, Thailand
Described here is the preparation of soluble azo dyes
1 and 2 from cardanol, a natural alkyl phenol obtained
from distillation of cashew nut shell liquid (CNSL). As
shown in Chart 2, the cardanol molecule contains a long
hydrocarbon chain meta- to the hydroxyl group, which is
key in making it useful as a solubilizing aromatic com-
ponent in many syntheses. In the past, several dyes have
been prepared from hydrogenated cardanol and various
aromatic amines for various purposes, such as oil-solu-
bilizing agent, functionalized industrial precursors and
coating materials [2–4]. For petrochemical use, synthesis
A. Petsom ꢀ P. Thamyongkit (&)
Research Center for Bioorganic Chemistry,
Department of Chemistry, Faculty of Science,
Chulalongkorn University, Bangkok 10330, Thailand
e-mail: patchanita.v@chula.ac.th
A. Petsom ꢀ P. Thamyongkit
Center of Excellence for Petroleum, Petrochemicals,
and Advanced Materials, Chulalongkorn University,
Bangkok 10330, Thailand
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J Am Oil Chem Soc (2012) 89:321–328
Experimental Section
OH
Materials and Methods
N
N
N
All chemicals were obtained from commercial suppliers
and used as purchased without further purification. 1H-
NMR and 13C-NMR spectra were collected in deuterated
chloroform (CDCl3) at 400 MHz (1H) and 100 MHz (13C).
Chemical shifts (d) are reported in parts per million (ppm)
relative to the residual CHCl3 peak (7.26 ppm for 1H-NMR
and 77.0 ppm for 13C-NMR spectra) and coupling con-
stants (J) are reported in Hertz (Hz). Mass analysis was
performed by using electrospray ionization time-of-flight
mass spectrometry (ESI-TOF–MS) technique. Absorption
spectra of dyes were collected in CH2Cl2 and absorption
N
Solvent Red 164
OH
N
N
N
N
coefficients (e) are expressed in M-1 cm-1
.
Solvent Red 26
Chart 1 Structures of Solvent Red 164 and 26
Non-commercially Available Compound
Fully hydrogenated cardanol (i.e., no alkene groups and
one-compound composition by 1H-NMR spectroscopic
and mass spectrometric analyses) was kindly supplied by
Dr. Nantanit Wanichacheva.
OH
R
Bis(azo) Dye 1
Cardanol
Following a published method [7], a mixture of p-phenyl-
enediamine (0.108 g, 1.00 mmol) in a 6% (v/v) aqueous
solution of concentrated hydrochloric acid (2.7 mL) was
reacted with a solution of sodium nitrite (0.080 g,
1.0 mmol) in distilled water (3.0 mL) at -2 °C. The
resulting diazonium salt was coupled by adding into an
alkaline solution at -2 °C. The alkaline solution was
prepared by dissolving potassium hydroxide (0.056 g,
1.0 mmol) in ethanol (2.0 mL), then cooling the solution to
0 °C and adding b-naphthol (0.144 g, 1.00 mmol) with
continuous stirring. The reaction mixture was left stirring at
-2 °C for an additional 1 h and then extracted with
CH2Cl2. The organic layer was separated and dried over
anhydrous Na2SO4. After removal of the solvent, the
mixture was purified by column chromatography on silica
gel [1% TEA in hexanes/ethyl acetate (1:1)] to give com-
pound 5 as an orange solid (0.250 g, 95%). The spectral
data of 5 are consistent with those previously described in a
literature [8]. Then, compound 5 (0.250 g, 0.912 mmol)
was diazotized and then coupled to hydrogenated cardanol
(0.304 g, 0.998 mmol) in the same manner as mentioned
above. The resulting crude products were extracted with
CH2Cl2. The organic phase was separated, washed
repeatedly with distilled water (4 9 20 mL), dried over
anhydrous Na2SO4, and then concentrated to dryness. The
resulting crude product was purified by column chroma-
tography on silica gel [1% TEA in CH2Cl2 and then 1%
R =
or
Chart 2 Structure of natural cardanol
of monoazo dyes from cardanol and aniline derivatives
as fuel markers in gasoline and diesel have been reported
[5]. In this study, we aimed to synthesize cardanol-based
red bis(azo) dyes for coloration of the regular-type gas-
oline. This work follows our previous study on a card-
anol-based porphyrin that exhibited improved solubility
and other excellent properties for a diesel fluorescent
marker [6]. Herein, we also report the investigation of
the properties of motor gasoline 91 blended with the
synthesized dyes according to ASTM standard and the
stability of a selected dye in base gasoline 91 to evaluate
their potential as colorants for commercial motor gaso-
line 91.
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J Am Oil Chem Soc (2012) 89:321–328
323
TEA in ethyl acetate/CH2Cl2 (1:4)] to give 1 as a red solid
(0.050 g, 9% overall). m.p. 126–128 °C. 1H-NMR: d (ppm)
0.82–0.87 (m, 3H), 1.21–1.71 (m, 26H), 3.11 (t,
J = 7.8 Hz, 2H), 6.74 (dd, J = 8.8 Hz, 2.8 Hz, 1H), 6.80
(d, J = 2.8 Hz, 1H), 6.83 (d, J = 9.2 Hz, 1H), 7.39–7.42
(m, 1H), 7.54–7.58 (m, 2H), 7.70–7.73 (m, 2H), 7.81 (d,
J = 8.8 Hz, 2H), 7.98 (d, J = 8.8 Hz, 2H), 8.54 (d,
J = 8.4 Hz, 1H); 13C-NMR: d (ppm) 14.1, 22.7, 29.1, 29.2,
29.4, 29.5, 29.66, 29.72, 29.99, 30.03, 30.2, 31.4, 31.5,
31.9, 32.1, 113.9, 116.5, 117.1, 118.5, 122.0, 124.3, 125.3,
126.2, 128.1, 128.7, 128.8, 128.9, 129.1, 130.7, 133.4,
141.2, 144.6, 145.0, 146.2, 151.5, 158.9, 174.7; ESI-TOF–
MS observed 579.578, calculated 578.362 [(M ? H)?;
M = C37H46N4O2]; kabs nm (e) 513 (31,948).
3-alkylphenoxide solution. The reaction mixture was left
stirring at a temperature below 0 °C for 1 h and the azo dye
product was extracted with toluene. The toluene layer was
separated, washed repeatedly with distilled water
(4 9 20 mL), dried over anhydrous Na2SO4, and then
concentrated to dryness. The resulting crude product was
purified by column chromatography on a silica gel [1%
TEA in hexanes/ethyl acetate (4:1)] to give a yellow
gummy solid (0.010 g, 1%). Due to a close Rf value of
compound 3 to those of unknown byproducts, compound 3
could not be completely recovered. 1H-NMR: d (ppm)
0.84–0.90 (m, 6H), 1.23–2.80 (m, 44H), 3.13 (t,
J = 7.6 Hz, 4H), 4.94–5.82 (m, 6H), 6.74 (dd, J = 8.8 Hz,
2.8 Hz, 2H), 6.81 (d, J = 2.8 Hz, 2H), 7.74 (d,
J = 8.8 Hz, 2H), 7.80 (d, J = 8.4 Hz, 4H), 7.97 (d,
J = 8.4 Hz, 4H); 13C-NMR: d (ppm) 13.8, 14.1, 22.6, 22.8,
25.55, 25.62, 27.2, 29.0, 29.25, 29.31, 29.39, 29.44, 29.6,
29.67, 29.72, 29.8, 31.4, 31.5, 31.8, 32.0, 113.8, 114.7,
116.4, 117.2, 123.3, 126.8, 127.5, 127.7, 128.0, 128.1,
129.3, 129.8, 129.9, 130.1, 130.4, 136.8, 141.9, 144.8,
146.1, 152.4, 158.4; MALDI-MS observed 808.674; cal-
culated average mass 808.612–814.612 [M = C54H78-n
N4O2; n = 0, 2, 4, 6]; kabs nm (e) 387 (10,950).
Bis(azo) Dye 2
Following the procedure described for the synthesis of
compound 1, natural cardanol (0.304 g, 1.00 mmol) was
used instead of the hydrogenated one. Compound 2 was
obtained as a red solid (0.150 g, 26% overall). m.p.
100–102 °C. 1H-NMR: d (ppm) 0.77–0.85 (m, 3H),
1.18–2.74 (m, 20H), 3.05 (t, J = 7.6 Hz, 2H), 4.87–5.76
(m, 4H), 6.67 (dd, J = 8.8 Hz, 2.8 Hz, 1H), 6.73 (d,
J = 2.8 Hz, 1H), 6.77 (d, J = 9.6 Hz, 1H), 7.32–7.36 (m,
1H), 7.48–7.53 (m, 2H), 7.64–7.67 (m, 2H), 7.75 (d,
J = 8.4 Hz, 2H), 7.92 (d, J = 8.4 Hz, 2H), 8.48 (d,
J = 8.4 Hz, 1H); 13C-NMR: d (ppm) 14.1, 22.6, 22.8, 25.6,
27.2, 29.0, 29.3, 29.4, 29.5, 29.6, 29.7, 29.8, 31.5, 31.8,
32.0, 113.9, 116.4, 117.2, 118.5, 121.9, 124.3, 125.3,
126.3, 128.1, 128.8, 129.2, 130.0, 130.4, 130.7, 133.4,
141.4, 144.7, 144.9, 146.2, 151.5, 158.7, 175.0; ESI-TOF–
MS observed 579.383, calculated 572.315–578.362
[(M ? H)?; M = C37H46-nN4O2; n = 0, 2, 4 or 6]; kabs nm
(e) 516 (31,345).
Bis(azo) Dye 4
Following the procedure described for bis(azo) dye 3 with
slight modification, 1,5-diamino-naphthalene (0.158 g,
1.00 mmol) was diazotized and coupled with cardanol. The
reaction mixture was extracted with tetrahydrofuran and
saturated ammonium chloride solution. The organic layer
was separated, washed repeatedly with distilled water
(4 9 20 mL), dried over anhydrous Na2SO4, and then
concentrated to dryness. The resulting crude product was
purified by column chromatography (silica, 1% TEA in
CH2Cl2) to give a yellow gummy solid (0.04 g, 5%). Due
to a close Rf value of compound 4 to those of unknown
byproducts, compound 4 could not be completely recov-
Bis(azo) Dye 3
Following a previously published procedure [5], benzidine
(0.184 g, 1.00 mmol) was added to a 50% (v/v) aqueous
solution of concentrated hydrochloric acid (1.2 mL) and
the resulting reaction mixture was vigorously stirred in an
ice bath. After the mixture was cooled to -2–0 °C, a
solution of sodium nitrite (0.138 g, 2.00 mmol) in distilled
water (1.0 mL) was added dropwise into the reaction
mixture while the reaction temperature was kept below
0 °C. Meanwhile, a 3-alkylphenoxide solution was pre-
pared by dissolving potassium hydroxide (0.112 g,
2.00 mmol) in methanol (1.0 mL), cooling the solution to
0 °C, and then adding cardanol (0.608 g, 2.00 mmol) with
continuous stirring to give a reddish-brown oil. Then the
diazonium salt solution was added dropwise to the cooled
1
ered. H-NMR: d (ppm) 0.77–0.83 (m, 6H), 1.18–2.74 (m,
46H), 3.13 (t, J = 7.6 Hz, 4H), 4.88–5.77 (m, 6H), 6.73
(dd, J = 8.8 Hz, 2.8 Hz, 2H), 6.77 (d, J = 2.8 Hz, 2H),
7.64 (t, J = 8.0 Hz, 2H), 7.78 (d, J = 7.6 Hz, 2H), 7.83
(d, J = 8.8 Hz, 2H), 9.03 (d, J = 8.4 Hz, 2H); 13C-NMR:
d (ppm) 13.8, 14.1, 22.6, 22.8, 25.5, 25.6, 27.2, 28.9, 29.0,
29.3, 29.4, 29.5, 29.6, 29.66, 29.71, 29.8, 31.5, 31.8, 32.1,
112.1, 113.8, 114.7, 116.4, 117.6, 126.1, 126.4, 126.8,
127.5, 127.9, 128.1, 129.3, 129.8, 129.9, 130.1, 130.4,
132.3, 136.8, 145.5, 146.3, 147.9, 158.3; MALDI-MS
observed 782.547; calculated average mass 782.597–
788.597 [M = C52H76-nN4O2; n = 0, 2, 4, 6]; kabs nm (e)
402 (8,086).
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Investigation of the Appropriate Dye Concentration
for Coloration of Gasoline 91
up to 50 °C. After 1, 2 and 3 months three solutions from
each flask were directly taken from the vials to the UV–Vis
measurement. The quantity of 2 in the blended gasoline 91
was determined by the calibration equation.
In the case of pure 2, a 200-ppm stock dye solution was
prepared by dissolving bis(azo) dye 2 (2 mg) in base gas-
oline 91 to a final volume of 10 mL. A series of the
solutions of 2 in base gasoline 91 at a final concentration of
4, 5, 6, 7 and 8 ppm was prepared. After that, the color of
the resulting solutions was compared to that of the com-
mercial gasoline 91, obtained from PTT Public Company
Limited, Thailand by a colorimeter to find the similar color
match.
Results and Discussion
Molecular Design
Two series of dyes were prepared. One containing cardanol
and b-naphthol moieties joined by a 1,4-phenylene central
unit (compounds 1 and 2, Chart 3). The introduction of the
b-naphthol group was intended to extend the conjugation in
the dye structure, resulting in the red-shift of the absorption
as observed in several red azo dyes, e.g., Solvent Red 164.
Compound 1 differs from compound 2 at the saturation of
its long alkyl chain on the cardanol moiety. Initially, the
hydrogenated cardanol was employed in the synthesis of
compound 1 to avoid the possible complication due to the
side reaction caused by double bonds on the long alkyl
chain of cardanol. The synthesis of compound 2 was
included to study the possibility of using natural cardanol
in the dye preparation.
In a similar manner, a 1,000-ppm stock solution of crude
bis(azo) dye 2 was prepared by dissolving crude 2 (10 mg)
in base gasoline 91 to a final volume of 10 mL and sub-
sequent final concentrations of 15, 16, 17, 18, 19 and
20 ppm were compared for a color match to the commer-
cial gasoline 91.
Effect of Bis(azo) Dye 2 on the Physical Properties
of Base Gasoline 91
A 6 ppm solution of pure bis(azo) dye 2 in base gasoline 91
was prepared by dissolving pure 2 (6 mg) in base gasoline
91 in a final volume of 1 L, while a 18-ppm solution of
crude 2 was prepared in the same manner by using crude 2
(18 mg) instead of the pure one. The physical properties of
both dyed gasoline samples, and base gasoline 91, were
investigated according to the ASTM test methods. The
physical properties of dyed and undyed gasoline samples
were determined twice in the second and the third month
during the 3 month period of the stability test after the
photophysical properties of the dye was proven to remain
intact.
The other series of bis(azo) dyes have two cardanol
peripheral groups linked to each other via a 4,40-biphen-
ylene (compound 3) or a 1,5-naphthylene central unit
(compound 4), considering that these linkers could possibly
OH
H31-n
C15
N
N
N
N
OH
Quantitative Determination and Stability Test
1
; n = 0
2; n = 0, 2, 4 or 6
of Bis(azo) Dye 2 in Base Gasoline 91
A series of the calibration solutions of pure bis(azo) dye 2
in base gasoline 91 was prepared at final concentrations of
2, 4, 6, 8 and 10 ppm and the absorption spectra of each
calibration solution were recorded by a UV/Vis spectro-
photometer. The calibration curve was plotted between
absorbance at 509 nm (y-axis) and the concentration of 2 in
base gasoline 91 (x-axis) and the best fitting linear
regression line was selected. This equation was used to
quantify 2 in the stability test described below.
HO
N
C15H31-n
N
N
C15H31-n
N
OH
3; n = 0, 2, 4 or 6
HO
N
N
H31-n
C15
C15H31-n
The stability test was performed with base gasoline 91
dyed with bis(azo) dye 2 at a final concentration of 6 ppm
on a UV–Vis spectrophotometer. Three 6 ppm solutions of
2 in base gasoline 91 were prepared and a 5-mL aliquot
was placed into each of nine sealed vials and stored up to
3 months in an ambient environment with the temperature
N
N
OH
4; n = 0, 2, 4 or 6
Chart 3 Target cardanol-based bis(azo) dyes 1–4
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J Am Oil Chem Soc (2012) 89:321–328
325
provide an extended conjugation system and, subsequently,
absorption in the long wavelength region. The 4,40-
biphenylene central unit in compound 3 is known to be
more flexible than the 1,5-naphthylene one in compound 4
and, hence, should be beneficial to the solubility of the dye.
However, the conjugation system may be disturbed by the
possibility of the bond rotation in the 4,40-biphenylene unit.
This will not occur in the case of the 1,5-naphthylene linker
in 4.
NH2
NH2
(i) HCl
(ii) NaNO2, -2 °C
(iii)
OH
Synthesis
in KOH/EtOH
The synthesis of bis(azo) dyes 1 and 2 relies on stepwise
double diazotization (Scheme 1). Firstly, commercially
available p-phenylenediamine was singly diazotized in a
stoichiometric manner and then the resulting diazonium
salt was coupled with an alkaline solution of b-naphthol to
give the monoazo compound 5. Subsequently, the diazo-
nium salt of 5 was formed and coupled with a hydroge-
nated or natural cardanol to obtain the desired compound 1
or 2 as a red solid in 9 or 26% overall yield, respectively.
The lower yield of compound 1 is attributed to the lower
solubility of the hydrogenated cardanol in the reaction
medium, compared to that of the natural one. Due to the
steric effect from the cardanol alkyl long chain, the cou-
pling of the diazonium salt and cardanol was found to be
relatively slow in general. The reactions gave several
unknown byproducts from competitive side reactions,
which may be hydrolysis of the diazonium salt, salt
decomposition, etc. These byproducts also caused com-
plications in the purification step.
OH
N
N
NH2
5
(i) HCl
(ii) NaNO2, -2 °C
(iii) hydrogenated
or natural cardanol
in KOH/EtOH
OH
N
N
C15H31-n
N
N
OH
1
2
; n = 0, 9% overall or
; n = 0, 2, 4 or 6, 26% overall
Compound
2
exhibited
a
satisfactory solubility
([10 mg/mL) in common organic solvents, such as
CH2Cl2, toluene and THF, and base gasoline 91. In
CH2Cl2, the solubility of compounds 1 and 2 (10
and [18 mg mL-1, respectively) were greater than that of
Solvent Red 164 (8 mg mL-1). This indicated the efficient
solubilizing effect of the unsaturated alkyl chain in natural
cardanol. With respect to the UV–Vis absorption, com-
pounds 1 and 2 showed absorption maxima in CH2Cl2 at
513 and 516 nm with absorption coefficients of 31,345 and
31,948 M-1 cm-1, respectively. These absorption data are
comparable to those of Solvent Red 164 that exhibited an
absorption maximum in CH2Cl2 at 508 nm with an
absorption coefficient of 33,627 M-1 cm-1. Thus, the
substitution of the peripheral phenyl group of the com-
mercial Solvent Red 164 by the natural cardanol group
improves the solubility of the dye and keeps the dye
absorptivity equally high. Due to the higher solubility and
the higher preparative yield from an easier preparation
procedure (i.e., no hydrogenation of the starting cardanol
was needed), compound 2 was chosen for further study.
Scheme 1 Synthesis of dyes 1 and 2
Compounds 3 and 4 were prepared from the double
diazotization of benzidine or 1,5-diaminonaphthalene,
respectively, and a stoichiometric amount of cardanol, as
shown in Scheme 2. Similarly to what was observed in the
preparation of dyes 1 and 2, these syntheses encountered a
slow reaction rate and the formation of several byproducts
that were difficult to completely isolate from compounds 3
and 4. Therefore, compounds 3 and 4 were obtained in
yields of only 1 and 5%, respectively.
As regards their absorption characteristics, both com-
pounds 3 and 4 appeared yellow in color with absorption
maxima in CH2Cl2 of 387 and 402 nm, and absorption
coefficients of 10,950 and 8,086 M-1 cm-1, respectively.
It is clear that the absorption maxima of compounds 1
and 2 were significantly red-shifted from those of com-
pounds 3 and 4. It is possible that the conjugation in
molecules 3 and 4 was disturbed by the bulkiness of the
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Investigation of the Appropriate Dye Concentration
for Coloration of Gasoline 91
H2N-Ar-NH2
(i) HCl
(ii) NaNO2, -2 °C
(iii) natural cardanol
in KOH/EtOH
To estimate the appropriate concentration of 2 in base
gasoline 91 to give the most similar color to that of the
commercial gasoline 91, the color of a solution of 2 in base
gasoline 91 at a concentration of 4–8 ppm was determined
in comparison with that of the commercial gasoline 91 by
mean of colorimetric analysis based on a CIE L*a*b*
system. The color difference was determined by the DE*
value. The measurement was performed with all samples at
once, therefore the typical measurement uncertainty
resulted from the instrument components and measurement
condition should not significantly affect this comparative
study. The results (Table 1) revealed that a 6 ppm solution
of 2 in base gasoline 91 provided the most similar color to
that of the commercial gasoline 91.
HO
N
C15H31-n
N Ar N
C15H31-n
N
OH
3
; Ar =
, 1%
4; Ar =
, 5%
To simplify and reduce the cost of the scalable pro-
duction of dye 2 as a gasoline colorant, we also attempted
to directly blend a crude mixture containing dye 2 in gas-
oline 91. The crude mixture was obtained from the same
synthetic procedure as that of the pure one, except that the
lengthy chromatographic purification in the second diazo-
coupling was omitted. In a similar manner to pure dye 2, a
series of the solutions of crude 2 at a concentration of
10–20 ppm was prepared and their color was compared
with that of the commercial gasoline 91. It was found that
an 18-ppm solution of crude 2 in base gasoline 91 provided
the most similar color to that of commercial gasoline 91
(Table 1). Therefore, the suggested concentration levels of
Scheme 2 Synthesis of dyes 3 and 4
long alkyl chains of the peripheral cardanol units. The
disturbance of the conjugation system was even more
pronounced in the case of compound 3 whose biphenyl
unit encounters the phenyl-ring rotation around the
phenyl–phenyl bond, compared to compound 4 which
has a more rigid naphthyl central unit. However, since
the expected red color was not obtained, compounds 3
and 4 were not taken into consideration in the next
study.
Table 1 Colorimetric data of solutions of pure and crude 2 in base gasoline 91 compared with those of commercial gasoline 91
Type of gasoline 91
La
ab
bc
DE*d
Commercial
86.45
23.42
14.90
Blended with pure 2 (concentration, ppm)
4
90.61
88.86
86.70
84.70
82.75
17.00
20.29
24.04
27.79
31.39
12.84
15.53
18.21
21.90
24.47
7.92
4.00
5
6
3.38
7
8.44
8
12.99
Blended with crude 2 (concentration, ppm)
15
16
17
18
19
20
a
86.15
86.11
85.57
83.47
82.45
81.21
17.23
17.88
19.06
22.37
23.64
25.36
11.83
11.68
12.17
13.20
13.59
13.94
6.92
6.42
5.22
3.59
4.21
5.41
L is lightness representing from 0 (black) to 100 (white)
b
c
d
a is chroma coordinate representing from ?a (redness) to -a (greenness)
b is chroma coordinate representing from ?b (yellowness) to -b (blueness)
DE* is color difference value calculated from DE* = [(DL)2 ? (Da)2 ? (Db)2]1/2
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327
pure dye 2 and its crude mixture to be used for coloration
of gasoline 91 and for further study in this research are 6
and 18 ppm, respectively. Although the crude preparation
was required to be used at a 3-fold higher concentration
than the pure compound 2, the yield of the crude 2 prep-
aration compared to that of the pure 2 was significantly
greater and thus its use instead potentially offers a signif-
icant cost and time saving opportunity.
significantly different from those of undyed gasoline and
followed the standard specification of the commercial
gasoline 91.
Quantitative Determination and Stability Test
of Bis(azo) Dye 2 in Base Gasoline 91
Generally, the azo dyes are known to be highly stable.
However, under storage condition the dyes exposed to
various light intensities, temperatures and humidity levels
that bring about a trivial possibility for the dye degradation
via, for example, anaerobic microbial process and photo-
catalytic destruction. Therefore, a stability test was taken
into consideration in this study. A standard calibration
curve of pure bis(azo) dye 2 in base gasoline 91 was pre-
pared by plotting the absorbance at 509 nm, which is an
absorption maximum of 2 in base gasoline 91, of a series of
the solutions of 2 in base gasoline 91 versus the concen-
tration of the solutions ranging from 0 to 10 ppm. A
standard calibration equation was found to be
Y = 0.0607X, with a linear correlation coefficient R2 equal
to 0.9999. This equation was then used to evaluate the
stability of 2 in base gasoline fuel. Generally, commercial
gasoline 91 is consumed within 3 months after it is
released on to the market. Therefore, in this study, the
stability test of 2 in base gasoline 91 was performed over a
period of up to 3 months under ambient conditions with the
temperature up to 50 °C. The test was carried out by
Effect of Bis(azo) Dye 2 on the Physical Properties
of Base Gasoline 91
This part is focused on the effect of bis(azo) dye 2 on
the physical properties of base gasoline 91 to ensure that
gasoline 91 blended with either the pure or crude
bis(azo) dye 2 preparations still has the qualified physi-
cal properties for commercial use. A sample of base
gasoline 91 containing 6 ppm of pure bis(azo) dye 2 and
another containing 18 ppm of the crude bis(azo) dye 2
were tested for the physical properties using the ASTM
test methods. The physical properties of both dyed gas-
oline samples were then compared with those of the
undyed (base) gasoline 91. Each sample was tested twice
in the second and the third month during the 3 month
period of the stability test. The results from both mea-
surements were almost identical and the average value is
reported in Table 2. The results revealed that the phys-
ical properties of both dyed gasoline samples were not
Table 2 Physical properties of dyed gasoline samples and undyed gasoline 91
Test item
ASTM
Limit
Type of gasoline 91
Undyed
Dyed with
Pure 2
Crude 2
Vapor pressure at 37.8 °C, kPa
Distillation at
D5191
54.5 max
53.4
53.6
53.1
Initial boiling point (IBP), °C
10%, °C
50%, °C
90%, °C
Final boiling point (FBP), °C
Residue, % vol.
D86–01
Report
34.4
53.0
95.6
123.9
156.6
1.4
35.8
54.0
96.6
123.9
156.7
1.3
35.9
54.6
96.8
124.0
156.6
1.3
Max. 70
90–110
Max. 170
Max. 200
Max. 20
Solvent Washed Gum,
mg/100 mL
D381
Max. 4
0.8
1.2
1.2
Silver strip corrosion
Sulfur, % w
D130
Max. no. 1
Max. 0.05
Max. 0.7
Max. 3.8
Max. 38
No. 1
0.0016
0.117
0.49
No. 1
0.0016
0.112
0.50
No. 1
0.0015
0.092
0.49
D5453
D604
Water, % w
Benzene, % v
D5580
D5580
D2699
Aromatics, % v
31.1
32.2
31.3
Research Octane Number (RON)
Min. 87.0
91.0
91.0
91.0
123

328
J Am Oil Chem Soc (2012) 89:321–328
stable in base gasoline 91 for at least 3 months. The fact
that bis(azo) dye 2 offers practical synthesis from an
inexpensive natural resource, a high solubility in base
gasoline 91, a satisfactory stability within the fuel storage
time, and the possibility to be used in its crude form in low
concentration supports the conclusion that bis(azo) dye 2
can possibly serve as a fuel dye for commercial use.
However, a further detailed investigation for using this dye
in the actual combustion cycle is required.
Table 3 Concentration of diazo dye 2 in base gasoline 91 after
1–3 months (initial level was 6 ppm)
Month Concentration of 2a (ppm)
Sample 1
Sample 2
Sample 3
Average
1
2
3
a
5.96 0.07 6.10 0.07 6.03 0.07 6.03 0.07
5.97 0.07 6.11 0.07 6.06 0.07 6.05 0.07
5.97 0.08 6.12 0.08 6.06 0.08 6.05 0.08
Average standard deviation, n = 3
Acknowledgments This research was partially supported by the
Center of Excellence for Petroleum, Petrochemicals and Advanced
Materials and the Graduate School, Chulalongkorn University. The
data on the physical properties of dyed and undyed gasoline were
recorded at the PTT Public Company Limited, Thailand. Hydroge-
nated cardanol was a gift from Dr. Nantanit Wanichacheva. We thank
the Publication Counseling Unit (PCU), Faculty of Science, Chul-
alongkorn University for language editing.
measuring the absorbance at 509 nm of a 6 ppm solution of
pure 2 in base gasoline 91 after 1, 2 and 3 months by a
UV–Vis spectrophotometer. The absorbance observed was
then converted into the dye concentration by the above
calibration equation. The results (Table 3) indicated that
there was no significant change in the concentrations of 2
in each gasoline sample throughout the 3 month period
and, hence, together with the above-mentioned results, it
can be concluded that bis(azo) dye 2 showed stability for at
least 3 months and can be practically used as a colorant in
gasoline 91 production.
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dyes from cardanol, a naturally occurring compound
obtained from extraction of CNSL, for use as a coloring
agent in gasoline 91. Besides the desirable red color with a
comparable maximum absorption and absorption coeffi-
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solvents and base gasoline 91. Based on the colorimetric
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mercial one is 6 or 18 ppm when being used in pure or
crude form, respectively. According to ASTM test meth-
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123