Acid/Base Liquid/Liquid Extraction of a Three Dye Mixture and Synthesis and
Recrystallization of Methyl Orange
Joe Puthenpurayil
CHEM 213H Section 001, Department of Chemistry, The Pennsylvania State University,
University Park, PA 16802
Abstract
Acid/base liquid/liquid extraction was employed to efficiently separate a threecomponent dye mixture consisting of unknown acidic, basic, and neutral dyes, which
were then identified by color. Methyl orange was synthesized from sulfanilic acid
sodium salt via a two-step procedure with a diazotization reaction followed by an
addition reaction. The methyl orange was purified via recrystallization with a low
percent yield of only 35%. The purified methyl orange was tested as a dye using a strip
of multifiber fabric and proved to be an effective dye for polar fabrics.
Introduction
Acid/base liquid/liquid extraction utilizes acid/base reactions in order to separate
organic compounds with varying pH values1, and acid/base liquid/liquid extraction was
used in the module to separate a mixture of three unknown dye components, one acidic,
one basic, and one neutral, dissolved in chloroform. After extraction, the components
were identified based on their colors.
Recrystallization is a technique employed to purify solid organic compounds1,
and recrystallization was used in the module to purify synthesized methyl orange (4)
from a two-step synthesis starting with sulfanilic acid sodium salt (1) (Scheme 1 & 2).
The purified methyl orange was tested by dyeing various fabrics and observing the
resulting colors.
Methyl orange was synthesized from sulfanilic acid sodium salt in a two-step
procedure. Sulfanilic acid sodium salt (1) was first converted to diazotized sulfanilic acid
(2) in a diazotization reaction with hydrochloric acid and sodium nitrite (Scheme 1). In
the second step, the diazotized sulfanilic acid (2) was combined with N,Ndimethylaniline (3) in an addition reaction to give methyl orange (4) (Scheme 2). Methyl
orange is a useful molecule since it is an orange dye, and its color varies based on the pH
of its environment; yellow in basic conditions and red in acid.
Scheme 1. Diazotization of Sulfanillic Acid Sodium Salt to Diazotized Sulfanilic Acid
2 1
Scheme 2. Synthesis of Methyl Orange from Diazotized Sulfanilic Acid
4
2
3
Results and Discussion
Acid/Base Liquid/Liquid Extraction and Identification of Dye Mixture
The acid/base liquid/liquid technique was successful in separating the threecomponent mixture of acidic, basic, and neutral dyes dissolved in chloroform. Aqueous
hydrochloric acid was added to the mixture to form an aqueous layer containing the basic
dye, which was extracted and had a light purple/pink color, and once neutralized, the
extracted basic dye had a redder color, so it was likely safranin. Aqueous sodium
bicarbonate was then added to the mixture to form an aqueous layer containing the acidic
dye, which was extracted and had a deep purple compound and remained purple once
neutralized, so the acidic dye was likely bromocrescol purple. The neutral dye remaining
in the organic layer had a teal color, so it was likely brilliant green.
2 Synthesis, Recrystallization, and Dye Testing of Methyl Orange
The two-step synthesis of methyl orange was carried out via macroscale
procedures, and after recrystallization and drying over four days afforded only a 35%
yield, less than the 61% - 73% yield anticipated in the module. The majority of the
product was likely lost in transferring the crude product to and from the vacuum filtration
apparatus and transferring the recrystallized pure product to and from the vacuum
filtration apparatus, because of tiny spills and residual material left in the glassware.
Water was used as the solvent for recrystallization since methyl orange is a polar
compound thanks to its sulfonate group.
The dye testing with a piece of multifiber fabric confirmed the methyl orange’s
ability to function as a dye, as portions of the initially white/off-white fabric remained
colored even after washing. The different materials of the multifiber fabric had differing
interactions with the polar methyl orange dye, and thus had different colors once dyed,
more polar fabrics like the polyamides, silk, wool, and polyamide nylon interacted more
strongly with the polar methyl orange and had vibrant orange colors once dyed, while
more nonpolar fabrics like polypropylene or polyester, bright filament had weaker
interactions with the polar methyl orange, and thus remained white or became only
slightly colored after dyeing.
Conclusion
The acid/base liquid/liquid extraction and identification of the three-component
dye mixture was successful as each component was isolated and displayed a
characteristic color for easy identification as safranin, bromocrescol purple, and brilliant
green. The two-step synthesis of methyl orange had a low percent yield of only 35%;
however, the recrystallization and subsequent dye testing with the synthesized methyl
orange was successful as evidenced by the dye’s strong interaction with and coloring of
the polar components of the multifiber fabric. Taking more care to avoid spills and
allowing a longer cooling period during the recrystallization could improve the low
percent yield from the synthesis and recrystallization of methyl orange.
Experimental
General Methods
All of the compounds used were bought from Sigma-Aldrich and used without
further purification. Multifiber #43 Fabric was used for the dye testing.
Methyl orange (4) Sulfanilic acid sodium salt (2.70 g, 13.8 mmol) was dissolved in 25
mL of water, then NaNO3 (0.950 g, 13.8 mmol) was added and stirred until dissolved.
The resulting solution was poured into a flask containing concentrated HCl (2.50 mL,
82.3 mmol) and 15 g of ice, until a precipitate of the diazotized sulfanilic acid formed
after 2-3 min. In a separate test tube, dimethylaniline (1.60 mL, 1.53 g, 12.6 mmol) was
mixed with acetic acid (1.25 mL, 21.8 mmol), then, along with a little water (~2 mL),
was poured into the mixture containing the diazotized sulfanilic acid precipitate and
stirred for 10 min. NaOH solution (18.0 mL, 3 M) was then added and the mixture was
stirred and heated to boiling, then cooled in an ice bath. The crude methyl orange
3 product was collected via vacuum filtration and rinsed with saturated sodium chloride
solution. The crude product was then recrystallized in water to give 1.429 g (35%) of the
orange solid pure methyl orange product.
Acknowledgements
Thanks to Anthony, Dr. Masters, and Sean for all the help and advice in the lab.
Thanks also to my hoodmates and classmates who also helped out when I was confused.
Finally, thanks to Penn State for providing the resources for the module and Sigma
Aldrich for the chemicals.
References
1. Williamson K.L.; Masters, K. M. Macroscale and Microscale Organic Experiments, 6th
ed.; Cenage Learning: United States, 2011.
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