Synthesis of Methyl Orange Dye

1. Synthesis of Methyl Orange Dye: Adding color

Juan A. Barrera
University of Houston-Downtown
One Main Street
Houston, Texas 77002
April 7, 2014




ABSTRACT



Synthesis of a Methyl Orange dye is a procedure accomplished by an azo coupling
between a diazonium ion and an aromatic substrate. Most synthetic dyes consist of the coming
together or coupling of the N-N functional groups (azo) of two different aromatic compounds.
The diaozonium ion emerges from a reaction of sulfanilic acid with sodium nitrite and
hydrochloric acid. Due to the fact that Sulfanilic acid is not soluble in acidic solutions it must
first be dissolved in a basic solution such as sodium carbonate. The addition of Hydrochloric
Acid creates the formation of nitrous acid and the precipitation out of the diazonium salt
intermediate. The careful addition of the aromatic substrate, N.N-dimethylaniline with the
diazonium ion creates the formation of methyl orange dye. The dried methyl orange crystals is
then used in dyeing tests of various fabrics. The fabrics are soaked in a solution of methyl
orange, water, sodium sulfate, and sulfuric acid for a couple minutes and inspected for dye
intensity. Different fabric structures display different dye intensity. The methyl orange is also
used as an acid, base indicator by displaying different colors upon addition of acids and bases.

2. Introduction
Dyes are an important aspect of culture that have been used for the purpose of adding
color to art drawings, hair, faces, and clothing. Colors add a unique and ascetic quality that
brings life and energy. Before the discovery and perfecting of synthetic dyes, there was only a
limiting amount of dye colors that were extracted from various plants. The accidental discovery
of synthetic dyes in the 1850’s followed by the discovery of azo dyes would change the dye
industry forever. Synthetic dyes allowed for an unlimited range of colors that would be useful for
industry. Azo dyes account for 50% of worldwide dye production and are used in textile, leather
dyeing, food production, cosmetics, paper printing and pharmaceuticals
[1]
.











Figure 1. Synthesis of Diazonium Ion and addition of N-N. dimethylalinine

The procedure to synthesize methyl orange dye is the same applied to other azo dyes.
This involves the coupling of an azo group between a diazonium ion and an aromatic substrate.
The positively charged diazonium ion acts as the electrophile to activate the aromatic substrate.
The formation of a diazonium ion requires a reaction between an aromatic amide and nitrous
acid. Sulfanilic acid is a compound that is insoluble in acid, therefore it must first be dissolved
in sodium nitrite. The addition of Hydrochloric acid will create nitrous acid along with the
diazonium salt ion as a precipitate. The aromatic amide added, N,N-dimethylaniline, reacts
highly with the diazonium salt creating methyl orange.














Figure 2. Synthesis of Methyl Orange Mechanism

3. Due to the fact that dyes are a major use in the textile industry, experimentation with
different fabrics to determine dyeing capability is always necessary. The major fabrics with
different properties tested include, nylon, polyester, silk, and cotton. Nylon is a synthetic fiber
and polyamide. There are several different types of nylon but they all share common
characteristics. There are composed of repeating units of amides that are run parallel to each
other forming hydrogen bonds.






Figure 3. Structure of common Nylon used in Textile industry. Nylon 6-6
[2]


Polyester is a unique fiber that contains ester functional groups in its main chain.
Polyester fabrics are characterized by their use in clothing, furnishing and bed sheets. The texture
is unlike natural fibers and has certain advantages such as high wrinkle resistance and durability.
The major component of polyester is Polyethylene terephthalate which is also used to
manufacture plastics of different degrees.







Figure 4. Structure of Polyethylene terephthalate
[3]

Silk is a natural protein fiber composed of polypeptides cross-linked with disulfide
bridges. Some of the basic and acidic amino acids provide many polar groups. The majority of
silk is composed of fibroin and is composed mainly by insects to form cocoons. The chemical
structure of silk consists of six amino acids linked in beta sheets. Silk, produced by the silkworm
Bombyx mori, is composed of 65,75% fibroin, 20,30% sericin and (,5%) wax, pigments, sugars
and impurities
[4]
.










Figure 5. Structure of Silk

4. Cotton is a natural fiber that is composed of cellulose. This polysaccharide is composed
of hundreds of connected D-glucose units. Cotton is characterized as a fluffy fiber that grows
inside of a protective capsule. Cotton is spun into threads that are used to produce textiles. The
cellulose that composes cotton is formed by a straight chain polymer. Multiple hydroxyl groups
on glucose form hydrogen bonds with neighboring oxygen forming a strong tensile strength
[5]
.









Figure 6. Structure of Cellulose
[6]


Methyl orange is an acid base indicator changing colors at different pH. At a pH greater
than 4.4 it turns orange in color. At a pH of less than 3.2, it turns a dark red color. Thus it is
possible to determine if certain substances are acids or bases when mixed with methyl orange.
In this experiment there was a methyl orange synthesis accomplished using Sulfanilic
acid, sodium carbonate, hydrogen-chloride, sodium nitrite, and N.N-dimethyl aniline. The
methyl orange was then used to dye several fabrics which included, cotton, silk, polyester, and
nylon. Methyl orange was also used as an acid base-indicator by mixing with different acidic and
basic reagents.

Materials and Methods
To perform a Methyl Orange dye synthesis there was the need of various reagents. The
reagents used included, Sodium Carbonate, Sulfanilic Acid, Sodium Nitrite, Water, Hydrogen
Chloride, N,N-Dimethylaniline, Glacial Acetic Acid, and Sodium Chloride. The initial setup
included the use of a 50ml Erlenmeyer Flask, 10 ml graduated cylinder, Pasteur pipette, spatula
and a hot plate.










Figure 7. Initial Experimental Setup

Before the experiment began, the glassware was cleaned, inspected for cracks and
assembled as shown in Figure 7. Glass ware used is always checked to see if in good condition

5. to perform experiment. The initial setup consisted of adding reagents to 50 ml Erlenmeyer flask
and heating them until homogenous. In another flask the N,N-dimethyl solution was mixed and
slowly added to the Erlenmeyer containing the sodium carbonate. The mixture was then heated
and then cooled in an ice bath. The ice bath consisted of a larger beaker filled with ice and water.
The mixture was cooled there for a few minute before being filtered via suction filtration.










Figure 8. Suction Filtration Setup

The suction filtration setup included the use of a filter paper, Buchner funnel, and a filter
flask. The goal was to completely isolate the product present in the filter paper and proceed to
place it in the watch glass for weight determination. Due to time constraints, the product in the
funnel was allowed to dry over the course of several days before being put in the watchglass and
determining weight. Once the methyl orange was dried, it was time to proceed with the dyeing
process. A very small amount of methyl orange roughly about 50 mg was dissolved in water with
sodium sulfate and sulfuric acid. This was mixed in a 100ml beaker and heated on the hot plate
to just below boiling point before inputting the four different fabrics. The fabrics were soaked in
the methyl orange for roughly 10 minutes before being taken out and washed with water. The
fabrics were inspected for staining ability.








Figure 9. Dye Staining Setup


In two test tubes a few methyl orange crystals were dissolved in a small amount of water.
In one test tube hydrochloric acid was added and in the other, sodium hydroxide was added. The
solutions were inspected for their color change and noted.

6. Figure 10. Methyl Orange Test
[7]
Experimental
The first step before the experiment took place was adequate safety precautions such as
putting on gloves, lab coat, and goggles. Some of the reagents used have hazards that include
skin, nose, and eye irritation when in contact. The glassware was inspected for any cracks or
signs of damage before being cleaned. All the reagents were obtained from the University of
Houston-Downtown stockroom. The initial procedure began with the Diazonium salt formation.
This required the dissolving of 0.06 g of sodium carbonate in 5ml of water. To this, 0.2 g of
sulfanilic acid monohydrate was added, from which the flask containing the solution was heated
until homogenous. The mixture was then cooled and 0.25ml of concentrated hydrogen chloride
was added. The solution was kept cold as the precipitate formed.











Figure 10. Diazonium Ion Formation

While the diazonium salt formed the azo coupling preparation began. In a beaker, 0.14 ml
of N,N-dimethylaniline with 0.10 ml of glacial acetic acid was mixed. This solution was added
dropwise to the diazonium salt and stirred vigorously.





Figure 11. Azo coupling between N,N-dimethyl aniline and Diazonium Salt

This solution was kept cool for a few minutes before 1.5 ml of NaOH was added. This
was then heated for roughly 15 minutes before addition of 0.5 grams of NaCl. This was then
cooled before being put through suction filtration with the setup shown in Figure 8. The methyl
orange product was allowed to dry over the course of several days before being taken out of
funnel for weight determination.

7. Figure 12. Methyl Orange molecule after synthesis
The dyeing test consisted of dissolving 50 mg of methyl orange in 30 ml of water
containing 1 ml of sodium sulfate and concentrated sulfuric acid. The solution was placed in a
beaker where it was heated to just below boiling. At this point the four different fabrics were
soaked in the solution for roughly 10 minutes before being taken out and washed with water. The
different fabrics which included, cotton, silk, polyester, and nylon had different dye intensities
due to their different structures. The methyl orange was then used an aid base indicator to see the
difference in color when acid and bases were added.

Data and Results
Once the Methyl Orange was synthesized and dried, it was time to obtain weight
determination. The weight recovered was .51 grams. It is virtually impossible to obtain 100%
yield therefore it is necessary to determine Theoretical yield using equation number 1. From the
theoretical yield it was possible to determine percent yield using equation 2.

Theoretical Yield (g) = Expected moles(mol) * Molar Mass (g/mol) Equation 1.

Percent Yield (%) = (Actual Yield (g) / Theoretical yield (g)) * 100 Equation 2.


The following Data indicates the various molar masses of the different reagents as well as
percent yield recovered.


Table 1. Data obtained from different reagents and amount of Methyl Orange recovered.








The following table indicates the different effects the dye test had on the various fabrics.
Columns represent the different fabrics, row, indicates the description.

Table 2. Dye test results.




Sulfanilic AcidSodium CarbonateHydrogen Chloride Sodium NitriteN,N-dimethylanilineMethyl Orange
Molar Mass (g/mol) 173.19 105.98 36.46 68.99 121.18 327.33
Beginning Mass 0.2 0.6 0.25 0.08 0.1338
Moles Used 0.001155 0.000566 0.004602 0.00116 0.001104
Theoretical Yield (g) 0.55
Experimental Yield (g) 0.51
Percent Yield % 92% Nylon Polyester Silk Cotton
DescriptionOrange (stong dye)No color (No dye)Orange(Strong dye)Weak dye

8. The acid base indicator test revealed a trend in color change. When an acid such as HCl
was added to dissolved methyl orange crystals, the solution turned red. When a base such as
NaOH was added, the solution turned orange. The more acid added, the redder it got, the more
base added, the more light orange it turned.
Discussion

The beginning portion of the experiment that consisted of the formation of the Diazonium
salt was straight forward and to the point. The first step began with the dissolving of sodium
carbonate. This was done to ensure that the sulfanilic acid dissolved in the proceeding steps that
involved acidic conditions. This was followed by the addition of sodium nitrite and hydrochloric
acid. The addition of the hydrochloric acid is the step that forms nitrous acid and the precipitate
salt. The instruction manual indicated that after the addition of the reagents into the 50 ml
Erlenmeyer flask the salt would have precipitated out. This however was not observed
immediately after even when the solution was cooled.
It is clear however that the salt precipitate did form as the reaction proceeded as it should
have. The reaction would have not worked without the presence of the diazonium salt. The
addition of N.N-dimethylaniline initiated the Azo coupling portion of the synthesis. The
dimethylaniline was added drop-wise and immediately started creating a dark red solution. After
the solution was made basic, it was heated to dissolve methyl orange and thereafter NaCl was
added. This was cooled in an ice bath to ensure formation of Methyl orange crystals. The
solution was slushy and additional NaCl was added to make it easier to transfer to Buchner
Funnel. The methyl orange was allowed to dry in the lab bench over several days to ensure good
crystals. The theoretical yield was 0.55 grams and the experimental was 0.51grams. This
accounted for 92% yield.
The crystals attached to the filter paper were orange in color and were removed using a
spatula. The instruction manual called for the use of approximately 50 milligrams of methyl
orange crystals to be dissolved. Being that this was such a small amount it was virtually
impossible to weight 50 mg. A measured weight of approximately 0.10 grams was obtained and
added to 30 ml of water along with 1 ml of aqueous sodium sulfate and 1 drop of concentrated
sulfuric acid. This was the dye solution in which the different fabrics were emerged in for a
couple of minutes. The four different fabrics obtained from the UHD-stockroom were labeled
and placed into the solution. The fabrics were allowed to stay in the heated solution for roughly
15 minutes before being removed and washed. Immediately after being rinsed with water there
were several differences observed. The initial fabrics were all white in color but after the dye test
only polyester remained white. Nylon and silk were completely orange in color with nylon
having a brighter orange glow to it. Cotton did not have a strong orange color, it retained a dirty
stained look to it. Polyester remained completely white with no sign of staining. Methyl orange
is considered to be a weak acid and is therefore able to stain nylon. With the exception of the
terminal acid and amine, there are no strong polar centers in nylon. The dyes is able to penetrate
the fibers pores and is non-covalently attached to the fiber. Polyester is very difficult to dye and
does not dye the usual method. The polyester fibers are non-porous and color does not stick by
the usual methods. Polyester contains nonpolar functional groups that prevent it from staining. In
silk when methyl orange interacts non-covalently, it binds by the combination of intermolecular
interactions that include hydrogen bonding and electrostatic forces. Silk is stained orange but
not as strong as in nylon. In cotton the dye is able to penetrate the surface pours and dye the

9. material. Cotton does not dye as strong as nylon or silk due to weaker Van der Waals and
hydrogen bonding.
The acid base indication ability of methyl orange makes it very useful to identify
substances as acids or bases. Any addition of an acid will make the solution turn red while
addition of base will make it turn orange. The higher presence of protons corresponds to acidic
conditions and higher concentrations of OH will correspond to basic solutions.

Conclusions





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