Synthesis of Methyl Orange Dye: Adding color

Juan A. BarreraUniversity of Houston-Downtown

One Main StreetHouston, 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.

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

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

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 MethodsTo 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

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.

Figure 10. Methyl Orange Test[7]

ExperimentalThe 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.

Figure 12. Methyl Orange molecule after synthesisThe 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 ResultsOnce 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 Acid Sodium Carbonate Hydrogen Chloride Sodium Nitrite N,N-dimethylaniline Methyl OrangeMolar Mass (g/mol) 173.19 105.98 36.46 68.99 121.18 327.33Beginning Mass 0.2 0.6 0.25 0.08 0.1338Moles Used 0.001155 0.000566 0.004602 0.00116 0.001104Theoretical Yield (g) 0.55Experimental Yield (g) 0.51Percent Yield % 92%

Nylon Polyester Silk Cotton

Description Orange (stong dye) No color (No dye) Orange(Strong dye) Weak dye

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

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

[1] Zhihui X, Ming Z, Jingyu W, Jianru L, Lixiang Z, Bo L. Visible light-degradation of azo dye methyl orange using TiO2/β-FeOOH as a heterogeneous photo-Fenton-like catalyst. Water Science & Technology [serial online]. November 15, 2013;68(10):2178-2185. Available from: Academic Search Complete, Ipswich, MA. Accessed April 5, 2014.

[2] Palmer, R. J. 2001. Polyamides, Plastics. Encyclopedia Of Polymer Science and Technology. doi:10.1002/0471440264.pst251

[3] PET: From Water Bottles to Polar Fleece, recycling in action!by Jeffrey Gotro on March 4, 2011http://polymerinnovationblog.com/pet-from-water-bottles-to-polar-fleece-recycling-in-action/

[4] Cao T, Wang Y, Zhang Y. Effect of Strongly Alkaline Electrolyzed Water on Silk Degumming and the Physical Properties of the Fibroin Fiber. Plos ONE [serial online]. June 2013;8(6):1-8. Available from: Academic Search Complete, Ipswich, MA. Accessed April 5, 2014.

[5] Structure and morphology of cellulose by Serge Pérez and William Mackie, CERMAV-CNRS, 2001. Chapter IV.

[6] Nishiyama, Yoshiharu; Langan, Paul; Chanzy, Henri (2002). "Crystal Structure and Hydrogen-Bonding System in Cellulose Iβ from Synchrotron X-ray and Neutron Fiber Diffraction". J. Am. Chem. Soc 124 (31): 9074–82. doi:10.1021/ja0257319. PMID 12149011.

[7] Sandberg, Richard G.; Henderson, Gary H.; White, Robert D.; Eyring, Edward M. (1972). "Kinetics of acid dissociation-ion recombination of aqueous methyl orange". The Journal of Physical Chemistry 76 (26): 4023–4025. doi:10.1021/j100670a024.

[8] Padias, Anne B. Organic Chemistry Laboratory Manual. 4th Edition; Hayden-McNeil University of Arizona 2013