Mengying Li.

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1 Investigating the Techniques of Acid- Base Extraction by separating three dye compounds & Recrystallization by purifying Methyl Orange Mengying Li Department of Chemical Engineering, The Pennsylvania State University, PA Abstract The separation technique of acid- base extraction was used to separate three unknown dye compounds that had different ph from the mixture. The identification of the unknown dyes compounds was performed based on the color of the dyes. Methyl Orange, a common dye, was synthesized and purified by recrystallization. The effectiveness of recrystallization was determined by calculating the percentage recovering. Different fabrics were also dyed and tested by methyl orange. Introduction A dye is a colored substance that has an affinity to the fiber by several intermolecular interactions. These interactions include electrostatic forces, van der Waals attraction, hydrogen bonding and covalent bonds. Good dyes have strong interactions with the fiber and will not fade or come off during the washing easily. (1) Acid- base extraction carries out simple acid/ base reactions to separate organic acids, neutral organics compounds and basic organic substance. For example, the addition of an aid to a mixture of acid, neutral and base organic compounds will make the base get protonated to form a salt. Salts are ionic and tend to be water-soluble. On the other hand, the acid and neutral compounds tend to stay in the organic layer. (2) Different dyes have different ph values. In this experiment, acid, base and neutral unknown dye compounds were separated from a mixture by acid- base extraction. After the extraction, the dyes could show their original colors and made them easy to identify. Methyl Orange [4] is a common dye that has an azo group. It was synthesized by the diazonium coupling reaction with diazotized sulfanilic acid [2] and N, N-dimethyaniline [3]. (Scheme 2) When HCl and NaNO 2 reacted, nitroso ion was formed. Nitroso ion reacted with the amine group from sulfanilic acid and formed a nitrosoammonium adduct that lost water under the acidic conditions after proton transfer. (3) This resulted in the formation of diazotized sulfanilic acid. (Scheme 1) N-N dimethylaniline was then protonated by acetic acid. The addition of sodium hydroxide neutralized the protonated amine of the N, N- dimethylaniline acetate salt and made it a good nucleophile to attack the electron deficient terminal nitrogen of the diazonium sulfanilic acid. The product might still contain other impurities besides methyl orange and further purification technique was needed.

2 Scheme 1 Diazotization of Sulfanilic Acid 1 2 Scheme 2 Synthesis of Methyl Orange Recrystallization is an important and inexpensive method for purifying solid organic compounds. First the compound to be purified is dissolved in hot solvent to become a solution. As the temperature goes down, the solubility of the compound goes down as well. The solution becomes saturated and tends to be recrystallized. The solid product from the recrystallization is the purified crude product. The impure organic compound will not form a crystalline structure and will stay within the solution. The effectiveness of recrystallization was accessed through the percentage recovery calculation of the crude product. A piece of Multifiber #43 Fabric that had 13 strips of different fiber was given and tested with the synthesized methyl orange. Different fibers had different structures and material and interacted with methyl orange differently and showed different colors. Result and Discussion Acid- base extraction of three unknown dye mixture. The acid-base extraction of a dye mixture proved to be an effective method for separation of dyes that had different ph. 1.5ml 3M HCl was used to extract the basic dye compound and 1.5ml, 1M NaHCO 3 was used to extract the acid dye compound. The neutral dye stayed in the organic layer. After the extraction, it was observed that the basic dye compound had the color between blue and purple and the acid dye compound had the color between red and purple. The neutral compound had the color of green. According to the Table 1 of possible dye unknowns from the lab guide, the neutral dye was identified to be Brilliant Green. The color between the acid and base dye compounds was too similar and it was impossible to determine the identities of these two compounds. This situation happened might caused by the change of ph. When acid compound was being extracted by the basic solution, acid compound got deprotonated and its ph increased. This resulted in the change of color. In order to make the dyes show their color under their original ph values, a few drops of HCl was added to the acidic dyes and a few drops of NaHCO 3 was added to the basic dyes. The acidic dye then showed the color of purple and the color of basic dye changed to red.

3 Thus it could be concluded that the acidic dye was bromocrescol purple, the basic dye was salfranin and the neutral dyes was brilliant green. Table 1. Possible dye unknowns (color) Acidic dyes Basic dyes Neutral Dyes Bromocrescol green (blue) Salfranin (red) Brilliant green (green) Bromocrescol purple (purple) Toluidine blue (blue) Oil red 0 (red) Quinoline yellow (yellow) Sudan I (orange) The Synthesis and Recrystallization of Methyl Orange. Methyl orange was synthesized from the diazonium coupling reaction with diazotized sulfanilic acid and N, N-dimethyaniline. The weight of the crude product was g. This exceeded the theoretical yield of methyl orange on the lab guide that was 2.5-3g. The excess water in the crude product could cause this situation. After the purification of the crude product via recrystallization using water as the recrystallization solvent, the weight of the methyl orange with certain amount of water was g and the percent recovery was 87.7%. The purification of methyl orange was successful in that it gave a good yield of desired products. However, since the crude product contained excess water, the percent yield could not be calculated precisely. In the future, using nitrogen as a way to evaporate excess water in the crude product may eliminate this problem and get better percent yield. Then the purified methyl orange was test by Multifiber #43 which had 13 strips of different fibers woven into it. The result was shown in table 2. Table 2 The result of methyl orange tested by Multifiber #43 Name of the fiber Color Acetate rayon filament 1 Light yellow SEF Fire retardant 1 Polyester, bright filament 1 Greenish yellow Cotton 1 Creslan 61 Disperse dyeable polyester 1 White Cationic dyeable polyester 1 Polyamide, nylon 6.6 Orange Polyacrylonitrile, polyacrylic 1 Silk 1 Orange Polypropylene White Viscose rayon Slightly orange Wool, worsted Red Fibers with few or no functional group on the chain accept dyes poorly. Acetate rayon fiber is cellulose that is acetylated on only two hydroxyl groups. SEF is a copolymer of the mostly acrylonitrile with vinyl chloride or bromide. Polyester, bright filament, disperse dyeable polyester and cationic dyeable polyester all contain ester functional group and few polar center within the polymer. Cotton and viscose are pure cellulose. Creslan 61 and polyacrylonitrile polyacrylic are only consisted of carbon and hydrogen and do not contain any functional groups. Polypropylene is a pure hydrocarbon polymer. Viscose rayon is regenerated cellulose. All the fibers described above do not have or have few functional groups. After these fibers were sink with methyl orange, the methyl

4 orange could easily being washed off from those fibers and left the fiber the color of white or slightly yellow. Polyamide, nylon 6.6, worst wool and silk all belong to the family of polyamide. Polyamide is a macromolecule with repeating unites linked by amide bonds, which provide many polar groups in wool, sink and nylon 6.6. The presence of these polar groups in the structures provides excellent binding sites for methyl orange, most of which are also charged. Methyl orange can have more interaction such as hydrogen bonding with these polar groups and can bind to these fabrics easily. The test result showed that only nylon 6.6, worst wool and silk were easy to dye with methyl orange due to multiple polar functional group they contain. Nylon 66 and silk had the color of orange and worst wool had the color of red. Conclusion The acid-base extraction of 3 unknown dyes mixture was effective as all the compounds were extracted and identified as expected. The similar color of the acid and base dyes could be altered and distinguished by changing their ph. The synthesis and the recrystallization of methyl orange were also successful. In the future, the usage of a high vacuum line can facilitate the drying process, evaporate as much water as possible and yield purer products. Silk, nylon 6.6 and worst wool were proved to be the best fibers to dye with methyl orange due to their multi amide bond and good interaction with the dye. Experimental General Methods All compounds were purchased from Sigma- Aldrich and used without further purification. Methyl Orange (4) Sulfanilic acid (2.712g, 13.8mmol) was dissolved in 25mL water and cooled down. Sodium nitrate (0.947g, 13.79mmol) were added to the solution and dissolved. 2.5ml concentrated HCl and g ice were also added to the mixture. A powdery white precipitated of diazonium salt was formed and treated with1.6ml of dimethylaniline and 1.25ml of glacial acetic acid. After min, a still paste appeared. Sodium hydroxide solution (18ml, 3M) was added to the paste. The mixture was heated till the boiling points and then cooled down by ice-bath. The crude product was recrystallized in water and afforded of orange paste. ( g, 87.7%) Acknowledgement I would like to sincerely and profusely thank my chemistry lab TA Steven Taylor for his guidance to the instrument usage and great support in completing my project. Reference (1)Masters, K. M. Chem 213M: Agricultural Science Module Lab Guide, Spring 2016 edition. (2) Williamson, K, L; Masters, K, M. Macroscale and Microscale Organic Experiments, 6 edition. Cengage learning, Inc, 2011 (3) Watson, S. E. Chem 122:Experiment 17 Preparation of Methyl Orange.

Experiment 17 Preparation of Methyl Orange

Experiment 17 Preparation of Methyl range In this experiment you will prepare methyl orange, an azo dye that forms beautiful orange crystals and is used as an acid-base indicator (Figure 17.1). The anion