Synthesis of 1-Phenylazo-2-Naphthol 1-Phenylazo-2-Naphthol
Natalie B. Nisce College of Home Economics, University of the Philippines, Diliman, Quezon City Date Performed: February 14, 2014 Date Submitted: March 5, 2014
Abstract The objective of the experiment w as to synthesize 1-phenylazo-2-naphthol, or Sudan 1, from phenyldiazonium chloride solution and -naphthol solution. The general reaction patterns for Sudan 1 involve diazotization and then coupling reaction with highly activated aromatic compounds. The experiment yielded 1.26g crude Sudan 1 dye which is 217% of the 0.58g theoretical yield. This discrepancy in yield can be accounted for by the possible presence of contaminants in the unrecrystallized crude product. The melting point of the product was determined to be within 118125, not too far from the theoretical range which is 131-133 ensuring that our results are somehow accurate. I. Introduction
Azo compounds have the functional group RN=N-R', where R can be either an aryl or an alkyl group. In the synthesis of an azo dye, the diazotization and the coupling reactions are employed. In diazotization reaction, a primary aromatic amine reacts with nitrous acid to form a diazonium salt. For the coupling reaction, t he diazonium salt becomes electrophilic towards the activated aromatic substrates to produce the coupling product.
Figure 1. General mechanism of diazotization and coupling reactions Azo dyes are often brightly colored and have been used commercially due to its simple preparation and cheap large-scale manufacture cost. Azo dyes are suitable for cotton, rayon, silk, and other cellulose-based fibers. The specific combination of the diazo salt and naphthol determines the color obtained. An advantage of
this dye is that it does not bleed and mix with other contrasting colors when placed side by side. People from India, Australia, and Indonesia have been using azo dye in their c rafts for thousands of years. However, in the United States, azo dyes have been banned for commercial use as food additives and in crafts supplies due to its possible carcinogenic effects. Despite its diminishing use, the synthesis of Sudan 1 is still a beneficial procedure t o perform in the laboratory because the mechanisms behind the experiment are relevant in the study, understanding and application of organic chemistry. One example is the synthesis of butter yellow, the artificial color additive for butter. Butter yellow is also produced t hrough the diazotization and coupling reac tions. Today, butter yellow is primarily used to study carcinogens and other medical chemical reactions. The purpose of this experiment is to synthesize Sudan 1, a bright red azo dye, using aniline as the primary aromatic amine reacted with -naphthol solution. The melting point of the crude product was also used determined. II. Methodology
To prepare the phenyldiazonium solution, 0.2mL aniline was added into a 50mL Erlenmeyer flask 1
along with 0.35mL distilled water and 0.5mL concentrated hydrochloric acid. The mixture was cooled in an ice bath until its temperature reached 4. Adding rock salt into the ice bath induces freezing point lowering to make the required temperature attainable. Once the mixture was at the required temperature, 1mL ice-cold distilled water was added into the mixture. Then, 0.33g of sodium nitrite crystals were gradually added. The temperature of the mixture was kept below 5. The -naphthol solution was prepared by dissolving 0.38g of -naphthol in 4.5mL 5% sodium hydroxide. The solution was cooled to 4 an ice bath. Still in the ice bath, a piece of fabric was dipped into the -naphthol solution for 2-3 minutes. The fabric was then retrieved from the solution and dried between filter paper.
Figure 3. Fabric in phenyldiazonium chloride solution The remaining phenyldiazonium chloride solution was slowly added to the -naphthol solution. After 5 minutes, the product was filtered, washed with cold distilled water and then dried.
Figure 4. Crude Sudan 1 dye Figure 2. Fabric in -naphthol solution Then, the fabric was again immersed, t his time in the phenyldiazonium chloride solution and instantly, the fabric turned bright red. After several minutes, the fabric was removed and rinsed in running water. Gloves were wor n throughout this process due to the possible carcinogenic effects of the product compound.
The melting point of the product was determined by crushing a sample of dried crude Sudan 1 dye and pressing it into a capillary tube. The capillary tube was then attached to a thermometer and both were submerged partially in a beaker of oil. The beaker was heated over a hot plate. As the Sudan sample began to disappear inside the capillary tube, the temperature was noted. Once the Sudan sample disappeared completely, the temperature was noted again.
III. Results and Discussion
The reaction between aniline and sodium nitrite crystals in the presence of concentrated hydrochloric acid needed to take place inside an ice bath because the 2
phenyldiazonium intermediate may convert back into aniline at higher temperatures.
Possible side reactions include the production of phenol by the direct substitution of OH from the solution to the diazonium salt. - can also attach the diazonium salt and substitute the azo-group to form side products.
Figure 5. Formation of diazonium salt The diazotization reaction begins with the bimolecular exchange of a proton and nitrogen. As a result, the nitrogen lone pairs create triple bonds with the nitrogen from sodium nitrite.
Figure 6. Formation of diazonium ion In coupling reaction, the diazonium salt reacts with carbon 1 of -naphthol to form a resonance stabilized intermediate. –OH donates its lone pair to Carbon 1 making it more electron rich. The diazonium salt attacks at carbon 1 of -naphthol since the intermediate formed is the most stable.
Figure 8. Side reaction when a nucleophile substitutes the azo-group A good dye must be safe for humans. It is unacceptable to use dyes that may be toxic or have hazardous effects on humans. A good dye must be able to adhere completely to the fiber of the product being dyed. The dye must not bleed when washed nor fade from wear and tear. To ensure this, a good dye must contain functional groups that bond intermolecularly with many surfaces. Sudan 1 is generally non-polar. It does not have functional groups that are compatible with the functional groups in cotton, which is generally polar due to its –OH groups. For Sudan 1 to be an effective dye on cotton, the ingrain dyeing process must be used. In ingrain dyeing, Sudan 1 is synthesized right in the presence of the cotton, as was done in the experiment, and so the dye is permanently trapped within the fibers of cotton. Theoretically, 0.58g of 1-phenylazo-2naphthol should have been produced. However, because the recrystallization procedure was omitted, the total product after the experiment came out to 1.26g, which is 217% yield. The over amount of yield may be due to contaminants and impurities present in the crude Sudan 1 product. The determined boiling point, 118-125 further supports that the product was not pure because the theoretical boiling point of 1phenylazo-2-naphthol is 131-133. IV. Conclusion
Figure 7. Coupling reaction
The objectives of the experiment were met since 1-phenylazo-2-naphthol or Sudan 1 dye 3
was successfully produced from phenyldiazonium chloride solution and naphthol solution. The final result is a yield of 1.26g Sudan 1, a bright red azo dye. The actual yield is 21 7% of the theoretical yield, 0.58g. If the experiment were to be performed again, I suggest that the recrystallization of the crude Sudan 1 be performed to ensure a pure final product.
V. References
Brown, W. H. et al. (2005). Introduction to rd Organic Chemistry, 3 ed . New Jersey: John Wiley and Sons, Inc. th
Chang, R. (2010). Chemistry, 10 ed. New York: Mc Graw Hill International. Curtin, D. Y., Fuson, R. C., Hermann, C. K. F., Morill, T. C., & Shriner, R. L. (1998). The systematic identification of organic th compounds, 7 ed. New York: John Wiley & sons, Inc. Eaton, D.C. (1989). Laboratory Investigations in Organic Chemistry . McGraw Hill Book Co., USA. th
Mc Murry, J. (2004). Organic Chemistry, 6 ed . New York: Brookes/Cole Thomson. Zubrick, J. W. (1997). The organic chem lab th survival manual, 4 ed. New York: Wiley.
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