Synthesis of 1-phenylazo-2-naphthol[1] Busog, Bea and [2]Villarante, Angelo Ismael M. [1] Institute of Biology, College of Science, University of the Philippines, Diliman, Quezon City [2] Department of Food Science and Nutrition, College of Home Economics, University of the Philippines, Diliman, Quezon City Date Performed: October 30, 2014 – November 04, 2014 Date Submitted: November 13, 2014 Abstract Azo compounds are known for their functions as dyes and coloring reagents. Formation of 1-phenylazo-2-naphthol, consists of two reactions: diazotization reactions and coupling reactions. In diazotization reactions, a diazonium salt is formed from aniline and nitrous acid (NaNO2 + HCl). While in coupling reactions, positively charged diazonium serves as the electrophile to the β-naphthol to give the coupling product. The experiment yielded 24.07% of the 0.54 g theoretically calculated result. And a 4.48%-11.19% %error range was calculated for the melting point determination. Possible errors are formation of side products and improper preparation of reagents. I. Introduction Two reactions comprise the synthesis of 1phenylazo-2-naphthol. The first of these reactions is called diazotization. This reaction forms one of the most versatile intermediate in organic synthesis, the diazonium salt. The intermediate is formed from the reaction of primary aromatic amines and nitrous acid. Figure 1.Diazotization reaction Diazo-compounds are the products formed from the coupling reaction, the second and last reaction of the synthesis, wherein the positively charged aryl diazonium ion serves as the electrophile towards the highly activated aromatic substrates such as phenols and anilines. Most of these diazo-compounds are used as acid-base indicators like methyl orange and methyl red and as food coloring agents such as butter yellow but some are used as staining agents and as textile dyes for fabric. Figure 2.Coupling reaction Textile dyes absorb light in the visible region through the functional group called augmenters called auxochromes. These includes the types –NHR, -NR2, -OH, and –OR. The simple azo dyes that were synthesized in 1-phenylazo-2-naphthol are capable of dyeing cotton as a developed or ingrain dye. Dyes that adhere firmly to the fibers without the aid of supplemental chemicals are within the method of direct dyeing. These fibers, like silk and wood, have many polar sites that bind strongly to the polar dyes such as malachite green, and methyl orange. In ingrain dyeing on the other hand, fiber such as those in cotton is impregnated with an amine, which is then diazotized and then developed by immersion in a phenol solution. The method of dyeing used is such that the dye is synthesized inside the fabric. Two components used in its synthesis will diffuse into the spaces between the fibers inside the fabric. Here, the component reacts within it forming the azo dye. In this experiment, Sudan 1 will be synthesized through diazotization and coupling reactions, its property as an ingrain dye also examined. (Organic Chemistry Manual 2014.) Levelness refers to how evenly distributed the dye is throughout the substrate. It relies on the use of the correct procedure based on the substrate and the agitation provided by the machinery being used. It is also derived from level initial padding of dye for a continuous dyeing. The resistance of a dye to removal or as well as washing with portions of cold water. causes the light to be absorbed.2 mL aniline. II.chromophores. after which 1 mL ice-cold distilled water was added. The extended conjugation of the two aromatic rings. The diazotization process starts when a proton and N is exchanged. The β-naphthol couples with the diazonium salt forming a resonance stabilized intermediate. 0. was cooled to 4C. . two-pot synthesis was used. 0. Two-pot synthesis is appropriate because it incorporates faster separation process and more efficient purification (Reusch. and maintained its temperature at below 5C. β-naphthol solution was prepared by dissolving 0. Filtering was done to the product. Coupling reaction of diazonium salt with β-naphthol.5 mL conc. Results and Discussion The synthesis of 1-phenylazo-2-naphthol consists of two reactions. or diazotization.35 mL water. the fabric was removed and pat dried. textile dyes also contain color fabric. A spatula-full NaNO2 crystal was added to the resulting cold mixture. The remaining phenyldiazonium chloride solution was added to the cold β-naphthol solution. A fabric was dyed in the β-naphthol solution. the diazonium ion was reacted with prepared β-naphthol solution. The mixture was allowed to stand at 4C for 1-5 minutes. The formation of the diazonium salt intermediate. destruction is fastness. HCl were added in a 50-mL Erlenmeyer flask. The mixture was cooled to 4C. After which weight determination was done for the % yield. In the synthesis of Sudan-1. The figure below shows the reaction. the –N=N. Aside from these chromophores. and 0. In terms of levelness though. dyeing was done. was formed by reacting aniline with HCl and NaNO 2. the ‘color bearers’. Diazotization of aniline with HCl and NaNO2 Next. thus making it have a few darkly stained lines and blotches.35 g β-naphthol in 4.in azo dyes. and melting point determination was done afterwards. Methodology In the phenyldiazonium chloride solution. III. 2013). The synthesized dye that we had made efficiently passed fastness since the red-orange dye did not wash out after several washes with water. then rinsed with running water.5 mL 5% NaOH (aq) in a 50-mL beaker. forming of the diazonium salt intermediate and coupling reactions. Prior to synthesis. from which the Nitrogen lone Figure 4. our dye was not evenly distributed all throughout the Figure 3. It is achieved mainly on the selection of dyes. This is the coupling reaction. It also depends on the removal of hydrolyzed reactive dye. Recrystallization was done using minimal hot ethanol. After which the fabric was immersed in the phenyldiazonium chloride solution. After soaking for 2-3 minutes. ranging from 119-140oC as oppose to the theoretical melting point of 134o C. If it was prepared under acidic conditions.position. After the fabric was soaked in the β-naphthol solution and pat dried.9% In the experiment.and ortho. Thus it would only react with strongly activated compounds.13 g 0. having it at only 24. we were able to obtain the melting point of the pure Sudan 1 within the range of 115-120oC and the crude. thus the product is formed by the ortho.positions with respect to activating substituent of benzene (McMurry. However. The figure below shows the reaction under basic conditions. As explained on Chemistry Section of the National Programme on Technology Enhanced Learning. 1955). When done at higher temperatures a possible side reaction may occur. delocalization of ions causes the salt to be a weak electrophile.07% Table 2. g Theoretical Yield %yield 0. which reacts with the benzene ring.19%. C Theoretical Melting 134% Point. Upon immersion.54 grams. Experimental Results 1-phenylazo-2naphthol. 2012). Diazotization under basic conditions. Table 1.positions. if the phenyldiazonium chloride was done in a basic medium. The purity of the synthesized dye that we obtained theoretically was accurate and close enough to the theoretical yield. thus it cannot produce strong interactions with anions or cations (Department of Textile and Apparel Figure 7.position is unstable due to unavailability of Hydrogen for substitution. in this case naphthol. Possible sources of error in the experiment could come from the preparation of the reagents used . as explained on the Chemistry Department of the Northern Virginia Community College. the βnaphthol will be protonated to form a salt. Figure 6. Melting Point Determination Experimental Melting 115%-120% Point.07% with an actual yield of 0. The figure below shows the detailed reaction mechanism. Afterwards. The percent yield we had obtained in the experiment was unexpectedly low. ingrain dyeing was done.and ortho. having OH as the strong activator (as seen from the intermediate). Figure 5. it reacts readily at weakly basic conditions. When the fabric was washed. C %error 4.48%-11. This indicated the synthesis of desired azo dye. the reaction mixture’s temperature was maintained at below 5C to prevent decomposition.54g 24. Sudan-1 The table below shows Experimental Results and Melting Point Determination (See Data Sheet for Calculations). Carbon 1 was attacked because the OH is in the para. Throughout the reaction process.48% to 11.pairs form triple bonds of N from NaNO 2 (DeTar et al. β-naphthol was prepared under basic conditions because as a phenol. the color was not washed off. Cotton lacks in strong polarized groups. Using the crude melting point range. the fabric’s color turned to orange. the diazonium salt is reduced to an aryl radical. Diazonium ion resonance forms. the percent error ranges from 4. indicating the dye was trapped between the fibers of the fabric. From the figure above. the fabric was immersed in the phenyldiazonium chloride solution. the para. The diazonium salt attacks the carbons at para.13 grams and a theoretical yield of 0. However. University of Washington). Belmont. Conclusion The experiment was successful in synthesizing Sudan-1 from the diazotization of aniline. Quezon City. 2008).missouri. W. [2] DeTar. 2014 [5] Synthesis of an Azo Dye. M. National Programme on Technology Enhanced Learning. < http://cotton. Department of Textile and Apparel Management. 2014.nvcc.edu/ > Acessed on November 10.in/ > Accessed on November 11. [4] Chemistry Section. 77(7). 2013.html > Accessed on November 12. Institute of Chemistry. North Virginia Community College. Another thing to be taken into account would be the formation of side products that may have formed during the reactions in the experiment.F and Turetzky. which yielded a 24. [3] Reusch. The calculated results could have deviated from the aforementioned discrepancies in the previous paragraph. University of Missouri.edu/ > Accessed on November 12. IV. References [1] McMurry. [6] Department of Chemistry. 1-phenylazo-2-naphthol (an azo dye) with big molecules can permanently diffuse the color into the fibers.edu/index. Organic Chemistry.chemistry. 2014. 2014. Michigan State University. only 0. University of Washington. . [7] Project Cotton.07% from the 0. The red-colored appearance of Sudan 1 with the structure below is because of delocalization. University of Missouri. 1955.N. p1745-p1750. < http://www. The light is absorbed in the visible region once it has synthesized in the fabric through the functional group called chromatophore and color deepeners called auxochromes (Department of Chemistry. cotton cannot produce interactions with 1-phenylazo2-naphthol. The Mechanisms of Diazonium Salt Reactions. < http://nptel. < http://depts.54 grams of the calculated theoretical yield. Organic Chemistry Academic Group.msu. Reaction of Amines. 2008. D.Management. University of the Philippines Diliman.13 grams of Sudan-1 was recovered.edu/ > Accessed on November 11. From the aforementioned statement. Journal of the American Chemical Society. 2014.. California: Brooks/Cole CENGAGE Learning. 2012. By using ingrain dyeing instead of direct dyeing. Department of Chemistry. V. These side products are the result of not being able to prevent keeping the temperature at 4oC. [8] Organic Chemistry Laboratory Manual. < http://www.washington. the purity of it. Department of Chemistry. J.ac. itself. or in the preparation of the 1-phenylazo-2-naphthol.