DATE PERFORMED: SEPTEMBER 14, 2011Synthesis of 1-Phenylazo-2-naphthol R.J. Bitare2, M.C. Endico1, & D. D. Orbe2 Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101 Philippines 1 Department of Chemical Engineering, College of Engineering, & 2Department of Psychology, College of Social Sciences and Philosophy, University of the Philippines, Diliman, Quezon City, 1101 Philippines ABSTRACT Synthesis of azo compounds can be achieved via the process of diazotization and subsequent azo coupling. In order to verify this reaction, 1-phenylazo-2-naphthol, commonly known as Sudan I, was synthesized via the reaction of a phenyldiazonium chloride solution with a basic β-naphthol solution. The crude product obtained was then subjected to recrystallization and its melting point was obtained. Its property as an ingrain dye was also examined. Through the prescribed procedures, a 55.2 % experimental yield, presumed to be pure 1phenylazo-2-naphthol, was obtained. The melting range obtained for the product was 80–84 oC, far-off from the theoretical value of 131 oC. Despite not being as close as theoretically predicted, the occurrence of the said reaction is still confirmed by the obtained experimental results. Introduction Azo compounds are organic compounds which bear the functional group R-N=N-R’ in which the hydrocarbons can be either an aryl or alkyl; they are formally defined as derivatives of diazene (diimide), HN=NH, wherein both hydrogens are substituted by hydrocarbon groups. [8] Azo compounds are often vividly colored, mainly due to their highly conjugated structure. Because of this property, azo compounds are usually used as dyes. One such example is 1-phenylazo-2-naphthol, more commonly known as Sudan I, an orange-red powdered substance. It was previously used as dye for textiles and as food coloring but was subsequently banned for such uses due to its carcinogenicity. Azo compounds are usually synthesized through diazodium coupling reaction, a type of electrophilic aromatic substitution. In order to synthesize an azo compound, arenediazonium salt is reacted with activated aromatic rings like phenols and other amines. The amine component of the compound must be less activated the coupling component. Meanwhile, the nitrogen in the salt serves as a bridge between the two rings in the reaction. The synthesis of 1-phenylazo-2naphthol utilizing aniline and β-naphthol is a two-step process involving diazotization and azo coupling, as shown by the following reaction diagram:[4] To pre-test the synthesis reaction. As such. patted dry with filter papers and immersed in the phenyldiazonium chloride solution. it doesn’t react or bond well with cotton fabric because of the lack of functional groups in the fabric. Experimental Detail Synthesis of 1-phenylazo-2-naphthol is divided into two major procedural reactions: the diazotization reaction and the coupling reaction. ingrain dyeing was done. this experimental methodology follows the same trend with the addition of ingrain dyeing as an application procedure. It was then removed. As a result.35 mL water and 0. The mixture was still maintained at about 4° C for 1-5 minutes before filtering the product and washing it with small portions of cold water. a 2 by 3 cm fabric was first soaked in the cold β-naphthol solution for about 2-3 minutes. After some more minutes. 0. 0. As a counter method to this limitation.NH2 + N N a N O 2 /H C l/H 2 O N Cl - OH N N a O H /H 2 O N OH Figure 1. a prominent red-orange dye formed within the fabric. The red-orange dye remained in the fabric. After the ingrain dyeing. ingrain dyeing was developed. There are two main preparations that were done during the course of this experiment: 1) preparation of the diazonium salt (phenyldiazonium chloride) solution and 2) preparation of the β-naphthol solution.5 mL 5% aqueous NaOH in a 50-mL beaker. synthesis of Sudan-1 using the combination of what remained of the 2 preparations was set. it was removed from the solution and rinsed well with running water. 0. To prepare the diazonium salt solution. This crude product was recrystallized .3 g of NaNO2 crystals was gradually added while maintaining the temperature below 5 °C. To do this. A β-naphthol solution was prepared by simply dissolving 0. General reaction to synthesize 1phenylazo-2-naphthol via azotization and coupling reaction This experiment aims to synthesize 1phenylazo-2-naphthol via the aforementioned reaction.5 mL concentrated hydrochloric acid were combined in a 50-mL Erlenmeyer flask strictly following the sequence of introduction as stated here. Instead of producing the dye independently then applying it to the fabric. As with the diazonium solution. A cold mixture was produced after 1-mL of cold distilled water was combined into the mixture.2 mL aniline. To this resulting mixture. The solution was then subjected to a decrease in temperature via an ice bath to about 4° C. Because of the nature of the Sudan-1 (1-phenylazo-2-naphthol) dye. this preparation was cooled down and maintained at a temperature of about 4 °C. Sudan-1 is synthesized inside the fabric so that it will be trapped in the individual fabric components where it will be formed.35 g β-naphthol in 4. Phenyldiazonium chloride solution was added into the β-naphthol solution slowly while stirring. the melting point of the product was determined using the common hot oil immersion technique. the reaction mechanism is as follows: N Cl Cl - N H - C o u p lin g .3 g of 1-phenylazo-2naphthol upon experimentation. The ability of amines to give ortho and para products shows that even in acidic medium.2% 80-84 oC The red-orange azo dye 1-phenylazo-2naphthol was obtained through the reaction of a diazonium salt intermediate formed from aniline with β-naphthol.19 mmol. dried and weighed along a pre-weighed filter paper to determine the over-all yield in the synthesis reaction. at very highly acidic concentrations.30 g 0. Cl + N - N aN O 2 + H C l D ia z o t iz a t io n OH N Cl Results and Discussions Table 1.H Cl N O + H N N OH Diazonium coupling of aromatic diazonium ions normally happen only with active substrates such as amines and phenols. Therefore.using minimal portions of hot ethanol in a steam bath.54 g 55. The expected yield was . + NH2 NH3 H Cl Finally. However. The latter may have been caused by an inefficient set-up while the former is being attributed to potential lapses during the filtration phases. Considering the size of the attacking species (in this aromatic electrophilic substitution). they are reacting in un-ionized forms.35 g of β-naphthol produced 0. 0. Of a very conspicuous note would be the discrepancy of the experimentally-determined melting point and that of what was theoretically proposed. The resulting red crystals were collected.2 mL of aniline and 0. This is the reason why . The experimenters posit 2 possible sources of error for this inconsistency: 1) a large amount of impurity in the final product and 2) a self-imposed miscalculation during the actual melting point determination.54 g or 2. Experimental Results OH + Weight of Sudan I Theoretical Yield Percent Yield Melting Point N 0. the experimental yield is just 55% of what could have been produced in a total and perfect synthesis. substitution occurs mostly in the para position relative to the activating group. no reactions occur because the concentration of free amines becomes too small. both of which are strongly activating ortho-para directors. For the particular method of synthesizing 1-phenylazo-2-naphthol perfomed in the experiment. there are also 2 possible side reactions that may result into 2 unwanted product formations. other dyes that can be prepared via a similar format include: O OH N N 1. + Nuc N N + Nuc a c id Figure 3. CH3 N CH3 . there are 2 possible ways of coupling with the β-naphthol. As shown in the figure above. this may also be a source of error as the pH levels weren’t monitored in the entire experiment. The nucleophile may substitute the nitrogen in the diazonium salt and may form other aromatic compounds like phenol. However. In addition to our product of interest. it was classified as a category 3 carcinogen [10]. the dye must be perfectly bonded with the material of the cloth. The best dye is the one which is capable of being absorbed by most fibers.e. The functional groups present in the dye determine the strength of adhesion between the dye and the textile. which can be prepared by using aniline as the amine and β-naphthol as the coupling component. A dye is considered ideal if it is absorbed by the target fibers efficiently. Consequently. The second one is the possibility for a decomposition reaction due to heightened temperatures. As discussed earlier. of these 2. For this to happen. Sudan 1 is not an efficient dye because its particle sizes and its reactivities are not efficient for use with certain textiles (i. [7] N N H N H O + + H C N OH Figure 2. Side reaction wherein a nucleophilic substitution involving nucleophiles such as –OH occurs. . This is particularly due to unmatched structures that inhibit direct bonding. Aside from 1-phenylazo-2-naphthol. This dye may have a structure ideal for bonding with the material of mostly used textiles. Resonance structure of the attack of the diazonium ion on carbon 1 of β-naphthol.concentrations of acidity are controlled in this experiment. In this case. The first one is the direct substitution of a nucleophile present in the interacting solution. the substance is potentially harmful and may cause cancer in humans. However. the attack on carbon 1 is preferred because it favors retaining the resonance-stabilized structure of the ring and sets the positive charge at a position favorable to the entire synthesis. the product reverts back to aniline (the reverse reaction of what is in Figure 1). Meaning. Practical applications for the main product of this synthesis reaction was said to be in the field of dyeing. cotton). O which can be prepared by using OH O NH2 CH3 NH2 HO S O O CH3 as the amine and component. but it also opens up concerns about sound experimental techniques used by the experimenters during the course of the experiment. This. the fact that 1-phenylazo-2-naphthol was produced and had given a positive qualitative result (redorange dye) validates the theoretical reaction of diazotization and its corresponding coupling reaction. Not that this only severs an empirically tested and theorized physical property of Sudan 1 (melting point).2% yield of a probably still impure sample of Sudan-1. N CH3 2. the experimenters recommend further investigation on more efficient ways of a total organic synthesis for 1phenylazo-2-naphthol. a complementary test (melting point determination). With this at hand. Conclusion H3C The final results show that the experiment was able to give a 55. OH O OH NH2 O OH S N O S O OH S CH3 O O N O O N NH2HO N HO S O O Regardless of the percent yield. OH O which can be prepared by using N OH NH2 S as the amine and as coupling H3C N O O CH3 as coupling N component. and as coupling 3. in correspondence. . tells us that the primary objective of this experiment to prove that an azo dye synthesis exists via the said reactions has been satisfactorily reached. ‘ . Despite all this. seem to be a problematic issue in this experiment. NH2 which can be prepared by using as CH3 N CH3 the amine and component. 19 mmol Sudan I × 0.. UP Diliman.uga. 2011.). T. B. [7] March.edu/chem36/Web %20Syn06/Exp31Syn06.21mmol Sudan I 248. W..uk/webprojects2002/pric e/azo.-U. V. J. Retrieved September 19. Hammond. Quezon City: Institute of Chemistry. 2011.d.2 mL Aniline × 1cm3 1. Diliman.edu/diazotization.A.References [1] Bristol.21mmol Sudan I =55.19 mmol Aniline × 1 mmol Sudan I =2. from Chemistry of Dyes: http://www. (n. 719-720. [3] Carey. Experimental Organic Chemistry. Organic Chemistry (5th ed. 2008. W. Moustafa G..ac. J.. U.). Mol.35 g β −naphthol × 1mol β −naphthol =2. [9] Mohrig. [4] Chemistry. from http://courses. E.28 g Percent Yield: Yield= 1. T. Diazotization reactions. Freeman. L.R. "The induction of cytochrome P450 1A1 by sudan dyes". E. J. 1968. P. F. Iverson. S.htm [2] Brown. S. United States of America: Brooks/Cole Cengage Learning. C.chem. Synthesis of the Dye Sudan I. 289291. Organic Chemistry (3rd ed.C. Foote. Neckers. [8] McMurry. Theoretical yield: 2.30 g Sudan I × 1 mol Sudan I =1..2 2. Morrill.). C. Organic Chemistry (7th ed.psu.43 mmol β−na 144. 22 (2): 77–84.17 g ∴ Aniline is thelimiting reagent .54 g Sudan I 1mmol Sudan I Actual Yield: 0.pdf [5] Georgia. (2005). 941-945.19 mmol Sudan I 1 mmol Aniline 2. Ibrahim Z. Fujita S.Q. 1998. (2008). Singapore: Thomson Learning.G.1265 g cm 3 0.. Biochem. Azo Dyes. Sakamoto K. (1996). & Anslyn.d. C. [10] Refat N.019 g 1 mol C 6 H 5 CH 2 OH × × =2 mL 93.). A. D. University of the Philippines. (n.19 mmol Sudan I .24828 g =0. 398-400.). Ishizuka M. USA: McGraw-Hill. (2002). from http://asmehta. S.. o...bris. 2011. Retrieved September 19... N.. H. McGraw-Hill.chm. Toxicol. Retrieved September 20.S.htm l [6] Institute of Chemistry. J. Appendix Calculations: 0. Organic Chemistry Laboratory Manual.myweb. (2008). Advanced Organic Chemistry.H.