Fr3 Synthesis of 1 Phenylazo 2 Naphthol

THE SYNTHESIS OF 1-PHENYLAZO-2-NAPHTHOL

ABSTRACT

I. INTRODUCTION

Azo-compounds, compounds with general formula patterns are coupling products from the reaction of arenediazonium salts with phenols and other amines. Azo dyes are easily prepared using the coupling mechanism resulting to its cheap large-scale manufacturing cost. Azo compounds are brightly colored compounds due to optical reactivity with light of it chromopore functional group, . “Sudan-1” of 1phenylazo-2-naphthol is synthesized in this experiment. Dyeing the textile using azo-dyes requires different techniques in accordance to the nature of the textile fabric to be processed. A textile which cannot be dyed using simple adsorption undergoes ingrain dyeing wherein the azo dye is made right in the middle of microspaces between the fabrics. The general reaction pattern for Sudan synthesis first undergoes azotization and then coupling reaction with highly activated aromatic compounds.

II. METHODOLOGY

Figure 1. The general reaction pattern for the azotization-coupling reaction includes two-step process. The physical properties of the obtained crystal such as melting point and boiling point are then determined to provide comparison with commercially produced Sudan dyes.

III. RESULTS AND DISCUSSION Aniline is reacted with NaNO2 crystals under extremely acidic solutions using HCl or H2SO4 in a very cold temperature. The phenyldiazonium intermediate easily decomposes back into its aniline counterpart at slightly higher temperature, thus the solution is maintained in an ice bath a constant temperature of 5OC. The reaction for diazotization process is:

Figure 2. The formation of azonium salt is achieved by the azotization reaction at 0OC. The diazonium salt by-product is very reactive. It can be used to yield different kinds of substituted benzene products like aryl halides, aryl amide and phenols. Alkyl amine can also be synthesized by reacting it with NaNO2 or HNO2 to yield alkanediazonium product; however, the reaction by product cannot be isolated due to its high reactivity. The azotization process starts with the bimolecular exchange of proton and N, in which the nitrogen lone pairs create triple bonds with the N from NaNO2.

Figure 3. The mechanism of formation of azonium ion by the bimolecular attack of nitrite to the aniline. The phenyldiazonium salt byproduct then undergoes either nucleophilic substitution of diazonium-coupling reaction. In diazoniumcoupling reaction the diazonium salt attacks the carbon in the para- and ortho- position with respect to the activating substituent of the benzene. For this experiment β-naphthol couples with the diazonium salt forming a resonancestabilized intermediate.

Figure 4. The coupling reaction of the diazonium salt with β-naphthol occurs with the attack of the diazonium salt with on the paracarbon of the β-naphthol. The attack of the diazonium salt the carbon next to the –OH in the β-naphthol is favored due to the presence of more resonance representation for the products.

Figure 6. Side reaction due to the nucleophilic substitution of a nucleophile such as –OH or – NR2 with the azo-group in th ediazonium salt. The decomposition of diazonium salt also occurs if the solution is not kept at the advised temperature. The diazonium salt easily reverses back to aniline a slightly higher temperature than the boiling point. The overall result is the low percent yield for the azo compounds.

Figure 5. Some of the resonance structure of the coupling reaction intermediate. The final coupling product is “Sudan-1” or 1-phenylazo-2-naphthol azo dye. Rock salt is added in the ice bath because in induces the colligative property of solution called freezing point lowering. Thus, ice melts at a much lower temperature below OOC. Among the possible side reaction in the experiment is the direct substitution of any nucleophile present in the interacting solution. In this case the diazonium salt in the reaction can be made into a phenol by the direct substitution of –OH in the solution. Other nucleophiles such as –NR2 or –NH2 can also easily substitute the azo-group in the intermediate salt.

A good dye is the one that bonds perfectly well with clothes’ fiber. The presence of functional group responsible for the intermolecular attraction of the dye molecules and the fiber ensures adhesion of the dye to the textile. An ideal dye should then contain groups that bonds with most types of fabrics. “Sudan-1” contains molecules incapable of direct bonding with the cotton fiber. The adhesion between the Sudan molecules and the cotton fiber is very weak. In cases like this, ingrain dyeing is the most appropriate for this application. In the process of ingrain dyeing, the Sudan dye is synthesized right in the spaces between the fibers such that they are permanently trapped inside the fiber spaces of the cotton. Application Diazotization products are powerful reaction intermediate that can be used to synthesize many monosubstituted aromatic compounds. The following amine pair and aryl compounds are used to synthesize the final product shown on the right. Synthesis of butter yellow a (artificial colors of butters) can also be produced using the usual azotization and coupling reaction. Butter yellow is primarily used nowadays to study carcinogenesis and other medicine related chemical reactions. Recommendation

IV. REFERENCES

Alsoph, C. et al. Elements of Organic Chemistry as Revealed by the Scientific Method. Massachusetts: Addison-Wesley Publishing Company. 1996 Brown, W. H. et al. Introduction to Organic Chemistry 3rd edition. New Jersey: John Wiley and Sons, Inc. 2005. McMurry, J. Organic Chemistry 6th edition. New York: Brookes/Cole-Thomson. 2004. Organic Chemistry Laboratory Manual. Institute of Chemistry, University of the Philippines Diliman. 2006. Young, H. et al. University Physics. Massachusetts: Addison-Wesley Publishing Company. 2004.