Synthesizing 1-Phenylazo-2-Naphtol Lab Report

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The experiment made use of two reactions in synthesizing 1-phenylazo-2-naphtol, also known as Sudan-1. The first is the diazotization reaction in which a diazonium salt is formed from the conversion of primary aromatic amines, such as aniline, to compounds with the nitroso functional group using a nitrous acid, such as HNO2. The diazonium salt was then used as an electrophile in a coupling reaction with an aromatic compound, β-naphthol. Recrystallization was conducted and yielded 0.18 g of a red-orange compound. The percent yield was determined to be 33.33%, based on the theoretical yield of 0.54g. Through soaking a fabric with the phenyldiazonium chloride dye, its ingrain property was also determined. The experiment was able to synthesize …show more content…
This benzenediazonium cation was then used for the azo coupling reaction with β-naphthol leading to the formation of an azo compound precipitate. The objective was to produce 1—phenylazo-2-naphthol or Sudan-1 and to test the ingrain property of the produced compound as well as the determination of its melting point.
II. Methodology A 50-mL Erlenmeyer flask was used to mix 0.2 mL of aniline, 0.35 mL of water and 0.5 mL of concentrated HCl for the synthesis of the phenyldiazonium ion. The mixture was cooled in an ice bath until the temperature reading reached and maintained at about 4°C, with the help of rock salts. About 1 mL of ice cold water and a spoon-full of NaNO2 were added to the cold mixture.
While keeping the resulting mixture below 5°C, in a 50-mL beaker, 4.5 mL of 5% aqueous NaOH was added and 0.35 g of β-naphthol crystals were dissolved in it, which resulted to the β-naphthol solution. This was also cooled in an ice bath, maintaining the temperature at approximately
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The product was allowed to cool for a certain amount of time until it completely dried before the weight was determined. A small portion of the synthesized crystals were used to determine the compound’s melting point. III. Results and Discussion The synthesis of phenyldiazonium chloride is made possible by reacting aniline with NaNO2 in an acidic environment. HCl reacts with NaNO2 forming the nitrous acid desired, HNO2 [6]:
H+(aq) + NO2-(aq)  HNO2(aq) (1) The whole reaction was done in a cold environment since at high temperatures, a different compound is produced along with nitrogen gas as a side product [6]:
C6H5NH2 + HNO2  C6H5OH + H2O + N2 (2) The desired compound was produced at low temperatures, in which the lone pair from the amine group of the phenyldiazonium ion attacks the positively charged N from the NO+ ion, leading to a hydrogen leaving the -NH2-N=O group. An alcohol is then formed through resonance stabilization and will react with a free hydrogen ion to form a better leaving group, -OH2. Water leaves the compound which leads to the production of a resonance stabilized cation, phenyldiazonium.

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