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CHEM 214
David Harpp

Chemistry 222 Fall 2012 1 By: Krishnaa Siva Date: November 8, 2012, Thursday 1:30-5:30 PM Lab Group TA: Mathieu Bedard Experiment 6: Azo Dyes 1. Objective: 1 mark What is the purpose of this experiment? The purpose of this experiment is to prepare the azo dye of methyl red by the diazonium coupling reaction of N,N-dimethylaniline with Anthranyl diazonium chloride, which was obtained from the Anthranilic acid. Use the melting point test to check if it was indeed methyl red that is produced. 2. Introduction: 2 marks Brief description of the concept/reaction studied – azo dyes, electrophilic aromatic substitution The basic structure of an azo dyes is Aromatic group-N=N-Aromatic group'. Azo group is the name of the structure that has the nitrogen double bond. Azobenzene derivatives have a conjugated pi-electron system, which cause the absorption of different wavelengths of light and is the reason why we witness a colored compound. Azo dyes are synthesized by the conversion of the primary amine (R-NH2) into a diazonium salt with the help from substances such as sodium nitrite and then have this salt react with another substance that contains an aromatic ring (ex. Dimethylaniline). It is the electron releasing resonance effect that allows for the reaction between the diazonium salt (the electrophile: diazonium cation) and the aryl unit. The regioselectivity in the diazonium coupling reaction is at the para position due to the presence of the large phenyls and alkyl groups. 3. Reaction Equation: 2 marks Include proper structures and data for reactants and products [molar mass, concentration, density, volume, mass, moles, etc – including theoretical yield] Chemistry 222 Fall 2012 2 Molar Boiling mass Melting Point Density (g/mol) Point ( ̊ ) ( ̊ ) (g·cm−3) Volume/ Mass Moles Anthranilic 5.104 x acid 137.14 146.0-147.0 - 1.40 0.07 10^(-4) 0.52 mmol Sol'n of sodium nitrite in water (Values for 0.52 x 10^(- Sodium 3) of sodium Nitrite) (69.00) 271.0 - 2.17 (300 µl of solutin) nitrite 10% Hydrochloric acid (Hydrogen (1.49x10^(- Chloride) (-36.46) (-112.0) (-85.0) 3)) 550.0 µL - N,N- Dimethylanil 0.71 x 10^(- ine 121.18 2.0 194.0 0.96 89.0 µL=85.0 mg 3) Theoretical: Theoretical: 5.104 x 179.0-182.0 10^(-4) Experiment Experimental al: 169.0- Crude: 1.485 174.0 x 10^(-4) Experiment Theoretical: 0.1375 g al Crude: Experimental- Crude Product: 0.04 g 3.713 x Methyl Red 269.30 - 0.79 Pure Product: 0.01 g 10^(-5) 4. Procedure: 2 marks Summary of lab procedure – what YOU did, third person, past tense – be concise! Chemistry 222 Fall 2012 3 To a 3.0 mL conical vial, 0.07 g of anthranilic acid, a magnetic spine vane, and 550 µL of 10% hydrochloric acid was added(for the hydrochloric acid a Pasteur pipette was used). Next, the condenser was added to the vial. Since the solution inside the vial did not seem to be a homogenous solution right away, it was placed it on a hot place for stirring purposes until it became a homogenous solution . Next, to cool the solution in the vial, it was placed in an ice bath, and that ice bath with the vial was placed on top of the hot plate with the stirring still taking place. It was left stirring with the ice bath for 10 minutes. In a beaker, some (greater than 300 µL) 0.52 mmol solution of sodium nitrite was poured and this beaker was also placed in the ice bath to cool. A thermometer was placed in the ice bath, which had the two solutions, in order to monitor the temperature. When both solutions were at approximately 5 C ̊, 300 µL of the nitrite solution was taken using a Pasteur pipette and it was slowly added to the solution in the anthranilic acid solution in the vial that was being stirred. While doing this step, it was made sure that the temperature remained at approximately 5 C ̊. After 5 min, the solution of anthranyldiazonium chloride was texted for the presence of excess nitrous acid with the placement of a drop of the solution on a potassium iodide-starch paper. An immediate blue color was not seen, therefore more nitrite solution was added to the vial. The solution was left to stir for a couple of minutes and then this process was repeated and an immediate blue color was observed. Next, the air condenser was removed from the vial, 89 µL of N,N-Dimethylaniline was added quickly to the vial, and then condenser was reattached. The solution was left to stir for 15 minutes, while making sure the temperature was still around 5 C ̊. 200 µL of 0.83 mmol solution of sodium acetate was then transferred to the vial with the reaction mixture using the Pasteur pipette (without removing the air condenser). The solution was left to stir for an additional 20 minutes, while making sure the temperature was still around 5 ̊ C. The vial was then removed from the ice bath and it was left out (on top of the hotplate?) for 15 min so that the solution. returns to room temperature. Next, 100 µL of 10% aqueous NaOH solution was added to the reaction mixture in the vial using a pipette and then it was left to stand at room temperature for another 30 minutes. The crude Methyl Red was collected through vacuum filtration using a Buchner Funnel. The reaction flask was rinsed with 0.5 mL of water, and is rinse was then used to wash the crystals as well. In addition to this, the crystals were washed with 0.5 mL of 3 M acetic acid, and then again with 0.5 mL of water. The weight and melting point of the crude product were then taken. Following this step, the crude product was dissolve in 2.0-2.5 mL of methanol in a flask (this was placed in a beaker with hot water for faster dissolution). The solution was then cooled in an ice bath, and the pure methyl red crystals were collected with again performing vacuum filtration using a Buchner funnel. The weight, melting point and IR of the product was taken. (This entire experiment was performed in the fume hood.) Chemistry 222 Fall 2012 4 5. Results: 5 marks a. Table 1: Yield and Physical Properties Crude Azo Dyes Purified Azo Dyes Yield (g) 0.04 g 0.01
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