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CHEM 222 Study Guide - Azo Coupling, Electrophilic Aromatic Substitution, Pasteur Pipette

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beigecockroach512

15 Sep 2013

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McGill University

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Experiment 6: azo dyes: objective: 1 mark. 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: 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. It is the electron releasing resonance effect that allows for the reaction between the diazonium salt (the electrophile: diazonium cation) and the aryl unit.

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Related Questions

Write a formal procedure about the expiremnt ( please note where the procedure is starting just write it)

-SYNTHESIS OF A DYE, METHYL ORANGE is the electrophile. Therefore the same rules as for any electrophilic aromatic substitution ap- ply: electron donating groups such as amines, ethers and alkyl groups activate the aromatic contact with the skin should be avoided substrate and are ortho-para directors, hlAvoid breathing the fumes. As a general rule groups such as carboxylic esters and nitro all aromatic amines should be considered as Safety Considerations N.N-Dimethylaniline is quite toxic. Any groups are deactivators and meta directors The first step in an azo coupling is the forma Normal precautions apply to the use of concentrated acids. on of the diazonium ion intermediate, which is formed by reaction of an aromatic amine with nitrous acid. This process is called diazotation. Sodium dithionite slowly decomposes in water Nitrous acid is sodium nitrite and hydrochloric acid. For the rotten egg smell). Some people with asthma reaction in this experiment, the diazoniu of sulfanilic acid has to be formed. However sulfanilic formed in situ by reaction of and forms H,S, which really smells bad (the m ion might be highly sensitive to these chemicals. acid is not soluble in acidic solution, and the medium in this reaction has to be acidic to form the nitrous acid. This problem is circum- vented by dissolving the sulfanilic acid first in alkaline solution by addition of sodium carbon ate. At the beginning of the reaction, when HCI is added, two things will happen: nitrous acid Procedure In a small Erlenmeyer flask, dissolve 0.06 g of sodium carbonate in about S mL of water. Add 0.2 g of sulfanilic acid monohydrate and heat to reflux until it is homogeneous. Cool to room formed in situ and the sulfanilic acid will temperature and add 0.08 g of sodium nitrite and stir until homogeneous. Cool in an ice water bath for 5-10 minutes until the temperature is below 10 Â°C. Add 0.25 mL concentrated hy precipitate out as a very finely divided precipi tate, which is highly reactive. The diazonium salt of the sulfanilic acid will be formed, which is also insoluble in the reaction medium, but drogen chloride to the solution. The diazoniu again very finely divided. The diazonium ion salt should precipitate as a finely divided whi will react immediately with the highly reactive bresipitate, Keep this solution cold N,N-dimethylaniline to form methyl orange Methyl orange is an acid base indicator: At In a vial or flask, mix 0.14 mL. of N,N-dlimethyl pH > 4.4, methyl orange exists mostly as the aniline with 0.10 ml. of glacial acetic acid. Add yellow negative sulfonate ion, while at pH