Some..(A) Describe the synthesis of azo dyes and the full chemical equations for each step.

Size: px

Start display at page:

Download "Some..(A) Describe the synthesis of azo dyes and the full chemical equations for each step."

Emma Gilmore
5 years ago
Views:

1 A2 Chemistry: F324 Rings, Polymers and Analysis Amines Learning Outcomes: All.. (E) Most.. (C) Explain why amines are basic Draw the structure of a primary secondary and tertiary amine Describe the reactions of amines with acids to form salts Describe the preparation of amines reaction from halogenoalkanes Describe the preparation of aromatic amines from nitrobenzene 1 Further reading: Some..(A) Describe the synthesis of azo dyes and the full chemical equations for each step. Activity 1: Brain Storm. In small groups state all the chemical facts and properties that you know about amines. Amines Strength of Amines Amines are bases, a base is a. The simplest amine is ammonia (NH 3 ). An amine group is NH 2. Structures of Amines: Primary Secondary Tertiary Quaternary

2 2 Basic Strength of Amines. The strength of the amine as a base depends on three things: 1. the availability of the nitrogen s lone pair to bond with the H + 2. the stability of the positive ion formed 3. the solubility of the amine. K b is a constant that is used to measure the strength of a base. The larger the value of K b, the stronger the base. The table below gives some values of K b for some amines: Amine K b /mol dm -3 Ethylamine 5.1 x 10-4 Diethylamine 10.0 x 10-4 Triethylamine 5.6 x 10-4 Phenylamine 4.2 x Question. List the order for basicity of the amines in the table above starting with the most basic... In phenylamine the delocalised system of the benzene ring draws in the lone pair on the nitrogen. Thus the lone pair on the nitrogen is less available for bonding with H + ions. Additionally, the pulling of the electrons into the benzene ring increases the density of the positive charge making the positive ion less stable. Ethylamine is a primary amine and therefore has only one alkyl group to donate electrons towards the nitrogen atom. Diethylamine is a secondary amine and has two alkyl groups to feed electrons to the nitrogen atom. This not only makes the lone pair on the nitrogen more accessible but it also reduces the density of charge on the positive ion making it more stable. Diethylamine is therefore a stronger base than ethylamine. Activity 2: Reactions with Acids to Form Salts a. Reactions with hydrochloric acid Amines are basic so react with acids to form an ammonium salt

3 3 Preparation of Amines a. Aliphatic Amines. Aliphatic (straight chain) amines can be formed from halogenoalkanes using hot alcoholic ammonia. b. Aromatic arenes Aromatic amines can be formed by the reduction of nitroarenes using tin and concentrated hydrochloric acid. Synthesis of Azo Dyes. The nitric(iii) acid (commonly called nitrous acid) is made by adding sodium nitrate(iii), NaNO 2, to concentrated hydrochloric acid. Nitrous acid is unstable so must be produced in situe. a. Diazotisation NaNO 2 + HCl! HNO 2 + NaCl When reacting phenylamine with nitrous acid the mixture must be kept below 10 C to form the diazonium salt. This reaction is known as diazotisation. If the temperature is raised above 10 C the diazonium ion decomposes to nitrogen gas as it is very unstable.

4 4 b. Coupling reaction The phenyldiazonium ion behaves as an electrophile, and will attack another arene molecule such as phenol. Electrophilic substitution takes place at position 4, producing 4-hydroxyphenylazobenzene. The compound formed is energetically stable, yellow/orange azo dye (azo group is N=N-) Azo compounds are used for. Questions: 1. What is the formula of the following: a. Nitrous acid b. Diazonium ion.. c. Ethanol. d. Ammonia.. e. Phenol.. 2. Give a balanced equation for the formation of nitrous acid. 3. Name the following amine structures. a. b. c. 4. Why are amines very important biological molecules? 5. Are amines basic or acidic, explain your answer?

5 5. 6. What is the general formula of an amine?. 7. Write a balanced equation for the rections of: a. Nitric acid with butylamine Past Exam Question. In this question, one mark is available for the quality of use and organisation of scientific terms. 4-Methylphenylamine can be manufactured from benzene in three stages. Describe how benzene could be converted by these three stages into 4-methylphenylamine. Include the structures of the intermediate compounds A and B. State the reagents and conditions. Give a balanced equation for each stage. (June 2008) 11 marks.

6 6 Activity Feedback: 6: Tell me two things. that you have done well today that you know now that you didn t know at the start of the lesson that you could have done better next lesson that you would like to know more about Notes.

7 7

OCR Chemistry A H432. Amines are described as primary, secondary or tertiary depending on how many carbons are bonded to the N atom.

OCR Chemistry A H432. Amines are described as primary, secondary or tertiary depending on how many carbons are bonded to the N atom. OCR Chemistry A 432 About amines: can be considered as derivatives of ammonia, with one or more of the atoms replaced by alkyl groups. They are noted for their unpleasant, often fishy odours. We classify