How was the first artificial dye made? | 16-18 years

In these activities a directed activity related to text (DART) describes the making of mauve, the first artificial aniline dye, as a setting for organic synthesis. Students compare Perkin’s original patent with a more modern technique, identifying the compounds and methods involved.

These activities will work within a series on aromatic chemistry, providing an historical context for work on reactions of benzene and developing reaction pathways, as well as exploring practical constraints.

Learning objectives

Students will recognise that:

• Organic synthesis involves a series of steps using set techniques.
• Mauve was made from ‘coal-tar’, a by-product of the gas industry.
• Chemical nomenclature has changed as chemists developed greater understanding of the formulae and structures of the materials they use.

Sequence of activities

Introduction

1. As an introduction, invite students to look at the colours in the clothes they and you are wearing, or discuss the latest colour fashions and how these change seasonally.
2. Find out if students are aware of indigo as an ancient dye still used in producing denim, using this as a link into looking at the first ever artificial dye to be made commercially.
3. Relate their responses to the learning objectives.

Activity: How was mauve made?

1. Give each student a copy of the sheet ‘How was mauve made?’.
2. Arrange for students to work individually on the first two sections, but in pairs or groups for the third section. (Note: students can peer review responses to the first two sections.)
3. Circulate and support as students work through the first two sections of the DART. (Note: the most difficult part will be working out the modern chemical names of the compounds listed in the procedures. Additional resources will be needed to support this section.)
4. Ask the students to
   • Get into groups or pairs.
   • Review each other’s responses to the first two sections.
   • Discuss answers to the final section, agreeing on responses.
   • Decide who should feedback to the class.

Plenary

In a plenary:

1. Review responses to any contentious aspects of the first two sections.
2. Check flowcharts for completeness.
3. Check chemical names are correct.
4. Check the reaction pathways for chemical sense.
5. Clarify points to confirm understanding.
6. Review responses to the third section.
7. Draw out relevant points, including:
   • Perkin’s lack of detailed measurements – why was this?
   • Use of phrases like ‘sulphate of’ and ‘base enough’ chemical names were not accurate – why have these changed?
   • Small measurements used in the modern process – how are these measured?
   • Techniques such as suction filtration, evaporation and mechanical mixing developed since Perkin’s day. How do techniques affect the outcomes of chemical procedures?
   • Our understanding of structures and formulae has developed enormously since 1856 (prior to the existence of the periodic table), for example, communication and collaboration between chemists has developed; and these changes meant we had to develop systems for naming compounds consistently.
   • Perkin can be regarded as the world’s first chemist involved in synthesis of new organic compounds – an entire branch of chemistry developed from his work.

Feedback

Collect responses for written feedback. Focus on understanding of chemical nomenclature, reaction pathways and techniques.

Commentary

Students work alone, then have their work peer reviewed in pairs or small groups. This permits development of ideas in a secure way as students compare their answers to the questions. Group work enables pooling and sharing of ideas learned through the individual work.

Teacher written feedback supports the development of understanding about organic synthesis.