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Synthesis of Indigo: A Laboratory Experiment, Study notes of Chemistry

International University Institute of Luxembourg (IUIL)Chemistry

Instructions and information for a chemistry lab experiment on the synthesis of indigo, a traditional dye. Students are asked to balance the reaction, calculate molar masses and yields, and record quantities used. Videos are also provided to demonstrate the procedure and the dyeing process.

Typology: Study notes

2021/2022

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bg1
Name: _______________________________
Syntheis of Indigo
Chem 42 “Lab” Spring 2020
You can read the background for this experiment in the Chem 42 lab manual, pages 53-54.
Indigo is a traditional dye in India, extracted from the indigo plant, Indigofere tinctoria. It was
first made synthetically in 1880 by Adolph von Baeyer, using the reaction shown below. It is not
an especially efficient reaction, so it is not used industrially, but it makes for a straightforward
laboratory-scale synthesis.
1. Carefully count the number of each type of atom on the reactants and products side to
verify that the reaction is balanced:
Reactants
Products
sodium
nitrogen
oxygen
carbon
hydrogen
2. Calculate the molar masses of indigo, 2-nitrobenzaldehyde (NBA), and acetone, using the
formulas given above.
3. Watch this video showing the basic procedure for this synthesis of indigo.
C
C
CC
C
C
C
C
C
O
C
C
C
C
C
C
N
C
C
C
CC
C
N
C
C
C
C
O
O
C
H
O
H
H
H
H
H
H
NO2
H
H
HHH
H
H
H
HH
H
H
H
H
C7H5NO3
2-nitrobenzaldehyde
pale yellow solid
C3H6O
acetone (liquid)
density = 0.784 g/mL
2
2
2NaOH
C16H10N2O2
indigo
2NaCH3CO24H2O
pf2

Partial preview of the text

Download Synthesis of Indigo: A Laboratory Experiment and more Study notes Chemistry in PDF only on Docsity!

Name: _______________________________

Syntheis of Indigo

Chem 42 “Lab” Spring 2020

You can read the background for this experiment in the Chem 42 lab manual, pages 53-54.

Indigo is a traditional dye in India, extracted from the indigo plant, Indigofere tinctoria. It was

first made synthetically in 18 80 by Adolph von Baeyer, using the reaction shown below. It is not

an especially efficient reaction, so it is not used industrially, but it makes for a straightforward

laboratory-scale synthesis.

1. Carefully count the number of each type of atom on the reactants and products side to

verify that the reaction is balanced:

Reactants Products

sodium

nitrogen

oxygen

carbon

hydrogen

2. Calculate the molar masses of indigo, 2-nitrobenzaldehyde (NBA), and acetone, using the

formulas given above.

3. Watch this video showing the basic procedure for this synthesis of indigo.

C

C

C C

C

C

C

C

C

O

C

C

C

C

C

C

N

C

C

C

C C

N C

C

C

C

C

O

O

C

H

O

H

H

H

H

H

NO^ H

H 2

H

H H H

H

H

H

H H

H

H

C 7 H 5 NO 3 H^ H

2-nitrobenzaldehyde

pale yellow solid

C 3 H 6 O

acetone (liquid)

density = 0.784 g/mL

2 NaOH

C 16 H 10 N 2 O 2

indigo

2 NaCH 3 CO 2 4 H 2 O

  1. Record the quantities used in this reaction. Also calculate the number of grams of acetone, based on its density (0.784 g/mL). Show your work.

2-nitrobenzaldehyde: _______________ g acetone: _______________ mL

  1. Calculate the theoretical yield of indigo based on the masses of 2-nitrobenzaldehyde and acetone used. Which of these is the limiting reactant? ____________
  2. A typical mass of indigo for a reaction on this scale would be around 0.2 grams. Calculate the corresponding % yield.
  3. Watch this video, which shows vat dyeing with indigo. Normally, indigo does not dissolve in water. During the dyeing process, blue indigo is chemically reduced to leucoindigo (see below), which is colorless to yellow in color. This form of indigo is able to dissolve in water and can be soaked into cotton fabric. Once removed from the vat, the leucoindigo reacts with air, and in a few minutes is oxidized back to blue indigo, now stuck into the fibers of the cotton. In this example, the leuco-indigo looks green because some blue indigo is also present.

C

C

C

C

C

C

N

C

C

C

C C

N C

C

C

C

C

O

H O

H

H

H

H H

H

H

H H

C 16 H 10 N 2 O (^2) indigo

NaOH, Na 2 S 2 O 4 O (^2)

C

C

C

C

C

C

N

C

C

C

C C

N C

C

C

C

C

O

H O

H

H

H

H H

H

H

H H

leucoindigo anion