Distillation and pyrolysis of plant derived material such as wood or fossil fuels produce family of valuable carbonaceous byproduct known as Creosotes apart from other products. One of the major components of creosotes are cresols (methyl phenols). Often, cresols are obtained as a mixture of three stereoisomers, ortho-cresol (o-cresol), meta-cresol (m-cresol) and para-cresol (p-cresol).

Cresols are strong germicides and in low concentrations effective disinfectants and antiseptics. During 1880’s, an Italian company formulated a product Creolin obtained from creosote, which became popular disinfectant for cleaning kennels and farm yards. Another formulation containing cresols, formocresol was initially used in dentistry for root canal therapy. However, it was realized that ingestion of cresols caused burning of throat and abdominal pain and due to stringent safety regulations; its demand over the years has reduced. Cresol is also one of the components present in chemical mixtures used as wood preservative (in bridge work and railroad ties).

Today, cresol derivatives are used significantly in production of vitamin E and electronic encapsulation products (electronic components coated and molded with chemicals to protect from dirt, moisture and solvents). Due to surging demand for electronic gadgets, industries are anticipated to offer immense growth potential for cresol derivatives.

All isomers of cresols undergo bromination reaction with bromine quantitatively. Therefore, bromination reaction can also be used for identifying the isomers. Bromine can be generated in situ by addition of excess potassium bromate and potassium bromide solution in acidic medium. Excess unreacted bromine can then be estimated by its reaction with potassium iodide. The liberated iodine can be titrated with sodium thiosulphate. This is an interesting example of using titration techniques for distinguishing unknown samples.


Wood railroad ties impregnated with creosote

In the current experiment, you have been provided with two samples of cresol. One of the samples is 3-methyl phenol (m-cresol) whereas another is 4-methyl phenol (p-cresol).  You will investigate the two samples using bromination reaction and identify them.

Prerequisite (Theory)

Back titration

Iodometric titrations

Techniques

Use of pipette bulb

Titration technique

References

  • Wade, L. G. (2013, September 26). Cresol. Encyclopedia Britannica. Retrieved April 29, 2020, from https://www.britannica.com/science/cresol
  • Kellogg, Royal S, Price, O. W., & Cox, W. T. (1909). The Forests of the United States: Their Use; Volume No.171. Retrieved from
  • Schorlemmer, C. (1885). The History of Creosote, Cedriret and Pittacal. In Journal of the Society of the Chemical Industry (pp. 152–157).
  • Cresol Market Size, Share | Global Industry Analysis Report, 2016–2024. (2016, July). Retrieved April 29, 2020, from https://www.grandviewresearch.com/industry-analysis/cresol-market
  • Image: Railroad ties wood concrete, by LooiNLt, CC BY-SA 3.0, https://commons.wikimedia.org/wiki/File:Railroad_tieswoodconcrete.jpg#/media/File:Railroad_tieswoodconcrete.jpg
Glassware
▪ Burette (50 mL)1
▪ Burette (25 mL) 1
▪ Conical flasks7
▪ Dropper1
▪ Funnel2
▪ Pipette 25 mL1
▪ Measuring cylinder (10 mL)1
▪ Wash Bottle1

 Chemicals     
▪ H2SO4   3M, 50 mL
▪ KBrO3    250 mL
▪ Na2S2O3   200 mL
▪ KBr   0.5 g / vial (9 vials)
▪ KI   2.5 g / vial (9 vials)
▪ Sample Solution A   
▪ Sample Solution B
▪ Starch 5 mL
▪ Paraffin film strips (9 Nos)

 (molarity of Na2S2O3 will be supplied to you)

Hazard Symbols

Corrosive to skin 

Health Hazard 

Toxic 

Harmful 

Environmental Hazard

Procedure

1.1       Sample Solution A

Preparation of flasks for titrations

  1. Fill the burette (25 mL) with supplied potassium bromate solution.
  2. In a conical flask, pipette out 25 mL of the sample solution A. Then add25 mL of the potassium bromate solution with the help of burette.
  3. Add one vial of solid KBr and 5 mL of the 3 M sulphuric acid to the flask. Seal the flask using the parafilm supplied to you.
  4. Prepare 2 more flasks in similar manner. Shake each flask at intervals. Keep all the three flasks aside for 20 minutes.

1.2       Titration for solution A

  1. Meanwhile fill another burette (50 mL capacity) with sodium thiosulphate.
  2. At the end of 20 minutes, add one vial of solid KI to the first flask. Shake the content thoroughly for 1 or 2 minutes and start titrating the liberated iodine with sodium thiosulphate solution. 
  3. When the colour of the solution is pale yellow, add 1 mL of starch indicator with the help of dropper. At this instance, the solution will be blue in colour.
  4. Continue the titration till the solution becomes milky white in colour. Perform the titrations in similar manner for other two flasks.

1.3       Repeat the whole procedure given in 1.1 and 1.2 for sample solution B

1.4       Blank Titration

  1. In a clean flask, take 25 mL of potassium bromate solution from the burette. Add one vial of solid KBr and 5 mL of the 3 M sulphuric acid to the flask.
  2. Add one vial of solid KI to the flask. Shake the content thoroughly for 1 or 2 minutes and start titrating the liberated iodine with sodium thiosulphate solution.
  3. When the colour of the solution is pale yellow, add 1 mL of starch indicator with the help of dropper. At this instance the solution will be blue in colour.
  4. Continue the titration till the solution becomes colourless.

This reading gives total bromine present in 25 mL the bromate- bromide solution.

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Under Construction: will be available soon