ROUGH DRAFT authorea.com/115330

# Overview

Demand for decaffeinated coffee has been on the rise through the past 10 years. Ascertaining the best method for decaffeinating coffee beans has proven difficult, with a range of hopeful techniques used and then subsequently banned. The swiss water method has eventually emerged as the safest and most effective method, however this requires liquefied CO2, and a pressure of roughly 75 atmospheres, thus making it difficult and cost ineffective in to do in a school laboratory. However, organic substances such as ethyl acetate and dichloromethane are readily available and easy to make to the concentrations and volumes required for the decaffeination process. As an avid drinker (of coffee), this topic certainly carries personal significance. This topic carries extra significance at times of the day when I do not want to feel the side effects of caffeine, but enjoy the taste of coffee.
The following techniques should not be performed at home for consumption, however satisfying personal curiosity into this topic certainly merits the investigation.

# Exploration

## Background Information

It still remains unclear what the best solvent to decaffeinate caffeine solution is. Dichloromethane (CH2Cl2) seemed to be an effective solvent, with its usage for this purpose increasing rapidly throughout the 1970s. However, after being proven to be a carcinogenic, its use was subsequently banned in the decaffeinating process, leaving only ethyl acetate as a well known solvent fit for purpose.
Becuase of the effects of dichloromethane, it was decided that it should not be used in this investigation for the purpose of safety. Instead, ethyl acetate would be compared to another solvent. This solvent had to fit criteria satisfying safety, availability, ease of usage in the method to be applied, and ability to absorb caffeine. Cyclohexane was eventually chosen, as it is known that it would also absorb caffeine. To see that ethyl acetate is indeed an efficient solvent, cyclohexane would be used in the same method for decaffeinating caffeine solution that would normally use ethyl acetate.
There is no straightforward test for measuring caffeine content, however the most applicable one to use in a school laboratory is the iodine back titration. The essence of this method is that caffeine will react with iodine to form a precipitate. When this precipitate is filtered out, the remaining iodine can be titrated with soldium thiosulfate, to see how much iodine has been removed from the original known quantity, and therefore how much caffeine had been in the original mixture to react with the amount of iodine ’missing’, in the final filtrate.

## Kit list

The following apparatus were used in this exploration. If the uncertainty of a piece of apparatus is required in future calculations, the uncertainty is stated next to the piece of apparatus:

• 30cm3 measuring cylinder- $$\pm$$0.1cm3

• 150ml beaker

• Separting funnel

• 50ml Beaker

• Filter aparatus (funnel & filter paper)

• 50cm3 burette- $$\pm$$0.05cm3

• Burette

• Burette clamp

• Burette stand

• Pipette

• Weighing scales- $$\pm$$0.001g

• Weighing boat

## Method

Caffeine will react with an excess in iodine. However, this reaction only takes place in acidic question, so an acid must be present when attempting to react the two. This method relies on the fact that when caffeine reacts with iodine, it will form a solid precipitate that can be removed by filtration.
This means that if the amount of iodine added originally to the caffeine solution is known, and once the precipitate is removed there is a method of knowing how much iodine is present in a sample, one is able to compare the two amounts of iodine, and deduce how much iodine has been removed by the caffeine. This is shown in the two chemical equations below: $C_{8}H_{10}N_4O_2 + 2I_2 + KI + H_2SO_4 \rightarrow C_8H_{10}N_4O_2.HI.I_4 + KHSO_4$ and $I_2 + 2Na_2S_2O_3 \rightarrow 2NaI + Na_2S_4O_6$ where the $$I_2$$ in equation two is the remaining iodine after the precipitate is filtered out.

The use of these two chemical equations is shown below in the quantitative method:

1. Measure out 15cm3 of caffeine solution using a measuring cylinder

2. Add an excess of the solvent used (either ethyl acetate or cyclohexane, or nothing if the caffeine content to be determined was a control test) to decaffeinate the caffeine solution

3. Pour the mixture of caffeine solution and decaffeinating solvent into a separating funnel. Separate the two liquids by only letting the 15cm3 of caffeine solution out of the separating funnel, into a beaker

4. Add 10cm3 of 1M sulfuric acid to the caffeine solution.

5. Add 25cm3 of 0.040moldm-3 iodine solution to the sulfuric acid and caffeine solution. This will form a precipitate.

6. Filter out the precipitate and place the filtrate into a conical flask.

7. Add several drops of starch solution to the filtrate.

8. Titrate the remaining iodine solution with sodium thiosulfate of 0.025moldm-3 concentration.

9. Record the volume of sodium thiosulfate needed to make the filtrate turn from dark brown to colourless.