How effective is ethyl acetate as an organic solvent for decaffeinating a caffeine solution compared to cyclohexane?
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.
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.
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
Filter aparatus (funnel & filter paper)
50cm3 burette- \(\pm\)0.05cm3
Weighing scales- \(\pm\)0.001g
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: \