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I am performing a lab experiment in which I am extracting crude caffeine from different samples of tea. I have read a couple of similar experiments in which methylene chloride has been used to extract caffeine, owing to its volatile nature and caffeine's affinity to methylene chloride. I know chloroform can be used as a substitute for methylene chloride. I was wondering if carbon disulphide can used as a substitute in the experiment. Thank you very much!

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    $\begingroup$ Please have a look at the MSDS of all three solvents before you decide that you don't want to use $\ce{CS2}$ ;) $\endgroup$ – Klaus-Dieter Warzecha Mar 11 '16 at 9:39
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    $\begingroup$ With $\ce{CS2}$, one doesn't really need to look at the MSDS. One brief encounter with the compound itself would be quite enough. $\endgroup$ – Ivan Neretin Mar 11 '16 at 9:45
  • $\begingroup$ @IvanNeretin So true :D It's really nasty! But maybe, we can keep the students from using it without even trying. Unless absolutely necessary (Chugaev elimination), there's little need to touch that stinker. $\endgroup$ – Klaus-Dieter Warzecha Mar 11 '16 at 9:49
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I suggest to use a 1:1 mixture of dichloromethane and 0.2 M NaOH at room temperature.

The protocol was described by Tetsuo Onami and Hitoshi Kanazawa in J. Chem. Educ, 1996, 73, 556-557.

The authors mention that only trace amounts of caffeine are extracted from tea leaves with dichloromethane alone. They reason that due to the hight amount of tannines in the tea leaves, most of the caffeine exist in protonated form and is therefore bound to the tannines.

As an experimentally proven alternative, they suggest to treat the tea leaves with a mixture of dichloromethane and 0.2 M NaOH at room temperature!

According to the article, 20-30 mg of caffeine were extracted from a 2 g tea bag after shaking the above mixture for about ten minutes.


UPDATE
If you insist on the liquid-liquid extraction of previously prepared aqueous solutions and feel the urge to set up a percolator-type apparatus for continuous extraction, the Kutscher-Steudel glassware will not work with solvents that have a higher density than water.

For continuous extractions with solvents like $\ce{CH2Cl2}$, some different glassware has been designed and was described by S. Wehrli in Ein Apparat zur Extraktion von Lösungen mit schweren Lösungsmitteln and was published in Helv. Chim. Acta, 1937, 20, 927–931 (DOI)

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I personally would test some solvents. The one I have seen specifically for caffeine is warm ethanol. Better still might be to use it in conjunction with Soxhlet apparatus. Undergrad labs usually have these (at least they did when I was a lab demonstrator). The caffeine can then be crystallised from ethanol if not too dilute, depending how you want your product. I would not touch carbon disulfide again in my life if I could help it.

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  • $\begingroup$ I've never seen a Soxhlet extractor in an undergrad teaching lab. I've only used one once between my time in undergrad and grad school. $\endgroup$ – SendersReagent Mar 11 '16 at 13:15
  • $\begingroup$ Isaac Newton: "If I have seen further, it is by standing on the shoulders of giants." In other words, it's time for a good literature search, not wasting time experimenting willy-nilly. $\endgroup$ – MaxW Mar 11 '16 at 17:30
  • $\begingroup$ Yeah, that's for grad school. Or, even better, post-doc. $\endgroup$ – SendersReagent Mar 11 '16 at 18:13
  • $\begingroup$ What method are you using to compare the extraction efficiency and content of caffeine between samples? HPLC w/w assay? $\endgroup$ – Beerhunter Mar 11 '16 at 21:34
  • $\begingroup$ I don't know what undergrads learn now in practical sessions, but Soxhlet should be nothing special in a quality teaching laboratory. $\endgroup$ – Beerhunter Mar 11 '16 at 21:39

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