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I think that answer would be:

  1. Toluene and cyclohexane do not dissolve in water (since they are nonpolar), so I would first separate the water from the mixture with a separator funnel.

  2. A mixture of cyclohexane and toluene would be separated by fractional distillation. Cyclohexane, which has a lower boiling point than toluene, would be eliminated from the mixture.

Is there anything wrong in my answer? Would there also be anything to add?

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    $\begingroup$ Sounds good to me. $\endgroup$
    – Ivan Neretin
    Commented Apr 12, 2021 at 15:43
  • $\begingroup$ Cyclohexane and toluene may probably be difficult to separate by distillation. Toluene is not very different from benzene. And i know that benzene and cyclohexane are forming an azeotropic mixture (59% benzene) which boils at 77°C, that is lower than the boiling points of benzene and of cyclohexane. So I would not be surprised to learn that toluene and cyclohexane are making an azeotropic mixture. This should be checked. $\endgroup$
    – Maurice
    Commented Apr 12, 2021 at 16:19
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    $\begingroup$ Cyclohexane and toluene would not make azeotrope. Fractional distillation would do the trick. $\endgroup$
    – Mathew Mahindaratne
    Commented Apr 12, 2021 at 16:21

3 Answers 3

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Need to check ternary phase diagram of cyclohexane:toluene:water. There are azeotropes water:toluene at 89 °C (0.49:0.51) and water:cyclohexane at 69 °C (30:70).

Hence, first separate water if you can on the basis of density (layer separation or extraction). And then separate cyclohexane and toluene by fractional distillation. In fractional distillation, you need to repeat the vaporization–condensation cycle to achieve your desired quality.

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  • $\begingroup$ Could you please append the phase diagram you are referring to? $\endgroup$
    – andselisk ♦
    Commented Feb 9, 2022 at 6:10
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The first step will be to separate the water from the cyclohexane; a separatory funnel could be used, or the organic layer could be suctioned off with a pipette.

Toluene freezes at -95ºC; cyclohexane freezes at +6.46ºC. Dry ice (solid CO2) sublimes at -78ºC (Ref 1).

Get some dry ice, put the cyclohexane-toluene mix (in a test tube) into the dry ice, wait a little bit, pour off the toluene and let the cyclohexane melt. The separation will be ~90-95% complete. (The separation could be better on an industrial scale.)

The reference also describes some cooling bath temperatures above -78ºC. The very lowest temperature may not be needed, and higher temperatures might give better crystallization (i.e., large crystals of cyclohexane rather than a fine powder or a clunky solid mass).

Ref 1. https://en.wikipedia.org/wiki/Cooling_bath

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Distillation

The most effective and easiest way to separate the mixture of toluene and cyclohexane is simple distillation. Cyclohexane has boiling point is about 81°C, and toluene’s boiling point is 111°C.

References:

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    $\begingroup$ Simple distillation is not the most effective but easiest. If you look at the NMR of the first distillate, it is 1:2 mixture of toluene to cyclohexane. The residue is 8:5 mixture of toluene to cyclohexane. I made my point. $\endgroup$
    – Mathew Mahindaratne
    Commented Apr 12, 2021 at 16:43

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