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Chloroform as a solvent?

Discussion in 'MCAT Study Question Q&A' started by MBigD011, Jun 14, 2009.

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  1. MBigD011

    MBigD011

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    Chloroform = CHCl3, so its a polar molecule.

    This means that other polar items should be soluble within Chloroform, correct?
  2. loveoforganic

    loveoforganic -Account Deactivated-

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  3. sleepy425

    sleepy425

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    eh, well, chloroform is considered to be an organic (nonpolar) solvent. It has low solubility in water (they aren't miscible, it's something like 8 mg/mL in water, which isn't very high). Now, that being said, chloroform has weak polarity, and thus it will dissolve some moderately polar molecules. For example, methanol is much more soluble in chloroform than water is (I don't think they're miscible, but I've definitely had 15% methanol in chloroform which is a lot more soluble than water).

    So, basically, by virtue of the fact that chloroform is not miscible with water, it is an organic solvent. However, because chloroform does have some polarity, it can dissolve compounds ranging from moderately polar to moderately nonpolar. As a matter of fact, deuterated chloroform is the most commonly used NMR solvent because it's cheap, and because it will dissolve most compounds you'd be taking an NMR of (and also because, if you don't have very much of your sample, you can dissolve it up in the deuterated solvent, take the NMR, and then easily rotovap it off).
  4. loveoforganic

    loveoforganic -Account Deactivated-

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    Good write up. Never knew that solubility in water was the basis for organic/polar solvent classification. Just knew I always used CDCl3 for my Baylis-Hillmans in research.
  5. sleepy425

    sleepy425

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    lol, well, actually, you bring up a great point. My post was a bit incomplete. I've just always considered miscibility in water to be the distinction between a polar solvent and an organic solvent (this distinciton is very important for solvent extraction, since you almost always have an aqueous phase and another phase that is immiscible with water. for other applications, it's usually more about relative polarity, so there's not really a definitive break between "polar" and "nonpolar" compounds). I guess I should have been a bit more clear. You'll hear solvents like THF, DMF called polar solvents because they do have some polarity and are useful in dissolving functionalized organic compounds. So for Sn1/2/E1/2 all the solvents you'd use are polar solvents in the sense that the solvents do have some degree of polarity that makes it easier to solvate an alkyl halide or an alcohol. In the case of THF and DMF, I think of them as "organic" solvents because they have low water solubility. Acetone, which is a very common Sn2 solvent for alkyl chlorides (because the product, NaCl, is insoluble in acetone, so it crashes out and drives the equilibrium towards substitution), is more polar than THF and DMF and is miscible with water, so I think of it as "polar." Alkanes are truly nonpolar.

    I'm sorry if I made it a little less clear. The moral of the story is that polarity is relative. If two compounds are far enough apart in polarity, they will not be miscible. That doesn't mean that the less polar of the two compounds is nonpolar. It simply means that the polarity is just a lot less.

    Another example is a silica column or TLC plate. One of the most common mobile phases for silica chromatography is hexane/ethyl acetate. Ethyl acetate is an ester that clearly has some polarity. Hexane is obviously nonpolar. However, hexane and ethyl acetate are miscible, whereas ethyl acetate is not significantly soluble in water. So you could consider EtOAc to be polar because it is more polar than hexane (and in the separation, ethyl acetate is used because of its polarity, with higher EtOAc to hexane ratios giving faster elution of more polar compounds), but relative to water and several small alcohols, it is fairly nonpolar. It's all relative...
  6. loveoforganic

    loveoforganic -Account Deactivated-

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    I misunderstood, but to a smaller extent than you thought :p I did think you were saying that organic/polar terminology was based off differences in water solubility, but I knew that even if that were so, it was still just a convention. I know it's relative.
  7. Bernoull

    Bernoull

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    I thought miscibility meant soluble in any proportions?? If methanol is inmiscible in chloroform BUT miscible in water, by definition isn't it more soluble in water??
  8. sleepy425

    sleepy425

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    Yes, methanol is more soluble in water (I didn't say that it wasn't) than in chloroform. But methanol's solubility in chloroform is higher than water's solubility in chloroform. The statement that you bolded said that "methanol is much more soluble in chloroform than water is," not that methanol is much more soluble in chloroform than in water.
  9. Bernoull

    Bernoull

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    my bad... I guess i can use a visit to da optician..:eek::eek:
  10. MBigD011

    MBigD011

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    ah, thanks, I kept reading how chloroform is an organic solv and could not reconcile that with its actually being polar so just know its considered an organic solv will help for the test.

    OMG 2 more days!!

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