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Using Ionic Liquids To Replace Organic Solvents 7

Posted by timothy
from the good-for-melting-witches-too dept.
An Anonymous Coward writes: "The NY Times (free reg required) has a story about ionic liquids possibly taking over from some of the nastier organic solvents. Apparently these things have been around since the 40s, but are only just getting a lot of attention now. They are supposed to be a lot more environmentally friendly, offer all sorts of wonderful properties for carrying out chemical reactions, and so on. They may be cool and different, but are they really better? Salt on the roads in the winter causes all kinds of problems -- aren't other kinds of salts going to cause problems in large quantities? On the other hand, cool and different is good too."
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Using Ionic Liquids To Replace Organic Solvents

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  • Yes, a polar solvent works well with polar solute. That is why water (quite polar) disolves salts very well. I thought most organic solvents (benzine, acetone, etc) were not particularly polar, though, so I am not sure how these ionic liquids work compared to the organic solvents.
  • Another alternative is to use supercritical water. (ie, water at high pressures and temperatures). Apparently the chemistry of water changes dramatically as the temperature and pressure are increased, and it becomes pretty non-polar, and consequently can act as a solvent for all sorts of messy organics.

    At least, that's how I understand it -- it isn't my research or even my field so I don't really understand any of the details.
  • by meridoc (134765) on Monday April 30, 2001 @02:56PM (#255077)

    There's a difference between polar and ionic. Yes, the rule is "like dissolves like," so polar things dissolve polar things (and non-polar things dissolve non-polar things). Water and table salt are both polar; table salt (NaCl) also happens to be ionic.

    An ionic compound simply means that the pieces basically are held together by charge attractions. In the case of NaCl, chlorine is pulling so hard on the lone electron from sodium that it is almost removed; consequently, Na has a (net) postive charge and Cl has a (net) negative charge. The whole "opposites attract" thing keeps Na and Cl together as a tiny part of a table salt crystal.

    Nasty organic solvents are not always polar. Benzene, methane (and other pure carbon-hydrogen chains) are not. Water is highly polar, but because the earth has lots of water, it's cheap and available. Phenol and Xylene are very nasty and very polar. Acetone's not so bad (on a smallish scale).

    The NY Times article mentions "the salt," which may be confusing. A salt, in chemical terms, includes a whole family of things and is not limited to NaCl. Neither article intends on using sodium chloride as the ionic solvent (I don't think) because it has a high melting temperature (which is a good thing for the salt shaker in my cabinet). What the researchers in the articles are proposing is a substance that is ionic (like table salt, but not necessarily polar) that has large constituents so that the solvent would not get in the way of the desired reactions.

  • The nasty organic solvents tend to be non-polar, but so are things such as heavy metals, so the metals will be held by the Ionic liquid.
    The other thing about the salt they are using is that it must be a very weak Ionic bond, because the lowest Ionic bonded substance boiling point I have seen(in my limited experience) is about 600 celcius(silver niterate), table salt melts at ~6000 degrees celcius(unless I am being broken).

    This leaves one question, how do they do the heating, and what are their costs?

    If people can connect to one another even the smallest of voices will grow loud.
  • by Muad'Dave (255648) on Tuesday May 01, 2001 @06:16AM (#255079) Homepage
    the horrible chemistry 101 mistake?

    "Sodium chloride, the chemical name of table salt, consists of equal parts of sodium and chloride."

    That's like saying Prozac(tm) consists of equal parts Pro and Zac.

  • by Big Brass Balls (257794) on Monday April 30, 2001 @02:53PM (#255080) Homepage
    here [nytimes.com]. No need for that poofter registration bullshit.


    --
    Do I play Hockey? [nhl.com]
    Posting at -1 since April 18/01.

  • By switching the molecules used in the ionic liquids, chemists will be able to design custom properties in their solvents. Dr. Seddon estimates one trillion possible combinations. "You've got this incredible flexibility for getting the system right," he said. Ionic liquids can be mixed together to tweak their properties further.
    Dr. James Davis, a professor of chemistry at the University of South Alabama, gives the example of designing an ionic liquid that is able to bind with heavy metal pollutants like mercury and cadmium.
    Shaking contaminated water with the ionic liquid will enable the ionic liquid molecules to pull the heavy metals out of the water. The ionic liquid and water will then separate, and the clean water can be poured off.

    WOW! why didn't i heard of this earlier? think of all the applications: water filtration, metal collection, and it's all non-toxic and recyclable! if this really works, i'm going to have to add ionic solvents to my list to study...
    -stfrn, mad scientist

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