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Thread: Reflux

  1. #1 Reflux 
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    This question may be quite basic for the forum, but hey i havent even gone to university yet and have only just started organic chemistry.
    any help from the more qualified people out there would be much appreciated.
    How do you determine whether or not an organic reaction should be carried out under reflux?


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  3. #2  
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    Huh?! Just look it up. If it is a familiar reaction there will always be detailed instructions somewhere.

    Here is where we can use the phrase "reinventing the wheel."
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  4. #3  
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    Huh?! Just look it up
    in an exam situation its not particulary useful, i just wondered if the properties of the chemicals or the reaction type could determine whether or not you need reflux

    Here is where we can use the phrase "reinventing the wheel."
    sorry i don't understand what you mean by this, please elaborate
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  5. #4  
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    in an exam situation its not particulary useful
    Well, this is what happens when you ask only half a question. We thought you were faced with a true laboratory problem, not that you are merely humoring a teacher.

    Well, so you were asked this question as part of a larger scenario. You must give us the rest of the set up, all of it. Without any additional information the question is totally meaningless.
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  6. #5  
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    Well, this is what happens when you ask only half a question. We thought you were faced with a true laboratory problem, not that you are merely humoring a teacher.

    Well, so you were asked this question as part of a larger scenario. You must give us the rest of the set up, all of it. Without any additional information the question is totally meaningless.
    You misunderstand me, the question i asked was not set by a teacher, it was not in an exam paper.

    It is a question i asked myself, how can you determine whether or not to do a reaction under reflux. Any organic reaction notice i didn't specify.
    This question was also not asked as part of a larger scenario

    this is an example of where you make an assumption without all the information, and then insult someone for asking a question they need answering.
    I would try and find a clever phrase for it but i don't really think its necessary
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  7. #6  
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    If you don't reflux, the lighter component will boil off and the boiling temperature, which is the same as the reaction temperature, will increase. The higher temperature might result in reaction products you don't want. I don't know if this is the answer you were looking for, but it might be.
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  8. #7  
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    thats quite useful,
    so be lighter do you mean lower boiling temperature?
    so if you wanted an intermediate compound you would reflux?
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  9. #8  
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    Quote Originally Posted by jacketate
    so be lighter do you mean lower boiling temperature?
    so if you wanted an intermediate compound you would reflux?
    Yes, in a mixture of organics, the smaller molecules have the lower boiling point, so they boil off first. I'm not sure what you mean by your second sentence, but refluxing ought to help maintain a constant reaction temperature, as opposed to a steadily increasing one. If the desired products are specific to a certain reaction temperature, then you need to maintain that temperature.
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  10. #9  
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    alright cool, thats really helpful thanks.
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  11. #10  
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    You're welcome.
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  12. #11  
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    Appreciate your help in the reflux thing but wasn't sure about this point

    Yes, in a mixture of organics, the smaller molecules have the lower boiling point
    if for arguments sake you had a mix of ethanol and propane. surely the ethanol would have a higher boling point despite being smaller. because of hydrogen bonds
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  13. #12  
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    I was careless. When I wrote "smaller" I was thinking in terms of molecular weight, not physical size of the molecules, and also in terms of a homologous series. In a mixture of paraffins, propane boils off before butane. In a mixture of ethanol and propane, ethanol has the higher molecular weight (but only just) and a much higher boiling point, so no doubt other factors such as hydrogen bonds might be involved. Sorry if I confused you.
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  14. #13  
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    no problem once again thanks for your help.
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