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Changing the pH of an organic solvent.

  • 16-09-2009 5:52pm
    #1
    sunnyjim
    Closed Accounts Posts: 1,302 ✭✭✭


    Was thinking about heding to chromaforum for this, but though it's worth a try here. Any chemists here have any experience with using buffers or other methods for changing the pH of an organic solvent? Having a pain in the ass here with this.


Comments

  • #2
    SOL
    Registered Users, Registered Users 2 Posts: 1,155 ✭✭✭SOL


    What do you mean by the pH of an organic solvent?


  • #3
    sunnyjim
    Closed Accounts Posts: 1,302 ✭✭✭sunnyjim


    As in possible slight dilution of acetone with water, and adding some basic solution to bring up the pH.


  • #4
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    When I worked in a lab, we use 1M NaOH and 1M HCl to change the pH of anything (NaOH to arise the pH; HCl to lower it). Add them drop-wise though, and give the pH meter a minute to stabilise.


  • #5
    SOL
    Registered Users, Registered Users 2 Posts: 1,155 ✭✭✭SOL


    Okay, so I'm going to admit some ignorance here, but what does the term pH mean when applied to an organic solvent? I thought that pH is a function specific to water?

    If you want to change the pKa or deprotonate or protonate something in an organic solvent then you just chose the appropriate pKa of base/acid.


  • #6
    JOM34
    Closed Accounts Posts: 61 ✭✭JOM34


    Kevster wrote: »
    When I worked in a lab, we use 1M NaOH and 1M HCl to change the pH of anything (NaOH to arise the pH; HCl to lower it). Add them drop-wise though, and give the pH meter a minute to stabilise.
    A word of warning but from my limited experience it is very dangerous to add an acid to a solvent. Please don't do this! Majorly incompatible!


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  • #7
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    huh? Isn't that an acid to a base? I don't see much wrong with adding an acid to a solvent.. ...:confused: It depends on the solvent, of course, and the acid.


  • #8
    JOM34
    Closed Accounts Posts: 61 ✭✭JOM34


    Kevster wrote: »
    huh? Isn't that an acid to a base? I don't see much wrong with adding an acid to a solvent.. ...:confused: It depends on the solvent, of course, and the acid.
    Think you've answered the question. Just make sure the person covers all questions of compatability prior to task! I've worked in some industry applications and one golden rule was segregation of acids (HCL, H2SO4, HNO3 etc...). May not be relevant in this application.


  • #9
    JOM34
    Closed Accounts Posts: 61 ✭✭JOM34


    JOM34 wrote: »
    Think you've answered the question. Just make sure the person covers all questions of compatability prior to task! I've worked in some industry applications and one golden rule was segregation of acids (HCL, H2SO4, HNO3 etc...). May not be relevant in this application.
    Meant to say segregation of acids FROM solvents.


  • #10
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    Did you ever actually do the whole mixing an acid with a base thing? I did it over the summer at my job, simply because I didn't read the damn label on the box of one of the compounds that I was mixing. It was literally lik a mini explosion, but I mixed them too quickly. My heart nearly jumped out of my feckin chest.


  • #11
    Tangle
    Closed Accounts Posts: 9 ✭Tangle


    You cannot alter the pH of an organic solvent, nor can you measure it's pH using a pH meter, there are no free protons to measure. You can use a buffered aqueous system if your org. solvent is polar enough to be miscible with water.

    What is the nature of your quest, solubility, synthesis or chromatography? With a bit more insight into what you are trying to do I/we may be able to offer some advice.

    Adding acids to org. solvent is dangerous, Im not going to provide examples in case someone reading is stupid enough to try it out for the craic. In normal phase HPLC such additions of acids/bases act as modifiers to mask interactions on the column, therefore their interactions are not primarily related to pH


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