8
$\begingroup$

I am performing the following $\mathrm{S_N1}$ reaction:

$$\ce{t-BuOH + HCl -> t-BuCl + H2O}$$

I would also like to measure the rate of this reaction, but I cannot seem to find a way. I initially envisaged measuring the rate by using an indicator to tell when the conc. $\ce{HCl}$ had been used up.

However, I do not believe the reaction has gone to completion, thus why, when using my method of using an indicator, the indicator never changed colour, due to leftover acid - also Clayden's Organic Chemistry [1, p. 348] cites a 90% yield, presumably meaning not all of the acid reacts.

The reaction should take 20 minutes [1] at room temperature and so I don't think I can measure the rate by looking measuring a change in temperature. I do not know how else I could measure the rate.

enter image description here

enter image description here

  1. Clayden, J.; Greeves, N.; Warren, S. G. Organic Chemistry, 2nd ed.; Oxford University Press: Oxford; New York, 2012. ISBN 978-0-19-927029-3.
Improve this question
$\endgroup$
6
  • 2
    $\begingroup$ Measure the pH, and just measure the initial rate. $\endgroup$
    – DHMO
    Jan 12, 2017 at 17:29
  • $\begingroup$ As the reaction is very slow you could measure IR spectrum vs time, preferably using total reflection ( ATR) method. $\endgroup$
    – porphyrin
    Jan 12, 2017 at 20:58
  • $\begingroup$ Side-question: terminology-wise, should this reaction be considered an SN1 reaction or an acid-base reaction? Can a reaction be both? $\endgroup$
    – Don_S
    Mar 14, 2017 at 10:29
  • $\begingroup$ @Don_S The mechanism by which it occurs is SN1, therefore, I would consider it to be an SN1 reaction $\endgroup$
    – Saul McShane
    Mar 14, 2017 at 20:25
  • $\begingroup$ You can sample aliquots and use NMR or GC to compare peaks of your starting materials to products. $\endgroup$
    – Zhe
    Jul 12, 2017 at 12:18

1 Answer 1

Reset to default
1
$\begingroup$

If you want to measure it with an electronic device I would recommend some spectroscopic technique such as IR, Raman, 1H-NMR etc. or using a digital pH meter. For the spectroscopic techniques you should probably cool down the solution to minimize error during the measurement or alkalify it to avoid further reaction. However if you want to avoid these methods and you have enough soultion-volume you could try titrating it with NaOH solution and a proper indicator.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.