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.

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  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.
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    $\begingroup$ Measure the pH, and just measure the initial rate. $\endgroup$ – DHMO Jan 12 '17 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 '17 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 '17 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 '17 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 '17 at 12:18

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.


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