I was trying to make a $2\text{M}$ solution at $\text{pH}\, 7.5$ of Betaine $\ce {HCl}$. I started by weighing out the appropriate amount of Betaine $\ce {HCl}$, added some water and started stirring. At this point, the $\text{pH}$ of the solution was $\sim1-2$.

I went on to titrate the solution with $\ce {NaOH}$. At about $\text{pH}$ $3-4$ the betaine $\ce {HCl}$ was completely dissolved. as I added more base, I noticed that the solution began to warm up and give off a some sort of a "plasticy" smell and foamed a little bit. This began to happen at around $\text{pH}$ $5.5-5.7$.

It seems to me that the Betaine $\ce {HCl}$ is somehow reacting at high $\text{pH}$. I was wondering if someone can explain what may be happening to the Betaine $\ce {HCl}$.

  • $\begingroup$ Trimethylamine is quite a good leaving group $\endgroup$ – Waylander Mar 2 at 18:41
  • 1
    $\begingroup$ @Waylander That has nothing to do here. Helloo, this is hydrochloride! $\endgroup$ – Mithoron Mar 2 at 18:53

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