Yeah you should really learn to proper calculate stöchiometric amounts.
If you have a mixture, you will probably never get it to crystallise, considered the very low melting point of acetic anhydride and composition of the
mixture.
The 4-5ml of Ac2O you´ve added ruined any known properties of the mixture, now you´ve got something you can only assume what it is exactly composed
of.
4-5ml is way to much, when I said add a tiny amount Ac2O after hydrolysis, I meant somthing like just a drop, maybe two.
Still tho, your mixture is mainly AcOH(=GAA) now, mixed with the 4-5ml Ac2O(at least), which is why it wont freeze.
The mp of Ac2O is -73°C, so adding more Ac2O to the AcOH/Ac2O will of course not induce any kind of crystallisation.
Water will do that instead, but only if its the correct stöchiometric amount.
Substance mixtures usually don´t have the same melting point as the pure chemical itself, that is in fact one of the properties we use to
characterise and thus differentiate substances from each other.
If you want precise results, you have to work precise, this isn´t like baking a cake, where you use the quantities as some sort of nonbinding
recommendation, or even mix everything together solely by instinct.
Then it really is no surprise that it didn´t worked properly.
And another advice: if you keep proper documentation of your work, then you could just have looked how much Ac2O you´ve added in detail, thus be
enabled to add the correct amount of H2O, and convert the whole mixture into GAA/AcOH.
Make it a habit, as it can help to correct many accidental failures you´ve made, like demonstrated here. |
