Truly fantastic! Looks like you're living the dream with the perfect convergence of work and hobby.
While the analysis part was very well explained, I have one nitpick regarding the first part of the video. You refer to the aluminum as a catalyst,
which is incorrect. Since the aluminum is used in a stoichiometric amount and is consumed in the reaction, it is a reagent, not a catalyst. If it was
a catalyst, you wouldn't need to use a stoichiometric amount, and it would theoretically still be present as aluminum metal after the reaction is
over. It would also be nice to see some more discussion of the chemistry that is happening here, but I realize that this reaction is still not very
well-understood.
The following is somewhat speculative since I don't have definitive data to back me up, but what is most likely happening in this reaction is
analogous to the reaction that uses red phosphorus. The aluminum and iodine are reacting to produce aluminum iodide in situ, which reacts with the
methanol to produce methyl iodide and hypothetically aluminum hydroxide. The reason this reaction is more cumbersome and low-yielding than
the version using red phosphorus is that the byproducts in the phosphorus reaction remain soluble, while the aluminum compounds formed will clump up
and limit the reaction of the iodide/hydroxide intermediate. PI3 will readily give up all three of its iodines to leave behind
H3PO3. AlI3 gives up its first iodine to form AlI2OH, which is undoubtedly going to crash out of solution.
If you're lucky, a second iodine will react, but now that the mixture is heterogeneous, it's going to be a lot slower.
The elemental analysis that you showed for the solid byproduct supports this. If you take the percent mass compositions and divide by molar mass of
each element, you can get a crude molar ratio of the elements present. The oxygen to iodine molar ratio is roughly 2:1, so you probably have something
like Al(OH)2I as your main byproduct. While the ratio of aluminum to oxygen is just about 1:1, this can probably be chalked up to there
being excess aluminum metal present (which you can clearly see in the video, so not surprising). Exactly what compound(s) is/are formed here is likely
more complicated. Aluminum iodide itself exists as a dimer and there are numerous configurations of aluminum oxide-hydroxides, plus you still had bits
of aluminum metal in there too, so it isn't surprising that the XRD was unhelpful.
Edit: I should also note that I did a Sci-Finder search for anything on basic aluminum iodide, but it only turned up a few patents related to
anti-perspirant production that were very useless.
[Edited on 5-24-2020 by Texium (zts16)] |