A few months ago, I got quite excited when I found out that benzonitrile could be made by dehydrating benzamide, which can be made via thermal
dehydration of ammonium benzoate, using P2O5.
The dehydration of the amide should be just the same as dehydrating formamide or acetamide, and the preparation of the amide itself, by heating the
ammonium carboxylate, should also be as easy as the other ones, however the preparation of the ammonium benzoate is a lot more straight forward than
either the formate or acetate, because the benzoate is much more stable, and less soluble in water.
So, with these things in mind, and a reckless desire to waste phosphoric anhydride, I went about it.
I made the ammonium benzoate simply by dissolving benzoic acid in an excess 25% ammonia solution.
The dissolution was extremely slow, so I ended up recrystallizing the benzoic acid first to increase its surface area; then it dissolved fairly
quickly.
Once dissolved, I heated the solution in a dish on a water bath, once the water was all gone I had an almost quantitative yield of the salt.
The dry salt was then sealed in a glass tube and heated, immersed in sand, to around 200c for an hour.
Upon cooling, I found that the dry white salt had turned into a light brown, wet, waxy substance, presumably benzamide.
The substance melted readily, and was thus poured out of the tube.
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