Good idea, to make the transition gradually.
Here's a possible angle...
Explosives during World War One. The Germans could easily have run out of artillery shells after the British blockaded access to the massive guano deposits in South America that were the main source of Ammonia for making high explosives. German chemists solved this problem by inventing the first industrial process for producing ammonia.
(NB - you can fact check me, as I may have not quite got all those details right).
Ammonia is commonly used in many other processes, but is quite a simple chemical itself - should give you plenty of further leads to explore, as it was a critical moment in the development of industrial chemistry.
Hope that helps you.
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