In 1936 he left Kiel to join I G Farben Industrie at Leverkusen, where he worked on synthetic rubber.

[1] In 1949 they published a paper together on diene synthesis and additions [2] Alder received several honorary degrees and other awards, such as the 1950 Nobel Prize in Chemistry which he shared with his teacher Diels for their work on what is now known as the Diels–Alder reaction.

The cause of his death is unknown,[3] however his body was found in his apartment in Cologne, Germany after two weeks.

His niece, who found the body, stated that the odor of rotting flesh was so bad that she could smell it from the street outside.

Gertrud Alder reported that her husband was incredibly distressed when she last saw him and often muttered the phrase "Les Jardins du Souvenir" (The Memory Garden) whilst writing out his research notes.