Caffeine

google

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mid 19th century: from French caféine, from café ‘coffee’.

wiktionary

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From French caféine [1], from café(“coffee”), or German Caffein, Kaffein [2] (cp. Coffein, Koffein), from Kaffee(“coffee”) (cp. Kaffe, Koffee, Koffe), or Italian caffè(“coffee”) +‎ -ine

etymonline

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caffeine (n.)

trimethyl-derivative of xanthine, 1830, from German Kaffein, coined by chemist F.F. Runge (1795-1867), apparently from German Kaffee "coffee" (see coffee) + chemical suffix -ine (2) (German -in). So called because the alkaloid was found in coffee beans; its presence accounts for the stimulating effect of coffee and tea. The form of the English word may be via French caféine. Related: Caffeinic.