Or using their goddamn superpowers.
You could go with a dose strong enough to knock them out quicker, but that comes with the side effect of death. That's why anesthesiologists have to carefully take into account a patient's age, gender, weight, overall health, and many other attributes to prescribe a unique chemical cocktail, instead of haphazardly guessing. Everyone has their own unique fine line between going unconscious and shuffling off this mortal coil.
Now, there were records of supposed chloroform-assisted crimes (which likely inspired the pop culture trope), but they actually prove our point. Way back in 1850, in response to a public panic about the new substance being used for crime, John Snow (the one who convinced England that drinking sewer water was a bad idea, not the one who knows nothing) documented real-life cases of chloroform crimes. He found plenty of botched attempts, such as the case of an elderly clergyman who easily overpowered his rag-bearing attackers, and the case of a young woman who ripped a chloroform-soaked handkerchief away from her face and screamed for the police. But he found precisely zero examples of a chloroform-assisted crime actually succeeding.