Why did Mr. Jekyll turns himself into hyde?

Hey, the "Victorian society" which I mentioned simply meant the era which the story was set in. This would be around the mid 1800's. Back then people behaved under strict moral codes. Emotions like intense anger, bad manners, overt sexuality....were frowned upon. For this reason Dr. Jekyll, usually mild mannered and rather "boring", wanted to indulge in his darker side. He wanted to feel the exhilaration of being bad in a society that demanded he be a gentleman at all times.

its because that Doctor Jekyll has a strong curiosity and motivation to separate these two sides of a person's character. He reasoned with himself that if he could do this, then he could eradicate (get rid of) the unhappiness that exists in the "darker self ". That’s why he started to study mysticism, began to theorize the that all men have inherent dual nature.