If you want a non-hazardous (to humans) degreaser, d-limonene can be purchased food grade. It's just orange oil, has similar properties to kerosene, but is "generally recognized as safe" by the FDA and EFSA. Commonly found in liquid hand soap.

Basically, it's paint thinner you can drink.

It can also be used as an additive in petroleum based cleaners, in which case, definitely not a good idea to drink!

More to your question, I usually start with hot soapy water as a first pass, but it probably won't get your chain looking like new--need the degreasers for that.