The requirements will be at minimum a 2.7 cumulative GPA (out of 4) in your undergrad chemistry classes. Some schools (most probably in America) will require the GRE (http://www.ets.org/gre/
). More well known or schools with a larger graduate chemistry program will require a letter of recommendation. Any professor will do, does not even have to be a chemistry professor. Just somebody who has done the work that can state they think you can do it, and do it well.
I would not expect to get a PhD in under 5 years going straight from BS to PhD. But again, while you will not be making much money during this time, you can still be being paid to get your education; and all your student loans for undergraduate will be deferred during that time.
Also note, you do not even have to have a undergraduate degree in chemistry. Virtually any school will accept a undergraduate degree in Physics, or math, or chemical engineering, etc. They will just require you to do more traditional classes upfront.
To get a PhD you have to make an original contribution to your field of study. No time frame can really be put on that. And in chemistry there are many different fields, and depending on what school you go to, and what the faculty there focus on, and the kind of help you can get, some sub disciplines of chemistry will be much "easier" to produce an original contribution to the field of study then the other (note, being able to produce an original contribution and define it properly in a thesis and defend the thesis are two entirely different things).
Really, they almost do let just about anybody in with a bachelors degree in a scientific field (except in the very very top of the schools with the best and most well known chemistry programs). The requirements for the stipend and paid tuitions are higher. And getting in and being able to handle the workload are two different things!