Jack Stands,
Good Question.
Well, here in the US, you got have the EPA Regulations which briefly discuss what you can use or cannot, depending upon where you are using it, what they call SNAP Regulations:
"unacceptable, acceptable to use conditions, and acceptable subject to narrowed use limits".
Just read this
http://epa.gov/ozone/snap/refrigerants/lists/mvacs.html "Substitutes Acceptable Subject to Use Conditions for CFC-12 in Automobiles", this is the list you want to check an alternative refrigerant (meaning the car had R12 and you want to explore something else).
No matter what you do, document what you have in there and do it right! Meaning, if you put in something other than R12, there should be a label clearly seen near where the AC is serviced (engine compartment by compressor) so that when somebody else works on the car..... they know what's in there; otherwise you will get them very upset.
To answer your question on Duracool
http://www.epa.gov/ozone/snap/refrigerants/hc-12a.html