Can I attach a extract fan on a portable a/c unit exhaust hose?
I wouldn't without first consulting the manufacturer.  You are messing with the design parameters.  With that distance, you will loose all legitimate warrantee coverage. I'm not saying it couldn't be done but you would probable need automatic variable speed control based on discharge air temperature as well as built in purge delays and base airflow settings.  Or you could just play with it and try to hold discharge temp of between 110* and 120*.  Good luck. One day you are going to forget, not have enough cooling to the condenser, run the head pressure up and damage the compressor.