CarstenE:
Sorry. First time. wrong rotation.
It is still wrong 
CarstenE:
the adapter that is connected to serial2 gets no connection to the computer. I does not matter which one I use. ( I also changed the comports in the Sotware so that the address is correct)
Have you tried what I suggested - to check if the "new" adapter works with Serial3 ?
Have you tried changing the order in which you connect the USB devices? On Linux the order of connection determines the serial port names on the PC. And don't expect the USB TTL adapter to appear as the same COM port as the Uno.
...R