Bluetooth devices can be listed, connected and disconnected by clicking the Bluetooth icon in the top Panel in the Ubuntu Unity desktop. If you prefer to do these simple operations from the commandline, that can be done too.
To do this, we need the tools from the
$ sudo apt install bluez-tools
To list all the devices that have paired in the past:
$ bt-device --list
This lists each device with its name and UUID. The UUID of a device can be used to connect or disconnect from it.
To connect an audio device using its UUID, say
$ bt-audio --connect 00:02:3C:2F:F1:D4
To disconnect the same audio device:
$ bt-audio --disconnect 00:02:3C:2F:F1:D4
Tried with: Bluez-tools 0.1.38 and Ubuntu 14.04