Need help waiting on class change in a target element

I am doing a test of an ajax form that we have running, and one of the conditions it does is sets a buttons state using class based on some of the jquery.ui built-in classes.  Our form is running this very long running ajax routine (we are doing some complex file IO) is using signalr to send feedback back to the ui.  What I would like to do is check the state of a button html element on the screen, and wait while it has a specific class.  when that class disappears (the button becomes enabled) I would like to proceed.

Here is the buttons initial html:

<button class="jw-button-next ui-button ui-widget ui-state-default ui-corner-all ui-button-text-icon-secondary ui-state-hover ui-state-disabled" role="button" aria-disabled="false" type="button">

notice 'ui-state-disabled' there, that is what I want to be waiting to disappear.

Any suggestions?