How can I insert HTML attributes whth an existing TinyMCE button?

Let's say I insert an image into my post editor. When I select it and click the "align left" button, it automatically adds the alignleft CSS class to the image.

What I would like to achieve is that it also adds the HTML attibute align = "left", so that I would be left with :

<img src="http://ift.tt/1KvEBD9" class="wp-image-123 size-thumbnail alignleft" height="141" width="188" align = "left" />