Yeah, but why the Ottoman empire in particular?
This article provides some clue, I would think: http://en.wikipedia.org/wiki/Slavery_%28Ottoman_Empire%29#cite_note-2
It includes this sentence: "A circular of Jul. 20, 1871, introduces for the first time, the penalty of one year imprisonment for those who practice the slave trade." So it would seem that some Confederates believed the Ottoman Empire to be favourably disposed to slavery in the late 1860s. In the same way, there were Confederate slave owners who emigrated to Brazil following the US Civil War.