Ethereum is a completely different chain. There used to be something called blocktrade(s), which I am not familiar with, that might have supported such an exchange through the steemit interface-but i am not familiar with it. blocktrade(s) was an old witness that provided said services and Justin sun froze his account as part of Sun's centralization efforts.

Technically your steem, steem dollars, or SP is already in your wallet. If you want to trade a steem based coin for another type of coin (such as ethereum), you might need to go through a traditional exchange like bittrex. As usual, when starting [or using one irregularly] a new exchange-only send a small test amount to make sure it got sent to the right address.