Right-handers Mark Blackmar and Miguel Chalas are headed to the White Sox in the deal, which was made just a day before the Orioles must submit their projected playoff roster. Baltimore is in first place in the American League East.
By dealing De Aza when they did, the White Sox open a spot on the 40-man roster to add players who will be called up for the start of September. The White Sox could be interested in moving left-hander Carlos Rodon and infielder/designated hitter Andy Wilkins to the roster next week, and neither has a 40-man spot.
De Aza was hitting .243 with 19 doubles, five triples, five home runs and 31 RBIs in 122 games for the White Sox this season.
Blackmar, 22, is 10-1 with a 3.18 ERA and a .299 opponents’ batting average in 26 games (18 starts) with Single-A Fredrick of the Carolina League. He was a 16th-round draft pick by the Orioles in 2011.
Chalas, 22, is a combined 3-4 with a 4.48 ERA in 30 relief appearances with both Single-A Fredrick and Triple-A Norfolk. He was signed as a free agent by the Orioles in 2010.