Thornton averaged 12 strikeouts per nine innings in 2010, when he was an All-Star. That has dipped steadily since, to 6.8 this season. But he still averages 94-95 mph with his fastball and has hit 97 in recent games.
Red Sox pitching coach Juan Nieves was the bullpen coach of the White Sox for five years and has a lot of familiarity with Thornton.
“There is a certain comfort level there,” Cherington said. “The number one thing is the track record. He is a proven lefthanded relief pitcher and has been effective in the American League for a long time.”
Jacobs, 22, was a 10th round pick in the 2009 draft. The athletic outfielder hit .244 with 11 home runs and 44 RBIs for Single A Salem before a recent promotion to Double A Portland.
"He was the most impactful player available to us,” White Sox general manager Rich Hahn said.
Hahn told Chicago reporters that seven or eight teams were interested in Thornton.