Sonnenfeld: Ellen Kullman's exit bad for DuPont

Kullman's departure a mistake: Jeffrey Sonnenfeld

The announcement that Ellen Kullman will step down as DuPont CEO and chairwoman is bad news for the chemical company and for corporate America, Yale management professor Jeffrey Sonnenfeld said Tuesday.

"This is a company that performed very well under her," he told CNBC's "Squawk Box." "Two bad quarters, that shouldn't end somebody's term."

Read More DuPont CEO Kullman to retire; company cuts earnings outlook

DuPont has seen revenues slip recently due to weak demand for its agricultural business, but its shares have risen more than 100 percent since Kullman became chief executive in January 2009.

Sonnenfeld chalked up the departure to Kullman's desire to step down at a time when she had become a "lightning rod."

Last spring, DuPont became embroiled in a proxy fight with shareholder Nelson Peltz, who wanted the company to split its volatile materials business from the more stable agriculture, nutrition and health units.

In May, DuPont fended off an effort by Peltz's hedge fund, Trian Partners, to elect two members to its board.

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Sonnenfeld said the underlying problems at DuPont had nothing to do with Peltz's plan.

"The problem here has almost entirely to do with supply-chain ripple effects of China. China is not buying crops from Brazil," he said. "That's what's brought this down. Ag products is way down."

On Monday, DuPont lowered its 2015 earnings guidance to $2.75 per share from $3.10, due largely to the impact of a stronger dollar and weakness in Brazilian agriculture markets. Analysts had expected $3.19.

Sonnenfeld said he believed DuPont would sell off its agricultural products division once Kullman leaves. He said the company's sale of its coating performance business to private equity firm Carlyle Group was an example of selling a good unit at fire-sale prices.

The Carlyle Group completed its $4.3 billion acquisition in 2013 and renamed it Axalta Coating Systems. The company has seen its shares rise 4 percent since its November IPO and has attracted investment from Warren Buffett's Berkshire Hathaway.

Read More Berkshire buys nearly 10% stake in Axalta for $560M

Sonnenfeld said it was disappointing that DuPont did not have an internal candidate who could take the position permanently, but praised the company's choice of Ed Breen as interim CEO. Breen is a member of DuPont's board of directors and presided over the turnaround of security and fire protection systems firm Tyco, where he was CEO and chairman from 2002 to 2012.

—CNBC's Reem Nasr contributed to this story.