No chlorine in terephthalic acid
From the story titled Feds probe cause of freight train-garbage truck collision
Nick Materer, an Oklahoma State University chemist, said sodium chlorate, when combined with fuel, makes a more volatile mixture. "When you mix them together and add fire, they go boom," he said in a phone interview.
Materer said the chemical is usually shipped as a white powder but it can also be in a liquid solution. Either way, he said, the fumes can irritate the lungs if inhaled.
Exactly what triggered the explosion was being investigated, and Hohman said firefighters told residents of about 70 nearby homes that they could leave if they wanted to and shelter would be provided.
While one of the cars still burning late Tuesday was carrying terephthalic acid, the substance used in making plastics, another was carrying fluoroacetic acid, Hohman said. Although county officials played down the health risks posed by the burning rail cars, the National Institutes of Health website describes fluoroacetic acid as an "extremely toxic" constituent of many poisonous plants that is used to make products that kill rodents. It produces poisonous gases when burned, according to the NIH.
Materer said the gases contain chlorinated organics. He was less familiar with terephthalic acid but said it, too, contains chlorine.
IPBiz notes that terephthalic acid has chemical formula C6H4(COOH)2 and contains no chlorine.
Fluoroacetic acid has formula CH2FCOOH and contains no chlorine.
Charles Heidelberger did work on the biochemistry of fluoroacetic acid although he is better known for his work on fluorouracil [wikipedia: 5-FU was designed, synthesized and patented by Charles Heidelberger in 1957 ]