Synthesis
PFOA has two main synthesis routes, electrochemical fluorination (ECF) and telomerization. The equation below represents the ECF route with hydrofluoric acid reacting with octanoic acid chloride.
- H(CH2)7COCl + 17 HF → H(CH2)7COF + C7H16 + 2 C8F16O + HCl + H2
The equation above shows the multiple products of ECF. The target product, F(CF2)7COF (not represented) is produced as only 10–15% of the total product, while the main products are perfluorinated cyclic ether isomers, including FC-75. To yield PFOA, the perfluorinated acid fluoride is hydrolyzed. The PFOA formed by this method is a mixture of straight chain (78%), terminally branched (13%), and internally branched (9%) molecules, as ECF rearranges the carbon "tail" of the acid chloride. ECF also results in production wastes. 3M synthesized ECF PFOA at their Cottage Grove, MN facility from 1947 to 2002 and was the world's largest producer. ECF production continues on a smaller scale in Europe and Asia.
PFOA is also synthesized by the telomerization represented below, where the telogen is the organoiodine compound and the taxogen is the unsaturated tetrafluoroethylene.
- C2F5I + 3 C2F4 → C2F5(C2F4)3I
The product is oxidized by SO3 to form PFOA. Under reaction conditions, telomers form with varying length chains containing an even number of carbon atoms, as products mostly contain two to six tetrafluoroethylene taxogens. After oxidation, distillation is used to separate PFOA from the other perfluorinated carboxylic acids. The telomerization synthesis of PFOA was pioneered by DuPont, and it is not well suited to the laboratory. PFOA formed by telomerization is completely linear, in contrast to the mixture of structures formed by ECF.
Read more about this topic: Perfluorooctanoic Acid
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