Phenol decarboxylative/decarbonylative

As a minor pathway, L3 units are formed competitively to photo-Fries rearrangements some radicals formed in CO-O bond scissions may decarbonylate or decarboxylate before further radical recombination or hydrogen abstraction. This leads to the formation of hydroxy- and dihydroxybiphenyl units, aromatic ether structures, and phenol as end groups that further photolyzed into a mixture of species (in a convoluted absorption) that produces the yellowing of the PC film without any defined structure. 

Furan is produced by the catalytic decarbonylation of 2-furaldehyde or by decarboxylation of 2-fiiroic acid with copper powder in quinoline. Furan is a colourless, water-insoluble liquid of pleasant odour, bp 32°C. Addition of hydroquinone or other phenols inhibits polymerization, which occurs slowly at room temperature. 

Initially, a thermooxidative process takes place, due to the high oxygen content of phenolic resins. Conley and coworkers proposed that the first step, Eq. (24), is the formation of a hydroperoxide (36) which later fragments into phenols containing aldehyde and carboxyl groups.This is followed by a decarboxylation reaction which starts around 300°C and, finally, by a decarbonylation reaction which begins around 500°C. In addition, fragmentation reactions may occur above about 400°C, Scheme 1. 

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