1.4- Dioxin electrophilic addition reactions

Dioxin and 1,4-dithiin both undergo easy electrophilic addition reactions, e.g. of halogens to the double bonds. Alcohols under acid catalysis form ketal addition products. 

The double bonds in 2,3-dihydro-l,4-dioxin, 2,3-dihydro-l,4-oxathiin and 2,3-dihydro-1,4-dithiin undergo standard electrophilic addition reactions. Under acid catalysis, methanol adds to 2,3-dihydro-l,4-oxathiin to give 2-methoxy-1,4-oxathiane (66HC(21-2)842). Various examples are available of reactions of the double bonds with carbenoids to give bicyclo[4.1.0]diheteroheptanes (77LA910,78ZC15), and with alkenes in [2 + 2] cycloadditions (78CB3624). 

Electrophilic substituent factors for the -C6H5 XC1X and -OC6H5 XC1X groups, needed to calculate the OH radical addition rate constants for polychlorinated biphenyls (PCBs), polychlorodibenzo-p-dioxins (PCDDs), and polychlorodibenzofurans (PCDFs), appear in Atkinson (1996), with discussion of an approach to calculating the rate constants for the PCDDs and PCDFs. The room temperature rate constants for the reactions of the OH radical with phenanthrene and anthracene, recently measured by Kwok et al. (1994,1997), are lower by factors of 2.5-8 than the previous recommendations and rate data (Biermann et al., 1985 Atkinson, 1989), casting doubt on the previously proposed correlation between the OH radical addition rate constant and ionization potential (Biermann et al., 1985). 

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