Formation of semiquinones in aqueous solutions

Qumones are capable of reacting with a large number of radiation-produced primary species like eaq, H and OH [14-16]. While eaq and H may reduce quinones by one-electron reduction process to the semiquinone, OH may either add to the ring or some suitable substituent position and give rise to one-electron oxidation to some form of transient. Formation of semiquinones by y-radiolysis has been discussed in detail m earlier monographs [7,9,17-19] and will not be included here. Pulse radiolysis kinetic spectrophotometry technique [20,21] has opened up new scope for detailed studies [8-12,15,16,22-25] on semiquinones. On pulse radiolytic one-electron reduction of quinones, semiquinones may be formed as follows - 

In aqueous solutions containing sodium fonnate, the reaction may be  

As reaction (2) also takes place, yield of Q increases in this case. 

In aqueous alcoholic solutions containing either methanol or 2-propanol, following reactions take place. 

Higher alcohols may also be used. However, more branched radicals, e.g. CH2(CH3)2C0H (formed by reactions of OH / H with tert-butanol) are normally unreactive. 

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