Methods of Formation

The decomposition of benzoyl peroxide is discussed in more detail
below (p. 240).
(c) Oxidation/reduction by inorganic ions: Perhaps the best-known
example is the use of ferrous ion to catalyse oxidations with hydrogen
peroxide, the mixture being known as Fenton's reagent:

H.O.+Fe®® -* HO-+eOH + Fe®®®

The ferrous ion goes to the ferric state and a hydroxyl radical is liber­

ated. The lat^gr^cts as the effective oxidising agent in the system,

usually by abstracting a hydrogen atom from the substrate that is to

be oxidised:

HO- + H—X ->- H.O+'X

A rather similar reaction, but involving reduction of the inorganic

ion, may take place as the first step in the autoxidation of benzalde-

hyde (p. 253), which is catalysed by a number of heavy metal ions

capable of one-electron transfers:

Ph—C—H+Fe®«® -»• Ph—C + H®+»Fe®®

• 
  

  •

  
  

  (d) Electrolysis: The most common example is in the Kolbe
  electrolytic synthesis of hydrocarbons:

  
  

V o

II — 2 »0 II —2CO, dimerisation

2R—c—Oe —> 2R—C—O- —> 2R > R—R

an) (iv) (V)

The carboxyl anion gives up an electron on discharge at the anode

to yield the carboxyl radical (III) which rapidly decarboxylates to

form the alkyl radical (IV). These alkyl radicals then dimerise, in

part at any rate, to yield the expected hydrocarbon (V).

Electrolysis of ketones in aqueous acid solution results in their

reduction to pinacols (VII) via tiM^Fdical ion (VI)

+le& dimerisation RjC—Os H® RjC—OH

2R,C==0 > 2RjC—O® > | |

R,C—O^9 R,C—OH

(VI) (VII)