2-Aminophenol, reaction with benzoquinones

Such oxidations are especially easy, if electron-releasing groups such as hydroxyls or amino groups are located in para or ortho positions with respect to the amino groups. 3-Chloro-4-aminophenol stirred with sodium dichromate and sulfuric acid at a temperature below 35 °C gives a 58-63% yield of chloro-p-benzoquinone after the reaction mixture is allowed to stand at room temperature for 1 h [6J7]. Aminothymol is converted into thymoquinone on warming for 30 min with dilute sulfuric acid and sodium nitrite (equation 530) [451],... 

The oxidation of 4-aminophenols containing two or three pentafluoroethoxy groups to the corresponding 1.4-benzoquinones is accomplished with sodium dichromate and sulfuric acid.230 The reaction is carried out in such a manner that the second portion of the oxidizing agent is added after allowing the mixture to stand overnight, for example, the formation of 3.230... 

Hydroquinone (H2Q) is another developing agent and is commonly used in black-and-white processes, usually in conjunction with an auxiliary developing agent such as Metol (A -methyl-p-aminophenol), which is also called Elon, or Phe-nidone (l-phenylpyrazolidin-3-one) (see Figure 6), a heterocyclic agent (see Section 8.2.5). The overall reaction of hydroquinone with silver halide is shown in Eq. (15). In fact hydroquinone undergoes two sequential one-electron transfer steps, with an intermediate semiquinone (S ) and with p-benzoquinone (Q) as the final product. 

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