Process for the preparation of aromatic azo-compounds

A process for the preparation of an aromatic azo-compound 4

• 7
• or a salt thereof, comprising the step of treating aromatic amino-compounds 5 and 6
• 8
• with (i) hydrogen peroxide and acetic acid, followed by (ii) conc. sulphuric acid, to yield aromatic azo-compound 4 or a salt thereof, wherein
• each m and each n is independently 0, 1, 2, 3, 4 or 5, and
• each R1 and each R2 is independently an optionally substituted alkyl, alkenyl, alkynyl, aryl, arylalkyl, arylalkenyl, arylalkynyl, alkylaryl, alkenylaryl or alkynylaryl group which may include one or more heteroatoms N, O or S in its carbon skeleton, —F, —Cl, —Br, —I, —CF3, —CCl3, —CBr3, —CI3, —OH, —SH, —NH2, —CN, —NO2, —COOH, —R3—O—R4, —R3—S—R4, —R3—SO—R4, —R3—SO2—R4, —R3—SO2—OR4—R3O—SO2—R4, —R3—SO2—N(R4)2, —R3—NR4—SO2—R4, —R3O—SO2—OR4, —R3O—SO2—N(R4)2, —R3—NR4—SO2—OR4, —R3—NR4—SO2—N(R4)2, —R3—N(R4)2, —R3—N(R4)3+, —R3—P(R4)2, —R3—Si(R4)3, —R3—CO—R4, —R3—CO—OR4, —R3O—CO—R4, —R3—CO—N(R4)2, —R3—NR4—CO—R4, —R3O—CO—OR4, —R3O—CO—N(R4)2, —R3—NR4—CO—OR4, —R3—NR4—CO—N(R4)2, —R3—CS—R4, —R3—CS—OR4, —R3O—CS—R4, —R3—CS—N(R4)2, —R3—NR4—CS—R4, —R3O—CS—OR4, —R3O—CS—N(R4)2, —R3—NR4—CS—OR4 or —R3—NR4—CS—N(R4)2, all optionally protected, wherein
• each —R3— is independently a chemical bond, a C1-C10 alkylene, C1-C10 alkenylene or C1-C10 alkynylene group, and
• each —R4 is independently hydrogen, unsubstituted C1-C6 alkyl or unsubstituted C6-C10 aryl.