Definitions

Michler's ketone

Michler's ketone

Michler’s ketone is an organic compound with the formula of [(CH3)2NC6H4]2CO. This electron-rich derivative of benzophenone is an intermediate in the production of dyes and pigments, for example Methyl violet. It is also used as a sensitizer. It is named after the German chemist Wilhelm Michler.

Synthesis

The ketone is prepared today as it was originally by Michler using the Friedel-Crafts acylation of C6H5NMe2 using phosgene or equivalent reagents such as triphosgene (Me = methyl):
COCl2 + 2 C6H5NMe2 → (Me2NC6H4)2CO + 2 HCl

Uses

Michler’s ketone is an intermediate in the synthesis of dyes and pigments for paper, textiles, and leather. Ethyl violet (CAS#2390-59-2, CI Basic Violet 4) is prepared by the condensation Michler’s ketone with diethylaniline in the presence of phosphorus oxychloride:
(Me2NC6H4)2CO + C6H5NEt2 + HCl → [(Me2NC6H4)2C=C6H4NEt2]+Cl- + H2O

Condensation of Michler's ketone with N-phenyl-1-naphthylamine gives the dye Victoria Blue B (CAS#2580-56-5, CI Basic Blue 26) which is used for coloring paper and producing pastes and inks for ballpoint pens.

Michler’s ketone is commonly used as an additive in dyes and pigments as a sensitizer for photoreactions because of its absorption properties. Michler’s ketone is an effective sensitizer provided energy transfer is exothermic and the concentration of the acceptor is sufficiently high to quench the photoreaction of Michler’s ketone with itself. Specifically Michler’s ketone absorbs intensely at 366 nm and effectively sensitizes photochemical reactions such as the dimerization of butadiene to give 1,2-divinylcyclobutane.

References

  1. www.orgsyn.org

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