Patent GB-997396-A (GB)
Title: 2,4,5 - triphenylimidazole dimers
IPC: C07D233/54
Filed: 1963-03-21
Abstract: The invention comprises the dimeric compounds of formula <FORM:0997396/C2/1> where the imidazole rings contain two conjugated double bonds, A is a radical of formula <FORM:0997396/C2/2> where R1 is a substituent not containing an active hydrogen atom and R2, R3 and R4 are hydrogen or substituents free of active hydrogen, or where two of R1-R4 in adjacent positions form a benzo ring; the substituent or substituents ortho to the imidazole radical having a sigma constant below 0.7; and B and D are phenyl groups which may contain up to three substituents free of active hydrogen, two of which, if adjacent, may form a benzo ring; at least one of the ortho positions in each of B and D being unsubstituted.  The sigma constant is discussed in Chemical Reviews, 53, 191 (1953).  These compounds are prepared by oxidizing the corresponding 2,4,5-triphenylimidazoles in a liquid reaction medium, e.g. with alkaline potassium ferricyanide or with lead dioxide.  Suitable substituents in the benzene rings include alkyl, alkoxy, alkoxycarbonyl, alkylthio, dialkylamino, dialkylcarbamoyl, dialkylsulphamoyl, alkanoyloxy, N-alkylalkanamido, aryl, aryloxy, arylthio, halo, cyano and benzo.  Other substituents in particular examples include benzyl, benzylthio, benzoyloxy, N - ethylphenylsulphamoyl, phenylsulphonyl and nitro.  The products are often obtained in the solvated form, e.g. with ethanol.  The compounds of the invention are phototropic, i.e. they become coloured or more highly coloured on exposure to sunlight or U.V. light, and revert when removed from the light source.  Many such compounds are specified.  Starting materials.-2,4,5 - triphenylimidazoles substituted as follows in the 2-phenyl ring are prepared from benzyl ammonium acetate and the appropriate benzaldehyde or naphthaldehyde: (1) o-chloro, (2) 2,4-dichloro, (3) o-methoxy, (4) 2,4-dimethoxy, (5) 2,3-benzo, (6) o-bromo and (7) o-fluoro.ALSO:The invention comprises phototropic or photochromic compounds of the formula <FORM:0997396/C4-C5/1> where the imidazole rings contain two conjugated double bonds, A is a radical of formula <FORM:0997396/C4-C5/2> where R1 is a substituent not containing an active hydrogen atom, and R2, R3 and R4 are hydrogen or substituents free of active hydrogen, or two of R1-R4 in adjacent positions form a benzo ring, the substituent or substituents ortho to the imidazole radical having a sigma constant below 0.7 (see Chemical Reviews 53,191 (1953)); and B and D are phenyl groups which may contain up to three substituents free of active hydrogen, two of which, if adjacent, may form a benzo ring; at least one of the ortho positions in each of B and D being unsubstituted (see Division C2).  These compounds become coloured or more highly coloured on exposure to sunlight or U.V. light and revert when the light source is removed. They may be used in light-actuated sun shades or shields (see Division G2).ALSO:Glass, e.g. spectacle lenses or car windscreens, may be coated with a phototropic compound of formula <FORM:0997396/B1-B2/1> where the imidazole rings contain two conjugated double bonds, A is a radical of formula <FORM:0997396/B1-B2/2> where R1 is a substituent not containing an active hydrogen atom, and R2, R3 and R4 are hydrogen or substituents free of active hydrogen, or two of R1-R4 in adjacent positions form a benzo ring, the substituent or substituents ortho to the imidazole radical having a sigma constant below 0,7 (see Chemical Reviews, 53, 191 (1953)); and B and D are phenyl groups which may contain up to three substituents free of active hydrogen, two of which, if adjacent, may form a benzo ring; at least one of the ortho positions in each of B and D being unsubstituted (see Division C2).  In a specific example, a solution of dimethyl formamide containing cellulose acetate and the dimer of 2-(o-chlorophenyl)-4,5-diphenylimidazole is spread on a glass plate and dried with an infra-red heat lamp.