Лако-красочные материалы — производство

The reaction of keto acids (79) having no amino group with 3-alkoxy — diphenylamines (80) is used to synthesize 3 ‘-anilinofluorans (81), especially near-infrared-absorbing fluoran compounds (Eq. 6).

(6)

Table 7 shows melting points of a few near-infrared-absorbing fluoran compounds (81) thus prepared.

Preparation of 6′-[4-(4-Anilinoanilino)anilino]-2′-chloro-3′-methylflu — oran (81a). To concentrated sulfuric acid (10 g) was added 2-(5-chloro-2- hydroxy-4-methylbenzoyl)benzoic acid (3.4 mmol) followed by 4-anilino-4′- (3-methoxyanilino)diphenylamine (2.6 mmol). The mixture was stirred at room temperature for 24h, and poured into ice water (100ml). The precipitate was filtered off, washed with water, and then refluxed with a mixture of toluene (150 ml) and sodium hydroxide (20 g) dissolved in water (150ml) for 1 h. The toluene layer was separated, washed with hot water, and concentrated. The residue was then column chromatographed on silica gel to give 6′-[4-(4-anilinoanilino)anilino]-2′-chloro-3′-methylfluoran in 43% yield as a grayish white powder, mp 202-203 °C.