New Angular Phenoxazine and Triangular Benzoxazinophenothiazine Dyestuffs

Phenothiazine and phenoxazine and their derivatives were mainly traditionally applied as dyes and pigments in industry, but with time, found wider applications as antioxidant in lubricants and fuel, polymerization stabilizers, pesticides/insecticides, biological stains or labelings, acid-base indicators and as drugs [1,2]. Lauth’s violet (1) and Meldola (2) were foremost known phenothiazine and phenoxazine commercial dyes [3,4]. Meldola dyes are good colourant for papers and textiles.


INTRODUCTION
Phenothiazine and phenoxazine and their derivatives were mainly traditionally applied as dyes and pigments in industry, but with time, found wider applications as antioxidant in lubricants and fuel, polymerization stabilizers, pesticides/insecticides, biological stains or labelings, acid-base indicators and as drugs [1,2]. Lauth's violet (1) and Meldola (2) were foremost known phenothiazine and phenoxazine commercial dyes [3,4]. Meldola dyes are good colourant for papers and textiles. The intense colouration of phenothiazines and phenoxazine derivatives necessitated the functionalization of the parent structures with a few of synthesizing new dyes and pigments. Okafor and Okoro had reported the synthesis of new nonlinear polycyclic azaphenoxazine dyestuffs [5,6]. We have also recently described a rapid access to new angular phenothiazine and phenoxazine dyes via palladium catalyzed cross-couplings [1]. As a result of our interest in synthesis of new dyes, a convenient syntheses of new derivatives of phenoxazine and benzoxazinophenothiazine employing classical organic synthetic procedures is now reported.

EXPERIMENTAL
Melting points was determined with a Fischer-Johns apparatus and were uncorrected. 1 H NMR data were recorded with Brucker DPX 400 MHz spectrophotometer relative to TMS as internal standard. The chemical shifts and coupling constant J were reported in ppm (δ) and Hz respectively. UVvisible spectra were recorded on Cecil 7500 Aquarius 7000 Series Spectrometer at Chemistry Advance Laboratory (CAL), Sheda Science and Technology Complex (Shestco) Abuja, using matched 1cm quartz cells and methanol as solvent. Elemental analyses were obtained on Heraeus CHN-O rapid analyzer.
10-Amino-6-chlorobenzo[a]phenoxazin-5-one (5): To a mixture of 2,4-diaminophenol (4 g, 32 mmol) and anhydrous sodium trioxocarbonate(IV) (3.3 g, 31 mmol) in 250 mL twonecked flask equipped with magnetic stirrer, thermometer and reflux condenser, was added a solution of benzene (100 mL) and DMF (10 mL). The mixture was boiled for 0.5 h followed by addition of 2,3-dichloro-1,4-naphthoquinone (7.26 g, 32 mmol) and the entire mixture refluxed with continuous stirring for 5 h. At the end of the reaction the solvent was distilled off in vacuum. The slurry poured into 100 mL of distilled water and the crude product filtered out. The crude was recrystallized from aqueous ethanol to obtain the titled compound. Yield: 8. 5  10-Amino-6-phenylbenzo[a]phenoxazin-5-one (6): To a clean dry three-necked 10 mL round bottom flask containing 3 mL of dioxane was added 10-amino-6-chlorobenzo[a]phenoxazin-5-one (297 mg, 1 mmol), phenylboronic acid (146 mg, 1.2 mmol) and K2CO3 (276 mg, 2 mmol) and the entire mixture warmed to 40 °C under inert atmosphere. This was followed by addition of Pd(OAc)2 (9 mg, 4 mol %) and Xphos (33 mg, 7 mol %) and the entire mixture heated at 80 °C for 8 h. The reaction was cooled to room temperature and evaporated the solvent. This was followed by addition of 5 mL of water and the crude product extracted from water (10 mL × 3). The combined extracts were dried with MgSO4 and concentrated in vacuum to obtain the crude product which was purified by column chromatography ( (7): In a dried 250 mL two-neck round bottom flask containing 10-amino-6-phenylbenzo[a]phenoxazin-5one (19 g, 0.056 mol), acetic anhydride (5 mL, 0.052 mol) was added 5 mL of glacial acetic acid and Zn dust (0.08 g) and flask equipped with refluxed condenser. The mixture was gently boiled for 1 h and the hot liquid poured in a thin stream into 250 mL beaker containing 100 mL of water and stirred. The crude precipitate was filtered, washed with cold water and dried. The dried crude product was recrystallized from methanol-acetone mixture yielded the titled compound as reddish microcrystalline powder.

12-Aminobenzo[a][1,4]benzoxazino[3,2-c]phenothiazine (9):
2-Aminothiophenol (2 g, 17 mmol) and anhydrous sodium carbonate (1.8 g, 17 mmol) were added into 250 mL round bottom flask containing a solution of benzene (60 mL) and DMF (40 mL) and equipped with a magnetic stirrer, thermometer and reflux condenser. The mixture was warmed for 45 min until complete dissolution was achieved. Then 10-amino-6chlorobenzo[a]phenoxazin-5-one (5 g, 17 mmol) was added and the entire mixture refluxed for 10 h. The solvent was distilled off at the end of the reaction and slurry poured into cold water (300 mL) and warmed to dissolve inorganic material. It was left overnight, filtered and crude product washed with water and recrystallized from toluene to afford the titled compound as dark purple powder. Yield: 8.
The synthesized compounds impart pink and light pink on cotton fabrics. Among the compounds studied, only compound 11 exhibited a low colour property . Compounds 7, 8, 9 and 10 showed very high fastness to both mild and strong soap. Their light fastness is only fair and may be improved by increasing the amount of mordants used.