M. Segi, Takumi Yoshida
2021
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Journal
Heterocycles
Abstract
3,7-Bis(dialkylamino)phenoxazin-5-ium salts having different amino groups (dimethylamino, diethylamino, dipropylamino, dibutylamino, and pyrrolidyl) and counter anions (chloride, bromide, iodide, hydrogensulfate, and nitrate) were synthesized in up to 80% isolated yield as blue cationic dyes. In a d d i t i o n , 3 , 7 b i s ( d i e t h y l a m i n o ) p h e n o t h i a z i n 5 i u m a n d 3 , 7 bis(diethylamino)phenoselenazin-5-ium iodides were also synthesized in 20% and 17% isolated yields, respectively. Polypropylene fabrics were dyed with the above synthesized blue cationic dyes. As an evaluation result, it has been found that the moderate size such as diethylamino groups at the 3 and 7 positions of phenoxazinium salts is suitable for the dyeing ability. INTRODUCTION Polypropylene (PP) fibers have various excellent characteristics such as small specific gravity, heat resistance, rigidity, transparency, water resistance, chemical resistance, and good insulation. However, it is difficult to use PP fabrics for fashionable apparels due to the poor dyeing properties. This main disadvantage is attributed that PP has no dyeing site owing to the simple molecular structure. Various methods for dyeing of PP fibers have been studied and performed so far, for examples, spin-dyeing, mixing of a good-dyeing resin, surface modification method, and supercritical fluid method. Nevertheless some problems have been still remained, i.e. lack of color saturation, changes in physical properties, and increases in manufacturing and dyeing costs. To solve these problems, we investigated a novel dyeing method for PP fibers utilizing the colorless reduced form (leuco form, L-dye) of a cationic dye (Scheme 1). In our method, the permeability and affinity of the cationic dye for PP fibers would have been enhanced by reduction of the cationic dye with a reducing agent in basic aqueous solution followed by reoxidation of the adsorbed L-dye with an oxidizing agent in acidic conditions. The reduced compound (L-dye) of a cationic dye is very sensitive to air and is easily reoxidized. As a result, the cationic dye was strongly adsorbed onto the PP fibers. Thus, our method made it possible to dye PP fibers with various kinds of colors using some cationic dyes simply and inexpensively. In our previous report, we evaluated the dyeing ability for PP fiber using only commercially available cationic dyes, in which Basic Blue 3 (3,7-bis(diethylamino)phenoxazin-5-ium chloride) was the most effective for blue dyeing (Figure 1). Hence, we herein report the synthesis of several blue cationic dyes having different amino groups or counter anions compared with Basic Blue 3 and their blue dyeing abilities for PP fiber. In addition, 3,7-bis(diethylamino)phenothiazin-5-ium and 3,7-bis(diethylamino)phenoselenazin-5-ium iodides, which are sulfur and selenium analogs of phenoxazin-5-ium salt, respectively, were also synthesized and their dyeing abilities were investigated. Scheme 1. Estimated mechanism for dyeing of PP fiber with a cationic dye Figure 1. Basic Blue 3 and its reduced form RESULTS AND DISCUSSION 3,7-Bis(dialkylamino)phenoxazin-5-ium salt derivatives 3 were synthesized by the treatment of 3-dialkylaminophenols 1 and N,N-dialkyl-3-methoxy-4-nitrosoanilines 2 in acidic solutions, modifying the method reported by Ihara et al. (Scheme 2). Compounds 1a, 1b and 1d are commercially available. The synthesis of 3-dipropylaminophenol 1c, 3-(pyrrolidin-1-yl)phenol 1e, and nitroso-substituted compounds 2 are shown in Scheme 3. 3-Dipropylaminophenol 1c was prepared by N,N-dipropylation of 3-aminophenol in 99% yield. 3-(Pyrrolidin-1-yl)phenol 1e was obtained by cleavage of the L-dye L-dye L-dye