Deep Coloration of Wool Fibers Using Oxides of Inositol

Our laboratory has a strong interest in the Maillard reaction, a food coloring reaction, and has successfully used the Maillard reaction to color not only protein materials such as wool, silk, and leather, but also polyamide fiber with amino groups. However, it also became clear that very long reaction times, such as several days, are required to color theses fibers in dark colors. Interestingly, when the glucose oxides obtained by the Fenton reaction, one of chemical oxidations, was used instead of glucose, the coloring time was greatly reduced, and it became possible to color wool dark brown in a reaction time of about 2 hours. Since the Fenton reaction is highly reactive and cannot selectively oxidize the hydroxyl group of reducing sugars, it is assumed that the reaction solution also contains oxidized products of reducing sugars that are not involved in pigment formation. If the oxidized products of reducing sugars not involved in pigmentation can be reduced, further darkening of the wool can be expected. Therefore, in this study, we investigated the coloration of wool using inositol, a cyclic sugar alcohol. Since the hydroxyl groups of inositol are each present in a close chemical environment, the amount of byproducts from the Fenton reaction is expected to be suppressed. In fact, when wool was colored with inositol oxides obtained by the Fenton reaction, it was colored darker than the oxides of glucose having the same carbon number, and it was possible to color wool with a color close to black in about 2 hours of reaction time.