An investigation of anthraquinone-catalysed alkaline pulping via component modeling and electron spin resonance experiments

Abstract

The radical anion of anthraquinone (AQ•−) has been generated by the reduction of anthraquinone (AQ) with sugars in aqueous alkaline solution. This appears to be the first time that the radical has been observed (esr spectrometry) in an entirely aqueous medium. Alkaline methanol solutions of AQ, when irradiated with light, yielded colourless solutions also exhibiting strong esr signals characteristic of. AQ•−.The ability of various carbohydrate and lignin preparations to reduce AQ, or to oxidize the reduced forms of AQ, was also investigated, both by direct observation and by electrode potential measurements. In very concentrated alkali, AQ was reduced by glucose to a green solid thought to be a quinhydrone.

Tartaric acid, an efficient chiral auxiliary: new asymmetric synthesis of 2-alkyl-2-arylacetic acids

“…), 4.81 (AB q, 2 H, J = 5.9, = 14.4), 7.26-7.49 (m, 5 H); 13C NMR 7.6, 33.7, 52.2, 52.6, 76.3, 77.4, 115.2, 125.9, 127.8, 128.2, 140.7, 169.3; MS, m/e 295 ( + 1)+, 265 [(M + 1)+ -CH20].…”

“…On this basis, the four transition states 4-7 are proposed for the interaction of enol ethers E and Z with bromine (Figure 1). The higher proximity of the carboxyalkyl group (*COOR1) to the double bond in the transition states 4 with respect to that in 6 and 5 with respect to that in 7 determines a greater electron-withdrawing field effect, which makes the double bond of 6 and 7 more reactive than that of 4 and 5, respectively.…”

Change is permanent: thoughts on the fading of cochineal-based watercolor pigments

“…Anthraquinones have well-known antioxidant effects, even if they are not always potent [41]. Anthraquinone is used in the delignification of wood pulp for paper-making where its effect is thought to occur by electron transfer to a lignin molecule [42]. The antioxidant properties of anthraquinones are evident from the slow drying of oil paints that comprise red lakes.…”

UV‐Triggered Optical Response and Oxygen Scavenging Ability of a Water‐Soluble Poly(N,N‐dimethylacrylamide‐co‐2‐vinylbenzylanthraquinone) Copolymer

“…In fact, several AQ species (like hydroxy‐anthraquinone) are naturally occurring products, often proposed for biological/medicinal applications. Moreover, the catalyzed oxidation/reduction of AQ derivatives has been widely applied for the alkaline delignification of wood, while AQ or more elaborated derivatives are used or proposed for the production of hydrogen peroxide (anthraquinone process) . However, the vast use of anthraquinoidic derivatives is found in dye production, since a range of colors maybe obtained, as a consequence of the chemical structure of 9,10‐anthraquinone .…”