Spectrophotometric determination of aliphatic primary and secondary amines by reaction with p-benzoquinone

Films formed by the electrooxidation of p-aminophenol (p-APh) in aqueous medium: What do they look like?

“…In the present work, during the potentiostatic electrooxidation of p-APh on FTO surfaces at pH values of 4, 6 and 8, we observed, using in situ absorbance technique in the visible range, the same behavior (not shown) described by Hassan et al [19], thus corroborating that 1,4-addition reactions occur after the electrooxidation of p-APh.…”

“…Hassan et al [19] showed that Q has a maximum absorption at 430 nm and readily reacts with aliphatic primary and secondary amines in various water-miscible organic solvents to give an intense color with a large absorption band in the range of 400-650 nm (maximum absorption at 510 nm). In the present work, during the potentiostatic electrooxidation of p-APh on FTO surfaces at pH values of 4, 6 and 8, we observed, using in situ absorbance technique in the visible range, the same behavior (not shown) described by Hassan et al [19], thus corroborating that 1,4-addition reactions occur after the electrooxidation of p-APh.…”

“…However, the concentration of Q ÀÅ in solution is significant only in basic solutions, although the radical then becomes unstable [24]. The addition of amines to 1,4 benzoquinones to yield amine-substituted quinones is well described in the literature [14][15][16][17] and can follow the electrochemical or chemical pathways shown in Scheme 1 [18,19].…”

“…This proposition was formulated by Heras et al [2]. Hawley and Adams [1] suggest that Q, formed by hydrolysis of QI (pH-4.0 buffer, hydrolysis rate constant 0.129 s À1 ), rapidly reacts with p-APh via 1,4-addition (Michael addition) reactions, resulting in amine-substituted quinones [1,[14][15][16][17][18][19], mainly at pH > 5 [1]. The 1,4-addition of p-APh to QI may also occur [1].…”

Synthesis and Biological Evaluation of 2,5-Bis(alkylamino)-1,4-benzoquinones

“…Compounds 12 - 23 were synthesized by the reaction between p -benzoquinone 11 and various amines [ 32 , 33 , 34 ]. A 3:2 molar ratio of benzoquinone/amine was required due to successive reductions and oxidations involved in the formation of the products as shown in Scheme 1 .…”