Butterfly Pea Extract as AnAcid-Base Indicator
Anthocyanin contained flaviliumcation, which had conjugated double bond, thus led delocalization of positive
charge to the whole molecule and gave some structure resonance. The effect of resonance caused the pigment
structure can be more stable as flaviliumcation [15]. If nucleophile attacks carbon atom 2 (step a),
pseudobasecarbinol(B) will be formed. This species would undergo isomerization into chalcone (c) via water catalyzed‐tautomerization. Then, if a base attacks hydrogen atom of hydroxyl group (step b), quinoid will be formed
(Fig. 5). The formation of quinoid would extend the delocalization, thus, gave color change from red in acidic
condition to green in basic condition[16, 17]. The discolorationof indicator of butterfly pea extract in weak acid‐strong base titration was from pink to green.
Whereas, butterfly pea extract gave color change of green to pink in weak base‐strong acid titration (Table 2). The
pH range of the reference indicator of phenolphtalein and methyl orange are 8.0‐9.6 and 4.4‐3.1, respectively[11].
We concluded that butterfly pea extract could be applied as indicator in weak base‐strong acid titration.