Crystal violet lactone

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Crystal violet lactone, leuco form

Crystal violet lactone, protonated colored form

Crystal violet lactone (CVL) is a leuco dye, a lactone derivate of crystal violet 10B. In pure state it is a slightly yellowish crystalline powder, soluble in nonpolar or slightly polar organic solvents.

Its chemical formula is C₂₆H₂₉N₃O₂ and its CAS number is [1552-42-7].

The central carbon in the leuco form is in a tetraedric configuration, forming four covalent bonds. In acidic environment the lactone ring is broken, the central carbon loses one valence and becomes planar, interconnecting the π systems of the aromatic rings to form one large conjugated system acting as a chromophore with strong absorption in visible spectrum.

It was the first dye used in carbonless copy papers, and it is still widely used in this application. It is also the leuco dye component in some thermochromic dyes, eg. in the Hypercolor line of clothing. One of its novel uses is a security marker for fuels. It is now being used in the purple type of zubbles

It may cause allergic contact dermatitis in people handling the carbonless copy paper.