Crystal violet lactone (CVL) is a

leuco dye A leuco dye (from the Greek λευκό ''leuko'': white ) is a dye which can switch between two chemical forms, one of which is colorless. Reversible transformations can be caused by heat, light or pH, resulting in examples of thermochromism, ...

, a

lactone Lactones are cyclic carboxylic esters. They are derived from the corresponding hydroxycarboxylic acids by esterification. They can be saturated or unsaturated. Lactones are formed by lactonization, the intramolecular esterification of the corresp ...

derivate of

crystal violet Crystal violet or gentian violet, also known as methyl violet 10B or hexamethyl pararosaniline chloride, is a triphenylmethane, triarylmethane dye used as a histological stain and in Gram staining, Gram's method of classifying bacteria. Crystal ...

10B. In pure state it is a slightly yellowish crystalline powder, soluble in nonpolar or slightly polar

organic solvent A solvent (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...

s. The central carbon in the leuco form is in a

tetrahedral In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

configuration, with four

covalent bond A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...

s. In an acidic environment, the

ring is broken, with the oxygen detaching from the central carbon. This now-trivalent position is a planar

carbocation Carbocation is a general term for ions with a positively charged carbon atom. In the present-day definition given by the IUPAC, a carbocation is any even-electron cation with significant partial positive charge on a carbon atom. They are further ...

that is resonance stabilized, interconnecting the π systems of the

aromatic ring In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugation alone. The e ...

s and the

amino In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...

s. This single large

conjugated system In physical organic chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in a molecule, which in general lowers the overall energy of the molecule and increases Chemical stability, stability. It is Reson ...

is a

chromophore A chromophore is the part of a molecule responsible for its color. The word is derived . The color that is seen by our eyes is that of the light not Absorption (electromagnetic radiation), absorbed by the reflecting object within a certain wavele ...

with strong absorption in

visible spectrum The visible spectrum is the spectral band, band of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' (or simply light). The optica ...

, giving this compound its distinctive color. This chemical is usually drawn in the

resonance structure In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or '' ...

with the cation on nitrogen. : It was the first dye used in

carbonless copy paper Carbonless copy paper (CCP), also known as non-carbon copy paper or NCR paper ('no carbon required'—a backronym derived from its creator, National Cash Register), is a type of coated paper designed to transfer information written on the top shee ...

s, and it is still widely used in this application. It is also the

component in some

thermochromic Thermochromism is the property of Chemical substance, substances to change color due to a change in temperature. A mood ring is an example of this property used in a consumer product although thermochromism also has more practical uses, such as b ...

dyes, e.g. in the Hypercolor line of clothing. One of its novel uses is a security marker for fuels. Its limitations as a fuel marker have to be carefully contemplated by users, as Crystal Violet Lactone (leuco) readily transforms to the colored species in >10% Ethanol Containing Gasoline, imparting a strong color. Crystal violet lactone as a fuel marker was covered by the

BASF BASF SE (), an initialism of its original name , is a European Multinational corporation, multinational company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters are located in Ludwigshafen, Ge ...

patent DE4422336A1 until June 2014. It may cause allergic

contact dermatitis Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes ...

in people handling the carbonless copy paper.

References

{{reflist Triarylmethane dyes Anilines Lactones Carbocations