Pigment Red 170
Encyclopedia
Naphthol Red is an organic pigment
extensively used in automotive coating
s and painting.
It is produced synthetically by converting p-aminobenzamide into the corresponding diazonium compound
followed by diazotation with 3-hydroxy-2-naphththoic acid (2-ethoxy)anilide.
In the solid state the hydrazo tautomer
forms and several crystal
structures exist. In the initial α polymorph
the molecules are arranged in a herringbone pattern with extensive hydrogen bonding. The φ polymorph is more dense
and more stable and produced industrially by thermal treatment in water at 130°C under pressure. In this phase the molecules are planar and arranged in layers. Extensive hydrogen bonding exists within the layer but between layers the only interactions are Van der Waals force
s. Dense crystal structures are preferred for pigments used in coatings because in the event of Photochemical decomposition
the fragments are locked in place and are able to recombine. Research shows that by replacing the ethoxy group in this compound by a methoxy
group the crystal structure is less stable and in the final application and the color fades more easily. By careful selection of substituent
s it is possible to optimize crystal structure and improve optical properties .
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
extensively used in automotive coating
Coating
Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...
s and painting.
It is produced synthetically by converting p-aminobenzamide into the corresponding diazonium compound
Diazonium compound
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group R-N2+ X- where R can be any organic residue such alkyl or aryl and X is an inorganic or organic anion such as a halogen...
followed by diazotation with 3-hydroxy-2-naphththoic acid (2-ethoxy)anilide.
In the solid state the hydrazo tautomer
Tautomer
Tautomers are isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization. This reaction commonly results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond...
forms and several crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
structures exist. In the initial α polymorph
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
the molecules are arranged in a herringbone pattern with extensive hydrogen bonding. The φ polymorph is more dense
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
and more stable and produced industrially by thermal treatment in water at 130°C under pressure. In this phase the molecules are planar and arranged in layers. Extensive hydrogen bonding exists within the layer but between layers the only interactions are Van der Waals force
Van der Waals force
In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...
s. Dense crystal structures are preferred for pigments used in coatings because in the event of Photochemical decomposition
Chemical decomposition
Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...
the fragments are locked in place and are able to recombine. Research shows that by replacing the ethoxy group in this compound by a methoxy
Methoxy
In chemistry , methoxy refers to the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula O–CH3.The word is used in organic nomenclature usually to describe an ether...
group the crystal structure is less stable and in the final application and the color fades more easily. By careful selection of substituent
Substituent
In organic chemistry and biochemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon...
s it is possible to optimize crystal structure and improve optical properties .