Azo compounds are compounds bearing the functional group R-N=N-R', in which R and R' can be either aryl or alkyl. A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions In the context of organic molecules aryl refers to any Functional group or Substituent derived from a Simple aromatic ring, may it be Phenyl An alkyl is a Univalent radical consisting of Carbon and Hydrogen atoms arranged in a chain The N=N group is called an azo group, although the parent compound, HNNH, is called diimide. The more stable derivatives contain two aryl groups. The name azo comes from azote, the French name of nitrogen that is derived from the Greek a (not) + zoe (to live). Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14
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As dyes and pigments
As a consequence of п-delocalization, aryl azo compounds have vivid colours, especially reds, oranges, and yellows. In chemistry delocalized electrons are Electrons in a Molecule that are not associated with a single Atom or to a Covalent bond. Therefore, they are used as dyes, azo dyes for example Disperse Orange 1. A dye can generally be described as a Colored substance that has an affinity to the substrate to which it is being applied Disperse Orange 1 (4-anilino-4'-nitroazobenzene is a Dye of the Azobenzene class Some azo compounds, eg. methyl orange, are used as acid-base indicators due to the different colours of their acid and salt forms. Methyl orange is a PH indicator frequently used in Titrations. The development of azo dyes was an important step in the development of the chemical industry.
Azo pigments are colorless particles (typically earths or clays), which have been colored using an azo compound. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and Azo pigments are important in a variety of paints including artist's paints. Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid They have excellent coloring properties, again mainly in the yellow to red range, as well as lightfastness. The lightfastness depends not only on the properties of the organic azo compound, but also on the way they have been adsorbed on the pigment carrier. Azo pigments are advantageous because they are non-toxic.
Organic chemistry
Aryl azo compounds
Aryl azo compounds are usually stable, crystalline species. Azobenzene is the prototypical aromatic azo compound. Azobenzene is a Chemical compound composed of two Phenyl rings linked by a N=N Double bond. It exists mainly as the trans isomer, but upon photolysis, converts to the cis isomer. Aromatic azo compounds can be synthesized by using an azo coupling reaction, which entails an electrophilic substitution reaction where a aryl diazonium cation attacks another aryl ring, especially those substituted with electron-releasing groups. An azo coupling is an Organic reaction between a Diazonium compound and an Aniline or a Phenol. Electrophilic aromatic substitution or EAS is an Organic reaction in which an atom usually Hydrogen, appended to an aromatic system is replaced Diazonium compounds or diazonium salts are a group of Organic compounds sharing a common Functional group with the characteristic structure of R-N2+ [1] Since diazonium salts are often unstable near room temperature, the azo coupling reactions are typically conducted near ice temperatures. The oxidation of hydrazines (R-NH-NH-R') also gives azo compounds. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Hydrazine is a Chemical compound with the formula N2H4 It has an Ammonia -like odor and is derived from the same industrial chemistry [2]
Alkyl azo compounds
Aliphatic azo compounds (R and/or R' = aliphatic) are less commonly encountered than the aryl azo compounds. One example is diethyldiazene, EtN=NEt. [3] At elevated temperatures or upon irradiation, the carbon-nitrogen (C-N) bonds in certain alkyl azo compounds cleave with the loss of nitrogen gas to generate radicals. Photochemistry, a sub-discipline of Chemistry, is the study of the interactions between Atoms, small Molecules, and light (or Electromagnetic radiation Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell Owing to this process, some aliphatic azo compounds are utilized as radical initiators. In Chemistry, radical initiators are substances that can produce radical species under mild conditions and promote Radical polymerization reactions Representative is Azobisisobutylonitrile (AIBN) which is widely used as an initiator in polymerization. Azobisisobutyronitrile is a Toxic compound often used as a foamer in Plastics and Rubber and as a Radical initiator. Because of their instability, especially for aliphatic ones, care should be taken with the handling of azo compounds or an explosion may occur. An explosion is a sudden increase in Volume and release of Energy in an extreme manner usually with the generation of high Temperatures and the release
See also
References
- ^ H. An azo coupling is an Organic reaction between a Diazonium compound and an Aniline or a Phenol. Ponceau 4R (also known as Food Red 7, CI 16255, Cochineal Red A, New Coccine, Acid Red 18, SX purple) is a synthetic Ponceau S, Acid Red 112, or CI 27195 is a sodium salt of a Diazo dye that may be used to prepare a stain for rapid reversible detection of T. Clarke and W. R. Kirner (1941). "Methyl Red". Org. Synth.; Coll. Organic Syntheses is a Scientific journal that since 1921 has provided the Chemistry community with annual collections of detailed and checked procedures Vol. 1: 374.
- ^ March, J. “Advanced Organic Chemistry” $th Ed. J. Wiley and Sons, 1992: New York. ISBN 0-471-60180-2.
- ^ Ohme, R. ; Preuschhof, H. ; Heyne, H. -U. (1988). "Azoethane". Org. Synth.; Coll. Organic Syntheses is a Scientific journal that since 1921 has provided the Chemistry community with annual collections of detailed and checked procedures Vol. 6: 78.
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