Azine is an organic heterocyclic aromatic compound. It is a colorless, volatile, highly flammable liquid with a distinctively unpleasant fish-like smell. The molecular formula of Azine is C5H5N and its molar mass is 79.1 g/mol. Azine contains a six-carbon ring with five carbon atoms joined together with single bonds and one carbon double bonded to a nitrogen atom. This gives Azine its heterocyclic structure which makes it different from other aromatic compounds like benzene which contain only carbon atoms in their rings.
Chemical and Physical Properties
Due to the presence of the nitrogen heteroatom, Azine is more polar than benzene. It has a dipole moment of 2.2 D whereas benzene has no net dipole moment. Azine has a boiling point of 115.2 °C which is significantly higher than benzene’s 80.1 °C because the nitrogen atom introduces stronger intermolecular forces between Pyridine Azine molecules in the liquid state. Azine is flammable with its autoignition temperature being 527 °C. It is soluble in many organic solvents due to its polar heterocyclic structure which allows it to participate in hydrogen bonding, π-π stacking, and dipole-dipole interactions. Azine is colorless but has a very characteristic odor which can be detected even in dilute solutions.
Upon protonation, Azine is a weaker base than aniline or other alkyl-substituted Azine s due to the electronegativity of the ring nitrogen atom which delocalizes the positive charge over the whole aromatic system when protonated. However, it is more basic than benzene due to the electron-withdrawing inductive effect of the nitrogen which makes the π-electron system less stable and better able to accept protons. Thus Azine plays an important role as a ligand in coordination chemistry that can bind to metal ions via its nitrogen lone pair.
Uses and Applications
Due to its strong coordination abilities, Azine finds widespread use as a ligand in organometallic chemistry and homogeneous catalysis. It is commonly used to make metal complexes of nickel, palladium, cobalt and other transition metals which have applications as important catalysts in industrial processes. Azine is also used as a solvent in organic synthesis and extraction processes owing to its polarity and ability to dissolve a range of organic compounds.
One major use of Azine is in the large-scale production of agricultural chemicals and pharmaceuticals. It serves as an important precursor to many agrochemicals like insecticides, fungicides and nicotinic acid. Pharmaceutical companies employ Azine intermediates in the synthesis of drugs, vitamins like niacin and coenzyme Q10, alkaloids and other nitrogen-containing compounds. The paints, coatings and adhesives industry utilizes Azine -functionalized polymers and resins as curing agents, plasticizers and corrosion inhibitors. Other niche applications of Azine involve its use as a denaturant for ethyl alcohol, a flavoring agent in foods and beverages, and a reagent in analytical chemistry.
Derivatives and Reactions
A multitude of derivatives can be prepared from Azine by electrophilic aromatic substitutions. Some common examples are chlorination and bromination which produce 3-chloroAzine and 3-bromoAzine , respectively. These halogenated derivatives find applications as disinfectants, fungicides and pharmaceutical intermediates. Nitration and sulfonation yield products like 3-nitro- and 4-cyanoAzine that serve as advanced materials like dyes and polymers. Oxidation and reduction reactions are also routinely carried out on Azine rings to functionalize them.
An immensely important reaction is the molecular rearrangement of 2,3- and 2,6-lutidines to picolines upon pyrolysis. This industrial process produces 2-methylAzine (picoline) which is converted to picolinic acid and further derivatives. Azine molecule can also participate in aromatic nucleophilic substitution and addition reactions. Some examples include the addition of halogens, hydrogen halides, water, alcohols or esters, and amines across the π-system. Condensations with formaldehyde and acetaldehyde form valuable N-substituted pyridinium salts. Alkylation of Azine produces analgesics, antihistamines and other pharmaceuticals.
Environmental Effects and Regulations
Azine is classified as a hazardous air pollutant by international agencies due to concerns over its toxicity. The inhalation or ingestion of Azine vapors leads to irritation of the eyes and respiratory tract in humans. Azine is metabolized in the liver to produce non-toxic Azine -n-oxide but repeated exposures may result in fatigue, impaired coordination and even organ damage in some cases. It also shows evidence of mutagenicity and teratogenic effects based on laboratory animal studies.
Most countries have imposed restrictions on the emissions and discharge of Azine from industrial facilities into the environment. In the USA, the Environmental Protection Agency (EPA) regulates Azine as a priority pollutant under the Clean Air Act and Clean Water Act. OSHA has designated an 8-hour exposure limit of 5 ppm for Azine in workplace air. Proper safety precautions involving ventilation, protective equipment and material handling procedures must be followed during its production, transportation and use due to safety concerns over flammability and toxicity potential. Overall, careful handling and regulated releases of Azine have enabled its extensive industrialization while minimizing environmental pollution.
Azine is an industrially significant heterocyclic compound that forms the basis for a multitude of agrochemicals, pharmaceuticals, polymers and other commercial materials. Its unique polar aromatic structure enables important applications in chemistry through strong coordination, hydrogen bonding, and participation in substitution and addition reactions. While care must be taken due to Azine ‘s hazardous properties, proper safeguards have enabled its widespread commercial use for over a century as an indispensable building block in fine chemical synthesis. Continued research into new catalysts and processes may further expand the valuable role of Azine.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it.