110-86-1

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Questions And Answer

• Chemical Structure

  Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group (=CH−) replaced by a nitrogen atom. The pyridine ring occurs in many important compounds, including azines and the vitamins niacin and pyridoxine.
  
  Pyridine Lewis structure;

• Chemical properties

  Pyridine is a colourless flammable liquid with a strong and unpleasant fish-like odour.
  
  Pyridine ;

• Productions

  2.1 Separation from Tar
  Pyridine bases are a constituent of tars. They were isolated from coal tar or coal gas before synthetic manufacturing processes became established. The amounts contained in coal tar and coal gas is small, and the pyridine bases isolated from them are a mixture of many components. Thus, with a few exceptions, isolation of pure pyridine bases was expensive. Today, almost all pyridine bases are produced by synthesis.2.2 Chichibabin synthesis
  
  Fig. 2-1 Formation of acrolein from acetaldehyde and formaldehyde
  
  
  Fig. 2-2 Condensation of pyridine from acrolein and acetaldehyde
  
  The Chichibabin pyridine synthesis was reported in 1924 and is still in use in industry. Acetaldehyde and formaldehyde react with ammonia to give mainly pyridine. First, acrolein is formed in a Knoevenagel condensation from the acetaldehyde and formaldehyde. It is then condensed with acetaldehyde and ammonia into dihydropyridine, and then oxidized with a solid-state catalyst to pyridine. The reaction is usually carried out at 350-550°C and a space velocity of 500-1000 h ^-1 in the presence of a solid acid catalyst (e.g., silica-alumina). The product consists of a mixture of pyridine, simple methylated pyridines (picoline), and lutidine. The recovered pyridine is separated from byproducts in a multistage process.
  
  Fig. 2-3 Flow sheet of pyridine and methylpyridine production from acetaldehyde and formaldehyde with ammonia. A) Reactor; b) Collector; c) Extraction; d) Solvent distillation; e) Distillation
  
  2.3 Dealkylation of Alkylpyridines
  Pyridine can be prepared by dealkylation of alkylated pyridines, which are obtained as byproducts in the syntheses of other pyridines. The oxidative dealkylation is carried out either using air over vanadium(V) oxide catalyst, by vapor-dealkylation on nickel-based catalyst, or hydrodealkylation with a silver- or platinum-based catalyst. Yields of pyridine up to be 93% can be achieved with the nickel-based catalyst.
  
  2.4 Synthesis from Nitriles and Acetylene
  Liquid-phase reaction of nitriles with acetylene is carried out at 120-180 ?C and 0.8-2.5 MPa in the presence of an organocobalt catalyst and gives 2-substituted pyridines: 
  
  Fig. 2-4 Synthesis of 2-methylpyridine from nitriles and acetylene
  The trimerization of a part of a nitrile molecule and two parts of acetylene into pyridine is called Bönnemann cyclization. When using acetonitrile as the nitrile, 2-methylpyridine is obtained, which can be dealkylated to pyridine.
  
  2.5 Synthesis from Acrylonitrile and Ketones
  
  Fig. 2-5 Synthesis of 2-methylpyridine from acrylonitrile and acetone
  Synthesis from acrylonitrile and acetone gives 2-methylpyridine selectively, which can be dealkylated to pyridine. First, the reaction of acrylonitrile and acetone, catalyzed by a primary aliphatic amine such as isopropylamine and a weak acid such as benzoic acid, occurs in the liquid phase at 180 ?C and 2.2 MPa to give 5-oxohexanenitrile, with 91% selectivity. The acrylonitrile conversion is 86%. Then cyclization and dehydration of the initial product are carried out in the gas phase in the presence of hydrogen over a palladium, nickel, or cobalt-containing catalyst at 240?C to give 2-methylpyridine in 84% yield.
  
  2.6 Synthesis from Dinitriles
  In a vapor-phase reaction over a nickel-containing catalyst in the presence of hydrogen, 2-methylglutaronitrile gives 3-methylpiperidine, which then undergoes dehydrogenation over palladium –alumina to give 3-methylpyridine. And 3-methylpyridine also can be dealkylated to pyridine.
  
  Fig. 2-6 Synthesis of 2-methylpyridine from Dinitriles
  A one-step gas-phase reaction over a palladium-containing catalyst is reported to give 3-methylpyridine in 50% yield.
  
  2.7 Biosynthesis
  Several pyridine derivatives play important roles in biological systems. While its biosynthesis is not fully understood, nicotinic acid (vitamin B3) occurs in some bacteria, fungi, and mammals. Mammals synthesize nicotinic acid through oxidation of the amino acid tryptophan, where an intermediate product, aniline, creates a pyridine derivative, kynurenine. On the contrary, the bacteria Mycobacterium tuberculosis and Escherichia coli produce nicotinic acid by condensation of glyceraldehyde 3-phosphate and aspartic acid.
  
  2.8 Other methods
  Ethylene and ammonia react in the presence of a palladium complex catalyst to give 2-methylpyridine and MEP. Pyridine can be prepared from cyclopentadiene by ammoxidation, or from 2-pentenenitrile by cyclization and dehydrogenation. Furfuryl alcohol or furfural reacts with ammonia in the gas phase to give pyridine. 2-Methylpyridine is also prepared from aniline.;

• Uses

  3.1 Solvent
  Pyridine(110-86-1) is a polar, basic, low-reactive solvent, especially for dehydrochlorination reactions and extraction of antibiotics. In elimination reaction, pyridine acts as the base of the elimination reaction and bonds the resulting hydrogen halide to form a pyridinium salt. In esterifications and acylations, pyridine activates the carboxylic acid halides or anhydrides.
  
  3.2 Medicines
  Pyridine's chemical structure can be found in various medications that are synthesized thanks in part to pyridine. One example is a medication called esomeprazole, the generic name for Nexium. This is a medication that's used to treat GERD, or gastroesophageal reflux disease. Another example of a pyridine containing medication is loratadine, more commonly known by its brand name of Claritin. Loratadine helps in the treatment of allergies.
  
  3.3 Pesticides
  The main use of pyridine is as a precursor to the herbicides paraquat and diquat. The first synthesis step of insecticide chlorpyrifos consists of the chlorination of pyridine. Pyridine is also the starting compound for the preparation of pyrithione-based fungicides. Cetylpyridinium and laurylpyridinium, which can be produced from pyridine with a Zincke reaction, are used as antiseptic in oral and dental care products. Pyridine is easily attacked by alkylating agents to give N-alkylpyridinium salts. One example is cetylpyridinium chloride.
  
  Fig 3-1 Synthesis of paraquat
  
  3.4 Synthesis of piperidine
  Piperidine, a fundamental nitrogen heterocycle, is important synthetic building-block. Piperidines are produced by hydrogenation of pyridine with a nickel-, cobalt-, or ruthenium-based catalyst at elevated temperatures.
  C5H5N + 3 H2 → C5H10NH3.5 Ligand and Lewis base
  Pyridine is widely used as a ligand in coordination chemistry. As a ligand of metal complex, it can be easily replaced by a stronger Lewis base, which can be used in the catalysis of polymerization and hydrogenation reactions. After the completion of reaction, pyridine ligand replaced during the reaction can be restored again. Pyridine is also used as a base in condensation reactions. As a base, pyridine can be used as the Karl Fischer reagent, but it is usually replaced by alternatives with a more pleasant odor, such as imidazole.
  
  3.6 Others
  Except for above uses, Pyridine is also used to product polycarbonate resins, vitamins, food flavorings, paints, dyes, rubber products, adhesives, and waterproofing for fabrics. Pyridine is added to ethanol to make it unsuitable for drinking. It is also used in the in vitro synthesis of DNA. ;

• Toxicity information

  4.1 Toxicity Level
  Low Toxicity
  
  4.2 Acute Toxicity
  LD501580mg/kg (Large mice, oral); 1121mg/kg (Rabbit, through skin); inhaled by human 25mg/m3×20 min, irritation of conjunctiva and upper respiratory tract mucosa. Subacute and chronic toxicity: inhaled by large mice 32.3mg/m3×7 hours/day x5 days/week x6 months, increase in liver weight; inhaled by humans 20～40mg/m3 (long term), nerve damage, unsteady walking, digital tremors, low blood pressure, over-sweating, occasional liver and kidney damage. ;

• Hazards

  5.1 Health hazards
  Pyridine is extremely toxic by ingestion and inhalation. Vapors are heavier than air. its combustion produces toxic oxides of nitrogen. Pyridine is highly flammable (its flash point is just 17 ºC). Pyridine also could have neurotoxic and genotoxic effects.
  
  5.2 Fire Hazards
  Behavior in Fire: Vapor is heavier than air and may travel considerable distance to source of ignition and flash back. ;

• References

  1. https://en.wikipedia.org/wiki/Pyridine#Occurrence
  2. http://www.zwbk.org/MyLemmaShow.aspx?zh=zh-tw&lid=169038
  3. http://www.softschools.com/formulas/chemistry/pyridine_formula/378/
  4. http://www.hmdb.ca/metabolites/HMDB0000926 
  5. https://study.com/academy/lesson/pyridine-in-medicine-uses-synthesis.html#partialRegFormModal
  6. http://www.toxipedia.org/display/toxipedia/Pyridine
  7. https://www.chemicalbook.com/ProductChemicalPropertiesCB8852825_EN.htm
  8. https://pubchem.ncbi.nlm.nih.gov/compound/pyridine#section=Top
  9. http://www.ebi.ac.uk/chebi/searchId.do;jsessionid=E7088896622D62FC650863C2AD197CAA?chebiId=CHEBI:16227
  10. https://www.britannica.com/science/pyridine
  11. Shimizu, S.; Watanabe, N.; Kataoka, T.; Shoji, T.; Abe, N.; Morishita, S.; Ichimura, H. (2005), "Pyridine and Pyridine Derivatives", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a22_399
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