Pyridine having a chemical formula C5H5N is a primary heterocyclic organic compound. From the structural point of view, pyridine is related to benzene, wherein a methane group (=CH-) is substituted by a nitrogen atom. The ring of pyridine is found in various vital compounds, such as pyridoxine (B6), niacin (B3) and the azines.
In its natural form, pyridine is a monochrome liquid having a disagreeable odour. This organic compound can be made artificially from raw coal tar or from various other chemicals. Being a good solvent, pyridine is commonly used to liquefy other substances in it. In addition, this organic compound is utilized for making various different products including vitamins, medicines, paints, dyes, adhesives, rubber products, herbicides and insecticides. It is also used for making food flavourings. Pyridine can also be made synthetically by breaking down several natural minerals occurring in the environment.
Various foods consumed by us are flavourful and their flavour is attributed to many complex compounds containing pyridine. Pyridine is a very unstable organic compound and it quickly evaporates from its liquid form. Pyridine that is released in the atmosphere may take a very long period, varying from many months to several years, to break down and form other compounds. In addition, pyridine also readily blends with water. When pyridine is released into the soil or in water, this compound may take anything between a few days to some months to break down into other compounds.
A Scottish chemist named Thomas Anderson is credited with the discovery of pyridine way back in 1849. He discovered pyridine in the form of a component of bone oil. Anderson was successful in isolating pure pyridine two years after he discovered the organic compound. He was able to isolate pure pyridine using the fractional distillation method of bone oil. Pyridine is a feebly alkaline, colorless, water-soluble, highly inflammable liquid having a characteristic, disagreeable odour, somewhat similar to that of fish.
Pyridine is often employed in the form of a precursor to pharmaceuticals and agro-chemicals. In addition, this organic compound is also a vital reagent and solvent. This organic compound is also added to ethanol to make in unbefitting for drinking. Other uses of pyridine include using it to synthesize DNA in laboratory experiments. It is also used for synthesizing sulfa pyridine, a medication meant to treat bacterial and viral infections. Pyridine is also used in antihistaminic medications (mepyramine, tripelennamine), in addition to herbicides, bactericides and water repellents. Though a number of chemical compounds are not synthesized from pyridine, they still have the ring structure of this heterocyclic organic compound.
In the past (as mentioned above), people produced pyridine from raw coal tar, in addition to a form of by-product in the coal gasification process. Nevertheless, with the increase in the demand for pyridine, more economical techniques of producing this organic compound were developed and it began to be produced synthetically by synthesizing ammonia with acetaldehyde. Currently, over 20,000 tonnes of pyridine is manufactured globally every year.
The earliest reference that has been documented credits the Scottish chemist Thomas Anderson of discovering as well as isolating this organic compound way back in 1849. Anderson heated animal bones over high temperature and examined the oil released from the bones and its content. During his experiments, Anderson isolated several compounds from the bone oil and one of these was a colorless liquid with a objectionable smell. Two years later, he isolated pyridine from the crude liquid obtained from bone oil. According to Anderson, the substance he isolated from bone oil was very soluble in water and it easily dissolved in concentrated salts and acids when heated. Pyridine is just somewhat soluble in different oils.
As pyridine is highly inflammable, Anderson named the organic compound he isolated from bone oil pyridine - which has its origin in the Greek term pyr denoting fire. The suffix idine was added to pyr keeping in view the chemical nomenclature of the substance, like in toluidine, which suggests a carbon cycle comprising one nitrogen atom.
In fact, pyridine's chemical structure was determines several decades after Anderson discovered this organic compound and isolated it from animal bone oil. A German chemist Wilhelm Körner (1869) and a Scottish chemist and physicist James Dewar (1871) proposed that, like the similarity between naphthalene and quinoline, pyridine's chemical structure needs to be drawn from benzene by using one nitrogen atom to replace one C-H unit. Later, the scientific community confirmed the proposals put forth by Körner and Dewar during an experiment wherein pyridine was condensed to piperidine by using sodium in ethanol. Years later, in 1876, a British chemist William Ramsay combined hydrogen cyanide and acetylene into pyridine in a scalding iron-tube furnace. This was the first time that a heteroaromatic compound was synthesized.
The conventional techniques of producing pyridine resulted in very low yield of the compound. On the other hand, growing demand for this new organic compound led the scientists to search for newer and more efficient ways of making pyridine. The efforts yielded results in 1924 when a Russian chemist named Aleksei Chichibabin found a breakthrough. He invented the synthesis reaction to produce pyridine synthetically. The new method was based on reasonably priced reagents. Even today, this method is followed for large-scale production of pyridine.
Till date, there have been a small number of studies to determine the potential consequences of using pyridine on human health. Human case reports as well as studies undertaken on animals give the impression that the most significant concern of exposure to pyridine on human health is that it may harm the liver. In addition, there may be other health effects on humans following the use of pyridine and they include renal effects, neurological effects as well as irritation to the eye and skin. As of now, it is not certain whether use of pyridine may also be responsible for birth defects, reproductive problems and even cancer.
There are several derivatives of the organic compound pyridine and some of them are important drugs. In fact, some of these derivatives are vital constituents of many enzymes and vitamins. For instance, nicotinamide (also known as pyridine-carboxylic acid amide) is found in coenzyme I together with ribose, adenine and phosphoric acid constitute a vital two nucleotides. 2-methyl-vinyl pyridine is a vital raw material for manufacturing synthetic rubber. It is possible to obtain pyridine from various sources, such as naturally occurring coal tar or it can even be made from ammonia and acetaldehyde. Pyridine is a solvent; in addition, it can also be employed for industrial use in the form of an aid dye, a denaturing agent as well as a starter for an assortment of products, counting dyes, disinfectants, pharmaceuticals, adhesives, explosives and many others. This organic compound can also be used in food seasoning.
In Canada, pyridine is mostly used in the form of a corrosion inhibitor in pipelines as well as for oil and natural gas wells. There are a number of minor uses of pyridine too. The alkyl derivatives of pyridine include its use in the form of a corrosion inhibitor in cleaning in industries as well as de-scaling products in the closed water heat transfer systems. They are also used in the form of a formulant (also known as non-active ingredient) in various agricultural herbicides. In addition, pyridine is a secondary additive in cleaning products, especially for surfaces that come in contact with various types of foods.