Now pyridine is an important molecule, I happen to rather like pyridine and its derivatives. At several points in my life as a chemist I have used pyridine derivatives to do things.
While in John Plater’s lab in Aberdeen one of my favorite reagents for restricting the cross linking in a coordination polymer was to use 2,2′-bipyridine while when working in the group of the late Mike Hudson I used 2,2′-bipyridine as the core of the BTBP solvent extraction reagents. The synthesis for the BTBPs starts with 2,2′-bipyridine.
Now pyridine can be regarded as azabenzene, it is a benzene molecule in which one of the CH units has been replaced with a nitrogen atom.
The nitrogen lone pair points out into space at 120 degrees away from the two carbon nitrogen bonds in pyridine, it is on the same plane as all the atoms in the pyridine molecule are.
Pyridine is aromatic as it has 4n+2 pi electrons in a planar (flat) ring. As nitrogen is more electronegative than carbon the pi system of pyridine is more electron poor than that of benzene. The effect of the pyridine nitrogen is about the same as a nitro group attached to a benzene ring.
Much of the chemistry of pyridine is dominated by the lone pair on the nitrogen, this enables the pyridine to act as a base and to bind to metals. I am sure however with the d-block metals that pyridine is able to act as a pi-acid which will increase its ability to bind to metals. Some of the oligopyridines such as 2,2′-bipyridine are able to chelate to metals, it is interesting that Constable has made very large oligopyridines and done some interesting chemistry with them.
With iron(II) the chelating oligopyridines are able to form very dark red complexes, I have heard horror stories from people in nuclear reprocessing research community about the use of BTP in machines made from stainless steel. We will get onto that in a moment. First it is interesting that if a person holds a gun in their hand then they can deposit iron onto the skin of their hands. Depending on good your skin is at adsorbing iron from a gun, how long you hold the gun and a range of other things it can be possible to see shape of the steel parts of the gun which was held in the hand if the hand is treated with 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine. While funny shapes caused by holding iron does not mean beyond all reasonable doubt that a person has held a gun recently, it may help the investigation of crimes which involve guns.
Many of the BTPs have such a strong ability to form iron(II) complexes that their solutions can strip iron from stainless steels such as SS316L. In case you do not know what BTP is here is a diagram of it.
Here is a picture of the iron(II) complex of the parent BTP (R = H), you can see how the iron is binding to six nitrogen atoms.
BTP is an example of a molecule which has both azabenzene (pyridine) and triazabenzene (1,2,4-triazine) rings. The BTPs are able to extract americium(III) from nitric acid. The americium is extracted as a tris-BTP complex with nitrate anions as counterions which enables it to enter a solvent such as octanol. The steric demands of the BTP when it binds to the americium are smaller than those of a terpyridine also the BTP is a weaker Bronsted base. This reduction in Bronsted base strength enables the BTP to extract from rather strong nitric acid solutions. The parent terpyridine is a far weaker extraction agent which requires a carboxylic acid such as 2-bromodecanoic acid to be added and this system only will function at very low nitric acid concentrations. Here is 2,2′:6′,2”-terpyridne.
An example of its use as a base is in the synthesis of O-phenyl phenylphosphonochloridothioate. When I was working in Josef Novosad’s lab in the Czech Republic I wanted to make a phosphorus compound which was chiral at the a phosphorus atom. While I had originally had the idea of reacting phenylphosphonothioic dichloride with an excess of methyl magnesium iodide to form 1,2-dimethyl-1,2-diphenyldiphosphane 1,2-disulfide which could be cleaved with bromine to form methyl(phenyl)phosphinothioic bromide we found it was more convenient to react a mixture of phenol and pyridine with phenylphosphonothioic dichloride in diethyl ether. The pyridine reacted with the hydrogen chloride formed by the reaction of the phenol with the phenylphosphonothioic dichloride.
By the way pyridine has a horrible smell and there are wild stories about the effects of pyridine on male sexual health. I think that the stories about pyridine are a bunch of “urban myths“. But when I was an undergraduate I heard jokes about the subject. When I first used it there was a strange smell in the lab, I asked the PhD student (It was a lady) who was supervising us in the second year inorganic lab course what the smell was. She replied with “It will do more to you than it will do to me, and then stated it was pyridine”.
All very funny, but it is purely a myth. I have seen a review of the data from an experiment in which rats were fed pyridine in their drinking water. In rats pyridine does not have a harmful effect on the sexual health of the rats. There is a slight effect in female rats but it appears to be an artifact.
Pyridine will not make men go sterile. However if you contaminate yourself with pyridine it is likely to impede the process of someone else falling in love with you. I think that the stench of pyridine would discourage most people. If your clothing is contaminated with pyridine, I suggest you remove it and wash any contaminated parts of your body.