Talk:Pyridine

Stub?
This article seems reasonably complete to me, certainly not a stub. Someone more experienced with the proprieties of wiki should make the change, if appropriate.


 * I agree. Edited. Apocryphite 20:14, 21 March 2006 (UTC)

An amusing side-note....
http://sexcausescancer.ytmnsfw.com/ (Warning, may be considered NSFW)

Some YTMNDer and Wikipedian has reached a rather worrying conclusion about Vaginal lubrication and Pyridine... I'll quote both articles here if you don't want to go to YTMND.

From Pyridine: Pyridine is a clear liquid with an odor that is sour, putrid, and fish-like.... Pyridine is a harmful substance if inhaled, ingested or absorbed through skin, it is known to reduce male fertility and is considered carcinogenic as well.

From Vaginal Lubrication: "The lubrication fluid contains water, pyridine, squalene..." Shouldn't this be worrying? AKismet 04:12, 21 April 2006 (UTC)

^^ There are other products with Pyridine as well, including urinary track infection relief meds. Ever wonder where the "side effects may include" comes from?

That SMELL...
Ever since a bottle of pyridine was knocked over in the laboratory where I work, my coworkers and I have been *very* interested in the awful stuff. I would say that the odor of pyridine is actually indescribable. I mean I'm at a real loss for words beyond saying that it smells really, really bad. It doesn't smell like garbage, excrement, or sewage (what I would consider the heavy hitters of bad smells), and neither does it have the smell typical of aromatic compounds, which I don't mind at all. It's definitely nauseating, but I don't think it smells anything at all like fish! Not even the most putrid rotten fish odor could compete with pyridine.

Oceanstater 22:45, 30 June 2006 (UTC)

I can only agree with you on this. It is absolutely nauseating! In the article it says "a sour smell", and I don't think that is remotely true. I would say that is smells like rotten crab or some other shellfish.130.225.245.182 20:05, 9 January 2007 (UTC)

this may not make sense, but to me pyridine has a smell that is sickeningly, nauseatingly sweet.... don't get me wrong, there is absolutely nothing enjoyable about the odor. it is sweet, but a sweetness that only makes you ill....
 * Bofff! Thiols smell worse! (and there selenium analogues worse still...) Physchim62 (talk) 16:40, 12 January 2007 (UTC)
 * The smell of both pyridine and thiols are both bad and equally undescribable. I'd never smelled anything like either of them until I worked with pyridine in a lab that contained some thiols in the fridge!! Maybe the article could say at what conc the human nose can detect pyridine as a way to get across how bad it is. K.murphy 09:39, 10 October 2007 (UTC)

To me pyridine has always smelled like corn on the cob. Like smelling a thousand ears at once though. 70.141.255.250 (talk) 07:43, 13 November 2009 (UTC)


 * Maybe cadaverine and putrescine can give some inspiration?
 * Simon de Danser (talk) 11:13, 5 October 2020 (UTC)

Missing or Incorrect Citation Details in References
In the References section, reference #2 is listed as "Sherman, A. R. 'Pyridine' in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289X."

This DOI number does not match anything in the DOI system. The Encyclopedia of Reagents for Organic Synthesis (a.k.a. EROS) is published by Wiley (John Wiley & Sons), and as far as I can tell the last hardcopy version was published in 1995 and is listed by Wiley & Sons as ISBN: 978-0-471-93623-7.

There is also an online database now, also from Wiley, called e-EROS that is continuously updated. The Wiki article should provide the correct reference information. If obtained from the e-EROS database this should be noted, with the "last revision" date cited (and perhaps a link to the database web site?). —Preceding unsigned comment added by Betsy R. (talk • contribs) 20:27, 30 January 2008 (UTC)

Stoichiometry???
There is something wrong with the formula describing the industrial synthesis of pyridine:

CH2O + NH3 + 2 CH3CHO → C5H5N + 3 H2O

On the left side there are 13 H-atomes, whereas on the right side there are only 11. —Preceding unsigned comment added by 77.57.73.198 (talk) 10:31, 2 November 2008 (UTC)

You are right. Actually, an H2 molecule is needed among the products, as you can see in section 4.1 of the article (Chichibabin synthesis), in particular in the second reaction there reported. The text says that dihydropyridine is first formed, then oxidized (i. e., dehydrogenated) to pyridine. Ekisbares (talk) 17:10, 24 February 2019 (UTC)

Quantummechanical approach HOMO-orbital
In the article on phosphabenzeen or phosphorine it is stated the lone-pair on nitrogen is de HOMO of pyridine. As far is my knowledge on molecular orbitals reaches, orbitals from the &sigma;-framework are of lower energie then those used to build the &pi;-system. Is anybody able to write something on the subject?T.vanschaik (talk) 16:01, 13 January 2009 (UTC)


 * I just did a calculation in Spartan, which gives the HOMO and HOMO−1 as pi orbitals, and a sigma orbital that looks mostly like a lone pair as HOMO−2.


 * Even though the pi orbitals are higher in energy, if they react, the aromaticity of the system will be disrupted (other orbitals will be affected by the new geometry of the product or intermediate) - this may explain why pyridine often reacts through its lone pair. It does react via its pi system, not normally with electrophiles (because its electronegative nitrogen atom holds onto pi electrons tightly) but with nucleophiles, as in the Chichibabin reaction.


 * {|align="center" class="wikitable"


 * Pyridine-LUMO-plus-7-Spartan-3D-balls.png || Pyridine-LUMO-plus-1-Spartan-3D-balls.png || Pyridine-LUMO-Spartan-3D-balls.png || Pyridine-HOMO-Spartan-3D-balls.png || Pyridine-HOMO-minus-1-Spartan-3D-balls.png || Pyridine-HOMO-minus-2-Spartan-3D-balls.png || Pyridine-HOMO-minus-3-Spartan-3D-balls.png || Pyridine-HOMO-minus-4-Spartan-3D-balls.png || Pyridine-HOMO-minus-5-Spartan-3D-balls.png
 * LUMO+7 9.79376 eV || LUMO+1 3.84252 eV || LUMO 3.45515 eV || HOMO −9.36246 eV || HOMO−1 −10.35140 eV || HOMO−2 −11.14185 eV || HOMO−3 −14.09858 eV || HOMO−4 −14.72394 eV || HOMO−5 −15.61168 eV
 * }
 * }
 * }


 * Ben (talk) 21:24, 13 January 2009 (UTC)

Lead section
I recommend putting back the list of uses into the lead. While it is a bit exhaustive, it is also one of the few pieces in the lead that allow non-jargon speakers to understand what pyridine is. Without the addition, the lead is not as useful to the general reader. --Odie5533 (talk) 16:52, 15 March 2009 (UTC)
 * Hey, thanks for leaving a note and opening up the discussion. I dont feel very grumpy one way or the other so please dont take this comment the wrong way, because I do feel somewhat strongly about this kind of blanket statement "Pyridine is used as a precursor to agrochemicals (insecticides and herbicides), pharmaceuticals, paints, dyes, food flavorings, explosives, and disinfectants."  One could add this kind of statement to hundreds articles on chemical compounds, and I dont think that the information is useful aside from reminding the nonchemists that their world is fabricated from chemical building blocks. Also, the list is unweighted with respect to the various uses.  Or stated differently, one could add even more items to the list (polymers, sequestration agents, denaturants, ...).  This kind of statement does however belong in some general article about broad classes of compounds, such as heterocycles or organic compound.


 * If the nonchemist is trying to learn about pyridine, the descriptors early in the lede simple aromatic ring, heterocyclic compound, aromaticity, organic compound should tell them that this article is not the place to learn the ABC's of heterocyclic chemistry. Chemical editors generally (I think) do not agree with the well-intentioned wikipolicy (most of which we adhere to) that articles on specialized chemicals should be fully comprehensible to a non-chemist.  Hence we have created myriad topical articles to aid their comprehension.


 * So, to summarize, my reasons for contracting your list of uses are (i) it is factually dubious and (ii) the factoids do not help clarify the key concepts supporting a pretty specialized article. And again, the chem-editing community continues to dedicate serious time to more explanatory articles on broader topics (thus obviating the need to add such shopping list of app's). (Now maybe we should go check to see if the article on heterocycles lives up to my intentions!)


 * I hope that my comments do not come across as anything but respectful (and grateful). And again, if you feel strongly, go ahead and reinsert your bit.--Smokefoot (talk) 23:06, 15 March 2009 (UTC)

Electrochemical data
Where in the article is a good place to put this information? Or is there some other more appropriate place in Wikipedia? I couldn't find the oxidation potential during a simple search, so had to hunt down the source.

It's quoted as 1.4 V (vs. N.Ag.E) or 1.49 (vs. aqueous SCE) in.

Atenderholt (talk) 22:24, 22 October 2010 (UTC)

Hantzsch Synthesis Mistake
in the diagram for the hantzsch synthesis ammonium acetate is listed as NH2 OAC. this is should be NH4+ -OAc. could someone with more time on their hands fix this? Eggilicious (talk) 18:55, 3 February 2012 (UTC)
 * I replaced the image with a different one that correctly uses NH4OAc. -- Ed (Edgar181) 19:06, 3 February 2012 (UTC)

Kröhnke synthesis and reference criticism
The reference given for the Kröhnke synthesis (Lowry, et. al., 2004; #71) does not in fact refer to primary material describing that synthesis. Instead, it refers to an article wherein the authors report using Kröhnke, but refer to another article -- also not a primary reference -- for details. I stopped trying to trace it back at that point.

I was checking the reference in the first place, however, because the description and reaction scheme are inconsistent, and in some ways questionable. The text characterizes the Kröhnke synthesis as a condensation of a diketone with ammonium acetate, followed by an oxidation, but
 * 1) the reaction scheme shows ammonium acetate being used only in a preliminary, unmentioned, step to produce a diketone, and
 * 2) I don't see how the second step depicted in the scheme can be characterized as an oxidation.  On the other hand
 * 3) the second step surely requires a nitrogen source, but none is depicted; presumably this is where the ammonium acetate is supposed to come in.

Also, if I may be excused a spot of pedantry, there is no such thing as a "1,5-diketone". If a carbonyl moiety appears at position 1 then you have an aldehyde, or maybe a carboxylic acid / amide / etc., but never a ketone.

192.55.208.10 (talk) 20:06, 13 June 2014 (UTC)
 * Good eye. Keep it up. --Smokefoot (talk) 23:40, 13 June 2014 (UTC)


 * In an earlier version the entire section was referenced by the Gilchrist book on heterocyclic chemistry (https://en.wikipedia.org/w/index.php?title=Pyridine&oldid=142526636), this info has vanished. It is nice to have the original citation but it does not make sense to remove the JACS reference the image is based on. The image describes an example of this reaction. Yes, 1,5 diketones do exist. The square brackets indicate a intermediate reaction product formed after all ingredients were added. No inconsistency here. V8rik (talk) 18:22, 14 June 2014 (UTC)
 * Well we now have a citation to a secondary reference by the scientist who invented the reaction and wrote the overview. Seems like a no-brainer.  The previous description of the reaction (which I might have written) was misleading. Agreed, 1,5-diketones are well known, not sure what that remark was about. --Smokefoot (talk) 19:30, 14 June 2014 (UTC)

Hello, the subsituents of the alpha,beta-unsaturated ketone have to be switched or in the product R2 and R3 should be switched.2001:4CA0:2FFF:4:0:0:0:19 (talk) 08:15, 13 December 2016 (UTC) Andi T.

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metabolism of pyridine
Under "Health Issues", there is a figure of the metabolism of pyridine with the wrong product molecules: 2 and 4 hydroxy pyridine. They are shown with a C=0 group instead of the -OH hydroxyl group. The correct molecules appear on page 2 of reference 117. — Preceding unsigned comment added by Givatbrenner (talk • contribs) 14:59, 6 August 2017 (UTC)

Why do they use pyridine to make ethanol unsuitable for drinking?
Given it'sn't a hydrocarbon, how does it work? Alfa-ketosav (talk) 08:01, 26 April 2018 (UTC)
 * Why should it not work? Ethanol isn't a hydrocarbon either. Double sharp (talk) 10:28, 26 April 2018 (UTC)

A sentence not completely clear
In section 1.2.1 "Molecular properties", a sentence states that "However, because of the separation of the lone pair from the aromatic system of the ring affects, the nitrogen atom cannot exhibit a positive mesomeric effect". It is not clear to me the meaning of word "affects" in the context of the sentence. Has the sentence to be edited? Or it is just my poor knowledge of English (and chemistry)? Ekisbares (talk) 11:39, 24 February 2019 (UTC)
 * Looks like a typo to me. I removed it. Thanks. Pelirojopajaro (talk) 14:31, 24 February 2019 (UTC)

Big revision
Other editors are welcome to criticize or suggest further changes or reversions. The article was cut by about 15% by me today. For example original refs and discussion of pyridinium CrO3 reagents seems out of place in an article about pyridine. We have articles on those reagents. The lede was long. Some physical properties were repeated several times. The hydrogenation to piperidine was repeated. A lot of wording was dedicated to low yielding reactions.

The tricky aspect is that pyridine group does appear in many compounds, and we need to accommodate that theme while also writing about the parent heterocycle. Pyridine is not that useful (paraquat, solvent use, and specialized organic reagents). The picolines are probably more valuable commercially since the methyl group is a versatile handle. Pyridine vs pyridinium salts is not handled well. It would be reassuring for someone to check up on the general refs (Joule for example). --Smokefoot (talk) 22:33, 24 February 2019 (UTC)

Pyridoxine
Why is pyridoxine not mentioned even a single time in the current version of this article? 76.190.208.61 (talk) 20:27, 2 April 2021 (UTC)
 * Could you provide a reasoning on why it should be? --Leyo 14:59, 5 May 2021 (UTC)

SciFinder report for May, 2021
Research Topic "pyridine">references (381719)>refine "2020-" (15231)". Translation:
 * 381719 reports, patents, etc. have been published on pyridine according to Chemical Abstracts.
 * Since 2020-, 15,231 have appeared.
 * that is a lot.--Smokefoot (talk) 13:30, 5 May 2021 (UTC)

Basicity vs acidity in info boxes on wikipedia
Here, as on most pages for organic bases that I've seen, the info box features a section for "acidity". The listed value is then the pKa of the conjugate base. The result is that it is implied that pyridine itself is acidic with a pKa of 5, which is of course not the case. This is particularly confusing for students and laypeople but is a wider problem on chemistry wiki. Chemists often talk about "the pKa of pyridine", but they are aware that they are using a shorthand that is not strictly accurate. My suggestion would be to title the box "basicity" here for pyridine but anywhere else where appropriate and list the value as pKaH not pKa. Is there a general template for the info boxes where I can make the same comment?

128.176.215.76 (talk) 12:14, 20 April 2022 (UTC)

Toxicity to crabs and lobsters
If anyone with a better background in science than me is interested, Newcastle University have just completed a study (awaiting peer review) suggesting that pyridine is extremely toxic to crabs and other similar crustaceans. Zuriel147 (talk) 12:58, 30 September 2022 (UTC)
 * Interesting result, but the literature on pyridine is so vast, that the only references of interest are books and major reviews. --Smokefoot (talk) 13:28, 30 September 2022 (UTC)