Talk:Fehling's solution

General clarification
I attempted to name the complex Wikipedia gives as the oxidising agent, but overall I think it would be useful if someone could clarify the reaction mechanism and exactly what happens. The equations on the page were also conflicting so I removed one of them (the one which suggested the copper-tartrate complex was cationic - I hope I picked the right one!) This webpage suggests that a green suspension is formed along with a red ppt as a positive result, and I do remember this happening from doing the test myself. Also it gives a different structure for the copper-tartrate complex. If someone could clarify the correct complex structure and possibly add an example arrow-pushing mechanism, that would be great. Zynwyx (talk) 20:35, 23 January 2011 (UTC)

Is the reaction correct ?
When I started to check if the reaction was correct I found out that it might be false (please answer what you think of it)

First of all, why is there 2Cu2+ in the begininng ? since the bistartratocuprate(II) has only one ? And isn't there missing 2H20 in the end ?

To conclude, this is what I think the reaction should be (we can remove the elements which aren't reacting):

2Na+ +  2(C4H4O6)2-  +  2K+  +  Cu2+  +  2OH-  ---> [Cu(C4H3O6)2]4-  +  2Na+  +  2K+  +  2H2O

There might be an other possibility where one of the O- of each Potassium sodium tartrate reacts with the Cu2+ instead of one of the OH    - which would mean the drawing is false -(causing the loss of an H, as seen just before, which is caught by an OH- to form H2O), so the reaction becomes :

2Na+ +  2(C4H4O6)2-  +  2K+  +  Cu2+  +  2OH-  ---> [Cu(C4H4O6)2]2-  +  2Na+  +  2K+  +  2OH-

Again please tell me what you think and to understand what i meant, try drawing the molecules

P.S : I'm goint to start my second year of my technical degree in chemistry — Preceding unsigned comment added by Celte2 (talk • contribs) 17:27, 18 August 2012 (UTC)
 * You are correct, the first reaction is the correct one.JSR (talk) 17:36, 18 August 2012 (UTC)

Ok thank you so I'm going to edit the picture and try to upload the correct version. It might take some time since I've never done that — Preceding unsigned comment added by Celte2 (talk • contribs) 18:19, 18 August 2012 (UTC) May I use this opportunity to ask you a few questions ? Do you know the ph of the fehling's solution ? And if it reacts, for example, with glucose only when its in an alkaline environment ? — Preceding unsigned comment added by Celte2 (talk • contribs) 21:46, 18 August 2012 (UTC)


 * You should sign your posts. The use 4 ~'S at the end of the post will automatically sign your post. The pH would be basic, but I have not seen what the pH would be. It would be reacted with sugars at the pH level found under the conditions of the test.  It's been years since I've looked at the procedure.JSR (talk) 23:10, 18 August 2012 (UTC)

It seems I've made an error also, its [Cu(C4H3O6)2]4-. So if the glucose solution is pH=1, the reduction of glucose will still happen ?Celte2 (talk) 13:45, 20 August 2012 (UTC)
 * Had not noticed that. The pH of the test solution is a part of the test.  I do not remember how the test is conducted, but the test method utilized will be standardized. To be useful, if glucose is present, it give a positive test.JSR (talk) 13:51, 20 August 2012 (UTC)

I just noticed this too. I've corrected the uploaded image. Can someone check that I got it right and let me know? Barney Stratford (talk) 15:41, 25 May 2015 (UTC)

Proposed minor edit and possible additions
I believe this article could be more detailed and specific, and propose that this starts with a change from "ketone functional groups" to "aldehyde functional groups" Also, a small table showing exactly which types of functional groups it is generally able to react with might be helpful. On a basic level, this would be aliphatic aldehydes. This information should be helpful since fehling's reagent is usually compared to tollen's reagent which reacts with both aliphatic and aromatic aldehydes. I wouldn't mind making these changes, but I'd also like to confirm this knowledge before doing so. (This is also my first time trying to edit/improve an article) But given my inexperience, I think I'd be better if someone made it on my behalf. Mxksowie (talk) 15:38, 30 July 2014 (UTC)

Why should Fehling's solution be freshly prepared?
I've done a little poking around and found that air will oxidise the OH group bound to the copper atom into a ketone. The complex effectively then contains an alpha-hydroxy ketone, causing false positives when the solution is used.

I'm not clear in my mind about why the solution of Rochelle salt and sodium hydroxide doesn't itself oxidise. The redox potential of oxygen is much lower in an acid solution than an alkaline one. Is that something to do with it?

I don't consider myself to be sufficiently expert to write this into the article myself. Perhaps someone who is could verify what I've said here or add something along these lines to the article?

Barney Stratford (talk) 13:40, 26 May 2015 (UTC)

Outdated reference
http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-Fehling-e.htm Currently "Zugang nicht möglich" / "Access denied". — Preceding unsigned comment added by 84.48.181.148 (talk) 16:35, 9 December 2015 (UTC)

New research article on Fehling's solution
I just want to note, there are some new findings about Fehling's solution. The nature of the complex formed in Fehling's solution is [Cu(L-tartH-2)2]6- (tart = tartrate) Therefore, all hydroxyl groups are deprotonated and the ball and stick model showed in the article is false. Moreover, L-tartaric acid is used to prepare Fehling's solution, so the citation of the publication dealing with complex compounds of copper(II) and racemic tartrate is wrong (Albrecht, S.; Klüfers, P., "The Structural Chemistry of Text-Book Species: the Tartrato-Cuprates in Fehling's Solution", Z. Anorg. Allg. Chem. 2013, volume 639, 280-284.). The correct publication which has to be cited, can be found here: http://onlinelibrary.wiley.com/doi/10.1002/ejic.201600168/abstract. It would be nice, if somebody, who has already written several wiki articles, could correct these things. Thanks! — Preceding unsigned comment added by 46.244.176.152 (talk) 21:25, 2 November 2016 (UTC)
 * ✅--Smokefoot (talk) 00:57, 3 November 2016 (UTC)

What's the oxidation product?
It would be interesting to see information on the fate of the reducing agent. Will glucose be oxidised to gluconic acid?150.227.15.253 (talk) 10:36, 5 April 2018 (UTC)