Talk:Friedel-Crafts reaction
From Wikipedia, the free encyclopedia
 |
This article is within the scope of WikiProject Chemistry, which collaborates on Chemistry and related subjects on Wikipedia. To participate, help improve this article or visit the project page for details on the project. | ||
|
Article Grading: The article has not been rated for quality and/or importance yet. Please rate the article and then leave comments here to explain the ratings and/or to identify the strengths and weaknesses of the article.. |
|||
This article could perhaps do with a more thorough mechanism, explaining the action of the AlCl3? Sorry I can't do this myself, but my TeX skills are sorely lacking -- Tom
One of the reactions shown is the addition of a methyl group to a benzene. The mechanism for this addition involves the loss of the halogen from the alkyl halide and the formation of a carbocation. The methyl carbocation is far too unstable to allow for the addition of a methyl substituent to benzene through the Friedel-Crafts reaction. Furthermore, the reaction would not occur with even a primary alkyl halide (such as the addition of an ethyl group, as shown later in the article) as primary carbocations are also much too unstable to allow for addition. --Ian
Contents |
[edit] Stability of carbocations
No, methyl groups and primary alkyl halides CAN react in Friedel-Crafts alkylation. In the case of secondary and tertiary halides, the carboation is formed by the removal of the halogen ion by the Lewis Acid. However, because methyl and primary carbocations are NOT stable as you stated, the halide instead forms a Lewis acid-base complex with the acid, and this acts as the electrophile in this case: CH3CH2-Cl + AlCl3 -> CH3CH2-Cl(+)-Al(-)-Cl3. I'll add this later to the main article, with some fancy drawings. Jhum101 18:40, 23 February 2006 (UTC)
[edit] Wrong molecule used for reference
The article references making 2,4,6-triethylbenzene. However, not only is this wrongly named, it does not form as such. The foot-note lists an abstract for 1,3,5-Tris(aminomethyl)-2,4,6-triethylbenzene, but this is a different molecule, and the abstract doesn't even mention friedel-crafts. I'll fix this later, and add a new section on the limitations of friedel crafts reactions (specifically, polyalkylation, reactivity, and the para/ortho substitution.) Jhum101 18:40, 23 February 2006 (UTC)
Hi Jhum101, I agree that 2,4,6-triethylbenzene should be 1,3,5-triethylbenzene. This compound is the first reaction step in the eventual synthesis of 1,3,5-Tris(aminomethyl)-2,4,6-triethylbenzene (consult the complete article if you want to check this information). Also even though the article does not specify a friedel-craft, it can be deduced from the reaction conditions that it is one. V8rik 19:35, 23 February 2006 (UTC)
Hmm, I just looked over the article, but my problem with this section is that this is an exception to the normal rules about activating groups and ortho/para directors vs. deactivating groups and meta directors. This is a special case, and when most Friedel-Crafts reactions take place, the alkylated product further activates the ring, and promotes additional substitution in the ortho and para positions. The reaction in the reference has nothing to do with this activation, instead, relying on overall steric hinderance. It is possible, but in the grand scheme of the Friedel-Crafts reaction, the majority of product which undergoes polyalkylation does so in the ortho and para positions. Thermodynamics and stability are important concepts when considering the reaction, but in this case, the Hammond Postulate is applied, and the stability of the intermediates determines the product results. Sorry for the lengthy note, but this could be a confusing article for someone unfamilar with the topic, and this discussion may just overcomplicate the subject. Jhum101 04:23, 24 February 2006 (UTC) (also, I plan to update the main page with info on substituents, a detailed look at the mechanism and carbocations, other functional groups that can be used to form the carbocation (alkenes and alcohols), intramolecular Friedel-Crafts rxns, limitations with substituants, and polyalkylation. It's a lot of work, and right now, I have more pressing O-Chem labs to finish.)
Hi Jhum101, The best way to go forward I guess is to add content on general FC reactions. I am looking forward to read your contribution. My contribution does not involve an exception though, it is about reversible FC and associated with it thermodynamic reaction control. Also, Wiki readers are intelligent readers, we just have to make sure that basic topics are well separated from advanced topics in order not to get the reader confused. V8rik 23:46, 25 February 2006 (UTC)
Prehapts a seperate section on themodynamics and stability of products? This could be seperate from the general kinetics of Friedel-crafts reactions. Jhum101 02:25, 27 February 2006 (UTC)
- sounds like a plan, happy editing! V8rik 23:35, 27 February 2006 (UTC)
[edit] Stability of electrophile in FC acylation
The reason for lack of rearrangement of the carbocation electrophile in FC Acylation is "there are no carbocation rearrangements as an aromatic carbocation is very stable compared to alkyl carbocations." This is just wrong - the carbocation isn't aromatic. The reason is the resonance stabilisation where the empty shell of the Carbon interacts with the lone pairs of electrons on the oxygen in the acyl group. This should be changed, no? --DapBot 00:32, 15 June 2006 (UTC)
[edit] Errors in alkylation mechanism
According to the mechanism, you start and end with the same compound (benzene) and lose the R group somewhere along the way. Also, as mentioned previously the mechanism does not directly involve an alkyl carbocation as an intermediate. It would be good if someone could edit the mechanism to rectify these things.--Joe
[edit] Does anyone have a acylation mechanism?
anyone?
[edit] Reaction conditions
The article mentioned 'Reaction conditions are similar to the Friedel-Crafts alkylation mentioned above' in the Friedel-Crafts acylation section.
Many different sources give different conditions for this reaction, and I'm interested to know why, and what are the true conditions.
Crazyjoe 7 12:32, 24 June 2007 (UTC)
Chemistry is an experimental science and there seldom are "true" conditions apart from some prerequisites. For example, the Friedel Crafts reaction will definitely need a Lewis acid catalyst (e.g. FeCl3, AlCl3, etc), and to prevent hydrolysis of the catalyst, anhydrous conditions are desirable. Different temperatures and pressures and catalyst loadings will probably work, though they may affect yield and reaction time. This is representative of synthetic chemistry. --Rifleman 82 13:49, 24 June 2007 (UTC)
[edit] Error in Friedel-Crafts dealkylation section
The image and description of the Friedel-Crafts dealkylation reaction portray an alkylation, not a dealkylation.
- Incorrect: the text with the image clearly states that the product forms by a series of alkylations and dealkylations. V8rik 17:06, 12 July 2007 (UTC)
- I think the text needs some re-working to more effectively convey that this is the result of a series of alkylations and dealkylations, as a chemistry student I was almost thrown off by this
- I have made the text more clear V8rik 19:37, 12 August 2007 (UTC)
[edit] drugfuture.com
Sorry, but "drugfuture.com" links point to an illegal copy of the Merck index. I have already contacted Merck about the issue. 213.188.227.119 (talk) 15:08, 29 November 2007 (UTC)
