Debris and Talk:Friedel–Crafts reaction: Difference between pages

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{{chemistry}}

'''''Debris''''' (pronounced dayBREE) is a word used to describe the remains of something that has been otherwise destroyed.

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

Depending on context, debris can refer to a number of different things:

* In [[cosmology]], debris usually refers to the remains of [[spacecraft]] that have either fallen to [[Earth]] or are still orbiting Earth, and is generally known as ''space debris''. Space debris may also consist of natural components such as chunks of [[rock]] and [[ice]]. The problem of space debris has grown as various space programs have left legacies of launches, explosions, repairs, and discards in both low Earth orbit and more remote orbits. These orbiting fragments have reached a great enough proportion as to constitute a hazard to future space launches of both [[satellite]] and manned vehicles. Various government agencies and international organizations are beginning to track space debris and also research possible solutions to the problem. While many of these debris items, ranging in size from [[nuts]] and [[bolts]] to entire satellites and spacecraft, may fall to Earth, other items located in more remote orbits may stay aloft for centuries. The velocity of some of these pieces of space junk have been clocked in excess of 17,000 miles per hour. A piece of space debris falling to Earth leaves a fiery trail, just like a [[meteor]].

* In [[marine]] environments, debris usually applies to floating [[garbage]] such as [[bottles]], [[cans]], [[styrofoam]], cruise [[ship]] waste, and fishing paraphanalia.

== Stability of carbocations ==

* In [[geology]], debris usually applies to the remains of [[geological]] activity including [[landslides]], [[volcanic]] explosions, [[avalanches]], mudflows, and [[lava]] eruptions. Geological debris sometimes moves in a stream called a ''debris flow''. Debris flows are often referred to as mudslides, mudflows, or debris avalanches. They consist primarily of geological material mixed with [[water]]. The composition of this type of flow is mainly [[soil]] and other matter, such as [[trees]] and [[rock (geology)|rock]] fragments, that are picked up as the flow moves down a [[slope]] or [[channel]]. Debris flows may be generated when hillside [[colluvium]] or landslide material becomes rapidly saturated with water and flows into a [[channel]]. Heavy [[rainfall]], snowmelt, or high levels of ground water flowing through cracked [[bedrock]] may trigger a movement of this type. Debris flows and [[floods]] may also occur when strong rains on [[hill]] or [[mountain]] [[slopes]] cause extensive erosion and/or what is known as "channel scour". Debris flows can be as thick as wet [[mud]] mixed with rock, and can transport very large boulders. Debris flows may also eventually become thinner muddy flood waters as they deposit their heavier components. Geological debris flows tend to move in pulses as [[friction]] or other barriers are overcome during the flow. Sometimes earlier pulses or previous debris flows form [[levees]] that channel the flow until they are breached. The presence of older levees indicates the recurrence and characteristics of debris flows in a particular area. This can be important information for developing land on what are known as "[[alluvial]] fans".

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.

[[User:Jhum101|Jhum101]] 18:40, 23 February 2006 (UTC)

==Wrong molecule used for reference==

* In [[meteorology]], debris usually applies to the remains of [[human]] habitation and natural [[flora]] after [[storm]] related destruction.

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.)

[[User:Jhum101|Jhum101]] 18:40, 23 February 2006 (UTC)

Hi [[User:Jhum101|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. [[User:V8rik|V8rik]] 19:35, 23 February 2006 (UTC)

* In a general sense, the term debris is used to refer to man-made garbage.

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.

[[User:Jhum101|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 [[User:Jhum101|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. [[User:V8rik|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. [[User:Jhum101|Jhum101]] 02:25, 27 February 2006 (UTC)

* sounds like a plan, happy editing! [[User:V8rik|V8rik]] 23:35, 27 February 2006 (UTC)

==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?

--[[User:DapBot|DapBot]] 00:32, 15 June 2006 (UTC)

==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

==Does anyone have a acylation mechanism?==

anyone?

== Reaction conditions ==

The article mentioned in '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.

[[User:Crazyjoe 7|Crazyjoe 7]] 12:32, 24 June 2007 (UTC)