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lovelylaura
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[*] posted on 28-7-2004 at 21:16
Ochem HW help!


Hi! I know this may seem like an easy question but I am having trouble with these reactions... okay
A.) ortho-bromo benzene reacts with CH3COCl, AlCl3 to produce???? then that reacts with
1. KMnO4, OH-
2. H3O+ to produce????

B.) Benzoic acid reacts with
1. SOCl2
2. CH3CH2OH
to produce????

C.) Toluene reacts with
1. KMnO4, OH-
2. H3O+
3. HNO3, H2SO4 to produce???
** The problems are listed with the 1, 2, 3 right above the reaction arrow. Thank you SO much for any help!!!
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thunderfvck
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[*] posted on 28-7-2004 at 23:50


Okay, I shouldn't have given the direct answers without explanations or what not...So, here we go again:

A) o-bromobenzene does not exist. There's nothing to be ortho to, so you'll have to verify what's up with this one...

Anywho, CH3COCl has a wonderful leaving group, the chloride ion, ESPECIALLY WITH A LEWIS ACID LIKE AlCl3 (HINT HINT). So this happens, and what do we have, a carbocation? Hmm, so that beautiful oxygen's thinking, this isn't as erotic as I'd hoped, so maybe I'll share some of my bonds with my good friend carbon. And does she ever! Look at that triple bond that forms, wow, I'll call you an acyllium ion. But now that poor girl, oxygen, is suffering from positive charge syndrome, so that sexy beast of a benzene opens up one of those negative pi bond legs and tells that carbon to shove that bond back where it came from! Meanwhile mr. bromine says goodbye as he travels the world as a anion.

A Friedel-Crafts acylation. Could be wrong because a bromine is leaving instead of the usual proton in my examples, and the AlCl4 usually grabs this to form HCl and AlCl3, soooooo...?

And the KMnO4 will oxidize anything into a carboxlyic acid. HINT. The H3O+ merely protonates that which was lost in the OH- stage.

B) This one is very easy and you should be ashamed.

SOCl2 (pronounced socal-2) is a lovely specimen. He likes to react with carboxylic acids to produce SO-TOO who is originally from China! That sexy carboxylic acid has that OH group that not only screams OH OH, but moans like thunder when she has an orgasm. You see, socal-2 and carboxy-OH are about to engage in some serious love making. They have waited for this moment for ages, socal-2 in particular; he hasn't been touched in ages and will explode with the lightest of strokes. So they begin with the formal foreplay, and then the OH's start grabbing socal's "!S!"pecial spot and BOOM! Watch as that load rips past the sulfur onto socal's oxygen. And now they're tied together in intimacy, but socal's oxygen doesn't like the force blown all over her face, so she wipes it off and throws it right back onto that sulfur, who says NO! I WILL NOT SWALLOW ANYTHING THAT COMES OUT OF MY BODY! and tells a chlorine to fuck off. But that chlorine has some plans of his own, as he attacks the carbonyl carbon and throws THAT load off onto the oxygen. Man, now things are really getting feisty. Anyways, I think you can figure out the rest. Especially if you know that acyl chlorides (aka CH3COCl, HINT HINT) really like getting rid of those chlorines...And look at that oxygen on ethanol, man, I can smell the orgasms already...

C) Blah. Figure it out yourself for the oxidations, I went through that. ANyways, the HNO3/CONC H2SO4 will nitrate the ring. NO2 formed in situ with H2SO4! Positive charge on the NO2! The negativity of the legs of benzene! Let's spread that eagle! Carboxlyic acid's are meta directors.

Enjoy trying to interpret any of this.

:D



[Edited on 30-7-2004 by thunderfvck]




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Turel
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[*] posted on 29-7-2004 at 09:58
Awww.......NOT cool.


I am in the middle of an Uber-detailed response, and I refresh to see this? Not cool at all. I'll keep it in case you change your mind..... :(

-T
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chemoleo
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[*] posted on 30-7-2004 at 09:13


Lol thunder, what an imaginative reply ;)
L.L, do write back if this isn't helpful - because it is! ;)




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[*] posted on 30-7-2004 at 12:56
Mechanisms


There are several inaccurate statements in your post, thunderfvck. I was given a go-ahead to post my response now, so I shall, in it's entirety.

A.This is a Friedel-Crafts Acylation, and it produces 3-bromo-acetophenone:

The aluminum chloride (anhydrous) complexes with the acyl chloride to remove chloride ion, forming the stable species [AlCl4]- and the subsequently produced carbocationic species CH3C(+)O, which is stabilized through electron resonance between the carbonyl function from (+)C=O to C#O(+) where # = a triple bond.

CH3COCl + AlCl3 ---> AlCl4- + CH3C(+)O (resonance stabilized)

The positive species is subjected to electrophilic attraction to the aromatic negativity of the benzene core ring, and we get substitution. The site of attack is that which produces the highest probability for localized electron presence. Bromine is a decently electronegative element and does influence the electron distribution around the ring somewhat, giving measurably higher localized electron density at positions meta to the bromine atom; and thus we have a higher probability for substitution at these sites:

The positive acyl species bonds to a meta position carbon and transfers the positive charge there. Excluding the rest of the ring, the site of attack looks like:

CH3CO(+) + PhBr ----> CH3COC(+)H

The fabricated C-C bond between the ring and the acyl function is more than sufficiently strong to not retract under the current conditions, and furthermore, inductive effects from the additional electron withdrawing group now present (the acyl function) causes the destabilized carbon to retract an electron from the H to which it is bonded, and to extrude this proton, allowing for charge neutralization and retention of aromaticity.

CH3COC(+)H ---> CH3COPhBr + H(+)

This extrusion of a proton is extremely favorable, as the intermediate ring is highly strained from the destabilization.

1.The alkaline environment of -OH propagated solutions sufficiently converts the acetonphenone to its enol tautomer, from PhCOCH3 to PhC(OH)=CH2, in the form of resonant ionic species: PhCOCH2(-) <----> PhC-O(-)=CH2

The permanganate ion is more than able to react with this species; it tears it apart, destroying the carbon chain in the process. The alkene is easily oxidized to benzoic acid and CO2, resulting in destruction of the C=C bond formed by the enol and replacing each with C=O. Little formaldehyde, if any, is produced in this process; and any such that would be produced would be further oxidized by the permanganate to formic acid and subsequently to carbon dioxide.

2.Hydronium ions, as stated before, simply protonate the anionic species of the benzoic acid, giving you your final 'benzoic acid' product.

B.

1.SOCl2 reacts with benzoic acid, as said before, to form benzoyl chloride, hydrogen chloride, and sulfure dioxide. The polar positive character of S causes attraction with the lone pair of electrons in the carboxyl function C=O, resulting in two simultaneous electron and ion transfers:

Oxygen from C=O bonds to S, giving C(+)-O-S(-)-Cl (excluding all nonparticipating parties) and the subsequent extrusion of Cl- from the intermediate, as well as of a proton from the carboxyl, evolving HCl; and finally, electron transfer from C(+)-O(-) formed from loss of the proton, to regenerate the cabonyl C=O, giving the intermediate PhCOOSOCl.

Again with polar characters at work, we see further rearrangements: Electronegative chlorine further polarizes sulfur, and inductive effects shuttle this electron pull all the way to the carboxyl carbon atom. These resonances favor migration of chloride to the carbocationic center, because of the corresponding evolution of SO2 gas, as oxygen removes bonding from the carbocation and completes a double bond with sulfure. This removal of SO2 causes the migration to go to completion rather quickly and favorably, resulting in benzoyl chloride, PhCOCl and sulfure dioxide, SO2.

2.Reaction with ethanol is quite simple. Benzoyl chloride posesses a great leaving group: the chloride ion, as it is both electronegative and stable on its own. The electronegative pair of Cl and =O again subject the central carbon to conforming to positive polar character, and it thus exhibits electrical attraction to the lone pair of electrons on the alcoholic oxygen in EtOH.

As the lone pair are subjected to intermolecular attractive forces, these forces are felt on the attached hydrogen atom through induction and field effects. As the alcoholic oxygen lends orbitals for bonding with the polar carbon, its positive character decreases, allowing further removal of electrons by oxygen and chlorine, resulting in true ionization potentials.

The inductive effects upon the hydrogen atom cause it to become polarly positive, where it begins to experience the effects of field effects, and is attracted to the spatially nearby chlorine. We see removal of chlorine as chloride ion, as well as of hydrogen as a proton, evolving HCl and allowing the full orbital bonding between RO- and the carbocation, forming the ethyl ester of benzoic acid, PhCOOEt.

C.

1.Similar to before, permanganate ion attacks the methyl function off of the benzene ring. The mechanisms in place for this type of action are still under a lot of debate, relative to whether they are of radical or ionic natures. Permanganate ion can theoretically be used to stop at the aldehyde stage (benzaldehyde) with not so wonderful yields, but it will also easily oxidize toluene all the way to benzoic acid quite easily, and this is in fact the largest cause of low yields for isolation of the aldehyde state.

2.Again, hydronium ion serves to protonate the produced benzoate anion, giving benzoic acid.

3.Aromatic nitration reactions are inherently dirty, haha. You can talk about the theory of the clean reaction all day, and even use the purest reagents available, and at the end of the day, you will still almost always have a dirty mess afterwards. :)

It basically works like this:

We have already discussed how electrophillic attraction to the benzene ring affects reactions with positive species. A mixture of dehydrated nitric and sulfuric acids will (in theory, cleanly) produce nitronium ions, NO2(+) which are very electrophillic and reactive. What happens is the strong acids (both nitric and sulfuric acids are very strong acids) will protonate the nitric acid, forming a hydrogen bonded species that looks like two or more nitric acid molecules chained together (and hypothetically with possible sulfuric acid links in there too), giving an effective species (although not actually present as such) of H2NO3(+).

Sulfuric acid has very strong dehydrating properties, to the point where it even dehydrates itself (funny situation to me) forming polysulfuric acids and waters of hydration. The solution is able to remove H2O from the H2NO3(+) species, forming H2O + NO2(+) products.

The nitronium ion, in theory, cleanly, exhibits electrophillic attraction to the benzene ring, where it facilitates the run of the mill aromatic eletrophillic substitution by attaching to the ring at the point of probabilistic success, and transfers the positive charge to that carbon, which then shuttles the charge to the hydrogen it was bonded to, and spits out a proton, retaining its aromatic character.

Carboxyl functions are electron withdrawing functions, and as such, are meta position directing for further substitutions, so your most likely product would be meta-nitrobenzoic acid, or 3-nitrobenzoic acid. Since nitro functions are also electron withdrawing, it is unlikely that just mixture of nitric and sulfuric acids would polynitrate this compound, since each substitution decreases the delocalized electron density of the ring, making it less and less attractive to positive species.

More in side reactions to come later, possibly, if there is interest.

-T

[Edited on 30-7-2004 by Turel]
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[*] posted on 4-8-2004 at 01:50


Quote:

Sulfuric acid has very strong dehydrating properties, to the point where it even dehydrates itself (funny situation to me) forming polysulfuric acids and waters of hydration.


It seems unlikely to me that sulfuric acid would dehydrate itself. Are you sure you aren't confusing this with it's capability to protonate itself?




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Turel
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[*] posted on 4-8-2004 at 14:40
&raquo;98%


I don't know where the threshold is exactly, but I do know for certain that >98% H2SO4 will dehydrate itself, and form polysulfuric entities and water bound to sulfuric entities.

Protonation is the first step in the mechanism by which this occurs.
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[*] posted on 4-8-2004 at 18:44


Thunderfvck that is a beautiful response to lovelylaura! I can see that you are learning your organic chemistry very well indeed. When I took this course recently those same thoughts kept coming to my mind, i.e., male/female copulations of nucleophiles and electrophiles. But you have a greatly expanded this with a much more vivid imagination than I have. I don't think LL will know if she's doing chemistry or .....:D

[Edited on 5-8-2004 by Magpie]




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