nitroboy
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Simple Cl2 Addition
can the Chloro group be attached to any hydrocarbon through simply bubbling Cl2 through a solution?
my plan is C2H5OH + Cl2 to yield C2H4ClOH. will this work? or is a catalyst required like the addition of the OH- group to ethene using H3PO4?
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madscientist
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The chlorine will first attack the OH (turning the ethanol into acetaldehyde), then will proceed to chlorinate the other hydrogens.
I weep at the sight of flaming acetic anhydride.
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Turel
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Oxidation/Substitution
The Cl-Cl molecule will abstract an electron from the 1- carbon (ethan-1-ol) and will collapse to extrude a chloride ion, with the initial Cl now
attached to the 1- carbon. The polization shifts, Cl being more electronegative than OH, and inductive effects cause Cl's pull on C to also be
felt on the oxygen in OH.
The removal of the chloride ion left the 1- carbon positive, resulting in a bond distance shrinkage, brinking -OH closer to the carbocation. So close,
in fact, that the oxygen shifts electron orbital pairing to absorb the positive charge in favor of a carbonyl (C=O) bond. The H, having weak bonding
capability, and O+ being an electronegative species, absorbs the positive charge, resulting in a neutral C=O and a hydrogen bonded proton.(resonance)
The thermal energies released in these shifts causesthe loss of the proton into solution, which is attracted to the chloride ion formed earlier.
In order for the formed acetaldehyde to react further, it can react via two mechanisms, they being a base catalyzed tautomerization to the enol (vinyl
alcohol) followed by substitution, or via the same mechanism as above, although much slower than the base catalyzed route. However, base catalyzation
must be watched carefully, for it can be so reactive (and is the case with acetaldehyde) that you will induce a Haloform reaction and end up with
formate and chloroform.
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acx01b
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CH3CH2OH + Cl2 --> CH3CHO + 2(H+Cl-)
then i didnt undertsand
lol
does it work with I2 too?
because i have some iodine teincture (i2 in ethanol), and i already mixed it with water, and i never got any acidity.
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Turel
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Tinctures
Tincture of iodine is not I2 solvaed within ethanol. Tinctures use chemical adducts to drastically increase the solubility of I2 in alcohols, namely
adducts of povidone and potassium iodide.
Li/Na/K iodides will form triiodide adducts with I2 in solutions, causing more mass of I to be held within solvation. Povidone works similarly.
These additives would interfere with these reactions, as the active species in the solution is not I2, but is I3- ion. Add to this the fact that I2
makes a very poor oxidizer thanks to its low electronegativity compared to common functional groups, and that H-I is a decent reducing agent that is
enhanced by a very wide spectrum of catalysts, and you have a multitude of reasons why you would sense no acidity. I3- ion would also serve as an
effective reducing agent in this environment.
Even for addition of Cl2 to EtOH, the activation energy is significantly high enough that external heating is required during addition to start the
reaction. The reaction itself is quite exothermic, but requires thermal energy above ambient conditions to begin (assuming no catalysis).
The base catalyzed polychlorination reactions are even more exothermic, so very careful temperature control is crucial. It is common to get runaway
chlorinations due to heat, and is very frequently too hard to accurately moderate. Be careful if attempting this reaction in decent quantity.
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acx01b
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tks 4 theses precisions 
[Edited on 19-5-2004 by acx01b]
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nitroboy
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i was thinking it would yield Chloral Hydrate. thanks for the input though.
so the Cl- will rip the H+ off forming an acidic solution?
then start replacing all the H+ with Cl-. does this then mean it will be just 2 Cl's bonded to the C, and a C=O bond?
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Marvin
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Exhaustive chlorination (just by feeding in Cl2 until the solution will absorb no more) of absolute ethanol produces mainly HCl and the alcoholate of
chloral. Hydrolysis of the solid product enables you to crystalise chloral hydrate from the solution. Treatment with a base would produce
chloroform.
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nitroboy
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this is what i thought might happen.
when you add the Cl2 to the CH3CH2OH, the Cl- group will first attack the OH- group, replacing it and yielding water.
and then proceed to take all the H+ off and create an acidic solution with some of the Cl-. CCl3CCl3, was what i thought this would yield. can
somebody please tell me why this isn't the case ?
thanks. i am trying to get my head around all the replies at the moment...sorry if i sound kinda stupid.
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Marvin
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Cl2 wont displace an OH, but it will oxidise it to the aldehyde.
The aldehyde group is strongly activating, and the chlorine now replaces one by one each hydrogen on the CH3 group, until you end up with CCl3CHO.
This is chloral. In water and with hydroxide this is furthur oxidised to trichloroacetic acid, which easily decarboxylates to chloroform.
If you need more details I'm sure you can find them online by searching for the haloform mechanism.
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