| Pages:
1
2 |
DJF90
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
I don't know how many times this has to be repeated at ScienceMadness, but TCT and TCCA are not the same thing:
TCT is 1,3,5-trichloro-2,4,6-triazine, C3N3Cl3. It is a strong reagent capable of deoxochlorination, e.g, RCO2H to RCOCl, ROH to RCl etc.
http://en.wikipedia.org/wiki/Cyanuric_chloride
TCCA is trichloroisocyanuric acid, C3N3O3Cl3. It is an N-chloroimide, similar to N-chlorosuccinimide in its reactions. It is an electrophilic source
of chlorine ("Cl+" from a simple perspective). It is not capable of deoxochlorination reactions, although there are publications in the
literature using e.g. PPh3-TCCA to effect such transformations. http://en.wikipedia.org/wiki/Trichloroisocyanuric_acid
|
|
|
Amos
International Hazard
Posts: 1406
Registered: 25-3-2014
Location: Yes
Member Is Offline
Mood: No
|
|
Quote: Originally posted by DraconicAcid  | | Quote: Originally posted by Amos | | Thought I'd give this a try, but I wonder, do you absolutely require anhydrous zinc chloride? Couldn't one just use a hydrate formed easily from
hydrochloric acid and zinc metal, and just end up with a lower yield? |
You need the alcohol to coordinate to the zinc for the zinc to be catalytic; if there's water coordinated there already, the alcohol won't displace
it. |
Ah, thank you very much for explaining WHY. I know this can't be done with other metal chlorides like those of aluminum and iron(III), but can
hydrates of zinc chloride be strongly heated or dried to remove the water?
|
|
|
DJF90
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by Amos |
I know this can't be done with other metal chlorides like those of aluminum and iron(III), but can hydrates of zinc chloride be strongly heated or
dried to remove the water? |
See the OrgSyn prep (http://www.orgsyn.org/demo.aspx?prep=CV1P0142), note 5.
|
|
|
MrHomeScientist
International Hazard
Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by DraconicAcid | | Quote: Originally posted by Amos | | Thought I'd give this a try, but I wonder, do you absolutely require anhydrous zinc chloride? Couldn't one just use a hydrate formed easily from
hydrochloric acid and zinc metal, and just end up with a lower yield? |
You need the alcohol to coordinate to the zinc for the zinc to be catalytic; if there's water coordinated there already, the alcohol won't displace
it. |
I'm pretty late to the party here and don't know much about organic chemistry, so forgive me but:
Wouldn't all the water present in the "200 ml of HCl 37 w%" be immediately absorbed by the anhydrous zinc chloride anyway?
I made ZnCl<sub>2</sub> once but couldn't get it to crystallize - it just reduced down to a sort of syrupy liquid. Now that I have a
dessicator, I could probably crystallize it. Making it actually anhydrous, though, sounds challenging.
|
|
|
HeYBrO
Hazard to Others
Posts: 289
Registered: 6-12-2013
Location: 'straya
Member Is Offline
Mood: 
|
|
sorry to bring up an old thread- but i agree with MrHomeScientist would like to know the answer. I found this which is interesting but doesn't really answer the question fully, but partially discusses an equilibrium at the end (an equation). Is this
to due with the stability in the acidic conditions? I thought it would merely form the hydrated complex and be hydrolysed in these conditions but
evidently it still has its catalytic abilities.
[Edited on 31-3-2016 by HeYBrO]
[Edited on 31-3-2016 by HeYBrO]
|
|
|
Loptr
International Hazard
Posts: 1347
Registered: 20-5-2014
Location: USA
Member Is Offline
Mood: Grateful
|
|
An equilibrium exists between the alkyl halide and alcohol. Halide ions are stronger nucleophiles than hydroxide ions, so as long as they are present
in equi-molar amounts, the formation of the alkyl halide is favorable. The lewis acid catalyst helps to make the hydroxyl group a good leaving group,
and as long as acidic conditions are maintained, the halide ions wont leave the equilibrium to make a salt.
This is why basic conditions are required for its hydrolysis. The halide ions will react with the alcohol preferentially over the hydroxide ions, so
you take them away, and all that is left are the hydroxide ions. I think you know what happens after that... alcohol formation!
[Edited on 31-3-2016 by Loptr]
|
|
|
Loptr
International Hazard
Posts: 1347
Registered: 20-5-2014
Location: USA
Member Is Offline
Mood: Grateful
|
|
| Quote: Originally posted by MrHomeScientist | | Quote: Originally posted by DraconicAcid | | Quote: Originally posted by Amos | | Thought I'd give this a try, but I wonder, do you absolutely require anhydrous zinc chloride? Couldn't one just use a hydrate formed easily from
hydrochloric acid and zinc metal, and just end up with a lower yield? |
You need the alcohol to coordinate to the zinc for the zinc to be catalytic; if there's water coordinated there already, the alcohol won't displace
it. |
I'm pretty late to the party here and don't know much about organic chemistry, so forgive me but:
Wouldn't all the water present in the "200 ml of HCl 37 w%" be immediately absorbed by the anhydrous zinc chloride anyway?
I made ZnCl<sub>2</sub> once but couldn't get it to crystallize - it just reduced down to a sort of syrupy liquid. Now that I have a
dessicator, I could probably crystallize it. Making it actually anhydrous, though, sounds challenging. |
I don't know the exact case with regards to ZnCl2, but some metal chloride salts decompose while attempting to dry them, so it is common for their
preparation to exclude water entirely through the use of thionyl chloride, or something similar that will create the chloride salt and irreversibly
remove water. Another option is to use an anhydride, such as acetic anhydride, which will capture the water and not return it to the system.
With that being said, there are metal chlorides that can be made anhydrous through heating, but I only have experience drying a couple of them and
they certainly needed help. For example, I made anhydrous tin(II) chloride with heating of the hydrated form in a stream of dry HCl(g).
|
|
|
clearly_not_atara
International Hazard
Posts: 2694
Registered: 3-11-2013
Member Is Offline
Mood: Big
|
|
According to Wikipedia, if you simply heat ZnCl2 * 4H2O (hydrated zinc chloride) the product is the oxychloride. The salt H2O5Zn2Cl5 crystallizes from
concentrated hydrochloric acid. Dioxane might recrystallize anhydrous zinc chloride, but the mechanism is not clear (dioxane is very hygoroscopic, and
it forms complexed salts with some metal halides, particularly MgBr2).
Most people don't seem to consider anhydrous ZnCl2 to be the sort of thing that's easy to make or to come by. It might be possible to make anhydrous
ZnCl2 by oxidizing zinc with anhydrous CuCl2 dissolved in an organic solvent (such as acetone), precipitating CuCl. Unlike many metal halides, CuCl2
can be dried by heating, if it is sufficiently gentle.
|
|
|
Loptr
International Hazard
Posts: 1347
Registered: 20-5-2014
Location: USA
Member Is Offline
Mood: Grateful
|
|
I consider it available since it can be purchased online without a business account. In fact, the listing is for 10 lbs of anhydrous zinc(II)
chloride.
|
|
|
XeonTheMGPony
International Hazard
Posts: 1636
Registered: 5-1-2016
Member Is Offline
Mood: No Mood
|
|
Can zinc be combusted in a chlorine atmosphere?
|
|
|
PHILOU Zrealone
International Hazard
Posts: 2893
Registered: 20-5-2002
Location: Brussel
Member Is Offline
Mood: Bis-diazo-dinitro-hydroquinonic
|
|
Should work, but must be quite exothermic.
I have done it with preheated Cu and Al in a big Cl2 jar to get the dry chlorides but I have never done it with Zn...
[Edited on 13-8-2016 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
|
|
|
PHILOU Zrealone
International Hazard
Posts: 2893
Registered: 20-5-2002
Location: Brussel
Member Is Offline
Mood: Bis-diazo-dinitro-hydroquinonic
|
|
| Quote: Originally posted by clearly_not_atara | According to Wikipedia, if you simply heat ZnCl2 * 4H2O (hydrated zinc chloride) the product is the oxychloride. The salt H2O5Zn2Cl5 crystallizes from
concentrated hydrochloric acid. Dioxane might recrystallize anhydrous zinc chloride, but the mechanism is not clear (dioxane is very hygoroscopic, and
it forms complexed salts with some metal halides, particularly MgBr2).
Most people don't seem to consider anhydrous ZnCl2 to be the sort of thing that's easy to make or to come by. It might be possible to make anhydrous
ZnCl2 by oxidizing zinc with anhydrous CuCl2 dissolved in an organic solvent (such as acetone), precipitating CuCl. Unlike many metal halides, CuCl2
can be dried by heating, if it is sufficiently gentle. |
What would be the point to get ZnCl2 anhydrous in the present case if afterwards one uses 35% HCl wich contains 65% water?
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
|
|
|
clearly_not_atara
International Hazard
Posts: 2694
Registered: 3-11-2013
Member Is Offline
Mood: Big
|
|
I wasn't really meaning to comment on the viability of the procedure, only the generation of anhydrous ZnCl2. While I don't know if it's required for
this procedure, I am pretty sure it's required for eg the Quelet reaction.
|
|
|
PHILOU Zrealone
International Hazard
Posts: 2893
Registered: 20-5-2002
Location: Brussel
Member Is Offline
Mood: Bis-diazo-dinitro-hydroquinonic
|
|
| Quote: Originally posted by clearly_not_atara | | I wasn't really meaning to comment on the viability of the procedure, only the generation of anhydrous ZnCl2. While I don't know if it's required for
this procedure, I am pretty sure it's required for eg the Quelet reaction. |
OK now clear!
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
|
|
|
| Pages:
1
2 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
