Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
ferrous sulfate
I am getting materials together to make a few grams of quinoline via the Skraup synthesis. My procedure calls for the use of "ferrous sulfate" to
moderate a normally violent reaction.
What I have available is pottery grade ferrous sulfate heptahydrate. I've looked at Vogel, OrgSyn, and Cummings to see if any call out a specific
hydrate or lack thereof. None do. Each just says "ferrous sulfate."
In looking at Fisher and VWR catalogs it seems that the heptahydrate is all that is commonly available. So, it seems that the common nomenclature
used in the procedures assumes the usual hydration without actually specifying what it is. It seems like I have run onto this before.
I feel I need to understand this before proceeding for a couple of reasons:
1) the water of hydration for FeSO4*7H2O is about 45% of its weight.
2) the procedure specifies the use of dry glycerine indicating that excess water added will reduce yield.
So, my question to the forum is: In these quinoline procedures do you think that "ferrous sulfate" actually means ferrous sulfate in its commonly
available form, ie, FeSO4*7H2O?
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
woelen
Super Administrator
Posts: 8013
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
Yes, you may assume that ferrous sulfate is FeSO4.7H2O. The anhydrous sulfate is a white solid, which is very unreactive (it does not dissolve in
water). Anhydrous ferrous sulfate is hard to make, it cannot be made from hydrated ferrous sulfate, due to an internal redox reaction (iron goes to
+3, sulfate forms SO2).
If you use pottery grade ferrous sulfate, then first try to clean it a little bit. Usually pottery grade ferrous sulfate contains brown clumps, which
are basic ferric sulfate. These do not dissolve and should be removed.
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
Thank you Woelen. I shall proceed to the lab.
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Sure of that? I've left out crystals that partially dehydrated without turning to brown mush.
Tim
|
|
|
obsessed_chemist
Hazard to Self
Posts: 65
Registered: 23-3-2007
Member Is Offline
Mood: electronegative
|
|
A little off-topic, but...
I've contemplated a procedure for purifying garden-quality copperas (ferrous sulfate, heptahydrate). AFAIK, this source tends to be acidic from excess
sulfuric acid used in it's synthesis (unsure if pottery-grade copperas is similar in this regard?).
Firstly, ferrous hydroxide, an insoluble solid, can be prepared from lye and copperas:
FeSO4 + 2OH[−] → Fe(OH)2 + SO4[2−]
After washing the product several times with distilled water, it could then be added to a saturated solution of copperas, refluxed gently, filtered
through clean kieselgur, boiled, and finally recrystalized by slowly cooling the mother liquid.
[Edited on 5/4/2007 by obsessed_chemist]
|
|
|
UnintentionalChaos
International Hazard
Posts: 1454
Registered: 9-12-2006
Location: Mars
Member Is Offline
Mood: Nucleophilic
|
|
Glycerin isn't that hard to find fairly dry. If you buy "swan" brand glycerin, I'd consider using it straight up. It's meant as a skin care product,
so I do not doubt the purity, and it is really dry when fresh. I realized this the other day when I tried placing a drop of it on KMnO4 which to my
great confusion caused absolutely no reaction, even when left for several minutes. It eventually occured to me that some water must be necessary to
initiate it and with a drop of water, the pile started fuming and then burst into flames as expected.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
| Quote: | Originally posted by obsessed_chemist
A little off-topic, but...
I've contemplated a procedure for purifying garden-quality copperas (ferrous sulfate, heptahydrate). AFAIK, this source tends to be acidic from excess
sulfuric acid used in it's synthesis ...
[Edited on 5/4/2007 by obsessed_chemist] |
Adding ferrous hydroxide will produce basic sulfates, and moving the pH higher may decrease the stability of the Fe(II) around oxygen. Just
recrystallise the FeSO4 without adding hydroxide.
|
|
|
UnintentionalChaos
International Hazard
Posts: 1454
Registered: 9-12-2006
Location: Mars
Member Is Offline
Mood: Nucleophilic
|
|
Also, your synthesis uses H2SO4 in it, does it not? So why bother removing leftover acid?
[Edited on 5-4-07 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Recrystallization with a hot filtering step is all that is required. Wash and dry the crystals to remove more impurities (including free acid).
Tim
|
|
|
obsessed_chemist
Hazard to Self
Posts: 65
Registered: 23-3-2007
Member Is Offline
Mood: electronegative
|
|
^ - I was unaware that 'basic' iron sulfates existed. As I said, just an idea I had swimming around for a while; thanks for debunking the myth guys. I
stand corrected.
|
|
|
woelen
Super Administrator
Posts: 8013
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
| Quote: | Originally posted by 12AX7
Sure of that? I've left out crystals that partially dehydrated without turning to brown mush.
Tim |
There may be some efflorescence, but making real anhydrous FeSO4 is a completely different thing. It is my experience that making anhydrous salts from
hydrated ones is very difficult, except for a few alkali metal salts. For almost all other metal salts, there is (at least partial) hydrolysis, which
results in loss of acid and formation of basic salts. For some salts with strongly oxidizing anions, or strongly reducing cations, things even become
worse, due to decomposition and/or internal redox reactions. Ferrous sulfate is an example of the latter.
|
|
|
ordenblitz
Hazard to Others
Posts: 259
Registered: 18-7-2004
Location: Northwest
Member Is Offline
Mood: Bohr'd
|
|
I made mine by accident.
I placed my freshly crystallized and lovely blue FeSO4*7H2O in an argon flushed glove box to dry. By the second day it had turned completely white and
fallen to dust losing all of its water in the perfectly dry atmosphere.
|
|
|
UnintentionalChaos
International Hazard
Posts: 1454
Registered: 9-12-2006
Location: Mars
Member Is Offline
Mood: Nucleophilic
|
|
IIRC that is most likely the monohydrate, not the anhydrous form.
EDIT: found where I read that http://www.sas.org/tcs/weeklyIssues_2005/2005-07-15/feature2...
It says you may have had a combination of tetrahydrate and monhydrate. You could conduct the mistake again as an experiment and weigh the sample
before and after to get a definitive answer.
[Edited on 5-7-07 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
|
|
|
cnidocyte
Hazard to Others
Posts: 214
Registered: 7-7-2010
Member Is Offline
Mood: No Mood
|
|
I made some ferrous sulfate a while ago by adding conc. H2SO4 to steel wool, at first I thought it didn't work and I left it overnight to react fully
but when I was cleaning up the next day I noticed a pile of green crystals at the bottom of the solution. It was definitely ferrous sulfate but for
some reason it reeked. It had a bit of an H2S smell to it but it was something else, something I'd never smelled before. Wasn't a pleasant smell and
even after cleaning with water the flask still reeked of the stuff. Is that what ferrous sulfate smells like or was it impurities I was smelling?
Also I noticed this stuff barely dissolved at all in cold water but dissolved rapidly in hot water and made a brownish yellow solution.
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
I don't know what the smell is - is it a metallic smell?
This thread may help:
http://www.sciencemadness.org/talk/viewthread.php?tid=5529&a...
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
Picric-A
National Hazard
Posts: 796
Registered: 1-5-2008
Location: England
Member Is Offline
Mood: Fuming
|
|
The dissoloution of the ferrous sulphate probably reduced the H2SO4 to H2S and other noxious sulphur compounds which is probably reliable for the
smell...
I always find pure FeSO4 has a metallic smell, cant quite describe it but if you smell it you will know what i mean...
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
