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benzylchloride1
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I have read about also the use of oxalic acid with sulfuric acid for the preparation of carbon monoxide. Oxalic acid can be obtained cheaply. Formic
acid is better, but I can only obtain it from a scientific supply. I have read about a procedure for making the hexacarbonyls of Cr, Mo, W from the
anhydrous metal chlorides dissolved in ether in the presence of ethyl magnesium bromide by bubbling CO through the solution. The reaction uses about
6-8 liters of CO, and produces about two grams of the carbonyl from about 10g of the anhydrous metal chloride. The yield sucks, but it sure beats
spending $30+ per gram for these organometallic compounds. I am planning on running this reaction once I get the tube furnace that is needed to
prepare the metal chloride from the oxide and gaseous disulfur dichloride. I am fascinated by the chemistry of carbon monoxide complexes of transition
metals (carbonyl complexes) I will post more about my experiments as soon as I conduct them.Chromium, Molybdenum, Tungsten Carbonyls. The reaction
could be conducted by slowly passing dry CO through the reaction mixture until the reaction ceases to absorb CO. A mineral bubbler could be attached
to the inlet and outlet to indicate the flow rate in and indicate when the reaction is finished. A slight excess of oxalic or formic acid would be
used for generating the CO. CO can ve handled safely in a good fume hood. The apparatus should be completely sealed and the outlet lead into the
reaction mixture. The CO should be generated slowly so that a large excess is not vented to the atmosphere of the fume hood .
Procedure from Vogel for generating CO:
Carbon monoxide. This gas is readily prepared by the action of
concentrated formic acid (sp. gr. 1-2 ; about 90 per cent.) upon concentrated
sulphuric acid at 70-80°. The apparatus of Fig. / / , 48, 5 is
recommended. The distilling flask (500 ml.) is immersed in an oil bath
maintained at 70-80°, and is connected to two wash bottles containing
concentrated sulphuric acid. 125 grams of concentrated sulphuric acid
are placed in the distilling flask and 85 g. of the strong formic acid are
slowly added from the dropping funnel; a steady stream of gas is evolved.
The resulting carbon monoxide may contain traces of carbon dioxide and
sulphur dioxide . these impurities may be removed, if
desired, by passage of the gas through a tower filled
with potassium hydroxide pellets.
Carbon monoxide is very poisonous : all operations
involving its preparation and use must be carried out
in an efficient fume cupboard.
Here is the procedure from Preparative Inorganic Chemistry.
Cr(CO),, Mo(CO),, W(CO),
The hexacarbonyls of the chromium group are formed via
reaction of CO with a suspension of anhydrous halides of Cr, Mo
or W in a Grignard solution, followed by hydrolysis. The reaction
mechanism has not yet been elucidated.
The reactor vessel / in Fig. 343 is a one-liter flask fitted
with a two-hole rubber stopper. The dropping funnel t has a
considerably enlarged tip to prevent plugging during the reaction.
It is used for the addition of the Grignard solution (via a), as well
as that of CO (at b). Stopcock h is a gas vent which remains
normally closed during the reaction but which is occasionally
opened to allow flushing the reactor with CO. Flask f is fitted
exactly into the ice bath e, and the whole apparatus is vigorously
shaken on a machine. To monitor the CO consumption, a standardized
gasometer is connected to b via a drying train (whose
last tube is filled with P3O5).The reactor flask / is filled with nitrogen. The metal chloride
(10 g. of fine anhydrous CrCl3 powder; 17 g. of sublimed MoCls;
or 20 g. of WC16 [0.05 moles]) is introduced, and the vessel is
evacuated and filled with CO. A mixture of 50 ml. of anhydrous
ether and 50 ml. of anhydrous benzene is added through the
dropping funnel and the apparatus is then connected to the CO line.
The Grignard reagent is prepared from 12 g. (0.5 moles) of
Mg, 54 g. of C3HsBr and approximately 300ml. of anhydrous ether.
This solution is added to the metal chloride suspension first in
portions of about 5 ml. each, later dropwise. The initiation of the
CO reaction as well as its progress may be observed via a wash
bottle containing some cone. H3SO4 provided the stopcock of t is
closed. The absorption of CO, which for reasons unknown occasionally
slows down and then accelerates, is continued for about
4-6 hours after the addition of all of the Grignard reagent. The
reaction absorbs on the average 7 liters and occasionally up to
9 liters of CO.The reddish-brown reaction product is hydrolyzed by cautious
addition to a mixture of ice and dilute HsSO^ and the mixture is
then steam-distilled without prior removal of ether and benzene.
The steam distillation is continued for 3-4 hours or as long as
white needles of the carbonyl product are observed in the (descending)
condenser. The organic layer (benzene-ether) in the distillate
is separated and the aqueous phase extracted 3-4 times with fresh
ether. The combined ether extracts are concentrated by distillation,
keeping the temperature below 60 °C, and the residue is allowed
to crystallize in a refrigerator.
The yields of crude carbonyls are quite variable: in the case of
Cr(CO)6 they are 2 g. maximum, while up to 3-4 g. of W(CO)6
may be isolated. Higher yields of Cr(CO)s (up to 67%) are obtained
in an autoclave under high CO pressure (35-70 atm.). To remove
strongly adhering, odorous organic impurities, an immediate
vacuum sublimation of the hexacarbonyls is recommended.
Amateur NMR spectroscopist
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Jor
National Hazard
Posts: 950
Registered: 21-11-2007
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Do you do this in a fume hood at home?
As these metal carbonyls are really toxic, at least nickel carbonyl is.
You can also prepare CrCl3 by passing CCl4-vapour over Cr2O3, at very high temperatures in a tube furnace. You will have COCl2 byproducts, wich you
can bubble in toluene for later use.
Im not sure if pottery Cr2O3 will work. It is insufficient in many reactions, I heard, because of inertness. Is this true?
You can prepare very active Cr2O3 by decomposing ammonium dichromate. This way I made some Cr2O3 wich i used as a catalyst (heating it to red heat) to
oxidise ammonia with oxygen.
[Edited on 29-3-2009 by Jor]
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JohnWW
International Hazard
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Registered: 27-7-2004
Location: New Zealand
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In the formation of Cr(CO)6, Mo(CO)6, and W(CO)6, electron pairs from the C in the CO molecules would occupy the remaining three vacant 3d or 4d or 5d
orbitals and all three vacant 4p or 4p or 6p orbitals, of the zerovalent metal atoms. Because all 6 CO molecules would be equivalent by resonance,
this looks like a case of p-d orbital hybridization. However, they would not be as stable as Ni(CO)4 or Pd(CO)4 or Pt(CO)4, because the 4p or 5p or 6p
orbitals are at relatively higher energy levels than in Ni, Pd, and Pt. In the Ni, Pd, and Pt tetracarbonyls, the d valence orbitals are all full, and
the electron pairs from the COs occupy the vacant s and p orbitals (sp3 hybridization).
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benzylchloride1
Hazard to Others
Posts: 299
Registered: 16-3-2007
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Mood: Pushing the envelope of synthetic chemistry in one's basement
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Nickel carbonyl is one of the most toxic substances known. Most other metal carbonyls are toxic, but not to the degree of nickel carbonyl. I have
conducted some work at the university with iron pentacarbonyl which is probably the most toxic common metal carbonyl. This compound is a low boiling
liquid with a bad musty odor. The fume hood i have at home is very similar to the ones at the university. Before I work with Carbon monoxide, I will
install several detectors around the fume hood. The hexacarbonyls of Cr, Mo, and W are solids with high vapor pressures and can be handled safely in a
fume hood. I wonder if the corrosponding anhydrous bromides could be used in the reaction? These could be made by adding bromine to the metal of
choice in a reaction flask. The reaction would be initiated by adding a drop of water to form a small amount of the aqua complex. I have also found a
stable copper (I) carbonyl that could be prepared fairly easily. Copper (I) iodide is treated with sodium tris(3,5- dimethylpyrazolyl)hydroborate in
an ether solution. Carbon monoxide is bubbled through the solution until crystals of the complex form. The sodium
tris(3,5-dimethylpyrazolyl)hydroborate is prepared by heating sodium borohydride with 3,5-dimethylpyrazole until the evolution of hydrogen ceases. The
chemistry of metal carbonyl complexes is fascinating. It would be nice if there was a way of producing iron pentacarbonyl in useable quantities, 10g
without an autoclave and cylinders of CO.
Amateur NMR spectroscopist
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