Rhodium
(Chief Bee)
07-16-03 07:42
No 447706
      Chromyl chloride: Propenylbenzene to P-2-P
(Rated as: good read)
    

Chromyl chloride (CrO2Cl2) oxidation of Propenylbenzene to Phenyl-2-Propanone
Tetrahedron 25, 3441-3446 (1969) (../rhodium/pdf /p2p.chromylchloride.pdf)

It seems like CrO2Cl2 oxidizes the alkene to the ketone in reasonable yield (40%) in DCM, with some benzaldehyde as byproduct (15-25%).

One question remains - how do you make chromyl chloride easily, cheap & efficient?
 
 
 
 
    Aurelius
(Active Asperger Archivist)
07-16-03 08:16
No 447718
      Chromyl Chloride     

One more question that you forgot- "and safely?"

Post 428070 (algebra: "chromyl chloride", Stimulants)
Post 428132 (UncleFester: "a better recipe", Stimulants)
Post 428458 (lugh: "Inorganic Syntheses Vol II, p 205-7", Stimulants)
Post 108553 (dormouse: "vanillin from .... trees?  -dpHarma", Novel Discourse)

Act quickly or not at all.
 
 
 
 
    java
(Hive Bee)
07-16-03 08:50
No 447722
      Re: Chromyl Chloride preparation......     

About chromyl chloride ". The formation of chromyl chloride, a red gas, by heating a solid sample with potassium dichromate and concentrated sulfuric acid. When chromyl chloride is passed into water, a yellow chromate solution forms (bromides and iodides do not form analogous compounds).
taken from ,

http://www.c-f-c.com/supportdocs/cl2data2.htm

I hope this helps......java

We're  all in this world together,
 http://www.chiapaslink.ukgateway.net/
 
 
 
 
    Rhodium
(Chief Bee)
07-16-03 08:54
No 447723
      If it Looks Like Bromine and Smells Like Bromine..
(Rated as: excellent)
    

Well, it could be Chromyl chloride (CrO2Cl2): Both are blood-red liquids at room temperature and have similar irritating odors.  Chromyl chloride, however, is less dense (d. 1.911) than bromine (d. 2.928) and also more transparent to light.

Chromyl chloride belongs to the class of compounds known as acid chlorides, in which chlorine has replaced the ionic HO groups of the corresponding acid, in the present instance, chromic acid (H2CrO4, Figure 1):



As can be seen, chromium in these compounds is in its hexavalent state with oxidation number +6.

Chromic acid, and the related Dichromic acid (H2Cr2O7) and Chromium trioxide (CrO3) are strong oxidizing agents.  If sodium chloride is heated with potassium dichromate and dilute sulfuric acid, the chloride will be oxidized to chlorine:

(1)     2Cr+6 + 6Cl- -> 2Cr+3 + 3Cl2

However if these reagents are heated with concentrated sulfuric acid a displacement reaction occurs with formation of the acid chloride:

(2)      H2Cr2O7 + 4HCl -> 2CrO2Cl2 + 3H2O

The oxidation state of the chromium remains unchanged in this reaction, and so chromyl chloride, like chromic acid, is a strong oxidant.


Figure 2.

It is not a difficult matter to prepare small quantities of this reactive liquid in the home laboratory.  The chromyl chloride (b.p. 117 C) is recovered by distillation from the reaction mixture.  Since the vapor and liquid attack organic materials (including rubber stoppers) it is preferable to work with all glass apparatus. If you're fortunate enough to own or have access to a good selection of standard taper ground joint ware, or that venerable symbol of the chemist, a glass retort, then you'r e all set.  Otherwise, don't despair; I used the apparatus shown in Figure 2 with satisfactory results.  Rubber stoppers were used; these may have to be replaced after one or two uses in the corrosive environment. Applying a thin coating of silicone stopcock grease may retard attack The air condenser was bent from a length of glass tubing.  I recommend neon sign tubing, which is easily worked in a gas flame.  If you have some glass working expertise, you can blow a bulb in the riser to serve as a trap for any liquid that may spurt over.  The condensed CrO2Cl2 is collected in a U-tube cooled by immersion in a jar of cold water.

The distillation should be carried out in an efficient fume hood or in a well-ventilated area, preferably open air, as CrO2Cl2 vapor is toxic and extremely irritating(1).

Thoroughly mix 20 g potassium dichromate and 8 g sodium chloride (don' t use iodized table salt) and place in a 500 mL Erlenmeyer flask.  Add 100 mL conc. sulfuric acid and attach the condenser and receiver.  Heat cautiously with a Bunsen flame, taking care that the mixture doesn't froth and spurt over into the condenser.  Continue distillation until no more material distills over.  Theoretically, the yield should be about 20 g (10 mL) of CrO2Cl2.   Store in a glass-stoppered amber glass bottle.  Preferably it should not be stored for a long period of time (months or years) as the vapor tends to penetrate the ground joint and freeze the stopper into place.  Also the possibility of its falling into the hands of folks unacquainted with its hazards should not be dismissed.  To dispose of it safely, pour the liquid slowly into a large volume of cold water, observing ordinary safety precautions (adequate ventilation, protective clothing and eyeware).  The resulting dilute solution of chromic and hydrochloric acids can go down the drain as-is, or after neutralizing the acids with baking soda.

Chromyl chloride is a very reactive liquid and fumes strongly in air with evolution of fumes of chlorine and hydrogen chloride.  On one occasion when I unstoppered a bottle of CrO2Cl2 the liquid appeared to boil violently, presumably from evolution of these dissolved gases.  Initially chromyl chloride is hydrolyzed by moisture:

(3)         CrO2Cl2 + 2H2O -> H2CrO4 + 2HCl

This is followed by the redox reaction,

(4)      2H2CrO4 + 6HCl -> Cr2O3 + 3Cl2 + 5H2O

For electrochemical balance two equivalents of Cr are reduced from the +6 to the +3 oxidation state and six equivalents of chlorine are oxidized from the -1 to the 0 state.
 
To illustrate the energetic oxidizing power of chromyl chloride, place a small pool of alcohol (methanol, ethanol or 2-propanol will do) on a watch glass and allow a drop of CrO2Cl2 to fall onto it  The alcohol will ignite and burn.
 

Place a mL or two of CrO2Cl2 in a test tube supported in a test tube rack.  Cautiously add a little powdered sulfur from a spatula.  The mixture reacts violently, accompanied by a crackling sound and flashes of light and the tube erupts, flinging out excess sulfur and a violet-colored ash.

Similarly, a bit of white phosphorus burned on contact with CrO2Cl2 , though not with the violence encountered with finely divided sulfur.

Other combinations can be tried by the amateur.  Powdered metals (e.g., Al, Mg, Zn) should react.  It's been reported than ammonia ignites and burns on contact with CrO2Cl2.  ; (You can generate a stream of ammonia (NH3) by letting conc. ammonium hydroxide drip on dry sodium hydroxide in a gas generating flask.)

Chromyl chloride is used in organic synthesis of aldehydes and ketones (Etard reaction) and in the preparation of various coordination compounds of chromium.

Notes:

1. Treat this compound with respect!  Severe burning and blistering occurs if it gets in contact with skin, with severe or prolonged contact leading to ulceration.   Moist tissues such as the nasal mucosa and respiratory tract are particularly susceptible to damage, hence the need  for adequate ventilation of the work area.

Source: http://www.sas.org/E-Bulletin/2002-04-19/chem/column.html
 
 
 
 
    demorol
(Hive Bee)
07-16-03 12:46
No 447755
      Another way to Chromyl Chloride     

Another procedure from Patent GB270711

An Improved Process for the Production of Chromyl Chloride

Example 1
To a solution of 100 parts by weight of chromium trioxide and 150 parts by weight of conc. sulfuric acid there is slowly added 233 parts by weight of chlorosulfonic acid, preferably while stirring, and 18 parts by weight of water thereupon added. The reaction vessel is heated while stirring, in order finally to distill off the chromyl chloride. In this way 146 parts by weight of chromyl chloride are obtained, which corresponds to a yield of about 95%.

The reaction takes place in a similar manner, if HCl is introduced into the reaction mixture. However, the yield in such case is not quite as great as given above.

Example 2
25 parts by weight of chromium trioxide are suspended in 50 parts by weight of conc. sulfuric acid and 25.6 parts by weight of phosphorus oxychloride are added in a thin jet while stirring. The reaction product is distilled while stirring. The chromyl chloride passes over at 117°C. Yield 30-35 parts by weight corresponding to 80-93% of the theoretical yield.

It is necessary to dilute the chromium trioxide with sulfuric acid or suspend it therein, as otherwise the action of phosphorus oxychloride upon the chromium trioxide is too vigorous.

I'm dreaming of the white crystals.
 
 
 
 
    slappy
(Hive Addict)
07-16-03 13:02
No 447760
      Huh?     

Are you guys crazy? I wouldn't ever want to use the stuff. Chromic Acid either. The only thing that is good for is to get rid of bodies (or parts). Do you understand how corrosive and toxic this stuff is?

I know some crazy fucks that play with that stuff, but I don't think that they hold their health in any great regard. Case in point: Losing one's sense of taste, smell, and partial eyesight from getting to close to some HF fumes.
 
 
 
 
    Aurelius
(Active Asperger Archivist)
07-16-03 16:16
No 447790
      Slappy     

I'm with you on that point.  Notice I breifly brought up the safety issue in my reply above. I would have given a better warning, however, I figured Rhodium was aware of the properties of this chemical ( or family of chemicals). And although I thought that my addition was quite enough to allow for the synthesis of this compound, I'm glad to see that this thread filled out so quickly with high quality information and methods.

Act quickly or not at all.
 
 
 
 
    Rhodium
(Chief Bee)
07-10-04 03:27
No 518470
      P2P from n-Propylbenzene and Chromyl Chloride
(Rated as: good read)
    

Some Observations On The Étard Reaction
K.B. Wiberg, B. Marshall and G. Foster
Tetrahedron Letters 345-348 (1962) (../rhodium/chemistry /p2p.etard-1.html)



Article originally posted in Post 514112 (azole: "PhPr + CrO2Cl2", Russian HyperLab)

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