tomjuan (Hive Bee)
08-11-01 10:31
No 203499
      Acetaldehyde synthesis  Bookmark   

I am aware that potassium dichromate is capable of oxidizing ethanol into acetaldehyde. However, potassium dichromate is restricted, and synthesizing it, although possible, would require an extra step and some extra chemicals. I am trying to maximize the simplicity of my endeavors. Will H2O2 possibly work for the oxidation?
 
 
 
 
    tomjuan
(Hive Bee)
08-11-01 17:43
No 203587
      Re: Acetaldehyde synthesis  Bookmark   

Ummmm, never mind - I think I found my answer. Ethanol can be oxidized to acetaldehyde with H2O2 with an Fe(III) catalyst, but it doesn't sound easy (unless you are the liver of an alcoholic). I guess I'll just have to "acquire" the dichromate . . .
 
 
 
 
    moo
(Newbee)
08-12-01 14:33
No 203829
      Re: Acetaldehyde synthesis  Bookmark   

Couldn't the problem be solved by pinch of FeCl3 circuit board etchant?

understanding is everything
 
 
 
 
    tomjuan
(Hive Bee)
08-12-01 14:44
No 203838
      Re: Acetaldehyde synthesis  Bookmark   

I don't know, but in the literature I found, the oxidation was accomplished by binding the Fe(III) to some silicon compound, and they designed a special "reactor" to carry out the oxidation. I might do some experimentation, because yields are not as important as convenience to me.
 
 
 
 
    EzeKieL
(Newbee)
08-15-01 02:57
No 204738
      Re: Acetaldehyde synthesis  Bookmark   

Acetaldehyde, or Ethanal, CH3CHO -  is a colorless gas whose derivatives are of importance in medicine.  Both formaldehyde and acetaldehyde are produced by passing vapors of methanol and ethanol ( mixed with air) over heated copper as a catalyst.  The equation is --

             300 degrees Centigrade
       CH3OH + Cu ---------> HCHO + Cu + H2
     Methanol               Formaldehyde
    
          300 degrees Centigrade
C2H5OH + Cu ------------>  CH3CHO + Cu + H2
Ethanol                    Acetaldehyde

 
 
 
 
    tomjuan
(Hive Bee)
08-15-01 11:13
No 204836
      Re: Acetaldehyde synthesis  Bookmark   

Thank you for you reply. I'm not sure I'm actullay ready to try this yet - I don't have a lot of "real" glassware, and I'm not trying to blow myself up. I'll give it a shot when I'm better equipped, and I'll let you know how it went.
 
 
 
 
    foxy2
(Hive Addict)
08-17-01 20:12
No 205571
      Re: Acetaldehyde synthesis  Bookmark   

I found this posted somewhere with no references but it sounds good.
Foxy

    Place 260 mL of 23% sulfuric acid in a 1500-mL Florence flask. Connect an addition funnel to the flask, and set it up for vacuum distillation with a 500-mL receiving flask. The receiving flask should be immersed in a salt-ice bath to cool the distillate when it comes over. Although a setup for vacuum distillation is used, it is not necessary to apply a vacuum; the vacuum adapter merely provides a means of equalizing pressure. Prepare a solution of 100 g of sodium dichromate in 200 mL of water and 127 mL of ethyl alcohol. Factor in the amount of water that is already in the ethyl alcohol when making the solution, i.e. 100 mL of 95% alcohol has 5 mL of water in it already. Place this solution in the addition funnel, position the stem of the funnel so that it is about 3 cm above the surface of the acid. Heat the acid until it just begins to boil, then add the mixture in the funnel in a steady stream to the acid. It will not be necessary to heat the flask during the addition because it will generate its own heat. The heat will be sufficient to distill over the acetaldehyde along some alcohol and waste acetal. If acetaldehyde vapors begin to escape from the flask, regulate the distillation by decreasing the amount of dichromate solution being added. If the reaction flask does not boil on its own, gently heat it for a short time until boiling begins.
     The crude acetaldehyde thus obtained is difficult to distill from the alcohol and acetal mixed with it. It is therefore converted to aldehyde-ammonia, then back to pure aldehyde. Place the crude acetaldehyde in a Florence flask of suitable volume to contain no more than two thirds of the liquid. Attach a reflux condenser to the flask. Fill the condenser jacket with 30 C water. It is only necessary to have the warm water in the jacket, not flowing. Stop up the lower connecter to prevent water from leaking out. To the top of the condenser, attach a glass tube connected to a wash bottle filled with 50 mL of ether. This wash bottle is then connected to another wash bottle filled with 50 mL of ether. After all connections have been made, the crude aldehyde is heated to a gentle boil for 5-10 minutes. The ether will absorb the acetaldehyde as it boils off. If the ether begins to rise up into the connecting tube from the condenser to the wash bottle, increase the heating. Combine the ether into a 150-mL beaker immersed in a salt-ice bath. Bubble dry ammonia gas into the ether through a funnel or wide tube immersed near the bottom of the beaker. Add ammonia until the ethereal solution smells strongly of ammonia. After about an hour, pure ammonia-aldehyde should have separated out. Scrape the crystals from the beaker and collect them by suction filtration. Wash the crystals with a small amount of ether, and allow them to dry in a desiccator. The yield is about 30 g.
     To obtain pure acetaldehyde, dissolve 10 g of aldehyde-ammonia in 10 mL of water in a 50-mL Florence flask. Add 28 mL of cold 29% sulfuric acid to the flask and set it up for simple distillation. Heat the flask on a water bath to distill over the aldehyde. Place the receiving flask in a salt-ice bath to cool the volatile acetaldehyde.
     Acetaldehyde is extremely volatile and cannot be stored satisfactorily unless it is refrigerated or sealed in glass ampoules (not just capped), therefore it is necessary to prepare acetaldehyde each time it is needed. There is, however, an easier solution. A quick and easy way to store acetaldehyde is to polymerize it to paraldehyde, which can be handled and stored easily, then depolymerize when you need to use it. Now you can make a larger amount without worry.
     To polymerize acetaldehyde for storage, place it in a dry test tube and cautiously add 1 drop of concentrated sulfuric acid per 2 mL of acetaldehyde in the tube. Mix thoroughly, the polymerization will begin to take place. Some gentle warming can hasten the reaction. After some minutes add 3-4 mL of water per 2 mL of acetaldehyde, an insoluble precipitate of paraldehyde will form. As an aside, technically paraldehyde is a controlled substance. It is a sedative and a hypnotic drug useable by prescription only.
     To depolymerize paraldehyde back into acetaldehyde, place the paraldehyde into a round-bottom 200-mL Florence flask. Add 4-5 drops of concentrated sulfuric acid for every 20 g (20 mL) of paraldehyde in the flask. Set the flask up for fractional distillation, use glass in the fractionating column. Use a 125-mL Erlenmeyer flask as the receiver; keep it cool by immersing in an ice water (but not salt-ice) bath. Place a loose plug of cotton into the Erlenmeyer flask to help reduce evaporation loss; it must be loose. Care must be taken to prevent the cotton from coming into contact with the distillate. After setting up, heat the flask gently. The temperature of the distillate must not be allowed to rise above 35 C as it will only repolymerize. The acetaldehyde is now ready for use.



Do Your Part To Win The War
 
 
 
 
    terbium
(Hive Addict)
08-18-01 12:29
No 205672
      Re: Acetaldehyde synthesis  Bookmark   


formaldehyde and acetaldehyde are produced by passing vapors of methanol and ethanol ( mixed with air) over heated copper as a catalyst.



I am not certain that the air is necessary. I have produced hexaldehyde from hexanol by dripping it into a heated column contining copper chromite catalyst on pumice without the addition of any air. Watching the evolved hydrogen bubble through a bubbler attached after the receiving flask tells you when the column has reached reaction temperature.

Perhaps adding air is just used in large scale industrial processes to consume the hydrogen to produce some heat thus lowering the cost of the process by reducing the heating costs.

 
 
 
 
    Osmium
(Stoni's sexual toy)
08-18-01 13:44
No 205679
      Re: Acetaldehyde synthesis  Bookmark   

This is an oxidation, there is no hydrogen produced.
 
 
 
 
    Rhodium
(Chief Bee)
08-18-01 13:47
No 205681
      Re: Acetaldehyde synthesis  Bookmark   

It is a dehydrogenation (abstraction of H2 from the alcohol), which in essence is a kind of oxidation, but surely hydrogen is produced.

 
 
 
 
    Osmium
(Stoni's sexual toy)
08-18-01 14:59
No 205688
      Re: Acetaldehyde synthesis  Bookmark   

And copper metal can do that? I doubt it. I rather expect the copper surface (which consists of copper oxide) to act as an oxidiser, and the air is needed to reoxidise the copper, so no H2 would be produced but water will be.

IMHO. Or do you disagree?
 
 
 
 
    lugh
(Hive Bee)
08-18-01 16:22
No 205703
      Re: Acetaldehyde synthesis  Bookmark   

Other than from ethanol, most of the acetaldehyde that's been produced is from acetylene via a variety of methods.
 
 
 
 
    terbium
(Hive Addict)
08-18-01 16:28
No 205706
      Re: Acetaldehyde synthesis  Bookmark   


This is an oxidation, there is no hydrogen produced.



Excuse me but you are wrong.

 
 
 
 
    terbium
(Hive Addict)
08-18-01 16:37
No 205710
      Re: Acetaldehyde synthesis  Bookmark   


And copper metal can do that? I doubt it. I rather expect the copper surface (which consists of copper oxide) to act as an oxidiser, and the air is needed to reoxidise the copper, so no H2 would be produced but water will be.



As I said, with copper chromite catalysts and no air, hydrogen is produced. This is straight out of Vogel, 3rd Ed.:
"Place 100 g of n-hexyl alcohol in the dropping funnel. Switch on the current for the furnace and, after 2 hours, allow the alcohol to pass into the tube at the rate of 1 drop every 3-4 seconds. The commencement of dehydrogenation will be indicated by the production of white fumes at the point where the combustion tube enters the condenser and  by the passage of gas (hydrogen) in the bubbler at the extreme end of the apparatus."

 
 
 
 
    PolytheneSam
(Master Searcher)
08-18-01 17:08
No 205716
      Re: Acetaldehyde synthesis  Bookmark   

A good patent to look at is US 1892011 .  Here's a couple lines from it.

It is known that secondary alcohols, such as isopropyl alcohol, menthol, borneol and others, may be converted into the corresponding ketones by leading them over dehydrogenating catalysts....

It has now been found, that a 97-100% dehydrogenation of the alcohols can be attained if they are led over the dehydrogenation cartalysts in the presence of steam.....

As catalysts there can be employed metals such as nickel, cobalt, copper, preferably in a powdered form eventually admixed with hydrates or oxides of the alkali or alkaline earth metals.




Four examples are given.
http://www.geocities.com/dritte123/PSPF.html


http://www.geocities.com/dritte123/PSPF.html
 
 
 
 
    PolytheneSam
(Master Searcher)
08-18-01 18:01
No 205723
      Re: Acetaldehyde synthesis  Bookmark   

See also
http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=/netahtml/search-bool.html&r=0&f=S&l=50&TERM1=568/487&FIELD1=ORCL&co1=AND&TERM2=&FIELD2=&d=pall


http://www.geocities.com/dritte123/PSPF.html
 
 
 
 
    Osmium
(Stoni's sexual toy)
08-19-01 06:40
No 205822
      Re: Acetaldehyde synthesis  Bookmark   

Well terbium, copper chromite is a known dehydrogenation catalyst, I didn't know that copper works too.
 
 
 
 
    terbium
(Hive Addict)
08-19-01 10:58
No 205860
      Re: Acetaldehyde synthesis  Bookmark   


I didn't know that copper works too.



Neither do I. I wasn't the one who said it did.