zealot
()
02-07-03 02:38
No 405254
      Aromatic aldehydes from acids in one step
(Rated as: excellent)
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(electrolytic reduction by an amalgam of sodium at presence H3BO3)

Aromatic aldehydes smoothly turn out at electrolytic reduction corresponding aromatic acid on the mercury cathode at the presence of boric acid.
If to subject electrolysis water solution Na salts an aromatic acid, allocated sodium are dissolved in mercury and the formed amalgam reduction acid up to aldehyde. The solution all time should contain small surplus boric acid, and formed aldehyde should be deleted from electrolyte immediately. Therefore reduction conduct without a diaphragm at vigorous stirring at the presence of benzene which emulsion in a liquid and deletes aldehyde from sphere of reaction as soon as last will be formed.

Reception benzaldegyde from benzoic acid

Electrolysis made in a glass with diameter 100 mm. As the cathode mercury which pour on a bottom a layer in 10 mm serves. A current bring to the cathode by means of the copper wire protected by a glass tube which bottom end is shipped in mercury. In the center of a vessel establish powerful Hershberg mixer, and electro conductor a tube strengthen at a wall of a glass. During restoration a reactionary mix cool cold water.
For reception of a good yield it is necessary, that concentration of sodium in mercury was not lower than some minimum i.e. that at the moment of restoration mercury already contained the some amount of amalgams. For this purpose all over again subject electrolysis solution Na2SO4 and the mercury received thus containing sodium, use as the cathode. At recurrence of synthesis of such preparation it is not required, if use the mercury just serving by the cathode at the previous restoration.
For electrolyte prepare from 15 g benzoic acid which will precisely neutralize soda, then lead up volume solution up to 250 ml, add 15 g boric acid, 15 Na2SO4 and 100 ml of benzene. Reduction made an electricity 1,5-2 A, at time of reduction stirring should be so vigorous that represented milky-white emulsion.
After through a liquid will pass 8-9 h, mercury separate, benzene layer wash out bicarbonate of sodium, dry and solvent drive away. Benzaldegyde for clearing overtake with steam. Yield 12 g (91% from theor.).

Resorcylic aldehyde (2,4-dioxybenzaldehyde)

For electrolyte prepare from 19 g (0,123 mol) resorcylic acid which will neutralize bicarbonate of sodium, 15 g (0,24 ) H3BO3, 15 g (0,11 mol) Na2SO4, 250 ml of water and 250 ml of benzene. Reduction made since described above, receiving 14,8 g aldehyde (86% from .).

2,4-dimethoxybenzaldehyde

For electrolyte prepare from 22,4 g (0,123 mol) 2,4-dimethoxybenzoic acid which will neutralize bicarbonate of sodium, 15 g (0,24 mol) H3BO3, 15 g (0,11 mol) Na2SO4, 250 ml of water and 100 ml of benzene. Reduction made since described above, receiving 19 g aldehyde (93% from theor.).

The smaller yield of resorcylic aldehyde in comparison with 2,4- dimethoxybenzaldehyde
is connected, probably, with its smaller solubility in benzene and the greater solubility in water and, as consequence, courses of reaction of its further reduction.

3,4,5- thrimethoxybenzaldehyde

For electrolyte prepare from 26 g (0,123 mol) 3,4,5-trimethoxybenzoic acid which will neutralize NaHCO3, 15 g (0,24 mol) H3BO3, 15 (0,11 mol) Na2SO4, 250 ml of water and 100 ml of benzene. Reduction made since described above, receiving 22 g aldehyde
(91% from theor.).
 
 
 
 
    Osmium
(Stoni's sexual toy)
02-07-03 07:13
No 405302
      Nice, I especially like the last one.  Bookmark   

Nice, I especially like the last one.

Some comments and questions though:

- Refs?
- What anode material and what size? Located where? Around the stirrer shaft? Or around the inside of the container?
- Required Na content of the amalgam prior to the reaction?
- Required lenght of electrolysis? 9Ah?
- What reaction temperature?
- Distance between anode and cathode?
This ^^^^ will have an influence on the voltage required to achieve the desired current, and also on how much the reaction will heat up.
Did I get that right that the sodium amalgam was prepared by electrolysing a Na2SO4 solution under similar conditions plus some cooling prior to the actual reduction?
- For how long at what current densities?
- Approx. concentration of the Na2SO4 solution?

What's the structure of the H3BO3-aldehyde-compound? A geminal diester? Cyclic acetal-like?

R-CHO + 2 B(OH)3 ----> R-CH-[-O-B(OH)2]2 (???)
R-CHO + B(OH)3 ----> R-CH=[O2=B-(OH)]  (???)

A 1cm layer of Hg in a 10cm diameter glass container will weight a little more than 1kg! So people cannot scale this one up easily, but of course there is no reason why more material cannot be reduced by running this thing for longer.
Assuming a required electrolysis duration of 5 hours, no Na restoration for the amalgam being necessary and the yields being as reported this device could produce about 740g trimethoxybenzaldehyde, 640g of dimethoxybenzaldehyde or 400g plain benzaldehyde per week!

Don't drop the electrolysis container! Always handle it inside a bucket or plastic container.

I'm not fat just horizontally disproportionate.
 
 
 
 
    Rhodium
(Chief Bee)
02-07-03 13:09
No 405387
      Mercury behavior  Bookmark   

How thin a layer of Hg can you have on the bottom of a beaker without risking it to collect in isolated puddles instead of covering the entire bottom of the beaker?
 
 
 
 
    Osmium
(Stoni's sexual toy)
02-08-03 02:50
No 405578
      I assume about 5mm. The problem is the strong...  Bookmark   

I assume about 5mm. The problem is the strong stirring employed here

I'm not fat just horizontally disproportionate.
 
 
 
 
    zealot
()
02-18-03 06:50
No 409400
      Answers on aromatic aldehydes from acids  Bookmark   


- Refs?

No refs. Only one article in a book of organic chemistry by Houben at 1935 year.

- What anode material and what size? Located where? Around the stirrer shaft? Or around the inside of the container?

Stainless steel, around the stirrer shaft, near the wall of container.

- Required Na content of the amalgam prior to the reaction less than 2%

- Required lenght of electrolysis? 9Ah? Yes

- What reaction temperature? less low than room temperature

- Distance between anode and cathode? 2 inch

The solution of  50 g Na2SO4 in 500 ml of water electrolyzing  ~3 hour by the 4 A. 1% of amalgam will be received. Then the solution deleted and in a glass is added the Rm.

- What's the structure of the H3BO3-aldehyde-compound? A geminal diester? Cyclic acetal-like?   I dont know.
 
 
 
 
    Rhodium
(Chief Bee)
02-18-03 10:58
No 409464
      I am not sure if you by "less low than...  Bookmark   

I am not sure if you by "less low than room temperature" mean that it should be cooled below room temp, or if it is supposed to be run above room temp ("less low" is ambiguous in english).
 
 
 
 
    hermanroempp
(Hive Bee)
02-18-03 11:31
No 409479
      Below room temperature,  Bookmark   

I would say. I'm sure he runs a "cold cell", to keep the back-reaction of the sodium amalgam with the aqueous sulfate solution at a minimum.

Quidquid agis, prudenter agas et respice finem!
 
 
 
 
    Rhodium
(Chief Bee)
02-18-03 17:07
No 409586
      Electroreduction of carboxylic acid derivatives  Bookmark   

Electroreduction of carboxylic acid derivatives: ../rhodium/djvu /eberson.djvu (Kudos to lugh!)

DjVu file reader plugin: http://www.lizardtech.com/download/
 
 
 
 
    Lego
(Stranger)
03-03-03 10:37
No 413374
      The original reference  Bookmark   

The original reference is probably:

Berichte, 41, 4148-50, 1909

The author describes the reduction of salicylic acid and benzoic acid to the corresponding aldehyde in yields from 30-50% with exact the method mentioned above.

Zealot is a bit vaque concerning the reaction of the temperature, in Berichte the reaction cell is cooled by placing it in a water bath.
The article itself is of no further use because Zealot has posted everything of interest.



The candle that burns twice as bright burns half as long