ShadowWarrior4444
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Mood: Sunlight on a pure white wall.
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Acetaldehyde and Silver, Experimental Results
I've run across several notes in literature describing the production of acetaldehyde, some of which seem to be quite promising for the home chemist.
I have also attempted the small-scale production of acetaldehyde using my own modification to the electrolytic method.
To start, the electrolytic method:
One part denatured alcohol (95% Ethanol, 1% Methanol, 4% Water) was added to one part 33.5% sulfuric acid. At either end of the Petri dish was placed
a one sterling silver (92.5% Ag, 7.5% Cu.) The resistance of the cell at this time read at 22k Ohms. 1.4 Volts was then placed across the cell
supplied by a single AA battery (Alkaline, Duracell.)
Observations: Initially, light bubbling formed around the cathode, a light milky substance emanated from the anode until the entire Petri dish had
gone from clear to this new translucent white, no change in viscosity was observed. The scent of apples was evident at this time, with the scent of
Ethanol tapering off. This was left for 16 hours, and upon returning, a crystalline formation was observed from the cathode, and the anode had
degraded slightly. Light traces of acetic acid scent were noted, and the scent of acetaldehyde was markedly increased.
Theory: Research on acetaldehyde indicated that silver and copper were excellent oxidation catalysts for its production, as well as chemically
resistant to dilute H2SO4, and as such were used for the electrodes. Electrochemistry of Organic Compounds By Dr. Waltpier Lob also indicated that
when utilizing a sulfuric acid electrolyte, the acid was noted to become more concentrated at the anode--using this I hoped to polymerize the
acetaldehyde upon its creation, and extract it as solid paraldehyde.
Photos (sadly only the later half of the process was captured, this is after 2 days.):
  
[Hi-Res counterparts can be viewed by clicking the smaller ones.]
Interesting notes:
The anode seems to be corroded, however no slag is left behind, this suggests soluble silver compounds are present.
The precipitate formed at the cathode, and continues to creep along the dish as a mold might (probably along the field lines.)
The bubbles on the surface of the Petri dish I might attribute to dissolved CO2 generated at the cathode, though the anode too now shows bubbles.
The silver metal of the anode has developed a patina on the places that have not been submerged.
My central concern is now discovering what the white crystalline substance might be, I hope it is paraldehyde, as that seems to be the only polymer
that could form under these circumstances. (Formalin polymers are known as well, however I do not believe there was enough methanol to form
appreciable amounts of formalin and polymerize.)
Ancillary Production Methods:
These are ostensibly derived from Vogel's 5th, and may pique someone's interest.
Most promising:
POLYHYDRIC ALCOHOLS AND CARBOHYDRATES
If the neutral substance containing carbon, hydrogen and possibly oxygen is insoluble in ether but freely soluble in water, a polyhydric alcohol or a
simple mono- or di- saccharide (or related compound) is indicated. Treatment with concentrated sulphuric acid usually produces excessive charring.
Polyhydric alcohols are colourless viscous liquids, or crystalline solids. Upon heating with a little potassium hydrogen sulphate, they may
yield aldehydes (e.g. ethylene glycol yields acetaldehyde; glycerol gives the irritating odour of acrolein which can additionally be detected
with Schiffs reagent). Two confirmatory tests for polyhydric alcohols are as follows.
Second:
In the example (Expt 6.79) the reaction of the diazonium salt from ochloroaniline with benzene to yield 2-chlorobiphenyl is illustrative. It should be
noted, however, that when the liquid aromatic compound in which substitution is to occur is of the type ArZ, the directive influences which are used
to explain electrophilic substitution processes are not operative. Thus irrespective of the nature of the substituent Z, ortho-para substitution
predominates; this result supports the assumption that the substitution process is radical in type. Although the classical reaction occurs in a
two-phase system, the use of the more stable diazonium fluoroborates together with the phase-transfer catalyst 18- crown-6 can sometimes be more
convenient. The literature method for the preparation of 4-chlorobiphenyl in this way is given as a cognate preparation in Expt 6.79.3 The process of
deamination involves the replacement of the diazonium group by hydrogen, thus effecting the overall removal of the primary amino group. In a simple
procedure illustrated by the preparation of 1,3,5-tribromobenzene from 2,4,6-tribromoaniline (Expt 6.80), the amine is converted into the diazonium
sulphate in ethanol solution. Heating the solution brings about the reductive removal of the diazo group, the ethanol being oxidised to acetaldehyde.
Third:
m-Bromotoluene. To a cold mixture of 400 m1 of rectified spirit and 100 m1 of concentrated sulphuric acid contained in a 2.5-litre three-necked flask,
provided with an efficient mechanical stirrer, add 125 g (0.67 mol) of crude 4-amino-3-bromotoluene. Stir the solution and cool to 5 "C; then add
slowly a solution of 74g (1.07mol) of pure sodium nitrite in 135ml of water from a separatory funnel taking care that the temperature does not rise
above 10 "C. Continue the stirring for 20 minutes after all the nitrite solution has been added in order to complete the diazotisation (test with
potassium iodidestarch paper for the presence of free nitrous acid). Add 17.5 g (0.28 mol) of copper bronze (which has been washed with ether) or
copper powder (Section 4.2.19, p. 426) to the diazotised solution, and replace the stirrer by a long double surface condenser. Have an ice bath at
hand to cool the flask if the reaction becomes too vigorous. Warm the flask cautiously on a water bath until a vigorous evolution of gas commences,
then immerse at once in an ice bath to prevent loss through the condenser by too rapid evolution of nitrogen and acetaldehyde.
[Obligatory notice of Berne Convention attachment.]
[Edited on 6-22-2008 by ShadowWarrior4444]
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497
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I don't know what your mystery crystals are but I'm pretty sure they're not paraldehyde as it is a somewhat volital liquid. Maybe they're a silver
compound or complex?
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ShadowWarrior4444
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| Quote: | Originally posted by 497
I don't know what your mystery crystals are but I'm pretty sure they're not paraldehyde as it is a somewhat volital liquid. Maybe they're a silver
compound or complex? |
Upon closely examining the substance, it appeared to have a fractal-structure which caused a bit of a realization: That it must be elemental silver.
The silver slowly crept along the dish simply because it was electrically conductive and connected to the cathode--more silver was deposited along the
way.
I surmise that the reason this occurred is because silver was dissolved at the anode into an organic complex, followed by the plating of the metal at
the cathode. Due to the likely large molecular structure of the organic ligands, the silver plated in a fractal form. In conclusion, this would be an
excellent method for the home chemist to obtain finely divided silver.
Note: It may work for copper as well, as I noticed a brown precipitate at the cathode as well, this did not deposit in fractal form, but rather fell
off the cathode in a 'paste.' It is likely finely divided, as well.
[Obligatory notice of Berne Convention attachment, again.]*sigh*
[Edited on 6-22-2008 by ShadowWarrior4444]
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not_important
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Note that silver sulfate is slightly soluble in water, too. Try repeating this using just the electrodes and dilute H2SO4. Silver acetate has
roughly the same solubility as the sulfate.
Electrorefining uses an anode of an impure metal; a cathode of the pure metal, an inert conductor, or another metal that will be easy to separate from
the metal being refine. The electrolyte is generally related to electroplating solutions for the metal along with some free acid. A low voltage is
placed across the electrodes, lower than usually is used for electrowinning/electrosmelting or even electroplating. The metal dissolves from the
anode, plates out at the cathode, metals higher in the electromotive series stay in solution or in some cases precipitate out as insoluble salts,
metals lower in the electromotive series remain behind at the anode where they often appears as "anode slime".
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