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Author: Subject: Experimental: Alternative to Al/Hg - the Al/Cu
njl
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[*] posted on 30-11-2020 at 10:34


Can anyone provide more references for the activation of aluminum with copper ions? This thread had gone on for a surprisingly long time without citing any directly relevant literature. I do not doubt the efficacy of this system but there are several questions that remain unanswered here. Personally I am puzzled by the very nature of this reaction.

Is the Cu2+ ion actually relevant, or is it another species produced in situ?
Is the CuCl2 actually catalytic? If so, why does more need to be added in some instances?
Do we know the role the Chloride ion plays here? Is it somehow activating the aluminum by getting through the passive oxide layer?
When a solution of CuCl2 is dripped onto aluminum metal, copper can be seen plating out. If the Cu2+ is reduced to metallic copper, doesn't that imply that this process isn't catalytic?
Is using CuCl2 in the first place actually equivalent to in situ formation from CuSO4 + NaCl?
Several people have mentioned experimenting with various counterions. Do other halides work?

This article (https://sci-hub.st/https://doi.org/10.1021/ic402674z) claims that their copper catalyst was made by reducing copper salts with NaBH4, and that the same procedure was used for preparing nickel and cobalt particles. However, the reaction of NaBH4 with Ni2+ does not generate nickel metal nanoparticles, rather it forms the well characterized nickel boride (same goes for cobalt). Copper boride is (according to my research) a rare species at best, so the paper is essentially comparing metal nanoparticles to borides as though they were the same.

One of the few linked papers mentions the catalytic activity of Cu nanoparticles. Could it be that the active reduction reaction is the consumption Cu nanoparticles (as they are oxidized to Cu2+), followed by Cu2+ being reduced back to nanoparticles with the addition of aluminum?
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Corrosive Joeseph
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[*] posted on 30-11-2020 at 13:36


Quote: Originally posted by njl  
Can anyone provide more references for the activation of aluminum with copper ions?




/CJ

Attachment: Activation of Aluminum as an Effective Reducing Agent by Pitting Corrosion for Wet-chemical Synthesis.pdf (1.9MB)
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Corrosive Joeseph
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[*] posted on 30-11-2020 at 20:21


/CJ

Attachment: Mechanism of the Reaction of aluminum metal with copper (II) chloride solution.pdf (184kB)
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[*] posted on 1-12-2020 at 16:42


Quote: Originally posted by njl  
C
seen plating out. If the Cu2+ is reduced to metallic copper, doesn't that imply that this process isn't catalytic?


It is catalytic imo. U-Cu aka Urushibara copper

NEW HYDROGENATING CATALYSTS p203

The discovery of the Urushibara catalysts was due to the exploitation of a novel method for the reduction of estrone. Hence, we shall begin with some of the earlier methods which are now of historical interest. The reduction of estrone, established in this early period,3' involves the addition of precipitated nickel to an alkaline solution of estrone, to which aluminum chips are then added to liberate hydrogen. It has subsequently developed that precipitated copper, in place of the precipitated nickel, also gives estradiol-17/S in a good yield.27'
The modified method is the following: Zinc dust is added to 5 g of CuS04.5H20 dissolved in 100 ml of water, until the color of the copper(II) ion disappears. The pre-cipitated copper is washed with water and added to 50 mg of estrone dissolved in 65 ml of 10% potassium hydroxide solution. The solution is heated on a water bath with stirring, while 3 g of aluminum chips are added in small portions over a period of 10 hours. When the reaction is over, solid matter is filtered off, and the filtrate, made acid with hydrochloric acid, is extracted with ether. From the extract, 40 mg of estradiol-17/3 is obtained. Copper(II) chloride or copper(II) acetate may be used instead of copper(II) sulfate with almost the same result. A further modification consists in the use of zinc dust in place of aluminum chips. Zinc dust (4 g) is added in one portion to 50 mg of estrone dissolved in 65 ml of 10% potassium hydroxide solution. The solution is heated on a water bath with stirring and the precipitated copper, prepared from 5 g of copper(II) sulfate crystals and zinc dust, is added in small portions over a period of 10 hours. The yield of estradiol-17/? is the same as in the former method.

US4273679 Aluminum alloys having a high reducing capacity and preparation thereof

ABSTRACT
This invention relates to a process for the preparation of
aluminum alloys having a high reducing capacity for
use in reductions in organic chemistry. According to
this method a discontinuous heterodisperse superficial
alloy is formed by subjecting an aluminum alloy pre
pared by a metallurgical process to superficial activa
tion and/or treating aluminum with a salt of a metal
having a greater normal electrode potential than that of
aluminum; whereby the solution of said metal in a protic
solvent is reacted with granular aluminum and/or an
aluminum alloy. The catalyst prepared according to the
invention is especially suitable for the reduction of a
nitro or nitroso group into an amino group. The aluminun alloys having a high reducing capacity are also
within the scope of the invention.

EXAMPLE 7
27 g. of aluminum grains (Al content 99%) are heated
in 200 ml. of 0.1 N hydrochloric acid with 3g of copper
powder for half an hour at 50° C. to 70° C. After cooling the metal is filtered off and may be used for reduction.

EXAMPLE 11
27 g. of aluminum grains (Al content 99%) are activated in 200 ml. of a 40% aqueous acetic acid solution
at 60° C. to 80° C. with 5 g. of cupric sulfate.

EXAMPLE 3
123. g. of nitrobenzene are dissolved in a mixture of 65
300 ml. of water and 300 ml. of methanol, whereupon
200 g. of an aluminum treated according to Example 1
are added. To the mixture 800 ml, of concentrated
hydrochloric acid are added under reflux, with stirring
and cooling within 90 minutes. After cooling the metal
is filtered off, the methanol is distilled off in vacuo and
about 200 g. of sodium chloride are added. After stand
ing for some hours the aniline can be separated. After
fractionation 85g. of aniline are obtained. Yield: 91%.

EXAMPLE 4
21.7 g of freshly prepared crystalline 1-phenyl-2,3-
dimethyl-4-nitroso-pyrazolone-5 are suspended in 200
ml. of ice cold water. 20 g. of aluminum grains-activated according to Example 5-are added, at a temperature between 0° C. and -10 C. under stirring,whereupon 100 ml. of concentrated hydrochloric acid
are added dropwise. After 30 minutes the reaction mixture becomes colourless and the reduced product goes
into solution. The metal is filtered off. Thus 18.3 g of
1-phenyl-2,3-dimethyl-4-amino-pyrazolone-5 are obtained. Yield: 18.3.g., 90%.
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Corrosive Joeseph
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[*] posted on 16-12-2020 at 12:01


/CJ

Attachment: Reductive Ring Cleavage of Nonconjugated D2-Isoxazolines to b-Hydroxy Ketones with Aluminum and Copper(II) Chloride.pdf (103kB)
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