Raney Ni-Al alloy mediated hydrodehalogenation and aromatic ring hydrogenation of halogenated phenols in aqueous medium

Abstract

Raney Ni-Al alloy in a dilute aqueous alkaline solution has been shown to be a very powerful reducing agent and is highly effective for the reductive dehalogenation of polyhalogenated phenols and aromatic ring hydrogenation of phenols to the corresponding cyclohexanols.

Hydrodechlorination of Different Chloroaromatic Compounds at Room Temperature and Ambient Pressure—Differences in Reactivity of Cu- and Ni-Based Al Alloys in an Alkaline Aqueous Solution

“…Chlorinated phenols are common aquatic pollutants due to their biocidal properties and solubility in water [5][6][7]10,12,14,15,17,18,20,[26][27][28][29]31]. Due to this reason the possible reductive degradation of several chlorinated phenols was studied via HDC process testing both Devarda's Al-Cu-Zn and Raney Al-Ni alloys.…”

“…At least two reaction mechanisms are possible using Al-Ni as the HDC reagent. In most cases, Raney Al-Ni alloy in the alkaline aqueous solution is a much more active HDC agent than the commercial Raney Ni catalyst in co-action of different reductants in the same reaction medium [18][19][20][21][22][23][24][25]28]. As mentioned by Yang et al [28], the Al-Ni alloy is composed of a galvanic couple between the active Al anode and the stable Ni cathode after the dissolution of the Al 2 O 3 protection film by OH -.…”

“…Apart from bimetals, several Al-based metallic alloys containing Cu or Ni (Al-Cu and Al-Ni) have been published as very effective for HDC of Ar-Cls [18][19][20][21][22][23][24][25][26] due to the high quantity of Ni (or Cu, respectively) working as HDC catalysts compared with bimetals where electropositive metal (source of reductant) is covered with a thin layer of HDC catalyst. Raney Al-Ni alloy (which contains 50 wt.% of Al and 50 wt.% of Ni) in a diluted aqueous base seems to be an especially effective HDC reagent exploiting both the reduction potential of Al in the alkaline aqueous solution with the high HDC activity of in situ produced Raney Ni [18][19][20][21][22][23][24][27][28][29]. The role of the base in the HDC reaction mediated by the Al-Ni alloy was studied in several works [21,24,28,29].…”

Applicability of Nickel-Based Catalytic Systems for Hydrodehalogenation of Recalcitrant Halogenated Aromatic Compounds

“…This alloy contains 50 wt% of Al and 50 wt% of Ni bound in the form of Al 3 Ni and Al 3 Ni 2 . Different bases such as NaOH or KOH [88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104], alkali metal carbonates [89,94,95], NaF [100] or some alkaline salts of complexing agents [91,101] were proved for HDH processes. It was observed that Raney Al-Ni alloy is, especially in diluted aq.…”

“…It was observed that Raney Al-Ni alloy is, especially in diluted aq. NaOH or KOH, a very effective and universal HDH agent enabling quantitative HDH of Ar-Br, Ar-Cl compounds at elevated temperature [89,90,95,96,99,102,104] or even at room temperature [81][82][83][84][85][86][87][88][89][90][91][92][93][94]98,103].…”