Palladium on Carbon‐Catalyzed Aqueous Transformation of Primary Alcohols to Carboxylic Acids Based on Dehydrogenation under Mildly Reduced Pressure

Abstract

The catalytic dehydrogenation of alcohols to carbonyl products is a green sustainable oxidation with no production of waste except for hydrogen, which can be an energy source. Additionally, a reusable heterogeneous catalyst is valuable from the viewpoint of process chemistry and water is a green solvent. We have accomplished the palladium on carbon (Pd/C)‐catalyzed dehydrogenation of primary alcohols to carboxylic acids in water under a mildly reduced pressure (800 hPa). The reduced pressure can be easily controlled by the vacuum controller of the rotary evaporator to remove the excess of generated hydrogen, which causes the reduction (reverse reaction) of aldehydes to alcohols (starting materials) and other undesirable side reactions. The present method is applicable to the reaction of various aliphatic and benzylic alcohols to the corresponding carboxylic acids, and the Pd/C could be reused at least 5 times.magnified image

Silver‐Catalyzed Dehydrogenative Synthesis of Carboxylic Acids from Primary Alcohols

“…In addition, a binuclear rhodium complex with two terpyridine ligands and palladium on carbon have been used to catalyze the dehydrogenation to carboxylic acids where a reduced pressure was necessary with the palladium catalyst to remove the liberated hydrogen gas. In all cases, a catalyst loading between 0.1 and 5 % was employed and the reactions were carried out at elevated temperature with water or toluene as the solvent . In addition, a stoichiometric amount of a base was added such as NaOH, KOH, CsOH or Cs 2 CO 3 giving rise to the alkali metal salt of the carboxylic acid as the immediate product.…”

“…[2] Since then the transformationh as also been achieved with as everalo ther ruthenium complexes containing PNP pincer, [3] NNN pincer, [4] N-heterocyclic carbene [5] and 2,2'-bipyridine type [6] ligands. In addition, ab inuclear rhodium complex with two terpyridine ligands [7] and palladiumo nc arbon [8] have been used to catalyze the dehydrogenation to carboxylic acids where areduced pressure was necessary with the palladium catalyst to remove the liberatedh ydrogen gas. In all cases,ac atalystl oadingb etween 0.1 and 5% was employed and the reactions were carriedo ut at elevated temperature with water or toluenea st he solvent.…”

“…In all cases,ac atalystl oadingb etween 0.1 and 5% was employed and the reactions were carriedo ut at elevated temperature with water or toluenea st he solvent. [2][3][4][5][6][7][8] In addition, as toichiometrica mount of ab ase was added such as NaOH, KOH, CsOH or Cs 2 CO 3 giving rise to the alkali metal salt of the carboxylic acid as the immediate prod-uct. The addition of the base also makes the overall transformatione nergetically more favored andp revents deactivation of the catalyst by the carboxylic acid.…”

New Gateways to the Platinum Group Metal-Catalyzed Direct Deuterium-Labeling Method Utilizing Hydrogen as a Catalyst Activator

“…[24][25][26][27][28][29][30][31][32] In contrast, the present method under milder reaction conditions with a wide scope of substrates is useful and valuable to synthesize various types of deuterium-labeled sugars. 33,34) Encouraged by the novel aspect of the proposed reaction mechanisms for the H-D exchange reaction of alcohols (Section 2, Chart 5), we have focused on the development of dehydrogenative oxidation of alcohols into carbonyl products. Since the oxidation of alcohols traditionally required toxic and/or explosive oxidizing agents, 35) heterogeneously catalyzed dehydrogenation reactions are spotlighted as clean oxidation methods generating only H 2 utilized as the reductant in organic synthesis and energy sources.…”

Ruthenium on Carbon Catalysed Carbon‐Carbon Cleavage of Aryl Alkyl Ketones and Aliphatic Aldehydes in Aqueous Media

“…[11] According to the mechanism, Ru(0) on Ru/C would be oxidatively inserted into the OÀH bond of the enol form of valerophenone (1 a) to form ruthenium(II) enolate A. Although butanal (E) is certainly oxidized to the corresponding butyric acid (F, 4 a), [13] E also undergoes Ru/C-catalysed CÀC bond cleavage in a similar manner. Subsequent homolytic cleavage of the O-O and CÀC bonds of C affords acyl radical D and butanal (E) together with the hydroxyl radical, and then benzoic acid could be obtained from D and the hydroxyl radical.…”