A Recyclable, Metal-Free Mechanochemical Approach for the Oxidation of Alcohols to Carboxylic Acids

Abstract

The oxidation of primary alcohols under mechanochemical conditions in a Spex8000M Mixer/Mill was investigated. To facilitate ease of separation and recyclability, a polystyrene-bound version of a TEMPO catalyst was employed. When paired with Oxone® in a stainless-steel vial with a stainless-steel ball, several primary alcohols were successfully oxidized to the corresponding carboxylic acids. The product was isolated using gravity filtration, which also allowed for the polystyrene-bound TEMPO catalyst to be recovered and reused in subsequent oxidation reactions. Furthermore, it was demonstrated that the size and steric hindrance of the primary alcohol does not hinder the rate of the reaction. Finally, the aldehyde was selectively obtained from a primary alcohol under ball milling conditions by using a combination of non-supported TEMPO with a copper vial and copper ball.

Rational Functionalization Towards Redox‐Active TEMPO Stable Free‐Radical‐Hydrochar Composites

“…This is most likely the effect of a corresponding decrease of the base concentration since, during the next run performed in fresh solution (dashed curve in Figure S5d) the oxidation current reaches roughly 95 % of its initial value, demonstrating that the recyclability compares well with that reported for aliphatic alcohols oxidation at polystyrene-bound TEMPO catalysts. [47] The good redox activity stability as well as the electrocatalytic efficiency for alcoholic oxidation disclose the superiority of these sustainable composites compared to other TEMPO functionalized materials. [48]…”

Liquid Chromatography Analysis of Reactive Oxoammonium Cations

“…The reversible redox reactions of OCs are frequently used in organic synthesis to oxidize primary or secondary alcohols to the corresponding aldehydes/ketones or even carboxylic acids [2,3]. The oxoammonium cation can act as the oxidant itself or as oxidation catalyst in connection with cost-efficient inorganic oxidants like sodium hypochlorite or oxygen, offering a sustainable and green way to produce aldehydes, ketones, and carboxylic acids from alcohols [4][5][6]. Further fields of application are electrochemical energy storage, with the oxoammonium-aminoxyl redox couple as one of the best investigated systems with regard to organic batteries [7][8][9], and biological and pharmaceutical applications of the oxoammonium cation, e.g., as antihypertensives or pro-oxidants [10][11][12].…”

“…We could improve the reaction conditions by optimization and could apply the new protocol to three different oxoammonium cations. Namely, the Bobbitt salt (N-(2,2,6,6-tetramethyl-1-oxopiperidin-1-ium-4-yl)acetamide tetrafluoroborate) (4), the TMA-TEMPO (2,2,6,6-tetramethyl-1-oxo-4-(trimethylammonium)piperidin-1-ium dichloride) OC (5), and the TEMPOL (4-hydroxy-2,2,6,6-tetramethyl-1-oxopiperidin-1-ium chloride) OC ( 6) were chosen as model substances for oxidation catalysts, organic radical batteries, and pharmaceutical applications, respectively, due to their wide spread in their respective fields (Fig. 2).…”

Sequential Connection of Mutually Exclusive Catalytic Reactions by a Method Controlling the Presence of an MOF Catalyst: One-Pot Oxidation of Alcohols to Carboxylic Acids

“…54−62 Finally, a TEMPOfunctionalized polymer was also utilized for the oxidation of alcohols to carboxylic acids in mechanochemical systems. 63 This polymer-based catalyst, however, is the combinatorial system between TEMPO and another oxidant: Oxone. TEMPO is used in the aerobic oxidation of alcohols to aldehydes followed by the Oxone-catalyzed second oxidation to carboxylic acids.…”

“…This is because the second step in oxidation, autoxidation, is inhibited by radicals such as TEMPO. − Therefore, neither aerobic oxidation nor autoxidation can occur sequentially from alcohols to carboxylic acids in the same flask or in a single MOF pore. In the homogeneous system, the dehydrogenation and oxidation processes have been developed to convert alcohols to carboxylic acids with transition-metal systems − and metal-free systems. − It should be noted that the amino-oxy-radical-catalyzed aerobic oxidation of alcohols to carboxylic acids through iron-catalyzed reactions [the Fe­(NO 3 ) 3 /TEMPO system and TEMPO-consumption process] and the electrochemical methods (with amine-functionalized TEMPO) has been recently illustrated in the case of homogeneous catalysis. − Finally, a TEMPO-functionalized polymer was also utilized for the oxidation of alcohols to carboxylic acids in mechanochemical systems . This polymer-based catalyst, however, is the combinatorial system between TEMPO and another oxidant: Oxone.…”