Andrzej Sobkowiak

MnIIILx/t-BuOOH-induced activation of dioxygen for the oxygenation of cyclohexene

Abstract Several manganese (III) complexes (MnIIILx) in combination with tert-butyl hydroperoxide (t-BuOOH) activate dioxygen (O2) to oxygenate cyclohexene (c-C6H10) to its ketone, alcohol, and epoxide. The product profiles depend on the ligand and solvent matrix. With picolinate (PA), bipyridine (bpy), or triphenylphosphine oxide (OPPh3) as the ligand in py/HOAc (2:1 molar ratio) dominant product is the ketone [c-C6H8(O)] whereas Schiff–base complexes produce c-C6H8(O), c-C6H9(OH) and the epoxide in almost equal yields. However, in MeCN c-C6H8(O) is the dominant product for all of the complexes.

The influence of solvent on the reaction between iron(II), (III) and hydrogen peroxide

It has been found that in acetonitrile, in contrast to water, iron(III) is reduced by hydrogen peroxide, according to 2:1 stoichiometry. The reaction when performed by cyclic-voltammetry is an example of electrochemical catalytic processes of reductants. For the [Fe(III)]/[HOOH] ratios greater than 1, 1 mol of dioxygen is produced from 1 mol of hydrogen peroxide. The non-radical versus radical mechanism of the process has been discussed.

Iron(III, II)-induced activation of dioxygen for the oxygenation of cyclohexene and related unsaturated hydrocarbons

Abstract Labile iron complexes [e.g., [Fe III (bpy) 2 ] aq 3+ , [Fe II (bpy) 2 ] aq 2+ , [Fe III (H 2 O) 6 ] aq 3+ and [Fe II (H 2 O) 6 ] aq 2+ in base-free acetonitrile activate dioxygen for the direct oxygenation of cyclohexene [to ketone, alcohol, and epoxide; c- C 6 H 10 → O 2 c- C 6 H 8 ( O ) , c -C 6 H 9 OH, c -C 6 H 10 -epoxide] and related unsaturated hydrocarbons with allylic carbon centers. For example, the combination of 1 mM [Fe III (bpy) 2 ] aq 3+ /O 2 (1 atm)/1 M c -C 6 H 10 yields 51 mM c -C 6 H 8 (O), 42 mM c -C 6 H 9 OH, and 3 mM c- C 6 H 10 -epoxide within 24 h (about 100 catalyst turnovers−product molecules per catalyst molecule). With 1 mM [Fe II (H 2 O) 6 ] 2+ in place of [Fe III (bpy) 2 ] aq 3+ , the product yield is 35 mM c -C 6 H 8 (O), 16 mM c -C 6 H 9 OH, and 0.1 mM epoxide. Under anhydrous conditions, the combination of 1 mM [Fe II (bpy) 2 ] 2+ (MeCN)/O 2 (1 atm)/2 M c -C 6 H 10 in a 1-h reaction yields 48 mM c -C 6 H 8 (O), 43 mM c -C 6 H 9 OH, and 3 mM c -C 6 H 10 -epoxide. Excess ligand or added H 2 O inhibits the reaction rate, and 0.1 M H 3 O + , 0.3 mM α-tocopherol (vitamin E), or 1 mM 2,6-di- tert -butyl-4-methylphenol (BHT) completely suppresses product formation.

Electrochemical oxidation of 2-methylnaphthalene-1,4-diacetate

Cyclic-voltammetric measurements show that 2-methylnaphthalene-1,4-diacetate is electrochemically oxidized on glassy-carbon electrode in glacial acetic acid at +1.45V vs SCE. The process is irreversible and diffusion controlled. Preparative controlled-potential electrolysis indicates that 2-methyl-1,4-naphthoquinone is a sole product. The material and current yields of the process are 94 and 99%, respectively.

Unusual electrochemical oxidation of cholesterol.

It has been found that cholesterol undergoes direct electrochemical oxidation on platinum electrode in dichloromethane. Voltammetric measurements show that the process is controlled by the rate of electron transfer and the height of the oxidation peak is linear vs. concentration of cholesterol. Preparative electrolysis with separated cathodic and anodic compartments afforded dicholesteryl ether in a relatively high material yield. Depending on electrolysis conditions (composition of supporting electrolyte and electrolytic cell construction) various by-products with a 3beta-chloro, 3beta-acetoxy, or 3beta-acetylamino group were obtained.

Electrochemical oxidation of cholesterol

Summary Indirect cholesterol electrochemical oxidation in the presence of various mediators leads to electrophilic addition to the double bond, oxidation at the allylic position, oxidation of the hydroxy group, or functionalization of the side chain. Recent studies have proven that direct electrochemical oxidation of cholesterol is also possible and affords different products depending on the reaction conditions.

Electrochemical synthesis of glycoconjugates from activated sterol derivatives.

Several derivatives of cholesterol and other 3β-hydroxy-Δ(5)-steroids were prepared and tested as sterol donors in electrochemical reactions with sugar alcohols. The reactions afforded glycoconjugates with sugar linked to a steroid moiety by an ether bond. Readily available sterol diphenylphosphates yielding up to 54% of the desired glycoconjugate were found to be the best sterol donors.

A selective electrochemical method of glycosylation of 3β-hydroxy-Δ5-steroids

A new electrochemical glycosylation method is presented. According to the method cholesterol and other 3beta-hydroxy-Delta(5)-steroids can be selectively transformed to glycosides using non-activated sugars. The method is also useful for the synthesis of glycoconjugates with sugar linked to a steroid moiety by an ether bond.

Synthesis of urethane—acrylic multi-block copolymers via electrochemically mediated ATRP

The electrochemically mediated atom transfer radical polymerisation (eATRP) of n-butyl acrylate was investigated under a variety of catalyst concentrations. Poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers were prepared via electrochemically mediated atom transfer radical polymerisation (eATRP) using only 7 × 10−6 mole % of CuII complex. The successful chain extension and formation of penta-block copolymers confirmed the living nature of the poly(alkyl acrylates) prepared by eATRP. In this work, the tri-block and penta-block urethane-acrylate copolymers were synthesised for the first time by using tertiary bromine-terminated polyurethane macro-initiators as transitional products reacting with n-butyl acrylate, and subsequently with tert-butyl acrylate in the presence of the CuIIBr2/TPMA catalyst complex. The results of 1H NMR spectral studies support the formation of tri-block poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers, and penta-block poly(tert-butyl acrylate)-block-poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate)-block-poly(tert-butyl acrylate) copolymers.

Ultralow ppm seATRP synthesis of PEO-b-PBA copolymers

Poly(ethylene oxide)-block-poly(butyl acrylate) copolymers were prepared via simplified electrochemically mediated atom transfer radical polymerization (seATRP) utilizing only 1 ppm of CuII complex, which is the limit of a successful well-controlled polymerization. The presented seATRP system works under potentiostatic and galvanostatic conditions. The polymerization results showed similar molecular weight evolution while maintaining a narrow molecular weight distribution throughout the reactions. 1H NMR results confirm chemical structure of synthesized diblock copolymers. This ultralow ppm technique is promising candidate for polymerization from nanoparticles, flat surfaces, proteins, and DNA.