Kinetics and mechanism of ruthenium tetroxide catalysed oxidation of cyclic alcohols by bromate in a base

Summary Kinetic investigations on the RuO₄-catalysed oxidation of cyclopentanol (Cypol) and cyclohexanol (Cyhol) in alkaline KBrO₃ in the presence of Hg(OAc)₂ which acts as a bromide ion scavenger have been made in the 30°–45°C range. The reaction exhibits zero order kinetics in OH^– and is first order with respect to BrO ₃ ^– , substrate and RuO₄. The influence of Hg(OAc)₂ and ionic strength is insignificant. A transient complex, formed between HRuO ₅ ^– (the active species of RuO₄) and the cyclic alcohol, reacts with BrO ₃ ^– in a slow, rate determining step to give the products; the catalyst is regenerated.     

Facile electrochemical transformation of diazonium salts into carboxylic acids

The electrolyses of aryldiazonium tetrafluoroborates in dry DMF and Bu₄NHSO₄ as solvent-supporting electrolyte system, in the presence of CO₂ led to the corresponding arylcarboxylic acids in very good yields.     

Cobalt(II)-catalyzed oxidation of alcohols into carboxylic acids and ketones with hydrogen peroxide

The oxidation of aliphatic and aromatic alcohols into the corresponding carboxylic acid analogues and ketones has been carried out using 30% H₂O₂ and cobalt(II) complex 1 in good to high yields. The reaction is safe, clean and functions in the absence of additives.     

Kinetics of ruthenium(III)-catalyzed oxidation of arylthioacetic acids by Ce(IV)

The kinetics of ruthenium(III)-catalyzed oxidation of several arylthioacetic acids by Ce(IV) have been studied. The proposed mechanism involves the formation of a 1∶1 complex between Ru(III) and arylthioacetic acid, which then reacts with Ce(IV).     

An efficient and general method for resolving cyclopropene carboxylic acids

A general method is described for the resolution of cycloprop-2-ene carboxylic acids via diastereomeric N-acyloxazolidines prepared from enantiomerically pure oxazolidinones. Although a number of oxazolidinones were shown to resolve cyclopropene carboxylic acids, the oxazolidinones of S-phenylalaninol, S-phenylglycine and (1S,2R)-cis-1-amino-2-indanol are optimal in terms of resolving power and cost effectiveness. Separations were performed using simple flash chromatography, and because there is typically a large difference in R_f values it is possible to separate gram quantities of pure diastereomers in a single chromatogram. The cycloprop-2-ene carboxylic acids that can be resolved include those that are substituted at the 1-position by H, Ph, α-naphthyl, CO₂Me, CH₂OMOM, and trans-styryl; alkene substituents include Me, n-alkyl, Ph and tethered alkynes. Remarkably, 2-methyl-3-propylcycloprop-2-ene carboxylic acid can also be resolved with ease. The relative configurations of four diastereomerically pure oxazolidines were determined by X-ray crystallography. Reduction of the N-acyloxazolidinones with LiBH₄ give enantiomerically pure derivatives of 3-hydroxymethylcyclopropene that react with either MeMgCl or vinylMgCl and catalytic CuI to give enantiomerically pure products of syn-addition.     

Highly efficient epoxidation of cyclic alkenes catalyzed by ruthenium complex

The epoxidation of cyclic alkenes with molecular oxygen was efficiently completed in excellent epoxide yield using a novel ruthenium complex as catalyst under mild reaction conditions.     

Hydrogen peroxide oxidation of di(hydroxo)platinum(II) species in carboxylic acids

A facile procedure for synthesizing the mono(hydroxo)tris(carboxylato)platinum(IV) species has been achieved. The reaction of [Pt^II(OH)₂(dmpda)] (dmpda=2,2-dimethyl-1,3-propanediamine) with a 30% aqueous solution of H₂O₂ in the presence of a carboxylic acid produces a stable [Pt^IV(OOCR)₃(OH)(dmpda)] (R=Me, Et) complex in high yield. The crystal structures of [Pt^IV(OOCMe)₃(OH)(dmpda)] . H₂O (triclinic P1 bar, a=8.761(2) Å, b=9.245(3) Å, c=10.659(2) Å, =106.25(2)°, =93.90(2)°, =98.92(2)°, V=813.1(3) ų, Z=2, R= 0.0474) and [Pt^IV(OOCEt)₃(OH)(dmpda)] (monoclinic P2₁/c, a=12.777(4) Å, b=10.514(2) Å, c=14.971(3) Å, =107.40(2)°, V=1919.2(8) ų, Z=4, R=0.0611) show that the hydroxyl group has been selectively positioned at an axial site. The intramolecular hydrogen bond between the OH and C=O moiety exists (O(H)...=C, 2.83 Å for [Pt^IV(OOCMe)₃(OH)(dmpda)] · H₂O; 2.72 Å for [Pt^IV(OOCEt)₃(OH)(dmpda)]. Formation of the axial-mono(hydroxo)tris(carboxylato)platinum(IV) species may be ascribed to a combination of `reactive-equatorial effects' with `cis-addition' in the carboxylic acid.     

An efficient methyltrioxorhenium(VII)-catalyzed transformation of hydrotrioxides (ROOOH) into dihydrogen trioxide (HOOOH)

Dihydrogen trioxide (HOOOH) is formed nearly quantitatively in the low-temperature (-70 degrees C) methyltrioxorhenium(VII) (MTO)-catalyzed transformation of silyl hydrotrioxides (R3SiOOOH), and some acetal hydrotrioxides, in various solvents, as confirmed by 1H, and 17O NMR spectroscopy. The calculated energetics (B3LYP) for the catalytic cycle, using H3SiOOOH as a model system, is consistent with the experimentally observed activation energy (9.5 +/- 2.0 kcal/mol) and a small kinetic solvent isotope effect (kH2O/kD2O = 1.1 +/- 0.1), indicating an initial concerted reaction between the silyl hydrotrioxide and MTO in the rate-determining step. With the addition of water in the next step, the intermediate undergoes a sigma-bond metathesis reaction to break the Re-OOOH bond and form HOOOH, together with the second dihydroxy intermediate. The final step in the catalytic cycle involves a second, catalytic water that lowers the barrier to form H3SiOH and MTO.     

Oxidation reaction of steroid alcohols by ruthenium tetroxide

Oxidation of steroid alcohols by ruthenium tetroxide gives corresponding ketones in almost quantitative yields. The reaction provides a simple and convenient procedure for converting secondary alcohols to ketones in neutral media. The reconversion of ruthenium dioxide, produced during the oxidation, into the tetroxide with an appropriate oxygen donor such as sodium metaperiodate makes possible the oxidation of a given steroid alcohol to a ketone in the presence of a catalytic amount of ruthenium tetroxide.     

An efficient conversion of the carboxylic group of N-Fmoc alpha-amino acids/peptide acids into N-formamides employing isocyanates as key intermediates

Reaction of 96% formic acid with isocyanates derived from N-Fmoc alpha-amino acids/peptide acids catalyzed by DMAP has yielded a new class of stable formamides as crystalline solids which have been characterized by IR, 1H NMR, 13C NMR, and mass spectroscopy. Conversion of the side chain carboxylic acid of N-Fmoc-5-oxazolidinones of Asp/Glu into the N-formyl group also has been accomplished. The reaction is simple, mild, and high yielding.     

An efficient and practical system for the catalytic oxidation of alcohols, aldehydes, and alpha,beta-unsaturated carboxylic acids

Upon exposure to commercial bleach (approximately 5% aqueous sodium hypochlorite), nickel(II) chloride or nickel(II) acetate is transformed quantitatively into an insoluble nickel species, nickel oxide hydroxide. This material consists of high surface area nanoparticles (ca. 4 nm) and is a useful heterogeneous catalyst for the oxidation of many organic compounds. The oxidation of primary alcohols to carboxylic acids, secondary alcohols to ketones, aldehydes to carboxylic acids, and alpha, beta-unsaturated carboxylic acids to epoxy acids is demonstrated using 2.5 mol % of nickel catalyst and commercial bleach as the terminal oxidant. We demonstrate the controlled and selective oxidation of several organic substrates using this system affording 70-95% isolated yields and 90-100% purity. In most cases, the oxidations can be performed without an organic solvent, making this approach attractive as a "greener" alternative to conventional oxidations.     

Lipase-catalyzed transformation of poly(lactic acid) into cyclic oligomers

Enzymatic transformations into cyclic oligomers were carried out with the objective of developing chemical recycling of poly(lactic acid)s, such as poly(D,L-lactic acid) (PDLLA), poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA), which are typical biodegradable polymers. They were degraded by lipase in an organic solvent to produce the corresponding cyclic oligomer with a molecular weight of several hundreds. PDLLA (with a Mw of 84,000) was quantitatively transformed into cyclic oligomers by lipase RM (Lipozyme RM IM) in chloroform/hexane at 60 degrees C. PLLA (with a Mw of 120,000) was transformed into cyclic oligomer by lipase CA (Novozym 435) at a higher temperature of 100 degrees C in o-xylene. The oligomer structure was identified by 1H and 13C NMR spectroscopy and MALDI-TOF (matrix assisted laser desorption/ionization-time-of-flight) mass spectrometry.     

An efficient transformation of cellulose into cellulose carbamates assisted by microwave irradiation

Cellulose carbamates (CCs) were microwave-assisted synthesized from the native cellulose and urea under solvent-free and catalyst-free conditions. Types of raw materials, the effects of the reaction condition on the nitrogen content of CCs were investigated. CCs were characterized with infrared spectroscopy (FT-IR), ¹³C NMR spectrometry, X-ray diffraction, scanning electron microscopy and thermogravimetry. The results indicated that various source of native celluloses such as cotton linter, reed, bagasse and wood pulps with different degree of polymerization could be successfully converted to CCs by the efficient and environmentally friendly procedure. The nitrogen content of CCs increased with an increase of the urea content and the mass of the mixtures, as well as the pulsed times of microwave irradiation. CCs retained the cellulose I crystalline form of the native cellulose and the degree of crystallinity decreased with the incorporation of carbamates. This work provided a novel pathway for the preparation of cellulose carbamate, which is expected to be useful for the CarbaCell process.     

An efficient C-H oxidation protocol for alpha-hydroxylation of cyclic steroidal ethers

[reaction: see text] Various C-16 hydroxy steroids have been prepared with the aid of CrO(3)/Bu(4)NIO(4). Out of the two possible reaction courses, transition state B is favored because of less steric interference between substrate and CrO(4). Thus, C-H bonds at C-16 are oxidized selectively.     

A new oxidation of aldehydes to carboxylic acids

2-Hydroperoxyhexafluoro-2-propanol (HPHI) is a selective catalytic and stoichiometric reagent for the oxidation of aldehydes to acids under mildly basic conditions.     

Significantly improved oxidation of bio-based furans into furan carboxylic acids using substrate-adapted whole cells

Furan carboxylic acids are important building blocks in polymer and fine chemical industries. In this work, a simple substrate adaptation strategy was applied to improve the catalytic performances of Comamonas testosteroni SC1588 cells for the synthesis of various furan carboxylic acids. It was found that biocatalytic synthesis of 5-hydroxymethyl-2-furancarboxylic acid(HMFCA) was substantially promoted by adding histidine and increasing cell concentrations. HMFCA was produced in a quantitative yield from200 m M HMF in 24 h. Besides, the HMFCA yields of 71%–81% were achieved with the substrate concentrations up to 250–300 m M. It was firstly found that 4-tert-butylcatechol(TBC), as the stabilizer present in HMF, exerted a significantly detrimental effect on whole-cell catalytic synthesis of HMFCA at high substrate concentrations(more than 130 m M). In addition, a variety of furan carboxylic acids such as2-furoic acid, 5-methyl-2-furancarboxylic acid and 5-methoxymethyl-2-furancarboxylic acid were synthesized with the yields up to 98%.