Reduction Of Acetic Acid Research Articles

Selective Reduction of Acetic Acid to Acetaldehyde on Iron Oxides

The selective reduction of acetic acid to acetaldehyde on iron oxides has been studied in various pressure ranges. A good selectivity towards acetaldehyde could be achieved with molecular hydrogen continuously present in the gas phase and on a prereduced catalyst containing both a metal phase (zero-valent metal) and an oxidic phase. The pressure of acetic acid appears to influence the formation and the kind of by-products. At low pressures of acetic acid (0.015 mbar) ketene (CH2CO) is the most important (by-)product, while at high pressures (25 mbar) ketene has never been observed and acetone is the main (by-) product. Reaction mechanisms have been proposed for the selective reduction to acetaldehyde and for the formation of the (by-)products. Presumably the reduction to acetaldehyde occurs on the vacancy-rich oxidic layer, while hydrogen is dissociated on the zero-valent metal sites. The by-products are most likely formed via a common ketene-like intermediate.

Evaluation of some flavonoids as potential bradykinin antagonists

Fourteen flavonoids were evaluated for their effects as potential bradykinin (BK) antagonists. The compounds were evaluated in severalin vitro andin vivo (oral administration) systems; inhibition of BK induced contractions in isolated rat ileum and uterus, antagonistic effects of BK induced plasma extravasation, reduction of acetic acid induced writhing nociception and protection from endotoxic shock. Skullcapflavone II (3), baicalein (5), 5-methoxyflavone (11), 6-methoxyflavone (12) and 2′-methoxyflavone (14) showed effects in all the tests although the order of potency were somewhat varied.

Synthesis and structure-activity relationships of 14β-hydroxy-5α-pregnanes: pregnanes that bind to the cardiac glycoside receptor

5α-pregnane-3β,14β,20β-triol 3-α- l-rhamnopyranoside (8) and 3β-(α- l-rhamnopyranosyloxy)-5α-pregn-14-en-20-one (14) were prepared from uzarigenin by ozonolysis followed by zinc and acetic acid reduction and glycosidation. During the glycosidation reaction leading to (8) the corresponding ortho ester (9) was also obtained. Uzarigenin α- l-rhamnopyranoside (15) also was prepared. Synthesis of 5α-pregnane-3β,14β,20β-triol (20) is described. Structures were established by analysis of their NMR spectra. The binding affinity of 5α and 5β cardenolide and pregnane derivatives as a measured in a radioligand binding assay was determined and their structure-activity relationships compared. The receptor binding affinity of the 5α derivatives is les than that of the corresponding 5β derivatives.

Steady-state voltammetry of strong and weak acids with and without supporting electrolyte

Voltammetric reduction of perchloric, phosphoric, acetic, and ascorbic acid was investigated under steady-state conditions at platinum- and gold-disk microelectrodes. The dependence of the wave height of proton in perchloric acid on the concentration of supporting electrolyte (lithium perchlorate) was compared with the theory for currents limited by migration and diffusion. The wave height depends linearly on hydrogen ion concentration without and with supporting electrolyte up to 0.04 and 0.08 M, respectively

Synthesis of 3β,14-dihydroxy-5β,14β-pregnan-20-one C-3 derivatives: ozonolysis of digitoxin and digitoxigenin and their derivatives followed by zinc–acetic acid reduction to the C-21 methyl ketone

Ozonolysis of digitoxin, digitoxin tetraacetate, digitoxin tetrakis-(2,2,2-trichloroethyl carbonate), digitoxigenin, digitoxigenin acetate, digitoxigenin hemisuccinate and digitoxigenin 2,2,2-trichloroethyl carbonate followed by treatment with excess of zinc in acetic acid gave either the corresponding 21-hydroxy ester after 5 min or the 21-methyl ketone after 20 h. This procedure is more efficient than methods previously reported for the conversion of the α,β-unsaturated γ-lactone into an acetyl group and is applicable to the cardiac glycosides directly to give 14β-hydroxypregnan-20-one derivatives. Acidic hydrolysis of 14,21-dihydroxy-and 14-hydroxy-3β-tris(digitoxosyloxy)-5β,14β-pregnan-20-one is reported. Structures are based on 1H and 12C NMR assignments.

Zinc–acetic acid reduction of the steroid 4-en-3-one: novel conversion of the 4-en-3-one into the 2-en-4-one via a vinyl chloride

Transposition of a steroid 4-en-3-one to the 2-en-4-one has been carried out. 4-Chlorotestosterone acetate on Zn–HOAc reduction yields a mixture of the C-5 epimers of the 4-chloro-3-ene together with a C-3 dimer. The vinyl chlorides, after epoxidation followed by rearrangement and elimination, give the 2-en-4-one. A synthesis of 17β-hydroxy-5α-androst-2-en-4-one and 17β-hydroxy-5α-estr-2-en-4-one is described.

Reductive removal of the tert-hydroxy group in α,β-unsaturated γ-tert-hydroxyketones with chlorotrimethylsilane-sodium iodide. An alternative to zinc–acetic acid reduction

Chlorotrimethylsilane–sodium iodide effects reductive removal of the tert-hydroxy group in the α,β-unsaturated γ-tert-hydroxyketones (1), (3), (5), and (7).

Bromothiophene reactions. II. A novel rearrangement in the zinc and acetic acid reduction

AbstractThe elimination of the α‐bromine atoms of the bromothienylethanolamine derivatives 2a,b,c,d with zinc and acetic acid unexpectedly involved a migration of the ethanolamine side chain from the 3 to the 2 position in the thiophene ring. Experiments carried out with simpler analogous compounds 3, 4 and 6 seem to indicate that this rearrangement takes place only in those cases in which the carbon atom of the side chain next to the ring supports an oxygen atom capable of being protonated in the reaction medium. A tentative mechanism is proposed to explain the experimental results.

Selective removal of sulphur protecting groups of cysteine residues by sulphenyl halides

Sulphur protecting groups of cysteine, such as triphenylmethyl, diphenylmethyl, 4,4′-dimethoxydiphenylmethyl and acetamidomethyl groups, are cleanly removed by the action of 2-nitrophenylsulphenyl chloride in acetic acid and subsequent reduction of the S-(2-nitrophenylsulphenyl)cysteine residues formed to regenerate the thiol function.

Synthesis of diacetyldichlorofluorescin: A stable reagent for fluorometric analysis

Acetylation of the product of zine and acetic acid reduction of 2′,7′-dichlorofluorescein yielded a nonfluorescent material that was stable to autoxidation. This compound is assumed to be diacetyldichlorofluorescin (LDADCF). It has a potential use as a reagent for the determination and detection of materials that oxidize or catalyze its oxidation to the fluorescent state. LDADCF must be activated by treatment with dilute sodium hydroxide prior to use as a reagent.