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Carbonyls, zinc-acetic acid

By far the most important synthesis gas reaction is its conversion into methanol, using copper/zinc oxide catalysts under relatively mild conditions (50 bar, 100-250°C). Methanol is further carbonylated to acetic acid (see Section 22-7), so that CH3C02H, methyl acetate, and acetic anhydride can all be made from simple CO and H2 feedstocks. Possible pathways to oxygenates in cobalt catalyzed reactions are shown in Fig. 22-6. [Pg.1252]

A way of avoiding the difficulty of handling a-aminocarbonyl-compounds is to prepare them in the presence of the second component, with which they are to react. Zinc-acetic acid or sodium dithionite can be used to reduce oximino-groups to amino, while leaving ketone and ester groups untouched, hi the classical synthesis, which gives this route its name, the a-aminocarbonyl component is simply an amino derivative of the other carbonyl component, and it is even possible to generate the oximino precursor of the amine in situP ... [Pg.313]

Other cobalt catalysts that have been used for enantioselective C—C double bond reduction of a,/ -unsaturated carbonyl compounds are vitamin B12 in combination with zinc/acetic acid (up to 33% ee)S7 and bis(dimcthylglyoximato)cobalt(II) (12) with chiral amines as cocatalysts88 and molecular hydrogen as reducing agent. The best results have been obtained with complex 12 and quinine or (2.S )-A -[(/ )-1 -phenethyl]-2-quinuclidinecarboxaniide (hydrogenation of 1,2-diphenyl-2-propen-l-one 49% ee A, /V -dimethyl-5-benzylidenehydantoin 79% ee). [Pg.1043]

Pyridine s. under H2S Zinc/acetic acid Preferential reduction of hindered carbonyl groups Phthalimidines from phthalimides... [Pg.28]

Cyclic Peroxides. CycHc diperoxides (4) and triperoxides (5) are soHds and the low molecular weight compounds are shock-sensitive and explosive (151). The melting points of some characteristic compounds of this type are given in Table 5. They can be reduced to carbonyl compounds and alcohols with zinc and alkaH, zinc and acetic acid, aluminum amalgam, Grignard reagents, and warm acidified iodides (44,122). They are more difficult to analyze by titration with acidified iodides than the acycHc peroxides and have been sucessfuUy analyzed by gas chromatography (112). [Pg.116]

A reaction which is of considerable importance for the selective labeling of a position adjacent to a carbonyl group is the treatment of a-halo ketones (mainly bromides) with zinc in acetic acid-OD, or deuteriobromic acid at... [Pg.200]

An isoindol1 none moiety forms part of the aromatic moiety of yet another antiinflammatory propionic acid derivative. Carboxylation of the anion from -nitro-ethylbenzene (45) leads directly to the propionic acid (46). Reduction of the nitro group followed by condensation of the resulting aniline (47) with phthalic anhydride affords the corresponding phthalimide (48). Treatment of that intermediate with zinc in acetic acid interestingly results in reduction of only one of the carbonyl groups to afford the isoindolone. There is thus obtained indoprofen (49). ... [Pg.171]

Low -molecular-weight ozonides are explosive and are theretore not isolated. Instead, the ozonide is immediately treated with a reducing agent such as zinc metal in acetic acid to convert it to carbonyl compounds. The net result of the ozonolysis/reduction sequence is that the C=C bond is cleaved and oxygen becomes doubly bonded to each of the original alkene carbons. If an alkene with a letrasubstituted double bond is ozonized, two ketone fragments result if an alkene with a trisubstituted double bond is ozonized, one ketone and one aldehyde result and so on. [Pg.237]

Oz.onide (Section 7.9) The product formed by addition of ozone to a carbon-carbon double bond. Ozonides are usually treated with a reducing agent, such as zinc in acetic acid, to produce carbonyl compounds. [Pg.1247]

Purely aromatic ketones generally do not give satisfactory results pinacols and resinous products often predominate. The reduction of ketonic compounds of high molecular weight and very slight solubility is facilitated by the addition of a solvent, such as ethanol, acetic acid or dioxan, which is miscible with aqueous hydrochloric acid. With some carbonyl compounds, notably keto acids, poor yields are obtained even in the presence of ethanol, etc., and the difficulty has been ascribed to the formation of insoluble polymolecular reduction products, which coat the surface of the zinc. The adffition of a hydrocarbon solvent, such as toluene, is beneficial because it keeps most of the material out of contact with the zinc and the reduction occurs in the aqueous layer at such high dilution that polymolecular reactions are largdy inhibited (see Section IV,143). [Pg.510]

Bicyclo[4.2.0]octanes wiLh carbonyl groups adjacent to each bridgehead carbon cleave the central bond on reduction with lithium in liquid ammonia,158,159 with sodium/potassium alloy in the presence of chlorotrimethylsilane,160 with zinc in acetic acid,37 or with zinc amalgam in hydrochloric acid.15 7... [Pg.591]

Subtle variations in the structures of acyl groups attached to nucleosides have been made in order to allow such groups to be removed under mild or special conditions that do not affect other acyl groups. The (2,2,2-tribromoethoxy)carbonyl group is susceptible to non-hy-drolytic removal by using a zinc-copper couple in acetic acid thus, 3 -0-acetyl-5 -0-(2,2,2-tribromoethoxycarbonyl)- and 5 -0-acetyl-3 -0-(2,2,2-tribromoethoxycarbonyl)-thymidine gave170 3 -0-acetyl- and 5 -O-acetyl-thymidine in a yield of 75 and 60%, respectively. [Pg.41]

Fischli has used a related reagent, Cob(I)alamine,2 obtained by reduction of vitamin B,2 with zinc and acetic acid, as a catalyst for reduction with zinc and acetic acid of various unsaturated systems such as a,/ -unsaturated nitriles,3 esters,4 and carbonyl compounds,5 allylic alcohols and amines,6 and also isolated double bonds.6... [Pg.103]

A nitrochromone has three easily reducible functions and, for its reduction, conditions and reagents which have little or no effect on the carbonyl or the 2,3-double bond should be chosen. Nitrochromones are reduced by tin-hydrochloric acid, zinc-ammonium chloride, iron-acetic acid, iron-hydrochloric acid or sodium dithionite. It may be easier to control the severity of the conditions in catalytic hydrogenation. Scheme 29 shows that with proper choice of conditions (temperature, pressure, solvent, catalyst), it is often possible to optimize the yield of the desired product (527). Extending the reaction time from about 30 min to 2.5 h increased the yield of the chromanone (528) and none of the hydroxylamine (529) was then detected (70JCS(C)2230). [Pg.714]

Tetrafluoro-3-oxo-4-phenylbutanoic acid is reduced at both the activated a,a -positions and the carbonyl group to give 4-phenylbutanoic acid by the Clemmensen method in quantitative yield.125 In contrast, only the highly activated C3-F bonds are selectively reduced in ethyl 2,2,4,4,4-pentafluoro-3-oxobutanoate by treatment with sodium in diethyl ether (Table 3).126 A more efficient zinc reduction of ethyl 4.4,4-trifluoro-3-oxobutanoate in refluxing acetic acid results in complete hydrodefluorination of the trifluoromethyl group to give 21.104... [Pg.331]


See other pages where Carbonyls, zinc-acetic acid is mentioned: [Pg.147]    [Pg.114]    [Pg.310]    [Pg.231]    [Pg.354]    [Pg.510]    [Pg.573]    [Pg.125]    [Pg.169]    [Pg.320]    [Pg.290]    [Pg.152]    [Pg.455]    [Pg.276]    [Pg.275]    [Pg.113]    [Pg.83]    [Pg.123]    [Pg.126]    [Pg.339]    [Pg.658]    [Pg.961]    [Pg.48]    [Pg.423]    [Pg.405]    [Pg.569]    [Pg.356]    [Pg.125]    [Pg.328]    [Pg.1234]   
See also in sourсe #XX -- [ Pg.555 ]




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