Copper chromite aldehydes

Under certain conditions low selectivity may be due to unfavorable formation to conversion ratios for stable oxygen-containing intermediates, such as aldehydes, olefine oxides, acids, which seem to prevent the accumulation of valuable products. However, this reason cannot be the sole and general one. For instance, with typical catalysts for high conversion of hydrocarbons, such as magnesium and copper chromites, aldehydes undergo oxidation at 200-400° mainly to acids and only in part to C02. Under the same conditions hydrocarbons oxidize to water and carbon dioxide, minor amounts of aldehydes and acids being found in reaction products. 

This reaction is favored by moderate temperatures (100—150°C), low pressures, and acidic solvents. High activity catalysts such as 5—10 wt % palladium on activated carbon or barium sulfate, high activity Raney nickel, or copper chromite (nonpromoted or promoted with barium) can be used. Palladium catalysts are recommended for the reduction of aromatic aldehydes, such as that of benzaldehyde to toluene. 

Hydrogenolyses of carboxylic acids and esters to the corresponding aldehydes seems very attractive due to their simplicity. Copper chromites are the most widely used catalysts.15 Raney copper and zinc oxide-chromium oxide have also been used for this process.16-18 The hydrogenolysis of methyl benzoate to benzaldehyde was studied on various metal oxides at 300-350°C. ZnO, Zr02 and Ce02 presented high activities and selectivities (Scheme 4.8). 

Oxidation of II to V is similarly effected by periodic acid.8 Aldehyde V can be saponified and further decarboxylated8 by copper chromite in quinoline to give 5-methyl-2-furaldehyde, affording additional confirmation of the assigned formula. 

The hydrogenation step talces place in the conventional way in vessel packed with catalyst where the aldehydes and hydrogen are admixed at 200-300°F and 600-1200 psi. The catalyst is usually nickel or copper chromite on an inert carrier such as kieselguhr, silica gel, or alumina. The crude butyl alcohols are finally separated and purified by distillation. 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

In contrast to phenolic hydroxyl, benzylic hydroxyl is replaced by hydrogen very easily. In catalytic hydrogenation of aromatic aldehydes, ketones, acids and esters it is sometimes difficult to prevent the easy hydrogenolysis of the benzylic alcohols which result from the reduction of the above functions. A catalyst suitable for preventing hydrogenolysis of benzylic hydroxyl is platinized charcoal [28], Other catalysts, especially palladium on charcoal [619], palladium hydride [619], nickel [43], Raney nickel [619] and copper chromite [620], promote hydrogenolysis. In the case of chiral alcohols such as 2-phenyl-2-butanol hydrogenolysis took place with inversion over platinum and palladium, and with retention over Raney nickel (optical purities 59-66%) [619]. 

Nickel, Raney nickel and copper chromite are other catalysts suitable for hydrogenation of aldehydes to alcohols with little if any further hydrogenolysis. Benzaldehyde was hydrogenated to benzyl alcohol over nickel [43], Raney nickel [45] and copper chromite [50] in excellent yields. In the last-... 

Usually alcohols accompany aldehydes in reductions with lithium aluminum hydride [1104] or sodium bis 2-methoxyethoxy)aluminum hydride [544], or in hydrogenolytic cleavage of trifluoroacetylated amines [7772]. Thus terr-butyl ester of. -(. -trifluoroacetylprolyl)leucine was cleaved on treatment with sodium borohydride in ethanol to rerr-butyl ester of A7-prolylleucine (92% yield) and trifluoroethanol [7772]. During catalytic hydrogenations over copper chromite, alcohols sometimes accompany amines that are the main products [7775]. 

The advantage over most other kinds of reduction is that usually the product can be obtained simply by filtration from the catalyst, then distillation. The common catalysts are nickel, palladium, copper chromite, or platinum activated with ferrous iron. Hydrogenation of aldehyde and ketone carbonyl groups is much slower than of carbon-carbon double bonds so more strenuous conditions are required. This is not surprising, because hydrogenation of carbonyl groups is calculated to be less exothermic than that of carbon-carbon double bonds ... 

Another commercial aldehyde synthesis is the catalytic dehydrogenation of primary alcohols at high temperature in the presence of a copper or a copper-chromite catalyst. Although there are several other synthetic processes employed, these tend to be smaller scale reactions. For example, acyl halides can be reduced to the aldehyde (Rosemnund reaction) using a palladium-on-barium sulfate catalyst. Formylation of aryl compounds, similar to hydrofomiylation, using HCN and HQ (Gatterman reaction) or carbon monoxide and HQ (Gatterman-Koch reaction) can be used to produce aromatic aldehydes. 

Oxazolidines (53) are readily formed from aldehydes or ketones and ethanolamines they can be hydrolyzed with ease and show reactions that might be expected of the imino alcohol intermediate (54). Among these are the addition of Grignard reagentsand catalytic hydrogenolysis of the C—O Ixjnd (equation 28).This reaction is exothermic over Adam s catalyst in methanol but slower in acetic acid. Nickel and copper chromite are also effective but at higher temperatures and pressures,as is the case with palladium. The same cleavage occurs with LAH (unassisted)and with the borane-THF complex. ... 

Copper chromite, CuCr204, and mixtures of cupric oxide with chromium sesquioxide and special additives (the Adkins catalyst), dehydrogenate primary alcohols to aldehydes [354, 355] and secondary alcohols to ketones [354, 355, 356]. 

Over copper chromite on Celite (diatomaceous earth) at 300-350 °C, aliphatic alcohols with three to eight carbons are converted into aldehydes in 53-67% yields [354. Catalytic dehydrogenations over copper, silver, or both [7, 345] are carried out in a current of an insufficient amount of air or oxygen at 300-380 °C and give aldehydes in yields ranging from 70 to 100%. An example of an industrial dehydrogenation is the conversion of methallyl alcohol into methacrolein [4] (equation 204). 

The use of copper chromite at 40°C and atmospheric pressure was not very effective for selective carbonyl group hydrogenation. Unsaturated alcohols were produced from unsaturated aldehydes in low yields at low conversions and not at all from methyl vinyl ketone. 28 With unconjugated, unsaturated aldehydes, copper chromite is effective as a selective hydrogenation catalyst. Hydrogenation of 46 at 140°-160°C and 200 atmospheres gave better than 70% of the diene diol, 47. Increasing the temperature to 240°C resulted in the complete saturation of 46 (Eqn. 18.28). 29... 

Monochloroanilines are made by reduction of chloronitrobenzenes with either iron/acid or, nowadays, mainly catalytic hydrogenation. Catalysts include platinum, copper chromite and rhenium in conjunction with palladium38. The chloroanilines are used in the manufacture of colorants, agricultural products, pharmaceuticals and polymers. For example, o-chloronitrobenzene (29) is a source of o-nitroanilinc, o-phenylenediamine (1,2-benzenediamine) (30), o-aminophenol (19b), o-chloroaniline and 3,3 -dichlorobenzidine (31a). The o-phenylenediamine (30) is a particularly versatile intermediate, used to prepare thioureidoformates. Ring-substituted o-phenylenediamines with cyanoesters yield benzimidazoles that, on condensation with an aldehyde, followed by treatment with H2S, give a range of thioureas. 

A procedure for preparation of /8-methyl-8-valerolactone from 3-methylpentane-1,5-dioP shows that copper chromite is an effective catalyst for dehydrogenation. Presumably the reaction proceeds through the aldehyde and hemiacetal. The evolution of hydrogen is nearly quantitative and the yield of lactone high. 

Aldehydes are obtained from primary alcohols by removing H2 in the presence of a copper chromite (CuO Cr203) catalyst. To do this, alcohol vapor at 250-300 °C is passed over hot CuO Cr203. One hydrogen molecule from each alcohol molecule is removed in the reaction. Thus, the alcohol is oxidized to an aldehyde. A hydrogen molecule can also be removed from low molar mass alcohols using just CuO as the catalyst. 

Copper chromite catalyzes reduction of aliphatic aldehydes to the alcohol, and Ru-on-carbon appears especially effective in aqueous medium. 

Platinum oxide-Fe or Cu-containing catalysts allow hydrogenation of furfural to furfurylalcohol". Ruthenium catalysts (Ru—C, RuOj) are successful in this specific case they have an activity well preserved through reuses. Otherwise Ru exhibits little activity in the heterogeneous hydrogenation of aromatic aldehydes. Other heterogeneous catalysis include platinized (PtC ) Raney Ni and copper chromite. 

Copper chromite is successfully used at high P and T but homogeneous Ru catalysts selectively reduce the carbonyl group of unsaturated aldehyde at 35-50°C. ... 

Hydrogenation is effected in a steel shaking autoclave with a copper insert of 500 ml capacity. The ketone or aldehyde (0.25 mole) and copper chromite catalyst (4g)184 are introduced. For hydroxy aldehydes, anhydrous methanol (100 ml) is also added, to prevent formation of resinous products. For aromatic ketones the initial pressure of hydrogen is 300-340 atm, but for hydroxy aldehydes and hydroxy ketones 220-240 atm suffice. When alcohol is used, the temperature is kept at 200-250° until the pressure remains constant when no alcohol is used, a temperature of 180-195° suffices for reduction to the hydrocarbon. When hydrogenation is complete, the mixture is washed from the vessel with methanol or benzene, filtered from the catalyst, and worked up as usual. 

Conversion of the glycidic ester into the aldehyde is usually performed in two steps the ester is first hydrolysed by aqueous or alcoholic alkali, and the glycidic acid is then cleaved by heating with dilute hydrochloric acid or thermally in a vacuum in the presence of copper or copper chromite. 

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