Copper-chromite carboxylic acids

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). 

Interestingly, the Fischer indole synthesis does not easily proceed from acetaldehyde to afford indole. Usually, indole-2-carboxylic acid is prepared from phenylhydrazine with a pyruvate ester followed by hydrolysis. Traditional methods for decarboxylation of indole-2-carboxylic acid to form indole are not environmentally benign. They include pyrolysis or heating with copper-bronze powder, copper(I) chloride, copper chromite, copper acetate or copper(II) oxide, in for example, heat-transfer oils, glycerol, quinoline or 2-benzylpyridine. Decomposition of the product during lengthy thermolysis or purification affects the yields. 

The hydrogenation of HMF in the presence of metal catalysts (Raney nickel, supported platinum metals, copper chromite) leads to quantitative amounts of 2,5-bis(hydroxymethyl)furan used in the manufacture of polyurethanes, or 2,5-bis(hydroxymethyl)tetrahydrofuran that can be used in the preparation of polyesters [30]. The oxidation of HMF is used to prepare 5-formylfuran-2-carboxylic acid, and furan-2,5-dicarboxylic acid (a potential substitute of terephthalic acid). Oxidation by air on platinum catalysts leads quantitatively to the diacid. [32], The oxidation of HMF to dialdehyde was achieved at 90 °C with air as oxidizing in the presence of V205/Ti02 catalysts with a selectivity up to 95% at 90% conversion [33]. 

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. 

Amino-4-oxo-l,4-dihydro-l,8-naphthyridine-2-carboxylic acid (9, R = C02H) gave 7-amino-l,8-naphthyridin-4(177)-one (9, R = H) Dowtherm A, trace copper chromite, reflux 77%).758... 

Decarboxylation of tellurophene carboxylic acids occurs readily in quinoline solution under the action of copper chromite. In this way, 2-(3 (4 )-methoxyphenyl)tellurophenes have been obtained from 2-(3 (4 )-methoxyphenyl)-tellurophene-5-carboxylic acids <1980J(P2)971>. 

Difluoropyrrole (58) has been extensively used in the syntheses of octafluor-oporphyrins and other calyx( )pyrroles. This was first accessed by Leroy and Wakselman by barium-promoted copper chromite decarboxylation of 3,4-difluor-opyrrole-2-carboxylic acid in quinoline at 200°C. The acid was prepared in four steps beginning with a cycloaddition reaction of the protected aziridine 59 and chlorotrifluoroethylene (Fig. 3.26). 

Improvement to the decarboxylation of indole-2-carboxylic acids has been made by the use of microwave radiation. Under these conditions the copper chromite can be eliminated from the standard reagent mixture of copper chromite in quinoline and reactions are faster and cleaner <93JOC5558>. The ketene (399) generated from either the acid chloride or enol ester (398) of indole-3-carboxylic acid undergoes cyclic tetramerization to give the macrocyclic product (400) (Scheme 132) <91JHC1569>. 

Conventional decarboxylation of carboxylic acids involve refluxing in quinoline in presence of copper chromite and the yields are low. However, in the presence of microwaves decarboxylation takes place in much shorter time as illustrated in Scheme 14. 

Although acetals are much less reactive than their aldehyde precursors, under severe conditions conversion is possible. Thus, acetals have been reduced after removal of the hydroformylation catalyst in the presence or absence of water with copper chromite at high temperatures (750 °C) to give the corresponding alcohols [58]. Alternatively, acetals derived from a hydroformylation process have been oxidized in HCOOH to give the corresponding carboxylic acids and formyl esters, respectively [59]. 

With the preliminary results in hand, it was crucial that the C2 group on the indole could be readily removed. The C2 carboxylic acid derivatives of coupling products were initially employed toward this endeavor (Scheme 4). There are relatively few decarboxylation methods on indole acids reported in the literature, most of which utilize harsh reaction conditions. Nevertheless, Jagan tested several of the reported methods, including the use of copper chromite in quinoline at 215 °C, copper(I)oxide in DMA at 200 °C, and substoichiometric amounts of indole acid copper salts at 200 Much to his dismay, most of these reactions led to decomposition. Moreover, adjusting temperature or switching to microwave heating failed to provide the desired decarboxylation. 

Copper chromite/sodium carbonate Carboxylic acids... 

Copper chromite/sodium hydroxide Carboxylic acids from phthalides s. 13,111... 

A different interface is catalytic upgrading of fermentation broth, which uses both catalytic reduction and catalytic oxidation. For example, let s take a basic one that ought to be easy to do— reduction of a carboxylic acid to a primary alcohol. If you are doing it in a target-oriented, academic environment, you would use diborane. This has quantitative yields. The problem with that is that the stoichiometric reaction comes from boron trifluoride, I believe. That is where the diborane comes from. If you try to do the same thing with catalytic hydrogenation, you start seeing use of copper chromite and nickel catalysts. You can also do this on rhodium now. 

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