Copper chromite ester hydrogenation

Reduction. Hydrogenation of dimethyl adipate over Raney-promoted copper chromite at 200°C and 10 MPa produces 1,6-hexanediol [629-11-8], an important chemical intermediate (32). Promoted cobalt catalysts (33) and nickel catalysts (34) are examples of other patented processes for this reaction. An eadier process, which is no longer in use, for the manufacture of the 1,6-hexanediamine from adipic acid involved hydrogenation of the acid (as its ester) to the diol, followed by ammonolysis to the diamine (35). 

Ruthenium dioxide or ruthenium-on-carbon are effective catalysts for hydrogenation of mono- and dicarboxylic acids to the alcohol or glycol. High pressures (5,000-10,000 psig) and elevated temperatures (130-225 C) have been used in these hydrogenations 8,12,24). Yields of alcohol tend to be less than perfect because of esterification of the alcohol. Near quantitative yields of alcohol can be obtained by mixing ruthenium and copper chromite catalysts so as to reduce the ester as formed. 

Alcohols are the most frequently formed products of ester hydrogenolysis. The hydrogenation of esters to alcohols is a reversible reaction with alcohol formation favored at high pressure, ester at low pressure (/). Copper chromite is usually the catalyst of choice. Details for the preparation of this catalyst (/7) and a detailed procedure for hydrogenation of ethyl adipate to hexamethylene glycol (/[Pg.80]

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]. 

Acyloins were converted to mixtures of stereoisomeric vicinal diols by catalytic hydrogenation over copper chromite [972]. More frequently they were reduced to ketones by zinc (yield 77%) [913, 914], by zinc amalgam (yields 50-60%) [975], by tin (yields 86-92%) [173], or by hydriodic acid by refluxing with 47% hydriodic acid in glacial acetic acid (yields 70-90%) [916], or by treatment with red phosphorus and iodine in carbon disulfide at room temperature (yields 80-90%) [917] Procedure 41, p. 215). Since acyloins are readily accessible by reductive condensation of esters (p. 152) the above reductions provide a very good route to ketones and the best route to macro-cyclic ketones [973]. 

Complete reduction of unsaturated esters to sativated alcohols takes place when the esters are hydrogenated over Raney nickel at 50° and 150-200 atm [44] or over copper chromite at temperatures of 250-300° and pressures of 300-3 50 atm [52,1056] (p. 153). In contrast to most examples in the literature the reduction of ethyl oleate was achieved at atmospheric pressure and 270-280° over copper chromite, giving 80-90% yield of octadecanol [1074]. a.,P-Unsaturated lactones are reduced to saturated ethers or alcohols, depending... 

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]. 

Hydrogenation of esters, with copper chromite and Raney nickel, 8, 1 Hydrohalogenation, 13, 4 Hydroxyaldehydes, aromatic, 28, 1 a-Hydroxyalkylation of activated olefins, 51, 2... 

Esters may alternatively be reduced to primary alcohols either using hydrogen under pressure in the presence of a copper chromite catalyst,56 or with lithium aluminium hydride (Expt 5.38), but not with sodium borohydride which is insufficiently reactive. However it has been found recently that sodium borohydride in mixed solvents (methanol/tetrahydrofuran) reduces /1-ketoesters to 1,3-diols, and this method offers a convenient route to this type of compound.57... 

Like the parent compounds, the methyl ethers of aldobiouronic acids are resistant to acid hydrolysis, and it is difficult to carry out hydrolysis without some decomposition of the product. This difficulty has recently been overcome by reduction of the uronic acid residue with lithium aluminum hydride66-67 the resulting disaccharide then undergoes hydrolysis without difficulty. The first reduction of the uronic acid residue of a methylated aldobiouronic acid methyl ester was accomplished by Levene, Meyer and Kuna,69 who reduced the methylated aldobiouronic acid from gum arabic with hydrogen in the presence of copper chromite catalyst under the conditions previously used701 for reducing the acety-... 

The methyl esters can be fed directly to a hydrogenation unit, or more often are distilled to separate unreacted triglycerides which are recycled. The distilled methyl esters are hydrogenated at approximately 300°C and 3000 psig with a copper chromite catalyst in slurry form through tubular reactors. Excess hydrogen is used for reduction as well as agitation of the slurried catalyst. 

Alcohols from esters. The major problem is reaction selectivity. Paraffin by-product in alcohol results if the catalyst activity is too high. Yet the reduction of esters to alcohols is a difficult reaction. Copper chromite catalyst, 3000-5000 psig hydrogen, and a temperature of 270-300°C are required for the reduction. An alternate catalyst is CuO/ZnO, which is used for methyl ester reduction only. Hydrogen solubility in alcohol is limiting. 

The addition of other metals to promote skeletal catalysts has been the subject of a number of investigations including the use of V, Cr, Mn, and Cd for hydrogenation of nitro compounds [23], Cd in the hydrogenation of unsaturated esters to unsaturated alcohols [24], and Ni and Zn for the dehydrogenation of cyclo-hcxanol to cyclohexanone. The use of Cr as a promoter is particularly attractive as copper chromite catalysts arc used in a wide range of industrial applications. Lainc and co-workers [25] have made a detailed study of the structure of chromium promoted skeletal copper catalysts. 

Fatty alcohols are obtained by direct hydrogenation of fatty acids or by hydrogenation of fatty acid esters. Typically, this is performed over copper catalysts at elevated temperature (170°C-270°C) and pressure (40-300 bar hydrogen) [26], By this route, completely saturated fatty alcohols are produced. In the past, unsaturated fatty alcohols were produced via hydrolysis of whale oil (a natural wax occurring in whale blubber) or by reduction of waxes with sodium (Bouveault-Blanc reduction). Today, they can be obtained by selective hydrogenation at even higher temperatures (250°C-280°C), but lower pressure up to 25 bar over metal oxides (zinc oxide, chromium oxide, iron oxide, or cadmium oxide) or partially deactivated copper chromite catalysts [26],... 

After the hydrogenation autoclave is cleaned it is best to carry out one or two ester hydrogenolyses with copper chromite in order to remove the last traces of poison. The bomb may then be used for hydrogenations. 

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