Cuprous acetate

The butanes and butenes have only limited physical solubility in ammoniacal cuprous acetate solutions. Compounds of higher unsaturation (dienes and acetylenes) form addition complexes, so their effective solubilities are much higher. 

The presence of ligands, either in the form of added anions such as acetate or as co-solvents or solvents, such as pyridine, markedly affect the kinetics. In pyridine or dodecylamine solvents the hydrogenation of Ag(I) acetate follows simple second-order kinetics, as does that of Cu(I) acetate. This behaviour is also shown in aqueous solutions by Ag(I) in the presence of acetate ions and by an ethylenediamine complex of Ag(I) . The rate of hydrogenation of Cu(II) acetate, on the other hand, is independent of oxidant concentration. The rate of oxidation of hydrogen by Cu(II) acetate in quinoline is also independent of oxidant concentration , but does depend on the square of the concentration of cuprous acetate which acts as a catalyst. For further details of these complicating features, reference should be made to the original papers and to Hal-pern s review ... 

Individual runs show initial autocatalysis followed by zero-order disappearance of Cu(II) when the substrate is in considerable excess. The reaction is affected by added cuprous acetate, according to... 

The enamine adducts formed in the reaction of aromatic amines with DMAD have been found to undergo cyclization leading to heterocyclic compounds, and the mode of these reactions is to a considerable extent influenced by the reaction conditions, the catalyst employed, and also the nature of the functional groups present in the starting amine. The reaction of aniline with methyl propiolate in presence of cuprous acetate, for example, is reported to give a mixture of 2(lH)-quinolone (1) and 4(l//)-quinolone (2) [Eq. (1)]." On the other hand, dimethyl anilinofumarate (3), formed from aniline with DMAD, undergoes... 

There is some doubt about the kinetics of the activation of hydrogen by cuprous acetate in the closely related solvent, pyridine. Wright, Weller, and Mills (34) have reported that the rate-law in this solvent (and in dodecyl-amine) is first-order in cuprous acetate, suggesting heterolytic splitting of hydrogen. On the other hand, Wilmarth (33) has observed a second-order dependence similar to that in quinoline. The reasons for this discrepancy and for the difference between pyridine and quinoline, if real, are not clear. 

Cuprous Acetate, Cu(C2H302) wh crysts, de-compg rapidly in air can be prepd by heating cupric acetate to ca 250° (Ref 1). Cuprous acetate was patented by DeMent (Ref 7) as an ingredient of the following smoke-producing compn cuprous acetate 1.5, K iodide 0.6, K iodate 0.6,... 

The course of a typical hydrogenation of quinone (p-benzoquinone), catalyzed by cuprous acetate in quinoline solution, is shown in Fig. 1. As indicated here, the quantity of hydrogen absorbed increases linearly with time until a point is reached where a change in slope occurs. The... 

The rate of quinone hydrogenation depends in a nonlinear way on the concentration of cuprous acetate. Calvin carried out a brief kinetic study in which he noted that the rate of reaction was somewhat more than pro-... 

Fig. 2. Rate of quinone hydrogenation vs. cuprous acetate concentration (5).

The continuous curve shown in Fig. 2 was calculated from Eq. (5) by use of the following values for the two parameters K = 11.2 mole-1 liters, k — 41.9 ml. (at 515 mm.) min.-1 mole-1. This dimerization constant is in agreement with the approximate value established by separate ebulliometric experiments. It is clear that within experimental error the data can be fit by an expression of the form of Eq. (5) i.e., the data are consistent with the hypothesis that the active catalyst is a dimer of cuprous acetate. 

The shape of the reduction curve indicates that the reduction of cupric ion is autocatalytic. This conclusion is confirmed by the almost complete disappearance of the induction period when cuprous acetate is added, strikingly illustrated by a comparison of curves I and II in Fig. 4 (5). In both cases the quantity of hydrogen absorbed is close to the theoretical value for the reduction of Cu++ to Cu+. There is evidence that the presence of aniline in the quinoline is effective in providing some cuprous ion from cupric to initiate sufficient catalyst to start the reaction. 

The individual points in Fig. 5 represent instantaneous rates, picked off the curves for nine separate experiments in which cupric acetate or oxyacetate was reduced, as a function of the total amount of cuprous acetate present at the corresponding time. The total cuprous acetate was the... 

Fig 4. Hydrogenation of cupric acetate effect of cuprous acetate (5). 

On this basis one can deduce the course of cupric acetate hydrogenation during any single experiment, the rate again being assumed to be proportional to the concentration of cuprous acetate dimer. Figure 6 shows the agreement obtained between the theoretical curve (solid curve) and the observed data (circles) for an experiment in which the hydro-... 

Reduction and exchange hy use of deuterium, Calvin (1) made a preliminary experiment in which deuterium was used to reduce quinone in the cuprous acetate-quinoline system. The rate was 40 % slower than with H2. 

Wilmarth and Barsh (, ) studied in detail the conversion of o-p H2 by solutions of cuprous acetate in quinoline with the purpose of relating the conversion process to the hydrogenation process. Over the tempera-... 

Over the range of temperature and concentration studied, the rate of conversion by cuprous acetate in quinoline is expressible by the equation... 

Wilmarth and Barsh concluded that the most reasonable mechanism involves the assumptions that (1) the cuprous acetate is involved in a rapid monomer-dimer equilibrium (2) the dimer is the active species for conversion and (3) the concentration of the dimer is always small with respect to that of the monomer. 

Wilmarth and Barsh also compared the rate of reduction of cupric ion with that of o-p H2 conversion. They observed a close correspondence between rate of reduction of cupric ion and o-p H2 conversion, catalyzed by cuprous acetate, which was taken as experimental verification that the same activated intermediate is formed in both reactions. 

Effect of anion, solvent, complexing agents Salts of cuprous ion other than acetate have been tried as catalysts. Cuprous salicylaldehyde is effective in activating hydrogen at about the same rate as is cuprous acetate. Cuprous salicylaldimine, salicylaldehyde-urea, salicylaldehyde-... 

Cuprous acetate monomer, complexed with the quinoline solvent, is in rapid equilibrium with dimer. The equilibrium constant is such that dimer formation is incomplete. Activation of the hydrogen occurs by a slow reaction between dimer complex and dissolved molecular hydrogen. Following activation of the hydrogen, the substrate quickly reacts with the hydrogen. Reaction (11) is believed rate controlling. Weller and Mills (5) attempted to establish whether the reaction went through a two-step oxidation and reduction of the Cu1 catalyst however, the conclusion was that the reaction depicted above best fits the observed facts. 

The H2-D2 exchange occurs to an appreciable extent only under conditions when H (or D2) is not being absorbed rapidly in a chemical reaction such as the reduction of quinone or cupric acetate. This is consistent with the idea that the rate-determining step in the reduction is the activation of hydrogen by cuprous acetate (reaction (11)], the activated hydrogen being rapidly removed by reaction with quinone or Cu before it can return to the gas phase. 

Fig. 8. Model of cuprous acetate-quinolme-hydrogcn dimer structural formula II. X = hydrogen atoms attached to copper. (A) Hydrogen atoms close to one another (B) hydrogen atoms separated by rotating copper atoms.

Fig. 10. Reduction of cupric acetate instantaneous rate vs. total cuprous acetate concentration in pyridine, 100° (10).

Discussion The first-order dependence on the total concentration of silver or cuprous acetate for the hydrogenation rate can be interpreted on the basis either that the catalytically active species is a monomer or that it is a dimer, provided, in the latter case, that the dimerization constant is so high that substantially all the catalyst molecules are present as dimers. However, molecular-weight measurements showed that over the concentration range in which kinetic studies were made, dimerization of cuprous or silver acetate was small. This means that in this system it is the monomer of silver or cuprous acetate which is catalytically active, in marked contrast to the cuprous acetate-quinoline system (see above). 

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