chromic - yes, toss everything into the caustic activation, where most of the Al is consumed. But that will produce a useless catalyst. Check this out:
3.3. DETAILS ON INDIVIDUAL URUSHIBARA CATALYSTS
(a) U-Ni-A and U-Ni-B
Of all the Urushibara catalysts, U-Ni-A and U-Ni-B are the most
commonly used and have the widest applications. Either catalyst will serve for the same catalytic reduction, as there is no substantial difference in activity between the two catalysts. It sometimes happens, however, that one of them is to be preferred according to the kind and purity of the substance to be reduced, or according to the reaction conditions. Both U-Ni-A and U-Ni-B are produced from the same precipitated nickel that is deposited by the reaction between nickel salt solution and zinc dust. The precipitated nickel digested with acetic acid (or propionic acid) gives rise to U-Ni-A, and that digested with sodium hydroxide gives rise to U-Ni-B. In the latter case, the activity of the catalyst is somewhat reduced when the precipitated nickel is treated with an alkali solution of too high a concentration at too high a temperature, or when digestion is continued for a long time until the evolution of hydrogen subsides. Highly active U-Ni-B is obtained when the precipitated nickel is warmed with an approximately 10% solution of caustic alkali for 15 minutes. It contains considerable amounts of undissolved zinc and zinc oxide. In contrast, a good result is obtained in acetic acid treatment only when digestion is continued to such an extent that the zinc and zinc compounds almost completely dissolve away, and a small portion of nickel itself is dissolved to make the solution greenish. U-Ni-A consists of 70-80% nickel, together with a small amount of zinc folded into the former, and little, if any, zinc compounds are contained in it. The same amount of precipitated nickel prepared from nickel chloride and containing 1 g of nickel metal gives rise to Urushibara catalysts of different quantities; the gross weight of U-Ni-A is 1.1 - 1.4 g (nickel content ca. 0.85 g), whereas that of U-Ni-B amounts to as much as 5-10 g (nickel content nearly 1 g), the latter being far more bulky. A neutral catalyst is readily obtained when U-Ni-A is washed a few times with water after preparation. In contrast, alkali combines with U-Ni-B so firmly that a trace amount of alkali can not be removed without much difficulty. When alkali treated precipitated nickel, which is washed twice with water and twice with ethanol, is used in catalytic reduction, the solution in which the reduction takes place be- comes weakly alkaline (pH 9-10), as indicated by the pink color of phenolphthalein. Alkali-treated precipitated nickel, which is washed 5-6 times either with water or with ethanol, makes the solution only faintly alkaline, almost neutral to phenolphthalein (pH 8-9). Trace amounts of alkali are ultimately removed only when the catalyst is washed with water ten times or more, and subsequently many times with ethanol (or other solvent to be used in the reduction process to replace the wash-water.
U-Ni-B is effectively employed in catalytic reductions for which the presence of alkali is favorable; whereas U-Ni-A is appropriate for those reductions where the presence of alkali interferes. For example, a trace amount of alkali favors the reduction of ketones, aldehydes, nitriles, and oximes, for which the use of U-Ni-B is desirable. On the other hand, the reduction of aromatic nitro compounds is hindered by the presence of alkali and U-Ni-A can conveniently be used in this case.
It is nevertheless true that U-Ni-B can be used in neutral reductions, if it is washed thoroughly with water to completely remove alkali, and U-Ni-A can be used in the same reductions that are effectively conducted in the presence of U-Ni-B, provided a small amount of alkali is added. This is compatible with the fact that the activities of these two catalysts do not differ substantially from each other.
The above difference in the natures of U-Ni-A and U-Ni-B is successfully applied to selective reduction. For instance, m-nitroacetophenone gives m-aminoacetophenone in good yield in the presence of U-Ni-A or thoroughly washed U-Ni-B.
U-Ni-A is far less bulky than U-Ni-B, and has the apparent advantage that it can be readily dispersed into solution when used in liquid phase reduction. This matters little in a reduction under atmospheric pressure, as the reaction vessel can be shaken as vigorously as necessary to obtain thorough dispersion. In a high-pressure reduction, especially in a large scale reduction in a high capacity autoclave, however, the efficiency of reduction is mainly governed by the dispersability of fine catalyst particles into the solution. In such cases, U-Ni-B has a disadvantage, and in liquid-phase reduction at high pressure the use of U-Ni-A is always preferable. Addition of an appropriate amount of alkali may, however, be required in certain cases.
(b) U-Ni-BA
U-Ni-BA is prepared by the alkali treatment of the precipitated nickel which is obtained from nickel chloride solution and aluminum, instead of zinc dust. As the preparation of the precipitated nickel in this case requires much time, it is advisable to prepare and store in advance a large quantity of precipitated nickel, from which the required amount is occasionally removed and treated with alkali.
The U-Ni-BA catalyst consists primarily of nickel metal, along with a small amount of contaminant, so that the bulk of the catalyst is greatly reduced, and is even smaller than that of U-Ni-A for the same nickel content.
The main characteristic of U-Ni-BA is its ability to hydrogenate aromatic rings of benzene and naphthalene and their derivatives. U-Ni-A and U-Ni-B can hydrogenate phenols to cyclohexanols, but are inactive to other aromatic compounds. On the contrary, U-Ni-BA is effective for almost every aromatic compound, including phenols.
U-Ni-BA, like U-Ni-A and U-Ni-B, can be used for the hydrogenation of olefins, or the reduction of carbonyl and nitro compounds, but it gives somewhat poorer results. We can see this in the high-pressure reduction of acetophenone. For general purposes other than for benzene ring hydrogenation, the use of U-Ni-A or U-Ni-B, with their high activity, stability, and availability is recommended.
(c) U-Ni-AA
U-Ni-AA is prepared by warming the precipitated nickel which is deposited from nickel chloride solution by aluminum grains, with acetic acid saturated with sodium chloride. It consists of aluminum grains coated by nickel, as the nickel metal deposited on aluminum grains does not separate from the latter, which remain undissolved after acetic acid treatment owing to the mild reaction between aluminum metal and acetic acid. As the aluminum grains which support the nickel metal act as a carrier, U-Ni-AA can most conveniently be used for a vapor phase reduction.
It is to be noted that the use of U-Ni-AA is not confined to vapor phase reduction; it is also suitable for liquid-phase hydrogenation at room temperature and atmospheric pressure. This can be seen from the reduction of nitrobenzene in ethanol which, in the presence of U-Ni-AA, gives aniline in a 70% yield.
(d) U-Ni-C Catalysts
To promote the activity of U-Ni-A or U-Ni-B, it is desirable to reduce the particle size of the catalyst so as to facilitate its dispersion into solution. U-Ni-C catalysts comply with this requirement.
The particle size of Urushibara catalysts is seemingly determined by that of the precipitated nickel. To reduce the particle size of the precipitated nickel, it is necessary to retard the velocity of the ion exchange reaction; that is, to retard the speed of deposition of nickel. The optimum conditions for the slow and uniform deposition of nickel on zinc dust have been established. The precipitated nickel which is prepared by the reaction of zinc dust with nickel chloride solution of an appropriate concentration, either at room temperature or with cooling by running water or ice, is treated again in the cold with acetic acid or sodium hydroxide solution. In this way we obtain U-Ni-CA and U-Ni-CB. These catalysts, compared with ordinary Urushibara nickel catalysts, have a smaller particle size and exhibit higher activity, especially for liquid-phase reduction in an autoclave. These catalysts, however, require much time for preparation, and therefore lack the distinguishing characteristic of the general Urushibara nickel catalysts namely, speed in preparation.
(e) U-Ni(s) Catalysts
Another modified preparation of Urushibara nickel catalysts consists of the addition of nickel chloride crystals, instead of a nickel chloride solution, to zinc dust mixed with a small amount of water. Owing to the heat of reaction, local reaction is promoted and precipitated nickel is formed in a few minutes. It is digested with acid or alkali in the usual way, giving rise to two kinds of catalyst. They are U-Ni-A(s) and U-Ni-B(s).
The extreme ease with which the precipitated nickel is produced allows the U-Ni(s) catalysts to be prepared very quickly. This ease itself might mislead one to presume that the catalysts would have impaired activities. Nevertheless, they are sufficiently active for use in almost every reduction, and their activities are very close to, although not as high as, those of ordinary Urushibara nickel catalysts. For practical purposes, they may be widely used because of their simple preparation and high activities.
(f) U-Ni-A(HCl)
The use of hydrochloric acid in the digestion of the precipitated nickel greatly reduces catalytic activity. Therefore, U-Ni-A(HCl), which is obtained by treating the precipitated nickel with hydrochloric acid, is inadequate for ordinary purposes, except in certain instances where high activity is not desirable. Though the catalyst gives fairly good results in the partial hydrogenation of acetylenic compounds (see Section 6. 5. 4), it is practically of little use because the Urushibara iron catalyst is most profitable for such partial hydrogenations.
U-Ni-A(HCl) and U-Ni-A(s) (HCl) may be used for the reduction of benzoin under high pressure, but their activities can not compare with those of other U-Ni-A catalysts. The cause of the impaired activity is apparently that a considerable amount of nickel is dissolved when the precipitated nickel is treated with hydrochloric acid, so that the nickel content of the catalyst is diminished, or that some chlorine compound is adsorbed on the surface of the catalyst and behaves as a kind of poison.
(g) U-Ni-NH3
Precipitated nickel also gives rise to an Urushibara nickel catalyst on treatment with aqueous ammonia instead of sodium hydroxide. This is U-Ni-NH3. A considerable amount of ammonia remains even after washing with water. Ammonia is adsorbed on the catalyst far more strongly than is sodium hydroxide on U-Ni-B.
Catalytic reduction of nitriles or oximes yields primary amines together with secondary amines. The use of ammonia especially favors the formation of the former. Therefore, the yields of primary amines in the catalytic reduction of these compounds are higher in the presence of U-Ni-NH3 than in the presence of U-Ni-B.
(h) U-Co Catalysts
Urushibara cobalt catalysts are modifications of the Urushibara nickel catalysts, just as Raney cobalt is a congener of Raney nickel. Their activities compare with that of Raney cobalt and have properties very similar to the corresponding useful nickel catalysts. However, they are less useful for general purposes, as their activities are somewhat less and they are more expensive. In catalytic reduction of nitriles or oximes Raney cobalt surpasses Raney nickel in depressing the formation of accompanying undesirable secondary amines. Likewise, the U-Co-B catalyst was used for the same purpose and proved to be more effective than U-Ni-B. In general, the cobalt catalysts are known to be less active than the nickel catalysts for hydrogenation of the ethylenic bond, U-Co-B can effect the selective reduction of unsaturated nitriles to unsaturated amines, leaving the ethylenic linkage intact.
It should be remembered that U-Co-B is entirely inactive when used in ethanol saturated with ammonia. Therefore, ammonia should be precluded from U-Co-B, even in the reduction of nitriles for which the presence of ammonia is usually preferable.
(i) U-Cu Catalysts
In general, copper catalysts have an outstanding disadvantage in hydrogenation. This is the case with the Urushibara copper catalyst, which, like the Raney copper catalyst, is far less active than the corresponding nickel or cobalt catalysts. The Urushibara copper catalyst is quite unfit for catalytic reduction under atmospheric pressure, but can be used in reduction under higher pressure, provided the reaction is carried out at a temperature higher than would be appropriate for the nickel catalyst.
( j) U-Fe Catalysts
Crystals of iron(II) or iron(III) chloride are added to zinc dust mixed with a small amount of water, affording precipitated iron which, on treatment with acetic acid, furnishes U-Fe(II) or U-Fe(III), respectively. These Urushibara iron catalysts, like the Raney iron catalyst, have a distinct specificity in favoring the partial hydrogenation of acetylenic compounds to ethylenic compounds. Either U-Fe(II) or U-Fe(III) is suitable for this purpose. It must be remembered, however, that U-Fe-BA, which is prepared from iron(III) chloride solution and aluminum grains, is completely inactive in the hydrogenation of acetylenic compounds.
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