Copper borohydride

A very useful variant of the hydrazone reduction is the deoxygenation of aldehydes and ketones via the hydride reduction of tosylhydrazones (Caglioti reaction) The method is mild, convenient and widely applicable. While sodium borohydride was used in the earlier procedures, considerable improvements have been achieved through the uses of sodium cyanoborohydride, catecholborane, diborane, his-benzoyloxy borane and copper borohydride as reducing agents and HMPA, DMF, sulpholane, etc. as solvents. Use of the sterically crowded 2,4,6-triisopropyl tosylhydrazone derivative has greatly facilitated the reduction in some cases (equations 61-64). ... 

Common catalyst compositions contain oxides or ionic forms of platinum, nickel, copper, cobalt, or palladium which are often present as mixtures of more than one metal. Metal hydrides, such as lithium aluminum hydride [16853-85-3] or sodium borohydride [16940-66-2] can also be used to reduce aldehydes. Depending on additional functionahties that may be present in the aldehyde molecule, specialized reducing reagents such as trimethoxyalurninum hydride or alkylboranes (less reactive and more selective) may be used. Other less industrially significant reduction procedures such as the Clemmensen reduction or the modified Wolff-Kishner reduction exist as well. 

Sodium borohydride or dimethylarnine borane have found limited use as reduciag agents because of expense. In addition, bath stabiHty, plating rate, and deposit properties are inferior to those of formaldehyde-reduced baths. The deposit is a copper—boron alloy. Copper—hypophosphite baths have been iavestigated, but these are poorly autocatalytic, and deposit only very thin coatings. 

Braman et al. [34] used sodium borohydride to reduce arsenic and antimony in their trivalent and pentavalent states to the corresponding hydrides. Total arsenic and antimony are then measured by their spectral emissions, respectively, at 228.8 nm and 242.5 nm. Limits of detection are 0.5 ng for antimony and 1 ng for arsenic, copper, and silver. Oxidants interfere in this procedure. 

Yamamoto et al. [33] applied this technique to the determination of arsenic (III), arsenic (V), antimony (III), and antimony (V) in Hiroshima Bay Water. These workers used a HGA-A spectrometric method with hydrogen-nitrogen flame using sodium borohydride solution as a reductant. For the determination of arsenic (III) and antimony (III) most of the elements, other than silver (I), copper (II), tin (II), selenium (IV), and tellurium (IV), do not interfere in at least 30 000-fold excess with respect to arsenic (III) or antimony (III). This method was applied to the determination of these species in sea water and it was found that a sample size of only 100 ml is enough to determine them with a precision of 1.5-2.5%. Analytical results for surface sea water of Hiroshima Bay were 0.72 xg/l, 0.27 xg/l, and 0.22 xg/l, for arsenic (total), arsenic (III), and antimony (total), respectively, but antimony (III) was not detected. The effect of acidification on storage was also examined. 

In the method for [17] inorganic arsenic the sample is treated with sodium borohydride added at a controlled rate (Fig. 10.1). The arsine evolved is absorbed in a solution of iodine and the resultant arsenate ion is determined photometrically by a molybdenum blue method. For seawater the range, standard deviation, and detection limit are 1—4 xg/l, 1.4%, and 0.14 pg/1, respectively for potable waters they are 0-800 pg/1, about 1% (at 2 pg/1 level), and 0.5 pg/1, respectively. Silver and copper cause serious interference at concentrations of a few tens of mg/1 however, these elements can be removed either by preliminary extraction with a solution of dithizone in chloroform or by ion exchange. 

Lippard, S.J., Ucko, D.A. 1968. Transition metal borohydride complexes. II. Th reaction of copper(I) compounds with boron hydride anions. Inorg Chem 7 1051-1058. 

Reduction of cuprous chloride with sodium borohydride gives copper hydride which is a highly selective agent for the preparation of aldehydes from acyl chlorides [775]. 

Carbazoles, too, can be reduced partially to dihydrocarbazoles by sodium in liquid ammonia [460], or to tetrahydrocarbazoles by sodium in liquid ammonia and ethanol [460] or by sodium borohydride [457]. Carbazole was converted by catalytic hydrogenation over Raney nickel or copper chromite to 1,2,3,4-tetrahydrocarbazole, 1,2,3,4,10,11-hexahydrocarbazole, and do-decahydrocarbazole in good yields [430]. 

Alkyl chlorides are with a few exceptions not reduced by mild catalytic hydrogenation over platinum [502], rhodium [40] and nickel [63], even in the presence of alkali. Metal hydrides and complex hydrides are used more successfully various lithium aluminum hydrides [506, 507], lithium copper hydrides [501], sodium borohydride [504, 505], and especially different tin hydrides (stannanes) [503,508,509,510] are the reagents of choice for selective replacement of halogen in the presence of other functional groups. In some cases the reduction is stereoselective. Both cis- and rrunj-9-chlorodecaIin, on reductions with triphenylstannane or dibutylstannane, gave predominantly trani-decalin [509]. 

Reduction of unsaturated ketones to saturated alcohols is achieved by catalytic hydrogenation using a nickel catalyst [49], a copper chromite catalyst [50, 887] or by treatment with a nickel-aluminum alloy in sodium hydroxide [555]. If the double bond is conjugated, complete reduction can also be obtained with some hydrides. 2-Cyclopentenone was reduced to cyclopentanol in 83.5% yield with lithium aluminum hydride in tetrahydrofuran [764], with lithium tris tert-butoxy)aluminium hydride (88.8% yield) [764], and with sodium borohydride in ethanol at 78° (yield 100%) [764], Most frequently, however, only the carbonyl is reduced, especially with application of the inverse technique (p. 21). 

Refluxing of 9-fluorenone-l-carboxylic acid with zinc dust and copper sulfate in aqueous potassium hydroxide for 2.5 hours afforded 9-fluorenol-1-carboxylic acid in 94% yield [1004]. Reduction with sodium borohydride in aqueous methanol at 0-25° converted 5-ketopiperidine-2-carboxylic acid to /ra j-5-hydroxypiperidine-2-carboxylic acid in 54-61% yield [1005], On the other hand, reduction of V-benzyloxycarbonyl-5-ketopiperidine-2-carboxylic acid gave 89% yield of V-benzyloxycarbonyl-cis-5-hydroxypiperidine-2-car-boxylic acid under the same conditions [1005],... 

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]. 

Since sodium borohydride usually does not reduce the nitrile function it may be used for selective reductions of conjugated double bonds in oc,/l-un-saturated nitriles in fair to good yields [7069,1070]. In addition some special reagents were found effective for reducing carbon-carbon double bonds preferentially copper hydride prepared from cuprous bromide and sodium bis(2-methoxyethoxy)aluminum hydride [7766], magnesium in methanol [7767], zinc and zinc chloride in ethanol or isopropyl alcohol [7765], and triethylam-monium formate in dimethyl formamide [317]. Lithium aluminum hydride reduced 1-cyanocyclohexene at —15° to cyclohexanecarboxaldehyde and under normal conditions to aminomethylcyclohexane, both in 60% yields [777]. 

Considerable inter-element interference effects have been reported on the actual hydride-forming step. Elements easily reduced by sodium borohydride (e.g. silver, gold, copper, nickel) give rise to the greatest suppressions. These interfering ions may be removed by the addition of masking agents that complex with them. 

Peroxynitrite reacts with the active site of superoxide dismutase (SOD) to form a nitronium-like species (Fig. 37), analogous to the Fe EDTA reactions described earlier. However, copper in the active site of superoxide dismutase was necessary for the formation of the adduct. Removing copper from the active site by reduction with borohydride and dialysis against 50 mM KCN resulted in no adduct being formed, while restoration of copper to the active site gave back full enzyme activity. To account for the essential role of copper in the active site and the subsequent formation of 3-nitrotyrosine located 18-21 A distal from the active site, we proposed that peroxynitrite is attracted by the same electrostatic force field that draws superoxide into the active site (Beckman et al., 1992 Ischiropoulos et al., 1992b). Peroxynitrite appears to bind to copper in the active site to form a transient cuprous adduct as shown. 

---