Nickel tartrate

The most conventional investigations on the adsorption of both modifier and substrate looked for the effect of pH on the amount of adsorbed tartrate and MAA [200], The combined use of different techniques such as IR, UV, x-ray photoelectron spectroscopy (XPS), electron microscopy (EM), and electron diffraction allowed an in-depth study of adsorbed tartrate in the case of Ni catalysts [101], Using these techniques, the general consensus was that under optimized conditions a corrosive modification of the nickel surface occurs and that the tartrate molecule is chemically bonded to Ni via the two carbonyl groups. There were two suggestions as to the exact nature of the modified catalyst Sachtler [195] proposed adsorbed nickel tartrate as chiral active site, whereas Japanese [101] and Russian [201] groups preferred a direct adsorption of the tartrate on modified sites of the Ni surface. 

Sachtler [195] proposed a dual-site mechanism in which the hydrogen is dissociated on the Ni surface and then migrates to the substrate that is coordinated to the adsorbed dimeric nickel tartrate species. In their model, adsorption of modifier and reactants takes place on different surface atoms in contrast to Klabunovskii s proposal. Adsorbed modifier and reactant are presumed to interact through hydrogen bonding (Scheme 14.5). The unique orientation of adsorbed modifier molecules leads to a sterically favored adsorbed reactant configuration to achieve this bonding. 

Sachtler s group (73) and Yasumori (64) studied the IR spectra of silica-supported Ni modified with amino acid and 2-hydroxy acid and the XPS of TA-MRNi. Both authors deduced almost the same model as proposed by Suetaka. Recently Sachtler s group proposed other models as shown in Fig. 22 from results obtained in enantio-differentiating hydrogenations of MAA with nickel catalysts modified with nickel and copper tartrates (74). The nickel tartrate adsorbs at the vacant coordination site of nickel in this model. 

As a rule, synthetic chemists will consider only those new reactions and catalysts for preparative purposes where the enantioselectivity reaches a certain degree (e.g. >80%) and where both the catalyst and the technology are readily available. For heterogeneous catalysts this is not always the case because the relevant catalyst parameters are often unknown. It is therefore of interest that two types of modified Nickel catalysts are now commercially available a Raney nickel/tartrate/NaBr from Degussa [64] and a nickel powder/tartrate/NaBr from Heraeus [65, 66]. It was also demonstrated that commercial Pt catalysts are suitable for the enantioselective hydrogenation of a-ketoesters [30, 31]. With some catalytic experience, both systems are quite easy to handle and give reproducible results. 

Sachtler proposes a "dual site" mechanism where the hydrogen is dissociated on the Ni surface and then migrates to the substrate which is coordinated to the adsorbed nickel-tartrate complex. In this context it is of interest that the well known Sharpless epoxidation probably takes place on a dimeric tartrate complex of Ti. Sachtler suggests that both the anion and the cation have a function which varies according to the conditions used. It is not clear whether the spillover mechanism is also proposed for the reaction in solution [55]. 

In the hydrogenation of p keto esters (R, R) tartaric acid gives the (R) alcohols and the (S, S) tartaric acid gives the (S) enantiomers. Raney nickel is more effective than supported nickel catalysts. It appears that the active catalyst is nickel tartrate which is adsorbed on the catalyst surface and that the sodium bromide is adsorbed on the non-chiral active sites, thus, keeping them from promoting the non-selective hydrogenations. 2,84 -pj is procedure has been used to prepare the chiral intermediate in the synthesis of the Pine Sawfly sex pheromone. ... 

The development of the nickel tartrate system and its successful preparative applications for the hydrogenation of P-functionalized and methyl ketones have been reviewed by Tai and Harada [4]. The preferred catalyst is freshly prepared... 

The temperature, concentration, and pH of the modifying solution have strong influences on the effectiveness of the resulting modified catalyst. Increasing the time of modification and the concentration of modifier at optimal temperature and pH enhances enantioselectivity of the catalyst up to an optimal value due to corrosion of the nickel surface with formation of nickel-tartrate chelates coming into the solution. Therefore, for the best enantioselective effect the amounts of TA on the surface of Ni must reach an optimal value. 

Difference spectrum between unmodified Ni and TA modified Ni, at pH 5 (1), nickel tartrate (2), sodium tartrate (3) and tartaric acid (4) (according to Inoue et al. ). 

Hoek, A., and Sachtler, W.H.M. (1979) Enantioselectivity of nickel catalysts modified with tartraic acid or nickel-tartrate complexes, J. Catal. 58, 276 - 286. 

Studies have been reported of a large number of model reactions, and these have been systematically classified and analyzed by Blaser and Muller (1991). Industrial applications are relatively few, but with the availability of commercial catalysts, more applications are expected. Two such catalyst systems are reported to be available Raney nickel/tartrate/NaBr system from Degussa (Blaser and Muller, 1991), and nickel powder/tartrate/NaBr (Brunner et al., 1980). 

Archer, owing to very unfortunate coincidences, had mistaken acid potassium tartrate for the acetylamino acid. Goldfarb et al. prepared authentic 5-acetylamino-2-thiophenecarboxylic acid, mp 230 232°C (methyl ester, mp 171-171.5°C ethyl ester, mp 161°C), through reduction of 5-nitro-2-thiophenecarboxylic acid with Raney nickel in acetic anhydride and proved the structure by Raney nickel desulfurization to 8-aminovaleric acid. They also confirmed that the acid mp 272-273°C (methyl ester, mp 135-136°C ethyl ester, mp 116-117°C) is 4-acetylamino-2-thiophenecar boxy lie acid as originally stated by Steinkopf and Miiller. The statement of Tirouflet and Chane that the acid obtained upon reduction and acetylation of 5-nitro-2-thiophenecarboxylic acid melts at 272°C must result from some mistake as they give the correct melting point for the methyl ester. 

At normal current densities, about 96-98% of the cathodic current in a Watts solution is consumed in depositing nickel the remainder gives rise to discharge of hydrogen ions. The boric acid in the solution buffers the loss of acidity arising in this way, and improves the appearance and quality of the deposit. Although phosphides, acetates, citrates and tartrates have been used, boric acid is the usual buffer for nickel solutions. 

Dimethylglyoxime. The complexes with nickel and with palladium are soluble in chloroform. The optimum pH range for extraction of the nickel complex is 4-12 in the presence of tartrate and 7-12 in the presence of citrate (solubility 35-50 fig Ni mL 1 at room temperature) if the amount of cobalt exceeds 5 mg some cobalt may be extracted from alkaline solution. Palladium(II) may be extracted out of ca lM-sulphuric acid solution. 

D. Benzoin-a-oxime (cupron) (VII). This compound yields a green predpitate, CuC14Hu02N, with copper in dilute ammoniacal solution, which may be dried to constant weight at 100 °C. Ions which are predpitated by aqueous ammonia are kept in solution by the addition of tartrate the reagent is then spedfic for copper. Copper may thus be separated from cadmium, lead, nickel, cobalt, zinc, aluminium, and small amounts of iron. 

H. 8-Hydroxyquinaldine (XI). The reactions of 8-hydroxyquinaldine are, in general, similar to 8-hydroxyquinoline described under (C) above, but unlike the latter it does not produce an insoluble complex with aluminium. In acetic acid-acetate solution precipitates are formed with bismuth, cadmium, copper, iron(II) and iron(III), chromium, manganese, nickel, silver, zinc, titanium (Ti02 + ), molybdate, tungstate, and vanadate. The same ions are precipitated in ammoniacal solution with the exception of molybdate, tungstate, and vanadate, but with the addition of lead, calcium, strontium, and magnesium aluminium is not precipitated, but tartrate must be added to prevent the separation of aluminium hydroxide. 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

Fluoride, in the absence of interfering anions (including phosphate, molybdate, citrate, and tartrate) and interfering cations (including cadmium, tin, strontium, iron, and particularly zirconium, cobalt, lead, nickel, zinc, copper, and aluminium), may be determined with thorium chloranilate in aqueous 2-methoxyethanol at pH 4.5 the absorbance is measured at 540 nm or, for small concentrations 0-2.0 mg L 1 at 330 nm. 

Nickel electroless plating on a less noble metal is common.17 For example, the source of nickel can be nickel sulfate. The reducer can be an organic substance, such as formaldehyde. A chelating agent (tartrate or equivalent) is generally required. The nickel salt is ionized in water ... 

Brydon and Roberts- added hemolyzed blood to unhemolyzed plasma, analyzed the specimens for a variety of constituents and then compared the values with those in the unhemolyzed plasma (B28). The following procedures were considered unaffected by hemolysis (up to 1 g/100 ml hemoglobin) urea (diacetyl monoxime) carbon dioxide content (phe-nolphthalein complex) iron binding capacity cholesterol (ferric chloride) creatinine (alkaline picrate) uric acid (phosphotungstate reduction) alkaline phosphatase (4-nitrophenyl phosphate) 5 -nucleotidase (adenosine monophosphate-nickel) and tartrate-labile acid phosphatase (phenyl phosphate). In Table 2 are shown those assays where increases were observed. The hemolysis used in these studies was equivalent to that produced by the breakdown of about 15 X 10 erythrocytes. In the bromocresol green albumin method it has been reported that for every 100 mg of hemoglobin/100 ml serum, the apparent albumin concentration is increased by 100 mg/100 ml (D12). Hemolysis releases some amino acids, such as histidine, into the plasma (Alb). 

A secondary, more subtle, effect that can be utilized in the achievement of selectivity in cation exchange is the selective complexation of certain metal ions with anionic ligands. This reduces the net positive charge of those ions and decreases their extraction by the resin. In certain instances, where stable anionic complexes form, extraction is suppressed completely. This technique has been utilized in the separation of cobalt and nickel from iron, by masking of the iron as a neutral or anionic complex with citrate350 or tartrate.351 Similarly, a high chloride concentration would complex the cobalt and the iron as anionic complexes and allow nickel, which does not form anionic chloro complexes, to be extracted selectively by a cation-exchange resin. 

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