Mixed oxalates

The alkaloid may be separated from accompanying hyoscyamine by extracting most of it with ether and then crystallising the mixed oxalates from water, that of norhyoscyamine separating first. It crystallises in colourless prisms, m.p. 140°, [a]j, — 23-0° (50 per cent. EtOH), is soluble in alcohol or chloroform, less so in ether or acetone, and sparingly in water... 

Decompositions of oxalates containing the strongly electropositive metals yield an oxide product but the more noble elements yield the metal. Discussion of the mechanisms of these reactions and, in particular, whether metal formation necessarily involves the intermediate production of oxide which is subsequently reduced by CO has been extended to consideration of the kinetics of pyrolysis of the mixed oxalates [32]. 

Mixed oxalates and oxalato complexes (Table 31) also require further investigation. The sulfito and sulfato oxalates have been mentioned earlier (p. 1152) and an equally large number of carbonatooxalato spedes have been recorded,103,104 some of which may well be mixtures. In addition to the compounds listed in Table 31, products of the rather unlikely compositions K7[U(0H)(C204)2(C03)3]-6H20 and MU OHMQOaMCXfcJgHOHjO have been reported.103... 

Table 31 Actinide(IV) Mixed Oxalates and Oxalato Complexes...

If heated with alkalies, a mixed oxalate and acetate results, with evolution of water, thus—... 

Oxides. Industrially, the most important of this group is Y203 Eu3 +. The preparation is generally carried out by precipitating mixed oxalates from purified solutions of yttrium and europium nitrates. Firing the dried oxalates at ca. 600 °C is followed by crystallization firing at 1400-1500 °C for several hours [5.382],... 

Loss of a carbon atom from the precursor need not always result. Barton and Crich have introduced a related procedure based on the chemistry of mixed oxalates, an example of which is provided in Scheme 49.159 Double decarboxylation is involved in the decomposition of oxalate precursors, such as (39). Unfortunately, there are indications that this method may to be limited to tertiary alcohols one secondary alcohol derived mixed oxylate did not fragment completely to the alkyl radical. 

Purphal, W.K., T.D. Filer, and G.J. McNabb. 1984. Electrodeposition of actinides in a mixed oxalate-chloride electrolyte. Anal. Chem. 56 113-116. 

The product consists of very small crystals that need little grinding. Coprecipitation of mixed oxalates can also give intimate mixing. 

In routine qualitative analysis, it is probably best to boil the mixed oxalates (after washing with 2 per cent oxalic acid solution) with M potassium hydroxide solution, thereby converting them into the hydroxides. The precipitate is separated by filtration, washed with hot water, dissolved in the minimum volume of dilute hydrochloric acid and the solution divided into two parts ... 

Infrared and UV/vis data have been used by several authors to identify the C=C, C=0, and M—O stretches in the complexes synthesized 15, 18-21, 37, 38, 41, 44, 50, 54, 56, 58, 59, 64-66, 69, 74, 78, 80, 82, 103). Except in the initial research on first-row transition metal complexes of squaric acid, where these data were used in proposing structures, IR and UV/vis analysis have been used as supporting evidence for the particular coordination mode of the ligand 19,21,22, 45, 52, 59, 65). Infrared spectroscopy has also been utilized in the study of mixed oxalate/squarate complexes 118), although not to the same extent as in complexes of the oxalate ion. For example, Scott et al. studied the IR properties of Co(III) oxalate complexes with the hgand in a variety of chelating/bridging situations 119). 

The double inverse microemulsion method was also used to synthesize per-ovskite-type mixed metal oxides [ 155]. One microemulsion solution contained nitrate salts of either Ba(N03)2/Pb(N03)2, La(N03)3/Cu(N03)2 or La(N03)3/ Ni(N03)2, and the other microemulsion contained ammonium oxalate or oxalic acid as the precipitant. These metal oxalate particles of about 20 nm were readily calcined into single phase perovskite-type BaPb03, La2Cu04 and LaNi03. The calcinations required for the microemulsion-derived mixed oxalates were 100-250 °C below the temperatures used for the metal oxalates prepared by a conventional aqueous solution precipitation method. 

The precipitation of the mixed oxalates is carried out conveniently in a 1-1. Pyrex three-necked Wolff bottle, with standard-taper connections. One neck is fitted with a reflux condenser, another with a gas inlet tube, and the third with a separatory funnel. A Teflon-covered magnetic stirring bar rests in the bottle, which is set on an electric hot plate equipped with a magnetic stirring device. The iron powder (0.0800 mol, assayed for iron content) and magnesium acetate (0.0400 mol) are weighed into the bottle. 

The mixed oxalates show a gradual weight loss between 100-230 °C and two exotherms at 200 °C and 350 °C associated with the loss of organics. A further exotherm at 800 °C... 

Table 26 Actinide(IV) mixed oxalate and oxalato complexes.

The preparation technique of the methanol catalysts plays an important role on their catalytic behavior. For each catalytic composition a specific preparation technique is able to optimize the catalytic properties. The precipitation by Na2C03 seems to be the most suitable way for the preparation of copper zinc catalysts and also of promoted systems. But the use of precipitation of mixed oxalates allows the best methanol yield on copper-pyrochlore catalysts. 

The thermal decompositions of nickel(II)-cobalt(II) oxalate solid solutions were studied using TG and TM [103], A series of the mixed binary Ni(II)-Co(II) oxalate samples was prepared at 25% (atom) intervals across the system. Physical mixtures were also prepared by mixing the pure end members. The DTG and DTM curves showed that the decomposition proceeds to completion in two overlapping stages. The kinetics of the individual steps were not studied. From the DTG curves, the authors stated that the physical mixtures behaved as individual oxalates, while the coprecipitate decomposed as a single entity. The TM curves showed that the products formed from the physical mixture and the coprecipitate were distinctly different. The magnetic behaviour of the product from the coprecipitate was consistent with the behaviour predicted for a Ni-Co alloy, but the products from the physically mixed oxalate do not show the transition temperature predicted for an alloy. The kinetics of decomposition of iron-nickel mixed oxalates have been studied by Doremieux et al. [104]. 

During the decomposition of Ni-Co mixed oxalates the production of nickel metal accelerates reaction, because the nickel constituent reacts about 60 K lower than cobalt oxalate (Sections 16.4.2. and 16.4.4. above). The significance of the relative yields of metal and oxide in the decompositions of the mixed oxalates Co-Ni Co-Mg and Ni-Mg has been discussed [99],... 

Cu/Zn/X oxide catalysts were prepared by an oxalate-ethanol coprecipitation method. Ethanol solutions of nitrate of Cu, Zn and one additive were mixed (Cu/Zn/X molar ratio was 65/35/5), and then an ethanol solution of oxalic acid was mixed to precipitate the mixed oxalic salts. Only vanadium acetyl acetone was solved in a mixed solvent (acetone methanol =1 1), and it was used as V source. Ethanol was removed by vaporization followed by calcination in air at 623 K for 4 hours. 

Mixed oxalate-salicylate complexes of Cd of the stoicheiometry [Cd(oxXsal)] and [Cd(ox)(sal)2] have been detected stability constants for these, [Cd-(ox) ] " (n = 1—3), and [Cd(sal) ] "" (n = 1 or 2) have also been determined. ° In oxalate solution, Hg forms the mixed complexes [Hg(C204)X ]" ( = 1, X = SCN = 1 or 2 X = OAc, NO2, Br, or tartrate). The complexation of Cd by tartrate has also been investigated. Stability constants for mixed complex formation between piperidine and a variety of zinc and cadmium mono- and dicar boxylic acids have been reported. " ... 

A representative mixed oxalate-second linker compound is ACOXEV [Tb4 ( 204)2(0511604)4(1120)2] (Fig. 33) (140). The structure may be thought of as containing chains of two distinct Tb20i5 dimers that alternatively share edges and faces to propagate along [010]. These chains are then tethered through... 

Thus, as shown by the example in Scheme 42, sequential treatment of the trime-thylsilyl ethers of a variety of tertiary alcohols with oxalyl chloride and the parent thionohydroxamic acid furnishes mixed oxalate esters which undergo reductive deoxygenation on subsequent reaction with a tertiary thiol in refluxing benzene [46]. The selectivity of this method for tertiary alcohols arises as a consequence of the relativity slow rates of decarboxylation of primary and secondary alkoxycarbonyl radicals. 

As anticipated, by analogy with the chemistry of Barton esters, the same mixed oxalate esters can be used to prepare tertiary alkyl chlorides, simply by refluxing in carbon tetrachloride [47], and also for the creation of quaternary carbon centers through selection of either a Michael acceptor [46] or 2-(carboethoxy) allyl tert-butyl sulfide [46] as the radicophile. 

The phosphonates (42) and (43) have been prepared by reaction of the respective 3 -ketonucleosides with the lithium salt of diethylphosphite, followed by a variation of the Barton deoxygenation procedure involving the radical catalysed deoxygenation of an intermediate mixed oxalate ester, followed by deprotection. The reaction with diethylphosphite is stereoselective, whilst the radical catalysed deoxygenation affords a p/a (42/43) ratio of about 2 1. 

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