Malonic acid, chromium complexes

Li B, Lin A, Gan F (2006) Preparation and characterization of Cr-P coatings by electrodeposition from trivalent chromium electrolytes using malonic acid as complex. Surf Coat Technol 201 2578-2586. doi 10.1016/j.surfcoat.2006.05.001... 

Malonic acid CH2(C02H)2 (H2mal) (209) has a coordination chemistry with chrommm(III) closely resembling that of oxalate. Malonic acid is a slightly weaker acid than oxalic acid and slightly more labile complexes are formed. The tris complex is the most extensively studied, prepared by the reduction of chromate solutions or the reaction of chromium(III) hydroxide with malonate.917,918 919 The cis and trans diaqua complexes may be prepared by the reduction of chromate with malonate the isomers are separated by fractional crystallization. The electronic spectrum of the tris complex is similar to that of the tris oxalate and a detailed analysis of these spectra has appeared.889... 

The malonato complexes of chromium(III) are analogous to the oxalate complexes of chromium(III). Since malonic acid is a weaker acid than oxalic acid, the malonato complexes are expected to be more labile than the oxalato complexes. The dicarboxylate complexes of chromium(III) form a group of anionic complexes which are suitable for the study of octahedral complex reactivity. 

Bis-bipyridine-silver complexes were found to catalyze the B-Z (with malonic acid as substrate) reaction by Kuhnert and Pehl (1981-1). The reaction was shown to proceed in a heterogeneous medium due to the insolubility of the silver complexes. When organic compounds such as citric acid and 2,4-pentanedione, ethylacetoacetate and racemic malic acid were used as substrates, the oscillatory behavior was not observed. Kuhnert and Pehl (1981-2) also observed that the bipyridine complexes of chromium and osmium catalyze the B-Z reaction. 

IIIC) Kuhnert, L., Pehl, K. W. Bipyridine Complexes of Osmium and Chromium Catalyzing the 1981-2 Oscillating Reaction between Bromate and Malonic Acid. Chem. Phys. Lett. 84 (1) 159-162. 

It has been known for some time that tolerance towards high levels of both essential and toxic metals in a local soil environment is exhibited by species and clones of plants that colonize such sites. Tolerance is generally achieved by a combination of exclusion and poor uptake and translocation. Some species can accumulate large quantities of metals in their leaves and shoots at potentially toxic levels, but without any harmful effects. These metal-tolerant species have been used in attempts to reclaim and recolonize metal-contaminated wastelands. More recently such species have attracted the attention of inorganic chemists. There is abundant evidence that the high metal levels are associated with carboxylic acids, particularly with nickel-tolerant species such as Allysum bertolonii. The main carboxylic acids implicated are citric, mahc and malonic acids (see refs. 30 and 31 and literature cited therein). Complexation of zinc by malic and oxalic acids has been reported in the zinc-tolerant Agrostis tenuis and oxalic acid complexation of chromium in the chromium-accumulator species Leptospermum scoparium ... 

Several reports concern the formation of organic ligand complexes of iron(iii). The variation of rate with ligand concentration in the reaction with mandelic acid > is interpreted as a pre-equilibrium ion-pair formation followed by dissociative complex formation within the ion-pair, rather than as simple 5 n2 formation. This interpretation is similar to that proffered for formation of malonate and oxalate complexes of chromium(iii) (see above). Rates of reaction of iron(iii) with a variety of phenols are all very similar, suggesting that iron(iii)-water bond breaking is rate determining here also. Sulphosalicylate reacts with FeOH + by the same rate-determining loss of water from the iron(m). Rates of formation of iron(iii) complexes with acetate, monochloroacetate, and propionate have been reported. ... 

From an investigation of various Michael acceptors, it has emerged that ethoxymethylidene malonates are suitable for addition-elimination reactions with acetylides to give diacids (426) after hydrolysis and elimination. Upon heating in a-dichlorobenzene, these acids cyclise to give ylidenebutenolides (427)Chromium carbonyl complexes of acetylenes have been used to prepare 2-methoxyfurans and... 

Observations on the reaction of ethylmalonatopentaamminecobalt(III) with Cr(H20)g + introduce a new element of interest. The chromium(III) products are the chelated malonate (67%) with a corresponding amount of free alcohol and the monodentate ester complex (33%). Since ester hydrolysis in the latter species is slow, we conclude that hydrogen results from the ester in the chelate form. Again, since ring closure of the monodentate product complex is slow, chelation must have occurred before Cr is oxidized to Cr . It is possible that formation of the chelate as primary product is complete, and that this product reacts in part to yield the monodentate product before hydrolysis occurs. Activation based on electron transfer to trap a function which is sensitive to a substitution-inert metal ion acting as a Lewis acid could presumably be extended to other more interesting situations. 

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