Chromium acetate formate

Chromate conversion coatings for aluminum are carried out in acidic solutions. These solutions usually contain one chromium salt, such as sodium chromate or chromic acid and a strong oxidizing agent such as hydrofluoric acid or nitric acid. The final film usually contains both products and reactants and water of hydration. Chromate films are formed by the chemical reaction of hexavalent chromium with a metal surface in the presence of accelerators such as cyanides, acetates, formates, sulfates, chlorides, fluorides, nitrates, phosphates, and sulfamates. 

Evidence for the structure (CXXIII) of the hemiacetal is based on the extremely hindered nature of the derived aldehyde (CXXV) and carboxylic acid (CXXVII). Thus, the aldehyde exhibited a negative Cotton effect in methanol, which remained unchanged upon the addition of hydrochloric acid, indicating great resistance toward acetal formation. Attempts to prepare carbonyl derivatives of this aldehyde were unsuccessful. The acid CXXVII was prepared by oxidation of alcohol CXXIV with chromium trioxide in acetic acid. Comparison of the apparent dissociation constant of this acid (pX cs 9.45) with that for... 

Aluminum formate Ammonium sulfate Chromic acid Chromium acetate (ic) Chromium chloride (ic)... 

Steroidal 17-cyanohydrins are relatively stable towards chromium trioxide in acetic acid (thus permitting oxidation of a 3-hydroxyl group ) and towards ethyl orthoformate in ethanolic hydrogen chloride (thus permitting enol ether formation of a 3-keto-A system ). Sodium and K-propanol reduction produces the 17j -hydroxy steroid, presumably by formation of the 17-ketone prior to reduction. ... 

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

A plausible pathway is that the aromatisation of the cyclohexadienone 92 by a proton shift is accelerated in the presence of Ac20 under formation of acetate 93. The simultaneously generated acetic acid then cleaves the acetate to form the free phenol 94 (Scheme 44). This effect was observed for the first time during studies towards the total synthesis of the lipid-alternating and anti-atherosclerotic furochromone khellin 99 [64].The furanyl carbene chromium complex 96 was supposed to react with alkoxyalkyne 95 in a benzannulation reaction to give the densely substituted benzofuran derivative 97 (Scheme 45). Upon warming the reaction mixture in tetrahydrofuran to 65 °C the reaction was completed in 4 h, but only a dimerisation product could be isolated. This... 

For formation of anticorrosive and adhesion-improving protective layers on metals the cleaned surface is treated with aqueous acidic solution containing molybdate, chromium fluoride, phosphate, acetate, and Zn ions. As dispersant a mixture of 60% alkali salt of a phosphate ester, 20% alkylpolyglucoside, and 20% fatty alcohol ethoxylate was applied. This method passivates the metal surface by formation of an anticorrosive and protective layer that improves adhesion of subsequent coatings. 

Little information exists on low-T precipitation of borides from solution. Chromium, cobalt and platinum borides are the only ones claimed to have been obtained from aqueous solution ". Ni2B and C02B are precipitated from a solution of nickel or cobalt acetates by adding a solution of sodium tetrahydroborate ". The formation of these borides at RT gives amorphous products. Hence, heat treatment at 300-700°C leads to crystalline NijB as the main constituent, although the average composition of the precipitate corresponds to NijB . 

Oxidation of isopropyl alcohol by chromic acid in concentrated acetic acid solution has recently been studied by Wiberg and Schafer S spectrophotometri-cally. At 385 nm a rapid increase in absorbance (with a half life of about 6 sec) due to mono- and diester formation was noted. When the reaction was examined at 510 nm, first a rapid increase, then a decrease of the absorbance was found. Since at this wavelength only chromium species can absorb, the intermediate could be chromium(V) or (IV). The esr spectra of reaction mixtures showed a relatively sharp signal with a. g = 1.9805 value corresponding to chromium(V). The fact that the relative concentrations of the intermediate determined from the spectral data agree well with the intensity of esr signals, indicates that the same species is responsible for the both phenomena. It is then clear that the oxidation of isopropyl alcohol proceeds via chromium(V). 

Knowledge of stoichiometry of the induced reaction could help to distinguish whether chromium(V) or chromium(IV) species are involved in the oxidation of benzaldehyde. Thus, the Cr(V) hypothesis predicts that for each molecule of benzaldehyde oxidized two molecules of manganese dioxide should be formed, whereas the Cr(IV) predicts that one molecule of manganese dioxide should be formed for each two molecules of benzaldehyde oxidized. Unfortunately, the attempt to determine the stoichiometry of the induced reaction failed because the oxidized manganese species was not precipitated during the reaction presumably due to formation of acetate complexes in the concentrated acetic acid solution. 

Oxidising acetic acid by using chromium (VI) compounds is far less dangerous, if an aqueous potassium dichromate/sulphuric acid mixture is used. On the other hand, if hot evaporation of the medium is carried out and this gives rise to the formation of solid dichromate, the detonation due to the contact of solid salt with acetic acid cannot be avoided. 

Cr-ZSM-5 catalysts prepared by solid-state reaction from different chromium precursors (acetate, chloride, nitrate, sulphate and ammonium dichromate) were studied in the selective ammoxidation of ethylene to acetonitrile. Cr-ZSM-5 catalysts were characterized by chemical analysis, X-ray powder diffraction, FTIR (1500-400 cm 1), N2 physisorption (BET), 27A1 MAS NMR, UV-Visible spectroscopy, NH3-TPD and H2-TPR. For all samples, UV-Visible spectroscopy and H2-TPR results confirmed that both Cr(VI) ions and Cr(III) oxide coexist. TPD of ammonia showed that from the chromium incorporation, it results strong Lewis acid sites formation at the detriment of the initial Bronsted acid sites. The catalyst issued from chromium chloride showed higher activity and selectivity toward acetonitrile. This activity can be assigned to the nature of chromium species formed using this precursor. In general, C r6+ species seem to play a key role in the ammoxidation reaction but Cr203 oxide enhances the deep oxidation. 

The reaction of [Cr(NH3)5H20](C104)3 and NaN3 in dilute acetic acid solution at 60 °C affords the monoazido complex [CrN3(NH3)s](C104)2.647 The addition of less than one equivalent of KN3 to a solution of chromium(III) in molten KCNS at 185 °C produces a bathochromic shift in the visible spectrum consistent with the formation of the thermally stable complex [Cr CSJsNj3-.648 The neutral triazido complexes Cr(N3)3(NH3)3 and Cr(N3)3(py)3... 

Complexes of salicylate with chromium(III) have not been reported but the tris complexes of salicylaldehyde and chromium(III) may be prepared by refluxing [Cr(THF)3Cl3] with salicylal-dehyde and sodium acetate in ethanol.939 The acid hydrolysis of this complex was studied in detail, but the isomerism obviously possible for this complex was not apparently considered. Khan and Tyagi940 studied the formation of phthalate complexes of chromium(III). 

For the latter reaction very pure chromium is required to prevent formation of Cr34, but the reaction with a zinc amalgam is clean and is a convenient source of the strongly reducing species. Addition ofCr2 solutions to saturated solutions of sodium acetate precipitates chromium(U) acetate ... 

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