Cobalt dichromate

Cobalt Dichromate, CoCr207.II20, is obtained by heating "an aqueous solution of cobalt carbonate and chromic acid to a high temperature. It occurs as black deliquescent crystals.6... 

T14687>. The 1,3-dipolar cycloaddition of pyridinium ylides with a,P-unsaturated aldehydes or ketones in the presence of tetrakis-pyridme cobalt dichromate gives 1-acylindolizidines <97SC1395>. Similarly, pyridinium dicyanomethylides react with cyclooctyne to produce indolizidines <97JHC203>. 

TPCD = tetrakis-pyridino-cobalt dichromate = [Py4Co(HCi04)2J Hu. Y. Hu, H. Synth. Commun., 1992, 22, 1491. 

MetaUic cobalt dissolves readily in dilute H2SO4, HCl, or HNO to form cobaltous salts (see also Cobalt compounds). Like iron, cobalt is passivated by strong oxidizing agents, such as dichromates and HNO, and cobalt is slowly attacked by NH OH and NaOH. 

Transition metal ions. Transition metal ions impart color to many of their compounds and solutions, (a) Bottom row (left to right) iron(lll) chloride. copper ll) sulfate, manganese(ll) chloride, cobalt(ll) chloride. Top row (left to right) chromium(lll) nitrate, iron(ll) sulfate, nickel(ll) sulfate, potassium dichromate, (b) Solutions of the compounds in (a) in the order listed above. 

The above considerations will be illustrated by the simultaneous determination of manganese and chromium in steel and other ferro-alloys. The absorption spectra of 0.001 M permanganate and dichromate ions in 1M sulphuric acid, determined with a spectrophotometer and against 1M sulphuric acid in the reference cell, are shown in Fig. 17.20. For permanganate, the absorption maximum is at 545 nm, and a small correction must be applied for dichromate absorption. Similarly the peak dichromate absorption is at 440 nm, at which permanganate only absorbs weakly. Absorbances for these two ions, individually and in mixtures, obey Beer s Law provided the concentration of sulphuric acid is at least 0.5M. Iron(III), nickel, cobalt, and vanadium absorb at 425 nm and 545 nm, and should be absent or corrections must be made. 

Kharab P, Singh I. 1985. Genotoxic effects of potassium dichromate, sodium arsenite, cobalt chloride and lead nitrate in diploid yeast. MutRes 155 117-120. 

Furthermore, the EU regularly produces and regularly updates the list of substances of high concern, i.e. the SVHC list. The identification of a substance as a SVHC and its inclusion in the candidate list is the first step of the authorization procedure. The European Chemical Agency in Helsinki identifies from the candidate list priority substances to be included in Annex XIV of REACH (the authorisation list). The substances on the candidate list will most probably be liable to stricter regulation in the future (authorisation/banning) which will stimulate the substitution of these chemicals. Currently in June 2012, there are 84 substances included in the candidate list. Examples of chemicals on the candidate list which may be relevant for the leather industry are phenolphthalein, boric acid, cobalt dichloride, dichromate (although not used by leather industry), phthalates (DEHP, DBP and BBP), acrylamide and short-chain chlorinated paraffins. 

Hu and co-workers reported a facile synthesis of pyrrolo[2,l-n]phthalazine 205 by a 13-dipolar cycloaddition of phthalazium N-ylides generated from 203 with electron deficient alkenes to give 204, followed by treating 204 with tetrakispyridine cobalt(II) dichromate [Py4Co(HCr04)2, TPCD] to complete the aromatization <00JHC1165>. 

A useful method for the synthesis of 1-unsubstituted 2-arylindolizines is provided by the 1,5-dipolar cyclization of pyridinium ylides derived from 181, in the presence of the oxidant tetrakis(pyridine)cobalt(ll) dichromate (TPCD), which oxidizes the intermediate dihydroindolizine 182 (Scheme 43). The study demonstrated that the presence of an aryl group on the double bond was necessary for the reaction to occur. 

The 1,3-dipolar addition of ylide 223 with various dipolarophilic alkenes to produce 224 after aromatization of the adducts was reported to proceed significantly more selectively in the presence of MnOz than in the original reaction where TPCD (tetrakis(pyridine) cobalt(II) dichromate) was used as the oxidant in which 224 were minor by-products <99JCR(S)552>. 

Cobalt(II) acetate in conjunction with 9,10-dibromoanthracene is an efficient catalyst for the oxidation of 2-methylthiophenes (Scheme 99) (72ZOR2590, 74ZOB837). As mentioned in Section 3.02.3.3, aqueous potassium dichromate has been used for the oxidation of 3-methylthiophene to the corresponding carboxylic acid in 80-85% yield (65JOC1453). Alkaline KMn04 oxidation of alkylthiophenes gives low yields of the acids (52HC(3)364>. 

Katsarou A, Baxevanis C, Armenaka M, et al. 1997. Study of persistence and loss of patch test reactions to dichromate and cobalt. Contact Dermatitis 36 87-90. 

Blue copper(II) green nickel, iron(II), chromium(III), manganates yellow chromates, hexacyanoferrate(II), iron(II) orange-red dichromates purple permanganates pink cobalt, manganese(II). 

Cobalt and compounds SPA Sodium dichromate Cobalt oxide Cement Dyes Electroplating Paint Tanneries Catalysts... 

Cr(II) may be used to carry out all the reactions of Ti(III), but usually under milder conditions. Applications of Cr(II) as a reductant have been reviewed. The applications include Sn(IV) chloride in the presence of catalysts such as Sb(V) or Bi(III), Sb(V) in 20% HCl at elevated temperatures, Cu(II), silver, gold, mercury, bismuth, iron, cobalt, molybdenum, tungsten, uranium, dichromate, vanadate, titanium, thallium, hydrogen peroxide, oxygen in water and gases, as well as organic compounds such as azo, nitro, and nitroso compounds and quinones. Excess Cr(II) in sulfuric acid solution reduces nitrate to ammonium ion. The reduction is catalyzed by Ti(IV), which is rapidly reduced to Ti(III). 

Cobalt(III) Co -" Strontium Sr -" Dichromate Cr20 - Permanganate Mn04... 

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