Chromium carbonyl, decomposition

The nitrogen complex had already been synthesized in a solid matrix, but its decomposition kinetics and its further photolysis could be studied only in solution. The liquid noble gas technique is superior to the solid matrix technique, especially for the synthesis of multiple substituted chromium carbonyl nitrogen complexes. Their IR spectra were extremely complex in matrices, due to "site splittings" which arise when different molecules are trapped in different matrix environments /18/. 

Anhydrous chromium(III) nitrate may be prepared by the reaction of dinitrogen pentoxide with chromium carbonyl in dry carbon tetrachloride.800 The product has rather low thermal stability, is involatile and decomposition begins at 60 °C. 

CHROMIUM CARBONYL (13007-92-6) CjCrOj Contact with strong oxidizers, heat above 400 F/204°C, or contact with chlorine and fuming nitric acid causes decomposition that may be violent possibly explosive. Sensitive to light undergoes photochemical decomposition. On small fires, use dry chemical powder (such as Purple-K-Powder), foam, or COj extinguishers. Thermal decomposition releases carbon monoxide, carbon dioxide, and carcinogenic chromium(VI) oxide. 

Layers containing Cr and Cr3C2 have been produced by the thermal decomposition of chromium carbonyl (Owen and Webber, 1948 Lander and Germer, 1948). The metal will react with methane at 600°-800° (Campbell et ai, 1949). 

The MOCVD of chromium is based on the decomposition of dicumene chromium, (C9Hj2)2Cr, at 320-545°C.[ ]f ] However, the reaction tends to incorporate carbon or hydrogen in the deposit. It can also be deposited by the decomposition of its carbonyl which is made by dissolvingthe halide in an organic solvent such as tetrahydrofuran with CO at 200-300 atm and at temperatures up to 300°C in the presence of a reducing agent such as an electropositive metal (Na, Al, or Mg), trialkylaluminum, and others. 

Chromium oxide is deposited by the decomposition of chromium acetyl acetonate, Cr(C5H702)3, in the 520-560°C temperature range.[ 1 It can also be deposited by the decomposition of the carbonyl in an oxidizing atmosphere (CO2 or H2O), at low pressure (< 5 Torr).Dl... 

Stirring chromium trioxide (added in small portions) with the unheated solvent leads to the formation of a complex useful for oxidising alcohols to carbonyl derivatives. The trioxide must not be crushed before being added to the solvent, because violent decomposition may then occur. 

Transition metal complexes which react with diazoalkanes to yield carbene complexes can be catalysts for diazodecomposition (see Section 4.1). In addition to the requirements mentioned above (free coordination site, electrophi-licity), transition metal complexes can catalyze the decomposition of diazoalkanes if the corresponding carbene complexes are capable of transferring the carbene fragment to a substrate with simultaneous regeneration of the original complex. Metal carbonyls of chromium, iron, cobalt, nickel, molybdenum, and tungsten all catalyze the decomposition of diazomethane [493]. Other related catalysts are (CO)5W=C(OMe)Ph [509], [Cp(CO)2Fe(THF)][BF4] [510,511], and (CO)5Cr(COD) [52,512]. These compounds are sufficiently electrophilic to catalyze the decomposition of weakly nucleophilic, acceptor-substituted diazoalkanes. 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

It is now generally admitted that this reaction involves both one-electron and two-electron transfer reactions. Carbonyl compounds are directly produced from the two-electron oxidation of alcohols by both Crvl- and Crv-oxo species, respectively transformed into CrIV and Crm species. Chromium(IV) species generate radicals by one-electron oxidation of alcohols and are responsible for the formation of cleavage by-products, e.g. benzyl alcohol and benzaldehyde from the oxidation of 1,2-diphenyl ethanol.294,295 The key step for carbonyl compound formation is the decomposition of the chromate ester resulting from the reaction of the alcohol with the Crvl-oxo reagent (equation 97).296... 

The mass spectra of bimetallic carbonyl metal compounds with cyclic arsine ligands have been discussed (Table 10). Molecular ion peaks are present for the pentamethyl-cyclopentaarsine containing complexes of chromium and tungsten, (AsMe)5[M(CO)]2 (186,188). Their decomposition includes CO and/or M(CO)5 loss giving rise to the ions (AsMe)sM2(CO) + (n = 0-9), (AsMe)sM(CO)/ (n = 0-5), M As Me-" and MAs Me+ (m = 2-4), MjAs Me, M AsMe -" (m = 2-4), MAs (w = 2-5), MAsjCH and AsMOj The latter is the most abundant in the mass spectra . ... 

Cr produced by reaction of lower-valence states with hydroperoxides, can react with alcohols to produce chromate esters. These esters will, of course, decompose heterolytically, in the manner described above, to produce carbonyls and, for example, H2C1O3 [79]. A similar but somewhat altered mechanism of het-erolytic chromate ester decomposition has been proposed to explain differences noted among several alcohols in the oxidation of alcohols with Cr [81]. The use of chromium-containing catalysts to decompose hydroperoxides to carbonyls in reactions conducted without autoxidation has been frequently noted [82-85]. 

The best catalyst was found to consist of zinc oxide and copper (or copper oxide) with an admixture of compounds of chromium. The success of the operation depended upon (a) the absence of alkali, which would cause decomposition of the methanol and the production of higher alcohols and oily products, and (b) the complete elimination of all metals except copper, aluminum and tin from those parts of the apparatus which come in contact with the reacting gases. Contact of carbon monoxide with iron, nickel, or cobalt had to be avoided since they formed volatile carbonyls winch deposited metal, by decomposition, on the active catalyst surface and thereby acted as poisons to destroy activity. 

HIDROXILAMINA (Spanish) (7803-49-8) A powerful reducing agent. Aqueous solution is a base. Contact with water or steam causes decomposition to ammonium hydroxide, nitrogen, and hydrogen. Contaminants and/or elevated temperatures above (reported at 158°F/70°C and 265°F/129°C) can cause explosive decomposition. Moisture in air or carbon dioxide may cause decomposition. Violent reaction with oxidizers, strong acids, copper(II) sulfate, chromium trioxide, potassium dichromate, phosphorus chlorides, metals calcium, sodium, zinc. Incompatible with carbonyls, pyridine. Forms heat-sensitive explosive mixtures with calcium, zinc powder, and possibly other finely divided metals. Aqueous solution incompatible with organic anhydrides, acrylates, alcohols, aldehydes, alkylene oxides, substituted allyls, carbonyls, cellulose nitrate, cresols, caprolactam solution, epichlorohydrin, ethylene dichloride, glycols, isocyanates, ketones, nitrates, phenols, pyridine, vinyl acetate. Attacks aluminum, copper, tin, and zinc. 

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