Chromium , acetylacetonate

The addition of paramagnetic species, such as the metal ions Cu ", Mn, or CF", can have dramatic effects on both the observed spectmm and the relaxation behavior of a molecule. The added ion reduces nuclear relaxation times, and permitting more rapid data collection. In addition, faster relaxation rates minimize NOE effects in the spectra, which can be useful in obtaining quantitative intensity data. The most widely used reagent for this purpose is chromium acetylacetonate [13681 -82-8] known as Cr(acac)2. Practically speaking, the use of such reagents requires care, because at... 

Si NMR of hexamethyldisiloxane has been examined using a 750-MHz H resonance frequency, and a number of technical issues were discussed (Knight and Kinrade 1999). The use of chromium- acetylacetonate was used to reduce the Si relaxation time with a DEPT-45 pulse sequence. This indicated the potential application to the metabolism of organosilicon compounds. 

Approximately 1 g polymer and 0aQ6 M Cr(acac). were dissolved in CDCl. to prepare solutions for ySi and JC NMR spectroscopy. NMR spectra were run on a Varian XL-200 FT-NMR instrument. To aid in obtaining quantitative data, the solution was doped with 0.06 M chromium acetylacetonate [Cr(acac) )] to remove possible signal artifacts resulting from long spin-lattice relaxation times (T s) and tt> nucleay Overhauser effect, well-known features associated with 3Si and JC NMR spectroscopy. This permits quantitative signal acquisition. From the literature (16) and additional work done in this laboratory, it was expected that Cr(acac) would be an inert species. A solution of HMDZ (2.04 g, 12.67 mmole),... 

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

Figure I. 39.7 MHz Si NMR spectra of PSQ and APSQ obtained from PSQ-B in acetone-d6. Chromium acetylacetonate was used as a relaxation reagent, and transients were 5000. PSQ-A (Mw = 900) and PSQ-B (Mw = 9500) were purchased from Owens-Illinois and Petrarch Systems, respectively.

Quantification bv NMR spectroscopy The s proach used by Qarke et al( ) was adopted but the hydroaromatic range was extended from 22.5-50 ppm to 20-50 ppm this extension was necessary because the addition of 150 mg of chromium acetylacetonate to quench Nuclear... 

Treatment of chromium (III) acetylacetonate with acetic anhydride and boron trifluoride etherate yielded a complex mixture of acetylated chelates but very little starting material. Fractional crystallization and chromatographic purification of this mixture afforded the triacetylated chromium chelate (XVI), which was also prepared from pure triacetylmethane by a nonaqueous chelation reaction (8, 11). The enolic triacetylmethane was prepared by treating acetylacetone with ketene. The sharp contrast between the chemical properties of the coordinated and uncoordinated ligand is illustrated by the fact that chromium acetylacetonate does not react with ketene. 

Rhodium acetylacetonate differed considerably from the other metal chelates in the acetylation reaction (26). Under the same conditions that had given extensive acetylation of the cobalt and chromium acetylacetonates, the rhodium chelate reacted very slowly and formed only a small amount of the monoacetylated compound (XX). Fortunately, the hydrolytic stability of rhodium acetylacetonate is such that the Friedel-Crafts reaction can be carried out under vigorous conditions that would rapidly degrade the chromium and cobalt chelates. Thus treatment of rhodium acetylacetonate with acetyl chloride and aluminum chloride in dichloroethane afforded the mono- and diacetylated chelates (XX and XXI). No triacetylated chelate was isolated from this reaction. In a similar manner butyryl-and benzoyl-substituted rhodium chelates (XXIII and XXIV) have been prepared. These and other experiments indicate that the rhodium acetylacetonate ring is less reactive than the cobalt or chromium rings. 

The Mannich reaction is a particularly good method of introducing a reactive functional group into a sensitive aromatic nucleus. The reaction has been very useful in ferrocene chemistry. Treatment of chromium acetylacetonate under Mannich conditions yielded a tris-V,N-dimethylaminomethyl chelate (XXXIII). This remarkable substance was very difficult to purify because of its extreme solubility in all solvents ranging from n-heptane to water. The trisamino chelate (XXXIII) is a deep purple, hydroscopic oil and behaves like a typical organic amine. Reaction of this amine with methyl iodide afforded a trisquater-nary ammonium salt (XXXIV), soluble in water but insoluble in organic solvents. When this salt (XXXIV) was treated with cyanide ion, trimethylamine was lost and the cyanomethyl chelate (XXXV) was formed. 

Chromium compds, listing 3 C300—C302 chromium acetylacetone 1 A53 3 C300 chromium acetylide 1 A72 chromium (III) ammine complexes 1 A277 3C300... 

The polymerization of butadiene to 1.2 polymers with anionic Ziegler type catalysts has been studied by Natta and co-workers (46). They have shown that isotactic 1.2-polybutadiene can be produced by the use of catalysts which are made up of components which have basic oxygen and nitrogen structures such as triethylaluminum with cobalt acetylacetonate or with chromium acetylacetonate. Natta and co-workers have shown that either syndiotactic or isotactic structures are produced depending on the ratio of aluminum to chromium. Syndiotactic structures are obtained at low aluminum to chromium ratios while isotactic polybutadiene is obtained at high ratios. The basic catalyst component is characteristic of syndiotactic catalysts. Natta, Porri, Zanini and Fiore (47) have also produced 1.2 polybutadiene using... 

To reduce the nuclei s Tx relaxation time, relaxation agents are used. Relaxation agents are usually transition metal complexes, primarily ferric ethylenediaminetetraacetate or chromium acetylacetonate. Transfer of en-... 

USP 2712989 (1955) 8c CA 49, 14325-26 (1955) (Rocket proplnts obtd by colloiding NC with nitroparaffins, such as MeN02. They can also be used as expls. Ignition of these compns can be made easier by incorporating up to 3/5 chromium acetylacetonate) (See Vol 1, pA53-R and Vol 3, under Chromium) I)W.O.Baker,... 

Conventional Ziegler catalysts are not suitable for use with acrylonitrile because, among other reasons, the monomer reacts with the catalyst or forms complexes with it. Recently, modified catalysts have been developed in Natta s laboratory (106), using such combinations as Chromium acetylacetone plus dibutyl zinc,... 

Table VI summarizes important homogeneous Ziegler catalysts. The best known are the systems based on bis(cyclopentadienyl)titanium(IV), titanium alcoholates, vanadium chloride, or chromium acetylacetonate with trialkylaluminum or alkylaluminum halides.

Chromium hexacarbonyl Chromium acetylacetonate, carbon monoxide Reduction 75... 

In 1997, the major manufacturers of chromium compounds were (1) chromic(VI) acid, including chromic(VI) anhydride and chromic(VI) trioxide (total capacity 76,000 metric tons) American Chrome Chemicals Inc., Corpus Christi, Texas Occidental Chemical Corporation Specialty Business Group, Castle Hayne, North Carolina (2) chromium(III) sulfate Blue Grass Chemical Specialties, L.P., New Albany, Indiana Johnson Matthey, Inc., Ward Hill, Massachusetts Wayne Chemical Corp., Amarillo, Texas, Dakota City, Nebraska, and Milwaukee, Wisconsin (3) chromium(III) acetate Blue Grass Chemical Specialties, L.P., McGean-Rohco, Inc., Cleveland, Ohio The Shepard Chemical Company, Cincinnati, Ohio (4) chromium acetylacetonate MacKenzie Corporation, Bush, Louisiana The Shepard Chemical Company, Cincinnati, Ohio (5) chromium boride Cerac Incorporated, Milwaukee,... 

List of Chromium Compounds Chromium Acetylacetonate or Chromylacetyl-aeetone. See Vol 1, pA53-R Addnl Ref F.Bellinger et al, IEC 40, 1330 (1948) C.A42, 6115 (1948) [it was found that Cr acetylacetonate added in quantities of about 2% (together with 4% of gasoline) to nitromethane, prevented its detonarion when used a rocket ptcplnt such as for launching a buzz bomb]... 

SYNS CHROMIC ACETYLACETONATE CHROMIUM ACETYLACETONATE CHROMIUM(3+) ACETYLACETONATE CHROMIUM(III) ACETYLACETONATE CHROMIUM TRIACETYLACETONATE CHROMIUM TRIS(ACETYLACETONATE) CHROMIUM TRIS(2,4-PENTANEDIONATE) TRIS(ACETYL-ACETONATO)CHROMIUM TRIS(ACETYLACETON-ATO)CHROMIUM(III) TRIS(2,4-PENTANEDI-ONATO)CHROMIUM(3+)... 

Kinetics Studies. The sol-gel kinetics experiments were performed on a meth-anolic solution of 1.12 M dimer and 1.57 X 10" M chromium acetylacetonate [Cr(acac)3], a spin relaxation agent. Previous studies (12, 13) showed that Cr(acac)3 concentration does not affect the product distribution or reaction rate of TMOS-derived sol-gel solutions. The solutions were acid catalyzed (1.64 X 10" M HCl), and various amounts of water were added. To compensate for the exothermicity caused by dimer hydrolysis when water is added to the dimer-methanol solution, the alcoholic silicate solution was chilled in a thermostatically controlled bath prior to the addition of water. By adjusting the temperature to the appropriate level, the desired reaction temperature (25 1 °C) could be achieved within 60 s of mixing. At this time, the sample was removed from the thermostatically controlled bath and inserted into the spectrometer probe. 

Vinylcyclohexene and terf-butyl hydroperoxide, in the presence of chromium acetylacetonate, yield exclusively 4-vinylcyclohexene oxide [217]. 

First, for comparison, Cr/silica was activated by the one-step process. That is, it was simply calcined in air for 3 h at temperatures from 500 to 950 °C. Polymers were then made with these catalysts, and their LCB levels were evaluated. These values are represented by the center curve in Figure 129. LCB levels increased with activation temperature, as described in Section 9.3. Then another series of catalysts was activated by using the two-step procedure. Samples of the same silica, but containing no chromium, were each calcined for 3 h at the same temperatures ranging from 500 to 950 °C. Then each sample was impregnated with a solution of chromium acetylacetonate in dry toluene, followed by a final oxidation in air at only 500 °C. Polymers were then made with these catalysts at 100 °C with 0.24 mol 1-hexene L, and the measured LCB... 

The formation of cyclic structures and polymerization of aryl cyanates was followed from the changes in signal intensities of the reaction products. All intermediate spectra consist of two well separated signals arising from cyanate and triazine groups, respectively. Since a chromium acetylacetonate is added in order to eliminate the Nuclear Overhauser Effect and reduce the spin-lattice... 

Although a report of the successful reduction of the nitro group in chromium acetylacetonate appeared a few years ago 21), experimental details of the first instance in which reduction was effected were reported only recently 58, 59). Hydrogenation of the mononitrochromium chelate in ethanol over a palladium hydroxide catalyst gave the 3-amino chelate in about 70% yield 58, 59). 

Chromium hexafluoroacety-lacetonate, tris- (2-hydroxy-acetophenono) chromium, chromium acetylacetonate. Porasil A silica large porous spherical particles 0.5% pyridine-tolune... 

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