Cr catalyst

Poly(malic acid) is a biodegradable and bioadsorbable water-soluble polyester having a carboxylic acid in the side chain. The chemoenzymatic synthesis of poly(malic acid) was achieved by the lipase-catalyzed polymerization of benzyl (3-malolactonate, followed by the debenzylation. The molecular weight of poly(benzyl (3-malolactonate) increased on copolymerizafion with a small amount of (3-PL using lipase CR catalyst. ... 

Two Ni-Cr catalysts containing one 5 % nickd atomic and the other 10 % were tested for fluorination and dehydrofluorination reactions of CF3CH2CI. The results were compared to those obtained with chromium oxide alone. These reactions are performed only with the non fluorinated catalysts (table 2). 

Moreover a significant decrease in the formation of alkenes could be observed for the Ni-Cr catalysts. Consequently the presence of nickel dis voured the dehydrofluorination reaction while increasing the selectivity for the fluorination reaction. 

Ethanol can be derived from biomass by means of acidic/enzymatic hydrolysis or also by thermochemical conversion and subsequent enzymatic ethanol formation. Likewise for methanol, hydrogen can be produced from ethanol with the ease of storage/transportation and an additional advantage of its nontoxicity. Apart from thermodynamic studies on hydrogen from ethanol steam reforming,117-119 catalytic reaction studies were also performed on this reaction using Ni-Cu-Cr catalysts,120 Ni-Cu-K alumina-supported catalysts,121 Cu-Zn alumina-supported catalysts,122,123 Ca-Zn alumina-supported catalysts,122 and Ni-Cu silica-supported catalysts.123... 

Andreev and coworkers—promoting effect of Cu addition on Fe-Cr shift catalysts, and Raney Cu/Zn catalysis described by an associative mechanism. Andreev and coworkers240 added promoters to traditional high temperature shift Fe-Cr catalyst, and found that Cu and Co moved the maximum in the CO conversion curve to lower temperatures. No explanation was provided for the effect. 

The electroreductive coupling of the hindered aromatic ketones (367) has been achieved in a DMF-BU4NBr-(Hg) system by the aid of CrCh or MnCl2 as the electrocatalyst (Scheme 134) [484, 485]. The reductive coupling proceeds at a less negative potential [ 1/2 —1.44 —1.53 V (SCE)] than the reduction of the ketone (—1.63 —2.01 V). In some cases, Mn electrocatalysts favor the reduction to the carbinol (369), whereas a Cr catalyst promotes the formation of the pinacol (368). 

In Tables 2.3-1 and 2.3-2 the products formed by Ti- and Ni-catalysts are compared with those formed by Cr catalysts. Ni- and Ti-catalysts show an opposite behavior in the fff/ffc-isomer distribution of 1,5,9-cyclododecatrienes and in 2 1- vs. 

Cr-catalyst can perhaps pair the electrons of the half-filled d orbitals in two ways, leading to comparable control like in Ni- or Ti-catalysts. It can be assumed, that HOss/LUmCTI)- or HOM/LUss-interactions (Ni) may lead to the observed consequences. 

Hexane-1,6-diol was found to undergo an oxidation-cyclization process at elevated temperatures (250 °C) in the presence of a Cu-Cr catalyst supported on kieselguhr to yield 2,3,4,5-tetrahydrooxepin (68) (65JOC335). The final stage of the latter reaction involves a dehydration of the hemiacetal 2-hydroxyoxepane (75) as indicated in equation (38). An alternative type of base-induced cyclization (equation 39) involving intramolecular nucleophilic attack has been used in the synthesis of 4-ethoxycarbonyI-2,3,6,7-tetra-hydrooxepin (153) (73JOC1767). 

Amination of methyl dodecanoate or dodecanoic acid in the presence of supported Cu-Cr catalysts. 

Now the influence of water or ammonia on copper catalysts is being investigated. Previously A. BAIKER and coll, have shown that ammonia could modify the catalytic properties of copper catalysts used in the amination of alcohols (9). These authors noticed the formation of copper nitride after NH3 exposure at a temperature of about 300°C which is the reaction temperature of our study. The first results that we obtained in our study showed that both H2O and NH3 decrease significantly the copper dispersion in unpromoted catalysts and that this modification is less significant when Ca or Mn are added to the Cu-Cr catalyst. We are now studying what are the superfical modifications consecutive to the addition of promoters or/and water and ammonia. 

Generally, the issue of whether a truly solid Cr catalyst has been created for the aforementioned reactions is unresolved. This point is illustrated most clearly by all the work that has been devoted, in vain, to Cr molecular sieves (55-57). Particularly the silicates Cr-silicalite-1 and Cr-sihcahte-2 and the aluminophosphate Cr-AlPO-5 have been investigated. These materials have been employed, among others, for alcohol oxidation with t-BuOOH, for allylic (aut)oxidation of olefins, for the autoxidation of ethylbenzene and cyclohexane, and even for the catalytic decomposition of cyclohexyl hydroperoxide to give mainly cyclohexanone ... 

In 1991 a 15000t/a ammonia plant in Hubei Province, China came on stream. The hydrocarbon feed was converted mainly to H2 and CO under a pressure of about 0.8 MPa. The activity of a conventional Fe-Cr catalyst was not good enough when the inlet temperature of reaction bed was about 200°C... 

Glycerin49 Hydrogen peroxide/low boiling solvent with V, Mo, W, Ru or Cr catalyst Glycerin is distilled from the liquors... 

Pd-catalyzed cycloisomerization of (Z)-2-en-4-yne-l-thiols 111 gives substituted thiophenes 112. The mechanism involves electrophilic activation of the alkyne moiety by Pd(ll) followed by intramolecular cyclization, protonolysis, and aromatization (Scheme 25) <20000L351>. S-Endo cyclization of alkynyl thiols 113 using a Mo, W, or Cr catalyst affords dihydrothiophene 114 <2000S970>. 

Table 8 lists the Mo- and W-catalyzed polymerizations of acetylenes so far reported. The maximum MW s attained are shown in the Table. The polymerization behavior of each monomer will be explained in the following Sections 2.2 and 2.3. Recently it has been reported that bis(benzene)chromium, an organochromium compound, induces oligomerization of certain acetylenes 50). In the future, various Cr catalysts may be found as well as Mo and W catalysts. 

Transition metal complexes, particularly those of Group VIII, are popular catalysts. Of these, Pt and Rh are employed most frequently. A Cr catalyst is a unique catalyst for stereoselective hydrosilylation of 1,3-dienes. Catalysts based on Fe, Os and Ir are rarely used. 

Hydrosilylation of isoprene (57) has been well studied and the results are summarized in Table 2. Since 1,3-dienes are relatively reactive, metal complexes which do not catalyze hydrosilylation of common alkenes may be employed. Pd, Rh, Ni and Cr catalysts prefer 1,4-addition products with the (Z)-configuration. No catalyst is available which prefers 1,2-addition with high selectivity. 

Long-chain alcohols can be converted directly to A, A -dimethylalkyamines by the reaction with dimethylamine at 36°C in the presence of Th(S04)2 or in the presence of Cu-Cr catalyst and hydrogen at elevated temperamres and pressure (33, 34). 

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