Activated C-H Compounds


Organomagnesium reagent capable of reacting with active H compounds or in additions to C X  [c.152]

Silanes are much more reactive than the corresponding C compounds. This has been ascribed to several factors including (a) the larger radius of Si which would facilitate attack by nucleophiles, (b) the great polarity of Si-X bonds, and (c) the presence of low-lying d orbitals which permit the formation of 1 1 and 1 2 adducts, thereby lowering the activation energy of the reaction. The relative magnitude of the various bond energies is also an important factor in deciding which bonds will survive and which will be formed. Thus, it can be seen in Table 9.5, Si-Si < Si-C < C-C and Si-H < C-H, whereas for bonds for the other elements the energy C-X < Si-X. These data should  [c.338]

A distinction between these four possibilities can be made on the basis of the kinetic isotope effect. There is no isotope effect in the arylation of deuterated or tritiated benzenoid compounds with dibenzoyl peroxide, thereby ruling out mechanisms in which a C5— bond is broken in the rate-determining step of the substitution. Paths (ii) and (iii,b) are therefore eliminated. In path (i) the first reaction, Eq. (6), is almost certain to be rate-determining, for the union of tw o radicals, Eq. (7), is a process of very low activation energy, while the abstraction in which a C—H bond is broken would require activation. More significant evidence against this path is that dimers, Arz, should result from it, yet they are never isolated. For instance, no 4,4 -dinitrobiphenyl is formed during the phenylation of  [c.136]

This cleavage is a unimolecular (first-order) reaction. The thermal decomposition rates are affected by the stmcture of the organic peroxide and the decomposition conditions. For comparison purposes, the thermal activity of a peroxide can be expressed in terms of its 10-hour half-life temperature (10-h HLT, ie, the temperature required for 50% decomposition of a peroxide in a period of 10 hours). This temperature can vary from well below 20°C to well above 200°C. In comparing two peroxides, the one with the lower 10-h HLT is more thermally labile. Another comparison of thermal activity is by active oxygen content, which refers to the quantity of peroxide groups available for thermal decomposition. The concept of active oxygen content is based on the existence of one active oxygen in each oxygen—oxygen bond pair. It is usually expressed as a percentage, ie, (100)(16p[m where p represents the number of peroxide groups present and m represents the molecular weight (pure compound) and is adjusted for assay in diluted formulations. The phrase appears frequentiy in discussions of peroxide analysis and safety. Peroxide compounds or formulations having low active oxygen content are generally safer to handle than those with high active oxygen content.  [c.101]

Nickel hydrate, usually 5—10% cobalt added, serves as the active material and is mixed with a conductive carbon, eg, graphite. The active mass is mixed with an iaert organic biader such as polyethylene or poly(tetra uoroethylene) (TEE). The resultant mass is roUed iato sheets on a compounding mill or pressed iato electrodes as a dry powder on a nickel grid. The resultant electrodes offer a high energy density and low cost of fabrication. In performance, the plastic-bonded electrodes can support rates up to C/2, discharge capacity ia 2 h, at voltages equivalent to those of siatered electrodes, but at higher rates some derating occurs. Life of plastic-bonded electrodes has not been fully evaluated, but a life of 500 cycles appears attainable.  [c.558]

Can manufacturers often regenerate the catalyst beds on an aimual or biaimual basis during a weekend downtime. Both air lancing and an aqueous bath are utilized to remove noncombustible particulates that mask the active sites. Erequendy, condensed organic material on the catalyst is removed by short-term (4—6 h) heating excursions to 370 or 430°C the organic matter is removed much like a self-cleaning oven. The gaseous and organic smoke, which is usually evolved from the first few cm of catalyst bed depth, is oxidized in the latter part of the bed. If allowed to operate too long at temperatures that promote condensation, high boiling organic compounds, the subsequent carbon char that is formed, may require temperatures of 480 to 540°C to convert the carbon to carbon monoxide for subsequent oxidation. The higher temperatures required for bum-offs should be approached in small (0—30°C) increments to bring about slow evolution and partial oxidation this prevents autogenous combustion of local high concentrations of combustible material.  [c.515]

The required nitrite esters 1 can easily be obtained by reaction of an appropriate alcohol with nitrosyl chloride (NOCl). The 3-nitroso alcohols 2 formed by the Barton reaction are useful intermediates for further synthetic transformations, and might for example be converted into carbonyl compounds or amines. The most important application for the Barton reaction is its use for the transformation of a non-activated C-H group into a functional group. This has for example been applied for the functionalisation of the non-activated methyl groups C-18 and C-19 in the synthesis of certain steroids.  [c.26]

Electrophilic insertion reactions into C-H (and C-C) bonds under low-nucleophilicity superacidic conditions are not unique to alkane activation processes. The C-H (and C-C) bond activation by organome-tallic complexes, such as Bergman s iridium complexes and other transition metal systems (rhodium, osmium, rhenium, etc.), is based on somewhat similar electrophilic insertions. These reactions, however, cannot as yet be made catalytic, although future work may change this. A wide variety of further reactions of hydrocarbons with coordina-tively unsaturated metal compounds and reagents involving hypercarbon intermediates (transition states) is also recognized, ranging from hydrometallations to Ziegler-Natta polymerization.  [c.167]

As a class of compounds, nitriles have broad commercial utility that includes their use as solvents, feedstocks, pharmaceuticals, catalysts, and pesticides. The versatile reactivity of organonitnles arises both from the reactivity of the C=N bond, and from the abiHty of the cyano substituent to activate adjacent bonds, especially C—H bonds. Nitriles can be used to prepare amines, amides, amidines, carboxyHc acids and esters, aldehydes, ketones, large-ring cycHc ketones, imines, heterocycles, orthoesters, and other compounds. Some of the more common transformations involve hydrolysis or alcoholysis to produce amides, acids and esters, and hydrogenation to produce amines, which are intermediates for the production of polyurethanes and polyamides. An extensive review on hydrogenation of nitriles has been recendy pubHshed (10).  [c.217]

A biogenic origin for the carbonaceous material in petroleum is widely but not universally accepted. An inorganic origin of petroleum has been proposed (1,2) and there is a duaUst theory incorporating both biological and inorganic aspects (3). However, because inorganic processes generate racemic mixtures, the presence of optically active compounds in oils, especially the multiringed cycloalkanes (naphthenes), provides strong support for a biological hypothesis. Oils also contain the so-called chemical fossils or biomarkers, compounds having characteristic molecular stmctures that can be related to living systems. The compounds include isoprenoids, porphyrins, steranes, hopanes, and many others. The relative abundances of members of homologous series are often similar to those in living systems. The strong odd preference in the long-chain normal alkanes (>C is particularly well documented (4). In addition, the lack of thermodynamic equiUbrium among compounds (5), and the close association of petroleum with sedimentary rocks formed in an aqueous environment, suggests a low temperature origin. In this context, low temperature means less than a few hundred degrees Celsius as opposed to temperatures in the 700—1200°C range that characterize igneous processes involving siUcate melts. The elemental composition of petroleum (C,H,N,S,0), the isotopic composition of oils, and the presence of petroleum-like materials in more recent sediments are consistent with a low temperature origin. The evidence supporting a biological source for the material that generates petroleum is extensive (6—8).  [c.161]

Activity and Selectivity. The activity of a catalyst refers to its abiUty to promote the desired reaction whereas the selectivity relates to how effective a catalyst is at promoting only a specific reaction. The selectivity which is required in a particular hydrogenation depends on the functional groups present in the material being hydrogenated. Many common functional groups can be reduced by catalytic hydrogenation with varying degrees of difficulty, and often one functional group must be reduced selectively in the presence of other groups which are to be left unchanged. For example, in the reduction of aromatic nitro compounds the catalyst and reaction conditions must be selected so that the nitro group is completely reduced while the aromatic ring is left intact. Since aromatic rings are generally much more difficult to reduce than nitro groups, this reduction can be carried out very selectively. However, other cases exist where it is much harder to selectively reduce one functional group in the presence of another. An impressive example of the selectivity which can be achieved is in the reduction of 2,4-dinitroaniline [97-02-9] (C H N O. Not only is it possible to reduce one of the nitro groups to an amine while leaving the other unchanged, but through proper choice of catalyst and reaction conditions, either 4-nitro-l,2-benzenediamine [99-56-9] (1) (CgH. N202) (27) or 2-nitro-l,4-benzenediamine [5307-14-2] (2) (28) can be made in good yield.  [c.259]

Rhenium Carbonyls and Related Compounds. The parent compound of the low valent rhenium compounds is Re2(CO) Q. Dirhenium decacarbonyl [14285-68-8] a white crystalline compound, mp 177°C, is volatile and soluble in most organic solvents. Its preparation in a high pressure reaction between Re20y, H2, and CO was reported in 1941. It has a molecular stmcture of two square pyramidal Re(CO) groups linked by a metal—metal bond. This compound is available commercially as a specialty chemical. It is the precursor to other low valent rhenium carbonyl compounds, including the hahdes, ReX(CO), where X = Cl, Br, or I alkyl, aryl, and acyl compounds, Re(R)(CO) the hydride complexes ReH(CO) [16457-50-0], Re2()J.-H)2(CO)g [38887-05-7], and Re2()J.-H)2(CO) 2 [12146-47-3]-, and hydrocarbon complexes, including Re(CO)2(Tl-C H ) and [Re(NO)(CO)2( Tl-C H )]PFg [12306-73-9], Research in the 1980s and 1990s has focused on the photochemical activation of H2 by Re2(CO)2Q, formation of metal atom clusters, and on the reduction of a coordinated carbon monoxide ligand to methane or methanol. The latter reaction has received much attention because it provides mechanistic information about the Fischer-Tropsch reaction (see Carbonyl Coal CONVERSION PROCESSES).  [c.164]

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether.  [c.375]

Numerous half-sandwich compounds of the type [M()7 -C5R5)L2], M = Rh, Ir R = H, Me L = CO, phosphine etc.) are known and are useful reagents. [Ir()7 -C5Me5)(CO)2] for instance is an excellent nucleophile and is also used in the photochemical activation of C-H in alkanes. It is particularly effective in the latter role when supercritical CO2 is the solvent.  [c.1143]

With active methylene compounds, the carbanion substitutes for the hydroxyl group of aHyl alcohol (17,20). Reaction of aHyl alcohol with acetylacetone at 85°C for 3 h yields 70% monoaHyl compound and 26% diaHyl compound. Malonic acid ester in which the hydrogen atom of its active methylene is substituted by A/-acetyl, undergoes the same substitution reaction with aHyl alcohol and subsequendy yields a-amino acid by decarboxylation (21).  [c.73]

The largest apphcation for activated alumina as a catalyst substrate is in hydrotreating of petroleum feedstocks (qv) (34). The purpose of hydrotreating is threefold to increase the H/C ratio to remove O, S, and N impurities and to remove V, Ni, and other tramp contaminants, especially from residuum of heavier feedstocks. Specialized alumina-based catalysts typically promoted with compounds of Co, Mo, W, and Ni have been developed for these operations (34). The catalysts are usually in the form of extmdates having variously shaped cross sections (35) (circular, lobed, wagon-wheel) about one millimeter in diameter. Spherical catalysts 1 mm or less in diameter have also been described for hydrotreating (24). Much attention has been given to optimizing pore volume and pore size distribution of the activated alumina substrates used in these operations and the "optimum" properties vary with operating conditions and the petroleum feedstock being processed. In the 1990s, worldwide consumption of hydrotreating catalysts was estimated at 30,000—40,000 t/yr, increasing at about 6%/yr (36,37).  [c.156]

In 1984 a new class of naturaHy occurring cephalosporins containing a 7a-formamido group, was isolated (14—16). These compounds (Table 2) caHed chitinovorins (16) or cephabacin F (15) where F designates a formamido group in the 7-position, also have amino acids or oligopeptides at the C-3 position. An analogous 7a-hydrogen series, named cephabacin H, containing the same oligopeptides at C-3 has also been isolated (15). The derivatives aH have weak antibacterial activity. The 7a-formamido group imparts good P-lactamase stabHity (15) as is the case for the cephamycins. Chemical manipulation afforded a series of semisynthetic analogues having exceHent broad-spectmm activity (28—30).  [c.21]

Numerous other penicillin sulfones have been reported to be P-lactamase inhibitors, as illustrated in Table 5. The effect of C-6 substituents has been extensively explored starting with 6-APA sulfone (25, R = NH2, R = H, R" = R " = CH ), which has modest activity. Mechanistic considerations led to preparation of sulfones of poor substrates, compounds such as methicillin, cloxaciUin, nafaciUin, and quinaciUin sulfone (25,  [c.51]

Fig. 6. Breakthrough curves for aqueous acetone (10 mg 1" in feed) flowing through exnutshell granular active carbon, GAC, and PAN-based active carbon fibers, ACF, in a continuous flow reactor (see Fig. 5) at 10 ml min" and 293 K [64]. C/Cq is the outlet concentration relative to the feed concentration. Reprinted from Ind. Eng. Chem. Res., Volume 34, Lin, S. H. and Hsu, F. M., Liquid phase adsorption of organic compounds by granular activated carbon and activated carbon fibers, pp. 2110-2116, Copyright 1995, with permission from the American Chemical Society. Fig. 6. Breakthrough curves for aqueous acetone (10 mg 1" in feed) flowing through exnutshell granular active carbon, GAC, and PAN-based active carbon fibers, ACF, in a continuous flow reactor (see Fig. 5) at 10 ml min" and 293 K [64]. C/Cq is the outlet concentration relative to the feed concentration. Reprinted from Ind. Eng. Chem. Res., Volume 34, Lin, S. H. and Hsu, F. M., Liquid phase adsorption of organic compounds by granular activated carbon and activated carbon fibers, pp. 2110-2116, Copyright 1995, with permission from the American Chemical Society.

See pages that mention the term Activated C-H Compounds : [c.10]    [c.11]    [c.107]    [c.119]    [c.531]    [c.41]    [c.48]    [c.53]    [c.269]    [c.304]    [c.300]    [c.301]    [c.110]    [c.234]    [c.215]    [c.37]    [c.163]    [c.224]    [c.517]    [c.72]    [c.259]    [c.246]    [c.465]    [c.187]    [c.212]    [c.43]    [c.27]   
See chapters in:

The nitro group in organic synthesis  -> Activated C-H Compounds