Catalytic additives

A second commeicial route to aciylonitiile used by Du Pont, Ameiican Cyanamid, and Monsanto was the catalytic addition of HCN to acetylene... 

Applicability of Semiconductor Gas Sensors Research into the applications of this type of sensor has mainly been concerned with measuring carbon monoxide concentration in flue gases. Tests show that sensors follow the concentration of carbon monoxide in the flue gas. Improvement in sensor performance has resulted with the introduction of a catalytic additive (palladium or... 

Throughout this section attention is restricted to rate equations that include concentrations of only the substrate, H, and OH. The observed first-order rate constant, therefore, contains concentrations of only H and OH (the quantity [OH ] is often replaced by A",v/[H j). The substrate (reactant) may be ionizable. Rate equations containing the concentration of additional solutes (especially catalytic additives) can be developed as shown in Section 6.3. 

Carboxylic esters can be treated with ketones to give p-diketones in a reaction that is essentially the same as 10-118. The reaction is so similar that it is sometimes also called the Claisen condensation, though this usage is unfortunate. A fairly strong base, such as sodium amide or sodium hydride, is required. Yields can be increased by the catalytic addition of crown ethers. Esters of formic acid (R H) give P-keto aldehydes. Ethyl carbonate gives P-keto esters. 

The first is to add to the diesel fuel a catalytic additive, which accumulates in the soot particles formed. The catalyst is thus brought to the right place and there is contact. 

Some other enantioselective approaches have been attempted, still with moderate enantioselectivities, by making use of in situ systems containing a chiral NHC precursor. Luo and co-workers reported on the use of the bidentate chiral imidazo-lium salt 16, derived from L-proUne, in combination with [RhCia-COCcod)], leading to an enantiometic excess of around 20% [30]. The use of chiral imidazolium salt 17 in combination with [RhCl(CH2=CHj)j]j by Aoyama afforded slightly better ee (Fig. 7.3) [31 ]. So far, Bohn and co-workers have obtained the best enantioselectivities (up to 38% ee) for the catalytic addition of phenylboronic acid to aromatic aldehydes by using planar chiral imidazolium salts 18, derived from paracyclophane, in combination with [Rh(OAc)2]2 [32]. 

In addition, Rowlands has involved chiral sulfoxide-containing ligands for the catalytic addition of McsSiCN to aldehydes. " The ligand structure was based on a phenolic oxazoline scaffold with introduction of the sulfur substituent via cysteine derivatives. The best enantioselectivities of up to 61% ee were obtained with the bulkiest tert-butyl substituted ligand (Scheme 10.42). The effect of the sulfoxide configuration was studied, showing that the use of... 

Considerable effort has been directed towards the catalytic addition of HCN to vinylarenes since this represents a route to 2-arylpropionic acids, well-known anti-inflammatory agents.75 High levels of asymmetric induction are required (R)-naproxen has undesirable properties associated with it and only the ([Pg.277]

If R and R1 are not a methyl group, the process generates a chiral carbon center (C ). The overall catalytic addition of hydrogen to olefinic bonds generally is nearly always cis (7, p. 407) and to the olefinic face coordinated to the metal. This cis-endo-addition produces a chiral center(s) when one olefinic face is preferentially coordinated. 

Scheme 22.7 Catalytic addition of metallo-aldehyde enolates to ketones.

Scheme 6.19. Asymmetric catalytic additions of imines with non-Zr-based complexes.

Maruoka and co-workers recently reported an example of a Zr-catalyzed cyanide addition to an aldehyde [64]. As is also illustrated in Scheme 6.20, the reaction does not proceed at all if 4 A molecular sieves are omitted from the reaction mixture. It has been proposed that the catalytic addition proceeds through a Meerwein—Ponndorf—Verley-type process (cf. the transition structure drawn) and that the crucial role of molecular sieves is related to facilitating the exchange of the product cyanohydrin oxygen with that of a reagent acetone cyanohydrin. The example shown is the only catalytic example reported to date the other reported transformations require stoichiometric amounts of the chiral ligand and Zr alkoxide. 

Figure 5. Catalytic addition of Et2Zn with a fluorous binol ligand...

New multinary hydride structures (Li-Mg-B-N-H) were successfully synthesized and characterized using LiBfVLiNLL and MgH2. These hydrides show enhanced reaction kinetics at lower temperatures due to the nanocrystalline behavior of MgH2 having large surface area. Moreover, the catalytic addition drastically reduces the thermal decomposition temperatures of Li-Mg-B-N-H when compared to undoped complex hydrides. 

Kagan H, Namy JL (1999) Influence of Solvents or Additives on the Organic Chemistry Mediated by Diiodosamarium. 2 155-198 Kakiuchi F, Murai S (1999) Activation of C-H Bonds Catalytic Reactions. 3 47-79 Kakiuchi F, Chatani N (2004) Activation of C-H Inert Bonds. 11 45-79 Kakiuchi F (2007) Catalytic Addition of C - H Bonds to C - C Multiple Bonds. 24 1-33 Kalck P, Urrutigoity M, Dechy-Cabaret O (2006) Hydroxy- and Alkoxycarbonylations of Alkenes and Alkynes. 18 97-123... 

Acetic acid, CH3COOH, can be made by the oxidation of acetaldehyde, CH3CHO by catalytic addition of CO to methanol or by butane oxidation. Most acetic acid is used to make vinyl acetate or cellulose acetate, which are the intermediates for plastics, paints, adhesives, yarn, and cigarette filters. 

Alkylation, In petrochemicals, any reaction involving the thermal or catalytic addition of an olefin to a branch-chain hydrocarbon or aromatic hydrocarbon. The most notable example in petrochemicals is the addition of ethylene or propylene to benzene to produce ethylbenzene or isopropyl benzene (cumene). Other examples include the production of detergent alkylates. 

For enantioselective catalytic addition of vinylzinc reagents to aldehydes, see [52-70]. 

The catalytic additives that have been investigated in MgH can be roughly divided into three important groups metals/intermetallics, oxides, and chemical compounds that include hydrides. Their effect on the desorption properties of MgH will be discussed in the following sections. We are not going to discuss absorption since, as mentioned before, absorption is usually much easier than desorption. 

The well-known catalytic additive to MgH is Ni. So far, it has been added as a coarse powder with the size range of a few tens of micrometers. A short review of these early experiments is presented in [117], More recently, Hanada et al. [118] investigated the addition of nano-Ni to ball-milled MgH. Unfortunately, he used continuous desorption under He gas and the material desorbed 6 wt.%H2 at 160°C in 15,000 s. 

Metal oxides seem to be one of the most potent catalytic additives to MgH. A number of authors investigated only the absorption process of MgH catalyzed with a specific metal oxide without an insight into the desorption process. Obviously, the absorption... 

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