Carbon-Containing Intermediates

Carbon-containing intermediates often arise from two types of bond cleavage  

Heterolytic (polar) cleavage. Both electrons go with one group, e.g. 

Homolytic (radical) cleavage. Each separating group takes one electron, e.g. 

Carbocations are positively charged ions containing a carbon atom having only six electrons in three bonds  

---

CH4, but there is about a monolayer of carbon-containing intermediate that leads to CO and CO2. The interpretation of this tracing experiment is straightforward because carbon does not exchange with anything on the surface. Such is not the case for oxygen a switch from to at 600°C with no methane produces and O2 in quantities much larger than... 

Thus, TOFchem will always be smaller (often significantly so) than TOFsite, except where the concentration of metal surface atoms equals exactly the concentration of sites. TOFitk, on the other hand, will always be larger unless the concentration of intermediates (carbon-containing intermediates in the case of methanation) is equal to the concentration of sites. The only possibility of TOFitk ever being smaller than TOFsite is when there is significant readsorption of the product. However, usually in SSITKA experiments, care is taken to minimize readsorption by experiment and/or extrapolation [14]. 

The reaction transient studies utilized mainly involve the switch from a CO/H2 mixture to either H2 or D2 alone (reduction of carbon species on the catalyst surface). Sometimes a short step of helium flush and/or a short step of CO/Hj is used between the switch. This serves to either remove the adsorbed CO (present in large quantities) from the catalyst surface or replace it by adsorbed CO to distinguish the products formed from adsorbed CO and from other carbon-containing intermediates. 

At the beginning of the reaction, the curve representing the chemical species mass addition matches well the TOC curve. This indicates that most of the species remaining in the liquid phase are determined and quantified. At reaction times beyond 5 hours the species mass addition (-I-) curve consistently lays below the TOC curve. Greater separation between the two curves can be observed with increasing reaction times. In the worst case scenario, this difference is close to 10% of the initial phenol concentration and can be the result of two contributing factors carbon-containing intermediate species... 

The intermittent plasma-assisted vacuum deposition technique has been found to introduce the effective electrocatalytic activity and stability for CO2 reduction into metal phthalocyanine thin films formed on a glassy carbon. The films properties are significantly influenced by the chemical state of the Aim. It has been suggested that the electrode process is determined by the surface chemical reaction involving adsorbed H and/or H+ and a carbon containing intermediate ". ... 

However, the conversion of water (H2O) and carbon dioxide (CO2) into carbohydrates (CgHijOg) involves numerous chemical reactions and carbon-containing intermediate compounds. By using CO2 that contains radioactive carbon-14, scientists have been able to follow the chemical path of CO2 through the various intermediate compounds. 

Previous syntheses of terminal alkynes from aldehydes employed Wittig methodology with phosphonium ylides and phosphonates. 6 7 The DuPont procedure circumvents the use of phosphorus compounds by using lithiated dichloromethane as the source of the terminal carbon. The intermediate lithioalkyne 4 can be quenched with water to provide the terminal alkyne or with various electrophiles, as in the present case, to yield propargylic alcohols, alkynylsilanes, or internal alkynes. Enantioenriched terminal alkynylcarbinols can also be prepared from allylic alcohols by Sharpless epoxidation and subsequent basic elimination of the derived chloro- or bromomethyl epoxide (eq 5). A related method entails Sharpless asymmetric dihydroxylation of an allylic chloride and base treatment of the acetonide derivative.8 In these approaches the product and starting material contain the same number of carbons. 

During steady-state isotopic transient kinetic analysis, the 12CO was switched to 13CO and the carbon-containing adsorbed and gas phase species were monitored in the IR as they exchanged from the 12C to the 13C label. Particular attention was made to those species that exchanged on a timescale similar to that of the exchange of the product C02, as that species could be a likely intermediate to the water-gas... 

The six or seven-membered cyclic ethers that comprise the Brevetoxin subunits could be prepared by Mo-catalyzed RCM (Eq. 42) [13]. It is noteworthy that the most successful substrates were those in which R, =H and R2=Me. The first metal-containing intermediate in that circumstance therefore is likely to be that in which there is an oxygen bound to the alkylidene carbon atom yet that alkyli-dene behaves in a ring-closing reaction in the expected manner. 

Surface Water. Aniline degraded in pond water containing sewage sludge to catechol, which then degrades to carbon dioxide. Intermediate compounds identified in minor degradative pathways include acetanilide, phenylhydroxylamine, as,cA-muconic acid, p ketoadipic acid, levulinic acid, and succinic acid (Lyons et al, 1984). 

The purpose of the present paper is to offer a contribute to the understanding of the mechanisms of these reactions by using an IR spectroscopic method and well-characterized "monolayer" type vanadia-titania (anatase) as the catalyst. We will focus our paper in particular on the following subjects i) the nature of the activation step of the methyl-aromatic hydrocarbon ii) the mechanism of formation of maleic anhydride as a by-product of o-xylene synthesis iii) the main routes of formation of carbon oxides upon methyl-aromatic oxidation and ammoxidation iv) the nature of the first N-containing intermediates in the ammoxidation routes. 

---