Carbon oxidation level

Considering the various alkanes shown below, one sees that alkanes can have several different oxidation levels for carbon. Oxidation levels can range from —4 for methane and —3 for the carbon atom of methyl groups all the way to 0 for the quaternary carbon of neopentane. In spite of the several oxidation levels possible in alkanes, the functional group approach tells us that all are saturated alkanes and thus have the same functional equivalency and similar reactivity patterns. 

For alkenes, several carbon oxidation levels are again possible. Furthermore, both carbon atoms must be considered as part of the same alkene functional group. While the total oxidation level can go from —4 for ethylene (as the sum of the oxidation level of both carbon atoms in the functional group) to 0 for a tetrasub-stituted alkene, we again recognize that all are of the same functional class. 

If the synthesis gas contains traces of carbon oxides, ammonium carbamate will form upon mixing with the ammonia in the recirculating gas from the synthesis loop. The carbamate will clog and/or corrode downstream equipment. To avoid this condition, consider controlling the carbon oxides level in fresh makeup gas at less than 5 ppm88. 

Dehydration. Use of molecular sieve driers for final clean-up of the carbon oxides and water in the synthesis gas to less than 1 ppm levels has gained prominence in low energy ammonia plant designs. The sieves are usually located at the interstage of the synthesis gas compressor to reduce volume requirements. The purified make-up gas can then be combined with the recycle and routed direcdy to the converter. 

Sulfoxides are compounds that contain a sulfinyl group covalendy bonded at the sulfur atom to two carbon atoms. They have the general formula RS(0)R, ArS(0)Ar, and ArS(0)R, where Ar and Ar = aryl. Sulfoxides represent an intermediate oxidation level between sulfides and sulfones. The naturally occurring sulfoxides often are accompanied by the corresponding sulfides or sulfones. The only commercially important sulfoxide is the simplest member, dimethyl sulfoxide [67-68-5] (DMSO) or sulfinylbismethane. 

Catalytic Pyrolysis. This should not be confused with fluid catalytic cracking, which is used in petroleum refining (see Catalysts, regeneration). Catalytic pyrolysis is aimed at producing primarily ethylene. There are many patents and research articles covering the last 20 years (84—89). Catalytic research until 1988 has been summarized (86). Almost all catalysts produce higher amounts of CO and CO2 than normally obtained with conventional pyrolysis. This indicates that the water gas reaction is also very active with these catalysts, and usually this leads to some deterioration of the olefin yield. Significant amounts of coke have been found in these catalysts, and thus there is a further reduction in olefin yield with on-stream time. Most of these catalysts are based on low surface area alumina catalysts (86). A notable exception is the catalyst developed in the former USSR (89). This catalyst primarily contains vanadium as the active material on pumice (89), and is claimed to produce low levels of carbon oxides. 

Mechanistic aspects of the action of folate-requiring enzymes involve one-carbon unit transfer at the oxidation level of formaldehyde, formate and methyl (78ACR314, 8OMI2I6OO) and are exemplified in pyrimidine and purine biosynthesis. A more complex mechanism has to be suggested for the methyl transfer from 5-methyl-THF (322) to homocysteine, since this transmethylation reaction is cobalamine-dependent to form methionine in E. coli. 

As shown in Scheme 2, two heteroatom-carbon bonds are constructed in such a way that one component provides both heteroatoms for the resultant heterocycle. By variation of X and Z entry is readily obtained into thiazoles, oxazoles, imidazoles, etc. and by the use of the appropriate oxidation level in the carbonyl-containing component, further oxidized derivatives of these ring systems result. These processes are analogous to those utilized in the formation of five-membered heterocycles containing one heteroatom, involving cyclocondensation utilizing enols, enamines, etc. 

The role of the 1,1-bielectrophile in ring closures of this type is to provide a one-carbon unit (or heteroatbm) to close the cycle. Thus, the synthesis of the four-atom precursor with two nucleophilic centers 1,4 to each other is an appreciable challenge, especially to obtain a heterocycle at the desired oxidation level. The examples below illustrate the way this approach to synthesis may be gainfully utilized. 

The iron-carbon solid alloy which results from the solidification of non blastfurnace metal is saturated with carbon at the metal-slag temperature of about 2000 K, which is subsequendy refined by the oxidation of carbon to produce steel containing less than 1 wt% carbon, die level depending on the application. The first solid phases to separate from liquid steel at the eutectic temperature, 1408 K, are the (f.c.c) y-phase Austenite together with cementite, Fe3C, which has an orthorhombic sttiicture, and not die dieniiodynamically stable carbon phase which is to be expected from die equilibrium diagram. Cementite is thermodynamically unstable with respect to decomposition to h on and carbon from room temperature up to 1130 K... 

Folic acid derivatives (folates) are acceptors and donors of one-carbon units for all oxidation levels of carbon except that of CO2 (where biotin is the relevant carrier). The active coenzyme form of folic acid is tetrahydrofolate (THF). THF is formed via two successive reductions of folate by dihydrofolate reductase (Figure 18.35). One-carbon units in three different oxidation states may be bound to tetrahydrofolate at the and/or nitrogens (Table 18.6). These one-carbon units... 

Oxidation Number Oxidation Level One-Carbon Form Tetrahydrofolate Form... 

The UV and IR spectra eliminate structures with a CN double bond. The isomerism of nitrones and oxaziranes thus cannot be a result of CIS or traris arrangement of substituents about a double bond. The carbon atoms of an oxazirane are still at the oxidation level of the carbonyl compound used in its syntheses. By acid hydrolysis, for example, 2-terf-butyl-3-phenyloxazirane (9) can be split into benzaldehyde and tert-butylhydroxylamine fEq. (8)]. ... 

A list of compounds of increasing oxidation level is shown in Figure 10.5. AJkanes are at the lowest oxidation level because they have the maximum possible number of C-H bonds per carbon, and CO2 is at the highest level because it has the maximum possible number of C—O bonds per carbon. Any reaction that converts a compound from a lower level to a higher level is an oxidation, any reaction that converts a compound from a higher level to a lower level is a reduction, and any reaction that doesn t change the level is neither an oxidation nor a reduction. 

Worked Example 10.2 shows how to compare the oxidation levels of different compounds with the same number of carbon atoms. 

Compounds that have the same number of carbon atoms can be compared by adding the number of C-O, C-N, and C-X bonds in each and then subtracting the number of C—H bonds. The larger the resultant value, the higher the oxidation level. 

Sophorolipid is a glycolipid, ie it is composed of carbohydrate and lipid. It therefore contains moieties of widely different oxidation levels and its synthesis from single demand carbon sources has a high ATP demand. However, the demand for ATP is reduced if a mixture of glucose and C-18 alkane is used. If glucose and fatty add is used the ATP demand is reduced further and relatively high spedfic production rates can be achieved. 

Furans occur widely in nature and many are important commercially. Thus alcohol (29) is used in various insecticides. The carbon atoms. joined to the ring oxygen atom are at the carbonyl oxidation level so that (29) can be made by acid-catalysed cyclisation of (30). Analysis... 

In contrast to the transition metals, where there is often a change in oxidation level at the metal during the reaction, there is usually no change in oxidation level for boron, silicon, and tin compounds. The synthetically important reactions of these three groups of compounds involve transfer of a carbon substituent with one (radical equivalent) or two (carbanion equivalent) electrons to a reactive carbon center. Here we focus on the nonradical reactions and deal with radical reactions in Chapter 10. We have already introduced one important aspect of boron and tin chemistry in the transmetallation reactions involved in Pd-catalyzed cross-coupling reactions, discussed... 

Scheme 12.22 provides some examples of the oxidation of aromatic alkyl substituents to carboxylic acid groups. Entries 1 to 3 are typical oxidations of aromatic methyl groups to carboxylic acids. Entries 4 and 5 bring the carbon adjacent to the aromatic ring to the carbonyl oxidation level. 

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