Carbon carboxylate oxidation

In the endoplasmic reticulum of eukaryotic cells, the oxidation of the terminal carbon of a normal fatty acid—a process termed ch-oxidation—can lead to the synthesis of small amounts of dicarboxylic acids (Figure 24.27). Cytochrome P-450, a monooxygenase enzyme that requires NADPH as a coenzyme and uses O, as a substrate, places a hydroxyl group at the terminal carbon. Subsequent oxidation to a carboxyl group produces a dicarboxylic acid. Either end can form an ester linkage to CoA and be subjected to /3-oxidation, producing a... 

Figure 18-10 summarizes the successive oxidation products that can be obtained from alcohols. When the hydroxyl group, OH, is attached on an end carbon atom, an aldehyde and a carboxylic acid can be obtained through oxidation. When the hydroxyl group is on a carbon atom attached to two other carbon atoms, oxidation gives a ketone. Huge amounts of aldehydes and ketones are used industrially in a variety of chemical processes. Furthermore, these functional groups are important in chemical syntheses of medicines, dyes, plastics, and fabrics. 

Various nucleophiles other than methanol can be introduced onto the carbonyl carbon. Anodic oxidation of acylsilanes in the presence of allyl alcohol, 2-methyl-2-propanol, water, and methyl /V-methylcarbamate in dichlorometh-ane affords the corresponding esters, carboxylic acid, and amide derivatives (Scheme 24) [16]. Therefore, anodic oxidation provides a useful method for the synthesis of esters and amides under neutral conditions. 

Recently, acylsilanes have been utilized as useful intermediates in organic synthesis [57], For example, treatment of acylsilanes with the fluoride ion generates the corresponding acyl anions which react with electrophiles. On the other hand, by using the electrochemical method, acylsilanes serve as acyl cation equivalents because nucleophiles are introduced at the carbonyl carbon. Chemical oxidation of acylsilanes with hydrogen peroxide which affords the corresponding carboxylic acids has been reported [58], However, the anodic oxidation provides a versatile method for the introduction of various nucleophiles... 

Kolbe oxidation of carboxylate ions to radicals with loss of carbon dioxide (p. 312). The latter process gives highest yields of dimeric product at a platinum anode and only monomeric products from oxidation of the radical centre at a carbon anode. Oxidation of butadiene in methanol containing benzoic acid, at a smooth platinum anode, gives 45 % of the but-3-ene-l,4-diol diester [45]. 

In situ infrared study of catalytic CO oxidation over Au/Ti02 shows that the catalyst prepared from AuCls exhibits higher activity than those prepared from HAuC. The high activity of Au appears to be related to the presence of reduced and oxidized Au sites as well as carbonate/carboxylate intermediates during CO oxidation. Addition of H2O2 further promotes the oxidation reaction on Au/Ti02 catalysts. 

The reaction pathway, reactivity of the active sites, and the nature of adsorbed intermediates constitute the catalytic reaction mechanism. Our study has been focused on the investigation of the nature of adsorbed intermediates under reaction conditions. We report the results of in situ infrared study of CO and ethanol oxidation on Au/Ti02 catalysts. This study revealed the high activity of Au/Ti02 is related to the presence of reduced Au and oxidized Au sites which may promote the formation of carbonate/carboxylate intermediates during CO oxidation. 

The presence of various types of Au sites and carbonate/carboxylate species as well as variation in the OH intensity of Ti02 (not shown here) during the reaction suggests that CO oxidation over AuCb catalyst could follow the carboxylate mechanism which involves the reaction of adsorbed CO with OH to produce a carbonate/carboxylate species on Au cations and the decomposition of carboxylate to COz-iS, 10) Transient infrared study needs to be employed to further verily the role of carbonate/carboxylate species in the reaction pathway. (13)... 

The simplest and most generally useful synthetic method for metal diketonates is from the diketone and a metal such as a halide, hydroxide, oxide, sulfate, carbonate, carboxylate, etc. in a variety of solvents such as water, alcohol, carbon tetrachloride or neat diketone. Since many / -diketones are poorly soluble in water, use of an organic solvent or cosolvent may be helpful. Optionally, a base such as sodium carbonate, triethylamine or urea may be added. Addition of a base early in the reaction converts the diketone to its conjugate base, which usually has greater solubility in aqueous media.159 In some cases, metal halide complexes of the diketone form as intermediates, e.g. SnCl4(MeCOCH2COMe), which has been formulated as... 

The substance glucuronic acid can be considered to be glucose with carbon 6 oxidized to the carboxylic acid level. Glucuronic acid /3-glycosides are the metabolic fate of a number of obnoxious compounds found in plants. Draw the structure of glucuronic acid. From its name can you guess where it was first found ... 

When fats or oils are exposed to air, they react with the oxygen or water vapor to form short-chain carboxylic acids. The short-chain acids are volatile and have unpleasant smells and tastes. For example, the strong smell and sour taste of vinegar are due to acetic acid, a two-carbon carboxylic acid. The oxidation process is called rancidification and can make foods unpalatable. The characteristic smell of rancid butter is due to the presence of butyric acid (a four-carbon acid). (Rancidity can also be the result of the hydrolysis of fats or oils.)... 

Although the fatty acid oxidation scheme works neatly for even-numbered chain lengths, it can t work completely for fatty acids that contain an odd number of carbons. P-oxidation of these compounds leads to propionyl-CoA and acetyl-CoA, rather than to two acetyl-CoA at the final step. The propionyl-CoA is not a substrate for the TCA cycle or other simple pathways. Propionyl-CoA undergoes a carboxylation reaction to form methylmalonyl-CoA. This reaction requires biotin as a cofactor, and is similar to an essential step in fatty acid biosynthesis. Methylmalonyl-CoA is then isomerized by an epimerase and then by methylmalonyl-CoA mutase—an enzyme that uses Vitamin Bi2 as a cofactor—to form succinyl-CoA, which is a TCA-cycle intermediate. 

Specifically, D-glucose < maltose < maltotriose < amylose < starch < amylo-pectin < cellulose (Greenwood, 1967). Trends indicated are that thermochemical stability increases with the DP, branching, and 1,4-fi bonding. Chemical bonds other than 1,4-a and 1,4-(3 introduce heat and acid instability. Either of these two bonds is less easily depolymerized when the sixth pyranose carbon is oxidized to the carboxyl group rather than esterified for this reason, low-methoxyl pectin is more stable than high-methoxyl pectin. 

Carboxylate complexes are often synthesized by refluxing the acid with the metal salts (such as carbonate, sulfate, oxide, etc.), or by reaction of the sodium or silver salt of the acid with the metal halide. Insertion of CO2 into a-bonded organotransition metal species has also been used to generate carboxylate complexes, as has exchange reactions with metal alkoxides (see Section 3.3). 

Experiments with C- and H-acetate showed that the methyl group of acetate is the major precursor of methane and the carboxyl-carbon is oxidized to CO2, providing electrons for reduction of the methyl-carbon to CH4 [7,231,232]. However, Krzyeki et al. [233] showed that 14% of the methane produced by whole cells of an acetate-adapted strain of M. barkeri originated from the carboxyl-carbon, and an equivalent amount of CO2 came from methyl-group oxidation the reduction of carboxyl-carbon to methane has also been observed in extracts [7,234]. 

Metal oxides are usually prepared by calcinations of suitable precursors such as hydroxides, nitrates, carbonates, carboxylates, etc. This process usually gives oxides with pseudomorphs of the starting materials. When large amounts of thermal energy are applied for the decomposition of the precursors, it facilities sintering of the product particles and therefore aggregated particles are obtained. When mixed oxides such as spinel, perovskite, and pyrochlore are the desired products, heat treatment at higher temperatures is required. 

The two primary alcohol groups, viz., the two end carbon groups, become oxidized to carboxyl. The intermediate secondary alcohol groups become completely oxidized to carbon di-oxide and water and are thus destroyed so that the two end groups yielding the two carboxyls become directly linked as oxalic acid. As the end carbon groups are the only ones capable of existence as primary alcohol groups and therefore able to yield carboxyl on oxidation, the reaction as above written is in accordance with both the facts and the possibilities. 

As mentioned in Section IV.A.2, Leng and Pinto [3861 specifically addressed the effect of surface properties on the oxic and anoxic adsorption behavior of phenol, benzoic acid, and o-cresol. Commercial carbons were oxidized in air at 350°C, which is known [37] to introduce both CO- and C02-yielding surface groups nevertheless, from FTIR spectra, they concluded that the main differences are due to relative quantities of surface carboxylic groups. Presumably because the experiments were performed at pFl = 7.0, i.e., below the pK, of phenol, their explanation for the decrease in uptake with increasing surface oxygen was not the electrostatic repulsion but increased water cluster formation as well as increased removal of n electrons from the basal planes [450,674], which results in weaker dispersion interactions with phenol. ... 

The oxidation of a methyl ketone to a carboxylic acid with one less carbon by oxidants other than hypohalites is exemplified by the oxidation of 2-acetylfluorene with sodium dichromate. In addition to the methyl keto group, the methylene group is also oxidized (equation 432) [626]. 

Geraniol, CioHjgO, a terpene found in rose oil, adds two moles of bromine to form a tetrabromide, CioH gOBr4. It can be oxidized to a ten-carbon aldehyde or to a ten-carbon carboxylic acid. Upon vigorous oxidation, geraniol yields ... 

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