Carboxylation, lactones

Gibberellin A5 (C H Os) has a melting point of 260-61° and forms a methyl ester (m.p. 190-91°). The infrared spectra of Nujol mulls of the acid and ester (see Table II) show the presence of alcoholic hydroxyl, hydroxyl of carboxylic acid, unconjugated five-ring lactone, carboxyl (or ester) carbonyl, exocyclic methylene group, and a cis-disubstituted double bond. Catalytic hydrogenation of the methyl ester confirmed the presence of two double bonds. 

The reactions contributing to this oxidation current are the formation of surface oxides on the carbon (quinones, lactones, carboxylic acids, etc.) and the evolution of carbon dioxide. Binder et al.51 had previously examined the oxidation of numerous carbons in KOH, H2S04, and HjP04 but not at temperatures as high as those in the work of Kinoshita and Bett. 

Trialkyloxonium fluoroborates give better yields of lactim ethers than other alkylating agents because of the selectivity of these reagents in the O-alkylation of lactams. This was borne out by Meerwein at al.,42 who arranged carbonyl compounds according to their capacity to undergo alkylation with oxonium salts as follows lactams > acyclic amides > lactones > carboxylic esters > ketones > aldehydes. 

The sulfmylation of esters, - lactones, carboxylic acids, > amides and lactams may be effected by reacticm of the corresptHiding lithium enolates in THF at -78 to 0 C with dimethyl or difdie-nyl disulfides, or, less conunmily, with methyl or fdienyl sulfmyl halides. The enolates of ketones, however, are insufficioitly nucleq diilic to react with dialkyl sulfides unless HMPA is added to the re-acticm mixture, although they do react smoothly with diaryl sulfides. This difference allows the selective sulfenylation of esters in the presence of ketones (entry 5, Table 3). ... 

NaBHi is a much milder reducing agent than LiAlH,. In hydroxylic solvents it reduces aldehydes and ketones rapidly at 25° but is essentially inert to other functional groups epoxides, esters, lactones, carboxylic acids and salts, nitrile and nitro groups. Acid chlorides are reduced rapidly in diglyme or dioxane. 

Sodium borohydride is a widely used mild and selective reducing agent. It selectively reduces an aldehyde or ketone in the presence of esters, lactones, carboxylic acids, and amides in methanol or THF at room temperature. Reviews (a) Seyden-Penne, J. 

Boehm and Johnson Matthey titrations. Both titrations give information on the acidic or basic character. The procedures are described in [13] and [14]. Boehm method classifies the surface acidic sites in three types (called phenolic, lactonic, carboxylic), by growing strength of acidity. However, this arbitrary classification fails to attribute one surface acidic group to one type of acidity. Moreover, this method does not give very accurate results with solids containing few acidic sites. Nevertheless, it appears for our active carbon that "phenolic" sites are a majority. The amount of each type of acidic sites does not change very much with the nitric treatment. 

Treatment of dehydrooxoheteratisine (CD) with potassium tert-butoxide in feri-butanol leads to the y-lactone carboxylic acid, characterized as its methyl ester (CDXIV) [1787 cm i, (y-lactone), 1748 cm (cyclopentanone), 1728 cm i (C02Me, 1648 cm i (S-lactam)]. Its formation by cleavage of the initial retroaldol product (CDXII) to a S-lactone carboxylic acid (CDXIII) and subsequent isomerization to the y-lactone provides decisive proof for location of the tertiary hydroxyl at a position j8 to both the cyclopentanone and S-lactone carbonyls and four carbons removed from the S-lactone ether oxygen. 

Reduction of anhydrides to y-lactones. Carboxylic acid anhydrides are reduced by homogeneous hydrogenation catalyzed by this ruthenium complex... 

On treatment with hot aqueous alkali, only hydrolysis of the lactone ring occurs. However, on treatment of 19-oxodehydroheteratisine (24) with potassium t-butoxide in t-butyl alcohol, a y-lactone carboxylic acid (28) was isolated. This product may be formed as indicated in the Scheme. The rearrangement to (28)... 

C7H5O2, Mr 122.12, yellow cryst., mp. 69 °C. A widely distributed component of the defensive secretions of insects and millipedes. In some species of beetles the repellent activity is enhanced by solvents (hydrocarbons, lactones, carboxylic esters) which facilitate penetration of M. through the predator s cuticle. For biosynthesis, see ethyl-1,4-benzoquinone. 

C17H30O4 Lactone carboxylic acid from Lecanora rupicola... 

Q1H3804 Lactone carboxylic acid from Cladonia impexa... 

However, as pointed outby Lacoste and coworkers [14,15], the reactions expressed above and as Equations 6.1-6.9 do not explain polyethylene backbone scission or the formation of more complex decomposition products such as esters, lactones, carboxylic acids and xmsaturation [16-18]. 

Acetoxylichesterinic acid (neuropogolic acid) (29), 19-acetoxy-protolichesterinic acid (30), (-)-allopertusaric acid (31) and (-)-dihydropertusaric acid (32) are y-lactone carboxylic acids with an oxygen function in the side chain from Neuropogon trachycarpus (323)... 

Electrochemical corrosion of carbon supports was widely studied in the context of phosphoric acid fuel cell development (Antonucci et al. 1988 Kinoshita 1988), but recently also the low-temperature fuel cell community paid more attention to this process (Kangasniemi et al. 2004 Roen et al. 2004). Carbon corrosion in fuel cell cathodes in the form of surface oxidation leads to functionalization of the carbon surface (e.g., quinones, lactones, carboxylic acids, etc.), with a concomitant change in the surface properties, which clearly results in changes of the hydrophobicity of the catalyst layer. Additionally, and even more severe, total oxidation of the carbon with the overall reaction... 

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