Ketone splitting

Keratin, 5, 39 Ketene, 4, 3g 8, 124 Ketone hydrolysis, 7, 60 Ketone-splitting of acetoacetic ester, 7, 60... 

A methylene group between the oxadiazole ring and a carboxyl group acts like a malonic acid with respect to ease of loss of the carboxyl group. Likewise the acetyl group from an acetonyl side chain at C-5 is lost in basic solution, analogous to the ketone split in a fi-keto ester or / -diketone. This was recognized in the early work on oxadiazoles by Tiemann,48 Wiese,49 Richter,47 and Schubart.50... 

Problem 15.—Write the reactions for (a) the ketone splitting of aceto-acetic ester, and (/>) the acid splitting of the same ester. 

Sodium me/aperiodate (NalO ) in cold aqueous solution readily oxidises 1,2-diols with splitting of the molecule and the consequent formation of aldehydes or ketones thus ethylene glycol gives formaldehyde and pinacol gives acetone. In the case of a 1,2,3-triol, the central carbon atom of the triol... 

Although lead tetraacetate can attack many polar and nonpolar functions in the steroid molecule, its greatest reactivity is towards vicinal diols. These diols are generally cleaved so rapidly under stoichiometric conditions that other alcohol functions in the molecule need not be protected. Thus lead tetraacetate in acetic acid at room temperature splits the 17a,20-diol group in (9) to yield the 17-ketone (10), the allylic A -3jS-alcohol remaining intact during this oxidation. Since lead tetraacetate is solublein many anhydrous... 

The formation of ethyl acetoacetate occurs, according- to Claisen, in four steps. The presence of a small quantity of alcohol gives lise to sodium ethylate, which forms an additive compound with ethyl acetate. The latter unites with a second molecule of ethyl acetate yielding the sodium salt of ethyl acetoacetate, and splitting off alcohol, which reacts with fresh metallic sodium. The sodium salt on acidifying passes into the tautomeric (ketonic) form of acetoacetic ester. 

The salts of some enamines crystallize as hydrates. In such cases it is possible that they are derived from either the tautomeric carbinolamine or the amino ketone forms. Amino ketone salts (93) ( = 5, 11) can serve as examples. The proton resonance spectra of 93 show that these salts exist in the open-chain forms in trifluoroacetic acid solution, rather than in the ring-closed forms (94, n = 5, 11). The spectrum of the 6-methylamino-l-phenylhexanone cation shows a multiplet at about 2.15 ppm for phenyl, a triplet for the N-methyl centered at 7.0 ppm and overlapped by signals for the methylene protons at about 8.2 ppm. The spectrum of 93 ( = 11) was similar. These assignments were confirmed by determination of the spectrum in deuterium oxide. Here the N-methyl group of 93 showed a sharp singlet at about 7.4 ppm since the splitting in —NDjMe was much reduced from that of the undeuterated compound. 

If the original aldehyde or ketone has an a hydrogen, it is possible for water to split out in that way and enol ethers can be prepared in this manner ... 

In extrahepatic tissues, acetoacetate is activated to acetoacetyl-CoA by succinyl-CoA-acetoacetate CoA transferase. CoA is transferred from succinyl-CoA to form acetoacetyl-CoA (Figure 22-8). The acetoacetyl-CoA is split to acetyl-CoA by thiolase and oxidized in the citric acid cycle. If the blood level is raised, oxidation of ketone bodies increases until, at a concentration of approximately 12 mmol/L, they saturate the oxidative machinery. When this occurs, a large proportion of the oxygen consumption may be accounted for by the oxidation of ketone bodies. 

Where the + — terms refer to / an type excitations and the to a n - v type transition. These absorptions occur at longer wavelengths than the related model compounds (benzene and dimethylamine for Michler s ketone), have a high intensity, emax 104 liter/mole-cm, a small singlet-triplet splitting, and undergo a red shift of the absorption on going to a more polar solvent. 

First the interaction of selected tetramethylpiperidine (TMP) derivatives with radicals arising from Norrish-type I cleavage of diisopropyl ketone under oxygen was studied. These species are most probably the isopropyl peroxy and isobutyryl peroxy radicals immediately formed after a-splitting of diisopropyl ketone and subsequent addition of O2 to the initially generated radicals. Product analysis and kinetic studies showed that the investigated TMP derivatives exercise a marked controlling influence over the nature of the products formed in the photooxidative process. The results obtained point to an interaction between TMP derivatives and especially the isobutyryl peroxy radical. 

Ketone bodies are formed in the liver mitochondria by the condensation of three acetyl-CoA units. The mechanism of ketone body formation is one of those pathways that doesn t look like a very good way to do things. Two acetyl-CoAs are condensed to form acetoacetyl-CoA. We could have had an enzyme that just hydrolyzed the acetoacetyl-CoA directly to acetoacetate, but no, it s got to be done in a more complicated fashion. The acetoacetyl-CoA is condensed with another acetyl-CoA to give hydroxymethylglutaryl-CoA (HMG-CoA). This is then split by HMG-CoA lyase to acetyl-CoA and acetoacetate. The hydroxybutyrate arises from acetoacetate by reduction. The overall sum of ketone body formation is the generation of acetoacetate (or hydroxybutyrate) and the freeing-up of the 2 CoAs that were trapped as acetyl-CoA. 

In turn, the formed alkoxyl radical splits into ketone and the alkyl radical. 

The acyl radicals formed in ketone photolysis are excited and, therefore, rapidly splits into CO and alkyl radical (in the gas phase). Since aldehydes and ketones are products of oxidation, continuous hydrocarbon photooxidation is an autoaccelerated process. 

The formed hydroperoxide reacts with the carbonyl group. This interaction influences the kinetics of the oxidation of ketones due to the fast splitting of the formed peroxide to free radicals. 

Another probable reaction of homolytic decomposition of ester hydroperoxide is the intramolecular interaction of the hydroperoxide group with the carbonyl group of ester with the formation of labile hydroxyperoxide succeeded the splitting of the weak O—O bond (see decomposition of hydroperoxides in oxidized ketones in Chapter 8). 

Whereas the first reaction, which results in the synthesis of ketones, is much used because of the ease with which it usually proceeds, the introduction of alkyl groups proves much less satisfactory since, in the first place, the substitution goes further and, in the second, the alkyl groups may at the same time be partially split off again. The method of Fittig is usually to be preferred in this case. 

Fig. 11. Separation of a mixture of organic solvents using 50 cm long 100 (left) and 320 pm i.d. (right) monolithic capillary columns (Reprinted with permission from [112]. Copyright 2000 Wiley-VCH). Conditions temperature gradient 120 - 300 °C, 20 °C/min, inlet pressure 0.55 MPa, split injection. Peaks methanol (1), ethanol (2), acetonitrile (3), acetone (4), 1-propanol (5), methyl ethyl ketone (6), 1-butanol (7),toluene (8), ethylbenzene (9),propylbenzene (10),butyl-benzene (11)...

Among the major products in the olefin reactions are aldehydes and ketones. Such results correspond to the splitting of the double bond and the addition of an oxygen atom to one end of the olefin. 

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