Higher aliphatic ketones

This is a general method for the preparation of higher aliphatic ketones, it has been found suitable for the preparation of ketones from fatty acids containing 12 to 20 carbon atoms. 

We found also that carbomethoxymethylene triphenylarsorane reacted with a series of aliphatic ketones under very mild conditions (47). For example, with acetone it reacted at room temperature, whereas with higher aliphatic ketones at their refluxing temperature (boiling point of the aliphatic ketones). The yields of the a,/3-unsaturated esters were moderate. 

Methyl Ethyl Ketone. Methyl ethyl ketone (MEK) (2-butanone), CH3COCH2CH3, is the next higher aliphatic ketone homologue to acetone, and third to acetone and cyclohexanone as the most important commercially produced ketone. 

Oxidation of iso-propyl methyl ketone at 70—130° C produces methanol, acetone, acetic acid and isopropyl acetate [128], Koslenkova et al. [129] have studied the oxidation of higher aliphatic ketones (Ctl C13). 

Higher Aliphatic Ketones. The reactions of the higher aliphatic ketones ftdth formaldehyde under alkaline conditions are less complicated than those obtained with acetone and may, in general, be more readily controlled. 

Section IV, 135,5), but are unaflFected by the dimedone reagent (Section 111,70, 2). The general reactions are similar to those already given under Aliphatic Ketones (Section 111,74). Owing to their higher molecular weight, such derivatives as oximes and phenylhydrazones are frequently quite satisfactory. 

The ruthenium complex of 49 was chosen due to its easy accessibility and because preliminary experiments had shown that simple non-prochiral aliphatic ketones such as 4-methyl-cyclohexanone are quantitatively reduced. This positive outcome encouraged us to test various prochiral aliphatic ketones 64-75. The results using standard conditions are summarized in Fig. 23. Most substrates could be reduced in good yields and the enantioselectivities of six alcoholic products are higher than 85%, 2-decanone 67 and geranylacetone 68 showed even ee s of 95%, demonstrating that the concept works well not only for aromatic ketones. 

Figure 1.25 exemplifies the strucmres of certain efficient precatalysts for asymmetric transfer hydrogenation of ketones. Precatalysts C1-C3 use the NH effect described above. A turnover frequency, defined as moles of product per mol of catalyst per hour, of 30,000 h is achieved by using of C2 and an alkaline base in 2-propanol. A Rh complex C3 is an isolobal to the corresponding arene-Ru complex (see Figure 1.23). The Ru complexes C4 " and C5 without NH group in ligand catalyze the reaction by different mechanisms. A higher than 90% optical yield is achieved by using C5 in reduction of certain aliphatic ketones.

In Ketazine processes, hydrazine derivatives are obtained first. Ammonia is oxidized by chlorine or chloramines in the presence of aliphatic ketones. The products are hydrazones and isohydrazones. These are converted to ketazines with excess ketone. The ketazines or the intermediate hydrazine derivatives may be hydrolyzed to hydrazine after all the oxidizing reactants, such as CI2, NaOCl, or NH2CI are consumed. Unlike hydrazine, ketazines do not readily oxidize, and, therefore, the product yield is higher in these processes. 

Cyclic ketones react faster than the aliphatic ketones in the order cyclo-pentanone > cyclohexanone > higher-membered cyclic ketones. a-Substi-tuted ketones give the less substituted enamines, which in turn could be alkylated to put a substituent on this position of the ketone [51] (Eq. 11). 

Aliphatic ketones react more slowly than aldehydes with amines to form imines (see Table VII). Higher reaction temperatures, longer reaction times, and the removal of water aid in giving high yields of imines (80-95 %). Steric-ally hindered ketones react slowly. Methyl ketones require mild acid catalyst and are more prone to aldol condensation by-products than are methylene ketones [3]. 

Aromatic ketones react even more slowly than aliphatic ketones and require strong acid catalysts and higher temperatures to effect the isolation of good yields of imine. Acetophenone reacts with aniline at reflux temperature in the presence of aniline hydrochloride to give the imine [9] (see Table VIII). 

In the C4 and higher aldehydes, McLafferty cleavage of the a,j3 C—C bond occurs to give a major peak at m/z 44, 58, or 72,. .., depending on the a substituents. This is the resonance-stabilized ion formed through the cyclic transition state as shown above for aliphatic ketones (R = H). 

The versatility of 5-nitrosopyrimidines in pteridine syntheses was noticed by Pachter (64MI21603) during modification of the Timmis condensation between (262) and benzyl methyl ketone simple condensation leads to 4-amino-7-methyl-2,6-diphenylpteridine (264) but in the presence of cyanide ion 4,7-diamino-2,6-diphenylpteridine (265) is formed (equation 90). The mechanism of this reaction is still uncertain (63JOC1187) it may involve an oxidation of an intermediate hydroxylamine derivative, nitrone formation similar to the Krohnke reaction, or nucleophilic addition of the cyanide ion to the Schiff s base function (266) followed by cyclization to a 7-amino-5,6-dihydropteridine derivative (267), oxidation to a quinonoid-type product (268) and loss of the acyl group (equation 91). Extension of these principles to a-aryl- and a-alkyl-acetoacetonitriles omits the oxidation step and gives higher yields, and forms 6-alkyl-7-aminopteridines, which cannot be obtained directly from simple aliphatic ketones. 

Diamines grafted on MCM-41 revealed higher base catalytic activity because they were able to catalyse condensation between benzaldehyde and ethyl malonate which is usually less active than ethyl cyanoacetate. The catalytic activity was also high with less reactive carbonyl derivatives, such as cyclic or aliphatic ketones. Moreover, aldolization between acetone and aromatic aldehyde was also possible.11721... 

According to these, for purely aliphatic ketones the highest enantioselectivities are achieved for methyl ketones with a second, branched-chained alkyl substituent (84-94% ee). The value of 75 % ee obtained with the straight-chain hexan-2-one is, to the best of our knowledge, in any case better than anything achieved to date with nonenzymatic systems and homogeneous catalysis. Higher selectivities have been reported for reductions with stoichiometric amounts of chiral borohydrides (e.g. 80 % ee for the reduction of octan-2-one) [20]. 

Activated Charcoal Most nonpolar and moderately polar organic vapors alkanes, alkenes, chlorinated aliphatics, ketones, esters, ethers, higher alcohols... 

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