Ketones Experimental Procedure

The oxidation of trimethylsilylenol ethers under Wacker-type conditions gives rise to a,P-unsaturated ketones (Experimental Procedure below). This reaction was discovered by Saegusa and Ito and bears their names. The selectivity for the oxidation of unmodified ketones is somewhat lower. ... 

The following experimental procedure is suitable for ketones boiling above 175-200°. 

Another important synthetic method for the reduction of ketones and aldehydes to the corresponding methylene compounds is the Woljf-Kishner reduction. This reaction is carried out under basic conditions, and therefore can be applied for the reduction of acid-sensitive substrates it can thus be regarded as a complementary method. The experimental procedure for the Clemmensen reduction is simpler however for starting materials of high molecular weight the Wolff-Kishner reduction is more successful. 

Experimental Procedure 3.2.6. Alkylidenation of a Ketone 4-Methyl-1-phenyl-octa-1,3-diene [633]... 

This structural change is suppressed by the addition of tetrahydrothiophene (THT)19b. It prevents the formation of polymethylene zinc, i.e. (—CH2Zn—) . Without THT, a solution of 3 in THF yields polymethylene zinc at 60 °C. Monomeric bis(iodozincio)methane (3) is much more active for methylenation as compared to polymethylene zinc. As shown in Table 3 (entry 3), the addition of THT to the reaction mixture at 60 °C improved the yield of the alkene dramatically. Practically, however, its stinking property makes the experimental procedure in large scale uncomfortable. Fortunately, an ionic Uquid, l-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), plays the same role. Ionic liquid also stabilizes the monomeric structure of 3 even at 60 °C and maintains it during the reaction at the same temperature. The method can be applied to various ketones as shown in Scheme 14.4... 

V. Ketones / 134 Selectivity / 134 Stereochemistry / 135 Ether formation / 136 Experimental procedures / 136... 

III. Experimental Procedures / 406 Protection of ketones / 406 Protection of hydroxyl groups / 413... 

In the vast majority of cases, the equilibrium in Oppenauer oxidations is shifted to the right by employing an excess of oxidant. When aldehydes or ketones with a certain volatility are formed during Oppenauer oxidations, it is possible to shift the equilibrium by removing the product by distillation under reduced pressure, while oxidants with a low volatility, such as benzaldehyde, cinnamaldehyde or piperonal, are used.5 This experimental procedure, although very suitable for multigram scale reactions, is seldom employed because of the inconvenience of running a reaction while a distillation under vacuum is performed. 

The experimental procedure to be followed depends upon the products of hydrolysis. If the alcohol and aldehyde are both soluble in water, the reaction product is divided into two parts. One portion is used for the characterisation of the aldehyde by the preparation of a suitable derivative (e.g. the 2,4-dinitro-phenylhydrazone, semicarbazone or dimethone, see Aldehydes and ketones, Section 9.6.13, below). The other portion is employed for the preparation of a 3,5-dinitrobenzoate, etc. (see Alcohols and polyhydric alcohols, Section 9.6.4, p. 1241) it is advisable first to concentrate the alcohol by distillation or to attempt to salt out the alcohol by the addition of solid potassium carbonate. If one of the hydrolysis products is insoluble in the reaction mixture, it is separated and characterised. If both the aldehyde and the alcohol are insoluble, they are removed from the aqueous layer separation is generally most simply effected with sodium metabisulphite solution (compare Expt 5.82), but fractional distillation may sometimes be employed. 

Yen and co-workers [54] have reported an efficient one-pot procedure for the synthesis of 4,6-diaryl-2-pyridinones 3 based on a cyclocondensation reaction of iV-ethoxycarbonyl-methylpyridinium chloride or iV-carbamoylmethyl p3Tidinium chloride with an aromatic aldehyde and a substituted acetophenone. The MCR was performed under microwave irradiation (domestic oven) with NTUOAc/AcOH as the reaction medium. The nature of the substituents on the aromatic aldehyde and ketone seem to have little influence on the obtained yields. The highlights of this approach include a convenient and simple experimental procedure with easy product isolation (Scheme 3). 

The condensation of aldehydes and ketones with ethyl chloroacetate in the presence of sodium ethoxide or sodium amide produces a,/3-epoxy esters (Darzens). The scope, limitations, typical experimental procedures, and examples have been given. Briefly, aliphatic and aromatic ketones, and aromatic aldehydes react satisfactorily, whereas aliphatic aldehydes give poor yields. a-Halopropionic and a-halobutyric... 

The usual experimental procedure for carrying out reductions in the absence of an added proton donor entails the addition of a metal (Li, Na, K) to a solution of the substrate ketone in a mixture of NH3 and an ethereal cosolvent, usually ether or THF at the reflux temperature of liquid NH3. The metal is added until a permanent blue color is obtained and the reaction is stirred for 10 to 30 min. The excess Li is decomposed, traditionally with NH4CI or an alcohol however, sodium benzoate is probably superior. ... 

The metal-NHs reductions of carbonyl groups are exceedingly fast reactions for the reaction of acetone with an ammoniated electron the rate is 9 x 10 M" s". Although many, particularly older, published experimental procedures for the metal-NHs reduction of ketones employ prolonged reaction times with excess metal, these conditions are unnecessarily harsh. The reactions of carbonyl compounds with metals in NH3 are effectively instantaneous and by using short reaction times it appears that reduction of terminal alkenes and disubstituted alkynes can be avoided.In addition to the functional groups mentioned above, alcohols, amines and ethers, other than epoxides, are usually stable to reductions of aldehydes and ketones by dissolving metals. " ... 

Since its introduction early in this century, the deoxygenation of aldehydes and ketones to methyl or methylene derivatives, respectively, via base treatment of hydrazone intermediates (equation 1) has proven to be one of the most convenient and synthetically useful processes available for this important type of transformation. The reaction is termed the Wolff-Kishner reduction in recognition of the two original independent discoverers.However, the initial recipes introduced proved tedious and unreliable with many structural, especially hindered, examples. This led to substantial efforts devoted over the years to developing more convenient and successful experimental procedures, resulting in a number of improved and more reliable modifications which are most often utilized at present. More recently, modified procedures have been provided which utilize hydride reductions of p-toluenesulfonylhydrazone (to-sylhydrazone) derivatives and subsequent decomposition to release the hydrocarbon products under much milder and less basic conditions than those normally required for Wolff-Kishner reductions (equation 2). 

As in the previous cases changes in the e.m.f. of such a cell when MX is changed should be due to the changes in 02. The experimental procedure was the same as was used for measurements in di- >propyI ketone, and the results are tabulated below. 

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