Ketones, p-

These coloration changes are given by most compounds which possess the -CHj-CO— group for further examples, see Tests 4 (a) and (b) for Ketones, p. 344. 

Note, (a) Aqueous solutions of formaldehyde and acetaldehyde give these addition products, which are so soluble that they rarely separate this reaction is therefore an unsatisfactory test for these aldehydes. (6) These addition products are also formed by ketones (p. 345). 

Sulphuric add test. Heat 0 5 g. of citric acid or a citrate with 1 ml. of H2SO4 CO and COg are evolved and the mixture turns yellow, but does not char. Acetone dicarboxylic acid, OC(CH2COOH)g, is also formed, and is tested for after heating the mixture for 1 minute cool, add a few ml. of water and make alkaline with NaOH solution. Add a few ml. of a freshly prepared solution of sodium nitroprusside and note the intense red coloration (see Test 4 a) for ketones, p. 346). 

Acetone-Alkali coloration. Dissob-e a few crystals in i-2 ml. of acetone and add a few drops of aqueous XaOlI solution. A deep violet coloration is produced, and is turned red by acetrc acid but destroyed by mineral acids (see Test 4(6) for Ketones, p. 346, and also Test 2(0) p. 274). 

If used for the preparation of methyl benzyl ketone (p. 54) the product should not be dried. 

Other carbanionic groups, such as acetylide ions, and ions derived from a-methylpyridines have also been used as nucleophiles. A particularly useful nucleophile is the methylsulfinyl carbanion (CH3SOCHJ), the conjugate base of DMSO, since the P-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 549). The methylsulfonyl carbanion (CH3SO2CH2 ), the conjugate base of dimethyl sulfone, behaves similarly, and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF acylate 1,3-dithianes (see 10-10. )2008 Qxj(jatjye hydrolysis with NBS or NCS, a-keto aldehydes or a-... 

Certain ketoximes can be converted to nitriles by the action of proton or Lewis acids. Among these are oximes of a-diketones (illustrated above), a-keto acids, a-dialkylamino ketones, a-hydroxy ketones, p-keto ethers, and similar compounds. These are fragmentation reactions, analogous to 17-25 and 17-26. For example, ot-dialkylamino ketoximes also give amines and aldehydes or ketones besides nitriles. 

Ketone p-toluenesulfonylhydrazones are converted to alkenes on treatment with strong bases such as an alkyllithium or lithium dialkylamide.286 Known as the Shapiro reaction,2 7 this proceeds through the anion of a vinyldiimide, which decomposes to a vinyllithium reagent. Treatment of this intermediate with a proton source gives the alkene. 

Dibenzyl ketone p,p -Dimethyldibenzyl ketone p-Methoxydibenzyl ketone p.p -Dicyanodi benzyl ketone Dibenzyl ketone... 

Evidence that carbanion intermediates, e.g. (44), are involved is provided by carrying out the decarboxylation in the presence of bromine. This is without effect on the overall rate of the reaction but the end-product is now Me2CBrN02 rather than Me2CHN02— under conditions where neither Me2C(NO2)CO20 nor Me2CHN02 undergoes bromination. The bromo product (45) arises from rapid attack of Br2 on the carbanion intermediate (44), which is thereby trapped (cf. the base-catalysed bromination of ketones, p. 295) ... 

Primary nitro compounds are good precursors for preparing nitriles and nitrile oxides (Eq. 6.31). The conversion of nitro compounds into nitrile oxides affords an important tool for the synthesis of complex natural products. Nitrile oxides are reactive 1,3-dipoles that form isoxazolines or isoxazoles by the reaction with alkenes or alky nes, respectively. The products are also important precursors for various substrates such as P-amino alcohols, P-hydroxy ketones, P-hydroxy nitriles, and P-hydroxy acids (Scheme 6.3). Many good reviews concerning nitrile oxides in organic synthesis exist some of them are listed here.50-56 Applications of organic synthesis using nitrile oxides are discussed in Section 8.2.2. 

Ketone p-toluenesulphonyl hydrazones can be converted to alkenes on treatment with strong bases such as alkyl lithium or lithium dialkylamides. This reaction is known as the Shapiro reaction68. When w./i-LinsaUi rated ketones are the substrates, the products are dienes. This reaction is generally applied to the generation of dienes in cyclic systems where stereochemistry of the double bond is fixed. A few examples where dienes have been generated by the Shapiro reaction have been gathered in Table 669. 

The stereochemical outcome of the Wittig reaction can depend on the presence or absence of lithium salts. This may be due to a betaine intermediate stabilized by lithium cation. A stable adduct of this type has now been observed during a Wittig reaction. When Ph3P=CH2 is treated with 2,2 -dipyridyl ketone, P NMR shows the formation of an oxaphosphetane (72) and addition of lithium bromide gives the chelation-stabilized betaine lithium adduct (73). 

In many cases also the reduction agent itself influences the result of the reduction, especially if it is bulky and the environment of the function to be reduced is crowded. A more detailed discussion of stereochemistry of reduction with hydrides is found in the section on ketones (p. 114). 

Ketimines are reduced to amines very easily by catalytic hydrogenation, by complex hydrides and by formic acid. They are intermediates in reductive amination of ketones (p. 134). An example of the reduction of a ketimine is conversion of 3-aminocarbonyl-2,3-diphenylazirine to the corresponding aziridine by sodium borohydride (yield 73%), by potassium borohydride (yield 71%) and by sodium bis (2-methoxyethoxy) aluminum hydride (yield 71%) [939]. 

A dry 1-1. three-necked flask fitted with a mercury-sealed stirrer, a calcium chloride drying tube, and a 500-ml dropping funnel, protected by a calcium chloride drying tube, is surrounded by an ice-salt mixture at —11° Anhydrous methanol (130 ml) (Notes 1 and 2) and 161 g (1 mole) of /3-chlorovinyl isoamyl ketone (p 27) are poured into the flask (Note 3). A solution of 43 g (1 04 moles) of sodium hydroxide (97%) and 350 ml of absolute methanol (Note 4) is added dropwise with stirring over a period of 2 hours, during which time the bath temperature is kept between —11° and —8°... 

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