Other ketones

Biacetyl and acetylacetone have been studied by Salooja [47(a)] in a flow system. Biacetyl was rather reactive, appreciable reaction beginning at 350 °C and ignition occurring at about 530 °C under the experimental conditions employed acetylacetone began to react above 400 °C but ignited at 480 °C. Biacetyl was anomalous in that it did not appear to exhibit a zone of negative temperature coefficient of the rate of combustion, probably because no stable olefinic intermediates are formed in the oxidation process. Some measurements on the rate of slow combustion of methyl vinyl ketone have also been reported [47(b)]. 

The reactions of the simple ketones can be understood if it is assumed that there are several possible routes by which ketonyl radicals can react the competition between these routes is determined by the structure of the radical and by the temperature. 

In systems in which the formation of j3-radicals is possible it is necessary to write further reactions. 

Pyrolysis to the ketene is favoured at high temperatures [48—50], but except in the slow combustion of acetone [29] around 500 °C this does not appear to be an important reaction in the systems under consideration. 

Because of the difficulty of assigning any product to a unique route, it is not easy to establish even relative rate coefficients for the competing reactions of the ketonyl peroxy radicals. However, carbon dioxide yields are greatest in the low temperature regime, and therefore type I reactions are favoured under these conditions. 

Diacetyl oxidizes at 80°C with the formation of acetic acid, C02, methyl acetate, methylglyoxal, methanol, peroxide, and formaldehyde [135]. 

Unsaturated ketones oxidize with the formation of hydroperoxide in the a-position to the double bond [136] (cf. olefins), viz. 

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Aliphatic ketones containing the CH3CO— group restore the colour very slowly to SchifTs reagent other ketones have no reaction. 

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

The situation is similar for other ketones Special procedures for aldol addition and self condensation of ketones have been developed but are rarely used... 

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Ketones are an important class of industrial chemicals that have found widespread use as solvents and chemical intermediates. Acetone (qv) is the simplest and most important ketone and finds ubiquitous use as a solvent. Higher members of the aUphatic methyl ketone series (eg, methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone) are also industrially significant solvents. Cyclohexanone is the most important cycHc ketone and is primarily used in the manufacture of y-caprolactam for nylon-6 (see Cyclohexanoland cyclohexanone). Other ketones find appHcation in fields as diverse as fragrance formulation and metals extraction. Although the industrially important ketones are reviewed herein, the laboratory preparation of ketones is covered elsewhere (1). 

Stabilized lithium acetyhde is not pyrophoric or shock-sensitive as are the transition-metal acetyhdes. Among its uses are ethynylation of halogenated hydrocarbons to give long-chain acetylenes (132) and ethynylation of ketosteroids and other ketones in the pharmaceutical field to yield the respective ethynyl alcohols (133) (see Acetylene-derived chemicals). 

In the presence of strong acid catalysts many commonly used commercial alkyl hydroperoxides decompose to acetone to some extent. Consequendy, the diperoxyketals derived from other ketones and alkyl hydroperoxides are often contaminated with small amounts of diperoxyketals derived from acetone (1, X = OOR, = methyl, R = R = tert — alkyl). 

Liquid sulfur dioxide expands by ca 10% when warmed from 20 to 60°C under pressure. Pure liquid sulfur dioxide is a poor conductor of electricity, but high conductivity solutions of some salts in sulfur dioxide can be made (216). Liquid sulfur dioxide is only slightly miscible with water. The gas is soluble to the extent of 36 volumes pet volume of water at 20°C, but it is very soluble (several hundred volumes per volume of solvent) in a number of organic solvents, eg, acetone, other ketones, and formic acid. Sulfur dioxide is less soluble in nonpolar solvents (215,217,218). The use of sulfur dioxide as a solvent and reaction medium has been reviewed (216,219). 

The temperature must be carefully regulated, and in no case must it exceed 150°. In this preparation, as well as in the preparation of other ketones by the Nencki reaction, higher temperatures lead to the formation of a highly colored and resinous product which probably contains a little diketone. 

The unsaturated tetraoxaquaterene (accompanied by linear condensation products) was first synthesized in 18.5% yield by the acid-catalyzed condensation of furan with acetone in the absence of added lithium salts. Other ketones also condensed with furan to give analogous products in 6-12% yield.A corresponding macrocycle was also prepared in 9% yield from pyrrole and cyclohexanone. The macrocyclic ether products have also been obtained by condensation of short linear condensation products having 2, 3, or 4 furan rings with a carbonyl compound. ... 

The stereochemistry of reduction of 20-ketones with LiAlH4 is more influenced by substituents than that of other ketones. Usually reduction of the 20-ketone gives the more hindered -alcohol.208 stated that when C-17 has a substituent, the reduction yields almost quantitatively the 20)5-ol. However, the evidence on this point is conflicting Fukushima and Meyer claim that with a 17a-hydroxy present the 20a-ol is the predominant product except when an 11-ketone is being reduced simultaneously. Other results appear to support this conclusion, but... 

However, 17a,21-acetonides (103), as well as acetals of other ketones or aldehydes, can be easily prepared by acid-catalyzed exchange reaction with dimethoxypropane or other alkyl acetals in dimethylformamide or benzene. Enol etherification of the A -S-ketone also occurs with the former procedure. 

While the oxidation of ketones by peracids (Baeyer-Villiger reaction) has been used in steroids mainly for ring cleavage, it has occasionally been applied to 20-ketopregnanes for conversion to 17-acetoxy- or hydroxyandros-tanes. The synthetic utility of this method is limited since reactive double bonds and other ketones are incompatible with the reagent. 

Generally, the successful conversion of 20-ketopregnanes to 17-hydroxy-androstanes with peracids requires the protection of other ketones, with the exception of those at C-11, and possibly C-12 e.g., as ketals or cyanohydrins ) and isolated double bonds e.g., as dibromides). Unprotected hydroxyl groups do not interfere, except, as expected, a 17a-hydroxy-20-keto steroid is oxidized to the 17-ketone. The use of nitrate esters to protect... 

Isolated double bonds do not interfere with this reaction sequence, but other ketones (saturated or a, -unsaturated) will also form enol acetates, which in turn are capable of further reaction with 7V-iodosuccinimide. 

The chiral BOX-metal(II) complexes can also catalyze cycloaddition reactions of other ketonic substrates [45]. The reaction of ethyl ketomalonate 37 with 1,3-conju-gated dienes, e.g. 1,3-cyclohexadiene 5c can occur with chiral BOX-copper(II) and zinc(II) complexes, Ph-BOX-Cu(OTf)2 (l )-21a, and Ph-BOX-Zn(OTf)2 (l )-39, as the catalysts (Scheme 4.29). The reaction proceeds with good yield and ee using the latter complex as the catalyst. Compared to the copper(II)-derived catalyst, which affects a much faster reaction, the use of the zinc(II)-derived catalyst is more convenient because the reaction gives 94% yield and 94% ee of the cycloaddition product 38. The cycloaddition product 38 can be transformed into the optically active CO2-... 

By using other ketones instead of acetone homologous substances may be obtained. 

Sabina ketone, Cj Hj O, is not a natural constituent of essential oils, but is of considerable interest on account of its utility in the synthesis of other ketones. 

As the WT CHMO was known to react (S) selectively with simple four-substituted cyclohexanone derivatives [84—87], it was logical to test mutant 1-K2-F5 as a catalyst in the BV reaction of other ketones. For example, when 4-methoxycyclohexanone (38) was subjected to the BV reaction catalyzed by mutant 1-K2-F5, almost complete enantioselectivity was observed in favor of the (S)-lactone (39) (98.5% ee), in contrast to the WT, which is considerably less selective (78% ee) (see Scheme 2.11) [89]. 

Hence, enol esters such as isopropenyl acetate are good acylating agents for alcohols. Isopropenyl acetate can also be used to convert other ketones to the corresponding enol acetates in an exchange reaction ... 

Bisulfite addition products are formed from aldehydes, methyl ketones, cyclic ketones (generally seven-membered and smaller rings), a-keto esters, and isocyanates, upon treatment with sodium bisulfite. Most other ketones do not undergo the reaction, probably for steric reasons. The reaction is reversible (by treatment of the addition product with either acid or base ) and is useful for the purification of the starting compounds, since the addition products are soluble in water and many of the impurities are not. ... 

The mode of oxidation by Mn(III) pyrophosphate also seems clear cut from (i) the agreement between oxidation and enolisation rates for cyclohexanone and (//) the tendency for the rate to become independent of Mn(III) concentration at high concentrations. Several other ketones, however, were oxidised rather more slowly than they enolised . 

Other ketones besides acetone can be used for in situ generation of dioxi-ranes by reaction with peroxysulfate or another suitable peroxide. More electrophilic ketones give more reactive dioxiranes. 3-Methyl-3-trifluoromethyldioxirane is a more reactive analog of DMDO.99 This reagent, which is generated in situ from 1,1,1-trifluoroacetone, can oxidize less reactive compounds such as methyl cinnamate. 

The other ketone bodies are derived from acetoacetate P-hydroxybutyrate, by reduction with the involvement of NAD-dependent hydroxybutyrate dehydrogenase, and acetone, by decarboxylation of acetoacetate with the participation of aceto-acetate decarboxylase ... 

The red and orange forms of RhCl[P(C6H5)3]3 have apparently identical chemical properties the difference is presumably due to different crystalline forms, and possibly bonding in the solid. The complex is soluble in chloroform and methylene chloride (dichloromethane) to about 20 g./l. at 25°. The solubility in benzene or toluene is about 2 g./l. at 25° but is very much lower in acetic acid, acetone, and other ketones, methanol, and lower aliphatic alcohols. In paraffins and cyclohexane, the complex is virtually insoluble. Donor solvents such as pyridine, dimethyl sulfoxide, or acetonitrile dissolve the complex with reaction, initially to give complexes of the type RhCl[P(C6H6)3]2L, but further reaction with displacement of phosphine may occur. 

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