Carbonyl groups acetylacetone

Vinylogous amides, which have an enamine function in conjugation with a carbonyl group, constitute tridentate systems and thus open the possibility of alkylation on carbon, nitrogen, or oxygen. It has been found that the pyrrolidine enamine of acetylacetone gives rise to a carbon mcthylation but an oxygen ethylation product 41). The alkylation of cyclic 1,3-diketone-derived enamines has been studied 41,283). O Alkylation was found in alcohol solvents and predominant C alkylation in nonprotonic solvents. 

Studies of the base-hydrolysis mechanism for hydrolysis of technetium complexes have further been expanded to an octahedral tris(acetylacetonato)techne-tium(III) [30], Although a large number of studies dealing with base hydrolysis of octahedral metal(III) complexes have been published [31], the mechanism of the tris(acetylacetonato)metal complex is still unclear. The second-order base hydrolysis of the cationic complex tris(acetylacetonato)silicon(IV) takes place by nucleophilic attack of hydroxide ion at carbonyl groups, followed by acetylacetone liberation, and finally silicon dioxide production [32], The kinetic runs were followed spectrophotometrically by the disappearance of the absorbance at 505 nm for Tc(acac)3. The rate law has the following equation ... 

The acidity of a C-H is further enhanced if it is adjacent to two carbonyl groups, as in the 1,3-diketone acetylacetone. The enolate anion is stabilized by delocalization, and both carbonyl oxygens can participate in the process. This is reflected in the VK, 9 for the protons between the two carbonyls. 

It is concluded that the catalyst has in addition to acetylacetonates a reactant or its radical as one of its ligands, probably coordinated with the catalyst through its carbonyl group, enabling the oxidation reaction to proceed with the formation of acrylic acid by suppressing the side reactions as follows ... 

The mechanism, incidentally, for this acetylacetonate case is not unambiguous and it is possible that nucleophilic attack occurs at the ligand ring in one of the carbonyl groups. 

Under the same conditions, cobalt acetylacetonate afforded a mixture of four products the mono-, di-, and triacetylated chelates (XVII, XVIII, and XIX), along with the starting material. In contrast to the chromium chelates, the mixture of cobalt complexes was cleanly separated by chromatography. The identity of each of these products was established by an NMR spectrum. The presence of uncoordinated carbonyl groups was revealed by infrared absorption at 1675 cm.-1... 

Acetylacetone as a liquid at 40°C exists to the extent of 64% in the enolic form that absorbs at 1613 cm-1. The keto form and a small amount of unbonded enolic form may be responsible for two bands centering near 1725 cm-1. Interaction between the two carbonyl groups in the keto form was suggested as a cause for this doublet. The enolic O—H stretching absorption is seen as a broad shallow band at 3000-2700 cm-1. 

Two carbonyl groups greatly increase the acidity. For example, 2,4-pentanedione (acetylacetone, 2) has a pATa s 9, which is comparable to the O—H acidity of phenols (see Table 17-1). The reason is that the enolate anion 3 has the charge largely shared by the two oxygen atoms (cf. 3b and 3c). As a result, the enolate anion 3 is stabilized more with respect to the... 

The acetylacetone carbanion undergoes addition to the imine carbon atom of complex (92) but subsequent cyclization and deacylation processes occur (Scheme 42).212 The apical ammonia group is the most acidic and consequently is favoured to cyclize on to the carbonyl group. In the bis-(1,2-diaminoethane) complex related to the imine chelate (92), the two apical nitrogen atoms are no longer geometrically equivalent. Thus two products are formed when hydrogen cyanide is added to the complex and subsequent cyclization takes place (Scheme 43).213 However, the cyclization reaction is stereoselective. 

Some ketones such as /3-dicarbonyls contain substantial amounts of the enol at equilibrium. For example, acetylacetone in aqueous solutions contains 13% of 4-hydroxypent-3-en-2-one, which is stabilized both by an intramolecular hydrogen bond and the inductive effect of the remaining carbonyl group.17 When bromine is added to such a solution, a portion is initially consumed very rapidly by the enol that is already present at equilibrium. The ketone remaining after consumption of the enol reacts more slowly via rate-determining enolization. The slow consumption of bromine is readily measured by optical absorption. In acidic solutions containing a large excess of the ketone the slow reaction follows a zero-order rate law the rate is independent of bromine concentration, because any enol formed is rapidly trapped by bromine (Scheme 1). In this case, the amount of enol present at equilibrium may be determined as the difference between the amount of bromine added and that determined by extrapolation of the observed rate law to time zero, as is shown schematically in Fig. 2. 

Reaction between 74 and alkyl / -ketoacetates or acetylacetone under the same conditions, however, furnishes cyclic 1,1-enediamines 77 with loss of one acetyl group39. The evidence available indicates the involvement of a consecutive reaction between the initially formed 1,1-enediamines 75 and the methanethiol released at the condensation step97. The methanethiol attacks the more reactive carbonyl group of the enediamine 75 to form the intermediate 76, which undergoes elimination to give the deacetylation products 77 and methyl thioacetate (78) (Scheme 6). 75 can survive in this reaction... 

COD = 1,5-cyclooctadiene. " Olefinic carbon. acac = acetylacetonate. tfac = trifluoroacetylacetonate. hfac = hexafluoroacetylacetonate. At — 80°C. Bridging carbonyl group. " Terminal carbonyl group. 

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