Acetylacetone, enolization

Trimethylsilyloxy-3-penten-2-one cis) (acetylacetone enol trimethylsilyl ether) [13257-81-3 M 172.3, b 66-68"/4mm, 61-63"/5mm, d4 0.917, Up 1.452. Fractionally distilled and stored in glass ampoules which are sealed under N2. It hydrolyses readily in contact with moisture giving, as likely impurities, hexamethyldisiloxane and 2,4-pentanedione. [J Am Chem Soc 80 3246 795S.]... 

TrimethyIsiIyIoxy-3-penten-2-one (cis) (acetylacetone enol trimethylsilyl ether) [13257 ... 

Beryllium chemistry includes its S-diketonate complexes formed from dimedone (9), acetylacetone and some other S-diketones such as a,a,a-trifluoroacetylacetone. However, unlike the monomeric chelate products from acetylacetone and its fluorinated derivative, the enolate species of dimedone (9) cannot form chelates and as the complex is polymeric, it cannot be distilled and is more labile to hydrolysis, as might be expected for an unstabilized alkoxide. However, dimedone has a gas phase deprotonation enthalpy of 1418 9 kJmoD while acetylacetone enol (the more stable tautomer) is somewhat less acidic with a deprotonation enthalpy of 1438 10 klmoD Accordingly, had beryllium acetylacetonate not been a chelate, this species would have been more, not less, susceptible to hydrolysis. There is a formal similarity (roughly 7r-isoelectronic structures) between cyclic S-diketonates and complexes of dimedone with benzene and poly acetylene (10). The difference between the enthalpies of formation of these hydrocarbons is ca... 

Acetylacetone cobalt (II) Acetylacetone cobalt (II) salt. See Cobalt acetylacetonate Acetylacetone enol t-butyidimethylsilylether. 

Results from alkylation of acetylacetone enolates in dipolar aprotic solvents... 

Additionally, unsubstituted and 6-substimted 2-(perfluoroalkyl)-4/f-pyran-4-ones 4 have been prepared using alkyl enolates derived from p-dicarbonyl compounds. The reaction of acetylacetone enol ether with ethyl perflnoroalkanoates in the presence of i-BuOK, followed by p-TsOH catalyzed cychzation in benzene afforded pyrones 4a,b in 57-75 % yields. Similarly, the parent compounds 4c,d were obtained from the for-mylacetone derivative in 40-64 % yields [4]. Analogue 4e was accessible in low yield from the corresponding triketone [5] (Scheme 2). 

Ketones with labile hydrogen atoms undergo enol acetylation on reaction with ketene. Strong acid catalysis is required. If acetone is used, isoptopenyl acetate [108-22-5] (10) is formed (82—85). Isopropenyl acetate is the starting material for the production of 2,4-pentanedione (acetylacetone) [123-54-6] (11). 

Enols and alkoxides give chelates with elimination of alcohol. For example, in the reaction of the enol form of acetylacetone [123-54-6] all four alkoxide groups attached to zirconium can be replaced, but only two of the four attached to titanium (Fig. 3). Acetoacetic esters react similarly. 

P-Diketone Chelates. P-Diketones, reacting as enols, readily form chelates with titanium alkoxides, Hberating in the process one mole of an alcohol. TYZOR AA [17927-72-9] (6) is the product mixture from TYZOR TPT and two moles of acetylacetone (acac) reacting in the enol form. The isopropyl alcohol is left in the product (87). The dotted bonds of stmcture (6) indicate electron... 

Consider the equiUbria in an aqueous system composed of a bidentate ligand HA, eg, the enol form of acetylacetone, and a tetracoordinate metal, stmcture (8). The equations are... 

Quantitative analysis of mixtures is achieved by evaluating the integral steps of H NMR speetra. This is demonstrated in Fig. 1.11a for 2,4-pentanedione (acetylacetone) which occurs as an equilibrium mixture of 87 % enol and 13 % diketone. 

Any doubt about the existence of individual tautomers is now long past some tautomers can be crystallized separately (desmotropy), and others can be observed simultaneously in the same crystal (Section V,D,2) in summary, tautomers are not intrinsically different from isomers. Maybe it is worth mentioning that even two identical tautomers can differ. This is the case for the two intramolecular hydrogen-bonded (IMHB) enol tautomers of acetylacetone and for many NH-azoles they correspond to a doublewell profile for the proton transfer with both wells having the same energy (autotrope). 

Thenoyltrifluoroacetone(TTA), C4H3S,CO,CH2,COCF3. This is a crystalline solid, m.p. 43 °C it is, of course, a /1-diketone, and the trifluoromethyl group increases the acidity of the enol form so that extractions at low pH values are feasible. The reactivity of TTA is similar to that of acetylacetone it is generally used as a 0.1-0.5 M solution in benzene or toluene. The difference in extraction behaviour of hafnium and zirconium, and also among lanthanides and actinides, is especially noteworthy. 

When the nucleophile is a stabilized carbanion such as the enolate of acetylacetone, 1-benzoylacetophenone, diethylmalonate, or ethyl acetatoacetone, the reaction proceeds similarly. The monosubstituted complex is isolated as long as it contains an acidic hydrogen in the benzylic position. In addition, for the case of diketones CH2(COR)2 (R = Me, Ph, OEt), a deacetylation is observed in an acidic medium [92,93]. These features are the same as described above in the case of the substitution of Cl by stabilized carbanions in monochloroaromatics (the second chlorine being an inert arene substituent [99] Scheme XVII, Eq. (31) and Tables 10 and 11. 

Enolizable compounds can be used for Meerwein reactions provided that the keto-enol equilibrium is not too far on the side of the ketone for example, P-dicar-bonyl compounds such as acetylacetone are suitable (Citterio and Ferrario, 1983). The arylation of enol esters or ethers (10.12) affords a convenient route for arylating aldehydes and ketones at the a-carbon atom (Scheme 10-48). Silyl enol ethers [10.12, R = Si(CH3)3] can be used instead of enol ethers (Sakakura et al., 1985). The reaction is carried out in pyridine. 

Ligand-free catalysts have been prepared from the following types of nickel(II) compounds nickel salts of long-chain aliphatic or aromatic carboxylic acids (10, 11) or of sulfonic acids (11), nickel enolates of /3-diketones (11) [e.g., nickel acetylacetonate (4, 12)] or their imino derivatives (11, 13), nickel phenolates (11), dithiocarbamates (14), and mer-captides (15). 

Nickel-based Ziegler catalysts can be prepared using halogen-free or-ganoaluminum compounds of low Lewis acidity, e.g., dialkylaluminum alkoxides. However, the catalytic properties of these systems differ remarkably from those described above. The nickel components in such a case may be nickel acetylacetonate, or the nickel enolates of various other /3-dicarbonyl compounds (44, 45), in particular such halogenated /3-dicarbonyl compounds as hexafluoroacetylacetone (44, 46). 

---