Acétylacétone

|---- |Other names || diacétylméthane
β, δ-dioxopentane
AcAc |---- | Notation SPALLING HAMMERS || DC (=O) DC (=O) C |---- |----- |----- | Not of boiling || 473 K |----- |----- |----- |----- ! colspan=" 2" bgcolor=" #FFDEAD" | Card-index dangers |----- | || |----- | Principal dangers || Harmful |----- | Classification HAVE || Harmful ( Xn ) |----- | Index HAVE || 606-029-00-0 |----- | NFPA 704 || |----- | Card-index safety || Baker |----- | || Fischer |----- |----- |----- |----- | Codes R/S || Sentences of risk: |----- | ||R 10, R 22 |----- | || the Councils of prudence: |----- | || (S2), S21, S23 |----- | || S24/25 |----- | lethal Amount 50 || 790 mg/kg (way dermale)
575 mg/kg (oral way) |----- | Value of exposure || No the data |----- | Storage ||Category 4
(to store between +15°C with +25°C) |-----

The acétylacétone is a Composé organics of C₅H₈O₂ chemical formula. This Diketone named according to the Nomenclature IUPAC: pentane-2,4-dione , although this denomination can be subjected to deliberation (see hereafter), since it does not describe exactly the structure of the compound.

Properties

The forms Tautomeric S énol and Cétone of the acétylacétone coexist in solution, as shown figure 1. The symmetry C_2v of the form énol (form on the right for balance describes figure 1) was observed via various methods including the spectroscopy microwaves. The Hydrogen bond of the énol reduces the steric repulsion between the two carbonyls groups. The constant of balance K between the two tautomeric forms is of 11,3 in gas phase. This constant tends to grow in non-polar solvents: in the Cyclohexane: 42; in the Toluene: 10; in THF: 7,2; Diméthylsulfoxyde: 2; and in water: 0,23.

Preparation

Two traditional processes are used to synthesize the acétylacétone. In the first, the Acetone and the acetic Anhydride reacts thanks to the addition of BF₃ used like Catalyseur.

(CH₃CO) ₂O + CH₃C (O) CH₃ → CH₃C (O) CH₂C (O) CH₃

The second process implies the condensation catalyzed by base of acetone and the Acétate of ethyl, followed by an acidification:

NaOEt + EtO₂CCH₃ + CH₃C (O) CH₃ → NaCH₃C (O) CHC (O) CH₃ + 2 EtOH

NaCH₃C (O) CHC (O) CH₃ + HCl → CH₃C (O) CH₂C (O) CH₃ + NaCl

Because of the facility to carry out these syntheses, many analogues of the acétylacétonates are known. One can thus quote: C₆H₅C (O) CH₂C (O) C₆H₅ (dbaH) and (CH₃) ₃CC (O) CH₂C (O) DC (CH₃) ₃. The hexafluoroacétylacétonate is very largely used, to generate metal birds complexes in particular.

Ion acétylacétonate

ion acétylacétonate C₅H₇O₂⁻ is the combined Base of pentane-2,4-dione. Actually, the free ion does not exist in solution, but is related to a cation like Na⁺. In practice, the existence of the free anion, commonly abrévié in acac⁻ , is a useful model.

Chemistry of coordination

The Anion acétylacétonate form of the complexes with many ions of metals of transition in which the two oxygen atoms bind to metal to form a ring of chelation to six members. One can quote among these complexes: Mn (acac) ₃, VO (acac) ₂, Fe (acac) ₃, and Co (acac) ₃. Very complex of the form M (acac) ₃ is chiral (they are not superposable with their images in a mirror), as indicated on figure 2.

Moreover, the complexes M (acac) ₃ can be reduced by electrochemical way, with a reduction ratio depending on solvent and the metal center. The complexes double or triple of the type M (acac) ₂ and M (acac) ₃ are typically soluble in organic solvents, contrary to dependant metal halides. Because of these properties, these complexes are very largely used like precursors or reagents of Catalyze. The most important applications include their use as reagents of displacement NMR, like catalysts for the organic syntheses, and like precursors for catalysts of hydroformylation.
C₅H₇O₂⁻ binds sometimes to metals by its central carbon atom; this mode of connection is more common for metals of transition from the third period like the Platine (II) or the Iridium (III).

Examples of metal acétylacétonates

Copper II Acétylacétonate

Cu (acac) ₂, prepared by treatment of the acétylacétone with Cu (NH₃) ₄²⁺ and available in the trade, catalyzes the reactions of coupling and transfers of carbenes.

Copper I Acétylacétonate

Contrary to copper II chelate, the copper I acétylacétonate is a reactive oligomeric species with the air. It is employed to catalyze the reactions of Michaels.

Manganese III Acétylacétonate

Mn (acac) ₃, oxidant monoelectronic, is commonly used for the coupling of the phenol S.

Nickel Acétylacétonate

This compound is not the compound of formula Nor (acac) ₂, but the trimère ₃. It is a green solid soluble emerald in the Benzène, which is very much used in the preparation of the complexes Nor (O). Exposed to the atmosphere, ₃ is transformed into the chalky green monomeric hydrate.

Acétylacétonates with connections carbon

C₅H₇O₂⁻ binds sometimes to metals by central carbon (C3): this mode of connection is more current for metals dde transtons third period like the Platine (II) and the Iridium (III). The complexes Ir (acac) ₃ and the bases of the corresponding Lewis adduites Ir (acac) ₃L (or L is a amine) include/understand a carbon-dependant ligand acac. The infra-red spectrum of the oxygen-dependant acétylacétonates are characterized by bands ν_CO of relatively low energy (1535 cm⁻¹), whereas in the carbon-dependant acétylacétonates, the vibration of carbonyl occurs more close to the range of energy for the ketonic C=O, i.e. with 1655 cm⁻¹.

Other reactions with the acétylacétone

Among the other reactions implying the acétylacétone, one can quote:

déprotonations: very strong bases will déprotoneront the acétylacétone doubly, starting in C3 and but also in C1. The resulting species can be then alkylated in C-1.
like precursor for heterocycles: the acétylacétone is a changeable precursor for the heterocycles. Hydrazine reacts to give Pyrazol S, the urea gives Pyridimine S.
like precursor for the dependant imino-ligands: the acétylacétone condenses with the amindes to give, in a successive way, the mono ones and di- Dicétimine S in which the oxygen atoms in the acétylacétone are replaced by NR (or R = aryl, alkyl).
enzymatic depression: the enzyme acétylacétone dioxygénase cut the connection carbon-carbon of the acétylacétone, thus producing Acetate and the 2-oxopropanal. The enzyme is dependant with Fe (II), but it was however proven that it could also bind zinc. The degradation of the acétylacétone was characterized for the bacterium Acinetobacter johnsonii .
: C₅H₈O₂ + O₂ → C₂H₄O₂ + C₃H₄O₂
Arylation: the acétylacétonate moves halides since certain halogéno-substituted benzoic acids. This reaction is catalyzed by copper.
: 2-BrC₆H₄CO₂H + NaC₅H₇O₂ → 2 (CH₃CO) ₂HC) - C₆H₄CO₂H + NaBr

References

Quoted references

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