02.08.2020

alpha diketone reactions

The hydrogen present on the alpha-carbon is the alpha-hydrogen and it is slightly acidic in nature due to the carbonyl group and its resonance stabilization mechanism. We can make alpha-protons more easily-removable by using a beta-keto-ester. However, as a general rule between about 0.5 and about 1000, preferably between about 1 and about 500, most preferably between about 10 and 100, moles of water are advantageously employed per mole of the initial ketone reactant.The means of introducing the acid catalyst and water to the process is not particularly critical. Similarly when water is used as a solvent in a prior step of an embodiment of the invention or when steam distillation is employed, further water addition for the reaction with the aldehyde is not generally necessary.The temperature at which the reaction with the aldehyde is conducted is likewise not particularly critical so long as it is sufficiently high to provide a satisfactory reaction rate and sufficiently low to avoid significant thermal decomposition (and corresponding unsatisfactorily low yields) of the derived α-diketone product. For example, cyclohexane-1,2-dione (α-Diketones are potential pentadienyl cation precursors via tandem enolization/carbonyl activation. A 1.2 mole portion of paraformaldehyde is then reacted with the resulting mixture in the presence of 3.6 moles of aqueous HCl. Thus, for example, an amount of the selected aldehyde between about 0.5 and about 5, preferably between about 1 and about 5, more preferably between about 1 and about 3, most preferably between about 1.1 and about 2, moles of aldehyde per mole of the selected initial ketone reactant is advantageously employed.The aforementioned reaction with the aldehyde is conducted in the presence of an acid catalyst. A distinctive feature of this particular rearrangement, however, is its reversibility—as a result, the more stable α-hydroxy carbonyl compound is favored. It looks something like this: The #alpha#-carbon is the one adjacent to (on the right of) the carbonyl carbon.The #beta#-carbon is the very bottom-right carbon.Hence, #\mathbf(alpha,beta)#-unsaturated ketones have a double bond across the #\mathbf("C"_alpha-"C"_beta)# connection. 2,2-dimethyl-3,4-hexanedione), 1-cyclopentyl-3-ethyl-1,2-propanedione (i.e.

If there are two alpha-protons, they can both be removed and replaced with R from R-X. For example, suitable acid catalysts include organic and inorganic acids (especially the inorganic acids) exhibiting pKa values of about 3.0 or less.Examples of suitable inorganic acid catalysts include arsenic, chromic, hydrobromic, hydrochloric, hydroiodic, iodic, nitric, periodic, o-phosphoric, pyrophosphoric, selenic, selenious, sulfuric, sulfurous, etc.Examples of suitable organic acid catalysts include o-aminobenzosulfonic, benzosulfonic, bromoacetic, bromobenzoic, chloroacetic, o-chlorobenzoic, α-chlorobutyric, α-chloropropionic, cyanoacetic, γ-cyanobutyric, o-, m- or p-cyanophenoxyacetic, cyanopropionic, cyclopropane-1:1-dicarboxylic, dichloroacetic, dichloroacetylacetic, 2,2- or 2,5-dihydroxybenzoic, dihydroxymaleic, dihydroxytartaric, dinicotinic, fluorobenzoic, o-iodobenzoic, maleic, malonic, naphthalenesulfonic, oxalic, o-phthalic, picric, quinolinic, trichloroacetic, trifloroacetic, 2,4,6-trihydroxybenzoic, 2,4,6-trinitrophenol, and the like.Preferably the organic or inorganic acid catalyst exhibits a pKa value of about 2.0 or less. A general scheme for the rearrangement is shown below. The alpha-diketone deposited on glass was also converted successfully to pentacene film by photoirradiation. ##STR2##In addition, preparation of alpha-diketones by hydrolysis of acetylene derivatives and epoxy derivatives, as exemplified by equations (10) and (11) respectively, has been reported.

In addition, diacetyl can be synthesized through the acid catalyzed condensation of 1-hydroxyacetone and formaldehyde. Grinding roasted coffee beans produces greater surface area for the off-gassing of these and other chemicals (Akiyama et al. Viewed 4k times 0.

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