2.4- pentanedione, reaction with ammonia

When 1-phenyl-2,4-pentanedione is doubly deprotonated with potassium amide in ammonia, the ensuing aldol reaction with benzophenone gives the expected aldol (19). However, if sodium amide is employed to generate the dianion, the reaction product with benzophenone is the dihydro-7-pyrone (20 equation 36). This result suggests the intermediacy in the latter reaction of a dianion involving the benzyiic position. Further study of this interesting reaction is warranted. 

A sirup (obtained by treating D-mannose with ammonia) presumably containing D-mannosylamine, treated with ethyl acetoacetate, also gives compound (17). In the reaction with 2,4-pentanedione, 3-acetyl-2-methyl-... 

The addition of 2,4-pentanedione to liquid ammonia is a highly exothermic process. Also, ammonia vapor reacts with the /3-diketone to produce an insoluble ammonium salt, which tends to clog the tip of the addition funnel. Cooling the reaction mixture in dry ice-acetone reduces the vigor of the reaction and minimizes the dogging of the addition funnel. The 2,4-pentanedione should be added in spurts which fall on the surface of the reaction mixture rather than on the wall of the flask... 

The addition of 2,4-pentanedione to liquid ammonia is a highly exothermic process. Also, ammonia vapor reacts with the fi diketone to produce an insoluble ammonium salt, which tends to clog the tip of the addition funnel. Cooling the reaction... 

Takken (2) identified thiazoles and 3-thiazolines from the reaction of 2,3-butanedione and 2,3-pentanedione with ammonia, acetaldehyde and hydrogen sulfide at 20 °C. Study of tetramethylpyrazine (5) also showed that it can be readily formed in 3-hydroxy-2-butanone and ammonia model reaction at 22 C. Recent study of the model reaction of 3-hydroxy-2-butanone and ammonium acetate at low temperature revealed an interesting intermediate compound, 2-(l-hydroxyethyl)-2,3,4-trimethyl-3-oxazoline, along with 2,4,5-trimethyloxazole, 2,4,5-trimethyl-3-oxazoline, and tetramethylpyrazine were isolated and identified 4,5). We hypothesized that with the introducing of H2S, replacement of oxygen by sulfur could happen and sulfur-containing heterocyclic compoimds such as thiazoles and thiazolines could be formed along with oxazoles, oxazolines and pyrazines. 

In the reaction of 2,3-butanedione and ammonium sulfide at 25 °C, quantitation of volatile compoimds identified in the reaction is summarized in Table II. A pair of interesting intermediate compounds, 5-hydroxy-3-thiazolines, were tentatively identified by GC/MS-EI. 5-Hydroxy-2,4,5-trimethyl-3-thiazolines have been separated and identified by GC/MS-EI and NMR in the early study of volatile flavor conq)ounds of yeast extracts (S). They were also found in the reaction of 2,3-butanedione or 2,3-pentanedione with acetaldehyde, hydrogen sulfide and ammonia (2). 

It could be formed during coffee roasting by reaction of 2,3-pentanedione with acetaldehyde in the presence of ammonia. 

In model systems, the latter authors found it only when heating equimolar amounts of serine (and not threonine) with sucrose. Its formation during coffee roasting can be explained by reaction of 2,3-pentanedione with acetaldehyde in the presence of ammonia. 

A re-investigation of the reaction showed, in accordance with VotoCek s hypothesis, that the compounds obtained have properties (for example, color reactions, ultraviolet and infrared spectra, hydrolysis when examined chromatographically) similar to those of the /3-(glycosylamino) a, 8-un-saturated esters or ketones prepared directly from glycosylamines and i3-dicarbonyl compounds. The derivatives from L-rhamnose and ammonia with ethyl acetoacetate and with 2,4-pentanedione are, indeed, identical... 

Iron(II) bis(acetylacetonate) has been prepared by reaction of iron(II) sulfate in aqueous solution with 2,4-pentanedione in the presence of bases such as pyridine and ammonia and by reaction of iron I) chloride tetrahydrate in aqueous solution with the stoichiometric amounts of 2,4-pentanedione and piperidine. Neither publication reports yields and the lack of complete experimental details makes duplication difficult. The following procedure is a modification of that reported by Buckingham et al. and employs either anhydrous iron(II) chloride or the corresponding adduct with THF. The reaction is carried out in diethyl ether as solvent instead of water. 

Tfie complex Co(mac)2 (macH = 3-methyl-2,4-pentanedione) is the best catalyst for this reaction but is not available commercially. It Is prepared by treating a mixture of macH (2.40 g) and C0CI2 6H2O (2.50 g) in methanol (15 mL) and water (40 mL) with aqueous ammonia (ca. 2 M, 15 mL) under an inert atmosphere. The resulting orange soiid must be filtered under an inert atmosphere and dried under high vacuum at 90°C. 

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