Mechanistic Studies of 2-(1-Hydroxyethyl)-2,4,5-trimethyl-3- oxazoline Formation under Low Temperature in 3-Hydroxy-2-butanone/Ammonium Acetate Model Systems

Abstract

Volatile compounds formed from the reaction of 3-hydroxy-2-butanone/ammonium acetate at 25, 55 and 85 °C were investigated. Six compounds were characterized by gas chromatography-mass spectrometry (EI and CI). Among the volatile compounds identified, an interesting intermediate compound, 2-(1-hydroxyethyl)-2,4,5-trimethyl-3-oxazoline, was found. 15 N-Labeled ammonium acetate was used to confirm the structure of 2-(1-hydroxyethyl)-2,4,5-trimethyl-3-oxazoline. The formation pathway of these volatile compounds was proposed. In these model systems, 2-(1hydroxyethyl)-2,4,5-trimethyl-3-oxazoline was formed at the reaction temperature below 25 °C. On the other hand, tetramethylpyrazine was the major component when the reaction temperature was higher than 85 °C. The amounts of 2-(1-hydroxyethyl)-2,4,5-trimethyl-3-oxazoline and tetramethylpyrazine increased linearly with the increasing heating time at 55 °C. Protic solvents did not promote 2-(1-hydroxyethyl)-2,4,5-trimethyl-3-oxazoline formation but did favor the formation of tetramethylpyrazine. A kinetic study of 2-(1-hydroxyethyl)-2,4,5-trimethyl-3-oxazoline formation was also performed, and the activation energy was found to be 16.5 kcal/mol.

Accelerated green process of tetramethylpyrazine production from glucose and diammonium phosphate

“…However, OXZ is unstable at high temperature and its reducing speed is highly dependent on temperature. As 2,4,5-trimethyl-3-oxazoline and 2,4,5-trimethyl-oxazole ( Figure 2) were not detected during this work, OXZ was postulated to transfer back to C 4 compounds ready for the condensation of TMP [18]. The fact that the purified OXZ product can slowly break down to form acetoin and TMP even it is stored in the dark at 4°C (data not shown) further supports this opinion.…”

“…Acetoin can act as the precursors of many other kinds of compounds due to its reactive hydroxyl group and the hydrogens on the alpha position of the carbonyl group. Fu et al [18] revealed some side-reactions using GC-mass spectrometry (GC-MS) techniques. However, owing to the limitation of the gas chromatographic method, non-volatile derivatives may have been overlooked.…”

“…However, the current efficiency at 95°C is acceptable and if the reaction solution is heated to boiling point, TMP would be significantly entrained with the water vapour. In Figure 2 The simplified acetoin metabolic pathway in B. subtilis CICC 10211 (up) and the spontaneous reactions [18] of acetoin and ammonium (down). Bold arrows with solid, dot, and dash-dot lines are reactions taking place in stage I, II, and III in Figure 1, respectively.…”

Characterization of Volatile Compounds from the Reaction of 3-Hydroxy-2-butanone and Ammonium Sulfide Model System

“…They have the same GC-EIMS spectra as shown in Figure 1. This mass spectrum matches well with the spectral data published previously by Shu and Lawrence (1995) and Fu and Ho (1997). They were, therefore, identified as syn and anti isomers of 2-(1-hydroxyethyl)-2,4,5-trimethyl-3-oxazoline.…”

“…Thiazoles have also been found in various model systems involving either degradation of glucose in the presence of fragmentation of cysteine or cystine (Shu et al, 1885a,b) or reaction of these with reducing sugars (Kato et al, 1973) or furaneol (Shu and Ho, 1988). In recent studies on the reaction of 3-hydroxy-2-butanone with ammonium acetate at low tem-perature, an interesting compound, 2-(1-hydroxyethyl)-2,4,5-trimethyl-3-oxazoline along with 2,4,5-trimethyloxazole and 2,4,5-trimethyl-3-oxazoline, was isolated and identified (Shu and Lawrence, 1995;Fu and Ho, 1997). Our objective in the present study was to isolate and identify the oxazoles, oxazolines, thiazoles, and thiazolines from the reaction of 3-hydroxy-2-butanone and the ammonium sulfide model system.…”