Acetol formation

Imine Formation from an Aldehyde or Ketone 798 Enamine Formation from an Aldehyde or Ketone 800 Base-Catalyzed Addition of H2O to a Carbonyl Group 803 Acid-Catalyzed Addition of H2O to a Carbonyl Group 803 Acetal Formation—Part [1] Formation of a Hemiacetal 806 Acetol Formation—P ferma n of the Acetal 806... 

Technical ethyl formate was purified by washing with 3 per cent sodium carbonate solution, then with cold water, drying over anhydrous sodium sulfate, filtering, and fractionating. It is very important that all the materials used in the synthesis of acetol be anhydrous, as otherwise condensation products are formed. 

Nef prepared acetol in several ways, the more important of which depended upon the reaction between bromoacetone and potassium or sodium formate or acetate, and the subsequent hydrolysis of the ester by methyl alcohol.1 2 Acetol is also formed, together with pyruvic acid, by the direct oxidation of acetone by Baeyer and Villiger s acetone-peroxide reagent.3... 

Considering the products in the distillate (Table 2) the formation of acetol is typical over RNi-s, LDHs containing Cu or Cr and without catalyst. In the presence of Cu- or Cr-Mg-Al-HT the selectivity of acetol is close to 90 %, while the Ni-containing samples result in also ALA and ACR, referring radical processes. 

The formation of propanediols could be observed just over unmodified HT and Cu-Mg-Al-mo., but its selectivity was low. However, acetol can be easily converted into PDOs [3] in another reaction system. 

Both D-[l- C]xylose and D-[5- C]arabinose were exposed to a concentrated phosphate buffer solution (pH 6.7). 1-Hydroxy-2-propanone (ace-tol) was distilled from the heated solution. Radioassay indicated that similar labeling [3- C] occurred in the acetol from both pentoses, with loss of the configurational difference thus, a 3-ketopentose or its enediol was suggested as an intermediate. Further work with 3-0- and 6-0-methyl-D-glucose and with 1-0-methyl-D-fructose indicated that /3-elimination from a 3-ketose or, in the case of a hexose, from a 3-ketose or a 4-ketose, or both, tautomerization of the resulting a-diketone to a /3-diketone, and hydrolytic cleavage are essential steps in the formation of acetol. 

From the base-catalyzed degradation of D-fructose (pH 8.0), Shaw and coworkers147 identified 18 compounds, none of which was (a) isomeric with the starting material, or (b) a simple dehydration product. Among the products, the hydroxy-2-butanones and 1-hydroxy-2-propanone (acetol) were shown to participate in forming the carbo-cyclic products identified, but the mechanism of their formation was not elucidated. Several furan derivatives were isolated, but no lactic acid was isolated. In a similar study but with weak acid,41 most of the products were formed by a combination of enolization and dehydration steps, with little fragmentation. 

Hayami and his coworkers have studied the mechanism of formation of acetol and pyruvic acid from D-glucose- -14C, -6-14C, and -3,4-14C2, reacting in a concentrated, phosphate buffer solution.148-151 Their data supported the supposition that the products are formed from pyruvaldehyde by way of a Cannizarro reaction. As in the formation of lactic acid, the pyruvaldehyde can be formed either from the reducing or the nonreducing end of the D-glucose molecule, and the distribution of radioactivity in the pyruvic acid and acetol... 

The effect of reaction time on the major components of the reaction of cystine and DMHF in water is shown in Table IV. It is noteworthy that amounts of 2,4-hexanedione, 3,5-dimethyl-l,2,4-trithiolanes and thiophenones were found at a maximum after one hour. It was also found that the amount of 2-acetylthiazole increased with time and that acetol acetate decreased with time as expected. In the glycerol medium, the effect of reaction time on the major components is shown in Table V. Apparently, the 1,3-dioxo-lane, which is a ketal formed from glycerol and acetone, decreased over time. Also, long reaction time favors the formation of cyclic compounds, including 2,5-dimethyl-2-hydroxy-3(2H)-thiophene, cyclo-pentenones and 4,5-dimethyl-l,2-dithiolenone. 

The saccharinic acid was next prepared in 32 % yield from the halogen acid (XLIII) by treatment with silver oxide, but this approach was abandoned when good results were obtained from the acetol-form-ester. Reaction of l-chloro-2-propanone (XLVII) with sodium formate produced the monoformate of l-hydroxy-2-propanone (XLIX) which, through the addition of hydrogen cyanide and hydrolysis of the resulting cyanohydrin of l-hydroxy-2-propanone (L), yielded the desired racemic saccharinic acid (Vab). 

Chocarom Pyrazine isomers were isolated from the skin and flesh of potato Solanum tuberosum L.) cultivars after baking 4). 3,5-Dimethyl-2-isobutylpyrazine [2,5-dimethyl-3-(2-methylpropyl)-pyrazine] was isolated by Oruna-Concha, Craig, Duckham and Ames from the following potato cultivars - Cara, Nadine, Flanna and Marfona. 3,6-Dimethyl-2-isobutyl-pyrazine [3,5-dimethyl-2-(2-methylpropyl)pyrazine], was found by the same team in Cara and Marfona potato cultivars. 2,5-Dimethyl-3-isobutylpyrazine was also detected by Welty, Marshall and Grun in chocolate ice cream prepared from cocoa flavor (5). Both pyrazines were also found as key odorant compounds in dark chocolate by Counet, Callemien, Ouwerx and Collin (6). The role of amino acids in alkyl-substituted pyrazines formation in model systems containing pyruvaldehyde was examined by Mea (7). 2,5-Dimethyl-3-isobutylpyrazine was formed in the model system with valine. Both isomers were prepared synthetically by Chen (S) by reacting acetol, isobutyraldehyde and ammonium acetate, with low yield of 22.3%. Subsequent proprietary work by the author has improved the yield to 65%. 

As seen from the data in Table II, the enzyme enhances the eflFect of bound Mn on the C-3 protons of acetol phosphate, indicating the formation of an enzyme-Mn-substrate bridge complex. However, the enzyme-bound Mn has a smaller effect on the C-1 protons, indicating that the presence of the enzyme alters the structure of the Mn coordination complexes. Thus, in the absence of enzyme, from distance calculations and from stability constants, inorganic Mn forms a monodentate phosphate complex with acetol phosphate. 

In acidic conditions, at pH 7 or below, it undergoes mainly 1,2-enolization with the formation of furfural (when pentoses are involved) or HMF (when hexoses are involved). In alkaline medium, at pH > 7, the degradation of the Amadori compound is thought to involve mainly 2,3-enolization, where reductones, such as 4-hydroxy-5-methyl-2,3-dihydrofuran-3-one, and a variety of fission products, including acetol, pyruvaldehyde, and diacetyl are formed. 

Among the interaction products of alliin and IMP, acetol and acetoin were obviously derived from ribose, one of the degradation products of IMP. As an amino acid in nature, alliin would certainly catalyze the formation of these sugar degradation products. Other interaction products of IMP and alliin were heterocyclic compounds containing nitrogen and/or sulfur atoms such as pyrazines, thiazoles, pyrroles and thiophenes. 

There are a number of ways that a stepwise reaction can take place. These include direct reaction, interchange, and add chloride/anhydride. Direct reactions include formation of polyesters and polyamides. Typical interchange reactions involve acetol-alcohol, amine-amide, and amine-ester. The last-named are cases in which an anhydride or acid chloride are reacted with a glycol or amine. 

Figure 8.11 Formation of acetol, lactaldehyde and propane-1,2-diol.

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