Hydrogenation of Diacetyl

Hydrogenation of diacetyl (5) catalyzed by (S)-l-Ru gives a 74 26 mixture of meso-6 and S,S-6. Evidently in this reduction catalyst control favoring formation of meso-diols dominates over substrate control favoring formation of / or d-diols. 

In contrast, hydrogenation of 1,2-diketones that proceeds via 2-hydroxy ketones exhibits marked syn or meso selectivity (Scheme 60), although the enantiomeric preference follows the general sense given in Scheme 47 (92). Thus, (i )-BINAP-Ru-aided hydrogenation of diacetyl gives a 26 74 mixture of enantiomerically pure (R,R)-2,3-butanediol and the meso diol. 

The catalytic hydrogenation of diacetyl-D-pseudoglucal by the use of different catalysts produces varying compounds. Crude or distilled diacetyl-D-pseudoglucal in aqueous methanol, with Willstatter palladium... 

Hydrogenation of diacetyl-D-arabinal leads to diacetyl-dihydro-D-arabinal.30 In addition, a 4-acetyl-D-pseudoarabinal (XL) has been prepared and from it an ethyl glycoside, probably a mixture, was obtained.30-34... 

Figure 88. Laboratory Setup for the Catalytic Hydrogenation of Diacetyl to Acetoin.

A selective hydrogenation of diacetyl to acetoin can also be carried out in an electrolytic cell using a cathode with a high hydrogen overvoltage [83], It is recommended to start with a solution consisting of... 

The most suitable extractant is believed to be dichloromethane. A respective plant is shown in Figure 90. As can be seen, due to the recovery procedures, the production of acetoin by an electrochemical hydrogenation of diacetyl is more complicated than the catalytic process. 

The diacetylated ethane-1-hydrox-1,1-diphosphonic acid is prepared by dissolving the diphosphonic acid in acetic acid and adding acetic anhydride [114]. The sodium salt can be directly converted to the free acid form by passing it through an hydrogen cation exchanger. The bicyclic dimer is prepared by basic hydrolysis of diacetylated cyclic dimer, as shown in Eq. (70) ... 

The diazotization of o-diaminobenzene derivatives is the most common synthetic route to benzo-triazoles. Triazolo[6,7- /]phthalide (791) is synthesized in a seven-step sequence from phthalide in 24% overall yield as shown in Scheme 159. Triazolo[6,7-c ]dihydrocoumarin is similarly prepared in nine steps from dihydrocoumarin in 20% overall yield <92JHC1519>. Benzo[l,2-tf 4,5-tf jbistriazole (795) is synthesized from w-dichlorobenzene in five steps and 54% overall yield (Scheme 160). The hydrogenation of (792) is carried out in ethanol to give (793), which, without isolation, is diazotized at 0°C to afford diacetyl bistriazole (794) in 96% yield <86JOC979>. 

Pack, M. Y., Vedamuthu, E. R., Sandine, W. E. andElliker, P. R. 1968. Hydrogen peroxide-catalase milk treatment for enhancement and stabilization of diacetyl in lactic starter cultures. J. Dairy Sci. 51, 511-516. 

In a study of the diastereoselective hydrogenation of one of the chiral precursors of lysine, i.e., 170, this compound was hydrogenated in acetic anhydride and potassium hydroxide using Raney nickel to produce diace-tyllysineamide 171, A,AT-diacetyl-1,5-diaminopentane, and, if the amount of alkali is increased, imidazolono-1,3-diazocine 172. It was concluded that 172 arose from ring closure of 171 (87JOU306). 

Thiolacetic acid has been prepared from acetic acid and phosphorus pentasulfide 5 from acetyl chloride and potassium hydrosulfide 7 by the hydrolysis of diacetyl sulfide 8 from acetic anhydride and hydrogen sulfide 3-49 and from acetyl chloride and hydrogen sulfide in the presence of aluminum chloride.10 The procedure described 9 differs from other procedures employing acetic anhydride and hydrogen sulfide 3-4 most importantly in the use of alkaline rather than acidic catalysts, which the submitter found to cause slower absorption of hydrogen sulfide under pressure and to yield considerable diacetyl sulfide in addition to thiolacetic acid. 

Procedure Transfer an accurately measured volume of sample, equivalent to about 25 mg of diacetyl, into a suitable flask. Add 3 drops of phenolphthalein TS, and neutralize the acidity by titrating with 0.05 N sodium hydroxide to a faint pink endpoint. Add 0.25 mL of 30% hydrogen peroxide solution and 3 drops of 0.01% Osmic Acid. Mix, cover the flask, and allow it to stand in an incubator held at about 38° for not less than 4 h. Cool to room temperature, and titrate with 0.05 N sodium hydroxide to a faint pink endpoint. Each milliliter of 0.05 N sodium hydroxide is equivalent to 8.6 mg of diacetyl. 

Hydrogenation of a sulfur-containing substrate. Usually sulfur-compounds are not satisfactory substrates for catalytic hydrogenations. However, the diacetyl derivative (2) of dehydrobiotin (1) can be hydrogenated successfully with Pd/C as catalyst to enantiomerically pure N,N-diacetylbiotin methyl ester (3). The yield can be made quantitative by using hydrogen pressures of about 3000 psi and increased amounts of catalyst. ... 

Catalytic hydrogenation of 1,4-diacetyl-2,3-diphenyl-1,4-dihydropyrazine (46) over palladium-charcoal resulted in the rapid uptake of 1 mol of hydrogen with formation of 1,4-diacetyl-5,6-diphenyl-l, 2,3,4-tetrahydropyrazine (55) this addition of only one equivalent of hydrogen under these conditions is characteristic of a... 

A small portion of diacetyl molecules undergoes hydrogen abstraction to yield diacetyl radicals . 

Acyl radicals are prduced in photolysis of diacetyl, when hydrogen is abstracted from aldehyde, or when an oxvgen atom or an ozone molecule reacts with olefin. 

Lactic acid bacteria and bifidobacteria are preferred as protective and probiotic cultures, and have been used since the beginning of history as starter cultures. They have a long history of being safely used and consumed. LAB are widely used for fermentation of milk, meat, and vegetable foods. In fermentation of dairy products, lactose is metabolized to lactic acid. Other metabolic products, hydrogen peroxide, diacetyl, and bacteriocins may also play inhibitory roles and contribute to improving the organoleptic attributes of these foods, as well as their preservation (Messens and De Vuyst, 2002). 

The results plotted at Figure 1 seem to be useful for elucidation of the reaction pathway. In the course of butadione formation two hydrogen molecules of 2,3-butanediol must be eliminated. The elimination can proceed either simultaneously or step by step via consecutive elimination of hydrogen molecules and intermediate formation of acetoin. One can see that conversion of the latter into diacetyl proceeds faster and at lower temperature as compared to the conversion of butanediol. By increasing the temperature and conversion of butanediol the curve of acetoin formation passes maximum and the curve of diacetyl formation has an induction period. Thus, one can believe that the conversion proceeds mainly via consecutive elimination of hydrogen molecules and intermediate formation of acetoin ... 

Interesting observations were made in the ionic hydrogenation of imidazolone 627. Reduction of the unacylated imidazolone (R = H) yields a 1 1 (cisjirans) mixture of the saturated product 7. A similar reduction of the diacetyl derivative (6, R = Ac), where the double bond is more reactive because of dearomatization of the imidazolone ring, occurs with a high degree of diastcrcosclectivity. In contrast to the examples above, the c/.v-product is formed preferentially. 

---