2,5-hexanedione hydrogenation

Hexanedione Hydrogen cyanide Nickel Nickel carbonate, basic Nickel cyanide Nickel oxide (ous) Platinum Potassium alum anhydrous Potassium cyanide Potassium dichromate... 

Quantum-chemical calculations provided an explanation for the regioselectivity in 1-phenyl-1,2-propanedione hydrogenation and also for the lack of regioselectivity in 2,3-hexanedione hydrogenation. The differences in the... 

Other PK variations include microwave conditions, solid-phase synthesis, and the fixation of atmospheric nitrogen as the nitrogen source (27—>28). Hexamethyldisilazane (HMDS) is also an excellent ammonia equivalent in the PK synthesis. For example, 2,5-hexanedione and HMDS on alumina gives 2,5-dimethylpyrrole in 81% yield at room temperature. Ammonium formate can be used as a nitrogen source in the PK synthesis of pyrroles from l,4-diaryl-2-butene-l,4-diones under Pd-catalyzed transfer hydrogenation conditions. 

Enantioselective hydrogenation of 2,3-butanedione and 3,4-hexanedione has been studied over cinchonidine - Pt/Al203 catalyst system in the presence or absence of achiral tertiary amines (quinuclidine, DABCO) using solvents such as toluene and ethanol. Kinetic results confirmed that (i) added achiral tertiary amines increase both the reaction rate and the enantioselectivity, (ii) both substrates have a strong poisoning effect, (iii) an accurate purification of the substrates is needed to get adequate kinetic data. The observed poisoning effect is attributed to the oligomers formed from diketones. 

In this study enantioselective hydrogenation of diketones (2,3-butanedione (BD), 3,4-hexanedione (HD)) (see Scheme 1) was investigated in the presence or absence of ATAs using solvents, such as toluene and ethanol. In addition, the importance of the purification of these substrates will be discussed. The main goal of this study is to get further information about the effect of ATAs in case of substrates, such as of a,p-diketones. 

The results of hydrogenation obtained using different batches of 3,4-hexanedione and different purification methods are given in Table 1. The data... 

Figure 2 Conversion-enantioselectivity dependencies in the hydrogenation of 3,4-hexanedione A - reaction in toluene, B - reaction in ethanol.

Hydrogenation of 3,4-hexanedione was used to compare the behaviour of different supported platinum catalysts. The highest rate has been obtained over Pt/MCM-41 catalyst. It was the only catalysts, where the rate constant k2 exceeded ki, i.e., there was no catalyst deactivation during the catalytic run. It is... 

Table 3 Kinetic data of enantioselective hydrogenation of 3,4-hexanedione over different types of supported Pt catalysts.

Nonmetallic neurotoxins are frequently used in industry in manufacturing of chemicals and resins or as solvents. Some examples are hydrogen sulfide (which paralyzes specifically the nervous centers that control respiratory movement), carbon disulfide, -hexane, methyl -butyl ketone, and acrylamide. Exposure to all of these substances may occur through inhalation of vapors. In addition, carbondisufide and acrylamide may enter the system by dermal absorption. -Hexane and methyl -butyl ketone are not toxic by themselves but are activated by cytochrome P-450 to the neurotoxic hexanedione (CH3COCH2CH2COCH3). 

Silica gel G Butanol/1.5 A/HCI/2,5-hexanedione 100 20 0.5 Hydrogen sulfide group... 

Even though the Paal-Knorr pyrrole synthesis has been around for 120 years, its precise mechanism was the subject of debate. In 1991, V. Amarnath et al. investigated the intermediates of the reaction and determined the most likely mechanistic pathway. The formation of pyrroles was studied on various racemic and meso-3,4-diethyl-2,5-hexanediones. The authors found that the rate of cyclization was different for the racemic and meso compounds and the racemic isomers reacted considerably faster than the meso isomers. There were two crucial observations 1) the stereoisomers did not interconvert under the reaction conditions and 2) there was no primary kinetic isotope effect for the hydrogen atoms at the C3 and C4 positions. These observations led to the conclusion that the cyclization of the hemiaminal intermediate is the rate-determining (slow) step. 

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