Alcohols reduction solid-state

The proposed mechanism is given in Scheme 15. Initially the dissociation of water, maybe trapped by the molecular sieve, initiates the catalytic cycle. The substrate binds to the palladium followed by intramolecular deprotonation of the alcohol. The alkoxide then reacts by /i-hydride elimination and sets the carbonyl product free. Reductive elimination of HOAc from the hydride species followed by reoxidation of the intermediate with dioxygen reforms the catalytically active species. The structure of 13 could be confirmed by a solid-state structure [90]. A similar system was used in the cyclization reaction of suitable phenols to dihydrobenzofuranes [92]. The mechanism of the aerobic alcohol oxidation with palladium catalyst systems was also studied theoretically [93-96]. 

G. Canneri found that the treatment of a suspension of thallium sesquioxide in water with liquid nitrous anhydride, and subsequent evaporation of the soln., even in the cold under reduced press., yields, not thallic nitrite, but thallous nitrate. The latter is also obtained when soln. of thallic sulphate and barium nitrite are mixed in the cold, and the resulting liquid evaporated at low temp. That thallic nitrite is capable of existence in soln., although it cannot be obtained in the solid condition, is shown by the analyses and properties of the soln. The treatment of an aq. soln. of thallic nitrite with alcohol yields a precipitate of the sequioxide. In ethereal soln., thallic nitrite is far more stable, and the salt separates in the solid state on evaporation of the solvent it could not, however, be analyzed directly. Decomposition of thallic nitrite, with formation of thallous nitrate, takes place solely in accordance with the equation T1 (N02)3->TlN03+N2Os, neither intermediate reduction products nor thallous-thallic complex compounds being formed. 

Type of reaction reduction Reaction condition solid-state Keywords ketone, NaBH4, alcohol... 

When a mixture of powdered ketone and NaBH4 is kept at room temperature, reduction of the ketone occurs to give the corresponding alcohol [2], When the reaction is carried out in inclusion crystals containing a chiral host compound, the optically active alcohol can be obtained by enantio-control of the reaction by the chiral host. For example, treatment of inclusion crystals of acetophenone (2a) or o-methylacetophenone (2b) and (S,S)-(-)-1,6-bis(o-chlorophenyl)-1,6-diphenylhexa-2,4-diyne-l,6-diol (1) [3] with powdered BH3-ethylenediamine complex (3) in the solid state gave 4a of 44 % ee (96 % yield) or 4b of 59 % ee (57 % yield), respectively [4],... 

The relatively inexpensive and safe sodium borohydride (NaBH4) has been extensively used as a reducing agent because of its compatibility with protic solvents. Varma and coworkers reported a method for the expeditious reduction of aldehydes and ketones that used alumina-supported NaBH4 and proceeded in the solid state accelerated by microwave irradiation (Scheme 7) [50]. The chemoselectivity was apparent from the reduction of frarcs-cinnamaldehyde to afford cinnamyl alcohol. 

Reduction of ketone with NaBH4 also proceeds in the solid state. A mixture of the ketone and a tenfold molar amount of NaBH4 was finely powdered using an agate mortar and pestle and kept in a dry box at room temperature for five days, being stirred once a day. The reaction mixture was extracted with ether, and the dried ether solution was evaporated to give the corresponding alcohol in the yields shown in Table 15-2 [3]. 

Solid state reduction of alkyl aryl ketone 8 in an inclusion complex with the chiral host 10 with borane-ethylenediamine complex 2BH3-NH2CH2CH2NH2 gave optically active alcohol 9 in the optical and chemical yields summarized in Table 15-3 [7],... 

NaBH4 reduction of 8 included in -cyclodextrin also proceeded quite easily in the solid state. However, the product alcohol 9 in all cases gave only a modest level of optical purity [8]. 

While the practically complete decomposition of (49b) in aqueous solutions at ambient conditions takes hours (at pH 3-5) or minutes (at pH 1-3 or 5-10),202 this complex is stable for months in polar aprotic solvents (such as DMF or DMSO), or for years in the solid state.147 The dependence of the redox potential of the Crv IV couple on the nature of the solvent has been studied for (49b).147 A series of mechanistic studies of the electron-transfer reactions of (49b) with inorganic or organic reductants have been performed several reviews of these studies are available.13,155,203-205 Applications of (49b) for the selective oxidations of some alcohols or organic sulfides have been proposed.202,206,207... 

Sodium tetrahydridoborate Sec. alcohols from ketones Solid-state reduction... 

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