Alcohols from aldehyde hydrogenation

The formation of mercaptan is doubly important because of its relation to phytochemical reduction processes. The reaction is analogous to the formation of ordinary alcohols from aldehydes and it also indicates how the plant is capable of synthesizing intensely odorous substances from aldehydes and hydrogen sulfide in a simple manner. The isolation... 

This reaction has general application in the preparation of alcohols from aldehydes without a-hydrogens. 

Hydroformylation. Probably the best known catalytic carbonylation reaction is the hydroformylation, or 0x0 reaction, for producing aldehydes and alcohols from carbon monoxide, hydrogen, and olefins (eq. 9) (36). 

Other synthetic methods have been investigated but have not become commercial. These include, for example, the hydration of ethylene in the presence of dilute acids (weak sulfuric acid process) the conversion of acetylene to acetaldehyde, followed by hydrogenation of the aldehyde to ethyl alcohol and the Fischer-Tropsch hydrocarbon synthesis. Synthetic fuels research has resulted in a whole new look at processes to make lower molecular weight alcohols from synthesis gas. 

Nature has designed the active sites in the enzymes GO and glyoxal oxidase in order to perform a hydrogen-atom abstraction reaction from the a-carbon atom of an O-bound alcoholate (or aldehyde) in the rds. The essence of this chemistry is depicted in Fig. 8. 

Dehydrogenation. The removal of one or more hydrogen atoms from a molecule by chemical means, as in the conversion of alcohols to aldehydes. For example, methanol (CH3OH) can be oxidized to formaldehyde (HCHO) plus H2. ... 

Scheme 13 Enantioselective carbonyl tert-prenylation from the alcohol or aldehyde oxidation level via iridium-catalyzed C-C bond-forming transfer hydrogenation...

More recently, using the cyclometallated iridium C,(7-benzoate derived from allyl acetate, 4-methoxy-3-nitrobenzoic acid and BIPHEP, catalytic carbonyl crotylation employing 1,3-butadiene from the aldehyde, or alcohol oxidation was achieved under transfer hydrogenation conditions [274]. Carbonyl addition occurs with roughly equal facility from the alcohol or aldehyde oxidation level. However, products are obtained as diastereomeric mixtures. Stereoselective variants of these processes are under development. It should be noted that under the conditions of ruthenium-catalyzed transfer hydrogenation, conjugated dienes, including butadiene, couple to alcohols or aldehydes to provide either products of carbonyl crotylation or p,y-enones (Scheme 16) [275, 276]. 

Primary alcohols 121 undergo an efficient oxidative dimerization by [IrCl(coe)2]2 under air, without any solvent, to form esters 122 in fair to good yields (Equation 10.30) [54]. The reaction is initiated by the in situ generation of an Ir-hydride complex via hydrogen transfer from alcohols to afford aldehydes, followed by the dehydrogenation of hemiacetals derived from alcohols and aldehydes by action of the Ir-complex to afford esters. 

---