Aldehydes, catalytic

Although the Wittig reaction (section 4.3.1) and its modified versions provide highly effective and general methods for the aldehydes and ketones alkenation, there are several drawbacks in their use. To overcome these drawbacks, new methods which employ the transition metal complex reagents " as catalysts have been developed. A variety of catalytic aldehyde alkenation reactions have been reported with Mo catalyst other metals such as Re, Ru, Rh and Fe are also established as useful catalysts. Very mild conditions are required for catalytic alkenation short reaction times and high selectivities are generally observed. 

Catalytic aldehyde oxidation without a chain mechanism... 

Based on the above experimental observation combined with the assumption of 16-electron reactive intermediates, Heck and Breslow proposed a mechanism for the cobalt-catalyzed olefin hydroformylation, which gives a qualitative explanation of the catalytic aldehyde formation by a sequence of hydrido-, alkyl-, and acylcobalt complexes according to Scheme 1 (99). 

Because of the olefin isomerization that accompanies the stoichiometric and the catalytic aldehyde formation is also inhibited by carbon monoxide, it was assumed that HCo(CO)3 is the catalyst for this reaction as well according to the equilibria in Scheme 2 (99). 

A comparison of the rates of HCo(CO)4 formation from Co2(CO)8 with those of olefin hydroformylation can be seen in Table 7. The comparison of the rates shows that the rate of catalytic aldehyde formation is higher than the rate of HCo(CO)4 formation from Co2(CO)8 under the same conditions. 

Reductive Cleavage of Alkylcobalt Carbonyls. Saturated product-formation accompanies not only the catalytic aldehyde-formation as a side reaction but the stoichiometric aldehyde-formation as well. Beside carbonylated products substantial amounts (20-40%) of saturated product is the result of the reaction of various olefins and HCo(CO)4 using a low olefin HCo(CO)4 molar ratio. Under such conditions with 1-substituted vinylarenes and with conjugated diolefins almost exclusively the saturation of the carbon-carbon double bond occurs. See Table 13 for characteristic examples. 

By catalytic reduction of a p-unsaturated ketones, prepared from aldehydes by the Claisen - Schmidt reaction (see under Aromatic Aldehydes), for example ... 

The phenylacetic acid derivative 469 is produced by the carbonylation of the aromatic aldehyde 468 having electron-donating groups[jl26]. The reaction proceeds at 110 C under 50-100 atm of CO with the catalytic system Pd-Ph3P-HCl. The reaction is explained by the successive dicarbonylation of the benzylic chlorides 470 and 471 formed in situ by the addition of HCl to aldehyde to form the malonate 472, followed by decarboxylation. As supporting evidence, mandelic acid is converted into phenylacetic acid under the same reaction conditions[327]. 

As mentioned previously, aldehydes can be prepared by Stephen s method of reduction of nitriles by stannous chloride (37, 91). Polaro-graphic reduction of thiazolecarboxylic acids and their derivatives gives lower yields of aldehydes (58). Ozonolysis of styrylthiazoles, for example, 2-styryl-4-methylthiazole, followed by catalytic reduction gives aldehyde with 47% yield of crude product (30). 

For most laboratory scale reductions of aldehydes and ketones catalytic hydro genation has been replaced by methods based on metal hydride reducing agents The two most common reagents are sodium borohydride and lithium aluminum hydride... 

Reduction (Section 2 19) Gam in the number of electrons as sociated with an atom In organic chemistry reduction of carbon occurs when a bond between carbon and an atom which IS more electronegative than carbon is replaced by a bond to an atom which is less electronegative than carbon Reductive ami nation (Section 22 10) Method for the prepara tion of amines in which an aldehyde or a ketone is treated with ammonia or an amine under conditions of catalytic hy drogenation... 

Although stoichiometric ethynylation of carbonyl compounds with metal acetyUdes was known as early as 1899 (9), Reppe s contribution was the development of catalytic ethynylation. Heavy metal acetyUdes, particularly cuprous acetyUde, were found to cataly2e the addition of acetylene to aldehydes. Although ethynylation of many aldehydes has been described (10), only formaldehyde has been catalyticaHy ethynylated on a commercial scale. Copper acetjlide is not effective as catalyst for ethynylation of ketones. For these, and for higher aldehydes, alkaline promoters have been used. 

Oxo Synthesis. Ad of the synthesis gas reactions discussed to this point are heterogeneous catalytic reactions. The oxo process (qv) is an example of an industriady important class of reactions cataly2ed by homogeneous metal complexes. In the oxo reaction, carbon monoxide and hydrogen add to an olefin to produce an aldehyde with one more carbon atom than the original olefin, eg, for propjiene ... 

In the early 1920s Badische Arulin- und Soda-Fabrik aimounced the specific catalytic conversion of carbon monoxide and hydrogen at 20—30 MPa (200—300 atm) and 300—400°C to methanol (12,13), a process subsequendy widely industrialized. At the same time Fischer and Tropsch aimounced the Synth in e process (14,15), in which an iron catalyst effects the reaction of carbon monoxide and hydrogen to produce a mixture of alcohols, aldehydes (qv), ketones (qv), and fatty acids at atmospheric pressure. 

Commercially, pure ozonides generally are not isolated or handled because of the explosive nature of lower molecular weight species. Ozonides can be hydrolyzed or reduced (eg, by Zn/CH COOH) to aldehydes and/or ketones. Hydrolysis of the cycHc bisperoxide (8) gives similar products. Catalytic (Pt/excess H2) or hydride (eg, LiAlH reduction of (7) provides alcohols. Oxidation (O2, H2O2, peracids) leads to ketones and/or carboxyUc acids. Ozonides also can be catalyticaHy converted to amines by NH and H2. Reaction with an alcohol and anhydrous HCl gives carboxyUc esters. 

These precursors are prepared by reaction of fuming nitric acid in excess acetic anhydride at low temperatures with 2-furancarboxaldehyde [98-01-1] (furfural) or its diacetate (16) followed by treatment of an intermediate 2-acetoxy-2,5-dihydrofuran [63848-92-0] with pyridine (17). This process has been improved by the use of concentrated nitric acid (18,19), as well as catalytic amounts of phosphoms pentoxide, trichloride, and oxychloride (20), and sulfuric acid (21). Orthophosphoric acid, -toluenesulfonic acid, arsenic acid, boric acid, and stibonic acid, among others are useful additives for the nitration of furfural with acetyl nitrate. Hydrolysis of 5-nitro-2-furancarboxyaldehyde diacetate [92-55-7] with aqueous mineral acids provides the aldehyde which is suitable for use without additional purification. 

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