Other saturated aldehydes

The determinations by McDowell and Sharpies [62] of the rate coefficients for and for the propionaldehyde—oxygen system can be summarized by 

These values differ somewhat from the corresponding determinations for acetaldehyde [62]. However, the oxidation rates of the two aldehydes are similar (see Fig. 1), suggesting that either there is a fortuitous combination of 3, /24a and feg c values for the two systems or, as seems more likely, the difference between the propagation and termination coefficients for the two systems is less than the experimental determinations would suggest. 

The limiting high pressure decomposition of acyl radicals (RCO) 

In other respects, and particularly at lower temperatures, the oxidation of propionaldehyde closely resembles that of acetaldehyde. In particular, Fig. 3 shows that, in the early stages, the course of the reaction is in agreement with eqn. (VI) (p. 383), feia/ sc being 1/31 at 62.5 [43]. 

There is little published work on the oxidation of the butyraldehydes, most of what is available being concerned with oxidation in the hi temperature region. 

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Methylpentanal. Early studies of propanal and 1-butanal in the gas phase have been reviewed by Cundall and Davies (61). Only a few other saturated aldehydes have been studied recently, and 3-methylpentanal is one of them. Rebbert and Ausloos (195) have compared the direct and the triplet-sensitized photolysis of 3-methylpentanal, since this molecule can undergo two kinds of intramolecular rearrangement process / Norrish type II process 18, a primary or a secondary a-hydrogen atom transfer to the carbonyl oxygen, giving 1-butene or trans/cis-2-butene, respectively. 

The presence of the double bond modifies to some extent the reactions of the aldehyde group in acrolein it does not unite with ammonia to form an addition-product similar to that formed by acetaldehyde and most other saturated aldehydes. The union of acrolein with ammonia takes place according to the equation,—... 

The carbonyl-group carbon atoms of aldehydes and ketones have characteristic 13C NMR resonances in the range 190 to 215 8. Since no other kinds of carbons absorb in this range, the presence of an NMR absorption near 200 8 is clear evidence for a carbonyl group. Saturated aldehyde or ketone carbons usually absorb in the region from 200 to 215 8, while aromatic and a,p-unsaturated carbonyl carbons absorb in the 190 to 200 5 region. 

Concerning the hydrogenation of a,P-unsaturated aldehydes, monometallic systems based on transihon metals readily achieve the reachon, leading to saturated aldehydes (SALs), saturated alcohols (SOLs) and, to a lesser extent, unsaturated alcohols (UOLs) (Scheme 6.2). To improve the selechvity towards UOL, which is generally the desired product, diverse alternahves have been studied, such as the use of different supports, increased metal parhcle size and promotion of the metallic phase by the addition of other metals [73, and references therein]. 

From a thermodynamic point of view, the hydrogenation of the C=C bond is more favorable than that of the C=0 group. Since there are numerous other important processes to synthesize saturated aldehydes and ketones, the main objective of recent research efforts is to increase the selectivity of hydrogenation of unsaturated oxo compounds into unsaturated alcohols. The results summarized below clearly indicate the significant success achieved in the selective hydrogenation of unsaturated aldehydes. The hydrogenation of unsaturated ketones, in turn, cannot be accomplished yet with similar selectivities. 

Two examples of such applications are outlined in Scheme 3. In the first one imidazolidinone la 10 mol% catalyzed the conjugated addition of a plethora of variously substituted N,N-disubstituted anilines to ,/fun saturated aldehydes to afford highly enantiomerically enriched /3-aryl aldehydes 5 (ee 89-97 %) in good yields (>73 %) [3]. On the other hand, the use of cationic BINAP-Cu complexes 6 (1-5 mol%) was found to be effective in the stereocontrolled 1,2-addition of indoles to the N-tosyl-a-imino ester 7 in TFIF at -78 °C [4]. 

The reactions taking place in the vapour phase also occur in the condensed phase, and their mechanisms are probably similar. However, as may be expected on the basis of the results obtained for the gas phase photolysis, the formation of olefins, cycloparaffins, and CO is of less importance, while that of the saturated aldehydes is more important in the liquid phase or solution, where energy dissipation by collision is more efficient. The decarbonylation products were shown to be only of minor importance in the photolysis of liquid cyclopentanone and cyclohexanone . The unsaturated aldehyde was found to be the main product in the liquid-phase photolysis of cyclopentanone (methyl cyclohexanone . Unsaturated aldehydes were also identified in the photolysis products of other cyclic ketones in the liquid phase as well as in solution . ... 

ADH was isolated and partially purified from orange juice vesicles and examined for substrate specificity, maximum relative velocity (Vr) and affinity (1/Km) (12) Ethanol is the preferred saturated alcohol for reduction to the aldehyde based on Vr and 1/Km. Unsaturated alcohols, 2-propenol, 2-butenol and 2-hexenol, had comparable to or higher Vr s and l/Km s than ethanol. ADH had 5- to 30-fold greater affinity for saturated aldehydes than the corresponding saturated alcohols, whereas affinities of the unsaturated alcohols and aldehydes were similar. The apparent equilibrium constants (Kapp = 0.003 for ethanol - acetaldehyde pair) favor alcohol formation in the saturated series. Other aldehydes compete with acetaldehyde for the enzyme but the concentration of acetaldehyde is much higher than other aldehydes in juice vesicles and the 1/Km for acetaldehyde is 10 X higher than for other aldehydes found in the juice vesicles. 

Both these silyl enol ethers 50 and 52 could of course be hydrolysed to the saturated aldehydes, but that would be to sacrifice the useful reactivity of these intermediates in aldol and other reactions explored in chapters 2-6. A more productive development is to react the silyl enol ether with an electrophile and hence develop a synthesis from three components in two consecutive reactions.23 This approach has formed the basis of many modern syntheses as it develops the target molecule so quickly and is discussed in chapter 37 under tandem reactions . It is not necessary to trap the enolate with Me3SiCl when lithium cuprates are used with ketones as the lithium enolate is the product of 1,4-addition. You may choose the lithium enolate or the silyl enol ether, whichever is more appropriate for the next step. 

Ill) Conjugated Aldehyde, Acid, Ester, Nitrile, Nitro Functions. Double bond hydrogenation of a,)3-unsaturated potentially reducible groups other than ketones is also possible. Aliphatic saturate aldehydes are obtained in high yields by reduction over Pd,... 

Reduction. Conjugated acids are converted to saturated aldehydes by syngas at room temperature, using (acac)Rh(CO)2 in conjunction with a special guanidine as catalyst. Only CO is liberated as stoichiometric side product. Furthermore, conditions for this highly selective reaction do not disturb acetals, esters, carbamates, ethers, silyl ethers, sulfides and many other functional groups. 

The action of trialkyloxonium salts on aliphatic ethers leads to exchange of alkyl groups. Sulfoxides,212 nitriles,213 and disulfides214 can be alkylated smoothly by oxonium salts. Saturated aldehydes and ketones can be alkylated only if, like pinacolin and camphor, they contain a tertiary alkyl group neighboring the carbonyl group. Then for instance, the carboxonium salts obtained can be readily converted by alkali alkoxides into acetals and orthoesters which are difficult to obtain in other ways. 

Modification of V205 was investigated for propene oxidation to saturated aldehydes, acrolein, etc. The impurities added to V205 may be classified as falling into two groups acid (metalloid) anions of S04, P206, and other alkali cations such as Na, K, etc. 

The inactivation of CYP2B4 by aldehydes such as citral (an a,P unsaturated terpenoid aldehyde), and other 2iromatic aldehydes (cinnamaldehyde, benzaldehyde, and 3-phenylpropionaldehyde) is accompanied by bleaching of the heme chro-mophore that is not prevented by catalase, superoxide dismutase, epoxide hydrolase, GSH, or ascorbic acid ". The corresponding values revealed that saturated aldehydes are generally... 

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