Aldehyde hydrogens

Acidic hydrolysis of these hydroxyaLkyl hydroperoxides yields carboxyUc acids, whereas basic hydrolysis regenerates the parent aldehyde, hydrogen peroxide, and often other products. When derived from either aldehydes or cycHc ketones, peroxides (1, X = OH, = H, R, = alkylene or... 

Benzaldehyde is a versatile iatermediate because of its reactive aldehyde hydrogen, its carbonyl group, and the benzene ring. 

Aldehyde Hydrogen Reactions. The hydrogen of the aldehyde groupis readily oxidized to OH, forming benzoic acid [65-85-0]. 

ROSENMUNO < SAITZEW ReAldehyde Hydrogenation of acyl chlorides to aldehydes b) the presence of poisoned Pd catalyst. 

Functional groups that stabilize radicals would be expected to increase susceptibility to autoxidation. This is illustrated by two cases that have been relatively well studied. Aldehydes, in which abstraction of the aldehyde hydrogen is fecile, are easily autoxidized. The autoxidation initially forms a peroxycarboxylic acid, but usually the corresponding carboxylic acid is isolated because the peroxy acid oxidizes additional aldehyde in a... 

Benzoin -As a small cjnantity of potassium cyanide is (apable of converting a large quantity of benzaldehyde into bciv/oin, the action of the cyanide has been explained as follows. The potassium cyanide first reacts with the aldehyde and forms a cyanhydnn, which then condenses with another molecule of aldehyde, hydrogen cyanide being finally eliminated (Lapwortbj,... 

One aldehyde molecule has transferred its aldehyde hydrogen during course of the reaction onto another aldehyde molecule, which is why the reactants are called donor and acceptor (see below). 

The M - 1 peak due to the loss of the aldehyde hydrogen by a-cleavage is usually abundant. The loss of 29 Daltons is characteristic of aromatic aldehydes. Peaks at m/z 39, 50, 51, 63, and 65 and the abundance of the molecular ion show that the compound is aromatic. Accurate mass measurement data indicate the presence of an oxygen atom. 

Mechanisms of aldehyde oxidation are not firmly established, but there seem to be at least two main types—a free-radical mechanism and an ionic one. In the free-radical process, the aldehydic hydrogen is abstracted to leave an acyl radical, which obtains OH from the oxidizing agent. In the ionic process, the first step is addition of a species OZ to the carbonyl bond to give 16 in alkaline solution and 17 in acid or neutral solution. The aldehydic hydrogen of 16 or 17 is then lost as a proton to a base, while Z leaves with its electron pair. 

The strong electron-donating character of 0 greatly facilitates the ability of the aldehydic hydrogen to leave with its electron pair. Of course, this effect is even stronger in 40. When the hydride does leave, it attacks another molecule of aldehyde. The hydride can come from 39 or 40 ... 

These peroxidations affect the aldehydic hydrogen atom, but also hydrocarbon positions in position a of the ketonic carbonyl as already seen (see alcohol group on p.253). Butanone is one of the key compounds that are involved in accidents of this type. The peroxidation is slow, but it seems that when other compounds that can also be moderately peroxidised are present the process is aggravated by their combination. We have already seen an example of such an interaction between 2-butanol and 2-butanone. 

The keto carbonyl group can be hydrogenated fairly readily and many of the characteristics of aldehyde hydrogenations also apply here. Initially, the alcohol is produced, but overhydrogenation may result in hydrogenolysis of the C-O bond to form the alkane (Fig. 2.23). Acidic media facilitate hydrogenolysis whereas basic media or basic substituents inhibit hydrogenolysis. 

More recent advances in iridium-catalyzed aldehyde hydrogenation have been through the use of bidentate ligands [6]. In the hydrogenation of citral and cinnamaldehyde, replacing two triphenylphosphines in [IrH(CO)(PPh3)3] with bidentate phosphines BDNA, BDPX, BPPB, BISBI and PCP (Fig. 15.1) led to an increase in catalytic activity. 

Direct comparisons of the diamine system against the parent complex led to the conclusion that the effect of the diamine and KOH/i-PrOH activator decelerate olefin hydrogenation and in turn accelerate carbonyl hydrogenation. In the published report, there were no attempts to optimize turnover numbers or TOF for aldehyde hydrogenation. However, the catalyst has been shown to hydrogenate ketones with a SCR of 10000 at room temperature, which suggests that these catalysts represent the current state of the art in terms of activity and selectivity. 

Thiols catalyse radical-chain addition of primary aliphatic aldehydes (R CH2CH0) to terminal alkenes (H2C=CR R ) to give ketones, R CH2C0CH2CHR R. The thiol acts as an umpolung catalyst to promote the transfer of the aldehydic hydrogen to the carbon-centred radical formed when an acyl radical adds to the alkene. 

The C-H stretch for the aldehyde hydrogen tends to be a weak band in the 2,960-2,700 cm region of the spectrum. 

---