Aldehydes 1.4- additions

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... 

Figure 19.14 Carboxylic acid derivatives have an electronegative substituent Y = -Br, —Cl, -OR, -NR2 that can be expelled as a leaving group from the tetrahedral intermediate formed by nucleophilic addition. Aldehydes and ketones have no such leaving group and thus do not usually undergo this reaction.

Aldehydes and ketones show a strong C=0 bond absorption in the IR region from 1660 to 1770 cm-1, as the spectra of benzaldehj7de and cyclohexanone demonstrate (figure 19.17). In addition, aldehydes show two characteristic C-H absorptions in the range 2720 to 2820 cm-1. 

Dialkylboron enolates cannot accommodate an additional aldehyde ligand group and chelated TSs are not expected. When BF3 is used as the Lewis acid, chelation is... 

Additional aldehydes and ketones were also included in the U.S. Nationwide Occurrence Study dimethylglyoxal (2,3-butanedione), cyanoformaldehyde, 2-butanone (methyl ethyl ketone), trans-2-hexanal, 5-keto-l-hexanal, and 6-hydroxy-2-hexanone [11, 13]. Dimethylglyoxal was the most consistently detected of these carbonyl compounds (up to 3.5 pg/L) and was found at higher levels in plants using ozone. Maximum levels of 0.3, 5.0, and 0.7 pg/L were observed for cyanoformaldehyde, 2-butanone, and trans-2-hexenal, respectively 6-hydroxy-2-hexanone and 5-keto-1 -hexanal were only detected in early stages of treatment, and not in finished waters. 

The reduced chromium precipitate is soluble in saturated sodium bicarbonate solution but no additional aldehyde was obtained on extracting this bicarbonate solution with ether. 

The selective donor-acceptor concept can be transferred to other ThDP-dependent enzymes. For example, enantiopure mixed benzoins were obtained when 2-chlorobenzaldehyde reacted with a variety of selective donor aldehydes in the presence of BAL [67]. By performing various cross-benzoin condensation reactions with this enzyme, not only new selective donors but also additional aldehydes reacting selectively as acceptors, such as 2-iodobenzaldehyde or 2,6-difluorobenzaldehyde, could be identified. Again all the mixed benzoins generated exhibited an R-configuration and were obtained with high to excellent enantiomeric excesses [69]. 

The roundish flower head, the curd, of the cauliflower plant (Brasska oleracea var. botrytis) is the edible portion of this vegetable. It can be eaten raw in salads or as a pickled condiment in vinegar. More often it is boiled and eaten with the main meal or is converted into sauces and soups. Over 80 volatile compounds have been identified in raw and cooked cauliflower. Among the compounds potentially active in cooked cauliflower, certain sulfides such as methanethiol, dimethyl sulfide and dimethyl trisulflde have often been incriminated in objectionable sulfurous aromas and overcooked off-flavours [169, 177, 178, 181-183]. Additional aldehydes have been found to be the most abundant cauliflower volatiles, with nonanal as a major component [175,177]. A recent study showed that volatiles such as 2-propenyl isothiocyanate, dimethyl trisulflde, di-... 

The reaction of a 1,3-dithiolane (336) with n-butyllithium has been shown to result in fragmentation to the corresponding thiocarbonyl compound via the mechanism detailed in Scheme 73 (80JA3S77). The thiocarbonyl compound can react further with excess lithium reagent to provide the product of carbon addition (aldehyde precursors) or reduction (saturated ketones). 

Aldehydes and ketones react with alcohols to form hemiacetols and hemiketah, respectively. In this reaction the alcohols react in typical fashion as the nucleophile. When aldehydes and ketones are attacked by a nucleophile, they undergo addition. Aldehydes and hemiacetals, and ketones and hemiketals, exist in equilibrium when an aldehyde or ketone is dissolved in an alcohol however, usually the hemiacetal or hemiketal is too unstable to isolate unless if exists as a ring structure. If a second molar equivalent of alcohol is added, an oceiuf is formed from a hemiacetal, or a ketal is formed from a hemiketal. 

In addition to nucleophilic additions, aldehydes and ketones show an unusual acidity of hydrogen atoms attached to carbons alpha (adjacent) to the carbonyl group. These hydrogens are referred to as a hydrogens, and the carbon to which they are bonded is an a carbon. In ethanal, there is one a carbon and three a hydrogens, while in acetone there are two a carbons and six a hydrogens. 

The Prins Reaction is the acid-catalyzed of addition aldehydes to alkenes, and gives different products depending on the reaction conditions. It can be thought of conceptually as the addition of the elements of the gem-diol carbonyl hydrate of the aldehyde across the double bond. 

A flask containing nitrone (1 equiv) and imidazolidinone catalyst-HX (20 mol%) was charged with MeNC>2 (0.1 M), and then with the appropriate amount of H20 (3 equiv). After cooling the solution to the desired temperature, a,/ -unsaturated aldehyde (4 equiv) was added dropwise to the flask. Additional aldehyde (3 equiv) was added to the reaction mixture at 24-h intervals until the reaction was complete (96-160 h). The resulting solution was passed through a silica gel column with AcOEt. The removal of volatiles afforded an oily residue that was purified by silica gel chromatography to afford the title compound. 

Theee factors are discussed In groups (esters, amides) give more conjugate addition. Aldehydes are unhindered and very... 

We have presented all these points in order to make the reader realize why relatively few papers in the literature are concerned with the kinetics of aldehyde polymerizations. It is almost impossible to take into consideration all the facts that have been discussed in this introduction in each experiment. Consequently, most authors report simply the time versus conversion curve of the polymerization without a detailed scrutiny of the individual factors. In addition, aldehyde polymerizations are fast, in some cases almost explosive with poor temperature control, and many aldehyde polymerizations are carried out in a semibatch process with continuous addition of monomers, although we know commercial processes are carried out in continuous reaction. 

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