Aldehyde stability

Aldehyde-collidine, 30, 42 Aldehydes, stabilization against autoxida-tion, 37, 40... 

Compounds of the general formula 69 are prepared by cycloaddition of N-methyl- or A(-arylmaleimides with arylidene imines of AAs and in the presence of an aromatic aldehyde. Stabilized azomethine ylides are formed as intermediates, which then afford the cycloadducts. Several isomers are formed, and the influence of various metal salts and solvents was investigated (87BCJ4067 88T557). Similar transformations have been performed with A-ailyl glycine esters (91TL1359). 

Uses. Manufacture of adipic acid, maleic acid, hexahydrobenzoic acid, and aldehyde stabilizer for high-octane gasoline... 

Addition, of potassium cyanide to diethyl benzalmalonate, 30, 84 of sodium bisulfite, to cyclo-heptanone, 34, 25 to phenanthrenequmone, 34, 76 Adipyl azide, 36, 70 Adipyl hydrazide, 36, 69 Alanine, 33, 1 Aldehjde collidine, 30, 42 Aldehydes, stabilization against autoxidation, 37, 40 Aldehyde synthesis, 31, 92... 

The addition of metalated sulfones to aldehydes or ketones is a reversible reaction and the principal cause of failure in the Julia alkenation results from an unfavorable equilibrium at this stage. The reverse reaction is favored when the P-alkoxy sulfone adduct is sterically encumbered. Adducts derived from ketones are more vulnerable than those derived from aldehydes. Stabilization of the sulfone anion by conjugation with an aromatic ring or chelation with a proximate heteroatom are also important contributors to favoring the reverse reaction. However, by varying the metal counterion, the position of equilibrium can be adjusted. For example, the lithio derivative of the sulfone (61 Scheme 24) failed to... 

USE Identification of aldehydes stabilizer for resins and rubber. Intermediate in the manufacture of antihistamines. 

Alkyl substituents stabilize a carbonyl group m much the same way that they sta bilize carbon-carbon double bonds and carbocations—by releasing electrons to sp hybridized carbon Thus as then heats of combustion reveal the ketone 2 butanone is more stable than its aldehyde isomer butanal... 

The carbonyl carbon of a ketone bears two electron releasing alkyl groups an aldehyde carbonyl group has only one Just as a disubstituted double bond m an alkene is more stable than a monosubstituted double bond a ketone carbonyl is more stable than an aldehyde carbonyl We 11 see later m this chapter that structural effects on the relative stability of carbonyl groups m aldehydes and ketones are an important factor m then rel ative reactivity... 

Consider first the electronic effect of alkyl groups versus hydrogen atoms attached to C=0 Recall from Section 17 2 that alkyl substituents stabilize C=0 making a ketone carbonyl more stable than an aldehyde carbonyl As with all equilibria factors... 

Conjugation of the newly formed double bond with the carbonyl group stabilizes the a p unsaturated aldehyde provides the driving force for the dehydration and controls Its regioselectivity Dehydration can be effected by heating the aldol with acid or base Normally if the a p unsaturated aldehyde is the desired product all that is done is to carry out the base catalyzed aldol addition reaction at elevated temperature Under these conditions once the aldol addition product is formed it rapidly loses water to form the a p unsaturated aldehyde... 

Like the carbonyl group of aldehydes and ketones the carbon of a C=0 unit m a carboxylic acid is sp hybridized Compared with the carbonyl group of an aldehyde or ketone the C=0 unit of a carboxylic acid receives an extra degree of stabilization from its attached OH group... 

Stabilized anions exhibit a pronounced tendency to undergo conjugate addition to a p unsaturated carbonyl compounds This reaction called the Michael reaction has been described for anions derived from p diketones m Section 18 13 The enolates of ethyl acetoacetate and diethyl malonate also undergo Michael addition to the p carbon atom of a p unsaturated aldehydes ketones and esters For example... 

Antioxidants. The 1,2-dihydroquinolines have been used in a variety of ways as antioxidants (qv). For example, l,2-dihydro-2,2,4-trimethylquinoline along with its 6-decyl [81045-48-9] and 6-ethoxy [91-53-2] derivatives have been used as antio2onants (qv) and stabilizers (68). A polymer [26780-96-1] of l,2-dihydro-2,2,4-trimethylquinoline is used in resins, copolymers, lubricant oils, and synthetic fibers (69). These same compounds react with aldehydes and the products are useful as food antioxidants (70). A cross-linked polyethylene prepared with peroxides and other monomers in the presence of l,2-dihydro-6-ethoxyquinoline produces polymers with a chemically bonded antioxidant (71). 

Inductive and resonance stabilization of carbanions derived by proton abstraction from alkyl substituents a to the ring nitrogen in pyrazines and quinoxalines confers a degree of stability on these species comparable with that observed with enolate anions. The resultant carbanions undergo typical condensation reactions with a variety of electrophilic reagents such as aldehydes, ketones, nitriles, diazonium salts, etc., which makes them of considerable preparative importance. 

By using an aromatic aldehyde carrying an electron-releasing group the intermediate cation can be stabilized. This is the basis of the widely-used Ehrlich colour reaction for pyrroles, indoles and furans which have a free reactive nuclear position (Scheme 21). 

The stabilized phosphonium ylide (601) reacts with aromatic aldehydes to give N-phenacylpyrazoles (602) in good yields (73CC7). Ketone semicarbazones and ketazines react with two moles of phosphorus oxychloride-DMF, the Vilsmeier-Haack reagent, with the formation of 4-formylpyrazoles (603 R = H or PhC=CH2) (70JHC25, 70TL4215). 

The benzodiazepine fused azetes (353 R = Et, Pr) have been claimed as useful tranquilizers and sedatives (76BRP1448895). However, their stability and formation from benzodiazepines (352) by reaction with an aldehyde and base is hard to reconcile with the proposed structure. 

HORNER - WADSWORTH - EMMONS Olelination Wittig type reaction of ptwsptionale stabilized carbanions with aldehydes or ketones to form olefins... 

Enolates of aldehydes, ketones, and esters and the carbanions of nitriles and nitro compounds, as well as phosphorus- and sulfur-stabilized carbanions and ylides, undergo the reaction. The synthetic applications of this group of reactions will be discussed in detail in Chapter 2 of Part B. In this section, we will discuss the fundamental mechanistic aspects of the reaction of ketone enolates with aldehydes md ketones. 

According to this concept, the aldol condensation normally occurs through a chairlike transition state. It is further assumed that the stmcture of this transition state is sufficiently similar to that of chair cyclohexane to allow the conformational concepts developed for cyclohexane derivatives to be applied. Thus, in the example above, the reacting aldehyde is shown with R rather than H in the equatorial-like position. The differences in stability of the various transition states, and therefore the product ratios, are governed by the steric interactions between substituents. 

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