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Condensation of acetaldehyde

The selective intermolecular addition of two different ketones or aldehydes can sometimes be achieved without protection of the enol, because different carbonyl compounds behave differently. For example, attempts to condense acetaldehyde with benzophenone fail. Only self-condensation of acetaldehyde is observed, because the carbonyl group of benzophenone is not sufficiently electrophilic. With acetone instead of benzophenone only fi-hydroxyketones are formed in good yield, if the aldehyde is slowly added to the basic ketone solution. Aldols are not produced. This result can be generalized in the following way aldehydes have more reactive carbonyl groups than ketones, but enolates from ketones have a more nucleophilic carbon atom than enolates from aldehydes (G. Wittig, 1968). [Pg.56]

Reactions with Aldehydes and Ketones. The base-catalyzed self-addition of acetaldehyde leads to formation of the dimer, acetaldol [107-89-1/, which can be hydrogenated to form 1,3-butanediol [107-88-0] or dehydrated to form crotonaldehyde [4170-30-3]. Crotonaldehyde can also be made directiy by the vapor-phase condensation of acetaldehyde over a catalyst (53). [Pg.50]

Ethyl acetate [141-78-6] is produced commercially by the Tischenko condensation of acetaldehyde using an aluminum ethoxide catalyst (60). The Tischenko reaction of acetaldehyde with isobutyraldehyde [78-84-2] yields a mixture of ethyl acetate, isobutyl acetate [110-19-0] and isobutyl isobutyrate [97-85-8] (61). [Pg.50]

Reaction of one mole of acetaldehyde and excess phenol in the presence of a mineral acid catalyst gives l,l-bis(p-hydroxyphenyl)ethane [2081-08-5], acid catalysts, acetaldehyde, and three moles or less of phenol yield soluble resins. Hardenable resins are difficult to produce by alkaline condensation of acetaldehyde and phenol because the acetaldehyde tends to undergo aldol condensation and self-resinification (see Phenolic resins). [Pg.51]

The Reaction. Acrolein has been produced commercially since 1938. The first commercial processes were based on the vapor-phase condensation of acetaldehyde and formaldehyde (1). In the 1940s a series of catalyst developments based on cuprous oxide and cupric selenites led to a vapor-phase propylene oxidation route to acrolein (7,8). In 1959 Shell was the first to commercialize this propylene oxidation to acrolein process. These early propylene oxidation catalysts were capable of only low per pass propylene conversions (ca 15%) and therefore required significant recycle of unreacted propylene (9—11). [Pg.123]

In this manner, self-condensation of acetaldehyde is rninimi2ed and yields in the range of 77—85% are obtained. However, even with these precautions a detectable amount of 5-phen5l-2,4-pentadienal [13466-40-5] is invariably formed. [Pg.175]

An alternative route for n-hutanol is through the aldol condensation of acetaldehyde (Chapter 7). [Pg.233]

What is the structure of the enone obtained from aldol condensation of acetaldehyde ... [Pg.883]

There is evidence (in the self-condensation of acetaldehyde) that a water molecule acts as a base (even in concentrated H2SO4) in assisting the addition of the enol to the protonated aldehyde Baigrie, L.M. Cox, R.A. Slebocka-Tilk, H. Tencer, M. Tidwell, T.T. J. Am. Chem. Soc., 1985, 107, 3640. [Pg.1282]

In contrast to the above, other reactions have been found to require base assistance by water in the rate-determining step, i.e. the water activity does appear in the rate law. The mechanism formulated for the condensation of acetaldehyde in sulfuric acid is given in equation (63), following on from the enolization of Scheme 7, subsequent dehydration to crotonaldehyde occurring as shown in Scheme 8. The ky k2, k3 and k 3 steps shown were all studied.246... [Pg.44]

The above method is adapted from the procedure of Day and Thorpe.1 /3-Methylglutaric acid has been prepared by hydrolysis of jS-methylglutaronitrile 2 by condensation of crotonic ester with ethyl sodiocyanoacetate, and with sodiomalonic ester 3 4 and by condensation of acetaldehyde with malonic ester. ... [Pg.31]

The formation mechanisms and the nature of chromophores in PET are still a matter of discussion. Postulated chromophores are polyenaldehydes from the aldol condensation of acetaldehyde [73] and polyenes from polyvinyl esters [69], as well as quinones [74, 75], Goodings [73] has proposed aldol condensation as forming poly conjugated species by subsequent reactions of acetaldehyde molecules (Figure 2.16). [Pg.62]

The condensation of acetaldehyde with excess formaldehyde in the presence of aqueous calcium hydroxide yields pentaerythritol (62) esterification of the latter with absolute nitric acid yields the powerful explosive, pentaerythritol tetranitrate (PETN) (3). ... [Pg.108]

On an industrial scale, cinnamaldehyde is prepared almost exclusively by alkaline condensation of benzaldehyde and acetaldehyde. Self-condensation of acetaldehyde can be avoided by using an excess of benzaldehyde and by slowly adding acetaldehyde [154]. [Pg.110]

Examples are the formation of diacetone alcohol from acetone [reaction type (A)] catalysed by barium or strontium hydroxide at 20—30°C [368] or by anion exchange resin at 12.5—37.5°C [387], condensation of benzaldehyde with acetophenone [type (C)] catalysed by anion exchangers at 25—-45°C [370] and condensation of furfural with nitromethane [type (D)] over the same type of catalyst [384]. The vapour phase self-condensation of acetaldehyde over sodium carbonate or acetate at 50°C [388], however, was found to be first order with respect to the reactant. [Pg.342]

Langmuir—Hinshelwood-type equations were applied in some cases. The kinetics of the vapour phase condensation of acetaldehyde with formaldehyde to acrolein at 275—300°C over sodium-containing silica gel... [Pg.342]

The formation of deoxyribose, die pentose moiety of deoxyribonucleic acid, can occur directly from ribose while the latter is in the form of a nucleotide diphosphate. Deoxyribose-5-phosphate can also be formed by condensation of acetaldehyde and glyceraldehyde-3-phosphate. [Pg.282]

The carbon skeleton of butanoic acid may be assembled by an aldol condensation of acetaldehyde. [Pg.514]

Kobayashi (1989) reported the formation of Sotolon in wines by an aldol condensation of acetaldehyde and a-ketobutiric acid (derived from threonine) followed by lactonization (Fig. 7.11). During aging, ethanol is converted into acetaldehyde, thus allowing the formation of Sotolon (Silva Ferreira et ah, 2003). [Pg.235]


See other pages where Condensation of acetaldehyde is mentioned: [Pg.50]    [Pg.431]    [Pg.66]    [Pg.199]    [Pg.70]    [Pg.16]    [Pg.84]    [Pg.226]    [Pg.62]    [Pg.9]    [Pg.200]    [Pg.1414]    [Pg.49]    [Pg.258]    [Pg.143]    [Pg.147]    [Pg.397]    [Pg.341]    [Pg.343]    [Pg.345]    [Pg.459]    [Pg.468]    [Pg.524]    [Pg.67]    [Pg.477]    [Pg.485]    [Pg.166]   
See also in sourсe #XX -- [ Pg.21 ]




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