Acetaldehydes cleavage

The saponification of 0 labeled ethyl propanoate was desenbed in Section 20 11 as one of the significant expenments that demonstrated acyl-oxygen cleavage in ester hydrolysis The 0 labeled ethyl propanoate used in this expenment was prepared from 0 labeled ethyl alcohol which in turn was obtained from acetaldehyde and 0 enriched water Wnte a senes of equations... 

Most diaziridines are not sensitive towards alkali. As an exception, diaziridines derived from 2-hydroxyketones are quickly decomposed by heating with aqueous alkali. Acetaldehyde, acetic acid and ammonia are formed from (162). This reaction is not a simple N—N cleavage effected intramolecularly by a deprotonated hydroxy group, since highly purified hydroxydiaziridine (162) is quite stable towards alkali. Addition of small amounts of hydroxybutanone results in fast decomposition. An assumed reaction path — Grob fragmentation of a hydroxyketone-diaziridine adduct (163) — is in accord with these observations (B-67MI50800). 

Acenaphthylene, 58, 73 Acetaldehyde, 58, 157 Acetals, cleavage with iodotrimethylsilane, 59, 40... 

Evidence concerning the relative extents of C-C and C-H fission is less well defined for Ce(IV) and Mn(III) as compared with V(V). Pinacol is cleaved to acetone in all cases, but while Mn(IlI) pyrophosphate [like V(V)] oxidises pinacol much faster than butane-2 3-diol, the rate ratio with Ce(IV) is only approximately 3 and the production of acetaldehyde from butane-2 3-diol by Ce(IV) oxidation demonstrates C-C cleavage . It is probable, therefore, that Mn(III) oxidises the disecondary glycol by C-H fission. 

These enzymes catalyse the non-hydrolytic cleavage of bonds in a substrate to remove specific functional groups. Examples include decarboxylases, which remove carboxylic acid groups as carbon dioxide, dehydrases, which remove water, and aldolases. The decarboxylation of pyruvic acid (10.60) to form acetaldehyde (10.61) takes place in the presence of pyruvic decarboxylase (Scheme 10.13), which requires the presence of thiamine pyrophosphate and magnesium ions for activity. 

These cycloadducts, at their most elementary level, are excellent intermediates for the synthesis of 3-substituted furan derivatives. For example, Kawanisi and coworkers reported a synthesis of perillaketone 174 in which the critical step was a Paterno-BUchi photocycloaddition between furan and 4-methylpentanal in the presence of methanesul-fonic acid (Scheme 39)82. This reaction furnished two initial photoadducts, 172 and 173. The unexpected product 173 presumably arises from a Norrish Type II cleavage of 4-methylpentanal to give acetaldehyde, and subsequent cycloaddition with furan. The desired cycloadduct 172 was then converted uneventfully to 174 via acid-catalyzed aromatization and oxidation. 

A closer examination by ex situ analysis using NMR or gas chromatography illustrates that intrazeolite reaction mixtures can get complex. For example photooxygenation of 1-pentene leads to three major carbonyl products plus a mixture of saturated aldehydes (valeraldehyde, propionaldehyde, butyraldehyde, acetaldehyde)38 (Fig. 33). Ethyl vinyl ketone and 2-pentenal arise from addition of the hydroperoxy radical to the two different ends of the allylic radical (Fig. 33). The ketone, /i-3-penten-2-one, is formed by intrazeolite isomerization of 1-pentene followed by CT mediated photooxygenation of the 2-pentene isomer. Dioxetane cleavage, epoxide rearrangement, or presumably even Floch cleavage130,131 of the allylic hydroperoxides can lead to the mixture of saturated aldehydes. 

Cleavage to 2-phenyl-ethylamine, phenyl-acetaldehyde and phenyl-acetic acid N-acetylation... 

Photolysis of 59a in alcohols (ethanol or isopropanol) gave the corresponding indole 62 (R = H), by reductive diazo cleavage, together with acetaldehyde or acetone (66LA17). 

Amine promoters tend to give higher acetaldehyde rates relative to phosphines. Increasing the temperature to 200 increases the rate to 7.1 M/hr whereas decreasing the pressure to 2000 psig markedly lowers the rate. Lil is a critical component of the catalyst. Substituting Lil with Nal, KI, or CH I results in a substantial loss in catalytic activity. A key step in the postulated reaction mechanism, as outlined in Equations 16-18, is cleavage of methyl acetate by Lil to yield CH I and LiOAc (27). ... 

Thiolysis also proved useful for the analysis of derived tannins. Methylmethine-linked tannin-like compounds resulting from acetaldehyde-mediated condensation of flavanols (see Section 5.5.S.2) yielded several adducts when submitted to acid-catalyzed cleavage in the presence of ethanethiol, providing information on the position of linkages in the original ethyl-linked compounds. " Thiolysis of red wine extracts released benzylthioether derivatives of several anthocyanin-flavanol adducts, indicating that such structures were initially linked to proanthocyanidins. However, some of the flavonoid derivatives present in wine (e.g., flavanol-anthocyanins ) are resistant to thiolysis, while others (e.g., flavanol-ethyl anthocyanins) were only partly cleaved. Thiolysis, thus, appears as a rather simple, sensitive, and powerful tool for quantification and characterization of proanthocyanidins, but provides mostly qualitative data for their reaction products. 

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