Benzaldehyde acetals hydrolysis

The a-seconday isotope effect has been applied to the hydrolysis of 0-ethyl-S-phenyl benzaldehyde acetal hydrolysis by Faroz and Cordes (Eqn. 54) [33]. 

Chromium enolate chemistry exhibits diverse thermochemical facets. For example, contrast the energetics of enolate addition reactions to benzaldehyde and to benzaldehyde JT-bonded to Cr(CO)3 and of the enolate addition reactions to acetophenone and to acetophenone 71-bonded to Cr(CO)3. Thermochemical analysis is still unreported, although the reactions are synthetically usefuP . It is clear that the organic ligands are electronically coupled to the metallic center—PhCHO Cr(CO)3 is red, PhCH(OEt)2 Cr(CO)3 is yellow but benzaldehyde and its diethyl acetal are both colorless. It is well established that acetophenone, and presumably other acylated benzenes such as benzaldehyde, binds Cr(CO)3 rather more weakly than does toluene, and presumably other alkylated benzenes such as the aforementioned benzaldehyde acetal. The enthalpy of hydrolysis of the metallated acetal remains unknown other than it is therefore smaller than that of the unmetallated species . ... 

The pH-rate profile for hydrolysis of the benzaldehyde acetal (see Figure 7.10) indicates that of the species that are available, the monoanion of the acetal is the most reactive. The reaction is fastest in the pH range where the concentration of the monoanion is at a maximum. The neutral molecule decreases in concentration with increasing pH and the converse is true for the dianion. 

This hydrosilylation method can also be applied to the reduction of esters. The silyl acetal products can be hydrolyzed, resulting in net reduction of esters to aldehydes. For example, ethylbenzoate can be fully reduced in the presence of 0.1 mol % [Ir(coe)2Cl]2 and 1.5 equiv of diethylsUane at room temperature for 1 h to give benzaldehyde after hydrolysis (eq 3). The functional group compatibility is analogous to that of the amide reduction. 

Alkyl Isoquinolines. Coal tar contains small amounts of l-methylisoquinoline [1721-93-3] 3-methylisoquinoline [1125-80-0] and 1,3-dimetliylisoquinoline [1721-94-4J. The 1- and 3-methyl groups are more reactive than others in the isoquinoline nucleus and readily oxidize with selenium dioxide to form the corresponding isoquinoline aldehydes (174). These compounds can also be obtained by the hydrolysis of the dihalomethyl group. The 1- and 3-methyhsoquinolines condense with benzaldehyde in the presence of zinc chloride or acetic anhydride to produce 1- and 3-styryhsoquinolines. Radicals formed by decarboxylation of carboxyUc acids react to produce 1-aIkyhsoquinolines. 

Esters of cinnamic acid are used more extensively than the acid itself, and can be converted to the acid by standard hydrolysis protocols. The Claisen condensation between benzaldehyde and the appropriate acetate ester provides a direct, high yield route to the simple esters. 

The rates of both formation and hydrolysis of dimethyl acetals of -substituted benzaldehydes are substituent-dependent. Do you expect to increase or decrease with increasing electron-attracting capacity of the pam substituent Do you expect the Ahydroi to increase or decrease with the electron-attracting power of the substituent How do you expect K, the equilibrium constant for acetal formation, to vary with the nature of the substituent ... 

Problem 17.8 asked you to write details of the mechanism describing formation of benzaldehyde diethyl acetal from benzaldehyde and ethanol. Write a stepwise mechanism for the acid hydrolysis of this acetal. 

The trimethylsilyl ester of a-trimethylsilyacetic acid 1613 is converted by LDA and TCS 14 into the C,0,0-tris(trimethylsilyl)ketene acetal 1614 in 91% yield. Reaction of 1614 with benzaldehyde in the presence of ZnBr2 proceeds via 1615 to afford a high yield of trimethylsilyl cinnamate 1616 [18], which gives on work-up free ( )-cinnamic acid in nearly quantitative yield (Scheme 10.7). In contrast, reaction of the lithium salt of 1613 with benzaldehyde then acidic hydrolysis affords a 1 1 mixture of ( )- and (Z)-cinnamic acid in 86% yield [18]. 

The hydrolysis of the cyclic acetal, which was used as the connecting group between the polymer chain and the lipid, was confirmed both by the IR and the proton NMR spectra of the lipid recovered from the vesicular system after standing for 3 weeks at room temperature. The lactone absorption at 1805 cm-1 disappeared from the IR spectrum (Figure 6) as the result of hydrolysis. Furthermore, a new aldehyde absorption band at 1705 cm 1 was observed in the spectrum, which is related to the substituted benzaldehyde group of the hydrolyzed product. The proton NMR spectrum (Figure 10) also clearly showed the formation of the benzaldehyde, as indicated by the peak at 810.20 ppm. 

Cyclodextrins slow the rate of hydrolysis of benzaldehyde dimethyl acetal, PhCH(OMe)2, in aqueous acid as the substrate binds in the cyclodextrin s cavity, producing a less reactive complex. Added alternative guests compete for the binding site, displacing the acetal and boosting hydrolysis. 

Hydrolysis of benzaldehyde disalicyl acetal is characterized by a bell-shaped pH-rate const2int profile (Anderson and Fife, 1971a,... 

A recent example of a chemical study showing how strain effects could be important in an enzymatic reaction, dealt with the hydrolysis of benzaldehyde di-t-butyl acetal [18] (Anderson and Fife, 1971b). As shown by a Stuart-Briegleb model, substantial ground-state strain is present which would be partially relieved in the... 

Figure 6. Plot of t obsd vs. pH for hydrolysis of benzaldehyde disalicyl acetal in 50% dioxane—HjO at 25°.

Hydrolysis of the diethylacetal function employing p-toluenesulphonic acid in acetone, pyridinium p-toluene-sulphonate in EtOH, and a suspension of Si02 in hexane. In all cases the corresponding aldehyde is obtained in high yield as a Z E isomeric mixture. Transmetallation of acetal with Me2Cu(CN)Li2 followed by treatment with c-hexenones giving the 1,4-addition product. Alternatively, transmetallation with n-BuLi and reaction with benzaldehyde giving the expected alcohol. 

The main cyanogenic glycoside in laurel is prunasin, the P-o-glucoside of benzaldehyde cyanohydrin. The enzymic hydrolysis of prunasin may be visualized as an acid-catalysed process, first of all hydrolysing the acetal linkage to produce glucose and the cyanohydrin. Further hydrolysis results in reversal of cyanohydrin formation, giving HCN and benzaldehyde. 

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