Benzaldehyde diethyl acetal

The mechanism for formation of benzaldehyde diethyl acetal which proceeds m two stages is presented m Figure 17 9 The first stage (steps 1-3) involves formation of a hemiacetal m the second stage (steps 4-7) the hemiacetal is converted to the acetal Nucleophilic addition to the carbonyl group characterizes the first stage carbocation chemistry the second The key carbocation intermediate is stabilized by electron release from oxygen... 

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 light-catalyzed reaction between benzaldehyde diethyl acetal and NBS was previously shown (78) to produce ethyl benzoate, but the ethyl... 

To a solution of TiCl4 (2.6mmol) in dichloromethane (5 ml), cooled to —78 °C, was added a solution of benzaldehyde diethyl acetal (2.5 mmol) in... 

A solution of the trimethylsilyl enol ether of propionyl trimethylsilane (5 mmol) (Chapter 12) and benzaldehyde diethyl acetal (5 mmol) in dichloromethane (10ml) was added to a solution of BF3.OEt2 (5 mmol) in dichloromethane (5ml), cooled to —78 C. After being stirred for lh at -78°C and 2h at -30°C, the mixture was quenched with excess saturated sodium hydrogen carbonate solution, and extracted with ether. Concentration and distillation gave the product -ethoxy acylsilane, (4.6mmol, 95%). b.p. 105-106 C/2mmHg. Treatment of this alkoxy... 

Benzaldehyde, 43, 73, 123 Benzaldehyde diethyl acetal, 108, 110,122—3 Benzaldehyde dimethyl acetal, 34, 111 Benzenesulphonylhydrazonc, 13 Benzophenone, 137 Benzophenone cyanohydrin, 137 p-Benzoquinone, 137... 

Benzaldehyde diethyl acetal (5.94 g, 32.9 mmol) and triethyl phosphite (5.45 g, 32.9 mmol) were dissolved in dichloromethane (60 ml) under an inert atmosphere and cooled to -20°C. Boron trifluoride etherate (3.57 g, 35.2 mmol) was then added dropwise. The resulting mixture was allowed to return to ambient temperature over an 18-h... 

The simple cleavage of lactones 1 or 2 with alcohol and acid has not been reported. However, when 1 is treated with benzaldehyde diethyl acetal and hydrochloric acid, ethyl 3,5 4,6-di-0-benzylidene-L-gulonate (47) is formed in >90% yield.77,78 No other isomers were observed, and other acetals of benzaldehyde, as well as aliphatic aldehydes, afford similar products in good yield.77 D Addieco prepared36 similarly protected derivatives of L-gulonic acid by oxidation of l,3 2,4-di-0-ethylidene-D-glucitol (15), followed by esterification of the resulting acid with diazomethane. 

Alternatively, when 21 was treated with benzaldehyde diethyl acetal-hydrochloric acid, ethyl 3,5 4,6-di-0-benzylidene-L-gulonate (76) was formed in >90% yield. Diacetal 76 was efficiently oxidized to 77 (>90% yield) with dimethyl sulfoxide-trifluoroacetic anhydride, or by way of the nitrate of 76 and triethylamine. Hydrolysis of 77 then afforded ethyl L-xy(o-2-hexulosonate in 86% yield.383... 

Benzaldehyde diethyl acetal Water Benzaldehyde Ethanol... 

We think this example suffices to show that the use of neutral electrolyte solutions based on dipolar aprotic solvents may raise a lot of difficult questions with respect to both macroscopic and local, microscopic acidity or basicity. Adequate control experiments should be carried out, as correctly urged by Mayeda and Miller (1972), but these are not always easy to design. How difficult the problem can be is best shown by the fact that it was possible to effect transacetalization of benzaldehyde diethyl acetal in alkaline methanol solution by oxidizing hydrogen in the solution at a platinum anode (Schafer, 1974). In this experiment protons liberated at the anode must act catalytically in the inner part of the Nernst layer. 

Fio. 7. Logarithms of second-order rate constants (in units of min"i) for the hydrolysis of a series of para-substituted benzaldehyde diethyl acetals in aqueous solution (lower line) and in the presence of sodium dodecyl sulfate (upper line) plotted against the Hammett substituent constants (Dimlap et cU., 1969). 

Acetals and ketals having a second junctional group ate made by these procedures. For example, acrolein reacts with ethyl orthoformate in alcohol solution with ammonium nitrate as catalyst to give acrolein diethyl acetal (73%). On the other hand, it reacts with ethyl ortho silicate with anhydrous hydrogen chloride as catalyst to furnish (i-ethoxypropionaldehyde diethyl acetal (76%). p-Bromoacetophenone and ethyl orthoformate give the corresponding ketal in 65% yield. p-Methoxy- and m-amino-benzaldehyde diethyl acetals are made in a similar way in 96% and 85% yields, respectively. a-Keto esters like ethyl a-keto-n-butytate and ethyl a-keto-tr-valetate are converted to their diethyl ketals in excellent yields by the action of orthoformic ester in ethanol-hydrochloric acid solution. If the reaction is carried out in the presence of ethylene glycol instead of ethanol and, in addition, the volatile products are removed by distillation, then the ethylene ketal is formed in almost quantitative yield (cf. method 133). 

Problem 19.10 Suggest a convenient chemical method for separating unreacted benzaldehyde from benzaldehyde diethyl acetal. (Compare Problem 19.6, p. 639.)... 

When L-gulono-l,4-lactone (29) was treated with benzaldehyde diethyl acetal, ethyl 3,5 4,6-di-0-benzylidene-L-gulonate (32) was formed (49) in greater than 90% yield (Scheme 17). This derivative can be converted eflBciently into L-ascorbic acid by oxidation (> 90%) followed by hydrolysis of the resulting product to ethyl 2-keto-L-gulonate (L-x io-hexulosonate) (86%) and lactonization by either acid or base (90% ) to L-ascorbic acid. 

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