Ethyl orthopropionate

The hydrolyses of ethyl orthoacetate, ethyl orthopropionate, and ethyl orthocarbonate must occur with rate-determining proton transfer (A-SE2) even in purely aqueous solution. A solvent isotope effect of kH/kD = 0.7 has been found for ethyl orthocarbonate [159, 184]. 

Arbuzov, B.A., and Bogonostseva, N.P., The action of phosphorus trichloride on ethyl orthopropionate and ethyl orthosilicate, Izv. Akad. Nauk SSSR, Ser Khim., 484, 1953 Chem. Abstr.. 48. 99051. 1954. 

The stereoselectivity of the Qaisen rearrangement undergone by some carbohydrate allylic alcohols in the presence of ethyl orthoacetate and ethyl orthopropionate has been studied. A [2,3]-Wittig rearrangement on the carbohydrate template (65) gave olefin (66) (Scheme 2) which opened a new route to the 3-all lmalic acid... 

Ethyl orthopropionate and anhydrous ZnGlg added to a soln. of 2 g. cyclopent-4-ene-l,3-dione in acetic anhydride, and stirred 4hrs. at 80-90° 1.5 g. 2-(a-... 

Later investigators alcoholyzed imidate salts of other monobasic acids to obtain ortho esters of acetic [13, 14], propionic [15], butyric, valeric, caproic, isocaproic, benzoic [16], and phenylacetic acids [17]. For the latter alcoholysis reactions, the reaction time varies from a few days for the production of methyl orthopropionate to six weeks for ethyl orthobenzoate. McElvain reported that the reaction time is drastically cut by carrying out the reaction in boiling ether [18] or petroleum ether [19]. These conditions provide a reaction temperature below the decomposition point of the imidate salt to the amide. 

The hydrolysis reactions of acetals, ketals, and orthoesters are catalyzed by acids but not by bases. It has been found that these three groups of substrates are hydrolyzed via a common general mechanism — involving similar types of intermediates — though the rate-determining step may vary from case to case. In the hydrolyses of ethyl orthoacetate, orthopropionate, and orthocarbonate, general acid catalysis was unambiguously established for the first time by Bronsted and Wynne-Jones [158]. 

The A2 mechanism can be excluded with certainty for the hydrolyses of all orthoesters discussed. This is done on the basis of the determined volume of activation, AF = +2.4 cm3 (Table 1) for ethyl orthoformate [32], on the basis of the strongly increased rate in comparison to orthoformate (no steric hindrance) for orthoacetate and orthopropionate, and on the basis of the results of experiments with added nucleophiles for orthobenzoate [183] and orthocarbonate [192]. The observed AS values (Table 12) are in agreement with these conclusions. Consequently, the mechanism of orthoester hydrolysis must be either A1 or A-SE2, or possibly a concerted process with proton transfer and carbonium ion formation in the same step. 

In a similar manner, 1,1,4-cyclohexanetrimethanol (3.524 g, 20 mmol) was allowed to react with triethyl orthopropionate (3.634 g, 20 mmol). This reaction produced a polymer which remained in the cyclohexane solution. Precipitation into methanol yielded a polymer having a MW of 51 000 (GPC using polystyrene standards) and a Tg of 67.8 °C. The polymer was soluble in organic solvents with low or medium polarities such as methylene chloride, chloroform, ether, tetrahydrofuran and ethyl acetate. 

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