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Author: Subject: Acetaldehyde synthesis
clearly_not_atara
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[*] posted on 16-9-2020 at 06:21


In reality producing acetaldehyde isn't all that hard. What is hard is producing acetaldehyde in significant quantities and in such a way that it can be separated from the reaction mixture, condensed, and isolated.

It's difficult, for example, to condense a compound with bp 20 C when that compound is co-produced in the efflux stream with much larger quantities of water, bp 100 C, and when said gas stream emerges at nearly 200 C.

It is likewise not very easy to isolate acetaldehyde from aqueous rxn mixtures since its bisulfite adduct is not as insoluble as those of larger aldehydes, and it may polymerize under the alkaline conditions typically used for bisulfite adduct deprotection. Bisulfite adducts may also be deprotected with acid, but this produces copious SO2.

As such, the great majority of syntheses posted in this thread are not really solving the right problem. IMHO, if you want a practical synth of acetaldehyde, what you're really after is an oxidation of ethanol that produces 1,1-diethoxyethane -- acetaldehyde diethyl acetal -- in situ. This compound can easily be separated from the reaction mixture and pure acetaldehyde obtained by acidic cleavage under relatively mild conditions with few co-products. It is stable and can be stored.

To that end, I offer the direct photocatalytic oxidation of ethanol to 1,1-diethoxyethane over two catalysts: 1% Pt-doped TiO2 nanorods and Cd-Ni-Mo sulfide.

https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10...

https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10....

While the photocatalysts take a little work -- hardly impractical IMO -- they offer the possibility of one-step large-scale production of DEE qua acetaldehyde in a form that is stable and easy to isolate and store.

But be aware that while acetals such as DEE usually do not form peroxides, the risk must not be ignored.

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[Edited on 04-20-1969 by clearly_not_atara]
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