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Propionaldehyde may also be prepared by oxidizing 1-propanol with a mixture of sulfuric acid and potassium dichromate. The reflux condenser contains water heated at 60 °C, which condenses unreacted propanol, but allows propionaldehyde to pass. The propionaldehyde vapor is immediately condensed into a suitable receiver.
Thus, the yield of the valuable chemical is high, although the atom economy can be low. The final stage in the synthesis of pentaerythritol is an example. A solvent-free reaction has been reported involving grinding liquid 2-chlorobenzaldehyde with potassium hydroxide in a mortar and pestle: [7] Solvent-free Cannizzaro reaction
Another possible pathway is through the reaction of propynylidyne (C 3 H) with water. [4] Hazards. The compound is explosive, possibly because it tends to polymerize. [1]
Acrolein and malonic acid react in pyridine to give trans-2,4-pentadienoic acid with the loss of carbon dioxide. The Doebner modification of the Knoevenagel condensation entails the use of pyridine as a solvent with at least one of the withdrawing groups on the nucleophile is a carboxylic acid , for example, with malonic acid .
Aldol structural units are found in many important molecules, whether naturally occurring or synthetic. [8] [9] The reaction is well used on an industrial scale, notably of pentaerythritol, [10] trimethylolpropane, the plasticizer precursor 2-ethylhexanol, and the drug Lipitor (atorvastatin, calcium salt). [11]
The latter reaction is also viable laboratory synthesis. One laboratory technique for substitutive bromination treats propanol with a mixture of hydrobromic and sulfuric acids: CH 3 CH 2 CH 2 OH + HBr → CH 3 CH 2 CH 2 Br + H 2 O. Alternate synthetic routes include treating propanol with phosphorus tribromide [4] or via a Hunsdiecker reaction ...
Benzyl or tert-butyl acetoacetates also work well in this system, and with close temperature control, the tert-butyl system gives a very high yield (close to 80%). [10] N,N-dialkyl pyrrole-2- and/or 4-carboxamides may be prepared by the use of N,N-dialkyl acetoacetamides in the synthesis.
The figure below illustrates one of the commonly accepted models for stereoselection without any modification to the Henry reaction. In this model, stereoselectivity is governed by the size of the R groups in the model (such as a carbon chain), as well as by a transition state that minimizes dipole by orienting the nitro group and carbonyl oxygen anti each other (on opposite sides of the ...