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One exception is the decarbonylation of formic acid: H CO OH → CO + H 2 O. The reaction is induced by sulfuric acid, which functions as both a catalyst and a dehydrating agent. Via this reaction, formic acid is occasionally employed as a source of CO in the laboratory in lieu of cylinders of this toxic gas. [1]
Next, the thermal decarboxylation takes place through the acid chloride (with thionyl chloride) and the tert-butyl perester 6 (with tert-butyl hydroperoxide and pyridine) to 7; afterward, the acetal is once more removed in 8. A second Favorskii rearrangement gives 9, and finally another decarboxylation gives, via 10, cubane (11).
The decarboxylation of this compound by heat is essential for the psychoactive effect of smoked cannabis, and depends on conversion of the enol to a keto group when the alpha carbon is protonated. Upon heating, Δ9-tetrahydrocannabinolic acid decarboxylates to give the psychoactive compound Δ9- Tetrahydrocannabinol . [ 13 ]
The benzilic acid rearrangement is formally the 1,2-rearrangement of 1,2-diketones to form α-hydroxy–carboxylic acids using a base. This reaction receives its name from the reaction of benzil with potassium hydroxide to form benzilic acid. First performed by Justus von Liebig in 1838, [1] it is the first reported example of a rearrangement ...
If R 1 and R 2 (note equation at top of page) are different substituents, there is a new stereocenter formed at the alpha position when an enol converts to its keto form. Depending on the nature of the three R groups, the resulting products in this situation would be diastereomers or enantiomers .
The carbon then undergoes nucleophilic substitution. When heated with aqueous acid, the newly alkylated ester is hydrolyzed to a β-keto acid, which is decarboxylated to form a methyl ketone. [1] [2] The alkylated ester can undergo a second substitution to produce the dialkylated product.
A crossed aldol condensation is a result of two dissimilar carbonyl compounds containing α-hydrogen(s) undergoing aldol condensation. Ordinarily, this leads to four possible products as either carbonyl compound can act as the nucleophile and self-condensation is possible, which makes a synthetically useless mixture.
Under these conditions the condensation is accompanied by decarboxylation. [4] For example, the reaction of acrolein and malonic acid in pyridine gives trans-2,4-entadienoic acid with one carboxylic acid group and not two. [5] Sorbic acid can be prepared similarly by replacing acrolein with crotonaldehyde. [6]