Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

DBHYDKACBTIC ACID 267
HgC.CO.CH.COOR —>- H3C.COOH + H2C.COOH
I I +2R0H.
CH2.COOR H2C.COOH
Succinic acid
Another type of synthesis in which ethyl acetoacetate is used consists
in the coupling of two molecules of the ester to ethyl diacetylsuccinate
by the action of iodine on the sodium compound :
COOR COOR COOR
CH HC CH
2 || +I2—> I I +2NaI.
C—ONa CO CO
CH CH CH
Diethyl diacetylsuccinate
Here, also, as in the case of alkylation, it is found that the union
takes place between carbon and carbon. Information about the interesting
isomerism of the esters of diacetylsuccinic acid can be found
in the literature (L. Knorr).
Dehydracetic acid, which was mentioned on p. 252, is formed from
ethyl acetoacetate by intermolecular condensation. On boiling with
acids the lactone ring is broken and a triketocarboxylic acid is produced.
This acid loses CO2 and H2O and is thus transformed into dimethylpyrone:
O O
H3C-C CO
HC CH-COCH
I
o
The pyrone ring is of great importance because one of its oxygen
atoms exhibits very marked basic properties (Collie and Tickle).
Biologically, this ring arises through transformations of sugars (Kojic
acid). The oxygen atom which is in ether form behaves like trivalent
nitrogen and is capable of combining with acid to give salts which, by
analogy with the ammonium salts, are termed oxonium salts. This
property of the oxygen atom appears in many organic compounds.
Thus, solutions of ethers in concentrated sulphuric acid must be assumed
to contain oxonium sulphate which is hydrolytically decomposed by
water.
Baeyer was able to convert the tertiary salt produced by addition
of methyl iodide to dimethylpyrone by the action of ammonia into a
y-methoxy-derivative of pyridine and thus to make the following the