REACTION OF GAMMA-NONANOLACTONE WITH DEUTEROBROMIC ACID

Series of isomeric monohaloalkanoic acids may be prepared from gamma- or delta-alkanoic lactones by reaction with hydrogen halides. For exam ple, gamma-nonanolactone in 48% hydrogen bromide under reflux affords a 1:1.5:1.7:2.2:2.4 mixture of 4-, 5-, 6-, 7-, and 8-bromononanoic aci ds. In an examination of possible ways whereby such products are forme d, it has been found that the use of 48% deuterium bromide leads to th e introduction of up to 14 atoms of the isotope per bromoacid. Accordi ng to H-1, H-2, and C-13 nuclear magnetic resonance observations, howe ver, the major components of the isomer mixture contain 8-10 atoms of deuterium confined mainly to carbons 4-8, i.e., close to full deuterat ion of each of the carbons. This indicates that a prominent mechanism governing the formation of the bromoacid mixture involves repeated eli mination and addition of HBr ((HBr)-H-2) along a strictly limited segm ent of the carbon chain. Initiated at the C-4 bridge of the lactone an d characterized, hypothetically, by a succession of carbocation interm ediates, the halogenation reactions appear to include a repetitive mig ration of transient alkene functions from C-4 through C-8, and an acco mpanying series of ''zipperlike'' hydride (deuteride) shifts in the in verse direction.