598. Tracer studies in ester hydrolysis. Part XIV. The hydrolysis of bornyl and isobornyl acetates

Abstract

of bornyl and isobornyl acetate follows mechanism BA,2 in alkaline and A A~~ in dilute acidic solution. Hydrolysis of both esters is accompanied by extensive exchange between the carbonyl oxygen atom and the water of the solvent. It is suggested that the decomposition of the tetrahedral addition intermediate to products is unusually slow during hydrolysis of these esters.The kinetic form of the acid hydrolysis of isobornyl acetate suggests that there is a mechanistic change towards mechanism A a l l in more concentrated acid. Experiments with the model compounds isopropyl and t-butyl acetate support this conclusion. ISOBORNYL chloride (I; X = Cl) is unusually reactive in SN1 solvolyses, because the forming carbonium-ion centre in the transition state (11) is stabilised by delocalisation of sigma electrons.1u~b*2 This speeding of ionisation has been called " synartesis," or " anchimerism." The reactivity of the endo-isomer, bornyl chloride (111; X = Cl) is similar to that of other secondary alkyl chlorides,la because the transition state for its solvolysis is not stabilised by electronic delocalisation, and factors such as angle strain and non-bonding interactions are relatively small and self-cancelling.lb Me i' Therefore, it seemed likely that the acid hydrolysis of isobornyl acetate (I; X = OAc) would follow mechanism Aall, with accelerated formation of a carbonium ion from the conjugate acid (I; X = O.MeC+*OH), that the acid hydrolysis of bornyl acetate (111; X = OAc) would follow the more usual mechanism Agc2, and that in alkali both esters would be hydrolysed by mechanism BA,2. We were unable to use oxygen-18 to determine the position of bond fission in the acid hydrolysis of isobornyl acetate, because there is a * Part XIII, C. A. * There is kinetic and isotopic evidence which suggests that two water molecules are involved in A -2 hydrolysis of simple carboxylic esters, and that the second water molecule is donating a proton t o the alkoxy-gro~p.~ M. L. Bender, J . Amer.

Monoterpenes in the volatile leaf oil of Abies .times. arnoldiana Nitz

“…From these figures it may be concluded that acid-catalyzed hydrolysis of bornyl acetate takes place. Kinetics of this reaction have been discussed by Bunton et al (1965) and by Lajunen (1974). Obviously this hydrolysis only takes place to a small extent during distillation.…”

Essential oils and related products

“…The mechanism of hydrolysis of bornyl and isobornyl acetate in acid and alkaline media were described by Bunion, Khaleluddin, and Whittaker (79).…”