Total nonstructural carbohydrates (TNC) in plant tissue are underestimated by single enzyme (a-amylase or glucoamylase) extraction and overestimated by mild acid hydrolysis. A combination of glucoamylase and mycolase degraded starch completely to glucose at 60°C and pH 4.9. This dual enzyme extraction procedure was effective in determining TNC in plant tissues that do not accumulate fructosans. The reducing sugar (mainly glucose and/or fructose) extracts produced by enzymatic digestion of plant tissue were clarified with barium hydroxide and zinc sulfate solutions and analyzed by the Shaffer-Somogyi copperiodometric titration method. The dual enzyme method hydrolyzed pure starch derived from corn, wheat, and potato, and potato-soluble starch to about 100% glucose, whereas mycolase only yielded about 88% hydrolysis. Although corn starch was completely hydrolyzed in 2 h by the dual enzyme method, plant tissues required at least 24 h hydrolysis for maximum TNC values. Lead acetate precipitation of the protein in the dual enzyme extracts interfered with the copper-iodometric titration. Gelatinization of starch in plant tissue by autoclaving gave higher TNC values than heating on a hot plate for 5 min. The Schaffer-Somogyi copper iodometric titration method could be used to measure/or define the activity of certain enzymes.

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.

No abstract

The rates of acid-catalysed heterolysis of the C-0 bond of borneol (bornan-2,endo-ol), isoborneol (bornan-2,exool), camphene hydrate (2,3,3-trimethylnorbornan-2,exo-ol), and methylcamphenilol (2.3.3-trimethylnorbornan-2,endo-ol) have been measured. Camphene hydrate exchanges oxygen in aqueous acid more rapidly than it racemises by a factor of 38, while methyl camphenilol rearranges to a mixture of camphene hydrate and isoborneol, the C-0 bond heterolysis being slower than that of camphene hydrate by a factor of 1.3 x 1 03. lsoborneol both racemises and exchanges oxygen at the same rate, faster than borneol by a factor of 2-3 x lo5. The rate ratios for both pairs of alcohols are considered to be electronic as well as steric in origin.