- A transesterification-acetalization catalytic tandem process for the functionalization of glycerol: The pivotal role of isopropenyl acetate
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At 30 °C, in the presence of Amberlyst-15 as a catalyst, a tandem sequence was implemented by which a pool of innocuous reactants (isopropenyl acetate, acetic acid and acetone) allowed upgrading of glycerol through selective acetylation and acetalization processes. The study provided evidence for the occurrence of multiple concomitant reactions. Isopropenyl acetate acted as a transesterification agent to provide glyceryl esters, and it was concurrently subjected to an acidolysis reaction promoted by AcOH. Both these transformations co-generated acetone which converted glycerol into the corresponding acetals, while acidolysis sourced also acetic anhydride that acted as an acetylation reactant. However, tuning of conditions, mostly by changing the reactant molar ratio and optimizing the reaction time, was successful to steer the set of all reactions towards the synthesis of either a 1?:?1 mixture of acetal acetates (97% of which was solketal acetate) and triacetin, or acetal acetates in up to 91% yield, at complete conversion of glycerol. To the best of our knowledge, a one-pot protocol with such a degree of control on the functionalization of glycerol via transesterification and acetalization reactions has not been previously reported. The procedure was also easily reproduced on a gram scale, thereby proving its efficiency for preparative purposes. Finally, the design of experiments with isotopically labelled reagents, particularly d4-acetic acid and d6-acetone, helped to estimate the contribution of different reaction partners (iPAc/AcOH/acetone) to the formation of final products. This journal is
- Calmanti, Roberto,Perosa, Alvise,Rigo, Davide,Selva, Maurizio
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supporting information
p. 5487 - 5496
(2020/09/23)
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- Reactions of 3-Aryl-5-methyl-1,2,4-oxadiazoles with Benzyl Alcohol and with Benzylamine
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When heated with benzyl alcohol, 3-aryl-5-methyl-1,2,4-oxadiazoles afford mainly the aryl nitrile, benzyl acetate, and benzaldehyde.A number of other products, including 1,3,5-triazines, have been identified.Benzylamine and 5-methyl-1,2,4-oxadiazoles similarly give aryl nitrile and N-acetylbenzylamine, but the reaction is slower.However, in mixtures of the alcohol and the amine, the amine reacts the faster.Possible reaction mechanisms are discussed.The methyl group of the oxadiazole was shown to exchange its protons with those of benzyl alcohol more readily than the oxadiazole otherwise reacted with benzyl alcohol.
- Brown, Jonathan W.,Clack, Dennis W.,Wilson, David A.
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p. 117 - 122
(2007/10/02)
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- Reinvestigation of a Synthesis of (R,S)-Mevalonolactone
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An n.m.r. study of the reaction of 3-hydroxy-3-methylpentane-1,5-dioic acid (5) with excess of acetic anhydride is described.It has shown that 3-hydroxy-3-methylpentane-1,5-dioic acid anhydride (2), previously described by Scott and Shishido as an intermediate in their synthesis of mevalonolactone, is formed only transiently, along with 3-acetoxy-3-methylpentane-1,5-dioic acid (6).Both intermediates eventually give 3-acetoxy-3-methylpentane-1,5-dioic acid anhydride (3).To obtain (R,S)-mevalonolactone, sodium borohydride reduction of 3-hydroxy-3-methylpentane-1,5-dioic acid anhydride (2), prepared from the diacid (5) and N,N-dicyclohexylcarbodi-imide, is shown to be better than reduction of 3-acetoxy-3-methylpentane-1,5-dioic acid anhydride (3).
- Lewer, Paul,MacMillan, Jake
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p. 1417 - 1420
(2007/10/02)
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- Kinetics and Some Equilibria of Transacylation between Oxy Anions in Aprotic Solvents
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β-Deuterium isotope effects (β-DIE) determined in acetonitrile for the following reactions are: CH3COO- + 4-NO2C6H4O2CCL3 (L = H, D) (PNPA-L3), 0.958 +/- 0.007 (5-45 deg C); CH3COO- + 2,4-(NO2)2C6H3O2CCL3 (DNPA-L3), 0.964 +/- 0.011 (5-20 deg C; OH(1-) + PNPA-L3, 0.972 +/- 0.028 (25 deg C); 4-NO2C6H4O- (PNP-) + CL3COOCOCL3, 1.00 +/- 0.02 (20 deg C); 4-NO-C6H4O- (PNOP-) + CL3COOCOCL3, 1.00 +/- 0.03 (20 deg C). β-DIEs in benzene for two of these reactions are: CH3COO- + PNPA-L3, 0.957 +/- 0.045 (10-20 deg C); CH3COO- + DNPA-L3, 0.985 +/- 0.050 (5-10 deg C).The fraction of tetrahedral character at the transition state (TS) deduced from β-DIEs for reactions of CH3COO- + PNPA is 0.32 in both CH3CN and benzene, of CH3COO- + DNPA is 0.28 in CH3CN and 0.12 in benzene, and of OH- + PNPA is 0.21 in CH3CN.These values are similar to what is found in water and indicate TSs of essentially trigonal geometry.Isotope effects (CH3)2/k(CD3)2> of unity for ester formation from CL3COOCOCL3 with phenoxides might be interpreted by two contributing factors to the observed effect; one of the usual hyperconjugation source and the other from electoststic effect of the label in the departing CL3COO-.An equilibrium isotope effect (CH3)2/K(CD3)2> of 1.03 in the direction of ester formation is calculated.A Hammett correlation of reactions of substituted phenoxides with CH3COOCOCH3 in CH3CN yielded ρ = -2.54.The reaction of CH3COO- in CH3CN could not be effected with phenyl acetate.The reaction was endergonic (ΔG0 = +2.59 kcal/mol)with PNPA and exergonic (ΔG0 = -7.61 kcal/mol) with DNPA.Activation enthalpies of these reactions decrease from H2O to CH3CN to benzene, whereas activation entropies increase in this order.
- Kovach, Ildiko M.
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p. 2235 - 2241
(2007/10/02)
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