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The rate-limiting step in the hydration of 1-benzyldihydronicotinamide (la) and l-benzyl-3-acetyl-l,4-dihydropyridine (lb) is a slow proton transfer, as shown by the kinetic deuterium solvent isotope effects and buffer catalysis. Reactions in dilute HCI are strongly inhibited by cationic micelles of cetyltrimethylammonium bromide (CTABr) and the inhibition can he related to the micellar binding of the substrates determined spectrophotometrically or by solubility. Anionic micelles of sodium lauryl sulfate (NaLS) only weakly catalyze hydration in dilute HCI, and rate constants go through maxima with increasing [NaLS]. The dependence of rate on [NaLS] can he explained quantitatively in terms of substrate and hydrogen ion incorporation in the micelle and formation of an unreactive conjugate acid in the micelle. The equilibrium constants for unproductive protonation in the micelle corrected for reagent distribution are similar to those in water hut the rate constants are lower. Micelles of sodium ndode(:yl hydrogen phosphate are good catalysts, giving rate enhancements of -lo3 relative to those in water.The acid hydration of dihydropyridine derivatives (1) in aqueous solution is an enamine addition and involves proton transfer from HA followed by rapid attack of water upon the cation (2).4 13ecause of the biological importance of dihy- Rdropyridine nucleotides catalysis of this reaction is of considerable interest and we examined micellar effects in a model system. To date much of the mechanistic work has been on nucleotide derivatives, which are too hydrophilic to be good substrates for use with aqueous micelles, and therefore we first examined hydration of our substrates la,b in the absence of surfactants for purposes of comparison with the reactions in the presence of micellized surfactants. The protonations are irreversible in aqueous acid, but not in nonpolar solvents,5 and the reactions in aqueous solution are general acid catalyzed.6The slow protonation is assisted by electron release by the ring nitrogen, which is reduced by conjugation with the carbonyl group. The charge in the transition state, or the cation 2, is delocalized, but probably it is largely on the ring nitrogen as shown, and substrate protonation, probably on the carbonyl group, 3, should inhibit reaction. I CH,Ph 3Micelles of anionic surfactants typically speed hydrogen ion catalyzed reaction^,^ and we were interested in micellar effects upon the hydration of dihydropyridines because to date specific hydrogen ion catalyzed reactions have generally been examined. In these reactions the proton is fully transferred in the transition state whose formation involves other bond making or breaking steps.Cationic micelles of cetyltrimethylammonium bromide, CTABr, inhibit and anionic micelles of sodium lauryl sulfate, NaLS, weakly catalyze hydration of dihydronicotinamide derivatives.12 These experiments were in phosphate buffer so that the micelles could affect the buffer equilibria and have different, and perhaps opposite, effects upon the hydrogen io...

En el presente estudio se estima el potencial de producción de bioetanol en Ecuador, teóricamente obtenible a partir del aprovechamiento de residuos de cacao; para esto, se formuló un modelo matemático de la hidrólisis ácida en la celulosa de la corteza del cacao y su conversión a etanol por fermentación. Metodológicamente, el estudio se apoya en documentación oficial sobre la cantidad de biomasa residual de este cultivo nacional y provincial, y en un modelo cinético adaptado al caso en estudio. Se obtuvo 8,28 Mml de bioetanol, de cuya mezcla con gasolina extra, en una proporción 5:95 v/v, resulta la gasolina Ecopaís E5C. Se estimó una producción de 166 Mml de E5C, correspondiente al 10 % de la producción nacional para el año 2017 y 56 % de la producción para el año 2014, año en el que se estimó la biomasa residual de cacao. Asimismo, la región Costa aporta el 71 % de la producción nacional de bioetanol y de E5C, liderado por la provincia de Guayas, en la cual la gasolina E5 representa el 25 % de su consumo en 2017. Se concluye que esta ruta de producción de bioetanol es una opción atractiva de diversificación respecto al cultivo de la caña de azúcar, y agrega valor a una biomasa residual desechada actualmente. Los resultados teóricos constituyen la base para estudios más detallados en provincias que combinan un alto potencial de residuos del cacao y un consumo creciente de E5C, pero deben complementarse con investigaciones de corte experimental para corroborar su validez y aportar elementos que determinen la viabilidad de la ruta de producción de bioetanol estudiada.

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