Basicities of the Oxygen Atoms in Symmetrical and Unsymmetrical Acetals. Part I. The Determination of Base Strengths by Infrared Spectroscopy.

Kankaanperä, Alpo; Norris, K. H.; Clauson-Kaas, Niels; Svanholt, Karen; Olsen, Gert E.; Jansen, Gert; Lamm, Bo; Samuelsson, Benny

doi:10.3891/acta.chem.scand.23-1723

Cited by 12 publications

(9 citation statements)

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“…The acetal O ‐sites are considerably less basic than the hydroxyl ones. For the sake of comparison, monoprotonated formaldehyde acetals, ROCH 2 OR, where R is methyl‐, ethyl‐, and isopropyl, show p K a values −4.57, −4.13, −3.70, respectively 25. It is then expected that the p K a value of the protonated glycosidic O ‐site should lie within this range.…”

Section: Resultsmentioning

confidence: 99%

Which Controls the Depolymerization of Cellulose in Ionic Liquids: The Solid Acid Catalyst or Cellulose?

et al. 2010

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Cellulose is a renewable and widely available feedstock. It is a biopolymer that is typically found in wood, straw, grass, municipal solid waste, and crop residues. Its use as raw material for biofuel production opens up the possibility of sustainable biorefinery schemes that do not compete with food supply. Tapping into this feedstock for the production of biofuels and chemicals requires--as the first-step--its depolymerization or its hydrolysis into intermediates that are more susceptible to chemical and/or biological transformations. We have shown earlier that solid acids selectively catalyze the depolymerization of cellulose solubilized in 1-butyl-3-methylimidazolium chloride (BMIMCl) at 100 degrees C. Here, we address the factors responsible for the control of this reaction. Both cellulose and solid acid catalysts have distinct and important roles in the process. Describing the depolymerization of cellulose by the equivalent number of scissions occurring in the cellulosic chains allows a direct correlation between the product yields and the extent of the polymer breakdown. The effect of the acid strength on the depolymerization of cellulose is discussed in detail. Practical aspects of the reaction, concerning the homogeneous nature of the catalysis in spite of the use of a solid acid catalyst, are thoroughly addressed. The effect of impurities present in the imidazolium-based ionic liquids on the reaction performance, the suitability of different ionic liquids as solvents, and the recyclability of Amberlyst 15DRY and BMIMCl are also presented.

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Section: Resultsmentioning

confidence: 99%

Which Controls the Depolymerization of Cellulose in Ionic Liquids: The Solid Acid Catalyst or Cellulose?

et al. 2010

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“…Dissociation of a glycosidic bond occurs after protonation of the oxygen atom (pK a  4) 24 in the bond, which is the main cause to require a strong acid. We chose H 2 SO 4 for the mechanical reaction because of the highest degree of hydrolysis as well as the lowest price.…”

Section: Resultsmentioning

confidence: 99%

Hydrolytic hydrogenation of chitin to amino sugar alcohol

2017

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Chitin is the second most abundant biomass and characteristically contains nitrogen atoms in its monomer units. These favourable features promote chitin to be a potential resource for renewable organonitrogen compounds. 2-Acetamido-2-deoxysorbitol (ADS) is an attractive target in derivatives of chitin, but the conversion of chitin to ADS has not been reported so far.In this work, we demonstrate the catalytic conversion of chitin to ADS using mechanocatalysis in the presence of H 2 SO 4 and subsequent hydrolytic hydrogenation by H 2 SO 4 and Ru/TiO 2 without purification process. Our study clarified that the yield of ADS is strongly influenced by the reaction temperature and pH. The hydrolysis favourably proceeds at high temperature and low pH (2.0), but hydrogenation needs low temperature and specific pH of 34 to achieve high selectivity. Specifically, in the hydrogenation step, acid causes various side-reactions of amide and hemiacetal groups especially in the presence of Ru catalyst, whereas even a small amount of base drastically accelerates the retro-aldol reaction to form erythritol and N-acetylethanolamine.Therefore, a one-pot but two-step reaction is necessary to optimise both hydrolysis and hydrogenation steps and maximises the overall yield of ADS up to 52%.

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“…Values of pKa for the conjugate acids of a number of unsymmetrical dialkoxymethanes have been measured as well; see ref 23. Since the hydrolysis of these species usually involves acid catalysis, a quantitative understanding of their basic properties is highly desirable for attainment of a better understanding of the mechanism of these reactions.…”

Section: Basicities For Acetals Ketals and Ortho Estersmentioning

confidence: 99%

“…Second, rate constants for hydrolysis of acetals, ketals, and ortho esters increase with increasing electron donation from polar substituents located in that alkoxy function which does not leave in the rate-determining step (entries [22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”

Section: V Structure-reactivity Relationshipsmentioning

confidence: 99%