Preparation and n.m.r. assignments of cellulose mixed esters regioselectively substituted by acetyl and propanoyl groups

Iwata, Tadahisa; Azuma, Jun-ichi; Okamura, Keizo; Muramoto, Mieko; Chun, Byong-Wa

doi:10.1016/0008-6215(92)84113-7

Cited by 59 publications

(48 citation statements)

References 12 publications

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“…The value of DS was determined by integration of the peaks (1.93 to 2.15 ppm). 16 This calculation was further checked against the area of the protons of the AGU (7 protons, between 3.487 and 5.091 ppm).…”

Section: Characterization Of the Productsmentioning

confidence: 99%

Some aspects of acetylation of untreated and mercerized sisal cellulose

Ciacco¹,

Morgado²,

Frollini³

et al. 2010

J. Braz. Chem. Soc.

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Este trabalho apresenta alguns aspectos da acetilação em LiCl/N,N-dimethylacetamida, DMAc de celulose de sisal nativa e mercerizada (sisal e M-sisal). A mercerização da fibra em solução de NaOH resulta nas seguintes alterações: decréscimo de 29.9 % no índice de cristalinidade; diminuição de 16.2% no grau de polimerização e aumento de 9.3% no conteúdo de a-celulose. Estudo com espalhamento de luz de soluções de sisal, M-sisal, celulose microcristalina e algodão mostrou que elas se apresentam na forma de agregados, com números médios de agregação de 5.2, 3.2, 9.8 e 35.3, respectivamente. A presença destes agregados afeta a acessibilidade à celulose durante sua funcionalização. Acompanhamento do grau de substituição, DS, de acetato de celulose em função do tempo, mostrou que o mesmo aumenta por um intervalo de tempo de 5 h, seguido por um decréscimo após 7 h. Possíveis razões para este decréscimo são discutidas. Como esperado, M-sisal apresenta um DS maior que a sisal nativa.We report here on some aspects of the acetylation in LiCl/N,N-dimethylacetamide, DMAc, of untreated and mercerized sisal cellulose, hereafter designated as sisal and M-sisal, respectively. Fiber mercerization by NaOH solution has resulted in the following changes: 29.9% decrease in the index of crystallinity; 16.2% decrease in the degree of polymerization and 9.3% increase in a-cellulose content. A light scattering study of solutions of sisal, M-sisal, microcrystalline and cotton celluloses in LiCl/DMAc has shown that they are present as aggregates, with (an apparent) average aggregation numbers of 5.2, 3.2, 9.8, and 35.3, respectively. The presence of these aggregates affects the accessibility of cellulose during its functionalization. A study of the evolution of the degree of substitution, DS, of cellulose acetate as a function of reaction time showed an increase up to 5 h, followed by a decrease at 7 h. Possible reasons for this decrease are discussed. As expected, M-sisal gave a higher DS that its untreated counterpart.

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Section: Characterization Of the Productsmentioning

confidence: 99%

Some aspects of acetylation of untreated and mercerized sisal cellulose

Ciacco¹,

Morgado²,

Frollini³

et al. 2010

J. Braz. Chem. Soc.

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“…16 and 17; see Fig. 1, the final goal is to have 2,3-di-O-acetylcellulose (2,3-AcC)) by homogeneous tritylation (13,18). For identification of these products, we used a new method where the samples were completely propanoated (19,20) and the IDS values at the C-2, -3, and -6 positions were quantitatively determined by analyzing the two sets of triplets for acetyl and propanoyl carbonyls in 13 C NMR spectra (13,19,20).…”

Section: Introductionmentioning

confidence: 99%

“…However, to characterize precisely these cellulose derivatives in solution, it is essential to prepare samples with completely regulated architecture. The procedure of preparing these samples has recently been established by regioselective substitutions of three hydroxyls in cellulose (13,14) or developed by enzymatic polymerization under perfect control of regio-and stereochemistry (15). At present, we are interested in dynamic structures that were formed by cellulose diacetate (CDA) in polar solvents (5) through intermolecular hydrogen bonding between C-6 position hydroxyls.…”

Section: Introductionmentioning

confidence: 99%

“…1, the final goal is to have 2,3-di-O-acetylcellulose (2,3-AcC)) by homogeneous tritylation (13,18). For identification of these products, we used a new method where the samples were completely propanoated (19,20) and the IDS values at the C-2, -3, and -6 positions were quantitatively determined by analyzing the two sets of triplets for acetyl and propanoyl carbonyls in 13 C NMR spectra (13,19,20). Applying this method to commercial cellulose acetates (CA, TDS = 0.8-2.9) that were produced by partial hydrolysis of cellulose triacetate (TDS = 3.0), we found that CA with TDS > 2 on average has a distorted IDS distribution with preferential unsubstitution of C-6 position hydroxyl, which distortion would result in cluster formations of CA in polar solvents.…”

Section: Introductionmentioning

confidence: 99%

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Substituent Distribution in Cellulose Acetates: Its Control and the Effect on Structure Formation in Solution

Tsunashima

Hattori

2000

Journal of Colloid and Interface Science

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“…We have so far studied by dynamic light scattering the solution behavior of CA in polar solvents (mainly cellulose diacetate in DMAC) at the normal temperatures and established first and systematically their solubility behavior in dilute solution. [10][11][12][13][14][15][16] In this study process, with the use of a new 13 C-NMR (nuclear magnetic resonance) method of analyses for CA hydroxyls, [17][18][19] we analyzed the relation between the individual degree of substitution (IDS) of the C-2, -3, and -6 position hydroxyls and the solubility or the structural formation of CA in several single organic solvents. Further, we prepared 20 several architecture-regulated cellulose derivatives by regioselective substitution of C-2, -3, and -6 position hydroxyls by O-acetyls or trityls and found that 6TC (¼6-O-tritylcellulose) and 2,3Ac6TC (¼2,3-di-O-acetyl-6-O-tritylcellulose) (whose C-6 position hydroxyls were removed completely) were solved in a simple way with a single chain and a weekly selfassembled structure.…”

Section: Introductionmentioning

confidence: 99%

Low‐temperature dynamic light scattering. I. Structural reorganization and physical gel formation in cellulose triacetate/methyl acetate dilute solution at −99 – 45°C

et al. 2006

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Curious low-temperature solubility of cellulose triacetates (CTA; here we use nominally "CTA," but the sample still contains 7% of C-6 position hydroxyls) in an organic solvent, methyl acetate (MA), was studied by a newly designed low-temperature type of DLS apparatus, which enabled for the first time to investigate the structural change of CTA in solution from 45 degrees C down to -100 degrees C. A molecularly dissolved CTA was found to coexist with three types of self-assemblies over all the temperature ranges except for the three specific temperatures T* of 30, -10, and -75 degrees C. However, these multiple self-assemblies are not in real thermodynamic equilibrium but in a metastable state, which could be stabilized effectively by the intermolecular hydrogen bonding (HB) with the help of the dipole interaction at low temperatures. In more detail, with decreasing temperature, these assemblies performed the structural reorganization drastically at three T*'s and would finally be frozen in a physical gel structure at -99 degrees C; around the freezing temperature of MA, CTA molecules could be trapped homogeneously in the frozen MA. The crucial role in such structural reorganizations is played by the balance between the intermolecular HB and the dipole interaction worked in the highly electronegative solvent. Because these interactions, which are mediated by the solvent electronegativity, change drastically with temperature, they result in the control of not only the single CTA chain conformation (= the intramolecular HB) but also the binding ways of the intermolecular HBs between CTA molecules and they induce multitudinous metastable structures in solution. Here it is noted that HB could work mainly between the C-6 position hydroxyls in the anhydroglucose units of CTA and are essentially effective at low temperatures.

show abstract

Preparation and n.m.r. assignments of cellulose mixed esters regioselectively substituted by acetyl and propanoyl groups

Cited by 59 publications

References 12 publications

Some aspects of acetylation of untreated and mercerized sisal cellulose

Some aspects of acetylation of untreated and mercerized sisal cellulose

Substituent Distribution in Cellulose Acetates: Its Control and the Effect on Structure Formation in Solution

Low‐temperature dynamic light scattering. I. Structural reorganization and physical gel formation in cellulose triacetate/methyl acetate dilute solution at −99 – 45°C

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