Navzer D. Sachinvala

Sucrose-based epoxy monomers and their reactions with diethylenetriamine

Two sets of sucrose-based epoxy monomers, namely, epoxy allyl sucroses (EAS), and epoxy crotyl sucroses (ECS), were prepared by epoxidation of octa-O-allyl and octa-O-crotyl sucroses (OAS and OCS, respectively). Synthetic and structural characterization studies showed that the new epoxy monomers were mixtures of structural isomers and diastereoisomers that contained varying numbers of epoxy groups per sucrose. EAS and ECS can be tailored to contain an average of one to eight epoxy groups per sucrose. Quantitative 13C-NMR spectrometry and titrimetry were used independently to confirm the average number of epoxy groups per sucrose. Sucrose-based epoxy monomers were cured with diethylenetriamine (DETA) in a differential scanning calorimeter (DSC), and their curing characteristics were compared with those of diglycidyl ether of bisphenol A (DGEBA) and diepoxycrotyl ether of bisphenol A (DECEBA). EAS and DGEBA cured at 100 to 125°C and exhibited a heat of cure of about 108.8 kJ per mol epoxy. ECS and DECEBA cured at 150 and 171°C, respectively, and exhibited a heat of cure of about 83.7 kJ per mol epoxy. Depending upon the degree of epoxidation (average number of epoxy groups per sucrose) and the concentration of DETA, glass transition temperatures (Tgs) of cured EAS varied from −17 to 72°C. DETA-cured ECS containing an average of 7.3 epoxy groups per sucrose (ECS-7.3) showed no DSC glass transition between −140 and 220°C when the ratio of amine (NH) to epoxy group was 1:1 and 1.5:1. Maximum Tgs obtained for DETA-cured DGEBA and DECEBA polymers were 134 and 106°C, respectively. DETA-cured bisphenol A-based epoxy polymers degraded at about 340°C, as observed by thermogravimetric analysis (TGA). DETA-cured sucrose-based epoxy polymers degraded at about 320°C. Sucrose-based epoxies cured with DETA were found to bind aluminum, glass, and steel. Comparative lap shear tests (ASTM D1002–94) showed that DETA-cured epoxy allyl sucroses with an average of 3.2 epoxy groups per sucrose (EAS-3.2) generated a flexible adhesive comparable in bond strength to DGEBA. However, DETA-cured ECS-7.3 outperformed the bonding characteristics of both DGEBA and EAS-3.2. All sucrose-based epoxy polymers were crosslinked and insoluble in water, N,N-dimethylformamide, tetrahydrofuran, acetone, and dichloromethane.

Deoxycelluloses and related structures

The syntheses of various deoxycelluloses and related structures (cellulosenes and anhydrocelluloses) from the mid-1920s to the present are critically reviewed. General synthetic strategies to prepare deoxycelluloses include nucleophilic displacement of good leaving groups. Distinctions are made between reaction of cellulosics under homogeneous and heterogeneous conditions. Recent advances in the preparation of halodeoxycelluloses have led to high degree of substitution fluorodeoxycelluloses and bromodeoxycelluloses. Applications for the deoxycelluloses are numerous and characterized by biological, chemical or physical end uses.

The physical and NMR characterizations of allyl‐ and crotylcelluloses

Tri-O-allylcellulose (degree of polymerization, DP ∼112) was prepared in ∼91% yield, and tri-O-crotylcellulose (DP ∼138) was prepared in ∼56% yield from microcrystalline cellulose (DP ∼172, and polydispersity index, PDI ∼1.95) using modified literature methods. Number-average molecular weight (Mn = 31,600), weight-average molecular weight (Mw = 191,800), and PDI = 6.07 data suggested that tri-O-allylcellulose may be crosslinking in air to generate branched chains. The polymer was stabilized with 100 ppm butylated hydroxy toluene (BHT). The material without BHT experienced glass transition (Tg, differential-scanning calorimetry, DSC) between −2 and +3 °C, crosslinked beyond 100 °C, and degraded at 298.6 °C (by thermogravimetric analysis, TGA). Mn (45,100), Mw (118,200), PDI (2.62), and thermal data (Tg − 5 to +3 °C, melting point 185.8 °C, recrystallization 168.9 °C, and degradation 343.6 °C) on tri-O-crotylcellulose suggested that the polymer was formed with about the same polydispersity as the starting material and is heat stable. While allylcellulose generated continuous flexible yellow films by solution casting, crotylcellulose precipitated from solution as brittle white flakes. Dynamic mechanical analysis (DMA) data on allylcellulose films (Tg − 29.1 °C, Youngs modulus 5.81 × 108 Pa) suggest that the material is tough and flexible at room temperature. All 1H and 13C resonances in the NMR spectra were identified and assigned using the following methods: Double-quantum filter correlation spectroscopy (DQF COSY) was used to assign the network of seven protons in the anhydroglucose portion of the repeat unit. The proton assignments were verified and confirmed by total correlation spectroscopy (TOCSY). A combination of heteronuclear single-quantum coherence (HSQC) and 13C spectroscopies were used to identify all bonded carbon–hydrogen pairs in the anhydroglucose portion of the repeat unit, and assign the carbon nuclei chemical shift values. Heteronuclear multiple bond correlation (HMBC) spectroscopy was used to connect the resonances of methines and methylenes at positions 2, 3, and 6 to the methylene resonances of the allyl ethers. TOCSY was used again to identify the fifteen 1H resonances in the three pendant allyl groups. Finally, a combination of HSQC, HMBC, and 13C spectroscopies were used to identify each carbon in the allyl pendants at 2, 3, and 6. Because of line broadening and signal overlap, we were unable to identify the conformational arrangement about the C5 and C6 bond in tri-O-allyl- and tri-O-crotylcelluloses.

Characterization of tri-o-methylcellulose by one- and two-dimensional NMR methods†

Tri-O-methylcellulose was prepared from partially O-methylated cellulose and its chemical shifts ( 1 H and 13 C), and proton coupling constants were assigned using the following NMR methods: (1) One-dimensional 1 H and 13 C spectra of the title compound were used to assign functional groups and to compare with literature data; (2) double quantum filtered proton-proton correlation spectroscopy ( 1 H, 1 H DQF-COSY) was used to assign the chemical shifts of the network of 7 protons in the anhydroglucose portion of the repeat unit; (3) the heteronuclear single-quantum coherence (HSQC) spectrum was used to establish connectivities between the bonded protons and carbons; (4) the heteronuclear multiple-bond correlation (HMBC) spectrum was used to connect the hydrogens of the methyl ethers to their respective sugar carbons; (5) the combination of HSQC and HMBC spectra was used to assign the 13 C shifts of the methyl ethers; (6) all spectra were used in combination to verify the assigned chemical shifts; (7) first-order proton coupling constants data (J H,H in Hz) were obtained from the resolution-enhanced proton spectra. The NMR spectra of tri-O-methylcellulose and other cellulose ethers do not resemble the spectra of similarly substituted cellobioses. Although the 1 H and 13 C shifts and coupling constants of 2,3,6-tri-O-methylcellulose closely resemble those of methyl tetra-O-methyl-β-D-glucoside, there are differences with regard to the chemical shifts and the order of appearances of the resonating nuclei of the methyl ether appendages and the proton at position 4 in the pyranose ring. H4 in tri-O-methylcellulose is deshielded by the acetal system comprising the β-1→4 linkage, and it resonates downfield. H4 in the permethylated glucoside is not as deshielded by the equitorial O-methyl group at C4, and it resonates upfield. The order of appearance of the 1 H and 13 C resonances in the spectra of the tri-O-methylcellulose repeat unit (from upfield to downfield) are H2 < H3 < H5 < H6a < H3a < H2a < pro R H6B < H4 < pro S H6A « H1 and C6a < C3a < C2a < C6 < C5 < C4 < C2 < C3 « C1, respectively. Close examination of the pyranose ring coupling constants of the repeat unit in tri-O-methylcellulose supports the 4 C 1 arrangement of the glucopyranose ring. Examination of the proton coupling constants about the C5-C6 bond (J 5,6A and J 5,6B ) in the nuclear Overhauser effect difference spectra revealed that the C6 O-methyl group is predominantly in the gauche gauche conformation about the C5-C6 bond for the polymer in solution.

Selective conversion of O-succinimidyl carbamates to N-(O-carbamoyl)-succinmonoamides and ureas

N-Monoalkyl-O-succinimidyl carbamates reacted with primary and secondary amines to produce ureas. However, N,N-dialkyl-O-succinimidyl carbamates reacted with primary and secondary amines, via succinimide ring opening, to afford N-(O-carbamoyl)-succinmonoamide derivatives. This ring-opening trend was also true with hydroxy and alkoxy nucleophiles. Herein, general methods for the synthesis and NMR characterization of N-(O-carbamoyl)-succinmonoamides are reported.