Rachid El Gharbi

Structural analysis of alfa grass (Stipa tenacissima L.) lignin obtained by acetic acid/formic acid delignification.

Alfa grass lignin obtained by the acetic acid/formic acid/water CIMV pulping process was characterized by FTIR and (1)H, (13)C-(1)H 2D HSQC, and (31)P NMR spectroscopies. Lignin samples purified by further dissolution/precipitation or basic hydrolysis steps were also analyzed. The CIMV alfa lignin is a mixture of low molar mass compounds (M(n) = 1500 g/mol) of SGH type with β-O-4 ether bonds as the major interunit linkage. The crude lignin contains fatty acids and residual polysaccharides. It also contains large amounts of acetate and hydroxycinnamates, mostly in the γ-position of β-O-4 interunit linkages. Although partial acetylation induced by the process cannot be excluded, the absence of aromatic acetates and acetylated polysaccharides in crude lignin demonstrates the mildness of the process. By combining smooth alkaline hydrolysis and dissolution/precipitation steps to the CIMV pulping, it is possible to produce a purified lignin with a composition and a structure quite analogous to that of the native polymer in the plant.

UV/vis absorption and fluorescence spectroscopic study of novel symmetrical biscoumarin dyes

Abstract The optical properties of six new 3,3′-phenylenebiscoumarin dyes, differing by the substitution pattern of the central phenyl group and by the presence of methoxy substituents, were investigated in CH 2 Cl 2 by UV/vis absorption and fluorescence spectroscopy. The spectroscopic behaviour of one of the dyes was also analysed in five other solvents. By comparison with monocoumarins, the absorption and emission spectra of the biscoumarin derivatives were shifted to high wavelengths. Most of them displayed high fluorescence quantum yields (0.7–0.8) and lifetimes in the nanosecond range, which can make these dyes very useful as new fluorescent probes.

Polyesters bearing furan moieties, 2. A detailed investigation of the polytransesterification of difuranic diesters with different diols†

A two-step transesterification procedure was applied to combinations of difuranic diesters and both aliphatic and furanic diols. The reaction parameters (including the nature of the catalyst) were varied in both phases of the process and the results compared with those published for similar systems based on aromatic diesters. The best results related to the first phase of the synthesis were obtained using Zn(AcO) 2 , Pb(AcO) 2 or Ti(OBu) 4 at 200°C with a large excess of diol. The second phase, which led to the actual polymer at 200-240°C, called upon the catalytic action of SnC 2 O 4 , Sb 2 O 3 and Ti(OBu) 4 and was prolonged until the viscosity of the media ceased to increase. Specific problems, related to some fragile moieties, limited the success of these polymerizations to a number of combinations which gave polyesters bearing regular structures and molecular weights in the tens of thousands.

Polyesters bearing furan moieties

SummaryThis paper describes a preliminary set of results concerning novel systems in which the synthesis of furanic polyesters was conducted according to a transesterification procedure. Regular linear macromolecular structures were thus obtained with molecular weights well above those previously reported for similar polyesters prepared by more conventional routes.

A preliminary study on polyhydrazides incorporating furan moieties

Solution and interfacial polycondensation of difuranic dihydrazides with aromatic or aliphatic dicarboxylic acid dichlorides led to the corresponding polyhydrazides which were characterized in terms of structure and average chain length. Their conversion to the corresponding polyoxadiazoles was also examined. Model compounds were prepared to facilitate the synthesis and the characterization of the polymers.

Polyesters bearing furan moieties. Part 3. A kinetic study of the transesterification of 2‐furoates as a model reaction for the corresponding polycondensations

The kinetics and mechanism of transesterification reactions involving furanic esters (and aliphatic or aromatic counterparts for the sake of comparison) have been studied in detail using various catalysts and a wide range of experimental conditions. The purpose of this model investigation is to gather a thorough understanding of the process which simulates the corresponding syntheses of furanic polyesters. Whereas the orders in the two reagents was consistently unity, the order with respect to the catalyst varied from 0.5 to about unity as a function of increasing temperature and of the structure of the promoter used. In the case of Ti(OBu) 4 which was the catalyst most used, this behaviour was attributed to the existence of a monomer/dimer equilibrium of the catalyst molecules in the media selected for this work. The presence of the furan heterocycle produced a partial sequestration of the catalyst, through complexation induced by its dienic character, thus reducing the actual rate of transesterification. The existence of this complex was inferred by using unreactive furans as retarding additives and shown by FTIR spectroscopy.

Polyterephthalates Bearing Bio-based Moieties

Dimethyl terephthalate was reacted with 5,5′-Isopropylidene-bis(ethyl 2-furoate), 1,4:3,6-dianhydrohexitols and ethan-1,2-diol in order to obtain PET incorporating bio-based moieties. Polycondensation was achieved in two steps: (i) the formation of a hydroxyethyl-terminated oligomer by reaction of starting diester mixture with excess ED and, (ii) a polycondensation step with elimination of ED was used to obtain high molar mass copolyesters. Copolymers of various compositions were synthesized and characterized by 1H-NMR, SEC, DSC and TGA. The resulting materials are amorphous polymers (T g = 104–127 °C) with good thermal stability.

Synthesis of New bis-Iminocoumarins by Schmidt Reaction Catalyzed by Ion-Exchange Resins

Abstract A new synthetic route to bis-iminocoumarins is proposed which involves the synthesis of iminocoumarins from reaction of 2-hydroxybenzaldehydes with arylacetonitriles and their coupling with aromatic diamines. Ion-exchange resins were used as catalysts in both steps of this synthesis. The reaction parameters were varied and obtained using Amberlyst 15 resin in cyclohexane at 80°C.

Convenient Synthesis of a New Series of 3-Triazolonyl Iminocoumarins

3-Cyano-7-diethylamino-N-ethoxycarbonyl-iminocoumarin reacted with different hydrazines as N-nucleophiles to afford, in one step, a new series of 2-N-substituted 3-triazolonyl-iminocoumarins in good yields. In two cases, N-unsubstituted derivatives were also obtained. The structures of all the products obtained were confirmed by infrared, 1H NMR, 13C NMR, and elemental analysis. The optical properties of three of these compounds in dichloromethane and ethanol were reported.

Synthesis of Primary Amines by One-Pot Reductive Amination of Aldehydes

Abstract We report here a novel, one-pot, two-step reductive amination of aldehydes for the atom-economical synthesis of primary amines. The amination step has been carried out with hydroxylammonium chloride and does not require the use of a base. In the subsequent reduction step, a metal zinc/hydrochloride acid system has been used. This method is applicable to both aliphatic and aromatic aldehydes. The operational simplicity, the short reaction times, and the mild reaction conditions add to the value of this method as a practical alternative to the reductive amination of aldehydes. Supplemental materials are available for this article. Go to the publishers online edition of Synthetic Communications® to view the free supplemental file. GRAPHICAL ABSTRACT