Luc Rigal

Direct preparation of 5-hydroxymethyl-2-furancarboxaldehyde from polyholosides: a chemical valorisation of the Jerusalem artichoke (Helianthus tuberosus L.)

The selective synthesis of 5-hydroxymethyl-2-furancarboxaldehyde was carried out using a water-ion-exchanger-extracting solvent, triphasic system as developed earlier using d-fructose as a model substrate. The system was applied to the processing of various hexoses and of plant material extracts. In the case of polyholosides, particularly inulin, the ion-exchange resin catalyses both the hydrolysis of the plant polymer and sugar dehydration. The direct processing of Jerusalem artichoke extracts in the presence of ion-exchangers in the H+ form allowed HMF to be obtained selectively in the extracting solvent.

Isolation and characterisation of hemicelluloses from sunflower hulls

The hemicelluloses extracted from sunflower hulls by repeated alternating oxidative and alkaline treatments were purified by precipitation with Cetavlon and then ion-exchange chromatography on DEAE-trisacryl. The resulting fractions were examined by hydrolysis, methylation, GLC-MS, and NMR spectroscopy. The hemicelluloses are of the glucuronoxylan type with the following structure -->4)-beta-D-Xylp-(1-->4)-[4-O-Me-alpha-D-GlcpA-(1-->2)]-bet a-D-Xylp-(1-->. The polysaccharides differed in the amount of branching; the ratio of the main fraction 4-O-MeGlcA:Xyl was 1:8-9.

Optimization of the conversion of d-fructose to 5-hydroxymethyl-2-furancarboxaldehyde in a in a water-solvent-ion exchanger triphasic system. Part II. Search for a local optimum of selectivity by the simplex method

Abstract The simplex method is applied to optimize the selectivity in the 5-hydroxymethyl-2-furancarboxaldehyde synthesis from d -fructose. The selected reaction system associates an ion-exchanger, used as a catalyst, which is not miscible with the aqueous phase containing the sugar. A high selectivity, combined with an important conversion rate, is obtained in mild operating conditions.

Xylitol production from olive-pruning debris by sulphuric acid hydrolysis and fermentation with Candida tropicalis

Abstract The debris of olive pruning is a renewable, low-cost and widely available agricultural waste. Its biochemical conversion by hydrolysis and fermentation was undertaken in the present study. Diluted acid hydrolysis was conducted in a heterogeneous stirred tank reactor at 90°C and at a low sulphuric acid concentration (0.0–1.0 N) for 300 min. To increase the d-xylose/d-glucose ratio into the hydrolysate, in another experiment amorphous cellulose and extracts were removed by means of a pretreatment in an extruder with 1 N H2SO4 at 70°C before the acid hydrolysis. The fermentation of hydrolysates was performed under microaerobic conditions in a batch bioreactor at 30°C and pH 5 with Candida tropicalis NBRC 0618. The controlled fermentation parameters included maximum specific growth rate, biomass productivity, rate of the specific substrate uptake, rates of specific ethanol and xylitol production, and overall yield of ethanol and xylitol. In the presence of 1.0 N H2SO4, the fermentation of the pretreated hydrolysate led to specific xylitol production rates and overall xylitol yield (0.1 g g-1 h for t=25 h; 0.49 g g-1, respectively) higher than those achieved without pretreatment (0.03 g g-1 h for t=25 h; 0.39 g g-1, respectively). Under these conditions, 53 g xylitol kg-1 of dry olive-pruning debris was obtained from the pretreated culture, whereas without pretreatment 70 g ethanol and 34 g xylitol were recovered.

Synthesis and structural features of new [5,7] orthocyclophanes, [7,7] cyclophanes and corresponding macrobicyclic cryptophanes.

Abstract The Baylis-Hillman reaction of dialdehydes with methyl acrylate, followed by acetylation of the resulting diols gave diacetates 3, 14, 16 and 20. Treated with ammonia, these diacetates afforded new cyclophanes and the corresponding macrobicyclic cryptophanes. Conformational analysis of the cyclophanes was described.

Optimization of the conversion of d-fructose to 5-hydroxymethyl-2-furancarboxaldehyde in a water-solvent-ion exchanger Triphasic system — Part I. Investigation of the main effects of the major parameters and of their interactions on the reaction

Abstract Two fractional factorial designs were used for the investigation of the synthesis of 5-hydroxymethyl-2-furancarboxaldehyde from d -fructose. The reaction system selected combines an ion-exchanger, used as a catalyst, with an extracting solvent which is not miscible with the aqueous phase containing the sugar, and affords mild operating conditions. The main effect of seven parameters and their interactions on four responses of the reaction system were quantified. An orientation for the optimization of the conversion rate to HMF as well as of the reaction selectivity can thus be proposed.

Synthèse du 5-bromométhyl- et du 5-chlorométhyl-2-furannecarboxaldéhyde

Abstract The action of hydrogen halides, sulfur and phosphorus halides, and halotrimethylsilanes on 5-(hydroxymethyl)-2-furancarboxaldehyde (1) led to the corresponding 5-(chloromethyl)- (2) or 5-(bromomethyl)-2-furancarboxaldehyde (3). Thus, treatment of 1 in diethyl ether solution with gaseous dry hydrogen chloride under very mild experimental conditions led to high yields of 2. The selective and quantitative conversion of 1 into 3 was achieved with bromotrimethylsilane. In the same manner, chlorotrimethylsilane gave high yields of 2 from 1. The latter compound was obtained by acid-catalyzed dehydration of d -fructose in dimethyl sulfoxide, and then converted into 2 without prior purification.

Ethylene removal for long term conservation of fruits and vegetables

Abstract A study of ethylene removal from the atmosphere of fruit storage rooms by catalytic oxidation was carried out. The efficiency of three catalysts was compared in a laboratory pilot reactor with experimental designs for temperature and ethylene concentration. A commercial prototype, devised volume (1800 m3) storage room filled with Golden Delicious apples (282 t). The conserved apples in the treated store were similar to the pre-storage samples for a number of instrumentally measured quality characteristics.

Ethylene removal in fruit storage rooms : a catalytic oxidation reactor at low temperature

Abstract During post-harvest conservation, climacteric fruit release ethylene whose accumulation speeds maturation, senescence and degradation processes in conserved fruits. The performance of an ethylene removal reactor working by catalysis at low temperature is studied. The main factors studied are catalyst temperature, ethylene concentration, flow rate of air-ethylene gaseous mixture and catalyst mass. Work based on the experimental designs (uniform shell design) of Doehlert yielded a better knowledge on the influence of the different factors studied and facilitated the optimisation of the conditions of ethylene removal. The catalytic procedure used ensures a very efficient oxidation with an efficiency of 100% at a temperature between 100 and 120°C. A commercial prototype has been devised by extrapolation of the results obtained on a laboratory scale.

The catalytic oxidation of 4,8-dihydroxy-2,6-Dioxabicyclo (3.3.0) octane [1R,4S,5R,8R] on platinum in the presence of oxygen: A study of the influence of the major parameters.

Abstract The oxidation of 4,8-dihydroxy-2,6-dioxabicyclo (3.3.0) octane [1R,4S,5R,8R] -or isosorbide- results in monoketone : 4-hydroxy-2,6-dioxabicyclo (3.3.0) octan-8-one [1S,4S,5R]. This reaction takes place in an aqueous acid solution, with a stream of oxygen and in the presence of a platinum on carbon catalyst. A fractional factorial design is used to determine the major parameters that influence the oxidation of isosorbide. The effect of the different parameters is analyzed and a technique for optimization of the reaction is suggested. A reaction scheme discussed which takes into account the experimental results and the molecular structure of the isosorbide molecule, as well as the influence of the pH on the rate of the reaction.