Literatura científica selecionada sobre o tema "Hexane Substitution"

Hexane is the most widely solvent used in the lipids extraction process, as the case of the sugarcane wax. However, the use of this solvent is highly harmful to the environment and to human health. Limonene is a monoterpene found in the citrus peel, with great potential for use as a green solvent. In this study, the partial and total substitution of hexane by limonene was performed in the process of the sugarcane peel wax extraction to evaluate the effect of this substitution on the physicochemical characteristics of the wax. The extracted samples were compared with a commercial wax sample (carnauba) using the Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Infrared by Fourier Transform (FTIR) analyses. Through this study, we can conclude that the waxes obtained from the use of the hexane and limonene mixture solvents presented similar physicochemical characteristics to those found in commercial waxes. Thus, the total and/or partial substitution of the hexane by solvents less harmful to health and the environment, such as limonene, can be an alternative in the wax extraction process.

Hexane is a solvent used extensively in the food industry for the extraction of various products such as vegetable oils, fats, flavours, fragrances, colour additives or other bioactive ingredients. As it is classified as a “processing aid”, it does not have to be declared on the label under current legislation. Therefore, although traces of hexane may be found in final products, especially in processed products, its presence is not known to consumers. However, hexane, and in particular the n-hexane isomer, has been shown to be neurotoxic to humans and has even been listed as a cause of occupational diseases in several European countries since the 1970s. In order to support the European strategy for a toxic-free environment (and toxic-free food), it seemed important to collect scientific information on this substance by reviewing the available literature. This review contains valuable information on the nature and origin of the solvent hexane, its applications in the food industry, its toxicological evaluation and possible alternatives for the extraction of natural products. Numerous publications have investigated the toxicity of hexane, and several studies have demonstrated the presence of its toxic metabolite 2,5-hexanedione (2,5-HD) in the urine of the general, non-occupationally exposed population. Surprisingly, a tolerable daily intake (TDI) has apparently never been established by any food safety authority. Since hexane residues are undoubtedly found in various foods, it seems more than necessary to clearly assess the risks associated with this hidden exposure. A clear indication on food packaging and better information on the toxicity of hexane could encourage the industry to switch towards one of the numerous other alternative extraction methods already developed.

The potential of using the bio-based solvent 2-methyloxolane, also known as 2-methyltetrahydrofuran or 2-MeTHF, as an alternative to petroleum solvents such as hexane, was investigated for the extraction of volatile compounds from hop cones (Humulus lupulus L.). Lab scale extractions were coupled with in silico prediction of solutes solubility to assess the technical potential of this bio-based solvent. The predictive approach was performed using the simulation software COSMO-RS (conductor like screening model for real solvants) and showed that the 2-methyloxolane is as good as or better than hexane to solubilize the majority of aromas from hop cones. The experimental results indicated that the highest aroma yield was obtained with 2-methyloxolane with 20.2% while n-hexane was only able to extract 17.9%. The characterization of aromas extracted by the two solvents showed a similar composition, where lupulone was the main component followed by humulone. No selectivity of the solvents was observed for any of the major analytes. Finally, a sensory analysis was performed on the extracts, showing that both concretes using 2-methyloxolane and hexane have similar olfactory profiles. The results indicate that 2-methyloxolane could be a promising bio-based extraction solvent for hexane substitution.

AbstractIn this study, an evaluation of the enantioselective of a chiral flavanone with 2'‐OH substitution (5,7,2'‐trihydroxyflavanone) on ring C was studied by high performance liquid chromatography using the cellulose tris(3,5‐dimethylphenyl carbamate)‐based stationary phase with n‐hexane and iso‐propanol doped with 0.1% (v/v) trifluoroacetic acid as a mobile phase. Column temperature and mobile phase composition were investigated in the assessment of the chiral separation by considering the enantiomeric resolution factor (Rs). Also, the absolute configurations of single enantiomers were determined by measuring CD spectra based on the exciton‐coupling method. The results pointed out that the 2'‐hydroxy group was capable of advancing the enantioselective of flavanones on the cellulose tris(3,5‐dimethylphenyl carbamate)‐based stationary phase when the column temperature was higher than 30 oC and the mobile phase was of 10% iso‐propanol doped with 0.1% (v/v) TFA in n‐hexane. The absolute configuration determination showed that the enantiomer with the 2S configuration was the first eluted and, consequently, the elution order of the enantiomers of 5,7,2'‐trihydroxyflavanone at optimal conditions was in contrast to 5,7,4'‐trihydroxyflavanone and 5,7‐dihydroxyflavanone. The 2'‐OH substitution on the phenyl moiety appears to be capable of inducing or altering the strength of inter‐and intramolecular interactions when the chiral selectors are immobilized on the silica stationary phase.

Since deuterium 2H (D) is an isotope of hydrogen 1H, the testing of the possibility of photochemical synthesis of marked chlorinated phenol, biphenyl and benzene using normal solvents was studied. The irradiation of full chlorinated compounds dissolved in normal solvents such as MeOH or n-hexane has led to a reaction substitution in which a chlorine atom was substituted by hydrogen atom forming less grade chlorinated chlorophenols, biphenyls and benzenes. The quantum yields of pentachlorophenol, decachlorobiphenyl and hexachlorobenzene under irradiation using polychromatic light were calculated and found to be 5.7 x 10-3, 1.6 x 10-2 and 1.2 x 10-2 Mol·Einstein-1, respectively. Depending on this study the production of marked chlorinated or non-chlorinated compounds using deuterated appropriate solvents such as MeOH d4 or n-hexane d14 is possible. However, more efforts should be made towards chromatographically separation of synthesized standards and byproducts in order to make the use of these marked compounds as standards in residue analysis feasible.

Since deuterium 2H (D) is an isotope of hydrogen 1H, the testing of the possibility of photochemical synthesis of marked chlorinated phenol, biphenyl and benzene using normal solvents was studied. The irradiation of full chlorinated compounds dissolved in normal solvents such as MeOH or n-hexane has led to a reaction substitution in which a chlorine atom was substituted by hydrogen atom forming less grade chlorinated chlorophenols, biphenyls and benzenes. The quantum yields of pentachlorophenol, decachlorobiphenyl and hexachlorobenzene under irradiation using polychromatic light were calculated and found to be 5.7 x 10-3, 1.6 x 10-2 and 1.2 x 10-2 Mol·Einstein-1, respectively. Depending on this study the production of marked chlorinated or non-chlorinated compounds using deuterated appropriate solvents such as MeOH d4 or n-hexane d14 is possible. However, more efforts should be made towards chromatographically separation of synthesized standards and byproducts in order to make the use of these marked compounds as standards in residue analysis feasible.

The crystal structure of a solvated zirconocene pentafulvene complex with a bulky adamantylidene substitution pattern, namely (η5,η1-adamantylidenepentafulvene)bis(η5-cyclopentadienyl)zirconium(IV)–toluene–n-hexane (8/1/1), [Zr(C15H18)(C5H5)2]·0.125C7H8·0.125C6H14, is reported. Reducing zirconocene dichloride with magnesium results in the formation of a low-valent zirconocene reagent that reacts readily with adamantylidenepentafulvene to give the aforementioned complex. Single crystal X-ray diffraction proves the dianion-like η5:η1binding mode of the fulvene ligand to the central ZrIVatom. The asymmetric unit contains four independent molecules of [η5:η1-adamantylidenepentafulvene]bis[(η5)-cyclopentadienyl]zirconium(IV), together with half a molecule of toluene disordered with half a molecule ofn-hexane (the solvent molecules have no direct influence on the complex). In each of the four complex molecules, the central ZrIVatom has a distorted tetrahedral coordination environment. The measured crystal consisted of two domains with a refined ratio of 0.77:0.23.

Suite à une première extraction d'huile végétale par pressage des graines oléagineuses, une huile résiduelle exploitable persiste dans le tourteau de graines, nécessitant une seconde extraction par solvant. Actuellement, l’hexane est le solvant principalement utilisé industriellement. Malgré ses caractéristiques favorables, telles que sa sélectivité envers les lipides et sa séparation aisée de l'huile par distillation, des préoccupations concernant sa toxicité et son origine non renouvelable ont incité à rechercher des alternatives. Ces travaux de recherche visent à identifier de nouveaux solvants plus sains, plus sûrs et respectueux de l'environnement, notamment des solvants bio-sourcés, pour l'extraction sélective de l'huile des graines oléagineuses.Pour atteindre cet objectif, une approche d'ingénierie inverse basée sur le Criblage à Haut Débit (CHD) et la Conception Moléculaire Assistée par Ordinateur (CMAO) a été employée pour concevoir des alternatives optimales adaptées aux exigences spécifiques liées à l'application. Le processus de formulation inverse a débuté par la définition de valeurs cibles pour les propriétés physico-chimiques clés (par exemple, le point d'ébullition, le point d'éclair) des solvants existants utilisés pour l'extraction d'huile. Ensuite, des structures moléculaires correspondantes à ces cibles ont été recherchées parmi des milliers de solvants à l'aide de l'outil CMAO IBSS (InBioSynSolv). Plus précisément, pour chacune de ces molécules, les propriétés sont prédites grâce à des modèles de contribution de groupe et comparées aux spécifications techniques, aux critères de sécurité et aux considérations environnementales et sanitaires. Un affinement supplémentaire des solvants candidats générés par IBSS a été effectué en étudiant l'affinité entre les solvants identifiés et les solutés cibles dans le tourteau, en comparant leur profil σ (déterminé à l’aide de l’outil COSMO-RS) et en calculant l'équilibre thermodynamique. Cette méthodologie associant divers outils de modélisation et des critères industriels a permis une sélection efficace d’une douzaine de candidats pour leur sélectivité vis-à-vis des lipides. Enfin, une validation expérimentale a été menée à différentes échelles pour corroborer l'efficacité des solvants alternatifs
Following an initial vegetable oil extraction through oilseed pressing, valuable residual oil persists within the oilseed cake, necessitating a further solvent extraction process. Hexane is currently the predominant solvent employed industrially for oilseed oil extraction. Despite its favourable characteristics such as lipid selectivity and ease of separation from oil through distillation, concerns regarding toxicity and non-renewable sourcing have prompted investigations into its replacement. This research aims to identify novel solvents for the selective extraction of oil from oilseeds that are healthier, safer, and environmentally sustainable, including bio-based solvents.To achieve this objective, a reverse engineering approach based on High Throughput Screening (HTS) and Computer Aided Molecular Design (CAMD) is employed to design optimal alternatives tailored to specific application requirements. The reverse engineering process began by defining the target values for key physicochemical properties (e.g., boiling point, flash point) of existing solvents used in oil extraction. Subsequently, molecular structures aligning with these targets were sought among thousands of solvents using the CAMD tool IBSS (InBioSynSolv). Specifically, for each and every molecule, the properties are predicted through group contribution models and compared against technical specifications, safety criteria, and environmental and health considerations. Further refinement of the candidate solvents generated by IBSS involved investigating the affinity between the identified solvent candidates and the target solutes within the cake, by comparing their σ-profile (determined using the COSMO-RS tool) and calculating the thermodynamic equilibrium. This methodology, coupling various modelling tools and industrial criteria, enabled an effective selection of a handful of candidates based on their selectivity towards lipids. Finally, experimental validation was conducted across various scales to corroborate the efficiency of the alternative solvents

The general principles discussed in Chapter 3 also apply to reactions of organometallic complexes. Because these systems do not have a wide range of structurally similar complexes with different metal atoms for comparative studies across the Periodic Table, comparisons are usually made down a particular group. However, there is a wide range of ligands available for studies of entering and leaving group effects. This area has been the subject of several recent reviews. A major difference from the systems discussed in Chapter 3 is that many of these complexes are soluble in organic solvents, including hydrocarbons. This can minimize the complicating factor of solvent coordination, but these solvents often have quite low dielectric constants so that various types of preassociation are more probable. The metal carbonyl family of compounds is typical of the range of structures and reactivities of organometallic complexes. The rate of CO exchange was examined in early studies, and this work is the subject of a recent review. The order of reaction rates is as follows: Where the rate law has been determined, the reaction is first-order in [M(CO)R] and zero-order in [CO]. This implies a D mechanism, since a solvent intermediate is unlikely for the "noncoordinating" solvents. This mechanism also is probable for other ligand substitutions. The main mechanistic exception to the above generalizations is V(CO)6, which has an Ia mechanism for PR3 substitution reactions. This compound is unique in that it is the only 17-electron metal carbonyl and also is by far the most labile. Some kinetic results for substitution on V(CO)6 in hexane are given in Table 5.1. The substitution rates have rather low ΔH* values, and the negative ΔS* values are typical of an associative process. The rates for various entering groups correlate with the basicity rather than the size, as measured by the cone angle. It has been suggested that formation of a 19-electron associative intermediate from a 17-electron reactant is much more favorable than a 20-electron intermediate from an 18-electron reactant.

Abstract Furanoses and pyranoses are hemiacetals. Glycosides are acetals. On paper, they are derived from furanoses and pyranoses by replacing the hydrogen of the hemiacetal hydroxyl group by an R group. These are thus mixed acetals, internal and external, whereby one of the acetal oxygens is derived from one of the alcohol functions of the sugar, and the other from the external hydroxylated compound, R-OH. It follows that there are four types of glycosides, corresponding to either a pentose or a hexose. Below are examples of four glycosides derived from galactose by substituting the hemiacetal hydrogen by a methyl group: methyl α-D-galactofuranoside 3.1, methyl β-D-galactopyranoside 3.2, methyl α-D-galactofuranoside 3.3, and methyl β-D-galactofuranoside 3.4.