RESUMEN
Isolation of heat-sensitive reaction products in post-synthesis workup procedures often requires ambient-or low-temperature solvent removal. In the method demonstrated here, solvent evaporation is driven by the pressure gradient between a distillation flask and a chilled receiver in an evacuated closed system containing a minimal amount of residual noncondensable gas. Using an all-glass apparatus, the method is exemplified by evaporation of solvent samples from a distillation flask containing 50 mL of either dimethylformamide, dimethyl sulfoxide (DMSO), or N-methylpyrrolidone (NMP). The distillation flask is suspended in a water bath at temperatures of 18-28 °C, the evaporated solvent is collected in a receiver chilled with liquid nitrogen, and the entire process is completed in 90-140 min. The practicality of this method is further illustrated on a bench-chemistry scale by DMSO and NMP solvent removal from solutions of benzophenone, monitored by gravimetric and 1H NMR methods. Modification of the demonstrated method to mimic freeze-drying conditions (by reducing heat flow to the distillation flask) can be used for recovery of water-soluble compounds including polymers and biopolymers. We propose the name "cryovap" for this solvent removal method.
RESUMEN
The backbone of 2-hydroxyisophthalic acid was identified as a potential metal oxide anchor because of the perfect alignment of all three of its donor groups for binding to inorganic surfaces. It can therefore be used in the design of organic linkers for metal oxide based hybrid materials. Optimized and scalable methods for the synthesis of 2-hydroxyisophthalic acid (1) and its 5-substituted derivatives: 5-bromo- (2), 5-sulfooxy- (3), 5-hydroxy- (4), and 5-PEG600 (5) are presented. Dynamic light scattering (DLS) demonstrated that compound 2 inhibits Fe(OH)3 precipitation when FeIII aqueous solutions are titrated with NaOH, while similar titrations in the presence of the structurally-related isophthalic and salicylic acids, both missing the third donor group, show turbidity at pHs as low as 2.3 and 3.5, respectively. The adduct synthesized from 4.5â nm γ-Fe2 O3 nanoparticles and 5 is water-, alcohol- and CH2 Cl2 -soluble, and forms stable aqueous colloids in the pH range of 4.4-8.7. Moreover, at a pH close to neutral these colloids survive at 100 °C, demonstrating the high practicality of 2-hydroxyisophthalic acid for nanoparticulate inorganic/organic hybrid material design.
RESUMEN
A simple experimental method for determination of the resonance energy by measuring the energies of combustion for two isomeric compounds, aromatic 1-tert-butyl-3,5-dimethylbenzene and nonaromatic trans,trans,cis-1,5,9-cyclododecatriene is proposed. Both compounds not only have the same molecular formula, but also contain the same number of sp2 and sp3 carbon atoms. After converting the obtained values into the gas phase heats of combustion and subtracting one value from another, the resulting mean resonance energy of 184 kJ/mol was obtained. The proposed method can be offered as an experiment for an undergraduate physical chemistry lab curriculum.
RESUMEN
In the course of development of novel capping ligands with variable steric factor, which will be used as an organic coating for metal oxide nanoparticles, a base-catalyzed nucleophilic oxirane ring-opening addition reaction between dimethyl 5-hydroxyisophthalate and allyl glycidyl ether was studied. The allyl-terminated 1-1, 1-2 and 1-3 adducts and dihydroxylated derivative of the 1-1 adduct, 5-diglyceroxy isophthalic acid, were synthesized. The latter binds to the surface of 5 nm γ-Fe2O3 nanoparticles in reaction with their surfactant-free diethylene glycol colloids.
RESUMEN
Magnetite nanoparticles in the size range of 3.2-7.5 nm were synthesized in high yields under variable reaction conditions using high-temperature hydrolysis of the precursor iron(II) and iron(III) alkoxides in diethylene glycol solution. The average sizes of the particles were adjusted by changing the reaction temperature and time and by using a sequential growth technique. To obtain γ-iron(III) oxide particles in the same range of sizes, magnetite particles were oxidized with dry oxygen in diethylene glycol at room temperature. The products were characterized by DLS, TEM, X-ray powder diffractometry, TGA, chemical analysis, and magnetic measurements. NMR r(1) and r(2) relaxivity measurements in water and diethylene glycol (for OH and CH(2) protons) have shown a decrease in the r(2)/r(1) ratio with the particle size reduction, which correlates with the results of magnetic measurements on magnetite nanoparticles. Saturation magnetization of the oxidized particles was found to be 20% lower than that for Fe(3)O(4) with the same particle size, but their r(1) relaxivities are similar. Because the oxidation of magnetite is spontaneous under ambient conditions, it was important to learn that the oxidation product has no disadvantages as compared to its precursor and therefore may be a better prospective imaging agent because of its chemical stability.