Microdetermination of phenols, carboxylic acids and phenolic acids by potentiometric and visual titrations in dimethylformamide

Potentiometric titration of phenols with sodium methoxide in dimethylformamide, with a glass-calomel electrode system, is limited to monohydric phenols substituted with electron-attracting groups and dihydric phenols in which the two -OH groups are substituted in isolated benzene rings. Brilliant Orange has proved to be a suitable indicator in the titration of all types of mono- and dihydric phenols. Titan Yellow is recommended as indicator for the titration of carboxylic acids. Simultaneous visual titration of -OH and -COOH groups is also described. A detailed study with 62 structurally different compounds covering the various groups is reported, and a suitable procedure for the microdetermination of each class of these compounds with an error of +/- 0.2% absolute or less is presented.     

Microdetermination of calcium and magnesium in a mixture

Summary A procedure is presented for the chemical separation and determination of mg quantities of calcium and magnesium, which is based on the selective carrying of calcium by ignited strontium sulphate leaving magnesium in the solution phase; the carried calcium is recovered by leaching with alcoholic sulphuric acid solution. Calcium and magnesium in the separated fractions are determined complexometrically using Eriochrome Black T as the indicator.

---

Zusammenfassung Ein Verfahren zur chemischen Trennung und Bestimmung von mg-Mengen Calcium und Magnesium wird vorgeschlagen, wobei Ca selektiv mit geglühtem Strontiumsulfat abgetrennt wird, während Mg in Lösung bleibt. Ca wird mit alkoholischer Schwefelsäure eluiert. Beide Metalle werden getrennt gegen Eriochromschwarz T komplexometrisch titriert.

     

Iodine catalyzed conjugate addition of mercaptans to α,β-unsaturated carboxylic acids under solvent-free condition

We have described herein molecular iodine catalyzed Michael addition of thiol to α,β-unsaturated carboxylic acids. This environmentally benign catalytic system (iodine) used under mild and solvent-free conditions to achieve the corresponding adducts in excellent yield.     

Ground and excited states of the monomer and dimer of certain carboxylic acids

The ground-state properties of the monomer and the dimer of formic acid, acetic acid, and benzoic acid have been investigated using Hartree-Fock (HF) and density functional theory (DFT) methods using the 6-311++G(d,p) basis set. Some of the low-lying excited states have been studied using the time-dependent density functional theory (TDDFT) with LDA and B3LYP functionals and also employing complete-active-space-self-consistent-field (CASSCF) and multireference configuration interaction (MRCI) methodologies. DFT calculations predict the ground-state geometries in quantitative agreement with the available experimental results. The computed binding energies for the three carboxylic acid dimers are also in accord with the known thermodynamic data. The TDDFT predicted wavelengths corresponding to the lowest energy n-pi* transition in formic acid (214 nm) and acetic acid (214 nm) and the pi-pi* transition in benzoic acid (255 nm) are comparable to the experimentally observed absorption maxima. In addition, TDDFT calculations predict qualitatively correctly the blue shift (4-5 nm) in the excitation energy for the pi-pi* transition in going from the monomer to the dimer of formic acid and acetic acid and the red shift (approximately 19 nm) in pi-pi* transition in going from benzoic acid monomer to dimer. This also indicates that the electronic interaction arising from the hydrogen bonds between the monomers is marginal in all three carboxylic acids investigated.     

Ketene methyl trialkylsilyl acetals as effective silylating agents for alcohols,carboxylic acids,mercaptans, and amides

Silyl-proton exchange reactions with ketene methyl trialkylsilyl acetals proceeded rapidly and quantitatively under mild conditions. The preparative silylation of alcohols, carboxylic acids, mercaptans, and amides is described.     

Titrimetric determination of certain mercaptans with mercuric chloride

A procedure is described for the semimicro determination of certain mercaptans, by means of their reaction with mercuric chloride. The acid liberated during the reaction is titrated with standard alkali after addition of sufficient potassium iodide to convert the surplus mercuric chloride into a stable soluble complex. The procedure has been applied to determine 0.12-1 mmole of these compounds; the results are accurate to within 0.5%.     

Semiconductor‐photocatalyzed degradation of carboxylic acids: Enhancement by particulate semiconductor mixture

Degradation of oxalic acid on particulate TiO₂, ZnO, CuO, Bi₂O₃, In₂O₃, and Nb₂O₅ under UV‐A light exhibits first‐order kinetics, and the degradation rates increase linearly with the photon flux. All the oxides show sustainable photocatalytic activity, and the photonic efficiencies of degradation of oxalate are very much lower than those of the acid. The ease of degradation of carboxylic acids is the following: formic > oxalic > acetic > citric. Intimate mixtures of two different particulate semiconductors kept under suspension and at continuous motion exhibit higher photocatalytic activity, revealing interparticle charge transfer. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 716–726, 2009     

Acidity of carboxylic acids: a rebuttal and redefinition

A recent theory of ionization of carboxylic acids divided the process of ionization into two steps and attributed the main importance to the electrostatic potential of the acid molecule. The origin of the acidity was thus seen in the high energy of the acid molecule and not in the stabilization of the anion by resonance. In this paper, the theory was revised on the basis of further calculations at an MP2/6-31++G(2d,p) level which followed in two steps the reverse process, protonation of the formate anion. The results were compared to those of the methanolate anion as reference. A contradictory conclusion was obtained: the reason for the acidity is in the electrostatic potential of the anion. As a model compound without resonance, 2,2,2-trifluoroethanol was investigated in the same way. The results were qualitatively similar, although any resonance in the anion is not possible. One can conclude that the acidity of carboxylic acids is due to the low energy of their anions; this follows unambiguously from the isodesmic reactions on the basis of either the experimental enthalpies of formation or the calculated energies. It is more difficult to decide whether this low energy is caused by resonance, because any model of the carboxylate anion without resonance is necessarily imperfect and the whole concept is not exactly defined. Several such models were reexamined and improved by separating the effect operative in the anion from those in the neutral acid molecule. While the electrostatic model did not allow any significant conclusion, two models based on VB calculation and on correlation analysis, respectively, furnished qualitatively concordant results: resonance in the anion is diminished by the resonance in the acid molecule, and both together are responsible for less than one-half of the acidity enhancement as compared to the acidity of alcohols. The ratio is reversed in water solution: resonance is then the more important factor responsible for some two-thirds of the enhanced acidity.     

Ipso-nitration of carboxylic acids using a mixture of nitronium tetrafluoroborate,base and 1-hexyl-3,4,5-trimethyl-1H-imidazolium tetrafluoroborate

An eco-friendly and a simple ipso-nitration protocol for a series of aliphatic and (hetero)aromatic carboxylic acids using nitronium tetrafluoroborate, 1-hexyl-3,4,5-trimethyl-1H-imidazolium tetrafluoroborate and base is reported. While contrasted with recently known decarboxylative ipso-nitration strategies for the preparation of nitro compounds, this protocol does not require a toxic metal catalyst and harmful volatile organic solvents. Moreover, this method is perfect for a broad range of functional groups and affords exclusively the ipso-nitrated product in moderate to good yields.     

Microdetermination of alpha-amino acids by spectrophotometric and titrimetric methods

Micro-methods for spectrophotometric and oxidimetric determination of alpha-amino-acids are described. They are based on a reaction of the acids with peri-naphthindan-2,3,4-trione hydrate at pH 2.5 to give a red precipitate of dihydroxy-peri-naphthindenone. The red product is dissolved and measured either spectrophotometrically at 243 nm or titrimetrically by reaction with iodine or N-bromosuccinimide. The results obtained by the three methods are concordant, the average recovery being 98 %.     

Co-crystallization of a benzimidazole derivative with carboxylic acids

The co-crystallization of a benzimidazole derivative (1, C₂₇H₂₆N₆O₃, 3-[[[2-[[(4-Cyanophenyl) amino]methyl]-1-methyl-1H-benzimidazol-5-yl]carbonyl]pyridin-2-ylamino]propionic acid ethyl ester), with fumaric acid (FA) and maleic acid (MA), has been performed. The FA and MA molecules, both are connected with two molecules of C₂₇H₂₆N₆O₃, giving birth to a three-components compound (1·0.5FA, C₂₉H₂₈N₆O₅) and a four-components compound (1·MA, C₃₁H₃₀N₆O₇). Single-crystal X-ray diffractions show that the three different planar moieties (4-cyanophenyl, benzimidazol, and pyridin-2-yl) in compound C₂₇H₂₆N₆O₃ display “cis-form” conformation (a) in the crystal of 1, while exhibiting “intermediate-state” conformation (b) and “trans-form” conformation (c) in compounds 1·0.5FA and 1·MA, respectively. Hirshfeld surfaces analysis, DFT calculations, DSC measurements, IR and Raman spectroscopy were performed, which revealed that the thermal stability of the three conformations follows the order c > b > a.     

Solubility of carboxylic acids in a matrix of uncross-linked polystyrene

Solubility diagrams of a series of carboxylic acids in a matrix of linear polystyrene have been measured using a gravimetric method on samples immersed in solvent, as reported earlier [Bernardo G, Vesely D. Eur Polym J 2007;43:938-48]. The results show that the amount of solvent, swelling the polymer, reaches an equilibrium saturation which has a unique and reproducible value for each system and temperature. An analysis based on Flory-Huggins theory shows that all data presented here can be well interpreted with an interaction parameter in a simple form: χ = a + (b/T). An excellent fit can also be obtained using the van’t Hoff equation. An analysis based on total and partial (Hansen) solubility parameters has also been investigated.     

Esterification of polymeric carboxylic acids

Polymers containing pendant carboxyl groups have been essentially completely esterified with little apparent change in molecular weight by the use of one of the following reagents: (1) trialkyl orthoesters, (2) dimethylformamide dialkyl acetals, (3) tertiary amines followed by alkyl halides, (4) quaternary ammonium hydroxide followed by alkyl halides. The use of some of these methods permits preparation of certain polymers that were previously not readily accessible.     

Molecular species in liquid carboxylic acids

Measurements of dielectric permittivity and electric conductance are presented for mixtures of carboxylic acids — formic, trifluoroacetic, acetic and propionic — and non-polar liquids. For the dielectric and associative behavior of carboxylic acids a knowledge of the cis—trans conformational equilibria of the monomeric acid molecules seems to be essential. Therefore the cis and trans conformations of these molecules have been calculated by the CNDO/2 and PCILO methods. Appreciable rotational barriers for their interconversion have been obtained.     

-trifluoroacylation - a convenient route to carboxylic acids

Trifluoroacetic anhydride will trifluoroacylate reactive aromatic and heterocylic nuclei without the aid of a Friedel-Crafts catalyst. The resulting trifluoromethyl ketone undergoes hydrolysis to yield the corresponding carboxylic acid. This provides a very simple route to aromatic and heterocyclic carboxylic acids.