Alkoxyl Oxygen Research Articles

The structure-property relationship of p-alkoxyl benzohydroxamic acids towards wolframite flotation: Theoretical and experimental investigations

Electron donating ability and hydrophobicity are of the two aspects related to flotation performance of a collector. To solve the insufficient collecting power of benzohydroxamic acid (BHA) in tungsten ores flotation, its derivatives p-alkoxyl benzohydroxamic acids (AOBHAs) were designed as the advanced wolframite collectors. The computational results inferred that compared with BHA, the p-π conjugation between the alkoxyl oxygen and phenyl ring enhanced the electron donating ability of AOBHAs. Meanwhile, AOBHAs exhibited higher hydrophobicity which increased with expanding the carbon chain length of alkoxyl. On this basis, MOBHA (p-methoxy BHA), EOBHA (p-ethoxyl BHA), POBHA (p-propoxyl BHA) and BOBHA (p-butoxyl BHA) were synthesized, and their flotation response towards wolframite was explored through adsorption, zeta(ζ)-potential and contact angle measurements as well as micro-flotation tests. The findings indicated that the adsorption capacities, rangeability of ζ-potential and hydrophobization to wolframite followed the sequence of BOBHA > POBHA > EOBHA > MOBHA > BHA. After pre-activation with 1.0 × 10−4 mol/L lead nitrate, the flotation recovery of wolframite reached about 12.6%, 87.6%, 93.1%, 93.4% and 95.2% for 2.0 × 10−5 mol/L BHA, MOBHA, EOBHA, POBHA and BOBHA, respectively. The experimental findings well supported the molecular design hypothesis.

Synthesis, Structure, and Magnetic Properties of a Twist Linear Tetranuclear Co 2 III Ln 2 III Complexes

A series of twist linear tetranuclear 3d–4f Co 2 III Ln 2 III [Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5)] complexes have been prepared under solvothermal conditions and structurally characterized with Schiff-base ligand 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propanediol (H4L). The two central Co ions are linked by two alkoxyl oxygen atoms, and one Ln ion lying above and the other below the Co–Co dimer, form a twist linear array. The magnetic susceptibility studies reveal antiferromagnetic or ferromagnetic behaviour, whilst dynamic magnetic studies indicate no slow magnetic relaxation for these complexes.

Complexation of Molybdenum(V) with Glycolic Acid: An Unusual Orientation of Glycolato Ligand in {Mo2O4}2+ Complexes

(PyH)5[Mo(V)OCl4(H2O)]3Cl2 and (PyH)n[Mo(V)OBr4]n reacted with glycolic acid (H2glyc) or its half-neutralized ion (Hglyc(-)) to afford a series of novel glycolato complexes based on the {Mo(V)2O4}2+ structural core: (PyH)3[Mo2O4Cl4(Hglyc)]. (1)/ 2CH 3CN (1), (PyH) 3[Mo 2O 4Br 4(Hglyc)].Pr(i)OH(2), (PyH)2[Mo2O4(glyc) 2Py 2] (3), (PyH) 4[Mo 4O 8Cl 4(glyc) 2].2EtOH (4), and [Mo 4O 8(glyc) 2Py 4] (5) (Py = pyridine, C 5H 5N; PyH(+) = pyridinium cation, C 5H 5NH (+) and glyc (2-) = a doubly ionized glycolate, (-)OCH 2COO (-)). The compounds were fully characterized by X-ray crystallography and infrared spectroscopy. The Hglyc (-) ion binds to the {Mo 2O 4} (2+) core through a carboxylate end in a bidentate bridging manner, whereas the glyc (2-) ion adopts a chelating bidentate coordination through a deprotonated hydroxyl group and a monodentate carboxylate. The orientations of glyc (2-) ions in 3- 5 are such that the alkoxyl oxygen atoms occupy the sites opposite the multiply bonded oxides. {(C6H5) 4P}[Mo(VI)O 2(glyc)(Hglyc)] ( 6), an oxidized complex, features a reversed orientation of the glyc(2-) ion. The theoretical DFT calculations on the [Mo(V)2O4(glyc) 2Py 2](2-) and [Mo(VI)O2(glyc)2](2-) ions confirm that binding of glycolate with the alkoxyl oxygen to the site opposite the MoO bond is energetically more favorable in {Mo(V)2O4}(2+) species, whereas a reversed orientation of the ligand is preferred in Mo(VI) complexes. An explanation based on the orbital analysis is put forward.

FTIR and molecular mechanics studies of H-bonds in aliphatic polyurethane and polyamide-66 model molecules

Model aliphatic polyurethane (APU) hard segment based on 1,6-hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO) were prepared. FTIR and molecular mechanics (MM) simulation were used to conduct the systematic studies on APU and polyamide-66 (PA-66) whose sole difference lies in the alkoxyl oxygen. It was found that the introduction of the alkoxyl not only increases the conformations in APU, makes it a possible H-bond acceptor, but also weakens the H-bond between NH and O C in APU. There are two conformers stably existed in APU with lowest energy, leading to eight H-bond complexes based on NH as donor and (1) O C as acceptor, and another two complexes based on (2) alkoxyl O and (3) urethane N as acceptors, whereas there is only one stable conformer in PA-66, leading to one H-bond complex. One predominant H-bond complex has been found in APU with probability of about 95%. The simulated results are consistent with the νNH and νC O band shifting in FTIR.

Infrared analysis of phase transitions in liquid crystal acrylate monomers bearing urethanic groups and cholesteryl as mesogen

An infrared analysis of phase transitions in three enantiotropic liquid crystalline acrylate monomers with different spacer lengths bearing urethane groups and cholesteryl as mesogen was carried out. Through heating and cooling, spectral modifications especially at the level of carbonyl, –NH– and urethane alkoxyl oxygen groups were found. These findings reveal the influence of hydrogen bonding on mesomorphic properties of the studied compounds mentioning that both liquid crystal transitions are evidenced by the spectral changes. For all the compounds studied, the values of the transition temperatures deduced from the spectral modifications are in good agreement with those obtained from DSC measurements.

SN2 reactions at amide nitrogen – theoretical models for reactions of mutagenic N-acyloxy-N-alkoxyamides with bionucleophiles

The reactions of N-formyloxy-N-methoxyformamide 4 with ammonia 2 and methanethiol 3 have been modeled at theAM1, HF/6-31G* and Density Functional computational levels. The reaction process is similar geometrically and electronically to classical SN2 reactions at carbon. Near- linear transition states reveal extensive charge separation and partial nitrenium ion character at the formamide nitrogen indicative of a non-synchronous process involving early stretching of the formate-formamide nitrogen bond. Activation energies, computed from pBP/DN* energies of HF/6-31G* ground state and transition state geometries, are in the range of experimental values and a strong solvation effect is predicted. Evidence for anomeric weakening of the N-formate bond by the geminal alkoxyl oxygen was obtained from a comparison of the reactions of ammonia with 4 and N-formyloxy-N-methylformamide 5. An N-alkyl group leads to a much larger activation energy in accordance with the experimental findings for N-acyloxy-N- alkylamides, which are resistant to attack by nucleophiles and are non-mutagenic.

Computational study (PM3) of the hydration of dipentylpyridine-2,5-dicarboxylate

Carbonyl oxygens are the main elements of dialkyl pyridine dicarboxylate which are able to form hydrates with water molecules. Oxygens of the alkoxyl groups and pyridine nitrogens can be only considered as additional elements to enhance the molecule hydrophilicity. The hydration is, however, limited in two phase extraction systems. The carbonyl oxygen at position 2 and the pyridine nitrogen can be considered as the hydrophilic center of dipentyl pyridine-2,5-dicarboxylate while the hydrophilic character of the ester group at position 5 can be neglected due to steric effects and the lack of any interaction with water molecules. The same probably concerns the alkoxyl oxygen at position 2. Hydrophilic effects of both the carbonyl oxygens at position 2 and the pyridine nitrogen and the location of the second hydrophobic substituent directly on the opposite side of the pyridine ring (at position 5) in respect to the ester group at position 2 predominate the structure for effective hydration adsorption and decreasing of the interfacial tension at hydrocarbon/water interfaces in comparison to various dipentyl pyridine dicarboxylates having other positions of the ester groups.

Study of intermolecular interactions in the equilibrium catalytic transesterification of esters

The interaction of alcohols ROH with esters PhCOOR (R = Me,n-Bu,n-C7H15) in binary mixtures and in solutions in non-polar solvents (CCl4, cyclohexane) was studied over a wide temperature range by Fourier IR spectroscopy. Even with a great excess of alcohol (up to 3000-fold molar excess), two bands are observed in the region ofv(CO) vibrations. The low-frequency band, which is down-shifted by 15–20 cm−1 with respect to thev(CO) band in the absence of alcohol, corresponds to ester molecules bonded by hydrogen bonds of the C=O...HO type. The high-frequency band is up-shifted by 3–5 cm−1 with respect to the esterv(CO) band. The discreteness of the shift, which is confirmed by the appearance of an isobestic point, indicates that an H-complex of yet another type is formed between the alcohol and the ester. The analysis of the data available allows one to conclude that complex formation involves the alkoxyl oxygen atom of the ester. The enthalpies of formation were determined forn-BuOH H-bonds with the esters and with the transesterification catalysts, i.e., As(OBu)3, B(OBu)3, and Ti(OBu)4.

Ultraviolet absorption spectra and electronic structure of (alkylthioalkyl)trialkoxysilanes

The authors have studied the ultraviolet absorption spectra of solutions of (alkylthioalkyl)-trialkoxysilanes in heptane and acetonitrile in the 4.5-5.3 x 10W m region. The experimental data obtained and the quantum chemical calculations carried out show that the alkyl substitutents at the sulfur atom exert an inductive and steric effect on the sulfide group, while the alkoxyl oxygen atoms experience the substituent effect across space. In molecules of compounds with one methylene group separating the silicon and sulfur atoms, an acceptor effect for the trialkoxysilyl group is apparent, changing the degree of binding for the electronic pairs of the sulfur atom.

The reaction of t-butoxyl radicals with glycidols and their O-tributyltin derivatives: homolytic 1,5-transfer of hydrogen and of tin from enoxyl oxygen to alkoxyl oxygen

The interaction of t-butoxyl radicals with glycidol, α-, β-, and γ-methylglycidol, and their O-tributyltin derivatives (A, M = H or Bu 3Sn) have been studied by ESR spectroscopy. ▪ The radicals B and C are formed successively. In C, the tributyltin group, or the hydrogen atom, then undergoes an intramolecular 1,5- rearrangement from enoxyl oxygen to alkoxyl oxygen, and the spectra of the enoxyl radical D are observed.

Intramolecular hydrogen bonding in cycloalkane-1,2-diol monoacetates

Intramolecular hydrogen bonding in cyclopentane- and cyclohexane-1,2-diol monoacetates was studied by high resolution infrared spectroscopy in the 3μ region. Intramolecular hydrogen bonding was exhibited by all compounds and the data are interpreted in terms of preferred conformations, assuming the acetate group to be exclusively in the "planar trans" form.trans-Cyclopentane-1,2-diol monoacetate exhibited two hydroxyl absorption bands. One band was assigned to free hydroxyl stretching and the other to hydrogen bonding with the carbonyl oxygen so that an equilibrium between two ring conformations must be assumed to exist in solution. With cis-cyclopentane-1,2-diol monoacetate only a strong high frequency band was observed, and this was attributed to hydrogen bonding to the alkoxyl oxygen.trans- and cis-cyclohexane-1,2-diol monoacetate both exhibited two hydroxyl absorption bands. With the former, the hydroxyl group was assumed to be exclusively in an equatorial position to permit hydrogen bonding to both the alkoxyl and carbonyl oxygens. Similarly, in the latter, the high frequency band was attributed to hydrogen bonding to the alkoxyl oxygen atom while the low frequency band was assigned to hydrogen bonding to the carbonyl oxygen.

The effect of organic substituents and structure of organophosphorus compounds on their extraction abilities for uranium

With 12 phosphates, 1 phosphonate, 1 phosphinate and 1 phosphine oxide, the pattern of uranium extraction from nitric acid media was investigated. The extraction was affected by the nature of the organic substituents attached to the phosphoryl group as well as by the solvent structure. Phosphates with aryl groups were not satisfactory extractants. The extraction ability increased as the alkyl group was made larger; phosphates with branching alkyl groups were better than phosphates with normal alkyl groups. Removal of the alkoxyl oxygen enhanced the extracting abilities. The relative order of the extracting abilities were: tri- n-butyl phosphine oxide and tri- n-butyl phosphinate > tricyclohexyl phosphate > diethylbutyl phosphonate > phosphates with branching alkyl groups > phosphates with normal alkyl groups > phosphates with aryl groups.

The effect of organic substituents and structure of organophosphorus compounds on their extraction abilities for uranium

With 12 phosphates, 1 phosphonate, 1 phosphinate and l phosphine oxide, the pattern of uranium extraction from nitric acid media was investigated. The extraction was affected by the nature of the organic substituents attached to the phosphoryl group as well as by the solvent structure. Phosphates with aryl groups were not satisfactory extractants. The extraction ability increased as the alkyl group was made larger; phosphates with branching alkyl groups were better than phosphates with normal alkyl groups. Removal of the alkoxyl oxygen enhanced the extracting abilities. The relative order of the extracting abilities were: tri-nbutyl phosphine oxide and tri-n-butyl phosphinate > tricyclohexyl phosphate > diethylbutly phosphonate > phosphates with; branching alkyl groups > phosphates with normal alkyl groups > phosphates with arly groups.

The second virial coefficients of mixed polar vapours

The second virial coefficients of binary mixtures of chloroform with methyl formate, n -propyl formate, methyl acetate, ethyl acetate and diethylamine have been measured in a ‘Boyle’s law apparatus’ at temperatures between 50 and 95 °C. The measured values are consistently higher than predicted by the theory of corresponding states, and a quantitative interpretation is proposed, based on the hypothesis that the esters and amine are partially dimerized and are involved in association with the chloroform by hydrogen bonding. A linear relation is shown to exist between the heats and entropies of association for the various mixtures, and the theoretical significance of this is discussed. There is some evidence that hydrogen bonds are formed through the alkoxyl oxygen by formate esters and through the carbonyl oxygen by acetate esters. The paper includes data on the second virial coefficient for the pure esters and for ethyl formate and methyl propionate.