V. A. Vasnev

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.

Study of intermolecular interactions in a system for equilibrium catalytic transesterification of esters. 1. Reaction of boron, titanium, and arsenic butoxides with esters according to IR fourier spectroscopic data

IR spectroscopy was used to study solutions of esters of PhCOOR (R=Me, Bu, C7H15, (CH2)2OBu) in B(OBu)3, Ti(OBu)4, and As(OBu)3 and in mixtures of the latter with CCl4 and hexane. It is shown that weak complexes form between the ester molecules and B(OBu)3 and Ti(OBu)4, As(OBu)3 behaves with respect to the esters as a nonpolar solvent. Intermolecular interaction of the esters with butoxides occurs at the alkoxide oxygen in the ester. A mechanism of the exchange of the alkoxyl radical in the reaction of Ti(OBu)4 with PhCOOMe is proposed on the basis of kinetic measurements.

Investigation of the complex formation of phenols with triethylamine by the method of proton magnetic resonance

1. Solutions of 24 phenols containing various types of substituents in dichloroethane were investigated by the PMR method. 2. Correlation equations relating the chemical shift of the OH group of the phenol to its acidity and the substituent constants (σ) of the benzene ring were found. 3. The value of the chemical shift of the proton of the hydroxyl group of phenol increases with increasing acidity. 4. The value of the reaction constant (ρ) increases as we go from autoassociates of phenol to complexes of phenols with triethylamine.

Study of intermolecular interactions in an equilibrium system in the catalytic transesterification of esters 3. Interaction of tetrabutyl titanate with alcohols from ir and NMR spectroscopic data

The reactions of tetrabutyltitanate (TBT) with alcohols have been studied using IR, Raman, and NMR spectroscopy. It has been shown that TBT is associated and has a centrosymmetrical structure. In nonpolar solvents (CCl4, cyclohexane) the associates do not break down on dilution. In the presence of butanol breakdown of the associates occurs accompanied by a reduction in the number, and even the disappearance, of bridging alkoxy groups.13C NMR results show that in mixtures of TBT and alcohols two types of exchange reaction take place simultaneously: between terminal and bridging alkoxy groups, and between TBT and the alcohol. In the case of n-BuOH the first type of exchange is retarded as the temperature is reduced to 283 K but the second is unaffected right down to 213 K. IR results show that alcohols form complexes with TBT in which the alcohol is bonded by a H-bond to the oxygen of the alkoxy group of the TBT and by the oxygen atom to the Ti of a second molecule of TBT. For the exchange reaction between TBT radicals and n-C7H15OH in a binary mixture of 1∶1 composition at 293 K, IR spectroscopy showed the degree of conversion in terms of alcohol to be 65% and the equilibrium constant Ke= 3.4. For MeOH in CCl4 solution the conversion amounted to around 100%.

Intermolecular interactions in the system of equilibrium catalytic transesterification of esters 2. Reaction of boron and arsenic butoxides with alcohols based on IR spectroscopic data

The reaction of alcohols ROH (R=Me, n-Bu, n-C7H15) with B(OBu)3 and As(OBu)3 in binary mixtures and in solutions in CCl4 was investigated by IR spectroscopy. B(OBu)3 forms equilibrium associates of two types with n-BuOH. Only one type of H bond is observed in a dilute solution of n-BuOH in As(OBu)3, but the donor sites in As(OBu)3 (As or O atoms) which participate in its formation were not established. The equilibrium constants of the reaction of exchange of butoxyl radicals in X(OBu)3 (X=B, As) with MeOH and n-C7H15OH were measured and at ∼20°C were, respectively, equal to 0.11 and 0.06 for BOBu3 and 0.67 and 0.44 for AsOBu3.

Complex formation by phenols with tertiary amines in aprotic media

Conclusions1.The equilibrium constants (Kg) and the enthalpies of formation of H-bonds in complex-formating reactions of phenols with tertiary amines in aprotic solvents fall with a rise in the polarity of the medium and in its capacity for specific solvation with the phenols.2.The introduction of the electron-accepting substituent chlorine into the para position of phenol leads to a considerable rise in Ke, but in the case of o-chlorophenol, because of the strong intramolecular H-bond the value of Ke is somewhat lower than for unsubstituted phenol.3.With an increase in the steric accessibility of the N-atom of a tertiary amine and a rise in its basicity, Ke increases. The tertiary amines studied form the following sequence of decreasing Ke values: (C2H5)3N > (C4H9)3N > (CH2=CHCH2)3N.

Cl35 nuclear quadrupole resonance spectra of some carboxylic acid chlorides

1. The Cl35NQR spectra of a number of carboxylic acid chlorides were investigated. 2. The change in the Cl35NQR frequencies in the series of acid chlorides of meta- and para-derivatives of benzoic acid is due to the inductive effect of the substituent.

Properties of solutions of some polyacrylates obtained by low-temperature polyesterification

1. A study was made of the properties of solutions of the polyacrylates of dimethyldian and terephthalic acid, obtained by low-temperature polyesterification. 2. The constants K anda of the Mark-Houwink equation and the value of the statistical segment are quite dependent on the conditions of running the polycondensation, in particular, on the reaction temperature.

Effect of reactivity of bisphenols on basic rules of low-temperature polyesterification

1. A study was made of the basic rules for the low-temperature polycondensation of the acid chloride of terephthalic acid with dichlorodian and dimethyldian, i.e., with bisphenols that differ in their acidity constants. 2. Polyacrylates of higher molecular weight are obtained with increase in the acidity of the bisphenol, i.e., with increase in its reactivity. 3. When the polycondensation is run in a medium which dissolves the polymer, the dependence of the molecular weight values of the polyacrylates on the reaction temperature has the shape of a curve with two maxima. 4. When the polycondensation is run in a medium which does not dissolve the polymer in a wide temperature range, the value of the reduced viscosity of the polyacrylate remains constant.

Acylation of phenol with the hydrochlorides of carboxylic acid amides

1. A study was made of the acylation of phenol with the hydrochlorides of carboxylic acid amides in nitrobenzene solution. 2. The hydrochlorides of the N,N-dialkyl-substituted amides of carboxylic acids possess the highest acylating capacity. 3. The formation of the N-protonated form of the amide is apparently one of the possible paths for progress of the acylation reaction.