Acidity constant aldehydes

The gas phase photooxidation of crotonaldehyde has been studied by Blacet and Volman.21 The product is crotonic acid, which condenses out of the system as soon as it is formed. The quantum yield of oxidation was found to increase steadily over the 3660-2380 A. wavelength range. At constant aldehyde pressure, the quantum yield was independent of oxygen pressure at 3130 and 2804 A. At 2537 A., however, the quantum yield increased rapidly with the oxygen pressure and a chain mechanism is likely. Addition of nitrogen at 2537 A. caused a marked decrease in the quantum yield indicating that excited molecules are involved. 

Finally, several equilibrium and kinetic properties of aldehyde-bisulfite adducts were found to be linearly related Taft s a parameter (Betterton et al.t 1988). These compounds, which include a-hydroxymethane sulfonate and other a-hydroxyalkyl sulfonates, may be important reservoirs of S(IV) species inj clouds, fog, and rain. Fairly good relationships were found between equilibrium properties (e.g. acidity constants) and Sir values, but rates constants for) nucleophilic addition of S03 to the aldehydes showed only a crude fit, Similarly, poor results were found in applying a to hydrolysis reactions of] volatile alkyl chlorides (T. Vogel, University of Michigan, personal communh cation, 1989), and this has been shown to be a general characteristic of reactioni of alkyl halides with nucleophiles (Okamoto et al., 1967). 

At constant aldehyde concentration the rate is not quite linear in the hydroxide ion concentration but falls off more rapidly at low concentrations and becomes zero in slightly acid solution. 

The location of the hydroxyl and aldehyde groups ortho to one another in saUcylaldehyde permits intramolecular hydrogen bonding, and this results in the lower melting point and boiling point and the higher acid dissociation constant observed relative to -hydroxybenzaldehyde. 

Because of the unfavorable equilibrium constant in aqueous solution and the relatri e facility of the hydrolysis, acetals and ketals are rapidly converted back to aldehydes and ketones in acidic aqueous solution. 

Reaction is acid-catalyzed. Equilibrium constant normally favorable for aldehydes, unfavorable for ketones. Cyclic acetals from vicinal diols form readily. 

The concentrations of the different intermediates are determined by the equilibrium constants. The observation of immonium ions [Eq. (5)] in strongly acidic solutions by ultraviolet and NMR spectroscopy also Indicates that these equilibria really exist (23,26). The equilibria in aqueous solutions are of synthetic interest and explain the convenient method for the preparation of 2-deuterated ketones and aldehydes by hydrolysis of enamines in heavy water (27). 

On the basis of the dissociation constant values, it seems sensible to conclude that, in these moderately basic carbinolamines, the hydrogen atom of the hydroxyl group is suflQciently acid to be eliminated under the influence of an alkali and by its transfer to the nitrogen atom of the mesomeric anion, the formation of the amino-aldehyde form may result. Instead of the amino-aldehyde, however, the corresponding bimolecular ether (15a-c) can be obtained. " It can be concluded that the formation of the bimolecular ether (S l or 8 2 mechanism) and the formation of the amino-aldehyde (B-SeI or B-Se2 mechanism) are competitive reactions. It seems probable that where the first reaction can occur the latter one is pushed into the background. The triple tautomeric system postulated by Gadamer... 

In the flask is placed 64 g. of fuming nitric acid (sp. gr. 1.49) (Note 4), the stirrer is started and about one-sixth (Note 5) of the crude /J-chloropropionaldehyde is added (Note 6) very slowly through the separatory funnel. About 1 cc. of the aldehyde is added to the acid. The temperature remains constant for one or two minutes and then slowly rises. As the oxidation... 

Kinetic studies on reducing gas mixtures showed that the concentration of ammonia falls during the reaction, while that of HCN first rises and then stays almost constant. The amino acid concentration increases steadily as the reaction time increases, while the aldehyde concentration remains constant. 

Heptyl 3-Phenylpropyl Ether [Electrogenerated Acid-Promoted Reduction of an Aldehyde to an Unsymmetrical Ether].333 A mixture of 1-heptanal (1.0 mmol), 3-phenylpropoxytrimethylsilane (1.2 mmol), tetra-n-butylammonium perchlorate (0.1 mmol), and lithium perchlorate (0.1 mmol) was dissolved in CH2CI2 (3 mL) in an undivided cell. The mixture was electrolyzed under constant current (1.67 mA cm-2) with platinum electrodes at ambient temperature. After 5 minutes, dimethylphenylsilane (1.2 mmol) was added drop-wise and the electrolysis was continued (0.06 Faraday/mol). After completion of the reaction, one drop of Et3N was added and the solution was concentrated. The residue was chromatographed on Si02 to give 1-heptyl 3-phenylpropyl... 

In the multimedia models used in this series of volumes, an air-water partition coefficient KAW or Henry s law constant (H) is required and is calculated from the ratio of the pure substance vapor pressure and aqueous solubility. This method is widely used for hydrophobic chemicals but is inappropriate for water-miscible chemicals for which no solubility can be measured. Examples are the lower alcohols, acids, amines and ketones. There are reported calculated or pseudo-solubilities that have been derived from QSPR correlations with molecular descriptors for alcohols, aldehydes and amines (by Leahy 1986 Kamlet et al. 1987, 1988 and Nirmalakhandan and Speece 1988a,b). The obvious option is to input the H or KAW directly. If the chemical s activity coefficient y in water is known, then H can be estimated as vwyP[>where vw is the molar volume of water and Pf is the liquid vapor pressure. Since H can be regarded as P[IC[, where Cjs is the solubility, it is apparent that (l/vwy) is a pseudo-solubility. Correlations and measurements of y are available in the physical-chemical literature. For example, if y is 5.0, the pseudo-solubility is 11100 mol/m3 since the molar volume of water vw is 18 x 10-6 m3/mol or 18 cm3/mol. Chemicals with y less than about 20 are usually miscible in water. If the liquid vapor pressure in this case is 1000 Pa, H will be 1000/11100 or 0.090 Pa m3/mol and KAW will be H/RT or 3.6 x 10 5 at 25°C. Alternatively, if H or KAW is known, C[ can be calculated. It is possible to apply existing models to hydrophilic chemicals if this pseudo-solubility is calculated from the activity coefficient or from a known H (i.e., Cjs, P[/H or P[ or KAW RT). This approach is used here. In the fugacity model illustrations all pseudo-solubilities are so designated and should not be regarded as real, experimentally accessible quantities. 

In real systems (hydrocarbon-02-catalyst), various oxidation products, such as alcohols, aldehydes, ketones, bifunctional compounds, are formed in the course of oxidation. Many of them readily react with ion-oxidants in oxidative reactions. Therefore, radicals are generated via several routes in the developed oxidative process, and the ratio of rates of these processes changes with the development of the process [5], The products of hydrocarbon oxidation interact with the catalyst and change the ligand sphere around the transition metal ion. This phenomenon was studied for the decomposition of sec-decyl hydroperoxide to free radicals catalyzed by cupric stearate in the presence of alcohol, ketone, and carbon acid [70-74], The addition of all these compounds was found to lower the effective rate constant of catalytic hydroperoxide decomposition. The experimental data are in agreement with the following scheme of the parallel equilibrium reactions with the formation of Cu-hydroperoxide complexes with a lower activity. 

Bobrowski and Das33 studied the transient absorption phenomena observed in pulse radiolysis of several retinyl polyenes at submillimolar concentrations in acetone, n -hexane and 1,2-dichloroethane under conditions favourable for radical cation formation. The polyene radical cations are unreactive toward oxygen and are characterized by intense absorption with maxima at 575-635 nm. The peak of the absorption band was found to be almost independent of the functional group (aldehyde, alcohol, Schiff base ester, carboxylic acid). In acetone, the cations decay predominantly by first-order kinetics with half life times of 4-11 ps. The bimolecular rate constant for quenching of the radical cations by water, triethylamine and bromide ion in acetone are in the ranges (0.8-2) x 105, (0.3-2) x 108 and (3 — 5) x 1010 M 1 s 1, respectively. 

The kinetics of the ionic hydrogenation of isobutyraldehyde were studied using [CpMo(CO)3H] as the hydride and CF3C02H as the acid [41]. The apparent rate decreases as the reaction proceeds, since the acid is consumed. However, when the acidity is held constant by a buffered solution in the presence of excess metal hydride, the reaction is first-order in acid. The reaction is also first-order in metal hydride concentration. A mechanism consistent with these kinetics results is shown in Scheme 7.8. Pre-equilibrium protonation of the aldehyde is followed by rate-determining hydride transfer. 

Prins reaction, heteropolyacid catalysis, 41 156 Probe molecules, 42 119 acidic dissociation constant, 38 210 NMR solid acidity studies, 42 139-140 acylium ions, 42 139, 160 aldehydes, 42 162-163 alkyl carbenium ions, 42 154-157 allyl cation, 42 143-144 ammonia, 42 172-174 arenium ions, 42 150-154 carbonium ions, 42 157-160 chalcogenenonium ions, 42 161-162 cyclopentenyl cations, 42 140-143 indanyl cations, 42 144-147 ketones, 42 162,163-165 nitrogen-containing compounds, 42 165-170... 

Concerted acid-base catalysed enolizations of a range of simple aldehydes and ketones have been measured in water at 25 °C, using a range of substituted acetic acid-acetate buffers.The buffer plots yield rate constants for acid (A a) and base ( b) catalytic terms in the normal way at low buffer concentrations. Extension up to higher concentrations (as far as [total buffer] = 2 m, typically) yields the third-order term ( ab) via upward curvature of the plots. While ab does not have a simple correlation with either k or b, it does correlate with their product, i.e. 

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