Acetic acid dimerization constant

Typically, in specific solvents, the process of monomer formation [9.57] is characterized by considerably lower dimerization constants, as compared with those in universal media. In fact, acetic acid dimerization constant in water-dioxane binary solvent, the components of which are solvation-active in respect to the acid, vary in the 0.05-1.2 range. Replacing the solvent is often the only method to vary the molecular association state of dissolved compound. To achieve dimer concentration in 0.1 M solution of phenol in n-hexane equal to dimer concentration in nitrobenzene solution (50% at 25 C), it would be necessary to heat the solution to 480 C, but it is impossible under ordinary experimental conditions. 9.4.3 MIXED SOLVENT INFLUENCE ON THE CONFORMER EQUILIBRIUM Equilibrium took place in solutions... 

Figures 3a and 3an show fs DFWM spectra of acetic acid (CH3COOH) and per-deuterated acetic acid (CD3COOD) vapor from a gas cell experiment (300K). In contrast to formic acid, acetic acid shows only J-type recurrences from dimeric species in the fs DFWM spectra at room temperature. The difference of 45 ps between the position in time of the recurrences from (CH-)C00H)2 and (CD3COOD)2 is determined by the smaller rotational constants B, C of (CD3COOD)2. From the non-linear fitting (Fig 3b, 3bo) the rotational constants A=5,7 0.3GHz B+C=1657.2 1.2MHz of the acetic acid dimer (CH3COOH)2 and...

A=5.4+0.4GHz B+C=1445.2 0.5MHz of the per-deuterated acetic acid dimer (CD3COOD)2 were extracted. It was not possible to determine the rotational constants B and C independently due to the symmetric prolate top nature of the dimeric structure (Ray s asymmetry parameter k=-0.965). More detailed consideration of the fs DFWM spectra taken in the gas cell and in a supersonic expansion for the acetic acid dimer are under way in our laboratory and will be presented in a forthcoming publication. 

In a similar fashion we can define an equilibrium constant, Kim, for the formation of a homologous double bond of the carboxyl carboxyl (or acetic acid dimer-) type, as shown in Fig. 16. 

Conventionally, oil-phase (j = o) concentration of acetic acid is not large due to a low value of Ki . To increase it, organic amines, for example, are added to the oil phase. The basic amine (i — 3) complexes with acetic acid to form a complex i = 4. In the oil phase, acetic acid is present in three forms, whose concentrations are free acetic acid Cio, acetic acid dimer and the complex C40, where r = 2 refers to the dimer. The equilibrium constants for the various reactions (shown in Figure 5.2.6) are as follows (j= w for the aqueous phase) ... 

When diazomethane is slowly added to excess lactam, the anions formed can interact with unreacted lactam by means of hydrogen bonds to form ion pairs similar to those formed by acetic acid-tri-ethylamine mixtures in nonpolar solvents. The methyldiazonium ion is then involved in an ion association wdth the mono-anion of a dimeric lactam which is naturally less reactive than a free lactam anion. The velocity of the Sn2 reaction, Eq. (7), is thus decreased. However, the decomposition velocity of the methyldiazonium ion, Eq. (6a), is constant and, hence, the S l character of the reaction is increased which favors 0-methylation. It is possible that this effect is also involved in kinetic dependence investigations have shown that with higher saccharin concentrations more 0-methylsaccharin is formed. 

A kinetic study has been carried out in order to elucidate the mechanism by which the cr-complex becomes dehydrogenated to the alkyl heteroaromatic derivative for the alkylation of quinoline by decanoyl peroxide in acetic acid. The decomposition rates in the presence of increasing amounts of quinoline were determined. At low quinoline concentrations the kinetic course is shown in Fig. 1. The first-order rate constants were calculated from the initial slopes of the graphs and refer to reaction with a quinoline molecule still possessing free 2- and 4-positions. At high quinoline concentration a great increase of reaction rate occurs and both the kinetic course and the composition of the products are simplified. The decomposition rate is first order in peroxide and the nonyl radicals are almost completely trapped by quinoline. The proportion of the nonyl radicals which dimerize to octadecane falls rapidly with increase in quinoline concentration. The decomposition rate in nonprotonated quinoline is much lower than that observed in quinoline in acetic acid. 

As mentioned in section B. 1., only one rotational constant, (B + C), per molecule is available from the observed a-type spectrum (AK = 0, AJ = 1), and the results are given in Table 1. (B + C)/2 is essentially an effective diatomic molecule rotational constant, and therefore depends most strongly on the distance between the monomers of the complex. The rotational constants in Table 1 were best fitted with a model in which O. .. H—O distances were 2.67 A and O. .. H—N distances were 2.71 A. These O. .. H—O distances are somewhat shorter than the 2.73 A distance in formic acid dimer and the 2.76A distances in acetic acid dimer68. However, they are... 

No dimerization of acetic anhydride has been observed in either die liquid or solid state. Decomposition, accelerated by heat and catalysts such as mineral acids, leads slowly to acetic acid (2). Acetic anhydride is soluble in many common solvents, including cold water. As much as 10.7 wt % of anhydride will dissolve in water. The unbuffered hydrolysis rate constant k at 20°C is 0.107 min 1 and at 40°C is 0.248 min-1. The corresponding activation energy is about 31.8 kj/inol (7.6 kcal/mol) (3). Aldiougli aqueous solutions are initially neutral to litmus, they show acid properties once hydrolysis appreciably progresses. Acetic anhydride ionizes to acetylium, CH CO+, and acetate, CH - CO, ions in the presence of salts or acids (4). Acetate ions promote anhydride hydrolysis. A summary of acetic anhydride s physical properties is given in Table 1. 

The first coefficient describes the most common case, namely how much entropy AS flows in if the temperature outside and (also inside as a result of entropy flowing in) is raised by AT and the pressure p and extent of the reaction are kept constant. In the case of the secmid coefficient, volume is maintained instead of pressure (this only works well if there is a gas in the system). In the case of J = 0, the third coefficient characterizes the increase of entropy during equilibrium, for example when heating nitrogen dioxide (NO2) (see also Experiment 9.3) or acetic acid vapor (CH3COOH) (both are gases where a portion of the molecules are dimers). Multiplied by T, the coefficients represent heat capacities (the isobaric Cp at constant pressure, the isochoric Cy at constant volume, etc.). It is customary to relate the coefficients to the size of the system, possibly the mass or the amount of substance. The corresponding values are then presented in tables. In the case above, they would be tabulated as specific (mass related) or molar (related to amount of substance) heat capacities. The qualifier isobaric and the index p will... 

Effects of dimerization on results at 358 K, 1.0133 bar. Water-acetic acid solutions in vapor-liquid equilibria have been studied by Sebastiani and Lacquaniti [32], who give the following for the equilibrium constant for low-pressure, vapor-phase dimerization of acetic acid ... 

Use the one-phase multireaction algorithm in Figure 11.6 to determine the extent to which formation of tetramers of acetic acid affect the fractional conversion during esterification of ethanol. That is, repeat the vapor-phase calculation at 358 K, 1.0133 bar illustrated in the last part of 11.3.3, but now include not only dimers but also tetramers. (Spectroscopic evidence suggests that formation of trimers is unfavored [32].) Sebastiani and Lacquaniti give the equilibrium constant for formation of tetramers as [32]... 

P7.7 The equilibrium we need to consider is AaCg) 2A(g). A = acetic acid. It is convenient to express the equilibrium constant in terms of a, the degree of dissociation of the dimer, which is the predominant species at low temperatures. 

In mixed solvent, CCI4-C6H5CI, universal relation to acetic acid (because the mixed solvent components do not enter into specific solvation with the acid), the dimerization constant dependence on the temperature and permittivity in accordance with [9.52.a] and [9.56] is described by equation ... 

PI 3.2 Estimate the heat capacity of acetic acid along the vapor-liquid coexistence curve for both phases using the vapor pressure and ideal gas heat capacity correlations given in Appendix A and the dimerization and tetramerization constants from Table 13.6. 

Vapor pressure equation constants can be found in Appendix A. Calculate the dimerization and tetramerization constant of acetic acid using the parameters given in Table 13.6. 

The experimental findings are that the dimerization constants for a homologous series of carboxylic acids in water are much larger than the corresponding values in nonpolar solvents. For example, Kd for acetic acid in water is about 0.16 liter/mole, whereas in CCL4 the value is... 

Gaseous acetic acid molecules have a certain tendency to form dimers. (A dimer is a molecule formed by the association of two identical, simpler molecules.) The equilibrium constant Kc at 25°C for this reaction is 3.2 X 10. ... 

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