Measurements are reported on the initial reaction rates of the aldol condensation of acetaldehyde and of the reaction of acetaldehyde with formaldehyde, in sodium hydroxide solutions and in borate and carbonate buffers. The acidic properties of acetaldehyde and formaldehyde have been investigated, and the results are used to correct the hydroxide-ion concentrations in the kinetic experiments. The corrected results show that the aldol condensation is almost of the second order with respect to aldehyde, though the apparent order decreases slightly with increasing aldehyde concentration. The aldol condensation in buffer solutions exhibits general base catalysis, but does not obey the usual quantitative laws.The results are interpreted by assuming that the ionization and condensation steps of the aldol condensation have comparable rates, the former being the faster under most conditions. A similar interpretation applies to the previously unexplained kinetics of the acid-catalysed decomposition of the diazoacetate ion.19 The rate of reaction between acetaldehyde and formaldehyde is proportional to the first power of the acetaldehyde concentration, but independent of formaldehyde concentration, and is therefore governed by the rate of ionization of acetaldehyde. The value thus found for the rate of ionization is similar to that for acetone, and is consistent with the observed kinetics of the aldol condensation.

Hydration equilibrium constants for acetaldehyde, propionaldehyde, nand iso-butyraldehyde, and chloral in H 2 0 and D20 have been measured in the temperature range 25-90'.The equilibrium constant for formaldehyde has been determined in H,O over the same temperature range. The effects of added electrolytes on the activity coefficients of the hydrates and free aldehydes have also been investigated.

We report pK, values in aqueous solution at 298 K of the protonated forms of several aliphatic amides, viz., acetamide (pK, = -0.62 + 0.07), N-methylacetamide (-0.42 + 0.03), N,N-dimethylacetamide (-0.28 + 0.03), N,N-dimethylformamide (-1 . 2 + 0.5), urea (0.053 + 0.002) and thiourea (-0.9rf:O.l). pK, values are also reported for protonated acetamide and urea in aqueous solution in the temperature range 5-40°C and in D,O. A previously described conductimetric method was used for all measurements.

Previously unreported complications have been observed in the base-catalysed condensation of acetaldehyde in water. New experimental data are presented which firmly establish a reaction mechanism.

The rate of hydrolysis of trimethyl phosphate (tmp) has been measured at 90.5� as a function of solvent composition in water-dimethyl sulphoxide and water-ethylene glycol mixtures. The rate constant of the "spontaneous" hydrolysis decreases with decreasing water content; an acid-catalysed reaction, whose rate constant increases with decreasing water content, becomes dominant at low water concentrations. Solvent isotope effects in D2O have been measured for both the spontaneous and acid-catalysed reactions, and are close to unity in each case. Salt effects have also been studied In aqueous sodium nitrate and perchlorate solutions, and are found to be small. Reaction mechanisms are discussed in the light of the results obtained.

Catalytic constants for the hydrogen ion in the acid-catalysed hydration of aliphatic aldehydes have been found to be almost constant in a homologous series. Anomalies in the observed kinetics of the base-catalysed hydrations have been traced to the formation of appreciable quantities of addition compounds between the aldehydes and the catalysing bases. Evidence is presented for the existence of such compounds.

The activity coefficients of methyl acetate (MeOAc), ethyl acetate (EtOAc), n-propyl acetate (n-PrOAc), n-butyl acetate (n-BuOAc), and n-pentyl acetate (n-PeOAc) have been measured at 25 °C in concentrated aqueous solutions of electrolytes using the distribution technique. The salts used were LiCl, NaCl, KC1, CsCl, KF, KBr, NaNOg, and NaC104. In general, the results obtained are as might be expected. A mechanistic explanation is given of the trends observed and unexpected features in the data are explained with the aid of some assumptions regarding the nature of ionic hydration. The apparent molar volumes of MeOAc have also been determined over the full range of molalities for each of the salts used in the activity coefficient determinations. These measurements are then used in conjunction with thermodynamic data for the salt solutions (from the literature) to calculate the MeOAc activity coefficients according to the expanded McDevit and Long equations developed in an earlier publication. Similar, but less accurate calculations have also been done for the activity coefficients of the larger esters. In these cases, apparent molar volumes were determined only in water. The calculations are found to have mixed success.

The pKa of protonated formaldehyde has been estimated as -4.2, using spectroscopic and kinetic data obtained in concentrated acid solutions.