. Rate constants are reported for all of the major steps followed in the chlorination of acetone, including the chlorination of mono-and 1 , 1-dichloroacetone, the chlorination of hydroxyacetone, the chlorination and hydroxide-catalyzed rearrangement of 1,l-dihydroxyacetone, and the haloform cleavage of trichloroacetone. pK, values are reported for hydroxyacetone and monochloroacetone. Rate constants for the hydrolyses of chloroacetone and 1,l-dichloroacetone are reported; these reactions are probably not SN2 displacements but proceed by addition of hydroxide and intramolecular displacement.

Dimeric steroids can be formed by reductive amination of terephthalaldehyde with 3-amino steroids using cyanoborohydride. An amino group in the 11β-position can be blocked using a formyl group, and this can be removed by acid hydrolysis after dimerization. Trifluoroacetyl is not a suitable blocking group; although it can be removed by acid hydrolysis from monomeric steroids, it was only removed from the dimer under forcing conditions which caused degradation. The dimeric steroid is a catalyst for the hydrolysis of arylpropionate esters with good leaving groups. Acylation is markedly accelerated by hydrophobic binding of the aryl group of the substrate to the steroids. Rate enhancements, relative to imidazole, of up to 5.5 × 102 were obtained, and analysis of the data shows that the potential rate enhancement is 1.1 × 105. The magnitude of the hydrophobic binding is consistent with what was seen with earlier catalysts. Aggregation, even at very low concentrations, was a problem with anionic substrates.

No abstract

pKa values in aqueous solution have been determined for seven p-substituted acetophenones. The determinations are based on the diffusion-controlled reaction of an enolate with hypochlorous acid. The values determined for the acetophenones are as follows: substituent, value; H, 18.4; p-MeO, 19.0; p-F, 18.5; p-Cl, 18.1; p-Br, 18.0; p-NO2, 16.7; p-Me3N+, 17.1. ρ for these pKa values is −1.95. Using literature values for the enol content we show that most of this ρ value reflects substituent effects upon enolization. With relatively high hydroxide and low hypochlorite concentrations the major products from chlorination of acetophenones are the corresponding mandelic acids. Under similar conditions bromination of acetophenone gives benzoic acid.

Rate and equilibrium constants have been measured for the hydration and retroaldol reactions of cinnamaldehyde. The equilibrium constant for the 1,4-addition of water to cinnamaldehyde is 4.42 × 10−3. The rate constants for hydroxide catalyzed reaction, extrapolated to zero hydroxide concentration (to correct for the addition of hydroxide to the aldol carbonyl), are: [Formula: see text];[Formula: see text]; and [Formula: see text]. The rate of the formation reaction was measured by adding small amounts of acetaldehyde to alkaline solutions of benzaldehyde: [Formula: see text] and Koverall = 1480 M−1. The course of the synthetically useful reaction of acetaldehyde with benzaldehyde is discussed in the light of these results.