EXTRACTION OF METAL IONS BY 4-BENZOYL- OR 4-(3-NYTROBENZOYL-1-HEXYL- 3-METHYL-2-PYRAZOLINE-5-ONES

The extraction properties of solutions of 4-benzoyl- and 4- (3-nitrobenzoyl) -1-hexyl-3-methyl-2-pyrazolin-5-ones in chloroform were studied. The pH dependence of the degree of extraction is S-shaped. Ions Cu2+, Pb2+, Zn2+, Ni2+, Co2+, Mn2+, Cd2+, Ca2+, Mg2+ are extracted in the form of complexes with the ratio M (II): reagent determined by the equilibrium shift method equals to 1: 2. A lower equilibrium pH than the initial value indicates a cation-exchange extraction mechanism. The introduction of an electronegative nitro group into the benzoyl fragment of the reagent led to a shift in the pH50 values of the extraction of metal ions in a more acidic region. The presence of a correlation between the values of the Klopman hardness parameters of the above metal cations and extraction pH50 values was shown. The influence of the nature of the solvent on the extraction of zinc ions was studied. The addition of polar isopentanol to the extractant shifts the pH of the metal extraction to a more acidic region. In order to increase the pH50 value of zinc extraction, the solvents are arranged in a row: 30% isopentanol in CHCl3 < benzene < xylene < toluene < chloroform < dichloroethane. The introduction of additional neutral electron-donating hydrophobic organic compounds into the extract: 1-hexyl-3-methyl-2-pyrazolin-5-one, triisobutyl phosphate, trioctylphosphine oxide significantly increases the values of the partition coefficients of zinc. The observed synergistic effect is explained by the formation of a coordinatively unsaturated intracomplex compound of zinc with aroylpyrazolone, in which the free coordination sites are filled with neutral reagent molecules. In this case, water is replaced and due to the increased hydrophobicity of the complex, an increase in extraction occurs. Confirmation of the formation of a coordination-unsaturated zinc complex is a close to unity value of the slope of the decimal logarithm of the metal distribution constant for pH.

Applications of Propargyl Esters of Amino Acids in Solution-Phase Peptide Synthesis

Propargyl esters are employed as effective protecting groups for the carboxyl group during solution-phase peptide synthesis. The propargyl ester groups can be introduced onto free amino acids by treating them with propargyl alcohol saturated with HCl. The reaction between propargyl groups and tetrathiomolybdate is exploited to deblock the propargyl esters. The removal of the propargyl group with the neutral reagent tetrathiomolybdate ensures that most of the other protecting groups used in peptide synthesis are untouched. Both acid labile and base labile protecting groups can be removed in the presence of a propargyl ester. Amino acids protected as propargyl esters are employed to synthesize di- to tetrapeptides in solution-phase demonstrating the possible synthetic utilities of the methodology. The methodology described here could be a valuable addition to currently available strategies for peptide synthesis.