Abstract: A method of producing aromatic polyesters by polycondensation of diols and carboxylic acids, comprising polycondensating said diols and said dicarboxylic acids in the presence of a sulfur compound of a general formula: ##STR1## wherein R.sub.1 represents a substituted or unsubstituted aryl, alkyl or aralkyl group, X represents a halogen atom.

Abstract: The amidation and esterification of carboxylic acids with amines and hydroxyl group-containing compounds, respectively, are effected without incurring the drawbacks of reaction equilibrium by the reaction of the reactants, one of which has been activated in the reactive group by contact with a phosphonium salt obtained by reacting a phosphorous ester or phosphorous monoester salt with an organic base such as pyridine and an oxidizing agent such as halogens and mono or divalent mercury halide or acetate. The amidation can be applied to the preparation of peptides by the reaction of amino acids and/or peptides in which one of the reactive groups have been protected.

Abstract: The amidation and esterification of carboxylic acids with amines and hydroxyl group-containing compounds, respectively, are effected without incurring the drawbacks of reaction equilibrium by the reaction of the reactants, one of which has been activated in the reactive group by contact with a phosphonium salt obtained by reacting a phosphorous ester or phosphorous monoester salt with an organic base such as pyridine and an oxidizing agent such as halogens and mono or divalent mercury halide or acetate. The amidation can be applied to the preparation of peptides by the reaction of amino acids and/or peptides in which one of the reactive groups have been protected.

Abstract: Aromatic polyamides having high polymerization degree are produced by polycondensing an arylene containing aminocarboxylic acid, or a dicarboxylic acid with an aromatic diamine in the presence of a phosphorus compound, a tertiary amine and a metal halide using N-methylpyrrolidone and/or dimethylacetamide as a solvent.

Abstract: The amidation and esterification of carboxylic acids with amines and hydroxyl group-containing compounds, respectively, are effected without incurring the drawbacks of reaction equilibrium by the reaction of the reactants, one of which has been activated in the reactive group by contact with a phosphonium salt obtained by reacting a phosphorous ester or phosphorous monoester salt with an organic base such as pyridine and an oxidizing agent such as halogens and mono or divalent mercury halide or acetate. The amidation can be applied to the preparation of peptides by the reaction of amino acids and/or peptides in which one of the reactive groups have been protected.

Abstract: Aromatic polyamides having high polymerization degree are produced by polycondensing an arylene-containing aminocarboxylic acid, or a dicarboxylic acid with an aromatic diamine in the presence of a phosphorus compound, a tertiary amine and a metal halide using N-methylpyrrolidone and/or dimethylacetamide as a solvent.

Abstract: The amidation and esterification of carboxylic acids with amines and hydroxyl group-containing compounds, respectively, are effected without incurring the drawbacks of reaction equilibrium by the reaction of the reactants, one of which has been activated in the reactive group by contact with a phosphonium salt obtained by reacting a phosphorous ester or phosphorous monoester salt with an organic base such as pyridine and an oxidizing agent such as halogens and mono or divalent meercury halide or acetate. The amidation can be applied to the preparation of peptides by the reaction of amino acids and/or peptides in which one of the reactive groups have been protected.

Abstract: Polyamides are produced by reacting a dicarboxylic acid with a diamine or polycondensing an amino acid in the presence of a phosphorous acid ester of the formula, R.sup.3.R.sup.4.HPO.sub.3, wherein R.sup.3 and R.sup.4 may be the same or different and are individually an alkyl, aralkyl or aromatic group which may have at least one substituent, such as diphenyl phosphite, and an organic base such as pyridine.