Abstract: The hue of a methylene-crosslinked polyphenylene polyisocyanate continuously produced by the reaction with phosgene in an inert solvent of a polyamine mixture obtained by condensation of aniline and formaldehyde in the presence of an acid catalyst is improved by first removing any residual phosgene followed by heat treatment in the presence of hydrogen chloride gas.

Abstract: A fractionation process of a methylene bridged polyphenylene polyisocyanate mixture obtained by phosgenating condensation product of aniline and formaldehyde is disclosed.In order to apply the above mixture to a variety of uses, the process separates the mixture into fractions by giving primary attention to the content of 4,4'-and 2,4'-isomer of diphenylmethane diisocyanate and at the same time reduces the content of impurities having acidity and hydrolyzable chlorine.

Abstract: Optically active serine can be racemized at a high reaction rate under the relatively mild conditions by treating the optically active serine in an alkaline solution in the presence of pyridoxal phosphate or salicylaldehyde and an alkaline compound.

Abstract: A process for purifying tryptophan so as to contain almost no unreacted indole and a process for recovering unreacted indole with a very high percentage are provided, the purification process comprising passing a reaction fluid of tryptophan prepared from indole as raw material by means of an enzyme function, through a porous type, cation exchange resin layer, to cause the ion exchange part of the resin to absorb tryptophan, while to cause the porous part of the resin to adsorb indole, followed by eluting only the tryptophan with an alkali or acid aqueous solution, and the recovery process comprising subjecting tryptophan to repeated treatments of adsorption onto and elution from the ion exchange part of the resin and regeneration followed by eluting indole adsorbed onto the porous part of the resin with a water-containing organic solvent miscible with water and isolating indole from the resulting elute.

Abstract: Hydrochloric acid is added to a solution containing L-cysteine, L-cystine, L-serine and an inorganic salt until it contains at least 15% by weight of hydrochloric acid. The solution is held at a temperature of at least 20.degree. C. so that the L-cystine and the inorganic salt may form a solid, and the solid is removed from the solution. The solution is cooled to a temperature not exceeding 10.degree. C., so that crystallization may take place to form the monohydrate of L-cysteine hydrochloride. The monohydrate is separated from the L-serine in the solution.

Abstract: Disclosed is a method for separating lycine and L-serine from a solution containing both of them in the dissolved state and, in particular, a reaction solution obtained from a fermentation or enzymic conversion process for the preparation of L-serine by using glycine as the raw material. This method is based on a chromatographic technique utilizing the differential affinity of L-serine and glycine for a strongly acidic ion exchange resin.

Abstract: In a process for the production of 2,3-dichloropropionitrile by the chlorination of acrylonitrile, the improvement which comprises chlorinating acrylonitrile in the presence of pyridine or an alkylpyridine in combination with an alkaline earth metal carbonate.