Abstract: A refined dihydroxyaryl compound, for example, catechol, having a high degree of purity and a very low metal content is produced by evaporating a starting dihydroxyaryl compound in a distillation column, condensing the vapor fraction in a condenser connected to a top outlet of the distillation column, and collecting the condensed fraction from the condenser into a storage tank through a conduit, wherein the condenser and optionally the conduit and/or the storage tank have inside surfaces thereof formed from a metal material containing at least 25% by weight of nickel, and the condensed dihydroxyaryl compound fraction is brought into contact with the specific nickel (25% or more)-containing metal inside surface.

Abstract: Oxamide is produced in a high purity by a process comprising (A) melting a starting material comprising 70 to 100 wt % of an oxalic acid diester of an aliphatic alcohol and 0 to 30 wt % of the same aliphatic alcohol as mentioned above, (B) feed-mixing an ammonia-containing gas to the starting material melt, while stirring, to produce oxamide and the aliphatic alcohol (by-product), (C) continuing the ammonia-feed-mixing procedure while controlling a feed rate of ammonia to an extent such that a content of the aliphatic alcohol in the reaction mixture is maintained at a level of 3 to 45% by weight, to produce a wetted solid reaction product comprising the resultant oxamide and the aliphatic alcohol, and then (D) collecting the oxamide from the reaction product by evaporating away the aliphatic alcohol.

Abstract: Oxamide granules are produced by (A) feed-mixing ammonia to a starting material comprising 60 to 100 weight % of a diester of oxalic acid with a C.sub.1-6 aliphatic alcohol, and 0 to 40 weight % of the same aliphatic alcohol as mentioned above, to produce oxamide and the aliphatic alcohol as by-product, while controlling the aliphatic alcohol content to 5 to 40% based on the weight of the reaction mixture to provide the resultant oxamide wetted by the aliphatic alcohol; (B) granulating the wetted product while maintaining the content of the aliphatic alcohol at a level of 5 to 40% based on the weight of the wetted reaction product; (C) heat-evaporating away the aliphatic alcohol from the wetted granules; and optionally (D) re-wetting the resultant dry oxamide granules with water in an amount of 5 to 20% based on the weight of the dry oxamide granules; and (E) re-drying the re-wetted oxamide granules, to provide oxamide granules having an enhanced mechanical strength and form-stability in water.

Abstract: High purity crystals of a biphenyltetracarboxylic dianhydride produced by dehydration of a biphenyltetracarboxylic acid, which contain almost no biphenyltricarboxylic acid or its anhydride, or a small amount such as an amount of not more than 0.2 wt. %, are of value to produce an aromatic polyamic acid or polyimide having an increased high molecular weight. The high purity crystals of a biphenyltetracarboxylic dianhydride can be prepared from a biphenyltetracarboxylic acid by a dehydration process wherein the biphenyltetracarboxylic acid is heated under carefully controlled conditions.