Abstract: A novel crystalline adduct of diphenyl oxalate and phenol in a molar ratio of 1:2 and having a high purity is produced by melting a mixture containing diphenyl oxalate and phenol at a temperature of 100.degree. C. or more; cooling the melt to a temperature of less than 100.degree. C. to allow a resultant adduct of diphenyl oxalate and phenol in a molar ratio of 1:2 to crystallize and deposit from the melt; and collecting the crystalline adduct. Diphenyl oxalate with a high purity is produced by melting the crystalline adduct to dissociate it into diphenyl oxalate and phenol, and evaporating away the dissociated phenol from the melt to collect the dissociated diphenyl oxalate.

Abstract: A diaryl carbonate is prepared at a high yield and a high selectivity by heating a diaryl oxalate in the presence of an organic phosphorous compound to release carbon monoxide therefrom. A halogen atom-containing compound can be employed in combination with the organic phosphorous compound.

Abstract: A carbonic acid diester is stably and safely produced at a high selectivity and at a high yield by catalytically reacting carbon monoxide with a nitrous acid ester in a gas phase in the presence of a solid catalyst comprising a catalytic solid material carried on a solid carrier and comprising:(a) a platinum group metal and/or a compound thereof,(b) a compound of Fe, Cu, Bi, Co, Ni and/or Sn, and(c) a vanadium compound, molybdenum compound, tungsten compound, sulfuric acid and/or phosphoric acid.

Abstract: A carbonic acid diester is produced at a high stability and selectivity by catalytically reacting carbon monoxide with a nitrous acid ester in gas phase in the presence of a solid catalyst comprising a catalytic solid material carried on a solid carrier and comprising:(1) a first component consisting of a platinum group metal or a compound thereof,(2) a second component consisting of a compound of Fe, Cu, Bi, Co, Ni or Sn,(3) a third component consisting of a compound of V, Mo or W, and(4) a fourth component consisting of a halides, for example, fluorides or chlorides, organic acid salts, for example, formates or acetates, or phosphates of an alkali or alkaline earth metal.

Abstract: Both cyclohexanone and alkyl-substituted or unsubstituted phenol are simultaneously produced, in a one step reaction, by oxidizing, in the liquid phase, an alkyl-substituted or unsubstituted phenylcyclohexane of the formula (I): ##STR1## wherein R represents either a hydrogen atom or a methyl radical with an oxidizing gas containing molecular oxygen therein in the presence of hydrogen bromide.