Abstract: The invention relates to a process for the preparation of a conjugated diene from the corresponding carbonyl compound having the same number of carbon atoms by dehydration at a temperature of 300.degree. to 450.degree. C. using a catalyst comprising aluminium phosphate having the cristobalite structure. This catalyst is superior to aluminium phosphate having the tridymite structure in the dehydration of carbonyl compounds and has advantages over boron phosphate catalysts. Using the process, isoprene may be prepared from 2-methyl butanal and/or methyl isopropyl ketone in high yields. Unexpectedly aluminium phosphate having the cristobalite structure is markedly superior to boron phosphate in converting methyl isopropyl ketone, which is an intermediate product formed in appreciable amounts in the dehydration of 2-methyl butanal to isoprene. This superiority significantly improves the process economics of the conversion reaction of 2-methyl butanal to isoprene.

Abstract: The process relates to a method of improving the color and/or reducing the oxidized acids content of the disproportionated product obtained by heating rosin acids in rosin and tall oil with a catalyst comprising iodine, an iron compound and ammonia, an ammonium salt or an amine. The improvement comprises a pretreatment step in which the starting material is heated with an effective amount not in excess of 0.5% by weight of elemental sulphur, based on the weight of starting material for a period, usually less than one hour. As little as 0.1% by weight of sulphur is sufficient in most cases.

Abstract: Unsaturated acids in rosin or tall oil are disproportionated by heating the rosin or tall oil with a catalyst comprising iodine and an iron compound using ammonia, an ammonium salt or an amine as an additional component of the catalyst. Use of this additional component gives a remarkable and unexpected increase in reaction rate and enables the preparation of a disproportionated rosin containing 0.5% or less residual abietic acid, as measured by ultraviolet spectroscopy.