Green and Hickinbottom : The Rearrangement of up-Unsaturated 638. The Rearrangement of up-Unsaturated Alcohols to Xaturated Aldehydes and Ketones. Part I. The Preparation of up-Unsaturated Alcohols and 1 : 2-Diok and their Prototropic Change.
The rates of change of a number of +unsaturated alcohols into carbonyl compounds are compared with those of the corresponding 1 : 2-glycols, and a hypothesis to account for the observed results is developed.IN order to follow the change of an unsaturated alcohol or a 1 : 2-diol into a carbonyl compound a rapid and reliable method of estimating aldehydes and ketones in dilute solution was necessary. Several methods were tested against isobutyraldehyde and methyl isopropyl ketone. 2 : 4-Dinitrophenylhydrazine or dimedone did not give reproducible results. Modifications of Ripper's bisulphite method and of Romijn's alkaline iodine method were also unsuitable. Accurate and reliable results were obtained with the silver oxide method6 but it was time-consuming. Eventually a colorimetric method based on the use of Schiff's reagent was adopted for the estimation of aldehydes. For ketones, Mitchell and Smith's hydroxylamine method proved satisfactory provided that comparison was made with reference samples.The rates of change of 2-methylprop-2-en-1-01 and of 2-methylpropane-1 : 2-diol into isobutyraldehyde in presence of sulphuric acid were determined in water-dioxan (3 : 1 v/v), at 90" 5 0.1". The observed values of k, the first-order rate constant, are shown in Table 1.The rearrangements of unsaturated alcohol and the glycol are obviousIy both first-order * Part I, preceding paper.
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