No abstract

T h e heats of combustion, melting points, heats of fusion, boiling points, refractive indices and in four cases the densities have been determined on selected samples of the cyclanes with 4 to 9 C-atoms; some hitherto unknown transition points were discovered and the heats of transition measured. T h e heats of vaporisation a t 25" are estimated. Results of the measurements are discussed.a. Calibrafion of fhe fhermocouple. T h e measuring thermocouple of the micro-calorimeter 1 ) was calibrated in order to determine the absolute values of melting and transition points. This was done with the aid of some substances, the melting and transition points of which were accurately known from the literature:Melting and transition phenomena 2). Na,SO, . 10 H,O, transition point + 32.38 t-0.01' C 3 ) 4 ) Cyclohexane, 1.-87.08 k 0.05 5 ) ' 3)Toluene melting., -94.99 i-0.02 )Cyclopentane, lower trans.,, -150.77 i-0.05Na,SO, . 10 H,O Schuchardt "pro Analyse mit Garantieschein" was crystallised four times from water: cyclohexane and cyclopentane were selected samples of this investigation. The toluene sample was purified by Mulder l o ) , its AT amounting to 0.02" c.

The following substances were prepared with a view to the accurate determination of their heats of combustion: cyclobutane (from cyclobutanone, originating from the reaction between ketene and diazomethane) , cycloheptane, cyclooctane and cyclononane (from the cyclanones, which were made by ringenlargement from cyclohexanone) .The aim of this part of the research was the synthesis of samples of the cyclanes with 4 to 9 C-atoms, intended for the determination of the heat of combustion of these substances. With (he combustion calorimeter at the Vrije Universiteit values may be obtained which are in error by probably not more than 0.02 %. #The purity of the ultimate samples should be such, that the error in the measured heat of combustion, caused by impurity in the sample, is certainly less than the accuracy of the measurements.In order to obtain the quantity of material needed in the experiments, about 20 g of a highly purified product, at least 100 g should be prepared, the synthesis at each step allowing a separation of the desired substance from by-products.Purification of intermediates is essential to prevent related substances from taking part in subsequent reactions and so resulting in a large number of impurities in the final product. The degree of this purification depends on the nature of the by-products: experience shows that in many cases purification to the same extent as that of the final product is not needed.In our case the criterion set was, that the boiling range in fractional distillation had to be less than 1" and (or) the melting point had to be within 1" of the most probable literature value, as most substances concerned have a high depression of the melting point.

Purification of the cyclanes with 4 to 9 C-atoms was effected by fractional distillation. Progress of the purification was checked with the aid of melting curves of the fractions {heat content vs. temperature curves of the melting process). The impurity content of the final samples is estimated at less than 0.2 yo. A fractionating column with a rotating cylinder and a small calorimeter for measurements on melting and transition processes a t temperatures from -180" to +70" are described. 1 . Methods of purification.Whenever possible, the samples obtained in the preparations 1) were first treated with conc. sulphuric acid to remove all impurities except saturated hydrocarbons. Separation from the remaining impurities was performed by fractional distillation. Purification by Mulder's 2 ) method, consisting of successive partial meltings of the frozen sample, each time removing the liquid fraction, was also investtgated for the substances involved here. These experiments in a test model of a self-charging centrifuge, on cyclohexane and cyclooctane to which impurities were added, indicated that only a small purifying effect could be expected. Evidence was obtained that the cyclanes described here, form mixed crystals with small amounts of many substances, cf ").W i t h a view to purifying the cyclanes, with boiling points varying between 12 and 180° C, a fractionating column with a rotating cylinder 4 ) 5 ) having approximately 50 theoretical plates was constructed. Cyclononane, cyclooctane, cycloheptane and cyclohexane, becoming available before the new column, were purified by fractional distillation in column 1 1 ) . In order to obtain the highest possible yield of purest 1) This research was supported by grants from the "Nederlandsche Organisatie voor Zuiver Wetenschappelijk Onderzoek". Part I: Rec. trav. chim. 70, 1033Rec. trav. chim. 70, (1951.

In 1946 an investigation was started in this laboratory into the preparation, purification and properties of cycloparaffins. The heat of combustion of cyclobutane was recently determined. As the results of this determination might be of special interest in relation to strain in this simple molecule, publication prior to a comprehensive account of the work seems justified.,The impurity content of the selected sample was estimated from melting-curves at less than 0.2 %. The most probable impurity is