The properties of hydrocarbons containing a long aliphatic chain in which aromatic or alicyclic rings occur as, substituents. are of importance for the examination of high-boiling petroleum fractions and products obtained from them, such as lubricating oils. Of the hydrocarbons described in this paper dicetylbenzene has not been described in the literature: the remaining products have already been prepared by other investigators: except for octadecylbenzene and for cetylbenzene, the statements of the earlier authors do not guarantee that the desired hydrocarbon was obtained in the pure state.The degree of purity of the preparations obtained by us is not easy to Idetermine. As these hydrocarbons can only be distilled at a low pressure, a purification of the final product by ver)r sharp fractional distillation is not possible. In some cases the purity could not be checked by determination of a cooling curve, owing to the. very low rate of crystallization. A reasonable degree of purity of the final products could only be guaranteed, therefore, by using pure starting materials and by purifying the synthesized intermediate products as thoroughly as possible.The properties of the cetylbenzene and octadecylbenzene prepared by us are in good agreement with the statements of some earlier authors. Our preparations of the hydrocarbons IV, V I and VII no doubt have a much higher degree of purity than the preparations obtained by earlier authors. In this paper we give the refractive indices for 1 = 5876 and the specifics gravities. In a subsequent paper we intend to publish the refractive indices at other wave lengths and to. discuss the refractometric constants. An attempt to prepare dicetylbenzene by applying the W ii r t z reaction to a mixture of p-dibromobenzene and cetyl iodide was not successful, as dicetyl (C,,H,,) was formed almost exclusively. W e therefore prepared l-cetyl-
Mellitic acid may be prepared by oxidation of hexamethylbenzene by means of concentrated nitric add at 120-160"; this method has the advantage that the crude reaction product already consists of rather pure mellitic acid; the yield of the pure product is about 35 yo of the theoretical.The hexachloride of mellitic acid has been prepared in the pure state. W e investigated the directions .of M a u m e n 6-L e c u i r, for preparing the potassium salt of mellitic acid by thermal decomposition of the potassium salt of tartaric acid; we obtained only very low yields of mellitic a d d by this method.Mellitic acid is difficult to obtain, unless mellite is available: this There are various directions for the preparation of mellitic acid by oxidation of graphite, charcoal, anthracite, carbon black and similar materials with fuming nitric acid and/or with alkaline permanganate. The yield of mellitic acid is greatly dependent on the nature of the starting materials used l). Apart from mellitic acid, other polycarboxylic acids and oxalic acid are formed. J u e t t n e r separates the mellitic acid as ammonium salt, after a purification by electrodialysis. He obtains yields of 20 to 30 grams of mellitic add (determined as ammonium salt), calculated on 100 grams of carbon in the starting material.Although we have no doubt that, in the case of sufficient experience, the methods mentioned are suitable for obtaining mellitic acid, they are cumbrous and lengthy. and little attractive from the point of view of preparation. In our experience, purification by electrodialysis is time consuming and far from easy. mineral, however, is rare.J u e t t n e r .
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