V. I. KOMAREWSKY cally gave 2.1'/0.'' The formula indicated requires 4.BYc/b benzene. Cryoscopic Data.--The additional molecular weight data presented i n this paper were obtained by the standard technique^.^ The large tube procedure with camphor seemed to be more satisfactory for this work although both the large and small tube procedures gave satisfactory results using naphthalene as a standard. Preparation of Samples for X-Ray Examination.----Thetrimer and the tetramer readily forin supersaturated solutinns in benzene and ill benzene-alcohol. This makes i t possible to grow crystals of the various forms, particularly by seeding, which are suitable for single crystal Xray examination. The conditions leading to the formation of any particular form from solutions other rhan tly seeding have not been investigated. The fine grinding necessary to prepare the powder samples had no effect on the crystal structure of the polymorphs 1 4 and 1 1 4 . However, after short grinding in an agate mortar, A4 immediately gave a melting point of 200-201° instead of 18S-190°, which is that observed for the unpowdered material. Since t i 4 is stable indefinitely in contact with Aui.euu of JfiifeT Reports I w o e s f i g a f i o ? ~No. , 3287 (1935). (7) Reilly and R ae . "Physico Chemical Methods," D. Van Nost r a n d C o S e w T:ork. N . Y. (ii) 1 ' . .Y.
ii:O\
I RIBUTION FROM T H E DEPARTMEST O F CHEMICAL
its mother-liquor, it was possible to prepare powders suitable for X-ray examination by grinding in contact with the mother liquor. Surnrnarv 1. Two polymorphs of hexaphenylcyclotrisiloxane have been characterized by X-ray diffraction methods : an orthorhombic form identical with that described by Kipping and Robison, and a triclinic form, each of which, as well as their mixture, melts a t 18s-189'. 2 . Two stable polymorphs of octaphenylcyclotetrasiloxane have been characterized in like manner. One is triclinic and is identical with that described by Kipping and Kobison. The other is monoclinic and is identical with the form described by Burkhard, .Decker and Harker. Both of these forms as well as their mixture melt a t 200-201 O . 3 . A metastable polymorph of octaphenylcyclotetrasiloxane melting at 187-189' and a crystalline substance with the formula 2 [ (CsH5)2SiO]hC6H6 have also been isolated and their relationship to the two stable polymorphs have been described. 4. Hexaphenylcyclotrisiloxane and octaphenylcyclotetrasiloxane in equimolar proportions form a eutectic melting at 1G4-I 6.5'. CORSISG,l
RECEIVED JCSE 27, 1946
i YORK ~ ~
ENGINEERISG, ILLINOIS
INSTITUrE O F TECI-IVOLO(;S]
Cracking of ParafIin Hydrocarbons in the Presence of Aluminum Chloride BY V. I. KOMAREWSKY AND
S.C. ULICK
The reactions o i pure paraffin hydrocarbons in as aluminum metal it was possible to influence the the presence of aluminum chloride have been reaction by increasing isomerization while destudied exterBively. Of particular importance creasing cracking. In a previous study of the acare more recent works in which modern distilla- tion of aluminum chloride on natural hydrocarbon tion techniques have been used in identification mixtures from this Laboratory,3it was found that of the reaction products, as well as careful ex- by increasing the reaction time higher yields of perimentation to avoid any undesirable influence lower boiling isoparaffins were obtained in the of impurities.' As a result of these studies, the reaction product. I t was of interest to follow this products were demonstrated to be composed of observation with pure hydrocarbons, to study the isomers of t'iie charged hydrocarbon, higher and effect of time upon the nature and distribution o f lower boiling paraffins and highly unsaturated the reaction products and, if possible, t o determine hydrocarbons combined with aluminum chloride the kinetics for these reactions with pure hydroi n the so called lower layer. The formation of carbons. I n . the following work the action of these products clearly indicates that the follow- aluminum chloride-hydrogen chloride on n-hexane, ing reactions take place : isomerization, cracking heptane and octane was studied a t the boiling to lower boif:ing hydrocarbons and alkylation (de- point of each hydrocarbon under carefully constructive alkylation) with the production of hy- trolled conditions. In addition the reactions with drocarbons boiling higher than the original mate- octene-1 and neohexane were carried out. These rial charged. Part of the unsaturated fragments last hydrocarbons were studied for elucidation of formed by cracking combines with aluminum some questions of reaction mechanism. chloride into a lower layer. It was recently Experimental shown2 that by suitable use of promoters as well Material Used.-%-Hexane
(1) G r i m m i t t , Sensei, S m i t h , Burk and Lankelma, Tms J O U R N A L , 67, 910 ( 1 9 4 2 ) . ( 2 ) Griimrnitt, C';i
