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COMMUNICATIONS TO THE EDITOR
noted chain transfer agents and even the relatively strong H-C1 bond in hydrogen chloride is susceptible to free radical attack.20 (6) The isomerization of p-cymene (l-methyl-4isopropylbenzene) exclusively to l-methyl-d-n-propylbenzene is consistent with known free radical rearrangements*' in that the relative positions of the two ring substituents are unchanged during the isomerization. Experimental Autoclave Experiments.-One to 10 mole C of an isonierization promoter (organic halides, mercaptans, etc.) m d 0.1-0.5 mole of a n alkylbenzene were placed in i~ %(!c c . autoclave.*2 Xfter being sealed arid flushed with nitrogen, the autoclave was rocked and heated a t the desired temperature (300-525') for 1 to 3 hours. The gaseous product was vented from the cooled vessel into a brine-displaceinent gas holder. The liquid product was washed with 20'; sodium hydroxide solution, followed by water and dried over calcium chloride. \Vhen reactions were carried out in sealed glass tubes, a calculated amount of the alkylbenzene was placed in the autoclave with the sealed tube. This procedure equalized the pressures inside and outside of the sealed tube, thereby preventing bursting of the latter a t the elevated temperatures. Flow Experiments.--The alkylbenzene and promoter \yere placed in a pressure-tight, stainless steel reservoir vessel mounted on a Metrogram balance. The reactants were forced, at a desired rate crmtrolled by a needle valve, through a nitrogen-flushed line into a \-ertical reaction tube22 (approsimately 0.75 X 36 inches) held in an electrically heated furnace. This was accomplished b y maintaining a nitrogen pressure inside the stainless steel reservoir vessel l(JO-23! p.s.i. greater than t h a t in the reaction tube. The desired pressure in the reaction vessel (500-150(! p
11.
(10) C . LValling. J . A m Chriii. .So., 70, 1361 (1948). K . A . Greys, 11. Alderman a n d I;. R . I I a y u , i b d , 70, 8740 (1948). (20) J. H. Raley, 1; F. R u s t and \V. E. Vaughan, i b i k . 70, 2767
,1948). 1 2 1I 1%'. H . U r r y and S Sicc.iaides, i b t i f . , 74, jlCi8 ( l $ l 5 2 ) , '211 Ftainless steel a n d Hastelloy C reaction vessels were used with sulfur- and halogeii-containing promoters. respectively.
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maintained b y a Grove regulator below the furnace. The residence times for the reactants in the vertical reactor were calculated without correction for non-ideality from the rates of decrease in weight of the reservoir vessel as measured by the Metrogram balance. hen desired, oxygen or inert gases were metered into the vertical reactor through a second line. The liquid product was collected in an ice trap a t the bottom of the vertical reactor and the gaseous product in a brine-displacement gas holder. T h e liquid product was washed and dried as above. Product Analyses.-The gaseous and liquid products were analyzed both mass spectrometrically and by gas-liquid chromatographic techniques (g.1.c.) using a column packed with 30-40 mesh, silicone (DC-TlO)-impregnated firebrick. Compounds corresponding to the g.1.c. peaks were trapped and identified mass spectrometrically. lei?-Rutylbenzene and isobutylbenzene in the products were determined by infrared analyzes. For this purpose, peaks a t 13.10 and 1 3 . 5 5 ~respectively, , were used. Infrared analysis was also employed for the detection of o-cymene, wz-cymene and 1-methyl-3-n-prcipylbenzene resulting from the isomerization of p-cymene. These compounds apparently were not formed from p-cymene. The following autoclave esperiment is given as a typical esample for the isomerization of cumene. -\t 4%!" and 750 ., using one inole ( ~ iiodine promoter, 7'2(,)(of the cumene was converted in 60 minutes. From 1.0 inole o f curnene introduced, the following moles i d hydrocarbons were recovered: CHJ, 0.067; C!H6, [!.(!4:3; C:
