103
PROPERTIES OF HOMOLOGOUS ~-AZIDOALKANES
Jan., 1957
THE PREPARATION, DENSITIES, REFRACTIVE INDICES AND VISCOSITIES OF 1-AZIDOOCTANE, 1-AZIDOHEPTANE, I -AZIDOHEXANE AND 1-AZIDOPENTANE BY OLIVERL. I. BROWN,^ HELENE. CARY,~ GLENNS. SKINNER^ AND EVERETT J. WRIGHT~ ~ o n h - ~ b u i from k n the Research and Development Department, U.8.Naval Powder Factory, Indian Head, Maryland and f r o m the Chemistry Department, University of Delaware, Newark, Delaware Received September 7, 1066
Four homologous 1-azidoalkanes have been prepared and characterized by analysis, boiling point and infrared absorption :spectra (by Skinner and Wright). The densities and viscosities have been measured over the range 15 to 50"; refractive tindices referred to the D-line of sodium have been measured from 15 to 35' (by Brown and Cary).
Henkel and Weygand's procedure3for the preparation of 1-azidohexane was modified in several particulars. A solution of 45 g. (0.273 mole) of pure n-hexyl bromide in 200 cc. of methanol was heated with 22.5 g. (0.346 mole) of sodium azide and 30 cc. of water in a water-bath so as to maintain gentle reflux (75-80'). The oil separating was heavier than the medium but in 3 hours floated on the surface. After 15 hours 70 cc. of water was added to the ice-cold mixture which was now extracted four times with 60-cc. portions of a 1:1 mixture of ether and petroleum ether and once with 30 cc. of petroleum ether. The combined extract was extracted with 50 cc. of a solution of calcium chloride prepared from 160 g. of calcium chloride and 200 cc. of water. The ethereal layer was dried over calcium chloride and distilled, first to remove the solvent: Fractions I , 3.5 g. (10.8%); b.p. 60-65' (25.5 mm.); 11, 29.7 g. (85.6%), b.p. 63-64 (25.5 mm.); residue, negligible. This procedure similarly gave a distillate free of bromide (alcoholic silver nitrate) in the case of I-azidopentane and I-azidoheptane. 1-Azidooctane contained a small amount of bromide. A mixture of this product (153 g.), 375 cc. of methanol, 22.5 g. of sodium azide and 30 cc. of water was then refluxed for 3 hours with mechanical stirring. The substance (147 g.), b.p. 99' (27 mm.), was now free from bromide. Combined preparations of corresponding azides were fractionally distilled until the refractive indices were constant. The yields were more than 90%. The purified products had the following boiling points: Cg, 52' (40 mm.); Cs, 57.5" (19 mm.); C,, 74' (18 mm.); Ca, 443 (0.70 mm.). The infrared absorption spectra were all similar, showing bands for the azide group as follows: 3.02 (w), 4.00 (w), 4.8 (9) and 7.9-8.0 (8).
No explosive reaction resulted when a drop was allowed to fall upon a red hot iron plate. A drop gave a vigorous evolution of gas by addition to concentrated sulfuric. acid. They did not decolorize bromine in carbon tetrachloride. Analyses by Mrs. P. P. Wheeler (microanalyst, USNPF) are summarized in Table I.
TABLE I CARBON, H Y D R O GAND ~ N NITROGEN ANALYSES OF ~-AZIDOALKANES
Alkane I-Azidopentane I-Azidohexane 1-Azidoheptane 1-Aeido6ctane
Carbon % H drogen, % Nitrogen. % Calcd. Fbund Carcd. Found Calcd. Found 36.0,36.4 9.6 37.1 9.8 53.1 53.2 32.5 9.6 33.0 56.7 57.1 10.3 29.8 59.5 60.2 10.7 10.7 29.8 27.1 28.0 61.9 62.8 11.0 11.1
Measurements were carried out in a water-bath controlled to 0.005" by a Sargent Thermonitor controller. The thermometers were calibrated with an NBS certified platinum resistance thermometer. Densities were measured with a 1-ml. pycnomet.er of the Lipkin type which was calibrated wit,h purified benzene and with water.4 Experimental values are recorded in Table IT, except that densities of 1azidoheptane determined a t uneven temperatures were calculated to rounded temperatures by means of the least squares equation
d = 0.88218 - 7.545 X 10-4t .- 1.8667 X 10-V2 which fitted the seven experimental points with an average deviation of 0.0002 unit. A modified Ostwald viscometer was used for determining viscosities.6 In measuring refractive indices water from the controlled bath was pumped
TABLE I1 DENSITIES,VISCOSITIES A N D REFRACTIVE INDICES OF AZIDOALKANES (Parenthetical values are those of Skinner and Wright) to
15 20 25 30 35 40 45 50
octane 0.8695 .8658
(.8651) .8614 .8571 ,8531 .ti488 .8446 .8405
Density, g./ml. 1-Azidoheptane hexane 0.8704 0,8735 ,8663 ,8688 ( . 8667) ( . 8693) .8622 ,8647 .8579 .E4600 .8535 .8551 .8490 ,8506 .8445 ,8464 ,8398 ,8416
pentane 0,8790 ,8740 (. 8730) ,8695 .Si342 ,8598 ,8549 ,8500 .8446
Viscosity, centipoises 1-Azidooctane heptane hexane pentane 1.2886 1.0240 0.8154 0,6509
1.1039
.8877
,7190
.5885
.9GI8
.7790
,6361
.5187
.8382
,6901
.5712
,4697
The azides also gave a negative test for alcohol with ceric nitrate reagent. There was no explosive reaction when a drop was brought into contact with a red hot copper wire. (1) Department of Chemistry, Connecticut College, New London, Conn. (2) Department of Chemistry, University of Delaware, Newark, Del. Work performed under Navy contract. (3) ( a ) K. Henkel and F. Weygand. Be?., 76B, 812 (1943); (b) P. A. Levene, A. Rothen and M. Kuna, J . B i d . Chenk., i20, 777 (1937).
octane 1.4413 1.4391 (1.4385) 1.4369 1.4349 1.4326
Refractive, index ?ID I-Azidoheptane hexane
....
.... .. . .
1.4357 (1.4351) (1.4312) 1.4337 1.4294 1.4273 . 1.4251
....
.. .
pentane 1.4292
....
(1.4266) 1.4248
.... 1.4202
through a refractometer, Valentine No. 1091 (Abbe type), which had been calibrated with purified benzene, water and a standard glass plate. Molar refractions were calculated and recorded in Tabla I11 with the contributions of the azide group to the molar refractivity a t ZOO, using as values for atomic refraction C = 2.418 and H = 1.100. In studying the contribution of the azide group to molar refractions of seven different com(4) M. R. Lipkin, J. A. Dsvison, W. T.Harvey and 8.8.Kurte, Jr., Ind. Eno. Cham., Anal. Ed.. 16,55 (1944). ( 5 ) M. R. Cannon and M. R. Fenske. ibid., 10, 297 (18381,
SIDNEY W. BENSON AND JERRYH. Buss
104
Vol. 61
pounds J. C. Philip has found comparable values of 9 .oo, 9.00,8.75,8.95, 8.93, 8.75 and 8.91.6
of these lines increasing slightly with increasing molecular weight. It was found that all four straight lines converged to a common point at 1/T equal to 0.0013241, and that the TABLE I11 slope of each line was a linear function of the number of carCONTRIBUTION OF THE AZIDE GROUP TO MOLAR REFRACTION bon atoms. Thus one equation could fit the data for all four compounds. This equation is AT 20” 45*867n 205*66 0.060727n 1.38663 MRD - NI value log10 r) = Brown Skinner Brown Skinner T
-
Azide
n-Octyl n-Heptyl n-Hexyl %Pentyl Extrapolated.
nnd Cary
and Wright
47.174 47.15 42.593 42.52 37.909” 37.89 33.234b 33.25 Interpolated.
and Cary
and Wright
9.130 9.167 9.101 9.044
9.08 9.09 9.06 9.07
where n is the number of carbon atoms and q the viscosity in centipoises. The deviations of the experimental points from the straight line are shown in Table IV.
TABLE IV OF OBSERVED AND CALCULATED VISCOSITIES COMPARISON
The values obtained for viscosities of the aeidoalkanes were checked by plotting the logarithm of the viscosity against the reciprocal of the absolute temperature. I n each case the four points plotted fell in a straight line, the slopes (6) J. C. Philip, J . Chem. Soc., 101, 1866 (1912).
,
-
to
octane
15 25 35 45
100.30 100.12 100.68 100.37
heptane
for 1-Azidohexane
pentane
99.92 99.76 99.89 99.85
99.81 100.12 99.91 100.45
99.95 101.54 99.80 100.09
100
(qoba/qo&lod.)
a
THE THERMODYNAMICS OF BROMINATION OF TOLUENE AND THE HEAT OF FORMATION OF THE BENZYL RADICALi-3 BY SIDNEY W. BENSON AND JERRYH. Buss Contribution from the Chemistry Department, University of Southern California, Los Angeles 7, California Received September 7, 1066
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+
The equilibrium constant for the reaction CdIsCHa(g) Br2(g) e CeH&HzBr(g) HBr(g) has been measured at 150’ and found to be 7.2 X lo4,equilibrium being approached from both sides. This gives AF (4280 IC.) = -9.4 kcal./mole. T h e entropy of C6H5CH2Br has been estimated from s ectroscopic and other data as Sozm = 90.8 i 1- 8’423 = 102.2 f 1 A S (4280 K.) is then 3.5 cal./mole-deg. Together wit[ other known thermal data, this leads to &Y0f(C$&H2Br) = 20.0 0.9 kcal./mole and AH(2saoK.) = -8.0 f 0.9 kcal./mole which compares well with another less recise measurement. This value is 6 kcal. greater than that derived from bond energies for D(CeH6CH2-H) and D(CJIsC€frBr) assigned from kinetic studies. A review of the various kinetic studies which yield values for the heat of formation of CeH&H2 radicals shows a range of values from about 34 to 50 kcal./mole. Most of the data lie in the range 38-44 kcal./mole and it is felt that this latter is robably closest to the true value. This leads to a bond dissociation energy for toluene, D(C6H5CH2-H) of aboyt 84 kcal.rmole. Specific considerations are given of the pyrolyses of bibenzyl and toluene and it is concluded that despite the small amounts of decomposition permitted in the flow systems, secondary processes are still important and the interpretations of the data have been oversimplified. I n the p olysis of C8H5CHa,i t is shown that entropy considerations favor the process CeH&Ha + C&I CH8 in relation to C6&&8 + C6H5CH1 H despite the larger activation energy of the former. Quantitative estimates of the relative rates of these two processes are in reasonable accord with the ratios of CH4/H2 experimentally observed.
*
+
Introduction The bond dissociation energy of toluene, D(CsH5CHrH), has in recent years become a topic of considerable dispute. SzwarcJ4from kinetic studies of the pyrolysis of toluene in a flow system, assigned it a maximum value of 77.5 kcal. Later Van Artsdalen and c o - w o r k e r ~ from , ~ ~ ~ studies of the thermal and photochemical bromination of toluene derived a value of 89.9 kcal. which, however, can a t (1) The authors wish to express their appreciation to the Office of Ordnance Research, United States Army, for their support of the present work under Contraot No. DA-045-496-Ord-346 with the University of Southern California. (2) Presented at the Fall Meeting of the American Chemical Society, Atlantic City, New Jersey (September, 1956). (3) Taken in part from the thesis of Jerry H. Buss, t o be submitted to the Graduate School of the University of Southern California for the Ph.D. degree. (4) M. Sewarc, J . Chem. Phvs., 16, 128 (1948). The uncertainty in the aativation energy is estimated by Szwarc somewhat conservatively as zk4 kcal. ( 6 ) E. W. Swegler, H. A. Scheraga and E. R. Van Artadalen, ibid., 19, 135 (1951). (6) H. R. Anderson, H. A. Scheraga and E. R. Van Artedalen, ibid., ai, 1258 p953).
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best be considered an upper limit. More recently Steacie, et aLJ7repeated the pyrolysis studies on toluene in a flow system over an extended range of pressures and temperatures and found, contrary to Szwarc, that the kinetics were not first order and that the rates were sensitive to surface conditions and contact times. Although they refrained from assigning a bond dissociation energy they did point out that an Arrhenius plot of an assumed first-order rate constant, measured on a “conditioned” surface a t constant contact times gave an activation energy of 90 kcal., which is to be contrasted to the value of 77.5 kcal. obtained by Szwarc using a similar kinetic calculation. Schissler and Stevenson,* using mass spectroscopic measurements of the appearance potentials from various toluene deof the benzyl ion (C1H7+) rivatives, together with other thermodynamic data and some assumed bond energies derived a value for (7) H. Blades, A. T. Bladea and E. W. R. Steacie, Con. J . Chem., 81, 298 (1964). (8) D. 0. Schissler and D. P. Stevenson. J . Chem. Phya., 22, 161 (1964).
4
c
