NOTES
1584 J r [3oron-i! spin-coupling w i t h J B E3oron-ii spin-coupling w i t h
6
Chemical s h i f t
(6) Chemical
shif! of onuloyues f r o n perdi:uterodiSorane
JB= 47.5 c/,
n JB=39.7
‘-24 8 ,(-23.5)
Ji = 125.5
4 1
J e = 49.7 BH2 -3 6 (-3.6)
Fig. l-BL1 nuclear magnetic resonance tlattt of methyldiborane.
wethyldiborane could only be obtained in the preseuce of a significant excess of trimet>hylboranc. The excess of hrimethylborane (X in Fig. 1) maintains the concentration of tetramethyldiborane. Without the influence of trimethylborane upon the various alkyldiborane equilibria the tetramethyldiborane rapidlj disproportionates to produce trimethylbcrarie and the lesser alkylated diboranes. The spectra of the methyldibornnes may best be interpreted by pointing out two effects that apparently determine the resulting B” chemical shifts. First, alkyl groups tend to shift the associated boron nuclei t 3 lower field. In the symmetrical series diboranca, 1,Zdimethyldiborane and tetra-
Vol. 64
methyldiborane, the trend is to lower field with alkylation; these molecules are made up of two identical “halves.” Second, unsymmctrical substitution promotes an even greater divergence of chemical shift values. When two “halves” of the molecule differ b y one alkyl group the shifts to lower aiid higher field are enhanced; when the “halves” differ by two alkyl groups, the divergent shifts are e ~ greater; ~ n ie., the chemical shifts of 1,l-dimethyldiborane, where the divergence of BH, and BRz groups is about doubled. Certain cyclic alkyldiboranes (1,2-tetramethylenediborane aiid 1C-methyltrimethyle1iediborane)~have chemical shift values similar to those of 1 J-dimethyldiborane. Similar chemical shift behavior upon alkylation mas also observed in 2,4-dimethylenetetrab0raiie.~~~ l\;o resolution of boron-boron coupling could be detected 111 the spectra of any of the diboranes and certainly cannot exceed a few cycles (Fig. 1). NaBHEt,-BEto Exchange.-Sodium hydride reacts lyith triethylborane and is known to form a liquid which is immiscible with additional triethylborane. This liquid, saturated with triethylborane, produced a broad peak in the B” spectrum; ac. the excess triethylborane was removed the peak shifted to higher field. Addition of diethyl ether reduced the viscosity and narrowed the peak. ?Then excess sodium hydride was introduced into the sample, the spectrum remained unchanged. However, upon re-examination, several months later, the singlet had changed iiito a doublet centered at the chemical shift position of the previous singlet. Apparently rapid intermolecular exchange of the protons takes place at room temperature in the presence of even a trace of BEt3; thus, the boron nuclei spend a portion of their time as BEtl arid a portion of the time as NaB€lEt3. Exchange evideiitly c a n i d take place in the absence of a trace of triethylborane as removed by several months’ contact n-ith NaI-I. (7) H. G. Weiss, W. .J. Lehiiiann and I. Shapiro, J An& Chem Sop. ( 8 ) R. C. Harrison I. J . Soloinon. R 1) Hites and hl. J Klein Abstracts of the 135th ACS illeettng, Boston, Maas. also (Inorgan2c and A - d e a r Chem , 1960). (9) S. G. Gibbins I. Sbapiro and R. E. JVilliams J P h w Chem
KINETICS OF THE KEACTIOS OF HYDROGEN IODIDE AND Di-1-BUTYL PEROXIDE 19 CAIRBONTETRA(’HI,ORIDE1 BY GEORGEA. Lo A N D WI:NDELI,11. GRAVEN Chemistry Department, L‘niueruity G’, Oregon, E u g e n e , Oregon I- chemical methods is difficult,? a,s a result o f their unreactive behavior toward the usual oxidat ion-reduction reagents. In contrast to the behavior of hydropcroxidcs, such as t-but,yl hydroperoxide, or diacyl peroxides, such as dibenzoyl peroxide, di-t-butyl peroxide is not reduced readily by alkali iodide in the preseiice (1) Taken from the hI.A. thesis of G. .%. 1.0, Uni\.rrsit) of Oregon.
19GO. (2)
G. J . Minkoff. Proe. R o y . Soc. ( L o n d o n ) , 8 2 2 4 , 17fj (1954).
Oct., 1960
NOTES
of acetic acid,3 nor by concentrated aqueous solutions of hydriodic acid.4 The relatively sluggish nature of the reaction between hydriodic acid and dialkyl peroxides permits investigation of the kinetics of one type of reduction reaction of organic peroxides. Experimental Materials.-Di-t-butyl peroxide, the minimum purity of which was stated by Wallace and Tiernan Co. to be 97%, was further purified by fractional distillation under reduced pressure in an all-glass system. The fraction boiling a t 52.5 f 0.5” under 98.5 mm.,5 and exhibit.ing a refractive index, ~ * O D , of 1.3878, was used in this investigat,ion. Production of hydrogen iodide usually was accomplished by dropping 50% hydriodic acid on phosphorus pentoxide. In several runs hydrogen iodide, produced by heating 80% phosphoric acid with sodium iodide, was substituted without any apparent effect on the results. Nitrogen was used to sweep the hydrogen iodide through a calcium chloride drying tube cooled with ice and a trap cooled with Dry Ice-acetone into the reaction vessel. A fresh preparation under an atmosphere of Xlatheson’s “prepurified” nitrogen, was made for each individual run. Reagent grade carbon tetrachloride was used directly or dried over magnesium perchlorate without observing any significant change in the results. Methods.-For quantitative analysis of the organic reaction product, as well as t,he unreacted peroxide, an Infracord Model 137 spectrophotometer was employed. Reference to calibration curves prepared from absorbancies of standard solutions a t wave lengths corresponding to characteristic absorption bands of peroxide, 11.4 p , and alkyl iodide, 8.8 p , made possible the quantitative analyses which were necessary for determining the stoichiometry of the reaction. A colorimetric method, which was used for determination of iodine and hydrogen iodide concentrations, involved the use of a Klett-Summerson photoelectric colorimeter. Concentrations of iodine solutions in carbon tetrachloride within the range of 10-6-10-3M were determined with a precision of i 2 ? 4 from an empirical equation obtained by a least squares fitting of the absorbancies of standard iodine solutions to a Beer’s law expression. Colorimetric determinations of hydrogen iodide concentrations were carried out in the same manner as the iodine analyses after oxidation with dibenzoyl peroxide. A volumetric precipitation method using standard silver nitxate with eosin as an adsorption indicator was used t o check the accuracy of the colorimetric method. Agreement between the two methods approximated the previously cited average deviation of the colorimetric determinations. Kinetic studies of the reaction were carried out in a threeneck flask which was equipped with an inlet tube for introduction of hydrogen iodide into the carhon tetrachloride solution, an opening for introduction of the peroxide solution, a gas-tight stirrer and a stopcock arrangement for withdrawing aliquots of the reaction mixture while maintaining a nitrogen atmosphere within the vessel. The exterior of the vessel was covered to shield the contents from light before it was immersed in a Lo-temp constant temperature bath. d mercurial thrrmoregulator farilitated maintenance of a bath temperature constant to within f0.02’ for indefinite periods. The temperature of the bath was me:isured with a thermometer which had been calibrated against a platinum resistance thermometer certified by the National Bureaii of St,andards. Prior to the production of hydrogen iodide the gas-generation vessel and the reaction vessel, together with the carbon tetrachloride which it cont,ained, were deaerated with a s w a m of nitrogcn. Thv duration of flow of hydrogen iodide to the reaction vessel determined the initial concent,ration of the hydrogen iodide solution which was determined by colorimetric analysis of an aliquot prior to the addition of peroxiclc. JThile the hydrogen iodide solution was being produced in the rchaction vessel a di-t-butyl peroxide solution (3) F. H. Dickey. .J. I I-DlII I?
111
..
2 .0
5.2
.. 3.; 1.5 1.1
..
4.3 4.1 2.4
..
3.4 2.4 7.1 2.3 ..
1.1
1 8 1.1
:XI) 1.1
1, o 0 5;
In more than half of the kinetic runs thri proxitic: concentrations were 10 to 100 times as large ;M 10-4-10-3M initial hydrogen iodide conceiii ratioiis. Under these conditions t,he reaction was suffiiciciitlg rapid so that the final iodine Concentrations corresponded to the complet’ionof the reaction. Without exception the final iodine concent>rntimswere equal to one-half the init>ialhydrogen iodide concentrations, thus eliminating t-butyl iodide as a
1386
NOTES
Vol. 64
It was demonstrated that within the higher concentration range t-butyl alcohol in carbon tetrachloride was converted rapidly to t-butyl iodide by hydrogen iodide at room temperature. Therefore, stoichiometric equation ( 2 ) is considered to represent the reaction under conditions of low hydrogen iodide concentration.
3
e. N
(CH3)8COOC(CH3)3
0 -
2
Nx
-
\
P
v
N \
-
-
h
I
-1
-.
I
25
75
50
100
t (mid, Fig. 1 -Dependence of reaction rate on reactant concen) X l o T 3M,(HI) = 1.0 x trations. A : ( t - B ~ i ~ 0=~ )1.06 10-2 JI, T = 24.80"; B: (t-BuzOz), = 5.26 X JI, (HI), = 8.53 K Jf, T = 24.80'; C: (t-BuzOz), = 2.17 x 10-2 31, (HI), = 7.82 x 10-4 M, (~-BuoH), = 2.94 x 1 0 - ~ J fT, = 24.80'; D: (t-BuzOa), = 2.21 x 10-2 Jf, (HI), = 3.60 x 10-4A1f,T = 24.80'.
+ 2HI = 2(CHn)3COH + I?
(2)
For determining the order of the reaction with respect to hydrogen iodide runs were made with a 10 to 100-fold excess of peroxide whose concentration could be treated as constant throughout the reaction. The initial concentration of hydrogen iodide was determined colorimetrically and its decreasing concentration was computed from the iodine concentrations measured at successive time intervals. Straight lines were obtained when the square root of the hydrogen iodide concentration was plotted against time, thus indicating a half order rate dependence on hydrogen iodide concentration. Typical examples of such plots are shown by curves B, C and D of Fig. 1. For determining the order of the reaction with respect to di-t-butyl peroxide runs were carried out with constant hydrogen iodide concentration by keeping the solution saturated. The amount of peroxide consumed at successive time intervals was calculated from the amount of liberated iodine. Straight lines were obtained when the square root of the peroxide concentration was plotted against time, also indicating a half-order rate dependence on peroxide concentration. Curve A of Fig. 1 shows an example of these plots. Addition of t-butyl alcohol in moderate concentration to the initial reaction mixture had no effect on the results as shown by curve C of Fig. 1. The rate law (3) is suggested by the data which have been presented. d(I?)/di = B(~-Bu,O~)'/~(HI) /z
(3)
Confirmation of this rather unusual reaction rate expression was obtained from runs in which the reactant concentrations were comparable. Using the stoichiometry of equation 2 the rate law can be rewritten with the concentration of iodine as the dependent variable to facilitate integration, which yields the expression -log I
-
+
[{(HI),- 2(12))1/2 {2(t-B~202)~ - 2(Iz)]'/z]
=
Iit/3.26
+ coIl.itallt
(4)
where the i subscripts indicate initial concentraI tions. Data at three temperatures resulted in u w linear plots of the logarithmic term of equation 4 2's. time as shown in Fig. 2 . -111 Lirrhenius-type plot of the slopes of curves -4, I3 and C, mhirh I span a 20" temperature range, yields :I. straight I 75 150 225 300 line, the slope of which corresponds to ai1 activat ion energy of 22 kcal. t (min.), A reaction rate constant ICcan be computed from Fig. 2.----Effwt of temperature on react,ion rate. A : the slope of each of the three types of plots. TTalues ( t - I j U 2 0 2 j . i = i.08 x 10-3 M , HI)^ = 2.66 x 10--3J I , T = 34.90": -6: (t-€3uaOn)i = 1.08 X Af, (HI); = 1.70 X of k obtained from 18 runs at 24.80" ranged from T = 1.4.70"; C: (t-BuzOz)i = 2.17 X -Ifl 1.1-3.6 X set.-', with a mean value of 2.0 AI, T = 24.80'. (H1)i = 1.25 x ==I 0.7 X set.-'. Although the precision of possible reaction product. In this range of coil- measurement of k is unsatisfactory it should be centrations infrared absorption measurements could noted that in these runs the initial concentrations not be used to identify the organic reaction product. of hydrogen iodide and di-t-butyl peroxide were h
v
I
AT?,
I
Oct., 1960
1587
h'0TE:S
Grade 72-60, and baking the resulting membranes t'o render them insoluble. Polyvinyl alcohol membranes also were modified by forcing a dilute (less than 5y0) solution of hydrogen peroxide through them. Hydrogen peroxide solutions of higher concentration dissolved the membranes. d(Is)/dt = 2.6 X 1011 exp( -22000/RT)(t-B~i~O~)~/~(HI)~/~ Polyvinyl acetate membranes were prepared and tested, but were too flimsy to be evaluated a t these high pressures. Procedure.-All tests were made a t room temperatures ULTRAFILTRA4TION OF SALT SOLUTIONS using 0.1 M KaCl solutions. The concentration in the apparatus was maintained constant during the run. Flow AT HIGH PRESSURES rates are reported as microliters per hour per of memBY C. E. REIDA Z ~ DH. G. SPENCER brane surface. Values were limited to an accuracy of 1 5 pl.lhr.lcm.2. Salt rejection was determined by Mohr Department of Chemzstry, Unzverszty of Florrda, G'aznesvzlle, Floreda titration of the effluent and the solution in the apparatus. Reeezved Aprzl i& 1960 Frequent comparison of this method t o analysis by conductivity measurements showed agreement within 2% rejecDesalting by ultrafiltration recently has been tion. Successive determinations of the salt rejection, in investigated at pressures less than 100 atm.2-4 fractional reduction of chloride concent,ration, were m-ithin This work is a study of the effect of higher pres- zko.01. For cellophane, a different membrane was used in each sures on the desalting properties of three memrun, which was duplicated at each pressure except 340 atm., branes : polyvinyl alcohol, cellulose acetate and where only a single run was carried out. Flax rates for the cellophane. duplicate runs were reproduciblewithin &5 fil./hr./cm.z, and The bound mater and ion-selective theorieszs3for the salt rejection values did not differ more than 0.02. All the function of the membranes in the desalting the membranes were cut from the same 12 inch square of cellophane so that they might be as uniform as possible. process indicate that Convective and diffusive For the other membranes, the various pressures were applied flows are involved, and that the convective flow in succession t o a single membrane.
varied oyer 65-fold and 25-fold ranges, respectively, without observing evidence of a trend indicative of deviation from the rate law
of solution can be reduced by diminishing the pore size through the use of high pressure. Ticknor's proposal5 that diffusive and convective flows of pure liquids occur in cellophane, and that pore size determines the type of flow, is essentially equivalent to the bound water theory. The bound water theory also emphasizes that ions which do not fit into the bound water network do not participate in the diffusive flow. If this is essentially correct, these relationships apply &d
=f&
(1)
and Qc
= (1
-f)Q
(2)
where Q is the flow rate, f the fraction of the ions rejected, &d the diffusive flow rate, or the flow of pure water, and Qc the convective flow rate, or the flow of solution. Experimental Apparatus.-The desalting apparatus differs from the one reported previously3 in that the pressure is applied by means of a piston-type pressure intensifier instead of by compressed air, and the porous disc which supports the membrane was made of stainless steel (Micro Metallic Inc.) instead of porcelain. Pressures vere read directly from Bourdon pressure gauges. The backstrokes of the intensifier piston, which occurred a t intervals of 10 to 30 minutes, resulted in momentary pressure drops of as much as 20 atm. Flow rates, compared at 70 atm., were lower on this apparatus than those normally obtained on apparatuses with porcelain backing discs, which are more porous than the steel. However, the salt rejection values did not differ significantly. Comparisons of flow rates obtained with this apparatus should be significant, although different from those obtained with porcelain backing disks. Materials -Uncoated cellophane (du Pont PT-300) and celliilose acetate (du Pont CA-43), both approximately 0.88 r n l l (22 h ) thick, were tested without further treatment. Polyvinvl alwhol membranes, 0.6 mil (15 p ) thick, were prrpawd b\ ciwting iiqueous solutions of du Pont Elvanol,
__
1) Based o n t h r AI.$. thesis of H G. Spencer, February, 1958. ( 2 ) C. f Reid and C J. Breton, . I . A p p l . Polymer Scz., 1, 133 (1059). (3) J. G XcKelxey, IC. S. Spiegler a n d M. R. J. Wylhe, THIS JOT-RSAL.61, 174 (1957). (4) Proceedings of a symposium, "Saline Water Conversion," hjational Academy of Sciences and National Research Council, Publir a t i o n 568 \\ ashingtun, D. 1957. ~ 5 I) B l'ichnor, T t m J O U R \ ~ L62, , 1483 (1958).
c.,
Results The results of the ultrafiltration measurements are presented in Table I. Essentially, salt rejection increased smoothly with pressure in all cases except TABLE I RESULTS O F ULTRAFILTRATION h)rEASUREMEKTS Qd/P Qc/P Membrane P Q f 70 80 0.09 0.10 1.04 .09 0 . 7 3 .ll 135 110 .55 .14 .09 205 130 .10 .35 270 120 . 2 2 .12 .20 .37 340 110 Cellulose acetate 3TO 17 0.99 0.06 0.0006 205 14 .99 .07 ,0007 138 7 . 9 7 .05 ,0015 Polyvinyl alcohol 70 60 0.06 0.06 0 . 8 0 135 80 .10 .06 . 5 3 205 90 .16 .OT .3T 270 140 .20 ,lO .41 305 210 .16 .lI .58 (Failed a t higher pressure-very rapid floi7) Cellophane
70 50 0.09 0.07 0.64 170 80 .13 .Oti 41 (Failed a t higher pressure-very rapid flou-)
Polyvinyl alcohol
Polyvinylalcohol 100 110 0.13 0.1;; 0 . 9 6 (treatedwithH202) 170 120 .24 .I7 .54 (Failed a t higher pressure-very rapid flov-)
at the high pressures for one polyvinyl alcohol membrane, whirh could have resulted from the developments of a minutre leak before the large scale failure at higher pressures. Flow rates increased with pressure, with t,he except,ion that a maximum occurred at about 200 atm. for cellophane. Convective permeability, Oc,' P , decreased smoothly with pressure, except for the above ment'ioned polyvinyl alcohol membrane, while the diffusive permeability, QdIP, remained nearly constant or perhaps increased slightly. In the definition of diffusive permeability, P might better be replaced by the applied pwssure dif-
