Table I. Analysis of Federal Water Quality Administration Reference Samples Sample type Inorganic Inorganic Organic Inorganic and Organic
Given value, ppb Hg 0.34 4.2 4.2 6.3
Measured value, ppb Hg 0.34 4.4 4.3 7.0
organic compounds we have tested are mercresin [chloromercuriphenol(O)l, dimethyl mercury, and diethyl mercury, and in these tests, the recovery of mercury, as determined by comparison with ionic mercury standards, is quantitative within the precision of the measurements. The sensitivity of the method is illustrated by the calibration
curve in Figure 1. A mercury concentration of 0.1 p p b in a 50-ml sample is easily measured; lower concentrations can be determined with larger sample aliquots a n d longer eiectrodeposition times. The precision a n d accuracy of the method are estimated t o be =tlOz in the range 0.1 t o 10 p p b mercury. The method was applied t o mercury reference samples supplied by the Federal Water Quality Administration, with the results shown in Table I. The samples were stated t o contain mercury in ionic or organic form as indicated in t h e table; however, the actual compounds were not specified. RECEIVED for review May 13, 1971. Accepted July 20, 1971. The information contained in this article was developed during the course of work under Contract AT(07-2)-1 with t h e U. S. Atomic Energy Commission.
Determination of Unsaturation in Polyoxyalkylene Allyl Ethers via Brown Hydrogenation F. John Ludwig, Sr., and William R . Blade Perrolite Corporation, 369 Marshall Avenue, St. Louis, Mo. 631 19 DETERMINATION OF UNSATURATION in polyoxypropylene glycol polyurethane raw materials usually is done by means of a mercuric acetate procedure ( I , 2). There are a number of interferences with this method. A correction is required if the sample is not neutral t o phenolphthalein. Atmospheric CO:! titrates as a n acid and must be excluded. The system must be essentially anhydrous since water may hydrolyze the reaction product t o form basic mercuric salts. Inorganic salts, especially halides, must be absent from the sample because they interfere with the addition of mercuric acetate to the double bond. The procedure is not valid for compounds in which the unsaturation is conjugated with carbonyl, carboxyl, or nitrate groups ( I ) . Thus, for the measurement of unsaturation either in polyoxypropylene glycols, or in base catalyzed (e.g., NaOH) reaction products of ethylene oxide and/or propylene oxide with allyl alcohol which have not been purified to remove such interferences as water, CO?, and base, the mercuric acetate method is not satisfactory. The determination of total allyl and cis-propenyl unsaturation in polyoxypropylene glycols using infrared spectral and bromination procedures was reported by Dege, Harris, and MacKenzie (3). The C-C stretching adsorptions in the 5.9-6.2 I.tm region of the spectrum are subject t o interference from water and C-=O groups in by-products of oxyalkylation. Boyd and Roach demonstrated that allyl ether and allyl ester groups add halogen (I2 or Bra) quantitatively (4). In
our experience, in the correction for HBr substitution in the bromination procedure, basic impurities produce negative errors, and acidic impurities produce positive errors. Hence, the sample must be neutralized before bromine addition. The use of catalytic hydrogenation t o measure unsaturation in a variety of unsaturated compounds, and a n automatic hydrogen generator based o n sodium borohydride have been described in a number of papers by H. C. Brown and C. A. Brown (5-10). They showed that partial hydrogenolysis of a few compounds, such as 1-penten-3-01 a n d benzalacetone, occurred when hydrochloric acid was used t o decompose excess sodium borohydride and provide a hydrogen atmosphere. In this case, Brown and Brown found that acetic acid could be used instead of hydrochloric acid. When we measured the amount of unsaturation in diallyl ether, allyl glycidyl ether, allyl acetate, and allyl alcohol using a hydrochloric acid addition step, we obtained values that were 1.6-1.8 times larger than the theoretical value. Similarly, for oxyalkylated allyl alcohols, the measured amounts of unsatiiration were almost twice the calculated values when hydrochloric acid was used. It appears that cleavage of the C-0 bond in the structural unit C-CC---0was taking place under these conditions of hydrogenation. Consequently, as described below, we investigated the hydrogenation of several alkyl allyl ethers, of polypropylene glycols of 2000 and 4000 molecular weights, and of two __ (5) C. A. Brown and H. C. Brown. J . Amer. Chet77. Sac., 84, 2829
(1) D. J. David and H. B. Staley, “Analytical Chemistry of the Polyurethanes,” Vol. XVI, Part 111, Why-Interscience, New York, N. Y . , 1969. pp 291-294. (2) R. P. Marquardt and E. N. Luce. ANAL. CHFM.,39, 1655
(6) H. C . Brown, K. Sivasankaran, and C . A. Brown, J . O y . Cliem.. 28, 214 (1963). (7) H. C. Brown and C . A. Brown, TLJtruliedro/i,Sirppl., 8, Part I ,
(1967). (3) G. J. Dege, R . L. Harris, and J. S. MacKenzie, J . Anwr. Climm. Sac., 81, 3374 (1959). (4) H. M. Boyd and J. R. Roach, ANAL. CtfEhl., 19. 158 (1947).
149 (1966). (8) C. A. Brown and H. C. Brown, J . Org. Clrem., 31, 3989 (1Y66). (9) C. A. Brown: ANAL. CHEhl.. 39, 1882 (1967). (IO) C . A. Brown. S. C. Sethi. and H . C. Brown, ihid., p 823.
1888
(1962).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
oxyalkylated allyl alcohols using acetic acid in place of hydrochloric acid. EXPERIMENTAL
Apparatus. The Model 2-300 Delmar Scientific Laboratories Brown2 Hydro-Analyzer with 100-ml hydrogenation flask a n d 10-ml buret was used. Hydro-Analyzer Reagents. All chemicals were of reagentgrade quality. A 0.05M solution of chloroplatinic acid (this compound contains 4 0 x Pt by weight) was prepared by dissolution of 1.O gram of H2PtC16.6H?O in 40-ml of isopropyl alcohol. An approximately 0.5M solution of sodium borohydride was prepared by dissolving 10 grams of N a B H 4 in 500 nil of warm diglyme a n d filtering while hot (ca. 60 "C). A solution of about 0.05M sodium borohydride was prepared by dilution of 25 ml of the above 0.5M solution t o 250 ml with isopropyl alcohol. This solution was standardized by adding 20.00 ml of it to 15.00 ml of 0.1000Nhydrochloric acid with stirring, and backtitrating with 0.1000N sodium hydroxide t o a methyl red end point. The 0.05M sodium borohydride solution appears t o be stable for 3-4 weeks. Sources of Products Analyzed. The diallyl ether was Eastman White Label grade. The allyl n-hexyl ether and allyl a-glyceryl ether were purchased from K and K Laboratories. The polypropylene glycols P-2000 and P-4000 were obtained from the D o w Chemical Company. The polyoxyalkylene allyl ethers were prepared in the Tretolite Division Laboratories by addition of propylene oxide and/or ethylene oxide to allyl alcohol with N a O H catalysis. Procedure. One gram of activated charcoal a n d 2 ml o f 0.05M chloroplatinic acid solution are added to the hydrogenation flask, which then is attached to the apparatus. T h e buret a n d reservoir are filled with standard 0.05M sodium borohydride solution, excluding all air bubbles, and then fitted o n t o the hydrogenator valve in the mercury well. The flask is immersed in a water bath a t 25 "C. While stirring vigorously, 10 ml of 0.5M sodium borohydride in diglyme is injected slowly through the serum stopple onto the central well of the valve. After about 10 minutes of stirring, a 4-ml volume of acetic acid is injected into the flask. The system is allowed to equilibrate for 10 minutes. A 0.5- to 3.0-ml aliquot of a n isopropyl alcohol solution of the sample containing 0.2 to 2.0 mmol unsaturation is injected into the flask, and the buret stopcock is opened immediately. The stirring rate is adjusted so that n o more than 2 ml/min of sodium borohydride is used. When the flow of sodium borohydride stops, the buret is refilled to the zero mark. The buret readings for the first two aliquots are not recorded. Before injection of the next aliquot, the stopcock of the buret is opened partially for about 1 minute to permit equilibration of the pressure within the system by slow influx of NaBHI. Then, the buret is refilled and the third aliquot is added. The volume of sodium borohydride consumed is recorded. The pressure equilibration step must be carried out before each subsequent injection. The amount of hydrogen, in millimoles, which is reacted is calculated from the following equation: Hz, mmoles
=
4 V7M
+ V 7 )( P - 40) + 0.0160 (V? ~ _ _ _ _ _ (1) t + 273 - ---
where V , is the volume of standard sodium borohydride used, M is the molarity of the standard sodium borohydride, V , is the volume of sample solution injected, P is the atmospheric pressure in mm Hg, and t is the temperature in " C of the water bath. RESULTS AND DISCUSSION
The accuracy a n d precision of the hydrogenation of diallyl ether was studied at two different concentrations. The re-
Table I. Hydrogenation of Diallyl Ether mmol Hz No. of Measd, Concn, g/mP detn Theory mean Std dev 0.0112 13 0.11 0.11 0.0045 0.174 7 1.78 1.78 0.020 Sample size 0.50 ml. Table 11. Hydrogenation of Allyl n-Hexyl Ether and Allyl a-Glyceryl Ether Concn, Sample mmol Hz Compound g/ml vol, ml Theory Measda Allyl n-hexyl ether 0.318 0.50 1.14 1.13 Allyl a-glyceryl ether 0.426 0.40 1.29 1.28 Mean of three determinations. Table 111. Hydrogenation of Known Mixtures of Polyoxypropylene Glycol 2000 and Diallyl Ether mmol Hdg __ Calcdn Measd mean No. of detn Std dev 0.26 0.28 6 0.0051 0.40 0.41 10 0.0086 cL Calculated from the weights of diallyl ether and P-2000 in the mixture and from the measured value of 0.11 mmol Hp/gram for P-2000.
Table IV. Hydrogenation of Polyoxyalkylene Allyl Ethers Prep. _mmol _ Hn/gram Structural type No. Calcda Measdb CHz=CHCH,( Et0)yH 1 1.73 1.73 1.77 CH*=CHCH*( EtO),H 2 1.73 CH2=CHCH2(EtO),(PrO), H 1 0.429 0.438 CHz=CHCHz(EtO),(PrO),.H 2 0.429 0.419 Calculated from the weights of allyl alcohol and alkylene oxide reacted. Mean of four determinations.
sults are given in Table I. The 0.0112-gram/ml sample required about 0.4 ml of 0.05M sodium borohydride. At lower concentrations, errors in the buret reading will become larger, and lead to lower accuracy and precision. The hydrogenations of two other alkyl allyl (mono-) ethers gave the results which are presented in Table 11. Thus, accurate and reproducible hydrogenations of these three alkyl allyl mono-ethers were obtained using the HydroAnalyzer with acetic acid in place of hydrochloric acid. In addition, much shorter pressure equilibration times were required for acetic acid than for hydrochloric acid. Hydrochloric acid required a n equilibration time of at least three hours while acetic acid required about 15 minutes equilibration time. Five replicate analyses of a 0.6038 gram/ml isopropyl alcohol solution of polypropylene glycol P-2000 were made using 2.00-ml injections requiring 0.2 t o 0.3 ml of titrant. The unsaturation was calculated to be 0.11 mmol H2/gram with a standard deviation of 0.0099. Then, known mixtures of P-2000 a n d diallyl ether were analyzed with the result shown in Table 111. It appears from these known addition studies that the value of 0.11 mmol H2/gram in P-2000 itself was 0.010 mmol/gram low; this difference may be within the precision of the method for these relatively
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
1889
small volumes of titrant. When the hydrogenation of P-4000 was attempted in the Hydro-Analyzer, no uptake of hydrogen was measured, indicating much less unsaturation than in P-2000. Because of the non-availability of polyoxypropylene glycols which contain “known” amounts of unsaturation, two polyoxyalkylene allyl ethers of average molecular weights 580 a n d 2340 were synthesized by N a O H catalyzed addition of either ethylene oxide (EtO) of mixture of ethylene oxide and propylene oxide ( P r o ) t o allyl alcohol. Two-milliliter ali-
quots of these reaction mixtures, which were not purified by water washing, vacuum stripping, etc., were hydrogenated with the results presented in Table IV. The fairly good agreement between the calculated and measured amounts of unsaturation in these four oxyalkylate samples is evidence for the validity of the CH3COOH-modified hydrogenation procedure even in the presence of N a O H catalyst and reaction by-products. RECEIVED for review May 18,1971. Accepted July 19,1971
Effect of Inlet Residence Time on Analysis of Atmospheric Nitrogen Oxides and Ozone Samuel S. Butcher’ Department of Chemistry, Bowdoin College, Brunswick, Me. 04011
Ronald E. Ruff Department of Cicil Engineering, Unicersity of Washington, Seattle, Wash. 98105 OZONE,NITRIC OXIDE, AND NITROGEN DIOXIDE have been recognized as components of photochemical smog. The concentrations of these substances are monitored by many control agencies using a variety of instrument systems. T h e reaction between ozone and nitric oxide is sufficiently rapid that a change of light intensity in the instrument inlet prior t o chemical analysis can give rise to a systematic error. The magnitude of the error depends o n the residence time in t h e inlet; significant errors can occur for a residence time of 10 seconds.
Table I. Rate Constants for 25 “C,One Atmosphere Reference ki 0-25 hr-1 (1) k? 8.9 X ppm-2 hr-‘ (2) k .i 1320 ppm-lhr-l (3) 4 . 5 x 10-8 ppm-? hr-l (2) k; 0.19 ppm-’hr-l (ethylene) (4) ks 38 ppm-’hr-1 (trn/rs-butene-2) (4) ki; 1 . 3 x 10-7 ppm-1hr-I (methane) ( 5 ) ks 6.25 ppm-’1ir-l (6.) ki
CALCULATIONS AND DISCUSSION The importance of the light intensity is determining the relationship between the concentrations of NO, NO2, and 0 3 in the atmosphere has been discussed by Leighton ( I ) and more recently by Schuck and Stephens ( 2 ) . The fastest reactions for this system in the presence of sunlight are listed below.
+0
ki
(1)
O+02+M+03+M
kz
(2)
ka
(3)
NO2
0 3
+
/IV + N O
+ NO
+
NO2
+
0 2
If the concentration of oxygen atoms reaches a steady state, the rate expression for N O is given by d(NO)/dt = kl(NO9) k3(NO)(Os). Since, in the presence of sunlight, the two terms o n the right hand side of this equation are much larger than d(NO)/dt, we have, to a fair degree of approximation, (NO)(03)/(NOz) = k l / k 3 . If the light intensity decreases suddenly, as when the sample enters the analytical system inlet, reaction 1 is no longer important and the N O and 0 3 Visiting Scholar, University of Washington, 1970-71
concentrations decrease because of reaction 3. The actual rate of change will depend on a large number of factors including the magnitude of the light intensity change in the action spectrum of NO, and the concentrations of other atmospheric constituents. Some of the other reactions which should be considered are listed below.
+ Reactants Products 2 N 0 + 02 2NOz O3 + Hydrocarbons Products O 3 + N O z NO;, + O2 0
+
+
+
1890
ks
(5)
ke
(6)
kq
(7)
Values for the rate constants (1-6) are collected in Table I for 25 “C, 1 atmosphere pressure. Under most conditions, reactions 4, 5, 6, and 7 are too slow to be of importance for the expected residence times; these reactions will be neglected in the present analysis. We shall also assume that the light intensity drops to zero for a period of time (equal to the (3) M. A. A. Clvne. B. A. Thrush. and R. P. Wayne, Trcms. Frrrnd~iy Soc., 60, 359 i1964). (4) J. J. Bufalin! and A. P. Altshuller, C N I I J. . Clicrn., 43, 2243 (1965). (5) F. J. Dillemuth. D. R. Skidmore, and C. C. Schubert. J . Phys. C h m . , 64, 1496 (1960). (6) H. S. Johnston and D. M. Yoct, J . Chem. Pliys., 17, 386 (1949). \
(1) P. A. Leighton, “The Photochemistry of Air Pollution,” Academic Press, New York, N.Y., 1961. (2) E. A. Schuck aad E. R. Stephens in “Advances in Environmental Sciences and Technology, Vol. I,” J. N. Pitts and R . L. Metcalf, Ed., Wiley-Interscience, New York, N.Y., 1969.
(4 1
+
,
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
