auroyl peroxide, cumene hydroperoxide, and p-menthane hydroperoxide followed Beer’s law u p to 1 p.p.m. However, tert-butyl hydroperoxide deviated somewhat, and a calibration curve of concentration us. absorbance was necessarv for this compound. The validity of this method should be verified experimentally before applying it to peroxides other than those tested. For example, dialkyl peroxides, such as di-tert-butyl peroxide ( I O ) , do not react with benzoyl leuco methylene blue. The reaction was heat sensitive, and therefore, all work was done a t 24” i~ 1’ C. At 30” C., the results became very erratic. Because the color was also light sensitive, the solutions were stored in the dark while the color was developing. ilrtificial light caused irregular results, and sunlight ruined the determination completely by causing very excessive reagent blanks. The reagents were all stable in benzene solution and were usable for 3 to 4 weeks. The leuco dye was kept in a brown bottle
an-ay from direct light. The only reagent concentration that appeared to be critical was the zirconium naphthenate. If too much was added, the reagent blank became excessive. iilthough there was a waiting period for color development, it was simple to run 6 to 10 determinations a t the same time. The reaction \vas sensitive, and active oxygen was determined down t o less than 0.5 mg. Table I11 lists analyses of the five standard peroxides. -411 commercial peroxides which were used as standards were analyzed iodometrically. The precision of the method was obtained by running 7 to 16 replicate samples for each peroxide. For the four compounds which follow Beer’s law, the 95% confidence limits range from =!= 2.6 to =!= 1.7%.
ACKNOWLEDGMENT
The authors thank Marjorie C. Lyon and Thomas Gordon of the National
Cash Register Co. for supplying the benzoyl leuco methylene blue reagent. REFERENCES
( I ) AIIen, L. H., Paint Technol. 22 (248), 161 (1958). (2) Ibid., 22 (249), 205 (1958). (3) Ibid., 22 (250), 241 (1958). (4) Bawn, C. E. H., Mellish, S.F., Trans. Faraday SOC.52, 1216 (1956). (5) Egerton, A. S., Everett, A . J., Anal. Cham. Acla 10, 422 (1954). (6) Miller, G. L., “Zirconium,” Academic Press, New York, 1954. (7) Robey, R. F., Wiese, H. X., Ind. Eng. Chem. 17, 425 (1945). (8) Tobolsky, A. V., Mesrobian, R. B., “Organic Peroxides.” Interscience. Neiv York 1954. (9) Ueberreiter, K., Sorge, G., Angew. Chem. 68 (lo), 352 (1956). (10) Ibid., 68 (15), 486 (1956). (11) Venable. F. P.. “Zirconium and Its Compounds,” Chemical Catalog Co., New York, 1922. (12) Wagner, C. D., Clever, H. L., Peters, E. D., A X A L . CHEM.19,980 (1947). RECEIVED for review March 5, 1959. Accepted May 26, 1959. Division of An-
alytical Chemistry, 135th Meeting, ACS, Boston, llass., rZpril 1959.
Determination of Boric Oxide in Glass by Pyrohydrolysis Separation J. P. WILLIAMS, E.
E. CAMPBELL,
and THERESE
S. MAGLIOCCA
Glass Research and Developmenf Division, Corning Glass Works, Corning, The boric oxide in many glass compositions can be separated by a pyrohydrolysis-type reaction in which steam is passed over a mixture of glass sample, uranium oxide (UaOs), and sodium metasilicate nonahydrate (No2S i 0 3 . 9 H 2 0 ) at 1300’ to 1350°C. in a platinum tube. The boric acid in the distillate is determined by the usual mannitol-sodium hydroxide titration. The effects of glass sample size and composition, catalyst, temperature, and distillation rate are discussed. Quantitative separation can be expected from most glass compositions except those containing greater than 10% lead, 5% zinc, or 1% phosphorus oxides. A complete determination can be carried out in about 90 minutes. Pyrohydrolysis results compare favorably with more conventional methods of analysis for glasses containing from about 0.2 to 3070 boric oxide. ORIC OXIDE in
glass has been determined by opening u p the glass by carbonate fusion, dissolving the melt in acid. and separating the boron by dis1560 *
ANALYTICAL CHEMISTRY
N. Y.
tillation of methyl borate from methanol or controlled p H precipitation. The boron is then usually determined by titrating the mannitol-boric acid complex with standard sodium hydroxide (5). The American Society for Testing Materials ( 2 ) uses the methanol distillation procedure originally reported by Wherry and Chapin (I$), while Hollander and Rieman (6) and Webster (11) recommend controlled hydrolysis for separating the boron. Pyrohydrolysis separation of the halides has been investigated by a number of workers. Early mention of this process by Warf (9) was expanded in a later report (10). Most investigators have employed uranium oxide (U308) as an accelerator or catalyst. Powell and Menis ( 7 ) have reported both micro- and macroseparations of fluoride from inorganic materials and the effect of various catalysts, as well as the use of moist oxygen instead of steam. Susano, White, and Lee (8) suggested a nickel tube to replace platinum; Gillies, Keen, Lister, and Rees (3) described a silica apparatus, and Adams and
Williams (I) used Corning Code i900 96% silica glass. The high volatility of boric oxide a t glass melting temperatures, coupled with the knowledge that boric acid readily steamdistills (4) suggested that pyrohydrolysis so successfully applied to the separation of fluoride and other halides from inorganic materials might be useful for separating boric oxide from borosilicate glasses. APPARATUS
The apparatus (Figure 1) is a modification of other typical pyrohydrolysis setups. The reactor tube is fabricated from 1 5 4 1 platinum sheet shaped into a tube 1.00 inch in outer diameter and 17 inches long. Both ends of the platinum tube extend beyond the combustion furnace and after assembly are wrapped with asbestos to minimize heat loss. One end of the reactor tube is attached to a T-connector tube, which consists of a &inch horizontal length and a 17-inch vertical arm made from 1.0-inch outer diameter Corning Code 7900 tubing. The two horizontal end openings on the cross arm are 29/42 standard taper malt joints and the opening at the lower mi-
of the long vertical arm is a 24/40 male joint. One end of the short cross arm of the T-connector is pressed snugly into the slightly tapered platinum reactor tube while the other end serves as a sample port closed with a 29/42 standard taper female cap. The vertical arm connects to the steam generator. The condenser tube, formed from 10mil platinum sheet has an outer diameter of 0.25 inch and is 18 inches long. The condenser tube is welded at right angles to the closed exit end of the reactor tube and 15 inches of its length are surrounded by a 1.5-inch outer diameter Corning Code 7900 glass water-cooling jacket. This jacket has a water inlet a t the bottom and a large exit a t the top and is attached to the inner platinum tube with a one-hole rubber stopper only a t the bottom. The upper portion of the condenser tube operates at such high temperatures that attachment to the water jacket at this point is not practical. The resistance combustion furnace consists of a 1.75-inch outer diameter Zircofrax tube (The Carborundum CO.), 11-oundwith 64 turns of 40-mil platinum10% rhodium wire. The furnace ends which support the core consist of 0.5inch Transite disks 12 inches in diameter which are bolted to a cylindrical outer jacket of 16-gage black iron sheet. Furnace insulation between core and jacket is C-730 hydrated alumina (Aluminum Co. of America). Power to the furnace is adjusted with a Type V20M Variac Transformer (General Radio Co.) and is maintained with a Leeds & Sorthrup Rficromax controller and platinum-100/, rhodium thermocouple. Probing the interior of the reactor tube with a thermocouple indicates inner tube temperatures of 1300' to 1350' C. during pyrohydrolysis when the controller thermocouple located in the hottest zone between the platinum reactor tube and the furnace core is 1450' C. The steam generator consists of a 1liter round-bottomed Corning Code 7740 glass boiling flask, heated by a Variaccontrolled Glas-Col mantle. Boiling chips of microporous carbon are placed in the flask to promote smooth b d i n g . The boiling flask is connected by a standard taper 24/40 joint, to the long vertical arm of the T-connector tube nhich conducts the steam into the platinum reactor. To preheat t b steam before it enters the reactor tube, a Hevi Duty split tube combustion furnace (Hevi Duty Electric Co.) is placed around the long vertical arm of the T-connector tube. Water is added to the boiling flask through a side arm located on the lower end of the Tconnector tube just above the boiling flask. The twa furnaces, reactor and T-tube assembly, condenser jacket, and steam generator are all supported on a Flcxaframe rack (Fisher Scientific Co.) mounted on a movable platform. The platinum reactor tube and the framework are rvell grounded for protertion from electrical leakagc
suitable sized around-glass sample and an appropriateamounfof sodium metasilicate nonahydrate or pow 'ered chrome-magnesia refractory. For glasses containing more than 5% boric oxide, use a 0.25-gram glass sample and 0.1 gram of sodium metasilicate nonahydrate. For glasses containhlg less than 5% boric oxide use a 0.5-gram glass sample plus 0.1 gram of sodium metasilicate nonahydrate. For glasses which contain lead use 0.2 gram of powdered chrome-magnesia refractory in place of the sodium silicate. Intimately grind the mixture together until a fine powder less than 300 mesh results. Transfer quantitatively to a platinum-lined pretreated Alundum boat. Pretreat the boat by heating in
REAGENTS
Standard 0.10.V sodium hydroxide, prepared from 50% sodium hydroxide solution with carbon dioxide-free distilled water, protected from atmospheric carbon dioxide, and standardized with potassium hydrogen phthalate. Uranium oxide (U308),prepared by heating pure uranium dioxide at 900' C. Chrome-magnesia electrocast refractory (Corhart 104), Ceramic Research and Development Division, Corning Glass Works. PROCEDURE
Transfer 3.0 grams of powdered uranium oxide to a n agatemortar. Add a
llOV A t
e
A-[
L'
25/40
VARiAC CoNwcrEa TO IIOV P C
Figure 1.
Pyrohydrolysis apparatus
A. Code 7900 Vycor brand jacket 6.
tube
Table
Glass KO.
b
I.
Boric Oxide Determinations in Glasses
Type of Glass Soda lime" Borosilicate* Soda-borosilica te Soda-borosilicate Borosilicate Borosilicate
Conventional, %
Pyrohydrolysis BzOa, %
Difference, Av. -0 09 $0 10 0 00 -0 31 +0.18 -0.04
0 53,O 56,O 53 12 6, 12 6 9 79,9 72 27 90.27 20,27 50 13.32; 13.20' 5 12.39,12.49,12.50, 6 12.38, 12.51, 12.50 7 Soda lime 0 25 0 28,O 26,O 23 1 4 9 , l .42 1 2 0 , l 17 Barium-soda lime 8 Barium-borosilicate 9 5 4 5 , s 45,5 45 5 34 0 95,O 89 Barium-soda lime 10 1 3 1 , l .31 Barium-borosilicate 7 57 7 52) 7 61 11 Lead-barium 72 2 64 2 60.2 69 High silica 2 38,2 38 2 41 13 High silica 3 33 3 50 14 Calcium fluoride opal 0 94 0 87,O 99 15 Lead-borosilicate 14 81 15 12,14 95 16 Lead-borosilicate 15 82 15 80,15 63 17 14 G , 1 4 85 14 80 Borosilicate 18 13 43,13 43 13 55 Borosilicate 19 20 2 02 2 08,2 03 High silica 21 3 26 Zinc-borosilicate 3 47 22 1 34 1 0 9 , l 19 Zinc fluoride opal 1 45 1 0 9 , l 07 Zinc fluoride opal 23 24 1 22 0 79 Lead-barium 17 60 20 2,19 9 15 Lead-zinc silicate 4 5.3 3 50 Lead phosphate opal 26 27 Phosphate opal 12 59 11 55 Bureau of Standards Xo. 92 certified value 0.707, BzO,. Bureau of Standards No. 93 certified value 12.796 B& 1 2 3 4
a
E. Preheat furnace Code 7740 round-bottomed flask G. Glas-Col heating mantle H. Distilled water inlet 1. Rubber stopper
F.
Pt-wound furnace
C. Pt reaction tube D. Code 7900 Vycor brand glass T-connector
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0 64,O 62 12 5,12 5 9 8 0 , 9 72 27 83 13.05, 13.10 12.50
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VOL. 31, NO. 9. SEPTEMBER 1959
-
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* 156 1
the platinum reactor tube a t 1300" to 1350" C. and passing steam through the apparatus until the distillate amounts to a t least 500 ml. The boat need be pretreated only once and can be used repeatedly until it breaks. Introduce the boat and contents into the reaction tube which is a t operating temperature with steam passing through the system a t such a rate as to produce 5.5 =t0.2 ml. of distillate per rbinute. Collect five 100-ml. distillate fractions and titrate each fraction separately with standard 0.1ON sodium hydroxide. Carry out the acidimetric titration using a p H meter by first adjusting to pH L4, saturating the solution with mannitol, and then titrating to pH 6.8 as described by Webster (If). From the titration obtained for each fraction subtract the appropriate blank. If fluoride is present in the glass. add 2 grams of calcium chloride dihydrate to each fraction before titration. On completion of a run, remove the boat slowly, in successive stages from the reaction tube so as to minimize breakage of the Alundum boat by thermal shock.
86 I
"f
//
40
I
'I
wo
experiments with an apparatus using a Corning Code 7900 reactor tube (1) gave encouraging boric oxide recoveries a t 900" t o 1000" C., but because higher temperatures were indicated, a silica reaction tube which operated up to 1200" C. was tried. Recovery of boric oxide was improved a t 1200" C.; however, because a further increase in temperature was required, a platinum reactor tube patterned after Warf (9) and a platinum-wound furnace were built. By automatically controlling the furnace a t 1450" C. it was possible to maintain the inner portion of the reactor tube a t near 1350 " C. with steam passing through the tube. This was sufficient for quantitative separation of boric oxide. Figure 2 illustrates the recovery of boric oxide from a simple soda-alumina-borosilicate glass as a function of temperature. Rate of Recovery of Boric Oxide. The rate of the flow of steam was such t h a t 5.5 f 0.2 ml. of distillate per minute appeared t o be optimum. Faster rates of steam flow cooled the reactor tube below the 1300" to 1350" C. range and slower rates prolonged the distillation unnecessarily. Under the optimum conditions, the rate of separation of boric oxide seemed independent of the composition of the glass and of the amount of boric oxide present. The per cent boric oxide recovered in successive 100-ml. fractions of distillate is shown in Figure 3. The spread in points covers data for simple borosilicate, barium, high silica, and low lead glasses where the boric oxide content varied from 2 to 15%. Catalysts. Nearly all investigators 1562
ANALYTICAL CHEMISTRY
I
I
1100 liao TEMPERATURE ,T.
1x0
Figure 2. Pyrohydrolytic boric oxide recovery as function of temperature Mixture of 0.250 gram of borosilicate glass, 3.0 grams of UaOs, and 0.1 gram of NazSiOa. 9HzO pyrohydrolyzed a t temperatures indicated with distillation rate of 5.5 A 0.2 ml. per minute. Total distillate 500 ml.
Table II. Range of Constituents in Silicates Analyzed for Boron b y Pyrohydrolysis
Range of Constituent in Glasses Analyzed for 803, LT,
EXPERIMENTAL
Apparatus and Temperature. Early
I
I
loco
Constituent Si02 A1203 CaO
MgO BaO ZnO PbO N&O LizO Kz0 plob
F
Successfully 42 to 0 to 0 to 0 to 0 to 0 to 0 to 0 to 0 to 0 to 0 0 to
97 21 13 4 33 4 6 15 2 5
5
Unsuccessfully
10 to 20 10 to i o
1 to 3 . 5
have used uranium oxide (u308) as an accelerator for the pyrohydrolysis of halides, although Powell and Menis ('7) report tungstic oxide as being effective. I n this study, the substances tried as catalyst for the separation of boric oxide included silicon dioxide, vanadium pentoxide, chromic oxide, aluminum oxide, magnesium oxide, manganese dioxide, a chrome-magnesia electrocast refractory (Corhart 104), and sodium uranate. None of these materials was as effective as uranium oxide as an accelerator. Varying the amount of uranium oxide revealed that 3.0 grams was optimum for a 0.25- to 0.50-gram glass sample. Because even uranium oxide alone was not as effective as desired, a search was made for auxiliary catalysts to improve the rate and completeness of boric oxide recovery. As a result of the observation that more rapid and complete separations were obtained for high alkali-containing glasses, sodium metasilicate nonahydrate (Na2Si03.9 HzO) was tried with uranium oxide and found very effective. Investigation of the effect of varying the proportions of sodium metasilicate to uranium oxide
NLMBER OF IOOml DISTILLATE FRACTONS
Figure 3. Recovery of boric oxide as function of consecutive distillate fractions for five glasses of diverse compositions
indicated that the optimum accelerating effect was obtained with a mixture of 0.1 gram of sodium metasilicate nonahydrate and 3.0 grams of uranium oxide as the catalytic substance. Further investigation of auxiliary catalysts revealed that a mixture of 0.2 gram of chrome-magnesia electrocast (Corhart 104) refractory and 3.0 grams of uranium oxide was also effective. This catalyst mixture was particularly useful for glasses containing up to 10% lead oxide. Apparently the chromemagnesia refractory has the beneficial effect of retarding to a limited extent the volatilization of lead oxide. Distillate. The p H of the distillate was usually slightly alkaline, in the range of 8.5 to 7.5. Analysis of the first and second distillate fractions of a typical borosilicate glass indicated sodium and boron equivalent t o NaaBsOo and Na2B407,respectively. Distillates from glasses containing much lead were seriously contaminated with this element. Blank Determinations. Because of the high temperatures and large amounts of additives used, careful blank determinations were required. Pretreatment of the Alundum boats and platinum parts lowered the blank and hence was adopted as part of the procedure. A blank of 0.05 ml. of 0.10N sodium hydroxide per 100-ml. distillate fraction was considered satisfactory. RESULTS AND CONCLUSIONS
Pyrohydrolysis and conventional wet chemical results for boric oxide in a wide variety of glasses are compared in Table I. The inferior results for glass numbers 21 to 27 are considered due to the presence of excessive amounts of lead, zinc, or phosphorus in the samples. I n most instances the conventional method used was that proposed by Webster ( I I ) , although in a few instances glasses were analyzed by the ASTM procedure ( 2 ) . I n addition to differences in boric oxide content, these glasses varied in other oxide compositions (Table 11).
Considering the average difference column in Table I, it appears that pyrohydrolysis determinations show a negative bias of about 0.1 absolute %. The recovery curves shown in Figure 2 indicates that results might be more quantitative if the reactor tube temperature could be increased to 1400" C. On the other hand, different catalysts and operating conditions might enable the efficient recovery of boron a t lower temperatures. Boric oxide undoubtedly is incorporated into the silica network in a glass while fluoride is present as a fluxing agent and as such is much less rigidly bound. T~ improve the method further, Some of the mechanism by which boric oxide is
(6) Ibid., 18, 788 (1946). (7) Powell, R. H., Menis, O., .~NAL.CHEY. 30, 1546 (1958). (8) Susano, C. D., I%-hite,J. C., Lee, J. E., rbia., 27,453 (1955). LITERATURE CITED (9) Warf, J. C., National Nuclear Energy Series, Div. VIII, Vol. I, pp. 728 ff., ( I ) Adams, P. B., Williams, J. P., J. Am. "Analytical Chemistry of the ManCeram. ~S'OC.41,377 (1958). hattan Project," McGraw-Hill, New American Society for Testing MateYork, 1950. rids, Philadelphia, "Standards on Glass (10) Warf, J. c,,cline, p;.D,, ~ ~ ~ and Glass Products," C169-53 (1955). R. D., ANAL.CHEM.26, 342 (1954). (3) Gillies, G. M., Keen, N. J., Lister, (11) 34,Webster, 305~ (1951). P. A., J. A m . Ceram. S O C . B. A., R ~ D.,~ ~ ~ ,t E~~~~~ ~ R ~~ i G. Brit. C/M 255 (Oct. (12) Wherry, E. T., Chapin, W. H., J. Am. C h m . SOL 30, 1687 (1908). (4)Hiliebrand, F.,Lundell, G. E. F. (revised by Lundell, G. E. F Bright, RECEIVEDfor review Januarv 16, 1959. E[. A., Hoffman, J. I.), "Appiied Inorganic Analysis," 2nd ed., pp. 749 ff., Accepted April 28, 1959. Pittsburgh Conference on Analytical Chemistry and Wiley, New York, 1953. (5) Hollander, M., Rieman, W., IND. hpplied Spectroscopy, Pittsburgh, Pa., ENG.CHEM.,ANAL.ED.17,602 (1945). March 1959.
separated from the glass by pyrohydrolysis would be desirable.
g$5$:tab1. w.
Determination of Vinyl Ethers and Other Unsaturated Compounds Modified Mercuric Acetate Procedure JAMES B. JOHNSON and JOHN P. FLETCHER Development Department, Union Carbide Chemicals
A modified methoxymercuration method has been developed for the determination of vinyl ethers and other olefinic unsaturation. It is easier to perform and has a wider application than earlier methods. The sample is allowed to react with an excess of mercuric acetate in methanol to form the mercury addition compound and acetic acid, In the case of vinyl ethers, the reaction is conducted at - 10" C. Solid sodium bromide is added to convert the excess mercuric acetate to the bromide, permitting direct titration of the acetic acid with alcoholic potassium hydroxide. Data for the determination of 15 vinyl ethers and 2 7 miscellaneous olefinic compounds are presented. The standard deviation of the procedure for the determination of purity is 0.207&.
A
procedures employing mercuric acetate for the determination of olefinic unsaturation (1-4) have been reviewed by Polgar and Jungnickel ( 5 ) . This paper describes a modified procedure which can be used for the determination of a large number of unsaturated compounds including the vinyl ethers which have been largely ipnnred in earlier papers NALYTICAL
Co.,Division of
Union Carbide Corp., Soufh Charleston, W . Va.
REAGENTS
Mercuric acetate, approximately 0.12M solution in anhydrous, reagent grade methanol. Dissolve 40 grams of mercuric acetate (reagent grade) in sufficient methanol to make 1 liter of solution. Stabilize the reagent by the addition of 3 to 8 drops of glacial acetic acid. Filter the reagent before using. When used in the procedure, 50 ml. of the reagent should have a titration of from 1 to 10 ml. of 0.1N potassium hydroxide. Standard potassium hydroxide, 0.1N solution in methanol. Phenolphthalein indicator, 1.0% methanolic solution. Sodium bromide, reagent grade crystals.
sample and the blank to stand in the bath at - 10" C. or lower for 10 minutes. To each flask add 2 to 4 grams of sodium bromide and swirl the contents to effect solution. Add approximately 1 ml. of the phenolphthalein indicator and titrate immediately with standard 0.1N methanolic potassium hydroxide to a pink end point. Do not permit the temperature of the solution to exceed 15' C. during the titration. Because the method is based upon an acidimetric titration, take the usual precautions t o avoid interference from carbon dioxide. Reaction time and temperatures for other compounds are shown in Table 11. DISCUSSION
PROCEDURE FOR VINYL ETHERS
Pipet 50 ml. of the mercuric acetate reagent into each of two 250-ml. glassstoppered Erlenmeyer flasks. If a sealed glass ampoule is specified, use heat-resistant pressure bottles containing a few pieces of 8-mm. glass rod. Cool the contents of the flasks between - 10' and - 15" C. (A bath of chipped ice and methanol can be maintained below -10' C. for more than an hour without difficulty.) Reserve one of the flasks for a blank determination. Into the other flask introduce an amount of sample containing from 3.0 to 4.0 mea. of vinv! ether Allow both the
The vinyl ethers and certain other compounds react n.ith mercuric acetate in methanol to form mercury addition compounds which are unstable a t room temperature. These compounds can be determined quantitatively if the solution temperature is maintained below -10" C. during the reaction and is prevented from esceeding 15" C. during the titration step. Tin!-1 ethyl ether may also be determined by both the Martin (4)and Dns ( 1 ) procedures if these conditions of temperature arr observed. Presumably othtr viny! ethers may also be determined b r . these t w o prucedures if the temoeraturt
~
b
