Tl(I) Occurs in chloride m.dum. Ce(III) and Ce(IV) are well separated, whereas Sn(I1) and W I V ) do not differ much in their R, values. APPLICATION TO ALLOYSTEEL. An attempt has been made to detect and separate different metal ions present in a standard alloy steel (Bureau of Analyzed Samples No. 64a). Standard solution of alloy steel sample was chiomatographed (Table VI) using a solvent system containing TTA, LiCI, and HCI. The constituents Cr, V, W, and Fe could be separated in one hour. Since the spots can be eluted with appro-
priate reagents, separation can be followed by quantitative spectrophotometric determination. This method can be fruitfully utilized for ready column separation, All the chromatographic data (Tables I to VI) seem to indicate higher selectivities which may be due to both ion exchange and partition mechanism of CIESE ( I ) . RECEIVED for review March 9, 1971. Accepted June 1 1 , 1971. The authors thank the Council of Scientific and Industrial Research, New Delhi, for awarding a Junior Research Fellowship to one of the authors (CRB).
Quantitative Determination of Olefinic Unsaturation by Measurement of Ozone Absorption Martino M. Smits and Dirk Hoefman KoninkIijkelShell-Laboratorium,Amsterdam (Shell Research N . V.), The Netherlands MANYANALYTICAL TECHNIQUES exist for the determination of olefinic unsaturation. Most chemical methods used for this purpose are based on addition reactions to the double bond. An attractive titrimetric reagent for olefins is ozone, although of course many others are available. Ozone attack on ethylenic bonds is fast and fairly selective; no substitution takes place. In ozonolysis, the double bond is cleaved and fragments are formed of different nature, depending on the reaction conditions. As one mole of ozone adds quantitatively to one equivalent of double bond, the olefin content of a given sample can be calculated directly from the ozone consumption. Several analytical methods, varying in experimental details, are based on ozonization ( I , 2). The present paper describes a modification which is claimed to have advantages in speed and convenience over the other methods. As will be shown by the results, it is accurate and widely applicable. The procedure is as follows. A mixture of oxygen and ozone of constant composition is passed at constant flow rate through the sample solution, to which a colored indicator has been added. Immediately after the ozone has converted the olefins present, the color of the indicator changes, marking the end point of the analysis. The olefin content of the sample is then calculated by comparing the reaction time with that required by a calibration standard compound. The flow rate is controlled by a precision valve and a rotameter. Ozone is supplied by a commercial “dry” ozone generator, which has a very constant output. A potential source of error is the end-point detection. Visual observation of the fading of the indicator is subjective and, in colored samples, often difficult. Besides, it requires very close attention from the analyst. For this reason, we now use a photometric device with recorder. The reaction vessel is placed between a light source and a photocell. The absorption of the solution drops rapidly during discoloration of the indicator, resulting in a change in resistance of the photocell, which is recorded continuously. With the curve thus ob( 1 ) H. Boer and E. C. Kooyman, A d . Chim.Acta, 5, 550 (1951). (2) K. F. Guenther, G . Sosnovsky. and R . Brunier, ANAL.CHEM., 36, 2508 (1964). 1688
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Figure 1. Assembly of apparatus for ozonolysis tained, the time required for the ozonolysis can be defined accurately. EXPERIMENTAL
Apparatus. The ozonolysis equipment is assembled as shown in Figure 1 and consists of the following parts: (a) A high-pressure flow regulator (Brooks Instrument Division, Emerson Electric Co., Hatfield, Pa. 19440). (b) The ozone generator with built-in rotameter(c). A suitable instrument is that manufactured by “Fischer Labortechnik” (53 BonnBad Godesberg, Heerstrasse 35-37, Germany). On the front panel a calibration curve is sketched, giving ozone output in grams per hour rs. oxygen flow in liters per hour. As ozone is highly toxic and may cause severe irritation of the respiratory tract and the eyes, the instrument should be placed under a well-ventilated fume hood. (4 The reaction vessel, consisting of two parts connected by ground-glass joints held in position by springs. ( e ) The stirrer, bell-shaped in order to ensure thorough mixing of gas and liquid. It rotates at approximately 1200 rpm. Figure 2 shows the photometric circuit. Light source El and light-dependent resistor (LDR) R1both belong to a photoelectric relay (N.V. Instrumentenfabriek H. M. Smitt, Mid-
NO. 9, A U G U S T 1972
R2 1K
5v 3v
R3
47C K 1% HS
c;:
I t
35v
‘ I
1
I I
u
6V02A
Figure 2. Photodetector for titration
a b8.
\
1
1
I
I
I
0
60
120
180
240
L \
TIME, sec
\ Figure 3. End-point determination in ozonolysis
dellaan 3-5, Bilthoven, the Netherlands). Before entering the reaction vessel, the light beam passes through a n interference filter, which has its maximum transmission in the same region where the indicator solution shows maximum absorbance, Le., a t about 550 nm. Care has to be taken that the light path is not interrupted by the stirrer. Reagents. The indicator is Rouge Organol B.S. from “Cie FranGaise des Matikres Colorantes” (1 5 Boulevard de 1’Amiral-Bruix, Paris (16“), France). It is used as a 0.1% by weight solution in chloroform. Procedure. The ozone generator is allowed to stabilize for 30 minutes before the determination is carried out. The gas escapes via valve f into the hood. An amount of sample containing 1-2 meq of olefins is weighed into reaction vessel d and diluted with 40 ml of chloroform. One milliliter of the indicator solution is added. The reaction vessel is connected to the apparatus via joint g and the stirrer is started. The ozone is introduced into the reaction mixture via valve f, and at the same time the recorder is started. The ozonization is continued until the color of the indicator fades, which means that all olefins present have been converted. On the recorder chart the J-shaped curve levels off, as shown in Figure 3. The ozone supply can now be shut off by turning valvef. The same procedure is applied to a solution of a pure olefin. e.g., n-hexadecene-1, serving as a calibration standard. Blank determinations are made in the same way with pure chloroform, omitting the olefin sample. The time required for the ozonization of 1 mmole of hexadecene should be of the order of ten minutes. This can be achieved by adjusting the flow rate and ozone concentration of the oxygen stream. For each determination the end point of the reaction is defined, as illustrated in Figure 3. The distance r from the start t o the deflection point, corresponding with the reaction time, is measured.
Table I. Ozonometric Determination of Unsaturation of Olefins Ozone numberb Intake Mean Oletinu in grams Found Theory value 3-Heptene 0.1663 10.195 10.20 10.25 0.1827 10.299 0.1975 10.252 0.1733 1-Octene 8.88 8.93 8.909 0.2029 8.884 0.2423 8.835 2-Me-2-heptene 0.1462 8.93 9.29 9.146 0.2168 9.316 0.2472 9.418 0.1355 8.93 8.98 8.969 0.2128 8.954 0.2389 9.019 0.1496 8.68 8.93 8.674 0.2098 8.675 0.2380 8.688 J-Me-l,3-pentadiene 0.0681 25.4 24.4= 25.74 0.0686 25.06 1,3-Cyclohexadiene 0.0710 26.7 25. o c 27.63 0.0790 25.81 2,5-di-Me-2,40.0717 18.2c 18.3 18.31 hexadiene 0.0723 18.20 Di(cyc1opentadiene) 0,0925 15.3d 15.6 15.84 0.0951 15.39 10.2 Hex-iraw2-enal 10.26 All the oiefins tested are commercially available. Purity, as determined by GLC, >99%. * Milligram equivalent of ozone absorbed per gram of olefin. Calculated ior two double bonds per molecule. Per molecule of dimer two double bonds are left. ’/
Table 11. Ozonometric Determination of Unsaturation in Olefinic Samples Ozone number. Intake Mean CalcuSample in grams Found value lated ri-Eicoseneb 0.3730 3.55 3.58 3.57 0.4763 3.61 Propylene tetramer 0.0742 5.94 5.95 5.9Y 0.0773 5.97 0.1537 5.98 0.1556 5.91 0.2239 6.01 0.2318 5.88 Allyl chloride in I 0.3630 4.26 4.24 4.25d chlorobenzene 0.5053 4.19 0.5306 4.29 11 0.2025 6.00 5.91 5.87d 0.3265 5.89 0.4051 5.83 Milligram equivalent of ozone absorbed per gram of sample. * Mixture of double-bond isomers. Calculated for one double bond per molecule of tetramer. Determined by UV: between 5.95 and 6.00 meq/g. Samples prepared by mixing weighed quantities of components.
With these data, the olefin content of the sample can be calculated as follows: 0 3
supply
=
w,1000 (1,
-
1,)
E,
mmol/sec
where r is the measured reaction time, W the sample weight
in grams, and the subscripts s, c, and o refer to sample, calibration standard, and blank determination, respectively. E, is the equivalent weight of the calibration standard.
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Table 111. Ozonization of Non-Olefinic Compounds Compound Ozone number” 1000/Mb Cyclohexane
