the solution being titrated is made 12M in chloride ion, the decomposition rate is diminished to 0.3% per minute, but almost no chlorination of benzamide was noticed after 30 minutes. Bromine was also substituted for chlorine, but no ,IT-bromination was noticed in a reasonable time period. The following technique was then developed to eliminate errors due to the slight instability of the chlorinating agent. A direct titration was carried out, but the first experimental point after the end point was taken with only a ilight excess (usually about 25y0) of hypochlorite. The remaining points, which determined the second segment of the titration curve, were then assumed to be constant if the current decreased less than 1 pa. per minute. This procedure can be used successfully for primary aliphatic amides and
for aromatic amides which are not substituted or which are substituted only with alkyl groups. The presence of other functional groups substituted on the aromatic ring in general causes interference in the determination of the amide group. Electron-withdrawing groups such as nitro and carboxyl reduce the rate of N-chlorination, and also adversely affect the equilibrium constant. Electron-donating groups activate the ring so that chlorination of the ring takes place readily, and the exact stoichiometry of the titration reaction becomes uncertain. In addition, substituted groups such as amino, carbonyl, and hydroxy are easily oxidized by hypochlorous acid in the titration medium. Preliminary experiments indicate that a possible solution to this problem of interference by ring substituents is
exhaustive bromination in acid solution. If the unknown sample is treated w-ith bromine, most of the ring sites which would ordinarily be chlorinated during the titration are brominated. Also, easily oxidizable groups are oxidized by the bromine, and the excess bromine can then be driven off by heating. t-nder these conditions bromination on the amide nitrogen does not take place. LITERATURE CITED
( 1 ) Eigen, SI., Kustin, K., J . A m . Chem. SOC.84, 1355 (1962). ( 2 ) Post, W. R., Reynolds, C. A , , AXAL. CHEM.3 6 , 781 (1964).
WILLIAMR. POST CHARLES rl. REYKOLDS
Department of Chemistry I'niversity of Kansas Lawrence. Kan.
Determination of Adsorbed Ethylene and Propylene Oxides by Distillation and Titration SIR: h modified method for determining adsorbed volatile epoxides that is both simple and rapid has been developed. Such epoxides are not directly titrateable, due to very slow elution into the titrating medium and obscure end points. Mechanical preparation of the sample such as grinding or shrrdding does not materially improve this condition; it provides error through loss of the adsorbed volatiles during preparation and does not eliminate the obscure end points. Since hydrogen bromide reacts virtually instantaneously and the elution is of a physical rather t,han a chemical nature, other reactants-as in the method of Jay (3)-likewise do not make direct titration feasible. Methods using excess reactant with back-titration as in the procedures by Schecter, Wynstra, and Kurkjy (4) and Durbetaki (2) are also inadequate because of the prolonged elution and hence reaction time, and the varied interferences found with the different adsorbing materials. Current methods generally elute the epoxide by aeration and bubbling through a reacting solution; such techniques are time consuming and awkward to handle. In this method, adsorbed epoxides are released from the adsorbing material by distillation in monochlorobenzene, (Bollected in a receiving medium, and titrated with a standard hydrogen bromide solution, using crystal violet as a n indicator, as in the method by Ilurhetaki ( I ) . I h a u s e ethylene and propylene oxides are known to be quite reactive, it was anticipated that a reaction between these epoxides and the adsor1 172
ANALYTICAL CHEMISTRY
bents would take place during the distillation. Recovery studies were made by exposing t'he materials to pure ethylene and propylene oxides, weighing the amount adsorbed, and subsequently determining the epoxides by this procedure. Consistently low values were obtained, and the amount of unrecovered epoxide from each adsorbent followed the expected pattern in terms of individual adsorbent reactivity; in all cases, the value was minimal. Blank distillations and t h a t i o n s were conducted on unexposed samples of the same size to determine the reagent and indicator values and to compensate for any volatile reactant originally in the material. A11 such values thus obtained were found to be consistent and minimal for each adsorbent studied.
Table I.
Epoxide Recovery
Adsorbed Unrecovered Recovered, (mg./gram) (mg./gram) 5 Propylene oxide in gum rubber; 2-gram samples 1.8
5.0
9.6 12 8 19 9 22 1
0.0 0.2 0.2 0 2 0 7 O X
100.0 96.1 97.8 98 6 96 7 96 1
Ethylene oxide in gum rubber; 2-gram samples 0.7 1.2 4.8 5.2 16.1
0.1 0.1 0.4 0.6 1.4
87.5 88.0 92.1 89.4 91.2
(11.8)
1 3
88 9
EXPERIMENTAL
Apparatus. The apparatus used were as follows: a 250-ml. roundbottom flask wit'h 24/40 ground joint; a 300-mm. West condenser with 24/40 ground joints; a 75" connecting tube with 24/40 joints; a 105" adapter tube with 24/40 joint; a 75-ml. collecting flask; and a 250-ml. heating mantel with voltage regulator. Procedure. Place a n accurately weighed 2-gram sample of the adsorbent in the distilling flask with 2-3 glass beads and add 100 ml. of monochlorobenzene; apply apiezon "&" wax to the glass joints. Add 15 ml. of glacial acetic acid to the receiving flask, and connect the apparatus with the tip of the condenser adapter tube covered by the glacial acetic acid in the receiving flask. Set the voltage regulator a t 75 volts and distill unt'il one half of the monochlorobenzene has
&gram samples. Propylene oxide in tygon; 2-gram samples 1.4 12.9 14.5 17.0 24.8 39.3 52.3 63.4
0 1 0 2 0 4
100.0 102,7 99.4 100.4 99.4 99.0 101.5 100.4
Propylene oxide in polyethylene: 2-gram samples 1.0 1.1 3.5 3.8
0.0 0.0 0.0 0.0
100.0 100.0 100.0 100.0
distilled over. Smooth, semirapid, and consistent distillation (approximately 20 minutes) is essential. Rinse the adapter tube with 10 ml. of monochlorobenzene and titrate the distillate with the 0.1N hydrogen bromide in glacial acetic acid, using O.lyo crystal violet indicator in glacial acetic acid. Calculations : Milligrams of epoxide recovered per gram of sample material = nil. H l h X K X E.W. - wt. of sample ml. IIEr X N X E.W. wt. of blank sample Refer to calibration graph for total absorbed epoxide. Notes. T h e condenser is air cooled. Glassware must be scrupulously clean and d r y ; d o not use other glass joint lubricants. Glacial acetic acid is used in the receiving flask to prevent obscure end1)oints caused by traces of moisture in the sample. Small amounts of moisture do not otherwise interfere except for increased blank titers. For each different material that is tested for epoxide, it is necessary to determine blank values. Calibration. Several 2-gram samples of the adsorbent in question are exposed to the pure epoxide in a disiccator, for different lengths of time, to adsorb varying quantities of gas and are weighed t o determine the amount of gas adsorbed in each. A minimum of three samples, and pref-
erably five or six, should be run, covering the complete range of the expected epoxide concentration. The amount of epoxide recovered (a blank determination is run on several unexposed samples, and this average value subtracted from the value found on exposed samples is the amount recovered) from each sample by distillation and titration is then plotted against the amount adsorbed as determined by weight. I n subsequent determinations then, the total adsorbed epoxide is found by referring the amount recovered to this calibration graph.
Table II.
mg./gram found; 2-gram samples Polyethylene 0.2 0.2 Rubber
0.2 0.2 0.4 0.3
0.5 (0.9)o (0.9) Vinyl
RESULTS AND DISCUSSION
The unrecovered epoxide is presumed to be due to a reaction between the adsorbed epoxide and the adsorbent during distillation; the reaction product thus formed (unrecovered epoxide in milligram per gram of sample) increases with the epoxide concentration and is dependent on the nature of a given adsorbent. With controlled distillation for a specific period of time, recovery from the different adsorbents was consistent over a wide range of concentration, and with the construction of a calibration graph, is considered to be complete. Relative standard deviations for the determinations of ethylene and propylene oxides in gum rubber are 2.2% and 1.3%, respectively. Deviation in less reactive adsorbents is smaller. The detection limits of ethy-
Blank Determinations (calcd. as ethylene oxide)
a
0.1
0.2
5-gram samples.
lene and propylene oxides are 0.04 mg. and 0.06 mg., respectively. Data are presented in Table I. Table I1 gives the values obtained on conducting blank distillations and titrations. LITERATURE CITED
(1) Durbetaki, A. J., ANAL. CHEM.28,
2000 (1956).
(2) Durbetaki, A. J., Ibid., 30, 2024 fl%W. (3) Jay, R. R., Ibid., 36, 667 (1964). \ - - - - ,
(4)Schecter, L., Wynstra, J., Kurkjy, R. P., Znd. Eng. Chem. 48, 94 (1956).
Deot. of Research Aierican Sterilizer Co. Erie, Pa.
DONA. GUNTHER
N e w Method for Determination of Hydrocarbon-in-Water Solubilities Edward J. Forkas,' Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass.
IN
CONNECTION with a study of the bubble column slurry reactor (0, data on solubility of cyclohexene in water a t room conditions became necessary. No results were found in the literature. Published experimental methods applicable to hydrocarbonwater systems either required complex, expensive equipment or were suitable only for compounds much more soluble than cyclohexene. Against this background, a new method was developed as part of the reactor work. This technique requires only commonly available, inexpensive apparatus and yet is suitable for determination of extremely minute solubilities of hydrocarbons in water. During preparation of this report, the literature was thoroughly rechecked
1 Present address, Esso Research and Engineering Co., Florham Park, N. J.
for solubility methods applicable to gas-liquid and water-hydrocarbon systems. Among the additional references obtained were disclosures (8,
