Determination of 2,3=Dihydropyran by Bromination RICHARD L. MCCULLOUGHl AND K. G. STONE Kedzie Chemical Laboratory, Michigan State College, East Lansing, Mich.
H E addition of alcohols to 2,3-dihydropyran has recently been T reported (4, 9). I n order to develop a quantitative method for alcohol determination, some method for estimating 2,38,
dihydropyran was needed. A survey of the literature showed that bromination might be the most satisfactory, as the hydroxylamine hydrochloride method for vinyl ethers ( 7 ) would determine not only unreacted 2,3-dihydropyran, but also the alcohol addition compound. The bromination of 2,3-dihydropyran has been studied on a preparative scale (5, 6, 9); reactions Ia, Ib, 11, and 111 occur and must be recognized as contributing to some extent to the quantitative nature of the bromination.
Hz C
A-H
H&
Hz O
C-Br
HzC
C-Br
I
+Brz
\o'
Ib
I1
I
HzC
C-H
Sample,
G.
'O/
J.
Brz
I11
0.1198
Br
0.1158
Table I. Bromination of 2,3-Dihydropyran i n Solvents Other than Benzene Reagent, 0.1N Brz in CCla CHaCOOH CHICOOH Aq. KBrb Aq. KBrb
TI-eight of Sample,
G.
0.0725-0.1774 0.0589-0.1461 0.1108-O. 1739 0.1135-0.1571 0.0760-0.1364
% Recoverv 78:48-87.92 78.32-87.15 91.90-108.0" 39.98-79.91C 49.35-108. l d
s o . of
0.1472
Detn. 6 6
'169
d Time, excess.Brz, and temperature all very critical.
Preliminary experiments showed that the solvent was very important. Experiments using carbon tetrachloride, acetic acid, dioxane, and diethyl ether as the Eolvent and a solution of bromine in the solvent as the reagent all gave variable and inconsistent results. The presence of water with the acetic acid and dioxane improved the results. From further experiments using tn o-phase systems with agitation it was found that a mixture of benzene and aqueous potaseium bromate-bromide mixture with a small amount of hydrochloric acid to release free bromine and niercuric chloride as a bromination catalyst (1, 3) gave consistent, reproducible results.
0.1481
1.1481
EXPERIMENTAL
The solvents used in all the experiments-carbon tetrachloride, diethyl ether, acetic acid, benzene, and dioxane-were purified 1
0.9558 0.8360 0.9753
Av. 94.70 94.70 94.67 Av. 94.69
YES
1.0885 1.0596 1.0706
1.0267 1.0046 1.0144
Yes
1.1207 1.0338 1.0170 1.0638
1.0584 0.9787 0.9582 1,0022
94.32 94.81 94.75 Av. 94.63 94.44 94.57 94.21 94.21 4 v . 94.36
I1
0.1198
(CmHdrO
Distilled from Na
x
J.
H2 C
CCla CHaCOOH 1:l CHaCOOH-H20 Dioxane-HzO
Recovery,
G.
%
No
~
?h
Solvent
Recovered,
Table 111. Variables i n Bromination of 2,3-Dihydropyran i n Benzene-Water Mixtures
C-OH
\O/
Sample, G. 1.0093 0.8828 1.0302
2
I
H
/ \/ H& C-H I I H9C
Lot 1
H
HzC
'O/
J. gP
Table 11. Determination of 2,3-Dihydropyran by Oximation
/-\/
Ia
I
and dried by the usual procedures (g). The 2,3-dihydropyran used was distilled to remove nonvolatile .substances and then refluxed over metallic sodium and redistilled. The purity of the distilled 2,3-dihydropyran was determined by the method mentioned by Siggia ( 7 ) for the estimation of vinyl ethers using hydroxylamine hydrochloride.
Present address, Hooker Electrochemical Co., Niagara Falls, N. Y .
1206
0.2 M Time, HgCh, Recovery Lhn. LIl. G. 0'3' Stability of 2,3-Dihydropyran in Moist CsH6 5 20 0.1109 100 0.1110 0.1109 0.1110 0,1111 0.1108 0.1109 0.1111 Reproducibility of Bromination 5 20 0,1121 93.57 100 93.57 0.1121 93.49 0.1120 93.49 0.1120 93.49 0.1120 0.1083 93.52 0.1084 93.61 93.61 0.1084 Effect of Mercuric Chloride 0.1399 5 0 100 0.1394 0.1389 0.1399 0.1391 0.1402 1 0.1397 94.87 0.1392 94.59 5 0.1381 93.82 0.1379 93.68 0.1378 93.64 20 0.1377 93.57 0.1380 93.78 33 0.1380 93.78 0.1376 93.47 0.1377 93.57 0.1378 93.64 Effect of Excess Bromine 5 20 62 62 62 116 116 170 170 Effect of Time of Bromination 0.1386 93.60 2 100 2o 0.1386 93.60 0,1386 93.60 5 0.1388 93.70 0.1387 93.63
Excess Brz,
%
....
Kept, Hours 1
8
24 48
V O L U M E 2 4 , NO. 7, J U L Y 1 9 5 2
1207
The procedure in the preliminary experiments was to place 25 ml. of solvent in a 250-ml. iodine flask, add the sample of 2,3dihydropyran weighed in a glass ampoule, add from a pipet a 25ml. portion of the 0.1 Y bromine solution in the solvent, stopper the flask, and break the ampoule. After standing 10 miuutes 2 grams of potassium iodide dissolved in 25 ml. of water were added, and the solution was titrated with standard 0.1 N sodium thiosulfate solution to a starch end point. The difference between the volumes consumed by a blank and the sample is equal to the bromine taken up by the 2,3-dihydropyran. The heterogeneous bromination of 2,3-dihydropyran in the benzene-water mixture required a different procedure to minimize hydration of the double bond. Known solutions of 2,3-dihydropyran were prepared by weighing about 1.5 grams in a glass ampoule, breaking the ampoule under benzene in a 250-ml. volumetric flask, and making to the mark with benzene. I n all cases the displacement by the glass of the ampoule was less than 0.2 ml. The general procedure followed n a s to pipet a 25-ml. portion of the benzene solution into a 250-ml. iodine flask, freeze the benzene using an ice-salt bath in order to minimize hydration, and add 20 ml. of 0.2 ;If mercuric chloride solution, 4 ml. of 6 S hydrochloric acid, and a 100% excess of 0.25 potassium bromate-bromide solution, which must be standardized using potassium iodide and standard sodium thiosulfate solution. The flask was stoppered and placed on a mechanical shaker for 5 minutes. Two grams of potassium iodide dissolved in 10 ml. of water were added, and the solution was titrated with standard 0.1 Ar sodium thiosulfate solution to a starch end point with agitation to extract the iodine from the benzene layer. The difference between the milliequivalents of bromate put in and thiosulfate consumed multiplied by 0.04206 gives the grams of 2,3-dihydropyran found. RESULTS
A summary of the results using solvents other than benzene is given in Table I. It is clear that the conditions for bromination of 2,3-dihydropyran must be carefully controlled. The determination of 2,3-dihydropyran by hydrolysis and oxime formation is summarized in Table 11. All the determinations in benzene were done on material from lot 2.
The variables investigated for bromination in the benzenewater system were the stability of 2,3-dihydropyran in benzene that had not been dried, the reproducibility of the bromination, the amount of mercuric chloride needed as a catalyst, the effect of the excess bromine, and the effect of time. The study of the variables summarized in Table I11 shows that the optimum bromination conditions were 100% excess of bromine, more than 5 nil. of 0.2 Aif mercuric chloride as catalyst, and 2 to 5 minutes reaction time. Because the determinations by bromination are somewhat lower than those by the oximation method, some carbonyl impurity might be expected in the 2,3-dihydropyran, or incomplete bromination could be responsible. However, as the oximation method may be in error as much as 1% ( 7 ) ,the discrepancy is not serious. ACKNOWLEDGMENT
The authors wish to thank E. I. du Pont de Nemours and Co. for the generous supply of 2,3-dihydropyran which made this work possible. LITERATURE CITED
(1) Braae, Ben, ANAL.CHEM.,21, 1461-5 (1949). (2) Fieser, L. F., "Experiments in Organic Chemistry," 2nd ed., New
York. D. C. Heath and Co.. 1941. (3) Lucas, H. J., and Pressman, D., IND. ENQ.CHEM.,ANAL.ED., 10, 140-2 (1938). (4) Parham, 1%'. E., and-hderson,E. G., J . Am. Chem. Soc., 70,41879 (1948). (5) Paul, R., Bull. SOC. chim., (5) 1, 971-80 (1934). (6) Ibid., pp. 1397-1405. (7) Siggia, S., "Quantitative Organic Analysis Via Functional Groups," pp. 6 3 4 , New York, John Wiley & Sons, 1949. (8) Woods, G. F., and Kramer, D. N., J . Am. Chem. SOC.,69, 2246 (1947). (9) Koods, G. F., and Sanders, H., Ibid., 68, 2483-5 (1946). I
~~
RECEIVED for review March 4, 1962. Accepted April 8, 1962. Presented before the Division of Analytical Chemistry a t the 121st Meeting of the SOCIETY, Buffalo, Ii. Y . Abstracted from the thesis of AMERICAW CHEMICAL Richard L. McCullough for the master of science degree, December 1950.
Modification of Millin's Rapid Method for Determining Carbon and Hydrogen in Organic Compounds S. S. ISRAELSTAAI Department of Chemistry and Chemical Engineering, Unisersity of the Witwatersrand, Johannesburg, South Africa
ILLIN ( 4 ) showed that the time taken to determine the perM centage of carbon and hydrogen in a 250-mg. sample of coal could be shortened considerably (from about 3 hours t o less than 0.5 hour) by employing oxygen and air as the gaseous vehicle at a speed of 250 ml. per minute and by maintaining the temperature of a 45-cm. length of cupric oxide a t about 825 C., and a 22-cm. length of lead chromate a t 650" C. He recommended that a heated section a t the outlet end of the combustion tube containing a roll of copper, silver, or aluminum should be used to decompose oxides of nitrogen given off during the combustion of nitrogenous compounds such as p-nitrotoluene or p-toluenesulfonamide. The author of this paper, who was an interested observer of this work, was encouraged by Millin to modify the method particularly for organic compounds. The modified method was taught to advanced students over a period of 10 years; the results given in Table I, were obtained by them after a few days' tuition. Furthermore, the method gave good results for liquids such as diethyl ether, toluene, and nitromethane. Millin's method was modified in the following ways: The same scavenging train was used to purify both the air and the oxygen.
A White-Wright flowmeter ( 6 ) was included to measure the rate of flow of eases. The weight-of sample taken was reduced to about 100 mg. p i t h a consequential change in the procedure. S o special provision was made to eliminate oxides of nitrogen. For compounds containing halogen, sections of silver were introduced between the boat and the cupric oxide and between the latter and the lead chromate section. APPARATUS
The combustion tube (Figure l),15-mm. bore and 120 cm. in length, was of a good quality glass having a softening point not below 850" C. For this purpose a Jena Supremax combustion tube was used. The tube filling consisted of a 22.5-em. section of lead chromate and a 45-cm. section of previously ignited copper oxide in the form of wire or gauze. The combustion tube was heated by three resistance-wound tube furnaces, each having a diameter of about 3.8 em. Furnace F , 45 ern in length for the cupric oxide section, was wound t o give a temperature of 800' t o 825' C., furnace G, 22.5 cm. in length for the lead chromate section, was wound to give a temperature of 550" to 650" C. and the movable furnace, E, 15 em. in length, used for heating the boat, was wound so that a temperature range between 400" to 850" C. could be obtained. I n each case, an additional external resistance was included for each furnace by means of three variable autotransformers. A small
