1025
DECEMBER 1947 script, and made some valuable comments. They appreciate the assistance of John W. Copenhaver, who contributed valuable information that aided in the initiation of the problem. The authors also wish to thank Richard S. Towne and Mrs. Fred Maisch, who purified and distilled the aldehydes used to test the procedure. LITERATURE CITED
(1) Adams, E. W., and Adkins, H., J A m . Chem. SOC.,47, 135s-67
(1925).
(2) D’&ilelio,G. F., “Laboratory Manual of Plastics and Synthetic Resins,” p. 112, New York, John Wiley & Sons, 1943. (3) Feinberg, B. G., Am. Chem. J . , 49, 87-118 (1913). (4) Parkinson, A , , and Wagner, E., IKD. ESG.CHEX.,-4x.a~.ED.,6 ,
433-8 (1934).
M.,Monatsh., 21, 1079 (1900). Romeo, G.. and D’Amico. E.. Ann. chim. applicala, 15, 320-30 (1925). ( 7 ) Seyewetz and Bardin, Bull. SOC. chim., [3],33, 1000-2 (1905). ( 8 ) Seyewete and Gibello, Ibid., 131, 31, 691 (1904).
(j)Ripper,
(6)
RECEIVED January 1 , 1947.
Determination of Vinyl Ethers and Acetals And of Any Alcohol, Acetaldehyde, and Water Contained Therein SIDNEY SIGGI4, General Aniline 6;. Film Corporation, Central Research Laboratory, Easton, Pa. This procedure provides a means for quantitatively determining vinyl ethers and acetals and makes possible determination of acetaldehyde, alcohols, and water contained in the ether and acetal samples from the synthesis, or hydrolysis, of some of the vinyl ether or acetal. The acetals and vinyl ethers are determined by acid hydrolysis to acetaldehyde and determination of the acetaldehyde formed by the sodium sulfitesulfuric acid method. 30 distillation of acetaldehyde is necessary. Where vinyl ether and acetal are present in the same sample, t h e sample is hydrolyzed and total acetaldehyde determined. Then the sample is hydrogenated to reniove the vinyl ether as a n interference, and this hydrogenated sample is hydrolyzed. This yields
C
OhlMERCIAL vinyl ethers may contain alcohol, acetal-
dehyde, water, and acetal. Alcohol may come from the original reactants in the synthesis of the ether or may be formed by hydrolysis of ether. Acetaldehyde originates by hydrolysis of thc vinyl ether. .%cetals are a product of a side reaction in the vinyl ethcr synthesis, and water enters the system in the n-ashing process and sometimes with the alcohol. The procedure developed for assaying vinyl ethers is also adaptable for assaying acetals. Since acetal syntheses involve alcohols, acetaldehydes, and water, as do the vinyl ethers, the procedures used to determine these impurities in vinyl ethers were applied and found to work as w l l in the case of acetals. The scheme of analysis presented belon- makes possible the determination of acetaldehyde, alcohol, and n-ater in the presence of either, or both, vinyl ether and acetal. I t also makes possible t,he dctermination of vinyl ethers and acetals in the presence of both the above-mentioned impurities and of each other. There has been verv little done in the way of analytical procedures for vinyl ethers. Ruigh ( 7 ) attempted to determine divinyl ether in blood via hydrolysis to acetaldehyde. However, he encountered difficulty and had to resort to a more complicated method involving iodine pentoside. Attempts were made to determine vinyl ethers by quantitative hydrogenation, bromination, and titration with Karl Fiacher’s reagent. The hydrogenation method requires a long time to run an analysis and the reproducibility is poor. The reproducibility is poor also in the case of the Karl Fischer reagent. , Bromination yielded no comprehensive results. \Iore work ljas bccn done in acetal determination than in the
.
acetaldehyde from the acetal onlj Subtracting this value from the total acetaldehyde >ields acetaldehyde from the vinyl ether. Free acetaldehjde is determined by extracting the sample with sodium sulfite-sulfuric acid and titrating the excess acid. The vinyl ether and acetal values are corrected for free aldehyde in t h e sample. 4cetylation of the samples and determination of acetic a n h j dride consumed yield the amount of alcohol present. Water is determined by the Karl Fischer reagent. For pure vinjl ethers and pure acetals the method jields results good to *0.370, When samples contain one or more of the components mentioned above, the errors hare to be determined by accumulatiie error methods.
case of vinyl ethers. Many of the analytical methods are connected n i t h measurement of hydroljsis rates of acetals and are unsuitable for absolute acetal determination, since the measurements are of a relative nature. They are perfectly adaptable for determining rate of hydrolysis but cannot readily be used t o determine absolute amounts of acetal. Among such methods are those of Palomaa and Salonen ( 4 ) and of Tong and Olson ( I I ) , who followd the rate of hydrolysis of acetals via dilatometer measurements. There have been methods for acetals where the acetal was hydrolyzed and the acetaldehyde determined. The drawbacks in these procedures are due, in most cases, to the shortcomings of the acetaldehyde procedure used (9). Many of the procedures distill the acetaldehyde over into the medium in which it is to be determined. This step not only greatly increases the time required for an analysis but also can be a source of error. Peynaud ( 5 ) determined acetal by distilling acetaldehyde over into a potassium dihydrogen phosphate-disodium phosphate buffer containing sodium bisulfite and determined aldehyde by the iodometric measurement of excess bisulfite. This method has the disadvantage of the distillation, and the iodometric bisulfite method for aldehyde determination also has shortcomings (9). Orton and McKie (3) hydrolyzed and distilled acetaldehyde into sodium bisulfite using the Ripper (6) method for determining excess bisulfite iodometrically. They also used the Seyeweta and Bardin procedure (8) which determines increase in alkalinity of a sodium sulfite solution as acetaldehyde. Here again the distillation and weaknesses of the acetaldehyde procedures (9) limit the desirability of using this procedure.
V O L U M E 19, NO. 1 2
1026
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Hahnel and Lennerstrand (1) avoided the distillation and used a hydroxylamine method to determine acetaldehyde. The end points are admittedly bad, and dilutions to volume and color comparisons are necessary to obtain the end point. They also used iodometric-bisulfite procedures but realized the instability of the solution and the need for daily standardization. The procedure for determining vinyl ethers and acetals as described below requires only 30 minutes to run. Since all the reactions are run in the same closed vessel, there is less danger of loss by volatilization of acetaldehyde. Thereagents used are stable, and there are no end-point or equilibrium difficulties to harass the operator. There is no need for distilling the acetaldehyde to determine i t ; the acetaldehyde is determined in the hydrolysis reaction mixture. The procedure is accurate and precise to t0.37,. Figure 1. ApparatusforDeThe alcohol procedure used is that determination scribed by Ogg, Porter, and Killits (2). A ofvinyl Ethers pretreatment (hydrogenation) of the sample and Acetal is necessary in the case of the vinyl ethers, where water is also Dresent. before the alcohol procedure can be applied. N o pretreatment is necessary for determining alcohols in acetals. Hydrogenation of the sample is also necessary in the case of water determination. The procedure used is that described by Smith, Bryant, and Mitchell ( f O ) , cinploying Karl Fischer’s reagent. APPARATUS
For vinyl ether and acetal determination, the apparatus is as shown in Figure 1. The top portion, A , consists of a 500-ml. Erlenmeyer flask with a 29/26 standard-taper ground-glass female joint blom-n onto the bottom with glass stoppers to fit. To the mouth of the flask is attached a 6-mm. stopcock, and onto the stopcock is put a 29/26 standard-taper ground-glass male joint . The bottom portion of the apparatus, B, is a 500-ml. Erlenmeyer flask with a 29/26 standard-taper female joint sealed onto the mouth. I n determining the acetaldehyde, only the bottom portion of the apparatus is necessary. Alcohol determination requires 150- to 200-ml. Pyrex shortnecked Florence flasks equipped with ground joints to fit condensers. This enables the sample to be refluxed with the reagents and permits titration in the reaction flask without transfer. The hydrogenation apparatus is of simple construction (Figure 2). The hydrogenation vessel consists of a 250-ml. wash bottle equipped with ground joints for use with organic liquids. To its exit arm is attached a 2-way stopcock. The blowing arm is cut short, and a ground-glass female joint is attached t o accommodate the 25.4-cm. (10-inch) condenser. The bubble tower is used to control pressure during the hydrogenation. The height of mercury in the tower keeps the pressure in the apparatus conitant as excess hydrogen bubbles through the mercury. Increased pressure increases speed of hydrogenation. However, too much pressure is undesirable, since it opens the ground-glass joints. The apparatus can be modified to enable hydrogenation of four samples at one time, by lengthening the tube from the pressure control tower to the reaction section. Four separate reaction sections can then be led off this tube, all controlled by the same pressure. A stopcock between the condenser of each reaction section and the manifold should be included, so that the system ran be used for less than four hydrogenations if necessary. From 25 to 30 cm. of mercury were found suitable for rapid hirdrogenation tvithout causing the glass joints to open. A magnetic stirrer is used for agitation. A magnet attached to the shaft of a stirring motor acting on an iron paddle in the hydrogenation vessel provided agitation during the hydrogenation.
In the water determination, an automatic refilling buret is desirable, so that the Karl Fischer reagent has minimum contact with air. REAGENTS
Vinyl Ether, Acetals, and Acetaldehyde require standard 1 *\- sulfuric acid, standard 1 S sodium hydroxide, and 1 sodium sulfite. Alcohol requires a solution of 1 part of C.P. acetic anhydride to 3 parts of C.P. pyridine as the acetylating mixture. This solution should be prepared fresh each day. The indicator used in this analysis is a mixture of 1 part of 0.1% cresol red and 3 parts of 0.1% thymol blue (a few drops of sodium hydroxide solution are necessary to get dyes into solution). C.P. n-butyl alcohol is used as a imsh liquid. Water. The Karl Fischer reagent used is as prepared by Smith, Bryant, and Mitchell (10)-84.7 grams of iodine in a mixture of 269 ml. of C.P. pyridine and 667 ml. of C.P. methanol. The solution is cooled in ice water, and 64 grams of sulfur dioxide are added. PROCEDURE
A. Acetaldehyde. A measured sample (which should be hydrogenated if vinyl ether is present,) containing not more than 0.01 mole of acetaldehyde, is introduced into a 500-ml. glassstoppered Erlenmeyer flask containing 250 ml. of 1 M sodium sulfite solut,ion and 10 ml. of standard 1 -V sulfuric acid. The pH of the sodium sulfite-sulfuric acid solution is about 8.0, and no significant amount of acetal is hydrolyzed a t this pH. The mixture is vigorously shaken for 15 minutes to ensure extraction of all the acetaldehyde from the sample. The contents of the flask are then quantitatively transferred to a 600-ml. beaker. Electrodes from a p H meter are inserted in the solution, and the solution, while being mechanically stirred, is titrated with standard 1 N sodium hydroxide. For accurate results, a curve is plotted of pH us. milliliters of sodium hydroxide added, and the end point is determined exactly (9). For more rapid though slightly less accurate work the solut,ion can be titrated to a definite pH (pH at the end point as determined by experiment). The end point can be taken at pH 9.1 for acetaldehyde. The sodium sulfite contains some free alkali which will cause high result,sunless neutralized with sodium bisulfite (9). A qualitative test, the standard Tollens test for aldehydes, can be made on the sample. If negative, a quantitative aldehyde analysis is unnecessary. Samples containing vinyl ether do not have to be hydrogenated for this test. If a silver mirror forms,
Figure 2. Hydrogenation Apparatus
DECEMBER 1947 enough aldehyde is present to be determined quantitatively. Hon ever, if no mirror is formed after the shaking, or if only a very slight mirror is formed on the flask at the liquid surface, the amount of aldehvde present is too small to be determined quantitatively.
B. Vinyl Ethers and Acetals. A sample of 0.02'to 0.04 mole of ether or acetal is weighed in a sealed thin-walled ampoule and is introduced into section A of the apparatus shown in Figure 1 along with 50 ml. of standard 1 S sulfuric acid. Glass beads are included t o aid in breaking the ampoule. The apparatus is stoppered, the stopper being well greased to prevent any leakage of acetaldehyde, a n d i s totally immersed in an ice-water mixture for 5 minutes. The chilling is to create a decreased pressure in the flask by contracting the air above the liquid. The temperaturt of the solutions in the flask will drop to 10" to 15" C., about 8 below the boiling point of acetaldehyde. \T7hen the ampoule is broken, there will not be too great a pressure in the flask; if the flask is not chilled, the stoppers sometimes are forced open. In the case of methyl vinyl ether (boiling point 5-6" C.), the flask should be chilled thoroughly (20 minutes). The low boiling point of this ether causes the stoppers to blow as soon as the ampoule is broken. The stopper should be held firmly until the ether is hydrolyzed to prevent blowing out. After the flask is chilled, it is vigorously shaken to break the ampoule containing the sample, then for 15 minutes more to ensure complete hydrolysis of the sample. For most acetals and vinyl ethers, 15 minutes' shaking is sufficient, but for some-for example, di-n-butyl acetal-30 minutes are necessary to ensure complete hydrolysis. A Kahn shaker was used, in which the stopper is clamped on the flask while shaking is in progress. After hydrolysis is complete, A , containing the hydrolyzed sample, is attached to B , which contains 250 ml. of 1 M sodiuq sulfite. The joint connecting the two sections should be greased to prevent loss of acetaldehyde. Then the stopcock in A is opened, and the acid solution containing the aldehyde is shaken down into the sulfite solution. The acid and sulfite form bisulfite which consumes the acetaldehyde. After all the acid solution is down in B, some of the solution from B is shaken back into A to react with the acetaldehyde contained on the walls and on the glass beads. The whole ap aratus is vigorously shaken for a few minutes to assure removaf of all acetaldehyde from the atmosphere in both sections of the apparatus. The sections of the apparatus are then separated and rinsed quantitatively into an 800- or 1000-ml. beaker, and the solution is titrated with standard 1 Ar sodium hydroxide, using a pH meter as in the acetaldehyde determination. Plotting pH us. milliliters of sodium hydroxide is the most accurate method of determining the end point. However, this titration is large, and titrating to pH 9.1 incurs no very significant error. Any free aldehyde in the sample is determined and the value subtracted from the figures for vinyl ether or acetal.
If the sample contains aldehyde, vinyl ether, and acetal, the above procedure will yield a combined value for all three. The free aldehyde is dctermined separately, as described, and subtracted from the total aldehyde. The difference is the combined acetaldehyde from both the vinyl ether and the acetal. The procedure is repeated on a hydrogenated sample where the vinyl ether in the sample is saturated and no longer yields any acetaldehyde. The procedure on the hydrogenated sample will yield the acetaldehyde from the acetal (
