reduced, 18 equivalents are required. For 1,3,5triazido-2,4,6-trinitrobenzene the value of 19.62 indicates partial reduction of the azide groups. Although the end products have not been identified, reproducible results may be obtained with this method for the determination of nitro groups in gemdinitro and in trinitro compounds on the basis of the following assumptions: R-C( NOl)*-R R-C(NOJ1
+ 6e + 12e
+
R-C( NOz)- R
I
"9 +
R-C(NH2)*
1
NO2 R
R
If these values are used for the number of equivalents of titanium(II1) ,onsumed per mole of nitro compound, this method is suitable for the assay of such compounds. The reason why all of the nitro groups are not reduced is under investigation. Since the transition from nonexplosive to explosive compound often occurs when the third nitro group is introduced into a compound, impact sensitivity
Table V.
Impact Sensitivity of Compounds
Compound 2,2-Dinitropropane 4,bDinitropentanoic acid
Height, Mm. Failed at 600 Failed a t mn
Trinitromethane
LITERATURE CITED
"V"
2,2,2-Trinitroethanol
2,4,6-Trinitromesitylene 1,3,5-Triazido-2,4,6trinitr+
benzene Reference compounds for apparatus Nitroglycerin Tetryl Trinitrotoluene 5-kg. weight used for all tests.
600
300 100
100
250 600
in a steel cup, self-heating of the sample began a t about 85" C. and a t approximately 125" C. the compound -underwent a violent detonation, destroying the steel container and shearing off the connecting thermocouples. For safe storage this compound should be kept covered with water.
+
(1) Becker, W. W., Shaefer, W. E., "Determination of Nitro, Nitroso, and
Nitrate Groups,') in "Organic Analysis," Vol. 11, pp. 73-7, Interscience, New York, 1954. (2) Davis, T. L., "Chemistry of Powder and Explosives," pp. 436-8, Wiley, New York 1956. (3) Ficheroulle, H., Gay-Lussac, A,, M h . poudres 34,55 (1952). (4) Ibid., p. 121. (5) Ko!thoff, I. M., Belcher, R., "Volumetric Analysis," Vol. 111, pp. 610-19, Interscience. New York. 1957. (6) Maram, N.S., ZelinsG, R. P., J . Am. 72, 5329 (lg50). (7) Military Standard MIL-STD-286, Method 601.1, J~~~28, 1956. (8) Pieraon, R. H., Gantz, E. C., ANAL. CHEM.26,1809 (1954).
tests were run on all six compounds (Table V). Trinitromethane, although not shock-sensitive, has been known to undergo spontaneous detonation when stored in the solid state. For the other three compounds the order of increasing ( g ~ ' c o " m o , " ~ ~ 2 1 " d s , H ~ ~ ~ c ~ sensitivity to detonation by impact is N~~ Yo&, 1951. 2,2,2-trinitroethanol, 2,4,6-trinitromesit(10) Schechter, H., Zeldin, L., J . Am. ylene, 1,3,5-triazido-2,4,6-trinitrobenChem. SOC.73, 1276 (1951). when Go mg* Of the azido cornRECEIVED for review December 19, 1960. pound were heated a t 2" C.per minute Accepted April 5, 1961.
Use of Differential Reaction Rates to Analyze Mixtures of Organic Materials Containing the Same Functional Group Application to Mixtures of Alcohols Including Mixtures of Isomeric Primary and Secondary Alcohols and to Mixtures of Aldehydes and Ketones SIDNEY SlGGlA and J. GORDON HANNA Olin Mathieson Chemical Corp., 275 Winchester Ave., New Haven 4, Conn.
b Many reactions involved in organic analysis via the functional groups are second-order reactions. Proper choice of reaction conditions and plots of reaction rate data in the standard linear plot for second-order reactions makes possible analysis of mixtures of organic materials containing the same functional group. The linear secondorder plot contains a straight-line portion for each component in the mixture, from which the composition of the mixture can b e computed. Two functional-group analytical systems are shown to which the rate approach was applied-alcohol mixtures and mixtures of carbonyl compounds. 896
ANALYTICAL CHEMISTRY
T
HE same functional group on different organic molecules often exhibits differences in its rate of reaction with a given reagent. This difference in reaction rate can be due to the size and configuration of the molecule onto which the functional group is attached, or to the effect of substituents on the organic molecule. It is apparent that this difference in reaction rate might form the basis for a system of analysis which could differentiate between components in an organic system. Lee and Kolthoff (11) pointed out the potentialities of this approach and made some attempts to utilize reaction rates to analyze some mixtures.
A system of analysis is presented here which utilizes reaction rates to analyze mixtures of organic materials containing the same functional group. The approach used is different from that used by Lee and Kolthoff and has certain advantages, especially in termi of range of applicability. The approach described below uses the conventional plotting of secondorder reaction data. A second-order reaction is one where the rate is dependent on the concentrations of two reactants in the system. Hence, if A and B are reacting, their concentrations, a and b, determine the rate. If 2 describes the amount of A
I
and B that has reacted a t time t , then the rate of reaction, dx/dt, can be described as : -dx=
dt
'
k(b
P
- X ) ( a - Z)
On integration, taking into account that x = 0 when t = 0, and x = x when t = t, the equation develops as follows : 2303 ~ ( -b Z) = k t(b - a ) log F ) Plots of log (b-x)/(a-x) us. t in the conventional manner yield straight lines for second-order reactions. When two second-order reactions are proceeding in the same mixture, a curve with two straight-line portions is obtained if the reaction rates of the two reactions are sufficiently different. Many reactions used to determine organic compounds via their functional groups are second-order reactions. Some of these lend themselves very readily to rate studies, which makes possible the resolution of the components in the mixture. Below are two examples of reactions which have been found usable with this rate approach to resolve mixtures containing the same group. ANALYSIS OF MIXTURES OF ALCOHOLS INCLUDING MIXTURES OF ISOMERIC PRIMARY AND SECONDARY ALCOHOLS
The literature contains no general chemical method for the analysis of mixtures of two homologous alcohols or mixtures of isomeric primary and secondary alcohols. Methods (6, 17) for the specific determination of 2propanol in mixtures involve oxidation of the 2-propanol to acetone and subsequent determination of the acetone produced. Recently, a method (3) has been described for the determination of small amounts of secondary in primary alcohols. This also involves oxidation of the secondary alcohol to a ketone and colorimetric estimation of the ketone. The method described here is based on the differences in reaction rates of different alcohols with acetic anhydride. It is necessary to know the total hydroxyl content of the sample used in order to select the sample size and to make the calculations for the analysis. This can be done by a n established acetylation procedure (IS). The amount of the less reactive component is found by difference. REAGENTS
Reagent grade pyridine and reagent grade acetic anhydride. Titration indicator, a 2 to 1 mixture of 0.1% Nile-blue sulfate in 50% ethanol and 1% phenolphthalein in 95% ethanol. The alcohols used as standards were reagent grade chemicals.
3
I T
0
100 200 t (MINUTES)
300
Figure 1 . Second-order reaction curve for mixtures of butanols
slopes. The extrapolation procedure for the determination of the more reactive alcohol is illustrated in Figure 1. This plot is the second-order ' reaction curve for the mixture of 1butanol and 2-butanol listed in Table I. The line representing the slope of the less reactive alcohol (slope 2) is extrapolated to point A a t zero time. A line AB is drawn parallel to the time axis. The time, T,a t point B of intersection between this line and slope 1 is read, The concentration of the more reactive alcohol is then the concentration of alcohol reacted a t this time. For the example illustrated, T was found to be 59.5 minutes. From a plot of x us. t , the concentration of alcohol reacted in this time was found to be 0.0398 mole per liter. The total mole per liter of butanol present was 0.2000. Then 8?!?!
The propanols were dried over calcium chloride and distilled. PROCEDURE
A sample containing 0.05 mole of hydroxyl is transferred to a 250-ml. volumetric flask, using pyridine, and is diluted to almost 240 ml. with pyridine. Ten milliliters of acetic anhydride are pipetted into the flask and the mixture is rapidly diluted to volume with pyridine. The time is noted. At intervals, 10-ml. aliquots are pipetted into glass-stoppered flasks, 5 ml. of water are added to each, and the time is again noted. Each is allowed to stand a t least 10 minutes and then is titrated with 0.1N alcoholic potassium hydroxide. A blank is run by pipetting 10 ml. of acetic anhydride into a 250ml. volumetric flask and diluting to volume with pyridine. A 10-ml. aliquot of this is treated in the same manner as the sample. Log (b - ') is plotted us. t, where x (a
- 2)
is the decrease in concentration of reactant in time t, and a and b are the initial concentrations of alcohol and anhydride, respectively. If a mixture of two alcohols is indicated, straight lines are drawn, representing the two
Table 1.
0.2000
X 100 = 19.9% 1-butanol found
An alternate calculation i s as follows: Let a = al az, where al represents the concentration of the more reactive hydroxyl. When slope 2 is extrapolated to zero time,
+
z = alatf = 0
and (* - Z) = log k 2 L ) = value at log ( a - ad point ( A ) , the intercept ( t = 0).
For Figure 1, b
=
a =
0.415 0.2
and log
(a
- ad
= 0.369
a1 = 0.0396 mole per liter or 19.8% l-buta-
nol.
DISCUSSION AND RESULTS
If this method of analysis is to be successful, the difference between the specific rates of reaction of the components in the mixture must be large enough so that a separate and distinct linear plot is obtained for each com-
Alcohol Mixtures
% Primary Primary Secondary Present Found %Propanol 1.01 1.00" 1 1-Propanol 2 1-Propanol %Propanol 50.5 50.0b 2-Propanol 20.3 21 .Ob 3 1-Propanol 1-Amino-%propanol 49.6" 49.5 4 3-Ammo-1-propanol %Butanol 19.9 19.9 5 1-Butanol 74.8 64.2d 6 1-Octanol 2Octanol 3-Pentar 01 14.9 15.5 7 1-Pentanol Alcohol in excem of acetic anhydride. * Isocyanate reaction. 5 99.1% pure by acidimetric titration. d Concentration of primary alcohol L so large that points for portion of curve representing reaction rate of secondary alcohol are near end of reaction, where they are not reliable.
Mixture Number
Alcohols
VOL. 33,
NO. 7, JUNE 1961
897
ponent when the second-order reaction rate plot is made. However, no mixture of alcohols was encountered where this difference was not sufficient for this method to be used. From the standpoint of ease of following the reaction and for the best resolution of the til-o slopes, the most practical molar ratio of anhydride to hydroxyl is about 2to1. Since the rate of reaction is dependent on the concentration of the two reactants in the system, the rate may be increased by increasing the concentration of the alcohol or anhydride or of both. However, if the reaction is too rapid, difficulty is eyperienced with the resolution of the two portions of the curve. The concentrations of alcohol and anhydride chosen must not be equal, because then a = b and log will always be zero, and two ( a - 2) separate slopes will not be obtained. The data in Table I indicate the applicability of the method for the determination of primary alcohols in the presence of secondary alcohols. The results in Table I1 show that it is possible to determine an alcohol in the presence of its next higher homolog as well as in the presence of one further separated in the series. This is illustrated by the results for l-butanol in the presence of 1-pentanol. Table I11 contains data for polyhydric alcohols containing both primary and secondary hydroxyl groups. All of the reactions 1%ere followed for about 300 minutes. The reaction between isocyanates and alcohols can also be used to analyze mixtures of alcohols. Results for mixtures 2 and 3 in Table I were obtained in this way. Triethylenediamine was used to catalyze the reaction. A disadvantage of this system is the difficulty introduced by the presence of water in the reaction mixture. It was necessary to run a rate study on a blank along with the sample t o correct for any k i t e r in the reagents and solvents.
w)
Table II.
Alcohol 1-Propanol 1-Butanol 1-Pentanol
1-Heptanol
Table 111. Polyhydric Alcohols Containing Both Primary and Secondary Hydroxyl Groups
yoPrimary Alcohol Alcohol 1,2-Propanediol lJ3-Butanediol Glycerol
898
.
have a mensurable rate. The sample must also be dry. The preseiic'c of water when acetic anh-&itlc~ is used will cause some of the anhydridr t o bc consumed and change its concentration i n the misture, but this reaction nith small amounts of water (less than 1% of the sample) is rapid and has wbstaiitially no effect on the shape of the reaction plot, and thus none on tlic final result. However, large quantities of water will destroy sufficient anhydride to affect the esterification of the alcohol. If more than about i 0 7 , of the more reactive alcoliol is present in the mixture difficulty is experienced in plotting. -4s the react,ion approaches completion, the upper portion of the reaction rate plot levels out and becomes unreliable. Then, enough reliable points cannot be obtained to make a linear plot for the less reactive component. 1his difficulty is illustrated by results for mixture 6 in Table I. To overcome this, a known amount of the less reactive alcohol can be added to the mixture and the final result corrected for the amount added. To det,ermiiie small amounts of the more reactive alcohol in a mixture, it was found expedient to use a larger sample and have the alcoliol in excess of t.he anhydride. The result for mixt,ure 1 in Table I was obtained in this manner. The molar ratio of alcohol to anhydride was 5 t o 1. The method is generally limited to mixtures of t>mo alcohols. However, when the reaction rate plot was made for a nlixture of ethylene glycol, diethylene glycol, and triethylene glycol, three separat,e linear parts of the curve were noted. Calculation for the composition of the mixture shoved 18.9% found us. 19.3% ethylene glycol present, 33,2% found vs. 33.1% diethylene glycol present, and 47.9% found by difference us. 47.6% triethylene glycol present.
Mixtures of Homologous Alcohols
Less Reactive Alcohol 1-Octanol 1-Pentanol
iLIore Reactive
Ihe r w d o i i nith wate rappears to
I
Present
Found
50 . O 50.0 66.7
50.2
ANALYTICAL CHEMISTRY
50.5
66.4
More Reactive Alcohol Present Found 5.00 29.7
24.6
4.99 30.1 24.4
An attempt vas made to analyze mixtures of amines and mixtures of phenols in the same manner. However, in both cases, the reactions with acetic anhydride v-ere too rapid for the rate to be measured. Phthalic anhydride \T as substituted for acetic anhydride, but again, the amine reaction was too rapid. KO reaction betiveen phthalic
anhydride and phenol \vas detected, even a t elevated temperature. ANALYSIS OF MIXTURES OF ALDEHYDES AND KETONES
Chemical methods are available for the determination of aldehydes in the presence of ketones and for specific carbonyl compounds in a misture. However, none of these are general for the determination of onc carbonyl compound in the presence of another. A mixture of an aldehyde and a ketone can be analyzed by first determining the total carbonyl present, using a hydroxylamine hydrochloride method (2), then determining the aldehyde alone, using a bisulfite (f4)or an argentimetric method ( l a , 15). The amount of ketone is obtained by difference. Dimedone and cyanide (9) have been used to analyze mixtures of formaldehyde and propionaldehyde. DenigAs ( 4 ) used a modified Schiff reagent for the detection of formaldehyde in the presence of higher aldehydes. This has been used along with the standard Schiff reagent to analyze miytures of formaldehyde and 2-furaldehyde, and formaldehyde and acetone (18). Chromotropic acid has been used also to determine formaldehyde in the presence of higher aldehydes (1). Methods based on rates of reaction have been proposed. Ionescu and Slusanschi (IO) nere able to differentiate between formaldehyde and acetaldehyde by the rates of precipitation of the solid derivatives with dimedone. Lee and Kolthoff (11) have given a procedure based on the difference in reaction rates for the analysis of mixtures of two organic compounds which contain the same functional group. Calibration curves relate the concentration a t a chosen time with the original concentration. Analysis of mixtures of aldehydes based on the rate of decomposition of the bisulfite addition compound n as mentioned, but no data n ere given. Methods based on the competing rates of oxime formation have been proposed (6, 7 ) . These methods also use calibration curves to relate the amount of reaction after a period of time to the original concentration. The methods are limited to the determination of aromatic aldehydes in the presence of aromatic ketones where the difference in the reaction rates is large and the oximation of the aldehyde is complete when a very small amount of the ketone has reacted. The method proposed here also makes use of the different rates of reaction of carbonyl compounds with hydroxylamine hydrochloride. However, with this m e t h d , mixtures of carbonyl compounds can be analyzed when the reaction rates are much closer than those of aromatic aldehydes and aromatic
ketones, This method will resolve not only thc aliphatic aldehydes and ketones, but also mixtures of two aldehydes and mixtures of two ketones. The mixture is reacted with hydroxylamine liydrochloride, and the amount of reaction is determined a t successive time intervals. .4second-order reaction rate plot is made. If the carbonyls present react at different rates, the plot will show two straight-line portions. The contribution of the slower reacting component is separated from the slope of the more reactive component by extrapolation, and the more reactive component is then measured.
Figure 2 . This plot is the second-order reaction curve for the mixture of 2butanone and 3-pentanone. The concentration of the more reactive carbonyl compound is then obtained by a n operation similar to those described for alcohols. The total carbonyl content of the mixture is determined by a regular osimation procedure ( 2 ) . The difference is then a measure of the less reactive component of the mixture. DISCUSSION AND RESULTS
The reaction of carbonyl compounds with h\-drosylamine to form the oxime
9
pd
1 I
J/
,/
SLOPE 2-
PROCEDURE
The sample containing 0.004 mole of carbonyl is weighed and diluted t o 100 ml. with a 4 to 1 methanol-water solution. T o a n 800-ml. beaker are added 480 ml. of 4 to 1 methanolnater solution. A 10-ml. portion of 0.1N hydroxylamine hydrochloride in 4 to I methanol-water is pipetted into the solution. The beaker is placed in a n ice bath and the temperature lowered to 4' C., using mechanical agitation. For aromatic ketones, the reaction is allowed to proceed at room temperature. The glass and calomel elcctrodes of a pH meter are placed in the solution and the p H of the solution is adjusted to 3.5. X 10-ml. aliquot of the sample is pipetted into the solution and the time noted. The pH of the solution is maintained at 3.5 rt 0.02, using standardized 0.02N sodium hydroxide solution. The milliliters of sodium hydroxide solution added are noted a t 5-minute time intervals. The concentration of carbonyl reninining and the concentration of hydroxylamine hydrochloride remaining after time t are calculated. I n the second-order rate equation, the original quantitiw of carbonyl compound can be represented as a and the hydrosylamine reagent as b. The amount of each reacted after time t is represented as x. Then log ( b - ') is plotted us. t. (a- 2) If a mixture of tn-o carbonyl compounds is indicated, straight lines are drawn, representing the two slopes. The extrapolation procedure for the determination of the more reactive carbonyl compound is illustrated in
1.
2. 3. 4. 5.
REAGENTS AND APPARATUS
The methanol used as the solvent \\'as reagent grade, acetone-free material. The purities of the aldehydes and ketones used were determined by established methods (2, 12) and the synthetic mixtures prepared based on these analyses. A Beckman hlodel H pH-meter equipped with a glass and calomel electrode system was used for the p H measurements.
Table IV.
Analytical Results
Mixture h. Formaldehyde B. Acetaldehyde A. Acetaldehyde B. Acetone A. Acetone B. 2-Butanone A. Propionaldehyde B. hcetone A. 2-Butanone B. 3-Pentanone
6. A. Crotonaldehyde B. 3-Pentanone 7. A. 2-Pentanone B. 3-Pentanone 8. A. Cyclopentanone B. 3-Pentanone 9. .4. Cyclohexanone B. Cyclopentanone 10. A. Crotonaldehyde B. Hexaldehyde 11. A. Hexaldehyde B. 3-Pentanone 12. A. Cyclohexanone R. 2-Butanone 13. A. Benzaldehyde B. Salicylaldehyde 14. A. iicetophenone B. Benzophenone
%~A _ _ ~ Present Found 13.9 14.7
___
24.7 7.84
24.7 7.80
11.8
11.7
17.4 17.4 7.5
17.0 17.6 7.5
18.2
17.9
7.37
7.36
65.8
65.4
18.0
17.4
15.6
15.6
84.5
8G.1
28.3
28.0
8.4
8.0
I
T 10
20
t (MINUTES)
30
40
Figure 2. Reaction rate curve for mixture of 2-butanone and 3-pentanone
is second order (8, 16). Separate and distinct linear plots were obtained for each component in the mixtures when the second-order reaction rate plots were made. No mixture of carbonyls was encountered for which the rates of reaction were not different enough for this method t o be used. The concentration of either the carbonyl or the hydroxylamine hydrochloride can be varied to speed up or slow down the reaction. In no case, however, should the concentrations chosen be equal, because then a = b ( b - x) will always be zero, and and log G) two separate slopes will not be obtained. The procedure has been applied to mixtures of aldehydes, mixtures of ketones, and mixtures of aldehydes and ketones. Table IV shows that it is possible to determine an aldehyde or a ketone in the presence of its next higher homolog, as well as in the presence of one further separated in the series. Except in the case of the aromatic ketones, the reaction was run at 0' to
5' C. ilt higher temperatures, the reaction proceeds too rapidly to b e practical. For aldehydes and aliphatic ketones, the determination takes less than one hour. The aromatic ketones were reacted a t room temperature and required approximately 1.5 hours for the determination. Cyclopentanone reacted more rapidly than 3-pentanone and cyclohexanone more rapidly than cyclopentanone. For the other mixtures of aldehydes and mixtures of ketones tested, the carbonyl of lower molecular weight reacted more rapidly. For mixtures of aldehydes and ketones, the aldehydes reacted mor(> rapidly. Acidic or basic impurities in the sample interfere and should be neutralized before the determination is made. LITERATURE CITED
(1) Bricker, C. E., Johnson, H. R., ISD. ENG. CHEU., ANAL. ED. 17, 400-2
(1945). (2) Bryant, W. M. D., Smith, D. M., J. Am. Chem. SOC.57,57-61 (1935). (3) Critchfield, F. E., Hutchinson, J. -4., ANAL.,CHEM. 32, 862 (1960). (4) Denighs, G., Cornpt. rend. 150, 529-31 (1910). ( 5 ) Etienne, H., Ind. chim. belge 17, 455 (1952). (6) Fowler, L., ANAL.CHEM.27, 1686-8 (1955). VOL. 33, NO. 7, JUNE 1961
899
(7) Fowler, L., Kline, H. R., Mitchell, R. S.,Ibid., 27, 1688-90 (1955). (8) Hammett,,, L. P., "Physical Organic Chemistry, McGraw-Hill, New York, 1940. (9) Hoepe, G., Treadwell, W. D., Helu. chh. Acta 25,353-61 (1942). (10) Ionescu, M. V., Slusanschi, H., Bull. SOC.c h h . 53 (4), 909-18 (1933). (11) Lee, T. S., Kolthoff, I . M., Ann.
N . Y . A d . Sci. 53, 1093 (1951). (12) Mitchell, J., Jr., Smith, D. M., ANAL. CHEM.22, 746-50 (1950). (13) Siggia, S., "Quantitative Organic Analysis via Functional Groups," 2nd ed., Wijey, New York, 1954. (14) SigGa, S., Maxcy, W., IND.ENQ. CHEM., ANAL.ED. 19,1023 (1947). (15) Siggia, S., Segal, E., ANAL. CHEM. 25,640 (1953).
(16) Stempel, G. H., Shaffel, G. S., J. Am Chem. SOC.66, 1158 (1944). (17) Strache, F., Martienssen, E., Z. Lebmm.-Untersuch. u. Forsch. 104, 339 (1956). (18) Veksler, R. I., Zhur. Anal. Khim. 4,14-20 (1949); 5,32-8 (1950).
RECEIVED for review November 25, 1960. Accepted March 14, 1961.
Determination of Hydroxy and Amino Compounds Usi ng PyromeI Iitic Dia nhyd ride SIDNEY SIGGIA,
J.
GORDON HANNA, and ROBERT CULM0
Olin Mafhieson Chemical Corp., New Haven, Conn.
b Pyromellitic dianhydride offers definite advantages over acetic anhydride and phthalic anhydride as a reagent for the determination of alcohols and amines. The advantage of acetic anhydride is speed of reaction, but aldehydes interfere; phthalic anhydride suffers no interference from aldehydes, but the reaction is significantly slower than with acetic anhydride. Pyromellitic dianhyride's reaction rate with alcohols is comparable to that of acetic anhydride, and aldehydes do not interfere. Because it does not react with phenols, it also provides a rapid method for determining alcohols in the presence of phenols.
T
REAGENTS
Pyromellitic dianhydride, 0.5M in tetrahydrofuran. The pyromellitic dianhydride can be purchased from E. I. du Pont de Nemours & Co., Inc. PROCEDURE
A sample containing 0.010 to 0.015 equivalent of alcohol or amine is weighed and placed in a 250-ml. flask. Fifty milliliters of 0.5M pyromellitic dianhydride solution are pipetted into the flask, along with 10 ml. of pyridine.
Table 1.
The flask is placed on a steam bath for 2 minutes and then on an electric hot plate for 5 minutes. Most of the tetrahydrofuran will boil off during the heating. Twenty milliliters more of pyridine are added, and the heating continued for 3 minutes. A 20-ml. portion of water is added, and the mixture again heated for 2 minutes to hydrolyze the excess anhydride. The mixture is cooled to room temperature and is titrated with 1N sodium hydroxide to the phenolphthalein end point. A blank is run in the same manner, omitting only the sample.
Determination of Alcohols in the Presence of Aldehydes
Aldehyde ln Mixture,
BE most commonly used methods
for the determination of hydroxyl groups involve acetylation, using acetic anhydride (2, S), and phthalation, using phthalic anhydride (1, 6). Acetic anhydride reacts more rapidly than phthalic anhydride, but suffers interference from low molecular weight aldehydes (4). Phthalic anhydride can be used in the presence of aldehydes. Larger concentrations of phthalic anhydride are necessary for complete reaction. Phthalic anhydride is less volatile than acetic anhydride; therefore, there is less possibility for loss of reagent during heating. Phthalic anhydride can be used to determine alcohols in the presence of phenols. Pyromellitic dianhydride (PMDA) combines the advantages of the two reagents. It can be used in the presence of aldehydes; it is not volatile; it can be used to determine alcohols in the presence of phenols; and its rate of reaction is comparable to that of acetic anhydride. The time involved for analysis is approximately the same as that for the perchloric acid-catalyzed acetic anhydride reaction (@, although the PMDA method does require a heating period.
900
ANALYTICAL CHEMISTRY
Alcohol 1-Heptanol 1-Octanol 1-Heptanol 1-Heptanol Table II.
Aldehyde Added Formaldehyde Acetaldehyde Furfural Acrolein
%
10 50 50 50
Alcohol Recovered,
%
100.0
100.0 98.0 100.6
Determination of Alcohols and Amines
%:Purity PMDA method 99.7, 100.2, 99.7
Methanol 100.0,100.1 Ethanol 97.7, 96.5, 96.7 %Propanol 100.4, 101.2 1-Butanol 94.3; 94.9 1-Pentanol 101.9, 101.3 3-Pentanol 100.7, 100.4 1-Heptanol 99.8, 98.5 1-Octanol 98.9,99.2 ZOctanol 99.9,99.5 Allyl alcohol 99.8, 99.8 Cyclohexanol 98.4, 100.0, 100.0 l,>Propanediol 100.9 1,a-Butanediol 96.6, 96.6b Glycerol 98.5, 98.6 Aniliie 100.2, 100.2 2-Naphthylamine 98.1, 98.2, 98.0 112-Pro anediamine 99.2, 99.2 Diethylmine 99.5,99.4 N-Methylaniline Acetylation procedure ( 1 ) . * Sample contains 4.0yob_waterby Karl Fischer titration. Acid-titration.
Other method 99.6" 100.0~
97.2" 99.70 93.5" 101.1a
100.7a
99.40 98. g0 99.40 100.0" 101.3" 99.9" 96.2O 99.5" 100.5c 98.3" 99 2" 99. 2c I
