V O L U M E 2 3 , N O . 11, N O V E M B E R 1 9 5 1
1717
are easily detectable with a magnifying glass if sufficient time is allowed for the diffusion of the carbon dioxide t o the barium hydroxide meniscus. .4 blank is completely negative. If the sample contains halogens or sulfur it is necessary to introduce a little lead chromate ( 2 ) .
E
Icrn
n SCALE
Figure 1.
kpparatiis for Microdetection of Carbon
h further precaution can be made if any residue remains YI hich might accidentally be shaken into the barium hydroxide and produce a misleading turbidity. A small porous plug of ignited asbestos can he placed between the sample and the absorbing solution and held in place b y constricting the glass tubing. I n actual practice with the present apparatus, this has not yet been necessary, as the absorbent and sample are in different legs of the combustion tube. PROCEDURE
The apparatus is indicated in Figure 1. The combustion Ttube is constructed from 4-mm. borosilicate glass tubing and the perpendicular leg is drawn out into a long capillary. The apparatus is assembled, flushed with oxygen, and gently Hanied to remove any carbon. The gas is shut off and a small drop of freshly prepared saturated barium hydroxide is drawn into the perpendicular leg by capillary action. Using a microflame, the
capillary is sealed off a t A , so no contamination of the barium hydroxide drop will occur from the carbon dioxide of the gas flame. The apparatus is again flushed with oxygen and the horizontal leg is sealed off at B , using the same precautions. Stopper E is removed, the sample is introduced by means of a glass fiber or capillary t o point C, and the fiber or capillary is left in the tube. The horizontal leg is then sealed off a t D. (The conlpleted combustion tube is shown in Figure 1.) The sample is burned a t a dull red heat, either with a flame or by inserting the horizontal leg into a small tube furnace. I n a few minutes barium carbonate crystals will form at the barium hydroxide meniscus>giving a positive test for carbon. For inorganic carbonates the combustion T-tube is used alone without the oxygen introduction system. Saturated barium hydroxide is drawn into the perpendicular leg and sealed off as described above. The carbonate sample is contained in a short length of capillary which is placed approximately two thirds of the way down leg D. By the use of a capillary pipet, a drop of 6 N hydrochloric acid is placed halfway down leg D. The horizontal leg is then sealed a t D as described above and then a t point B. This reversal of order of sealing from that described in the main procedure is necessitated by the fact that if B is sealed first, the expansion of the air in the tube when heating point D will force the drop of acid out of the tube. Following the sealing of the T-tube, the drop of acid is pushed down the tube by gently heating a t D. When the acid drop contacts the sample, the carbonate will decompose, liberating carbon dioxide which will be absorbed in the barium hydroxide meniscus. The test for carbonate can be accelerated by brushing the drop of solution with a microflame in order to boil out the dissolved carbon dioxide. The same limits of detection are attained for carbonate as in the combustion met,hod. LITERATURE CITED
(1) Benedetti-Pichler, -4.A., “Microtechnique of Inorganic Atialysis,” New York, John Xiley 8- Sons, 1942.
( 2 ) Emich, F., and Schneider, F., “Microchemical Laboratory Manual,” Kew York, John \Tiley 8- Sons, 1932. (3) Feigl, F., “Chemistry of Specific, Selective, and Sensitive Reactions,’’ New York, Academic Press, 1949. (4) Feigl, F., “Laboratory Manual of Spot Tests,” New Tork, Academic Press, 1943. (5) Feigl, F., “Qualitative Analysis by Spot Tests,” New T o r k ,
Elsevier Publishing Co., 1946. RECEIVED March 14, 1951. Presented a t t h e Pittsburgh Conference on Analytical Chemistry and .4pplied Spectroscopy. Pittsburgh, Pa., .January 1951. T h e Knolls .4tomic Power Laboratory is operated by the General Electric Research Laboratory f u r t h e Atomic Energy Commission. The work reported here was carried out under contract N o . W-31-109Eng..;,?.
Determination of Carboxylic Acid Anhydrides in the Presence of Their Acids SIDNEY SIGGIA AND J. GORDON HANNA General Aniline & Film Corp., Easton, Pa.
;iLM and Sadeau ( 1 j employed aniline successfully to de-
nil termine acetic anhydride in acetylating mixtures for cellulose. This reaction can also be applied t o determining other carboxylic anhydrides in the presence of their acids. The approach circumvents many of the difficulties exhibited by the hydrolytic and titration procedures for determining anhydrides (3-6). hniline reacts with carboxylic acid anhydrides according to the following equation: 0
//
RC
“0
RC
/
+
c>
xHz+
0
A H c >
0
//
+Rc
\
OH
The carboxylic acids produced in the reaction or the free C ~ I ~ O Y ylic acids present in the original sample are weak acids; their bond with the aniline is so weak that the aniline can be titrated away from the carboxylic acids by the strong acid that is used t o titrate the excess aniline. In this way the aniline consumed in the reaction is a measure of the anhydride, and the free carbo\rylic acid present in the sample offers no interference. Succinic acid was found to be an exception; it does interfere in the determination of succinic anhydride, but not because of neutralization of the aniline by the acid. I n this case the reaction conditions for complete reaction of the anhydride had t o be so vigorous (1.5 hours a t 100” C.) that the free carboxyl groups liberated by that reaction, as well as the free carboxylic acid present, also reacted with the aniline to form the amide. The reaction between the acid and the aniline is not very fast, but the error introduced is significant. I n running pure succinic anhydride, the results were about 5 % high; when pure succinic
-
ANALYTICAL CHEMISTRY
1718 Table I. Determination of Anhydrides Acid-.\nhydride I\LlX
Anhydride -4cetic
Propionic Maleic
Reaction Time, Min.
Room
5
5
Room
16
Room
15
100 Room
1 5 hours
-
Reaction Anhyd. Anhyd. Temp.. Found, added, found, ' C. % % %
100.2
77.5
77.8
Aniline Recovered after Reaction with Acid Alone
99 2
rinhydride Phthalic
Acid-Anhydride nilx Anhyd. .4nhyd. Reaction added, found, T:niz..', Found,
Reaction Time, ?din. 1;
100
30
loo
5 45
100 100
5
Room
qQ 9
99.8 100.1 99.7 100 1 99.6 99.6 99 4 99 4 99 4 99 6 110 4
60 9
60 6
99 3
91 0
90 7
99 7
Camphoric
Butyric
Aniline ~ ~ after Reaction with Acid Alone 100 0
~
%
% '
%
100 5 99.8 99.5 102.0 101.2 21.6 100.0 100.1 100.3 99.8 100.1
50 8
80 3
87 5
88 0
99 3
87.2
86.5
98.8
All .ainples were diatilled or recrystallized until their C a n d H analyses were within =0,'2yoof theoretical.
100 8
_ _ ~ _ _ -
-
acid was treated with aniline under the same conditions as the anhydride, there was a very significant consumption of aniline. Along the same lines Table I indicates that maleic and phthalic acids would have interfered but for the fact that the anhydrides react rompletely under relatively mild conditions. A mixture of ethylene glycol and isopropyl alcohol ( 8 ) was used as solvent medium to accentuate the end point in the titration of the excess aniline. Titration in glacial acetic acid was tried, but difficulty with end points was noticed in analyzing some anhydride-acid systems. The glycol-isopropyl alcohol mixture could be applied to all the systems studied. Reagents. Ethylene glycol-isopropyl alcohol mixture, 1 to 1 by volume. Standard 0.2 N hydrochloric acid in ethylene glycol-isopropyl alcohol mixture (19 ml. of concentrated hydrochloric acid diluted to 1 liter with 1 to 1 ethylene glycol-isopropyl alcohol). C.P. aniline. Procedure. A sample containing approximately 0.004 mole of acid anhydride is accurately weighed in a 20. X 150 mm. test tube. If the sample contains an acid anhydride which requires heat for complete reaction, it is weighed in a 50-ml. condenser flask. Aniline is added to the sample drop by drop until 0.9 gram has been added. This is accurately weighed. The sample is allowed to stand in the test tube 5 minutes. The condenser flask is attached to a condenser in a reflux position and immersed in a beaker of boiling water for the required length of time. The reaction mixture is transferred quantitatively from the test tube or the condenser flask to a 150-ml. beaker with 1 to 1 ethylene glycol-isopropyl alcohol mixture. Ethylene glycol-iso-
propyl alcohol miu is added until the volume is approsiniately
50 ml. A pH meter is used to indicate the apparent pH after each addition of acid as the sample is titrated with 0.2 M hydrochloric acid prepared in the ethylene glycol-isopropyl alcohol mixture. The newtralization point is determined by plotting the apparent pH against milliliters of acid. A blank is run on the aniline by titrating an accurately weighed amount approuimately 0.4 gram, potentiometrically with 0.2 N hydrochloric acid in the ethylene glycol-isopropyl alcohol mixture Calculations (z
- a ) x normality of HC1 x mol. wt. of acid anhydride 1000 x wt. of sample
X
100 = %acid anhydride when a equals milliliters of acid used to titrate excess aniline, and z equals milliliters of acid needed to titrate total amount of aniline used, The aniline used should not be assumed to be loo%, but should be assayed so that this value is a correct one. The aniline can be assayed by titration as described above. LITERATURE CITED
(1) hlalm, C. J., and Nadeau, G. F., U. S. Patent 2,063,324 (Dec. 8 1936).
( 2 ) Palit, S., IND. ENG.CHEM.,ANAL.ED.,18, 2 4 M 1 (1946). (3) Smith, D. hf., and Bryant, W. hI. D., J . Am. C h . SOC.,58, 2 4 5 2 4 (1936).
(4) Smith, D. M.,Bryant, R. M , D., and Mitchell, J., Jr., Ibid., 62, 608-9 (1940).
( 5 ) Ibid.,63,1700-1 (1941). RECEIVED April 17, 1951.
50. cis-Terpinol (Anhydrous Form) Contributed by W-ILTER C. MCCRONE Armour Research Foundation of Illinois Institute of Technology, Chicago 16, Ill.
CH3
CHz-CH,
C'
/\
HO
CHZ-CHB
\ /
I I
CH3
CHg-C-OH
CHI
as a supplement to last month's description of the hydrate. Escellent crystals of anhydrous terpinol are obtained by slow sublimation in the Kofler block placed on a hot bar or other source of even heating at approsirnately 90" C. (Figure 1).
PI' OCTOBER this column reported that good crystals of the
CRYSTAL MORPHOLOGY Crystal System. Orthorhombic. Foim andHabit. Tablets by sublimation lying on the brachypinacoid { O l O } and showing the additional forms: prism ( l l O } ,
graphic data on the anhydrous material are included this month
Interfacial Angles (Polar). i i o h i i o = 110'38': o i i h o i i = 1 2 4 O 2'; 101 A 1;i ='108" 30'.
Structiiral Formula for &-Terpinol
I anhydrous form of cis-terpinol might be obtained by careful sublimation. This has turned out to be true, and the crystallo-
~
)
~
