May, 1945
DETERMINATION OF NITRILESWITH
[CONTRIBUTION FROM
THE
KARLFISCHER REAGENT
AMMONIA DEPARTMENT O F E . I. PU
P O N T DE
NEMOTJRS & COMPANY,
Analytical Procedures Employing Karl Fischer Reagent. XIII. of Nitriles1
777 INC.1
The Determination
BY J. MITCHELL, Jk.,AND WALTERHAWKINS Nitriles usually are identified after acid or alka- pyridine.16 The homogeneous solution is titrated diKarl Fischer reagent. line hydrolysis to the corresponding a ~ i d , ~and * ~ * rectly ~ Since , ~ with the nitrile group does not interfere, the sample can in some cases alcoholysiss or reduction7V8 has be .titrated directly for free water. The net titer plus proved feasible. Direct identification has been water originally present in the sample is a direct measure based on the preparation of crystalline derivatives of the equivalents of cyanide. of the nitriles with mercaptoacetic .acid9 and Analytical Results phloroglucinol.lo These methods were designed Several aliphatic and aromatic nitriles have primarily for qualitative identification and consequently have not proved generally applicable t o been analyzed by this method. In general the precision and accuracy are within f0.3%. Exthe quantitative estimation of nitriles. In the present investigation a method has been perimental data are recorded in Table I. These developed which is based on quaiititative hy- chemicals were analyzed as received, without drolysis of the nitrile to the corresponding amide further purification. The number of representative nitriles for which a 100% balance is RCN HnO = RCONH2 shown is considered sufficient for establishing the The nitrile is treated with an excess of water in order of precision and accuracy. Those which the presence of boron trifluoride and acetic acid. totaled low were assumed to contain inert imAfter hydrolysis the unused water is titrated di- purity. TABLE I rectly with Karl Fischer reagent. Net water beANALYTICAL DATAFOR NITRILES tween blank and sample is equivalent to the Found, wt. % nitrile originally present. Nitrile Nitrile Watet Total The new method is generally suitable for the (10)' 97.6 ' 0 . 2 2.3 99.9 determination of normal alkyl cyanides. Quan- Acetonitrile ( 6) 98.7 . 3 1 . 6 Propionitrile 100.3 titative results have been obtained on the normal ( 2) 93.6 .4 0 . 8 94.4 lower aliphatic nitriles, nitriles of dibasic acids Cyanoacetamide n-Butyronitrile ( 2) 99.0 . 2 1 . 2 100.2 and several aromatic cyanides.
+
7 -
'
( 2) 99.4 .o 0 . 4 99.8 n-Valeronitrile ( 1) 97.7 .1 Lauiyl cyanide 97.8 Adiponitrile' (10) 99.8 .2 .O 99.8 Reagents.-The hydrolytic reagent is prepared by disSebaconitrileb ( 4) 100.0 . 4 . o 100.0 solving 300 g. of dry boron trifluoride gas and 6.5.ml. of ( 2) 99 6 .2 .2 99.8 water in 500 ml. of glacial acetic acid (BF3.2CH8CO- Phenylacetonitrile O.H).llslz Karl Fischer reagent id prepared according to m-Toluoni trile ( 2 ) 100.6 .2 . I 100.7 directions given in an earlier publication.13 ( 2) 100.8 .4 .1 100.9 Analptica1Procedure.-The sample, containing tip to 10. p-Toluonitrile . 3 .1 .( 2) 97.6 p-Chlorobenzonitrile 97.7 milliequivalent: of nitrile, is weighed into a 250-ml. glass( 6) 96.5 .4 .1 96.6 stoppered volumetric flask. Twenty tnl. of the hydrolysis B-Napfithonitrile reagent is added. The flask is tigfitly stoppered'* and, a Figures in parentheses represent number of individual together with duplicate blanks, placed in an oven or water- determinations. Du Pont; all others Eastman Kodak bath a t 80 * 2' f o r t w o hours. At the end of this time Co. chemicals used without further purification. the flasks are removed, allowed to cool spontaneously to room temperature, then placed in a container of finely Other nitriles were found to give incomplete chopped ice during the careful addition of 15 ml. of dry but fairly precise results. Although m- and p-
Experimental
(1) Presented in part before the Division of Analytical and Microchemistry at the 106th meeting of the American Chemical Society, Pittsburgh, Pennsylvania, September 9 , 1943. (2) Frankland and Kolbe, A n i : . , 66, 298 (1848). (3) AIigelescu, Vasiliu and Kadvan, Bull. p c f . sci. acad. routtiairre, M, 220 (1939). (4) Rovira and Palfray, C o t n p f . r c r d . . 110, 306 (1940). (5) Rabinovitch and Winkler, C o n . J. Research, SOB, 221 (1942). (6) Backunts and Otto, Bcr., 9, 1590 (1876). (7) Ladenberg, ibid., 18,2596 (1885). (8) Cutter and Tarras, I n d . E n g . Chem., Anal. E d . , 13, 830 (1941). (9) Condo, Hinkel, Fassero and Shriner, THIS JOURNAL,69, 230 (1937). (10) Howells and Little, i b i d . , S4, 2451 (1932). (11) Meerwrin, Bcr., 66B,411 (1933). (12) Meerwein and Pannwitz, J . prakl. Chem., [II] 141,123 (1934). (13) Smith, Bryant and Mitchel1,'Txxs JOURNAL, 61, 2407 (1938). (14) Precision Scientific Co. 14799 spring clamps are convenient for this purpose.
toluonitrile and @-naphthonitrilereacted quantitatively, o-toluonitrile and a-naphthonitrile gave values of 89.5 0.5 and 80.9 * 0.2%, respectively. Methyleneaminoacetonitrile, presumably because of the inhibiting influence of the amino group, reacted only to the extent.of 80.9 f 0.2% and cyanoacktonitrile gave values of 88.8 * 0.9%. It is surprising that cyanoacetic acid" indicated only 37.1 1.4% reaction. The new procedure was developed from a series of experiments with various acid and basic catalysts. Sulfuric acid wag apparently satisfactory f
f
(15) Pyridine is essential at this point. I t combines with the boron fluoride thereby preventing esterification with the methanol during subsequent titration with the Karl Fischer reagent. (16) Eastman Kodak Company practical.
A. WEISSBERGER
776
Vol. 67
but the precision was poor ( * !%). With high concentrations of boron fluoride in ~nethariol variable dehydration occurred at elevated tetnperatures. Since ~lkaliesreact M rth the Karl Fischer reagent l7 only low conceiitration~could br tolerated which n crtb insufficieiit for norlnal alkaline hyclrolysis. The effects of concentration of boron trifuoride iri acetic acid, time and temperature 011 the hydrolysis of acetonitrile ant1 atliponitrile are rccorded in Table 11
also uniavorJAy affect the new nitrile technique. Alcoholic hydroxyl u ill csterify under these contlitioiis, quaiititatively eliniinating an equivalent aniotiiit oi wattr. Corlsequently, provided the hyciroxj.1 con tent can be determined by an iiiclepetitleiit iiiethutl," suitLible iorrectioiis to the iiitrili raluc c m be applied Cyaiiohytiriiis hyclroly7e readily. The norindl hydroxyl esterification catalyst (100 g. BF3/l.)I6 was sufficient to hydrctlye acetaldehyde cyanohydrin to the extent of about tjOq&; the net increase in water after two hours at 63' was equivalent to about 409A of the 'I'ADLE I1 hydrnsyl. Under conditions of the general nitrile FACTORSINFLCENCING T I I E HYDROLYSIS OF SITRILES procedure, however, both reactions are quan titaReagent, % tive giving a net water balance of zero Nitrile g. BF8/,1, Condition Reaction Littlt interference is observed with amides. Acetonitrile 100 1 hr., room temp. 3 5 Formamde, acetamide and adipamide gave L 00 1 hr . , 60 ' 9 values of 0.0, 0.3 atid 0.2% reaction, respectively. 360 I hr., 60 Gfi The authors are grateful to Donald Milton 360 2 hr., GO 91 Smith, under whose direction a portion of this 360 1 hr., 80 Y
\Vcissbergtr and I
