Determination of Nitrogen in Nitriles EUGENE L. ROSE AND HENRY ZILIOTTO, Chemical Warfare Service, Edgewood Arsenal, M d . potassium sulfate, 0.3 gram of anhydrous copper sulfate, 0.1 gram of selenium, and several boiling stones or glass beads. Heat the mixture gently a t first, then boil briskly, and continue digestion for 1 hour after mixture becomes clear green in color. A t no time should the volume of acid drop below 20 ml. Most of the iodine will have been removed by this time, but any remainink in the neck can be removed by applyin a flame thereto. Cool the mixture, add 250 ml. of water, and ,%en cool proceed with the distillation. Add sufficient 50% caustic solution to make the reaction stron ly alkaline (90 ml. are usually sufficient), pouring it down t8e side of the flask, so that it does not mix a t once with the acid solution. Add several pellets of zinc (20-mesh) to prevent bumping and without delay connect the flask to the condenser by means of the Kjeldahl connecting bulb, takin care that the tip of the condenser extends below the surface o? a measured quantity of standard 0.1 N sulfuric acid. Mix the contents of the flask and distill until all ammonia has passed over into the acid. Usually 125 to 150 ml. of distillate will contain all the ammonia. Titrate the distillate with standard 0.1 N sodium hydroxide solution, usin sodium alizarin sulfonate mixed indicator. The end point is in5icated by a change from green to bluish-gray color. Run a blank in the same manner &s that used for the sample.
A
REVIEW of the literature shows that the nitrogen in nitrile compounds can be determined by only a few methods, and that these leave much to be desired for ease and rapidity of analysis. The Dumas (3) method requires apparatus not always available in commercial laboratories and is troublesome with compounds of high nitrogen content and those of high volatility Methods based on reactions of sulfuric acid (6), hydrochloric acid (Z),or hydriodic acid (5) a t high temperatures and pressures in sealed tubes will give correct results with nitriles, but are undesirable because of the inconvenience of the procedure. The method of Fleury and Levaltier (4), employing benzoic and phosphoric acids, was found to require longer digestion time than the method described in this paper and, in addition, had the disadvantage of seriously etching the digestion flasks. Hydrolysis with 80% sulfuric acid and subsequent digestion gave quantitative yields of nitrogen with saturated aliphatic nitriles, but did not give quantitative or accurate results with unsaturated aliphatic nitriles. The strong reducing action of hydriodic acid as a preliminary to Kjeldahl digestion was made the basis of the present procedure. Hydriodic acid, however, is not a practical reagent, since once its container is opened the acid rapidly deteriorates. To obviate this objection it was thought advkable to react sulfuric acid with potassium iodide, both stable reagents, and permit the hydriodic acid formed to reduce the nitrile. The standard KjeldahlGunning-Arnold ( 1 ) nitrogen procedure, using selenium in addition to copper sulfate, would then be applied to complete the analysis.
(Ml. of H ~ S O IX iu' - ml. of NaOH X K) X 1.401 weight of sample RESULTS
Several nitrile compounds were analyzed by the method devised. Two of these compounds, acrylonitrile and acetonitrile, have boiling points below 100" C. and were included in the tests to show the applicability of the method to materials of high volatility. Cyclic, as well as aliphatic, compounds were analyzed and some of these, in addition to the nitrile group, contain a nitro group.
SOLUTIONS AND MATERIALS
Standard sulfuric acid solution, 0.1 N . Dissolve 4.9 grams of sulfuric acid, specific gravity 1.84, in 1 liter of distilled water. Standardize gravimetrically. Standard sodium hydroxide solution, 0.1 N . Diasolve 4.0 grams of C.P. sodium hydroxide stick in 1 liter of freshly distilled water. Standardize against 0.1 N sulfuric acid solution, using sodium alizarin sulfonate indicator. Sodium alizarin sulfonate indicator. Dissolve 0.9 gram of eodium alizarin sulfonate and 0.125 gram of indigo carmine in 100ml. of distilled water. Potassium iodide crystals, Merck reagent grade. Concentrated sulfuric acid, c.P., specific gravity 1.84. Copper sulfate, Baker's C.P. grade, anhydrous. Selenium metal, black, powder. Compound Zinc metal, Baker's C.P. grade, Liquid. 20-mesh. Benronitrile Potassium s u l f a t e , c r y s t a l s , Isocapronitrile Baker's C.P. grade. Sodium hydroxide solution, 50%. Dissolve 400 grams of sodium hyn-Butyronitrile droxide in 400 ml. of distilled water. Acrylonitrile Allow to stand 24 hours and decant Acetonitrile clear supernatant liquid. Solids p-Bromobenzonitrile METHOD OF ANALYSIS
Place a weighed quantity of sample containing 40 to 60 mg. of nitrogen in a digestion flask, add 1.5 grams of potassium iodide and 30 ml. of concentrated sulfuric acid, and heat on a steam bath for 45 minutes with occasional shaking. Add 10 grams of
To check the accuracy of the method the nitrogen contents of some of these samples were also determined by Friedrich's (6) modification of the Kjeldahl method adapted to a macro scale. For this purpose 2 ml. of hydriodic akid (density 1.7), a pinch of red phosphorus, and a weighed quantity of sample were sealed in a tube and heated for one hour a t 200" C. When cold, the tube wm opened, the contents were transferred to a Kjeldahl flask, and the mixture waa treated as in the Kjeldahl method. Reference to Table I shows that the results obtained on nitriles by these two methods are in very close agreement.
Table I. Determination of Nitrogen Formula
CHs(CHz)nCN
20.29
.....
CHz: CHCN
28.42
CHaCN
34.15
BrCIH&N
7'87
28.22\26,22
26,221
33.11
};;;;
7.88
9.88
.....
NOGHICHCN NOZCOHICN
17.29
.....
NOaCsHdCN
18.93
CNCHzCHzCN
8b.00
211
18' 93
Salicvlio acid method ( 6 )
.....
%%;}13,5*
p-Nitrophenylacetonitrile
Succinonitrile
Per Cent Nitrogen Friedrich method KI method
13.60 14.43
CsH&OCHzCN
pNitrobenaonitrile
Theoretical
CoHiCN (CHdtCH(CHdKN
Benaoylacetonitrile m-Nitrobensonitrile
- %N
::}
18.83
;;:g}ls.So
.....
13.42 ;::;:/19.77 -_
13.46 26,hij,.
28.16 2 8 . 2 9 2 8 . 2 3 26.25 2 8 . 1 3 33.13 33.18
:;::;
i:::;
;::;7 . 8 5
::::i
9.49
.....
. ....
212
INDUSTRIAL AND ENGINEERING CHEMISTRY DISCUSSION
The samples for analysis were not all analytically pure. Since there was insufficient time for their purification, it was decided to determine their nitrogen content by some accepted analytical method. Friedrich’s method for nitrogen determinations can be applied to a wide diversity of substances and for this reason was used as the standard by which results by the potassium iodide method could be compared. Results by both methods agree very closely. Even though some of the samples tested are volatile and one might egpect losses from the relatively high temperatures employed in open flasks, such is not the case. Compounds that have a nitro group in addition to the nitrile group yield all their nitrogen. Further work will be undertaken to determine whether the method can be applied to nitro compounds in general. Other types of nitrogen compounds which require special treatment before Kjeldahl digestion were also analyzed by the potassium iodide method, but sometimes with unsuccessful results. -111 the nitrogen in an azo dye, naphthalene-8-azo-p dimethylaniline, was recovered, whereas only part of the nitrogen of rn-xylene-azo-,&naphthol was so obtained. It seems that the position of substituent groups in these azo compounds may hinder attack by these reagents. Unsuccessful results were also obtained with hydrazine, pyridine, and inorganic nitrates. The presence of a few milliliters of water does not interfere with the analysis, but large dilution has a deleterious effect. Subsequent to the development of the above method it was de-
Vol. 17, No. 4
cided to determine the nitrogen due to nitrates in a mixture of nitrates and nitriles, using the standard salicylic acid-thiosulfate method ( 1 ) . It was found that the nitrile nitrogen was quantitatively recovered. Four nitriles were then analyzed by this salicylic acid method with results that compare well with the potassium iodide and Friedrich’s methods (see Table I). SUMMARY
Nitrogen has been determined in nitrile compounds by reduction with potassium iodide and sulfuric acid preliminary to digestion by the Kjeldahl method. No special technique or apparatus is required. Results by the new method compare well with those by the Friedrich method and can be obtained in much less time. The nitrogen in nitro groups substituted on aromatic compounds interferes by being reduced by the potassium iodide. The nitrogen of pyridine, hydrazine, nitrates, and certain azo dyes is also partly reduced. LITERATURE CITED
(1) Assoc. Official AQ. Chem., Official and Tentative Methods of
Analysis, 5th ed., p. 26 (1940). (2) Drushel, W. A., and Brandegee, M. M.,Am. J. Sei. (4), 39,398 (1915). (3) Dumas, J. B., Ann. Aim. phys.. 2 , 198 (1831).
(4) Fleury, P., and Levdtier, H., Bull. SOC. chim., 37, 330-5 (1925). ( 5 ) Friedrich, A., Kuhaas, E., and Schurch, R., Z. physiol. Chem., 216,68-76 (1933). (6) Guillemard, H., BUZZ. SOC.chim. (4), 1, 196-200 (1907).
Determination of W a t e r in Hydrocarbon Gases HARRY LEVIN, KARL UHRIG, AND
F. M. ROBERTS, The Texas Company, Beacon,
A method is described for determining water in normally gaseous hydrocarbons. I t i s based on the observation that when a gas containing moisture is contacted with cold dehydrated acetone, the water is retained b y the acetone, in which it can b e determined b y reaction with acetyl chloride, titrating the liberated acid. Olefins and diolefins d o not interfere and provision is made for correcting for interference b y acidic or basic constituents of sample.
A
STUDY of plant operations to determine factors affecting catalyst life made it important to have a method for determining the water content of normally gaseous hydrocarbon charge stocks. The requirement that it be independent of the variable composition of the test gas eliminated from consideration most of the methods proposed in the literature.
A dew-point method, involving wet- and dry-bulb thermometers or thermocouples, was proposed by Deaton and Frost ( 2 ) . Presence of high-boiling hydrocarbons interferes with such a method. Perry (8) condensed the hydrocarbon in a cooled weighed trap, evaporated the gas, and considered the increase in weight to be water, but stated the method is unsatisfactory if the samples contain heavy ends. Evans and Davenport ( 3 ) described a manometric method for water in gases removed from oils by evacuation, brtsed on reduction in the pressure of the gas upon exposure to a film of lithium chloride monohydrate. The manometer measurements are apparently applied to gas containing rather high concentrations of water and is unsuitable for the low concentrations with which we are concerned-namely, &s little as 0.001%. Todd and Gauger (f3) recommended determination of water vapor by near infrared absorption spectra, which requires rather elaborate apparatus. Silica gel and other activated drying agents are sometimes recommended. However, such absorbents are restricted to the determination of water in nonhydrocarbon gases, since they also absorb hydrocarbons (11).
Chemical methods are preferred by some investigators because they are specific for water. Henle (6) described an involved
N. Y.
procedure employing aluminum ethylate. Calcium carbide has long been used because of the ease with which it produces acetylene on exposure to water, the latter being estimated dy measuring the acetylene gasometrically (9), colorimetrically as cuprous acetylide (5), or gravimetrically as copper oxide (f4)‘ Such methods are unsuitable for the present purpose because of the nature of the samples and the small amounts of water involved. Bell (1) described a method utilizing the hydrolysis of a-naphthoxydichlorophosphine and Ross (10) used benzoic anhydride. Both methods are tedious. h test based on the change in color of cobalt bromide on hydration was proposed by the Natural Gasoline Association of America ( 7 ) , but the color changes are deceptive and uncertain. Fischer (4) used a methyl alcohol solution of iodine, sulfur dioxide, and pyridine, with which water reacts to form acid 2HzO
+ SO2 + Iz = His04 + 2HI
the water in the sample being estimated from the iodine consumed in a direct titration employing the iodine color as indicator. Roth and Schulz (11) use magnesium nitride to determine moisture in gas from the ammonia liberated.
MaN2
+ 6 H z 0 = 3Mg(OH), + 2SH,
Smith and Bryant (12) utilize the fact that acetyl chloride in the presence of pyridine reacts quantitatively with water to produce 2 moles of acid and with absolute alcohol t o produce 1,
+ HOH + o
x
COCHi \Cl / +ROH+
CHaCOOH
+ CHsCOOR
the increase in acidity of the sample over the blank with alcohol bPing equivalent to water in the sample. This formed the basis
