749
V O L U M E 24, NO. 4, A P R I L 1 9 5 2 disoloration, although its weight corresponds to that originally takeg, within limits of experimental error. The thorium dioxide residue in experiments 6 and 9 was dissolved by heating with concentrated nitric acid and a few milliliters of concentrated hydrochloric acid, evaporated to dryness on a water bath with occasional additions of 2 to 3 ml. of nitric acid, and extracted with 30 nil. of water, and the thorium was reprecipitated. Then 20 ml. of the filtrate were made alkaline with carbon dioxide-free ammonia. There was no turbidity nor even a faint color to shoFy the presence of the uranyl ion. Thus the amount of uranium impurity is so small that o r d i n a l - chemical tests fail to show its presence. One can attribute the diwoloration to occlusion of insignificant quantities of uranium. Even when the uranium-thorium ratio wan increased to 100, the discoloration showed no marked increase in intensit.y, nor did the thorium oxide residue show any overweight. I n a second precipitation a pure white residue of thorium dioxide was ohtained.
LITERATURE CITED
(1) Das Gupta. R. RI., J . Indian Cheni. Soc.. 6 , 777 (1929).
Gordon. Louis, Tanselow, C . H.. and If-illard, H. H., ANAL. CHEW,21, 1323 (1949). (3) Koelsch, C. F., J . A m . Chern. Soc., 53, 304 (1931). (4) Lakshmana Rao, B. R., and Raghava Rao, B. S. V,, J. Indzan (2) '
Chem. SOC.,27, 457 (1950). (5)
(6) (7) (8) (8) (9)
Llurtv. T. K. S.. Lakshmana Rao. B R.. and Ranhava Rao. B. S.i'., Ihzd., 27, 610 (1950). Xeish, A . C., Ckern. S e w s , 90, 196 (1904). Ryan, D. E.. MoDonnell, IT. J., and Ilearnish, F. E. AYAL. CHEW.,19,416 (1947). Smith, T. O., and James C., J . Am. Chew.Soc., 34,281 (1912). Venkataramaniah. RI.. and Raghava Rao. B. S. V., Analust, 75, I
5 5 3 (1950).
(IO) Venkataramaniah, ll.,Satyanarayanamurty, T. K., and Raghava Rao, H. S.V., J. Indian Chem. Soc.. 27, 81 (1950). (11) Willard, H. H.. and Gordon, Louis. ASLL. ( ' H E x . , 20, 165 (1948). R s c b : ~ v t nf u r rerein' AIarch 21, 1930.
.icrel)ted October li, 1931
Determination of Primary Aromatic Amines by Diazotization Using the Dead-Stop End Point H. G. SCHOLTEN' AND K . G. STONE Kedzie Chemical Laboratory. Michigan State College, East Lansing, Mich.
TH"
potle are applicable if availahle. I n any case a galvanometer xith n sensitivity of 0.01 microitmpere per millimeter of scale is d c4rahle. Purification of Amines. All amines determined were purified by recrystallization from a solvent. The first time an adequate amount of Norite was used to adsorti colored materials and a n y impurities t h a t were removable by this treatment. -4s quantitative recovery was no ohject, the ratio of S o r i t e t,o amine wits Siiigh and ;\hmed (8) proposed the use of a potentiomcJtric end usually 10 t o 25. T h e substituted benzoic acids and €1acid were recrystallized from mater: 2-naphthylamine and o- and p-nitropoint, but the time factor K:IS not changed. The use of potasanilines were recrystallized from 50% aqueous isopropyl alcohol : qium bromide as a catalyst has been recommended (6,7 ) and is ni-niti,oaniline was recrystallized from 7573 aqueous isopropy! 211niclst helpful for deci,easing the reiiction time. Clippinger and cohol: and isopropyl alcohol alone was used for t h e nitroamino1'0~1lk( 1 ) h a w suggested that nitrite may be used with cyanide tolucwia. All amines were dried briefly a t 105" and stored over barium oxide until used. f o r the ectablisl~mentof the di.:itl-.stem for the diazotization method l-naphthol-3,6-disulfonic acid, further identification was neces:tromatic amines it iras found th:it the cyanide vas not needed sary t o provide knowledge of the species. T h e sample gave a ir' the potrntial applied betwecri the platinum electrode? \vas 0.4 flanie test for sodium after moistening with hydrochloric acid. ;lectrometric titration of a sample dissolved in tyater n-ith 0.1 S volt. Pn,ler these condition+ i: current flowed R heriever an odium hydroxide showed an acid group nhose pIi was about 3.5 amount of nitrous acid equal to 0.05 ml. of 0.1 -1I sodium nitrite arid another whose p I i was about 8.5. -4s one form of H acid is solution IVM piesent in 200 to 400 nil. of reaction solution. The the monosodium salt with 1.5 moles of water of crystallization, n.r,rk reported here covers t h P use of the dead-stop technique for this form was used for calculating recoveries in the analysis. Independent Determination of Amines. The substituted tlit, tlct~c~rinination of primary aromatic amines and the use of benzoic acids were determined by dissolving samples in water a i d sulfanilic, acid as a stantlard fov sodium nitrite solutions. titrating with 0.1 S sodium hydroxide standardized against potassium acid phthalate t o a phenolphthalein end point. All other EXPERIMESTAL amines except o-nitroaniline were determined b y dissolving in t,he solvent given in Table I and titratiug t o a n end point,, using crysApparatus. The electrical circuit and electrodes descrilled by tal violet or methyl violet indicators as descrihed by Seaman and \\-erninioiit itrid Hopkinson ( I I ) are the basic requirements. T h e .4llen (6)with 0.2 S perchloric acid in glacial acetic acid also S:iI,gent IIoclel I11 manu:iI prrl:irograph and the Fisher Elccdrostandardized against, potassium acid r)hthalate (6). o-Sit,roaniline is so neakly hasic t h a t titration in acetic acid is not possible and no solvent ryas found Table 1. Determination of Pure Amines in ivhich the amine perchlorate was sufB y ;\cidinietry ficiently insoluble to permit the titration .i i i i i ne L C t,r f I S 0 . 0 Salvent Indicat.,r ( h l o r change ', on this basis. Since the method of puri100 2 = 0 2 fication was the same as t h a t which 100 0 f 0 4 100 1 = a 2 100 3 * 0 3 yielded high purity rn- and p-nitroani100 0 * 0 3 100 5 * 0 . 1 line, it n-o;id -seem that the ortho coniBlue to blue-green 99.5 i0.1 100 3 + a 1 2-Saphthylamine pound should also be of high purity. Blue-green toyellow-green 100.5 + 0 . 2 99 9 * 0 2 5-?;1tro-2-aminotoluene 9 9 9 i 0 2 4-Pl'itro-2-aminotoliiene Yellow t o colorless 1 0 0 . 3 zt 0 2 Procedure. Weieh samnlcs which o-Nitroaniline 99.9 r 0 . 1 \vill--drochloricacid (12 S),and 1 3 to 5 determinations. grain of potassium bromide as the c T i t r a n t was 0.1 ,\' XaOH with phenolphthalein indicator. catalyst. Insert the glass paddle of a .i T i t r a n t was 0.2 N HClO+ in HO.4c. e Titrant was 0.1 .V NaOH with electrornetric end point detection. power stirrer and the platinum wire I Crystal violet indicator. electrodes which have been cleaned in Methyl violet indicator.
ckterniination of primnr!. aromatic amines by diazotization (Equat'ion 1) has been troublesome because the detrrtion of t,he end point requir,ed :in external indic,:ttor. usuall?st:trch-iodide paper, and a period of waiting to alloir- the sodium riitrite added to react before teqtiny to see if a n excw? was present. R S H J CHI HSO? = RS?C>I 2I1,O (1)
+
+
+
f(jr
~
';
-
i.Calculated
-
as monosodium salt of 8-amino-l-naphthol-3,6-disulionic acid with 1 . j H?O ~
-
1 Present address. Dow Chemical Co.. Bay City. M i c h
ANALYTICAL CHEMISTRY
750 dichromate cleaning solution and well washed. Start the stirrer. Adjust t h e galvanometer t o a sensitivity of approximately 0.01 pa. per mm. and apply 0.4 volt across the electrodes. A current may flow a t this point, but it usually decreases t o almost zero immediately. Add 0.1 -21sodium nitrite solution (standardized against pure sulfanilic acid by this procedure) with the tip of the buret dipping into the solution a t such a rate t h a t very little current flows. S e a r t h e end point the current increases and a t this point it is advisable to stop the titration to permit the galvanometer t o become steady t o locate the reference point on the current scale. Add the nitrite solution in small increments and observe the movement of the galvanometer needle. T h e end point is indicated when the galvanometer shows a permanent deflection of about 0.1 pa. away from the reference point previously found. T h e end point is not very seiisitive, and care is necessary in the vicinity of the end point. Suhtract 0.05 mi. from the volume added to correct for the sodium nitrite used for the excess detected by the galvanometer. RESULTS
The dead-stop end point permits the introduction of siniplifications into the diazotization method for primary aromatic amines and provides more control of the process. Among the features which are possible, the fqllowing are noteworthy: (1) the loss of nitrous acid which would lead to high results is minimized, as it is formed by the addition of sodium nitrite only as rapidly as it is consumed. (2) Because the reaction rate is greater a t room temperature than a t O " , v hich ha- been previously reconiniendeti, the time for the analysis is ieduced. (3) The use of potassium bromide to catalyze the reaction reduces the time spent in the vicinity of the end point. ( 4 ) The use of an external indicator iunnecessary. (5) Deterniination mav be done a t room temperature. I n order to check thwe advantages 10 aromatic primary amines were analyzed by the procedure. The results are shown in Table I together M ith thP independent analyses bv acidimetric methods. STANDARDIZATION OF S0DIU.M NITRITE SOLUTION
Phillips and I a w y ( 4 ) havc rfiported a serious discrepancy in the concentration of sodium nitrite solutions based on the use of sulfanilic acid or standard potassium permanganate solution as the reference material. This work \vas repeated and the discrepancy was confirmed. The results using permiinganate averaged 1yo higher than those using sulfanilic3 arid nntl were much more variable. Some ohscrvations were made on sulfanilic acid to determine whcther it ha.
