1200
ANALYTICAL CHEMISTRY
atb well as the lines beyond the point at which the temperature is
LITERATURE CITED
measured, only a very slight trend in this direction is shown by the results in Table 111. -4s the fractions analyzed represent only a few tenths of 1% of the total sample, the results shown in Tahlr IT1 should he accurate on a total sample hasis.
(1) Office of Rubber Reserve (RFC), “Butadiene Laboratory Manual,” Method L.M. 2.1.51.1. Butadiene Analytical Committee, 1941. (2) Podbielniak Manual, “Hyd-Robot Instructions,” Podbielnisk, h c . , Chicago, Ill. ( 3 ) Podbielniak, TT. J., IND.ESG.CHEM.,. ~ - A L .ED., 13, 639 (1941). (4) Starr, C. E., Jr., Anderson, J. S., arid Davidson, V. &I., A s . 1 ~ . CHEM.,19,409 (1947). (5) Washburn, H. T,,Wiley, H. F,,arid Rock Y. >I., Ihid., 15, 541 (1943 1.
CONCLUSIONS
The results obtained show that distillatioil r:itCs as high :IS 100 (T. per minute may be employed with accuracy equal to that attained at the slower rates prescribed in the literature. Cut points between fractions could be raked somewhat over those previously 1 ) 1 ~ e s ( ~ iwith h ~ d a n d t i n g very slight incrt:asc in nccur:rcy.
HECEIY~:U >larch 15, 1948. Presented before the Bouthwe\t Regional Neeting, AXERICAS CHE\rIc.+L SOCIETI.Houston. Tex., December 12 anrl 13. 1947.
Water-Soluble Polycarboxylic Acids from Oxidation of Bituminous Coal Determination of Molecular Weights NATHAN BERMAN’
AND 13. C. IIOWiARD Coal Research Laboratory, Carnegie Institute of Technology, Pittsburgh, Pa.
The application of modifications of the MenziesWright molecular weight apparatus to the determination of the molecular weights of the watersoluble pol) carboxy acids formed by oxidation of coal is described. Acetone and methyl ethyl ketone were used as solvents and benzoic, salicylic, phthalic, and mellitic acids as standard solutes. For solutes that obey Raoult’s law there is a linear relation between the rise in the differential thermometer and the millimoles of solute present, if a constant volume of solvent is added to the apparatus and a constant
C
OKTROLLED oxidation of suspensions of bituminous coal in aqueous alkali by oxygen gas, a t elevated temperatures and pressures, results in a mixture of water-soluble carboxylic acids in yields as high as 60% bj- weight of the coal ( 1 ) . Simple aliphatic acids, acetic and oxalic, are formed in small amounts, but aromatic polycarhox acids predominate. Benzene di-, tri-! tvtra-, and pentacarbos) c acids have been isolated and there i.5 evidence of the presence in significant amounts of : i d s of more complex nucleus than the benzene ring. Because the acids differ both as to nuclear size and number of functional groups per molecule (equivalent weight) it is necessary, in foIlou.ing the effects of process variables and fractionation procedures, to have available rapid methods for determination of both equivalent and molecular weights. Determination of the former presents no difficulty, inasmuch as we are dealing lvith strong water-soluble arids, the equivalent weights of ti-hich arc’ readily determined by the usual titrimetric procedures. For the molecular weight determinations the Menzies-Wright apparatus ( 5 , 6 ) as modified in this laboratory and by Hanson and Bowman (P) has been found satisfactory from the standpoint of convenience, speed, and reproducibility. Data on four known solutes-benzoic, phthalic, salicylic, and mellitic acids-as well as on samples of the mixed aromatic acids recovtlrcd from the 1
I’meent addre..,
V n i v e r a i t y of California, Beverly Hills, Calif.
energj input to the boiler maintained. This constant relating the rise in the water therniorneter and molar concentration combines the classical ebullioscopic constant and the coefficient o f the water thermometer, and greatl) simplifies calculations. This constant is affected bj changes in barometric pressure, about 1.670 for each 10 mm., and detiations from Kaoult’s law are shown by departure from linearit) at higher concentrations. No such deviations greater than experimental error were obserted with these solutes in the ketonic solvents used.
oxidation of coal, are presented. Acetone and methyl ethyl I+ tone were used as solvents. A simple method for estahlishing thc constant for calculation of the results is described. REAGENTS AND APPARATUS
The acetone and the benzoic and salicyclic acids \yere ~Ialliiickiodt analytical reagent grade. The acetone \vas used without further purification. The phthalic acid (Eastman) was crystallized once from water. The mellitic acid was prepared by osid:ition of carbon black; the crude acid was precipitated as the ammonium salt and the free acid recovered by electrolysis of :in aqueous solution of the salt. The equivalent weight, by titration with 0.1 S alkali using phenolphthalein indicator, was found to hr 57.3: theoretical, 57.0. All the acids were dried 2 houw :it 110”C. before being used. The methyl ethyl ketone was ii commercial product fractioii:itetl through an 8-plate column, packed ivith O.125-inch stainless s t w l helices, a t a 20 to 1 reflux ratio. The cut used boiled bet\vc.cvi 78.5” and 78.8” C. (uncorrected). Two modifications of the apparatus were employed. The f k - t was the original type of 1Ienzies-\Vright apparatus without V N C uum jacket and with a removable Cottrell pump, modified fol. electric heating by the introduction of a helical coil of S o . IS Sichrome wire. The external diameter of the helix was such :I> t o allow the mouth of the Cottrell pump to pass over it and [ h e ends were brazed to 2-mni. tungsten leads sealed through thr glass. The total resistance of heater and leads was about 0.8 o h ~ n and the electrical energy for heating was supplied through H smull transformer. The second mot1ific:itinn \vas a recent model of t h e
V O L U M E 21, NO. 10, O C T O B E R 1 9 4 9 Table I .
1201
Helation between Barometric Presstire and Water Thermometer Coefficients
p,
I',
llm, H g
c.
Differential, Water, Thermometer ( 6 , A ) , lllll.,
Acetone j 6 . 1 4 1 (8) .55. 754 ;,5.558" .55.362 54,967
760
750 745 740 730
0
c.
RESULTS A N D DISCUSSIOS 81.77 8 0 . $52 78 ,83 i l l , 18 77 88
l l e r l i y l E t h y l Ketone f 7 )
760 7,50 745 740
77 99 .. 5176
"
___
1!38.2 195.4 104 0 102 6
78,95"
78.73 78.34
im
18!1 0
Iriti~riiiilati~d. ~
-
~~~~
~~
~
~
~~~
~
when the barometric pressure is 750 mm. is found to be 7.70 mm. per millimole in 25 nil. of added acetone, then with R barometric pressure of 740 mm., since the relations are linear, thc 79 18 vonstant will he 2* X 7.70 = 7.57.
-~~
.
~~
~
~ ~ a n s o l l - ~ ~ o ~apparatus, , . n ~ a l l supplied with v:leuunl jac.ket, fixed Cottrell pump, and radiant heater, drawing about 8 amperes at 2.5 volts. T h e wattage input varied *2% and within this variation no significant effects on the readings of the differenti:il thermometer were observed. PROCEDURE
Data t1,pical of the results with benzoic acid in acetone in thcz Type 2 apparatus are shown in Table 11. It is evident that the degree of reproduciblity is satisfactory and that there is no systematic change in A h / m over the concentration range used; the highcst concentration is about 3 mole %. Evidently t1evi:itions from Iiaoult's law for this system, ovrr this concentr:ttion range, :ire less than the rsperimrntal error. Positiw deviations from Raoult's l:iw (association) would he shown hy decreasing values of A h / m with increasing concentration. In Table I11 are given minimum, maximum, and average values of A h / m for salicylic., phthalic, and mellitic acids. These represent results of experiments in which concentrations of 1 to 10 millimoles of solute in 25.0 ml. of acetone were used. The average values of Ahj,rt corrected to.a 1)arometric pressure of 745 mm., :t ('ommoll value in this district, are shonn and it is evident that thp use of the pressure corrwtion improves the agreement. The :ivc>i':tgevalue of li for the four standard solutes, a t 74.5 mm.. is 7.55 iind this \ d u e ~v:ts uqod in the determinations n n tht* mixed :ic4ds. Satisfactory but lcss es:rctl\. reproducible results were o b t e i n d with the older Type 1 apparatus itnd using methyl ethyl ketone :is :t solvent. The difficulty probably lies in both the apparatus and thc lowcr purity of the solvent. I t n-as not found possible to us(' methyl (.thy1 ketone iu the refincd Type 2 apparatus because not vnough energy could be supplied through the radiant heater without exceeding the r:itcd ca:rp:i(ity. The very much greater
Uw:iusc~of' the known wide deviations of carboxylic- :icids from liaoult'c l:i\v in hydrocarbon solvcnts, only ketonic solvcr~ts1vcw usrti . ;\ftrr the zero reading of the thermometer was o1)t:iined in thc usual w:ty (Z), the solute, a.hen nonhygro.qcopir and wtdily prlletcd, was added in inrrrnients to a k t i ~ volumc~ ~ i of the solvent. \Yith solutes not adapted to pelletiiig, solutions of the required concentrations ~ w r prq)tircd (~ outsitlc the :\pp:ir:itus :rnd the appropriate volume of solution was added. ___~_________~~~__~ . .__ In methods for the ebullio'I'ahle 11. Helation hetw-een lIoles of Solute and A h scopic dctermination of molecsSolrcnt, 25.n ml. of acetone IJ = 744 mln. of T I E ular weights the problem of Yoliite, henzoic acid E = 19.2 watts est:rblishing the concentration t,,, ,,,illi,,,lili,\ 1.887 2 808 4.038 5.760 7.164 8.411 '1.573 1(J.:381 of thc tmiling solution enters. l h 1!.4 21.1 30.4 42.2 5.1 4 ($3.5 72.3 78.7 Ah ' ,,t , 62 7 ., i 2 , .i2 1.,50 760 T.55 7J.i 7.58 If, howrvrr, standardization is .iv, 7 .55 (wried out with solutes of .4t 745 m m . 7 6 0 knon.ii molecular weight, and ~___-___~ ~ _ ~ _ _ _ _ ~ ____if the ratio of solvent in the 'I'ahle 111. Values of Ahlm for Saliqlic, Phthalic, and solution to the total added re\lelli tic Acids niaiiis cvnstsnt a t all times, the difficulty is ol)vi:itctl (.$). Eeaf25.0 t i l l . of acetone uscd in each instance, sorial)lc ronstancy in this respect can tie attained hy :I c~oti.*t;int Barotnctric Pressurr. l h /in l h / m (at c~riri~g.~. input to an electric heater and some care :ts to r:rte of doliitc l l n i . Ilg ZIin. Max. A\-. 715 hlin.) flow and t rriiperature of condensing water. This proccdurtl, whirh Salicylic acid 730 7.22 7.47 i.33 z.48 has k)rcw followed in the present work, rcwdts in :i vcry simple Phthalic acid 740 2.38 7.61 i.46 52 acid 1.60 7 . 0 0 i . 7 2 7 AT, relation t x t w e n the observed rise 011 thc water thcmionirtrr aiitl __~___~ the molar eonc~ntrationof the solution, Ah = hi,wli(~r0Ah is the risc and ni is molar ronceiitration. This relation lioltis, for :I Table IV. \Ioleciilar Weight of l l i x e c l iromatic icids solutc otx,ying Ilaoult's law, bec*ause over the short tempvr:tture from Coal intervals with Lvhirh we are concerned the change in w p o r prrsd o l i ent 2.5 0 nil of acetone I> = 744 11ini. o i f i n sure of the n:iter in the thermometer with teniperaturc is linear. Differential Therniometer Headings The constant, k , caonveniently espressed iis millimetcr per milliLeft Rirht a r m, arni, lloleciilar mole of solutt. in 25 ml. of added solvcrit, combines thr r1:issical Solute, ( ; r a i i i h L . ciii. I?,cin. L IC A h , ZIni. Weight" c~l~ullioscopic. constant for the particular solvrmt eniployod Ivith 2.14 o n 0 !>8 0.3103 3.411 3.31 t h c x trnipcrature coefficient of the water thermonicter. T h e use 0 5832 8.70 "74 o t this combined constant greatl?, simplifies ca:il(wlations in 0,6923 3.96 3.04 0 , 844.i 4 . 4 0 : i. .53 niolec~ularw i g h t determinations. 1 ,!JO 1 027 I n8 This cwnst:int is somewhat :iffwtcd I)>. changes iri t)~ironirtric prc~ssurc~,:itlout 1.6% decrease for cnch 10-mm. decrease in " r a l ( . i i l a t r . d i r o i n the rclatiun: t)aronirti~ic~ pwsiiure, and th(2 c s w t magnitude of thv c ~ f f w tcan be R x g x 1000 lIoleciilar w i d i t = cdculattd lrom boiling point trmpor:iture data for the solvent emAh 1)loyeti and the temperature coefficicnts of the water thtmiionic h t t v . Th(h required data for acetone and methyl ethyl ketone are givtm in 'l'ahle I. Thus, for rstrmple., if thc c-onst:int det rrmined ~~
~
~
~~~
"'
I
2
ANALYTICAL CHEMISTRY
1202 Table V.
Molecular Weights of Fractionated Acids Weight
Fraction 1 2
3
4 5 6
R
Grams’ 463 499 284 97 39 17 535
AIolecular Weight 199 235 256 280 326 374 442
Moles 2.32 2.12 1.11 0.34 0.12 0.04 1.21
Mole ‘X
7.26
100.0
-
1934
32.0 29.2 15.3 4.7 1.6 0.5 16.7
Table V illustrate the use of the method in following fractional separation by solvents. In this separation about 2 kg. of the mixed acids, of average molecular weight 250, were subjected to a fractionation process by ether-pentane miutures. The weights of the fractions recovered and the average molecular weights found for each fraction are shovin. From these data the “number average” molerular weight is calculated. In view of recovery losses and the difficulty of complete elimination of solvents, the agreement of the number average, calculated from the fractionation data, with the value for the original mixture, is satisfactory and lends confidence to the values for both the original mixture and the fractions. LITERATURE CITED
sensitivity of the water thermometer with the higher boiling solvent, more than twice the rise per millimole, emphasizes the importance of having a differential thermometer filled with a l o m r boiling liquid than water if low boiling solvents such as acetone are to be employed. Differential thermometers filled with a number of different liquids have recently been described (5). The data of Tables I\‘ and F’ show the application of the method to the mixed acids recovered from the oxidation of coal. Those in Table IV refer to a typical unfractionated mixture such aa is recovered from the pilot plant operations and those in
(1) Fianke, N. W., and Kiebler, M . W., Chem. I n d s . , 58, 580 (1946). (2) Hanson, W. E., and Bowman, J. R., IXD.EN. CHEM.,ANAL.ED., 11, 440 (1939) ; also directions supplied with apparatus, W. E. Hanson. (3) Kitson, R. E., and Mitchell, J., ANAL.CHEM.,21, 404 (1949). (4) Mair, B. J., J . Research Natl. Bur. Standards, 14, 345 (1935). (5) Menzies, A . W. C., J . Am. Chem. Soc., 43,2309 (1921). (6) Menzies, A. W. C., and Wright, S. L., Ibid., 43, 2314 (1921). (7) Shell Chemical Co., San Francisco, Calif., “Methyl Ethyl Ketone,” p. 23,1938. (8) Swietoslawski, W.,“Ebulliometrio Measurements,” pp. 64-9, New York, Reinhold Publishing Corp., 1945. RECEIYED March 10, 1949.
Determination of Organic Hydrazines SIDNEY SIGGIA AND LESTER J. LOHR General Aniline & Film Corporation, Easton, Pa.
A procedure is described for determining organic hydrazines by oxidation with cupric sulfate and measurement of the liberated nitrogen.
S
EVERAL oxidants have been used in determining hydraziries and hydrazine salts: potassium iodate (5, 6, 9), potassium permanganate ( 4 , 6 , 9 ) ,potassium bromate (IO),iodine (6,9), calcium hypochlorite (If ), chloramine T (8), potassium ferricyanide (7), ceric salts (S),and cupric ion (1, 2). The amount of hydrazine waa usually determined by measuring the oxidant consumed. When potassium ferricyanide was used as the oxidant (7), the nitrogen evolved was collected and measured. I n attempting to use the above oxidants to determine hydrazines of the type RKHSR,, it n-as found that the reaction wab slow, and a quantitative amount of the oxidant was not consunied. Heat caused undesirable side reactions such as the oxidation of side chains, but, although the warm oxidation proceeded in indeterminate manner, the nitrogen was liberated quantitatively from the hydrazine. A nitrometric method based upon these observations has, therefore, been developed. Potassium iodate, potassium permanganate, and ceric sulfate were tried as oxidants but were found to have disadvantages. Iodine was liberated from the potassium iodate which sublimed through the apparatus and into the nitrometer. Ceric sulfate and potassium permanganate caused the reaction to proceed in an indeterminable manner. Cupric sulfate in sulfuric acid oxidized the hydrazine quantitatively and could be easily handled in the apparatus. The oxidation for the monosubstituted hydrazines proceeds according to the following reaction:
---
CUSOl
RNHNH~,H~SO~ P O1
rn=s
*
+
HSO~-
Heat
2H20 +ROH
Ht0
+ Xz + HtSO,
The reaction mechanism for the more highly substituted hydrazines is uncertain, but the nitrogen is liberated quantitatively. The time required for a determination varies from 46 minutes to 1.5 hours, depending upon the oxidizability of the hydrazine being determined. This procedure, because of its specificity for hydrazines, is preferred to methods that do not differentiate between hydrazines and other nitrogen-containing compounds, such as the Kjeldahl and Dumas methods. APPARATUS
The apparatus, shown in Figure 1, consists essentially of a r e action flask, F , in which the nitrogen is liberated, a Lunge nitrometer, J , in which the liberated nitrogen is measured over 50% potassium hydroxide, and a cylinder of purified carbon dioxide, A , which is used to displace the air from the apparatus prior to an analysis and to sweep the liberated nitrogen into the nitrometer. Tne 100-m1. reaction flask, F , is attached to the apparatus by a $24/40 joint. The reagents are introduced through the separatory funnel, G, and the delivery tube, L, which has a maximum diameter of 3 or 4 mm. and a constriction a t the bottom to prevent displacement of the liquid during decomposition of the sample. The reflux condenser, H , which is sealed to -11,has an internal diameter of 12 mm. and allows vigorous refluxing of the reactants. The carbon dioxide rate is controlled by the needle valve, B , and is estimated by the bubble counter, E , which is filled with an inert liquid such as butyl phthalate. Other essential parts of the apparatus me the safety manometer, C, the leveling bulbs, D and K , and the three-way stopcock, I , which permits by-passing the nitrometer. Commercial tank carbon dioxide is purified prior t o use by venting rapidly about 50% of the carbon dioxide from the cylinder. A cylinder of carbon dioxide purified by this procedure contains a negligible impurity and contains sufficient carbon dioxide for several hundred analyses.
